Glass Industry Catalogue La029511

Transcript

EUROTHERM ® FLEXIBLE SOLUTIONS Glass Industry C ATA L O G U E Glass INTRODUCTION PROCESSES ENERGY SOLUTIONS CASE STUDIES KNOWLEDGE Complete document re-order reference LA029511 Main contents HA029511 Issue 1 i Eurotherm: International sales and service Understanding and providing local support is a key part of Eurotherm’s business. Complementing worldwide Eurotherm offices are a whole range of partners and a comprehensive technical support team, to ensure you get a service you will want to go back to. AUSTRALIA Sydney Eurotherm Pty. Ltd. T (+61 2) 9838 0099 F (+61 2) 9838 9288 E [email protected] AUSTRIA Vienna Eurotherm GmbH T (+43 1) 7987601 F (+43 1) 7987605 E [email protected] BELGIUM & LUXEMBOURG Moha Eurotherm S.A/N.V. T (+32) 85 274080 F (+32) 85 274081 E [email protected] BRAZIL Campinas-SP Eurotherm Ltda. T (+5519) 3707 5333 F (+5519) 3707 5345 E [email protected] DENMARK Copenhagen Eurotherm Danmark AS T (+45 70) 234670 F (+45 70) 234660 E [email protected] FINLAND Abo Eurotherm Finland T (+358) 22506030 F (+358) 22503201 E [email protected] FRANCE Lyon Eurotherm Automation SA T (+33 478) 664500 F (+33 478) 352490 E [email protected] GERMANY Limburg Eurotherm Deutschland GmbH T (+49 6431) 2980 F (+49 6431) 298119 E [email protected] HONG KONG & CHINA Eurotherm Limited North Point T (+85 2) 28733826 F (+85 2) 28700148 E [email protected] Guangzhou Office T (+86 20) 8755 5099 F (+86 20) 8755 5831 E [email protected] Beijing Office T (+86 10) 6567 8506 F (+86 10) 6567 8509 E [email protected] Shanghai Office T (+86 21) 6145 1188 F (+86 21) 6145 1187 E [email protected] Eurotherm is also represented in the following countries: SPAIN Madrid Eurotherm España SA T (+34 91) 6616001 F (+34 91) 6619093 E [email protected] SWEDEN Malmo Eurotherm AB T (+46 40) 384500 F (+46 40) 384545 E [email protected] SWITZERLAND Wollerau Eurotherm Produkte (Schweiz) AG T (+41 44) 7871040 F (+41 44) 7871044 E [email protected] INDIA Chennai Eurotherm India Limited T (+91 44) 24961129 F (+91 44) 24961831 E [email protected] UNITED KINGDOM Worthing Eurotherm Limited T (+44 1903) 268500 F (+44 1903) 265982 E [email protected] IRELAND Dublin Eurotherm Ireland Limited T (+353 1) 4691800 F (+353 1) 4691300 E [email protected] www.eurotherm.co.uk U.S.A. Leesburg VA Eurotherm Inc. T (+1 703) 443 0000 F (+1 703) 669 1300 E [email protected] ITALY Como Eurotherm S.r.l T (+39 031) 975111 F (+39 031) 977512 E [email protected] www.eurotherm.com Algeria Azerbaijan Bahrain Bangladesh Benin Bosnia and Herzegovina Bulgaria Burkina Faso Cameroon Canada Czech Republic Egypt Georgia Greece Guinea-Conakry Hungary Indonesia Iran Iraq Israel Ivory Coast Japan Jordan Kazakhstan Kenya Kuwait Latvia Lithuania Malaysia Mali Mexico New Zealand Niger Nigeria Oman Pakistan Philippines Puerto Rico Qatar Romania Russia Saudi Arabia Serbia and Montenegro Singapore Slovak Republic Slovenia South Africa Sri Lanka Thailand Togo Tunisia Turkey Turkmenistan UAE Ukraine Uzbekistan ED55 KOREA Seoul Eurotherm Korea Limited T (+82 31) 2738507 F (+82 31) 2738508 E [email protected] Represented by: NETHERLANDS Alphen a/d Rijn Eurotherm B.V. T (+31 172) 411752 F (+31 172) 417260 E [email protected] NORWAY Oslo Eurotherm A/S T (+47 67) 592170 F (+47 67) 118301 E [email protected] POLAND Katowice Invensys Eurotherm Sp z o.o. T (+48 32) 2185100 F (+48 32) 2177171 E [email protected] © Copyright Eurotherm Limited 2007 Invensys, Eurotherm, the Eurotherm logo, Chessell, EurothermSuite, Mini8, Eycon, Eyris, EPower and Wonderware are trademarks of Invensys plc, its subsidiaries and affiliates. All other brands may be trademarks of their respective owners. All rights are strictly reserved. No part of this document may be reproduced, modified, or transmitted in any form by any means, nor may it be stored in a retrieval system other than for the purpose to act as an aid in operating the equipment to which the document relates, without the prior written permission of Eurotherm limited. Eurotherm Limited pursues a policy of continuous development and product improvement. The specifications in this document may therefore be changed without notice. The information in this document is given in good faith, but is intended for guidance only. Eurotherm Limited will accept no responsibility for any losses arising from errors in this document. ii Printed in England 10.07 Main contents Issue 1 Glass INTRODUCTION Eurotherm® Glass Industry Executive Summary Strength Through Wide-ranging Application Experience Glass Catalogue Part No. HA029511U001 Iss. 1 Printed in England 10.07 i Glass ii Introduction contents Issue 1 Glass Eurotherm® Glass Industry Executive Summary Leading the way in Innovation and Solutions Eurotherm, part of the Invensys group of companies, is a global supplier of automation and process control systems and products to the process and manufacturing industries, of which the Glass market represents a major part of its supply. By combining automation and process control knowledge with world class specialist products, Eurotherm is able to offer an extensive range of the most cost effective Glass solutions. Eurotherm is committed to developing products and services specifically for the Glass industry to enable the continual reduction of costs, while maximising productivity. ● Serving the diverse demands of glass applications Eurotherm is recognised for its expertise in working with both end users and process equipment suppliers to produce advanced solution systems. ● A successful history in supplying scalable automation solutions Eurotherm has over 40 years of history in providing scalable system solutions to a large and expanding customer base. Solutions are designed to meet your business needs by applying wide ranging control systems knowledge to the critical factors identified by glass customers that will help to ensure that they are successful and competitive in a demanding manufacturing world. Increase process efficiency Helping to reduce cost of production through: ● Optimising the process and equipment usage. ● Optimising energy usage. ● Reducing waste through increased accuracy of control and specialist control algorithms. ● Curtailing rework and reducing scrap by improving consistency and repeatability. ● Increasing plant availability using plant proven, reliable control systems. ● Reducing and eliminating paper trails by utilising extensive data management, archive and reporting facilities. ● Enhancing personnel productivity with a structured view of plant operation and training. Reduce cost of ownership Eurotherm control systems are designed to provide you with the best value, reducing plant downtime and maintenance costs, by: ● Ensuring increased equipment availability through the use of products with high MTBF, redundant control strategies, online re-configuration and hardware ‘Hot Swap’ capability. ● Utilising up-to-date proven technology designed to international standards with the future firmly in focus. ● Offering total life cycle support including commissioning, training and on-site support service. Eurotherm Glass Industry Executive Summary Issue 1 1 Glass Improve product quality Achieve marketplace leadership through quality and customer satisfaction by: ● Decreasing the risk of human errors with secure recipe management systems and advanced control strategies. ● Improved, more demanding, quality tolerances by application of process diagnostics and process modelling. ● Out-of-specification product identification, with automatic alerts. ● Improved information flow with seamless integration to business systems. Providing vertical integration At Eurotherm we understand that our control systems form an important part of your demand for overall business efficiency. Systems are designed to include, or be part of, the integration of the shop floor automation and the business scheduling systems to provide access to: ● Information transfer systems via relational databases and secure historic data files. ● Business systems with Enterprise Resource Planning systems, such as SAP. ● Manufacturing planning systems (MRP, MRP2). Meeting legislation and regulatory requirements We recognise the importance of legislation and accreditation in the Glass industry. Our control systems are designed to facilitate regulatory compliance at all levels of the solution, by: 2 ● Comprehensive secure data management solutions that assist customers’ needs for long-term traceable provenance of their products. ● Eliminating guesswork and making more accurate and timely decisions to improve safety. ● Providing tighter control to lower emissions and provide cleaner effluent. Eurotherm Glass Industry Executive Summary Issue 1 Glass Eurotherm is pleased to be involved with Glass industry original equipment suppliers and end user customers from across the world. Some of our major customers include: Kanthal – Philips Lighting - Tamglass - Owens Illinois - Draka Comteq Fibre - PPG - OSRAM - Corning - Owens Corning - Asahi Vetrotex - Glaverbel - AGC Automotive - Bormioli - Seves - CNUD EFCO - FIC - BH-F - Pilkington - Schott - HORN - Nikolaus SORG - Swarovski - Riedel - Technoglas - Air Products - Air Liquide - Essilor - Hankuk Glass - Henry F. Teichmann - Johns Manville - TG Huanan Glass - Changjiang Float Glass Reputation Eurotherm has a reputation for delivering process control and automation solutions that provide you with measurable financial advantages of saving time, money and resources. These savings are achieved by providing solutions that can reduce energy costs and improve plant/process productivity, while enhancing the quality of products. World-wide presence Operating through Eurotherm companies, authorised agents and channel partners across the world guarantees you access to local expertise backed up by global specialists. Regional systems engineering centres in strategic locations, operate advanced engineering methodologies to provide high quality, reliable systems solutions on time and within budget. Above all, at Eurotherm we believe in understanding and solving your needs through personal contact and individual commitment. This blend of capabilities within our global organisation creates an unmatched opportunity of success for our customers. Eurotherm Glass Industry Executive Summary Issue 1 3 Glass 4 Eurotherm Glass Industry Executive Summary Issue 1 Glass Strength Through Wide-ranging Application Experience Our range of application experience could help you to increase productivity and lower costs. All of our solutions in the glass industry are flexible and scalable to suit your process exactly. Example applications Furnace control Glass manufacture requires a high level of accuracy and reliability in the control of the furnace to achieve consistent glass quality, to avoid energy losses and to keep emissions within legislated boundaries. Reliability is particularly important at critical stages in the process such as the Furnace Reversal. Our T2550 PAC (Programmable Automation Controller) is designed with integral redundancy and is synchronised to a real time clock to ensure that this process can be managed safely and efficiently. ● High availability with dual redundant processors ● World renown accuracy of control ● Continuous, precise glass level control ● Cross-limiting lead/lag combustion control ● Fuel flow/ratio control ● Oxygen trim ● Fuel switch over control Boosting power control and monitoring Molten glass is a conductor of electricity. Passing high currents through the glass produces direct heating in the resistance presented by the glass. This heating is beneficial as it heats the ‘colder’ bottom glass in the furnace. This heated bottom glass rises towards the top and has a stirring effect which helps with melting and heat transfer. Boosting is often used to meet periodic fluctuations in demand or to support the pull rate of a furnace at the end of its operating life. Boosting may also help to reduce NOx emissions. For electrical power control and monitoring in fibre glass, float glass, containers and insulation applications, Eurotherm supplies the complete systems including the electrical cabinets, power controllers and necessary transformers. ● Environment protection with electro-static filters to control particle emissions ● Controlled convection currents to promote homogeneity Strength Through Wide-ranging Application Experience Issue 1 1 Glass Tin bath and roof heating The bath is the forming part in a flat glass production process where it is taken from the furnace spout at 1100°C and leaves the bath at 600°C when it is solid. While in the bath the glass travels through heating, fire polishing and cooling zones. Modern flat glass systems require precise temperature control for these multiple zones. Eurotherm control systems provide power control with multi-parameter influence. Annealing lehr Glass enters the annealing lehr at 600°C, at which it can support its own weight but still has many internal stresses. Annealing lehrs have several temperature control zones through which the glass is slowly cooled. These must be properly monitored and controlled for consistency and quality of the glass. This cooling process is critical for the cutability and maximum yield of finished glass. ● Multi-zone temperature control ● Easy monitoring with local and central HMI solutions ● Heat-cool ● Speed control ● Setpoint changes and control stability to 0.5°C in a range of 0-2000°C Bushing temperature control Glass fibre manufacture requires a high level of accuracy and reliability to achieve a consistent quality in the fibre produced. The Eurotherm bushing temperature control application has been specifically designed to control temperature cycling in glass fibre manufacture and has been shown to bring: ● Increased efficiency ● Improved recovery time ● Increased availability and productivity ● Setpoint depression and ramping - allowing control of the temperature profile during a production cycle ● ‘Cold bushing’ protection preventing thermal shock to the bushing in the event of operational or mechanical failure ● Better than 1°C resolution ● Operation with one or two thermocouples - efficient implementation in complex control systems requiring programmed start-up of a heat sensitive process from stand-by condition 2 Strength Through Wide-ranging Application Experience Issue 1 Glass Electrical motor control Throughout the glass industry electrical motors are used in raw material transport, in exhaust gas handling, in glass forming, in annealing, in cutting and many more applications. Speed, torque and position are critical process parameters in obtaining quality products and should be controlled with high accuracy and reliability. For speed and motion control Eurotherm provide the complete systems including: motors AC DC or servo drives and electrical cabinets. Eurotherm is particularly well known for its expertise in synchronizing speed and torque in multiple motor applications such as top roll control in a tin bath, or squeezing roll and unwind control in the rolled wired glass process. ● Open or closed loop vector control ● Wind/unwind control ● Speed or torque synchronisation ● Top rail control ● Squeezing roll control ● Conveyor control ● Cooling fan control Windscreen forming Windscreens are formed by feeding flat sheets of glass through a tunnel furnace. Each sheet is carried by a very precise mould. The temperature rise will soften the glass and gravity lets the glass take the form of the mould. The tunnel furnace has a temperature controlled pre-heating zone and an electrical power controlled forming zone. The thermal energy from metallic resistor elements or from medium wave infra-red elements is transferred to the screen in a combination of air-heating and infrared emission. The forming zone has always been divided into hundreds of sub-zones. With the car industry demanding more and more tightly banded tolerances and introducing more complicated forms and shapes, such as top roofs, the number of sub-zones is increasing rapidly. Complete Eurotherm temperature control, power control and supervisory systems for windscreen forming are in operation world-wide. ● Accurate multi-zone temporature control ● Accurate open or closed loop power control ● High packing density of power controllers to reduce cabinet and floor space ● Advanced single cycling firing for infra-red elements, eliminating DC components ● Power controller setpoint transfer and monitoring by digital communication, reducing the I/O requirements of the control system ● Feed through control Strength Through Wide-ranging Application Experience Issue 1 3 Glass Environmental monitoring In protecting our habitat the glass industry is making major contributions with the reduction of waste emissions to air, land and water. Monitoring of emissions is the starting point of emission reduction. Eurotherm has over 40 years of experience in providing process and environmental monitoring systems. ● Continuous NOx, SO2, Chlorides, Fluorides etc. monitoring ● Filter pollution monitoring and automatic filter cleaning control ● Tamper proof data logging Production of glass for the life science industry More and more life science industry companies are forcing their suppliers to adhere to Good Manufacturing Practices. A requirement for GMP production facilities is to make use of GAMP4 validated control and monitoring systems. With its vast experience in the life science industry Eurotherm is extremely well fitted to assist the glass industry with complex implementation of systems that can be validated in accordance with GAMP4. Please refer to our Life Sciences Brochure for more detailed information on this subject. Process modeling Process modeling and simulation is becoming more and more practiced in process development activities or advanced furnace and feeder control. Modeling and simulation requires vast amounts of process data. Process control systems are the main data source and should therefore have an easy to implement and use interface with modeling and simulation systems. Eurotherm Control and Monitoring Systems are known for their ease of implemention and use with OPC and ODBC interfaces. ● OPC Servers with tag browse facilities ● ODBC interfaces ● Data collection in relational databases 4 Strength Through Wide-ranging Application Experience Issue 1 Glass PROCESSES Processes Glass Bushing Windscreen Forming Oxygen Monitoring in Exhaust Gas Making Glass Containers by Automatic Process Making Flat Glass by the Float Process Glass Fibre Manufacturing Control Manufacturing Optical Fibre Manufacture of Tubing Making Glasses and Light Bulbs Secondary Glass Processing Product Manufacturing Glass Fibres Stoichiometric Combustion Control using the 2704 Controller Stoichiometric Combustion Control using the 3500 Controller Modulating Burner Combustion Control for Glass Furnaces and Hearths Lambda Control Reducing NOx Emissions Thyristors and Transformers Control of Silicon Carbide Heating Elements using SCRs Glass Catalogue Part No. HA029511U002 Iss. 1 Printed in England 10.07 i Glass ii Processes contents Issue 1 INDUSTRY Glass Bushing Application Note Power control of platinum draw-plate: glass wire manufacture Making glass Glass Glass Glass wire manufacturing requires a high temperature stability of the drawplate to ensure a good quality of the wire, one important parameter being a constant diameter. To obtain this stability, the temperature control is made with a Eurotherm controller giving a very high stability and a thyristor stack which ensures that the right electrical power is injected into the load. This stack is a true power controller giving a constant power for a constant demand even if the load resistance or the supply voltage varies. The physical configuration of the control loop is very classical: Melted Glass Thyristor unit Platinum draw-plate 3 to 5V Thermocouple Setpoint 0-10V Power signal Wire of Glass 2704 Communication bus with control process and supervisory system 75 Units 471, TE10P or 7100A + 2704 The final load, where temperature must be kept constant, is the draw-plate itself made in platinum which has a high positive temperature coefficient for its resistance: 55 x 10-4 per °C. The cold resistance is about 8 times less than the resistance when at the correct temperature. In the cold condition the load is nearly a short-circuit. The thyristor stack current limit must handle this characteristic without any damage both for the stack and the load. The stack will allow the right level of current to flow through itself and through the load requiring a fast current limit action. When hot, the load resistance is still very low. The load supply voltage is a few volts, but the current needed to get the right power is very high: a few thousand amperes, so a steep down transformer is needed to draw the power from the 380V supply. The thyristor stack controls the transformer primary. The stack current rating needed is then only 150 Amps for up to 57 KW maximum load power, depending on draw-plate size. To control the exact active power transferred to the load, the stack is a Eurotherm true power controller 471 type 150A/400V using a true power measurement method: product of instantaneous values of current (I) and voltage (v). P=1 T ∫ v(t).i(t).dt Due to the temperature coefficient of the platinum, the transformer primary control and the high temperature stability required, the thyristor is working in phase angle firing mode. Glass Bushing Application Note Issue 1 1 Glass The control loop is closed by a temperature measurement on the draw-plate sent to the 2704 controller. The achieved temperature stability is 0.1°C at working temperature. The Eurotherm controller with Digital Communication provides the facility to remotely control and supervise 75 couples of controllers/471. To have access from the control room, where the supervisory system is installed, to the level of power delivered by each 471 stack, the 0-10V output power signal available on each 471 is sent to each associated controller on its external setpoint input, calibrated to 0 - 57 for 0-10V which gives a direct reading of power. Another possibility for the thyristor unit is to use a TE10P true power controller which offers communication (Modbus or Profibus) for connection on the communication bus. All thyristor power units parameters can be available to operators in the control room: power, current, unit status, alarms etc. The manufactured glass wire is then used in different parts of industry: ● Reinforced plastic in the car industry ● Shock absorber for trucks ● Ski manufacturing industry ● Leisure boat manufacturing ● Glass fiber insulating materials 2 Glass Bushing Application Note Issue 1 INDUSTRY ● Reduced installation cost ● Improved process control efficiency Windscreen Forming Application Note Eurothem has always been very present and successful in power glass applications such as: ● Flat glass: roof heating, annealing ● Bottle manufacturing: boosting, feeder heating ● Glass wire manufacturing: boosting, feeder heating, bushing ● Windscreen forming Making glass Glass Glass The principle of windscreen forming is that the flat windscreen is going through a tunnel furnace on a very precise form. There is one type of form per type of windscreen. When at the right temperature, the soft glass will take accurately the form banding by gravity. The first part of the furnace is the temperature controlled pre-heating zone. The second part is the forming zone with precise electrical power control. Heating elements are metallic resistors, medium wave infra-red, with a low temperature coefficient. Heat transfer to the windscreen is a combination of air heating and infra-red emission. The quality and precision of the windscreen banding is given by the accuracy of the pre-heating zone temperature control and the accuracy of forming zone power control. For such furnaces, the number of zones can be very high, typically 100 to 300 zones. The present tendency is to increase the number of zones to improve precision of banding and to manufacture more complicated and varied windscreen shapes. The total power of such furnaces ranges from several hundred kW to several MW. The architecture of the installation in terms of electrical control is as follows: ● A PLC supervisory system is controlling the furnace: temperature in pre-heating, zone, power in forming zone. ● The power control of the heating elements is made with multi-channel communicating thyristor power units - TU Series for both pre-heating and forming zones. ● Firing mode: single cycle. ● Control mode: true power V x I, very important for banding accuracy. ● Through a communication link (Modbus or Profibus depending on type of PLC), all TU parameters are available (read and write) on the supervisory system: power setpoint, load output power, status word/alarms. Windscreen Forming Application Note Issue 1 1 Glass Serial communications link Modbus or Profibus protocol n TU units TU 4 channel Fast setpoint transfer On the furnace forming part, during the process time each windscreen stays in a heating zone; its next working setpoint, for the next heating zone it will move into, is loaded in each TU channel. When all the windscreens reach their next heating zone, a single command through the communication link will transfer all pre-loaded setpoints for each zone as an active setpoint within a few milliseconds. 2 TU 4 channel Advantages of Eurotherm solution ● Thyristor firing mode: single cycle - perfectly adapted for this application. ● Power control mode for a better process control. ● Multi-channel TU unit reduces installation cost: floor space saving and smaller panels, lower cost per channel. ● Very good accuracy of TU power control V x I : absolutely necessary to get a better process control and windscreen banding accuracy. ● Communication ● Reduces cost of installation (wiring etc). ● Improves process control efficiency and quality. Windscreen Forming Application Note Issue 1 INDUSTRY ● Combustion efficiency ● Emission reduction Oxygen Monitoring in Exhaust Gas Application Note Oxygen monitoring systems are used widely in exhaust monitoring in the glass industries. The instrument is not required to perform a control function, but is used to interpret the information from the oxygen probe and to handle the probe cleaning function. The oxygen probe connects directly to the process inputs of the instrument. The instrument then performs the linearisation of the probe signals to determine the amount of oxygen in the atmosphere. A typical oxygen monitoring system schematic is shown in Figure 1. Making glass Glass Glass Oxygen Probe Input Self-Clean Output Self-cleaned Solenoid Exhaust Oxygen Probe Channel Reference Air Port Figure 1 Oxygen monitoring system schematic Commissioning the oxygen monitor is straight forward, since no control configuration is required. The oxygen level may be configured to read percentage, log of concentration or parts per million. Once configured, the probe diagnostic page displays the oxygen level, the probe mV signal and the probe temperature. This is illustrated in Figure 1. The oxygen level may be used to optimise the combustion process. Oxygen Monitoring in Exhaust Gas Application Note Issue 1 1 Glass 2 Oxygen Monitoring in Exhaust Gas Application Note Issue 1 INDUSTRY ● Container ● Blow and Blow ● Press and Blow Making Glass Containers by Automatic Process Application Note Most bottles and jars are now made automatically by one of the two methods shown below. Making glass Glass Glass The Blow and Blow Method Molten ‘gobs’ of glass are delivered into a mould known as a ‘blank’ or parison mould. A puff of compressed air blows the glass down into the base of the mould to form the neck or ‘finish’ part of the bottle or jar. A second blast of compressed air is then applied through the already formed neck of the container to form the ‘parison’ or pre-form for the bottle against the walls of the parison mould cavity. The thick walled parison is then transferred to the final mould during which time the surface of the glass ‘reheats’ and softens again enough to allow the final container shape to be fully formed against the walls of the final mould cavity by the application of either compressed air or vacuum. The container is then removed and transferred to an annealing oven (lehr) where it is reheated to remove the stresses produced during forming and then cooled under carefully controlled conditions. The Press and Blow Method Molten ‘gobs’ of glass are delivered into the parison mould and a plunger is used to press the glass into the parison shape. The final mould stage of the process is the same as that described for the Blow and Blow process. Raw materials are automatically mixed and fed into the furnace where they are heated and fused at approximately 1500°C Glass melting furnace Molten glass is fed into a machine where it is automatically blown. Bottles are made in two stages. First a parison shape is blown. This is transferred to a second mould in which the bottle is blown to its final form. Bottles are inspected and despatched for subsequent filling, capping and labelling. Annealing lehr in which bottles are reheated and gradually cooled to prevent stresses developing. Making Glass Containers by Automatic Process Application Note Issue 1 1 Glass The Press and Blow Process 1 Gob dropped into blank mould 2 Plunger presses blank shape 3 Blank blown 4 Blank shape 5 Blank transferred to blow mould 6 Final shape blown 7 Finished jar The Blow and Blow Process 1 Gob dropped into blank mould 2 Neck formed 4 Blank shape 3 Blank blown The IS process has now universally replaced almost all others. It is not certain whether ‘IS’ denotes its inventors, Ingle and Smith, or its main characteristic which is independent synchronised units with a synchronised gob distribution system to each section (i.e. Individual Section). IS machines can comprise several sections and 10 & 12 section or 16 to 20 section tandem machines are now common. The 5 Blank transferred to blow mould 6 Final shape blown 7 Finished bottle machine can operate on the blow and blow or press and blow principle and double gob production, i.e. delivery of two gobs of glass at the same time is common. Triple and quadruple gob machines are also increasingly used. The machine is currently capable of producing more than 600 containers per minute. BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Making Glass Containers by Automatic Process Application Note Issue 1 Glass Glass The float process - invented by Sir Alastair Pilkington in 1952, makes flat glass. This process allows the manufacture of clear, tinted and coated glass for buildings, and clear and tinted glass for vehicles. INDUSTRY There are around 260 float plants worldwide with a combined output of about 800,000 tonnes of glass a week. Flat glass ● Float process ● Rolled process Making glass ● Making Flat Glass by the Float Process Application Note A float plant, which operates non-stop for between 11-15 years, makes around 6000 kilometres of glass a year in thicknesses of 0.4mm to 25mm and in widths up to 3 metres. A float line can be nearly half a kilometre long. Raw materials enter at one end. From the other, plates of glass emerge, cut precisely to specification, at rates as high as 6,000 tonnes a week. In between lie six highly integrated stages. Stage 1: Melting and refining Fine-grained ingredients, closely controlled for quality, are mixed to make a batch, which flows into the furnace which is heated to 1500°C. Float today makes glass of near optical quality. Several processes - melting, refining, homogenising - take place simultaneously in the 2,000 tonnes of molten glass in the furnace. They occur in separate zones in a complex glass flow driven by high temperatures, as the diagram shows. It adds up to a continuous melting process, lasting as long as 50 hours, that delivers glass at 1,100°C, free from inclusions and bubbles, smoothly and continuously to the float bath. The melting process is key to glass quality and compositions can be modified to change the properties of the finished product. Batch 1.500°C Refining zone Melting Homogenisation 1.600°C Cooling zone 1.100°C Glass flows in a large float furnace Stage 2: Float bath Glass from the melter flows gently over a refractory spout on to the mirror-like surface of molten tin, starting at 1,100°C and leaving the float bath as a solid ribbon at 600°C. The principle of float glass is unchanged from the 1950s, but the product has changed dramatically: from a single equilibrium thickness of 6.8mm to a range from sub-millimetre to 25mm; from a ribbon frequently marred by inclusions, bubbles and striations to almost optical perfection. Float delivers what is known as fire finish, the lustre of new chinaware. Making Flat Glass by the Float Process Application Note Issue 1 1 Glass Stage 5: Inspection Surface tension Ribbon forming process Tractive force Gravity 1.050°C Final ribbon 600°C Surface tension The float process is renowned for making perfectly flat, flaw-free glass. But to ensure the highest quality, inspection takes place at every stage. Occasionally a bubble is not removed during refining, a sand grain refuses to melt, a tremor in the tin puts ripples into the glass ribbon. Automated on-line inspection does two things. It reveals process faults upstream that can be corrected enabling computers downstream to steer cutters round flaws. Inspection technology now allows more than 100 million measurements a second to be made across the ribbon, locating flaws the unaided eye would be unable to see. The data drives 'intelligent' cutters, further improving product quality to the customer. Scanner Stage 3: Coating Laser Coatings that make profound changes in optical properties can be applied by advanced high temperature technology to the cooling ribbon of glass. On line Chemical Vapour Deposition (CVD) of coatings is the most significant advance in the float process since it was invented. CVD can be used to lay down a variety of coatings, less than a micron thick, to reflect visible and infrared wavelengths, for instance. Multiple coatings can be deposited in the few seconds available as the glass ribbon flows beneath the coaters. Further development of the CVD process may well replace changes in composition as the principal way of varying the optical properties of float glass. Glass ribbon Detector Inspection by laser scanner Stage 6: Cutting to order Hot glass Diamond wheels trim off selvedge - stressed edges - and cut the ribbon to size dictated by computer. Float glass is sold by the square metre. Computers translate customers' requirements into patterns of cuts designed to minimise wastage. Resistive gas Hard coating The rolled glass process The rolling process is used for the manufacture of patterned flat glass and wired glass. A continuous stream of molten glass is poured between water-cooled rollers. Chemical vapour deposition Stage 4: Annealing Despite the tranquillity with which float glass is formed, considerable stresses are developed in the ribbon as it cools. Too much stress and the glass will break beneath the cutter. The picture shows stresses through the ribbon, revealed by polarised light. To relieve these stresses the ribbon undergoes heat-treatment in a long furnace known as a lehr. Temperatures are closely controlled both along and across the ribbon. Patterned glass is made in a single pass process in which glass flows to the rollers at a temperature of about 1050°C. The bottom cast iron or stainless steel roller is engraved with the negative of the pattern; the top roller is smooth. Thickness is controlled by adjustment of the gap between the rollers. The ribbon leaves the rollers at about 850°C and is supported over a series of watercooled steel rollers to the annealing lehr. After annealing the glass is cut to size. Wired glass is made in a double pass process. The process uses two independently driven pairs of water cooled forming rollers each fed with a separate flow of molten glass from a common melting furnace. The first pair of rollers produces a continuous ribbon of glass, half the thickness of the end product. This is overlaid with a wire mesh. A second feed of glass, to give a ribbon the same thickness as the first, is then added and, with the wire mesh "sandwiched", the ribbon passes through the second pair of rollers, which form the final ribbon of wired glass. After annealing, the ribbon is cut by special cutting and snapping arrangements. BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Making Flat Glass by the Float Process Application Note Issue 1 INDUSTRY ● Glass fibre ● Glass wool Manufacturing Glass Fibres Application Note Glass in the form of fibres has found wide and varied applications in all kinds of industry. Its composition depends on the intended use. Making glass Glass Glass For building insulation and glass wool the type of glass used is normally soda lime. For textiles, an aluminoborosilicate glass with very low sodium oxide content (E glass) is preferred because of its good chemical durability and high softening point. This is also the type of composition employed for the fibres used in the reinforcement of plastics, familiar for their application in protective helmets, boats, piping, car chassis and many other articles. In recent years, great progress has been made in making optical fibres which can guide light and thus transmit images round corners. These fibres are applicable to endoscopes for examination of internal human organs, changeable traffic message signs now in common use on motorways for speed restriction warnings and communications technology for transmitting telephone conversations much more efficiently than copper cable. There are two broad groups of glass fibre products: continuous glass fibre which is used for the reinforcement of plastics, rubber and cement; and glass wool, which is used for thermal insulation and which is produced by the Crown process. Glass fibre manufacture Continuous glass fibre is a continuous strand, made up of a large number of individual filaments of glass. Molten glass is fed from the furnace or "tank" through a channel or "forehearth" to a series of bushings which contain over one thousand six hundred accurately dimensioned holes or "forming tips" in its base. A constant head of glass is maintained in the tank and forehearth and the temperature of the glass in the bushings is controlled to very fine limits. Fine filaments of glass are drawn mechanically downwards from the bushing tips at a speed of several thousand metres per minute, giving a filament diameter, which may be as small as nine microns, or one tenth the diameter of a human hair. From the bushing the filaments run to a common collecting point where size is applied and they are subsequently brought together as bundles, or "strands", on a high-speed winder. Glass fibre is produced in a range of filament diameters and strand dimensions to tight tolerances for different end uses. It is used to strengthen and stiffen thermosetting plastics, thermoplastics, nylon and polypropylene as well as inorganic matrices, such as gypsum. Glass wool manufacture Glass wool is made in the Crown process. From the forehearth of the "tank" a thick stream of glass flows by gravity from the bushing into a rapidly rotating alloy steel dish "Crown" which has several hundred fine holes round its periphery. Manufacturing Glass Fibres Application Note Issue 1 1 Glass The molten glass is thrown out through the holes by centrifugal force to form filaments, which are further extended into fine fibres by a high velocity blast of hot gas. After being sprayed with a suitable bonding agent, the fibres are drawn by suction onto a horizontally moving conveyor positioned below the rotating dish. The mat of tangled fibres formed on the conveyor is carried through an oven which cures the bonding agent, then to trimmers and guillotines which cut the product to size. The mat may be further processed into rigid sections for pipe insulation. The mats are made into many products for heat and sound insulation in buildings, transport vehicles and domestic appliances. 1. 2. 3. 4. 5. 2 1 Tank Forehearth Spinners Conveyor Curing oven 6. Trimmers 7. Slitters 8. Bandsaw 9. Guillotine 10. Rolling machine 3 5 4 6 7 8 9 10 BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Manufacturing Glass Fibres Application Note Issue 1 INDUSTRY ● Optical fibre ● Chemical vapor deposition Manufacturing Optical Fibre Application Note Communications are increasingly based on electro-optic systems in which telephones, television and computers are linked by fibre optic cables which carry information by light. Making glass Glass Glass Making glass optical fibres is a highly specialised aspect of glass manufacture. Optical fibres consist of two distinct glasses, core of highly refracting glass surrounded by a sheath of glass with lower refractive index between the two glasses, it is guided by total internal reflection at the coresheath interface to the other end of the fibre. In theory, a wide range of glasses can be used as long as the difference in refractive index is appropriate but the higher the refractive index of the core relative to that of the sheath glass, the greater the carrying capacity of the fibre. A typical system available commercially comprises a germanium doped silica core and a borosilicate cladding. The aim in manufacture is to produce a fibre of glass which is so pure and free from defects that light inserted at one end will emerge at the other end a distance of 1 kilometre or more away. There are many manufacturing processes being used to produce cored fibre; two of these will illustrate the principles. All the processes require ultra-pure starting materials. Chemical vapour deposition High silica glass fibres are prepared by chemical vapour deposition in which layers of SiO, are deposited to make a preform, either on the outside of a mould or on the inside of a fused silica tube. The layers are doped during the deposition to control the refractive index. The preform is then drawn to a rod and subsequently to a fibre of 100-150mm diameter. The surface is protected from damage by a plastic coating. Deposited layer of SiO2 Glass lathe Exhaust Multi burner torch Gas mixing & control Silicane gas Additives Manufacturing Optical Fibre Application Note Issue 1 1 Glass The double crucible method The double crucible uses purified glasses in separate cricibles in a controlled atmosphere furnace. Fibre drawn from the tip consists of a uniform core drawn from the central crucible and a cladding drawn from the outer crucible. Raw materials Atmosphere control Furnace Platinum crucibles Core Cladding Optical fibre Winding machine BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Manufacturing Optical Fibre Application Note Issue 1 Glass Glass Manufacture of Tubing Application Note The Danner Process ● Tube glass ● Danner process ● Vello process Making glass INDUSTRY The Danner process was developed for the continuous production of glass tubing and rods. Subject to equipment design the process can make tubing of 1.6mm to 66.5mm diameter and rods of 2.0mm to 20mm diameter at drawing rates of up to 400m a minute for the smaller sizes. Glass flows from a furnace forehearth in the form of a ribbon, which falls on to the upper end of an inclined refractory sleeve, carried on a rotating hollow shaft or blowpipe. The ribbon is wrapped around the sleeve to form a smooth layer of glass, which flows down the sleeve and over the tip of the shaft. Tubing is formed by blowing air through a blowpipe with a hollow tip and rods are made by using a solid tip on the shaft. The tubing is then drawn over a line of support rollers by a drawing machine situated up to 120m away. The dimensions of the tubing are determined as the glass cools through its setting point at the catenary or unsupported section between the blowpipe and the first line roller. A given range of size is based on the diameter of the refractory sleeve, and variations within the range are obtained by adjusting the temperature of the glass, the rate of flow, the pressure of the blowing air and the speed of the drawing machine. The Vello Process The Vello process was a later development with a production capacity greater than that of the Danner process but based on a different principle. Glass flows from a furnace forehearth into a bowl in which a hollow vertical mandrel is mounted or a bell surrounded by an orifice ring. The glass flows through the annular space between the bell and the ring and travels over a line of rollers to a drawing machine up to 120m away. Tubing is made by blowing air through a bell with a hollow tip and rod is produced by using a bell with a solid tip. The dimensions of the tubing are controlled by the glass temperature, the rate of draw, the pressure of the blowing air and the relative dimensions of the bell and ring. Molten glass flows from the tank past a rotating hollow mandrel. The tubing is drawn off mechanically. Air pressure through the mandrell and the rate of drawing influence diameter and wall thickness. The tubing is cut off to required lengths, and the ends fire-finished. Rotating mandrel Melting Tractor Cutting and guaging Drawing Warehouse Manufacture of Tubing Application Note Issue 1 1 Glass BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Manufacture of Tubing Application Note Issue 1 INDUSTRY ● Light bulbs ● Westlake machine Making Glasses and Light Bulbs Application Note Automatic domestic glassware production The Westlake machine was developed for blowing bulbs for domestic lamps and radio valves at production rates of up to 75,000 a day (gross). It has since been adapted for making drinking glasses, including stemmed ware, at up to 55,000 a day (gross). Making glass Glass Glass The machine copies the action of a handblower in gathering glass from the furnace, forming a parison and blowing the article in a cast iron mould. Twelve pairs of spindles or blowpipes, together with their blowing air valves and past moulds, travel around a central column. The gathering equipment is carried on top of the column and sets of cams are fitted around the column to control the sequence of operations. Glass is gathered by vacuum into a pair of blank moulds and the pairs of blanks are transferred in turn to each pair of spindles. The spindles are rotated and swung down, and air is introduced to form each blank into a parison, controlling the profile and distribution of the glass before blowing the required shape in the wetted mould. The mould opens and the spindle jaws release the article that is then transferred to the stemming machine. Here the neck formed in the mould is reheated and stretched to the required length. The article then passes to the burn-off machine where oxygen-gas flames remove the "moil" or waste glass, which was originally formed at the gathering position, and the finished piece is conveyed to the lehr for annealing. Electric light bulb envelope production The ribbon machine was developed for the high-speed manufacture of bulbs for domestic lamps, auto lamps, vacuum flasks, etc. Its main feature is that glass travels through it in a straight line rather than on a rotary path as with the Westlake machines. Production rates in excess of 1000 a minute can be achieved. Continuous chain of blowheads pierce ribbon of glass pushing it in parison form through holes in the continuous belt on which the ribbon travels. When moulds are in position, the glass is blown to the finished shape of the bulb. Rotating disc separates ribbon of glass from blown bulb Ribbon of glass continues to cullet bin and is re-used Ribbon of glass flows from forehearth of furnace Glass bulbs drop into scoops on continuous rotating turntable which ejects them onto conveyor belt Conitinuous chain of blow moulds close around parison Making Glasses and Light Bulbs Application Note Issue 1 1 Glass From the furnace forehearth molten glass flows down between two rotating water-cooled rollers and onto the Ribbon machine. On leaving the rollers the ribbon of glass is carried through the machine on a series of orifice plates, forming a continuous belt pierced with holes. As the ribbon moves forward, a continuous chain of blowheads does the glassblower’s job for him. It blows the glass through the hole and the "blister" forms into a bulb inside a rotating mould, which meets and closes around it from below. Still moving forward on the ribbon, the shaped bulb is released from its mould, cooled by air jets and then tapped off the ribbon to fall onto the scoops of a rotary turntable which tips it onto a conveyor belt. This carries it through an annealing lehr and air cooling to inspection and packing. The unused part of the ribbon passes direct to a cullet system for re-melting. More than 1,000 bulbs per minute can be produced on such a machine. BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Making Glasses and Light Bulbs Automatic Process Application Note Issue 1 INDUSTRY ● Glass processing ● Annealing ● Toughening ● Coating ● Decorating Secondary Glass Processing Application Note Annealing Glass, like most other materials, contracts on cooling. However, due to its low thermal conductivity, it does not cool uniformly and the surfaces, which cool more rapidly, shrink more quickly than the centre. This produces uncontrolled strain in the article. If the internal surface of an unannealed container is scratched, the container will disintegrate. Badly annealed glass articles cannot withstand thermal shock and are liable to break in use. The excessive strain can be avoided by slow cooling at a controlled rate, called annealing. Annealing is done in an oven, called a lehr, through which glass articles pass on a slowly moving conveyor belt. Making glass Glass Glass A container, for example, would enter a lehr at approximately 450°C. As the conveyor moves through the lehr, which is approximately 20m long, the temperature is at first increased to about 560°C, at which the glass just begins to flow and is then gradually reduced to a temperature at which no further strain can be induced, and then cooled by fan air to room temperature. The time required for this process depends on the size of the article and the wall thickness but is normally completed in less than an hour. Toughening Glass has an extremely high compressive strength. Glass can be thermally strengthened by inducing invisible thin layers in compression on the outer surfaces. In order to break such toughened or tempered glass, the compression has to be neutralised and additional tension applied. Toughening is obtained by re-heating the glass article uniformly to a temperature just above that at which deformation could take place and then rapidly cooling the surfaces by jets of air. If one can imagine a sheet of glass as consisting of three layers then the process becomes easier to understand. The air jets rapidly cool and freeze solid the outer layers while the inner layers continue to contract. While it is contracting it exerts compression on the outer layers while putting itself under tension. This method can be applied to flat glass or simple shapes like curved car windscreens or even tumblers. Glass thickness must be uniform, not too thin, and the shape of the article must be such that all surfaces can be uniformly cooled at the same time. Bottles do not satisfy these conditions and cannot be toughened in this way. However, it is possible to toughen bottles chemically by immersing hot bottles in a molten potassium salt. Potassium ions replace sodium ions on the surface and, being larger, create a very thin layer of compression. Toughened glass cannot be further processed since any damage to the surface will expose the centre layer, which is in tension, and the glass will shatter. The shattering of a car windscreen is a good example of this phenomenon. Coating The coating of glass surfaces has been practiced for centuries. Mirrors are a good example of this art. However, this method of giving glass new hysical, chemical and optical properties has made great strides in the last few decades. Lightweight glass containers are coated with organic compounds to give the surfaces a degree of lubricity and thus preventing abrasion in handling. This adds strength to the container and has enabled glass manufacturers to make a lighter and better product. Coating containers with tin compounds also produces a stronger product. Coating glass containers with plastic materials for added strength and safety is a further way of lightweighting or increasing internal pressure resistance. Secondary Glass Processing Application Note Issue 1 1 Glass Decorating Formed and annealed glass may be further processed. This may be done by taking away from or adding to the surface of the glass. It may also be heated, manipulated, and reshaped. These methods include: i. Taking away: A disturbance of the surface of glass may result in a matt or obscured finish. Where a transparent surface is then required this is produced by polishing on felt or wood wheels by hydrofluoric acid solution. ii. Adding: Vitreous enamels, which are glasses that melt at relatively low temperature and can be coloured, may be applied to the surface of formed glass. Metal compounds can also be applied. In both these cases the article is then reheated after application of the enamel or metal coating so that it fuses permanently to the surface of the glass. Also metal films can be applied by spraying, or by chemical or vapour deposition; and Decorating Domestic Glass. iii. Manipulating: Glass which has been formed and annealed may be reheated and manipulated into a new shape. It then has to be re-annealed and may be toughened. Other forms of decorations are etching with hydrofluoric acid, sandblasting and vitreous enamelling. In the latter, vitreous enamels, which are low melting point glasses held in an aqueous medium are deposited on the glass through very fine wire mesh screens and are then fired in an enamelling furnace. The enamel thus becomes an integral part of the glass article. BRITISH GLASS information courtesy of the British Glass web site: www.britglass.co.uk 2 Secondary Glass Processing Application Note Issue 1 INDUSTRY Glass Fibre Manufacturing Control Application Note Glass fibre manufacture requires a high level of accuracy and reliability to achieve a consistent quality in the fibre produced. Making glass Glass Glass Eurotherm® has wide experience in glass furnace control, having installed many systems over the last 40 years, and their instrumentation has been proved time and again in the field. Bushings control ● Bushing control ● Setpoint depression and ramping ● Line break detection ● Power surge protection by output limits ● Dual thermocouple protection The bushings control application has been developed specifically to control temperature cycling in glass fibre manufacture, with facilities for: ● Setpoint depression and ramping, enabling control of the temperature profile during a production cycle. ● ‘Cold bushing’ protection, preventing thermal shock to the bushings in the event of operational or mechanical failure. The bushings control application offers better than 1°C resolution and can operate with one or two thermocouples, making its implementation in complex control systems requiring programmed start-up of a heat sensitive process from stand-by condition highly efficient. Setpoint depression and ramping The main aim of the control module is to control bushing temperature under PID action and, whilst doing this, ensure that the physical bushing is not subject to severe changes in temperature that may damage the bushing. Figure 1 shows a typical setpoint profile for the bushings control module. During normal running mode, when actually winding glass fibre onto a drum, the target temperature of the bushing is entered by the operator. This value is never changed by the control strategy and is referred to as the nominal setpoint. The motor automatically ramps down its speed to compensate for the increase in diameter of the drum. When the bushing is ready for production but the variable speed motor is not winding the glass fibre onto the storage reels, a setpoint depression, also entered by the operator, is used by the strategy to reduce the control setpoint. The bushing is in a ‘background’ mode with a limited amount of fibre being produced. After changing the winding drum, the operator can initiate a setpoint depression recovery. The control setpoint is ramped at a configurable rate from the depressed setpoint to the local setpoint value. The bushing gets re-heated to normal operating temperature ready to produce another drum of fibre. Setpoint deviation recovery Setpoint Setpoint Setpoint Normal running depressed depression recovery Setpoint depressed Time Figure 1 Typical production cycle Glass Fibre Application Note Issue 2 1 Glass On power-up or after a power failure to the bushing heating power supply (bushing ‘cool’), the controller enters a setpoint deviation recovery mode where the control setpoint is kept close to the current process variable, then ramped to its target value. This action prevents generation of large control errors. Output limiting When the bushing is ‘cool’, the control module limits the controller output to a value selected from a break point curve depicted in Figure 2. A high limit is generated based on the current value of the process variable. The operating region is represented by the shaded area in the graph. 100% Control output limit 0% PVmin Bushing temperature PVmax Figure 2 Output protection limits HR084055U001 2 Glass Fibre Application Note Issue 2 INDUSTRY ● Zirconia probe input ● Temperature ● Oxygen ● Probe diagnostics ● Maths and logic ● Open communications Stoichiometric Combustion Control using the 2704 Controller The 2704CC is a fully programmable controller suitable for stoichiometric combustion in glass furnace applications. It is capable of being used solely to control the Lambda potential of the furnace, or as an integrated controller where this variable is controlled in conjunction with temperature. Additional features provide maths and combined logic functions. White paper Glass Glass At the heart of the controller is a specially designed function block capable of accepting most zirconia probes. Standard features include diagnostics indicating that the probe is about to fail and should be replaced. For standard applications, controllers are shipped pre-configured to the users specification, using a simple to complete order code. User customisation can be achieved by reconfiguring the controller via its front panel interface or the Eurotherm® iTools configuration software. The 2704CC is fully compatible with the standard 2704 process controller which is capable of up to three PID control loops; data sheet number HA026669. Oxygen Setpoint Probe Temp Probe mV °C mV Zirconia Function Block - Oxygen Control Loop Oxygen Trim Probe Fault Zirconia input ● Compatible with most zirconia probes ● Oxygen ● Probe impedance monitoring The 2704CC can interface directly to most commonly available zirconia probes including STG Cottbus, Barber-Colman, Drayton, SSI, Marathon and Bosch Lambda. The zirconia probe input can be configured to measure oxygen making the 2704CC ideal for applications such as glass furnaces. Diagnostic facilities are also included. Continuous measurement of probe impedance ensures optimum furnace operation. Stoichiometric Combustion Control using the 2704 Controller White Paper Issue 1 1 Application blocks and graphical wiring editor ● Mathematical calculations ● Combination logic ● Real Time Clock ● Timing Functions Operators include; Add, Subtract, Log, Exp, SQRT, AND, OR, Max, Min, Select and many more. Application blocks enable the user to create custom solutions by internally wiring analogue and digital operations together in flexible ways. Up to 250 soft wired connections are available to produce intelligent control strategies. Other functions are available including timers, totalisers and a real time clock. 2 iTools graphical wiring editor Stoichiometric Combustion Control using the 2704 Controller White Paper Issue 1 INDUSTRY Stoichiometric Combustion Control using the 3500 Controller The 3500 is a fully programmable controller suitable for stoichiometric combustion control in glass applications. White paper Glass Glass It is capable of being used solely to control the Lambda potential of the furnace, or as an integrated controller where this variable is controlled in conjunction with temperature. Additional features provide maths and combined logic functions. ● Zirconia probe input ● Temperature ● Oxygen At the heart of the controller is a specially designed function block capable of accepting most zirconia probes. Standard features include an automatic probe cleaning routine diagnostics indicating that the probe is about to fail and should be replaced. ● Probe diagnostics For standard solutions controllers can be configured with features and user screens as described in this application note. ● Maths and logic ● Open communications User customisation can be achieved by reconfiguring the unit either via the front panel or the comprehensive PC based Eurotherm® iTools. A complete data sheet on the dual loop version of the 3500 is available HA029045. Oxygen Setpoint Probe Temp Probe mV °C mV Zirconia Function Block - Oxygen Control Loop Oxygen Trim Probe Fault Zirconia input ● Compatible with most zirconia probes ● Oxygen ● Probe impedance monitoring The 3508/04 can interface directly to most commonly available zirconia probes including STG Cottbus, Barber-Colman, Drayton, SSI, Marathon and Bosch Lambda. The zirconia probe input can be configured to measure oxygen making the 3500 ideal for applications such as glass furnaces. Diagnostic facilities are also included. Continuous measurement of probe impedance ensures optimum furnace operation. Stoichiometric Combustion Control using the 3500 Controller White Paper Issue 1 1 Application blocks and graphical wiring editor ● Mathematical calculations ● Combination logic ● Real Time Clock ● Timing Functions Operators include; Add, Subtract, Log, Exp, SQRT, AND, OR, Max, Min, Select and many more. Application blocks enable the user to create custom solutions by internally wiring analogue and digital operations together in flexible ways. Up to 250 soft wired connections are available to produce intelligent control strategies. Other functions are available including timers, totalisers and a real time clock. 2 iTools graphical wiring editor Stoichiometric Combustion Control using the 3500 Controller White Paper Issue 1 INDUSTRY ● Burner modulation ● Air/fuel cross-limiting ● Regulation of excess air ● Oxygen trim ● Total heat control Modulating Burner Combustion Control for Glass Furnaces and Forehearths Application Note Fossil fuel burners are often used as the principal medium for delivering energy to industrial furnaces and ovens. Increasing focus on reducing energy costs has led manufacturers to concentrate on new burner design techniques and important advances in efficiency gains have been made over the years. Burner management and control systems must be equally adaptive. Eurotherm® provides efficient, well implemented control techniques capable of reducing operating costs whilst providing resources for greater flexibility in plant management and control. Burner combustion generally includes one or a combination of the following methods: ● Regulation of excess air ● Oxygen trim ● Burner modulation ● Air/fuel cross-limiting ● Total heat control Excess air regulation Zone of max. efficiency Loss due to unburnt fuel –40 –20 0 20 Loss due to heat in stack 40 60 In actual practice, gas, oil, coal burning and other systems do not do a perfect job of mixing the fuel and air under the best achievable conditions. Additionally, complete mixing may be a lengthy process. Figure 1 shows that in order to ensure complete combustion and reduce heat loss, excess air has to be kept within a suitable range. % Excess air Figure 1 Burner efficiency The regulation of excess air provides: ● A better furnace heat transfer rate ● An ‘advance warning’ of flue gas problems (excess air coming out of the zone of maximum efficiency) ● Substantial savings on fuel Modulating Burner Combustion Control for Glass Furnaces and Forehearths Application Note Issue 1 Application note Glass Glass Glass Oxygen trim When a measurement of oxygen in the fuel gas is available, the combustion control mechanism can be vastly improved (since the percentage of oxygen in the flue is closely related to the amount of excess air) by adding an oxygen trim control module, enabling: ● Tighter control of excess air to oxygen setpoint for better efficiency ● Faster return to setpoint following disturbances ● Tighter control over flue emissions ● Compliance with emissions standards ● Easy incorporation of carbon monoxide or opacity override Cross-limiting combustion control is highly effective and can easily provide the following: ● Optimisation of fuel consumption ● Safer operating conditions by reducing risk of explosion ● Fast adaption to variations in fuel and air supplies ● Satisfaction of the plant demand for steam Optional O 2 Trim Combustion demand from master loop Oxygen analyser Burner modulation AT PID Modulation control is a basic improvement in controlling combustion. A continuous demand signal is generated by a controller monitoring the furnace atmosphere. Air pressure, flow and temperature Air pressure, flow and temperature O2 Setpoint Cross-limiting module Desired % excess air Reductions in temperature lead to an increase in firing rate. The advantages of introducing burner modulation in combustion control include: Air control element Fuel control element ● Fuel and air requirements are continuously matched to the combustion demand ● Furnace temperature is maintained within closer tolerances Enhanced cross-limiting ● Greater furnace efficiency ● Weighted average flue gas temperature is lower Double cross-limiting combustion control is an enhancement to the above. It is achieved by applying additional dynamic limits to air and fuel setpoints. This translates to having the actual air/fuel ratio maintained within a preset band during and after transition. This method protects against having the demand signal driving the air/fuel ratio too lean, therefore reducing heat loss. Air/fuel cross-limiting Flow Figure 3 Cross-limiting combustion control with 06 trim Air Fuel Demand Time Figure 2 Cross-limiting combustion mechanism A cross-limiting combustion control strategy ensures that there can never be a dangerous ratio of air and fuel within a combustion process. This is implemented by always raising the air flow before allowing the fuel flow to increase, as shown in Figure 2, or by lowering the fuel flow before allowing the air flow to drop. Figure 3 depicts a simplified control block diagram of the cross limiting combustion circuit. Combination firing of multiple fuels simultaneously can also be easily accommodated within the scheme. 2 Modulating Burner Combustion Control for Glass Furnaces and Forehearths Application Note Issue 1 Glass Glass It can be advantageous and cost effective to mount a thyristor unit in the primary circuit of a transformer. The following article describes precautions to be taken. INDUSTRY General White paper Thyristors and Transformers Transformers are frequently used in electrical energy applications for one of three purposes: ● Roof heating i. To achieve galvanic isolation ● Boosting ii. To achieve a reduction of the supply voltage at the load ● Lehr heating iii. To achieve an increase in the supply voltage at the load The use of thyristors with transformers needs some care as the ‘inrush’ current on connecting the supply to the transformer can easily exceed the maximum current rating of the thyristor unit and cause failure of the semiconductor fuse. The inrush current is of the order of 20 times the normal running current, as a rule of thumb. Consider first the single-phase case: Where thyristors are connected between transformer and load, the thyristor unit characters are determined by the load only and no attention needs to be paid to the transformer. In many cases, though, thyristors are connected in the transformer primary - i.e. between the supply and the transformer for reasons of economy; generally one pays more for current than for voltage capacity. In these cases, it is important to observe some straightforward precautions. If the B-H curve of Figure 1 is considered, it is a matter of chance where on the curve, thus the magnetic state of the transformer, the equipment is left on disconnection. Even if, as is usual with thyristors, the state is left corresponding to H=0, there will be residual magnetism in the transformer core. The problem is what whilst the circuit is switched off as current falls to zero, it is switched on as voltage rises from zero. Unity power is rare! B Flux Density Curve followed by flux with ‘negative’ magnetising current 1.0 (Typical) H Amphere Turns 1.0 Notes: 1. ‘Positive’ and ‘negative’ directions are symmetrical Curve followed by flux with ‘positive’ magnetising current 2. Shape and especially width of B-H curve depend upon type of iron used Figure 1 B/H Curve If no precautions are taken then, one time in two, switching on will drive the transformer into saturation in the same direction, allowing excess current to flow. In practice, the fuse will fail about one time in four. Thyristors and Transformers White Paper Issue 1 1 Glass On switching on, if the rms current is increased carefully from zero, the inrush problem will be overcome. This technique is referred to as ‘soft start’ and in most cases is necessary over only a few cycles. Where current limiting also is required on starting, this same ‘soft start’ is usually satisfactory for both requirements. Once running, the magnetic state of the transformer can be easily inferred, so the same soft-starting precaution is not always necessary every time the load is re-energised, having been ‘off’ for a period - as is common in temperature control applications. Even so, the problem of ‘off with current, on with voltage zeros’ remains. To cope with this, a technique of burst firing with delayed first cycle firing has been developed. Usually a delay of half a half-cycle (as shown in figure 2) is satisfactory for most applications, though the enhancement to be able to adjust the delay start from zero to 90° as a commissioning feature - to cope with individual Q factors - is almost always beneficial. Thus inrush currents can be minimised whilst the benefits of burst firing control are realised. A further complication lies in the property of the three sine waves of the three-phase system to ‘cancel each other out’ enabling a three-phase system the ability to operate without a neutral wire. In a similar way, a three-phase transformer is designed often with three limbs only, so that the three fluxes - which follow the voltages - also ‘cancel each other out’. Unfortunately, this cancelling is true only at the fundamental frequency of the supply (50Hz in the UK). Most transformers are controlled by thyristors in the ‘phase angle’ mode, which means that the current in the windings consists of a range of odd harmonics; dominant amongst which is the third harmonic, (setting aside the fundamental). Reference to Figure 3 will demonstrate that, far from ‘cancelling out’, the third harmonics reinforce each other. This property can have interesting effects on a transformer core, resulting from overheating, since the flux will try to ‘close’ via any metal in the vicinity - frequently the steel case. FUNDAMENTALS ‘typical’ current waveform R Y B Current waveform with pure inductance R x° =R 90° Typical lag <90° = zero current with typical industrial load =Y 90° lag on voltage = zero current with pure inductance Voltage Waveform Figure 2 1/2 Cycle firing delay Shows different size for clarity =B Sum of 3rd Harmonics Figure 3 Third harmonic Designers are still required to exercise considerable caution when working with loads which are other than purely resistive, however, as experience of control using burst firing techniques in the primary of transformers is still limited. Further, where the technique is used with confidence with elements which run at relatively low temperature, there may be difficulty - either mechanical or thermal - in the case of high-temperature elements. The guidance of the element manufacturer should always be sought when in doubt. There are two easy ways to avoid difficulty. The first is to wind the primary (usually, though the secondary is equally suitable) in ‘delta’ so that the three fluxes will add in a ring round the core, with a resultant of zero. The alternative is to use a five-limb transformer the outer limbs forming the return paths. These are not the only way to avoid a problem, nor is it guaranteed that they are always satisfactory. However, they are the most usual and fail only in very unusual cases. The well-established ‘phase angle’ method of control is now thought to be suitable for all applications. There are many installations which have been running without problems for years which do not employ a delta. For whatever reason, whether it is because the transformer is lightly loaded or the third harmonic content is low at the normal working point, or a combination of other factors, these systems emphasise that the rules concentrating the third harmonic are only guidelines. If in difficulty, the designer would be well advised to seek expert assistance from manufacturers with considerable applications experience. Multi-phase transformers All the precautions necessary when using single-phase transformers are necessary in the case of multi-phase installations. There are one or two additional considerations occasioned by the interaction of three phases. The principal consideration is the need to keep the three limb fluxes equal by keeping the three driving voltages equal unless the system has been specially designed otherwise. This means that the three phase currents will be unequal to the extent that the load impedances are unequal. In particular, it is difficult without taking special precautions to equalise the power in three zones - even if this were possible it would be unlikely to be achieved except at one specific element temperature - unless the furnace or load is designed with this need in mind. Scott-Wound transformers These are applications, including two-zone furnaces and salt baths where, for supply reasons, energy for only two zones is taken equally (as near as possible) from the three phases of the supply. The tool which is often used for this function is the Scott-wound transformer. The ‘Scott’ is a three-to-two arrangement where the primary is usually star and the two secondaries are usually separate, as shown in Figure 4. This highlights the fact that a three-phase transformer cannot be treated in any way as three separate units - its economy lies in the interaction of the phases. 2 Thyristors and Transformers White Paper Issue 1 Glass R SUPPLY SEC V #2 Y SEC Y #1 B Figure 4. ‘Scott Windings’ All the rules and guidelines applying to 3-phase transformers apply also to ‘Scott’. The notable exception is the delta-primary which is not practical. For this reason, Scott transformers are often wound with five limbs when used with thyristors. Additionally, the unusual flux patterns often necessitates a slower ‘soft start’ than with the ‘conventional’ transformer, as because of the harmonic content of load currents, the line currents will not be equal for all phase angle conditions and the power will not necessarily be equal in the two load circuits. The one really important precaution is the avoidance of parasite voltages in the primaries which can damage thyristor equipment. This can occur where secondaries are not, in fact, galvanically isolated. A current flowing in one can pass, wholly or partly, through the other and this can in turn generate through ‘backwards’ transformer action, an e.m.f in its appropriate primary. If the thyristor unit in this circuit is off, the e.m.f. can be large enough to cause damage. Where this problem is likely, expert advice should be sought. In all transformer applications of thyristors, it should be remembered that the transformer is essentially a 50Hz device - it is indeed a very good 50Hz. The generation of all the harmonics will cause the core to warm up more than in ‘normal’ use and this, coupled with the need to avoid inrush current difficulties means that the core should be run at a relatively low flux density. A value of around 1.2 Tesla is usually used. Eurotherm offer an on-site advisory service in the choice of suitable thyristors. Thyristors and Transformers White Paper Issue 1 3 Glass 4 Thyristors and Transformers White Paper Issue 1 INDUSTRY ● Silicon carbide elements ● Control methods Control of Silicon Carbide Heating Elements using SCRs 1. Characteristics of silicon carbide heating elements: 1.1 Construction Silicon carbide is a ceramic material with relatively high electrical conductivity when compared to other ceramics. Elements are produced by pressing or extruding and then sintering. White paper Glass Glass Typical heating elements are rods or tubes, with diameters between 0.5 and 3 inches and lengths from 1 to 10 feet. They have metalized ends for electrical connections, and they often have both connections at one end, with two helical slots which stop short of the other end, thus approximating a twisted hairpin form. 1.2 Electrical characteristics The resistance of these elements varies with both temperature and time. The nature of these variations depends on the particular grade of material and manufacturer. For most types, the resistance is high when the material is cold, decreasing as temperature rises, reaching a minimum at typically between 1000°F and 2000°F, then increasing again as its temperature rises further. When kept at a high temperature, the resistance of the material increases with age. The change in resistance can be of the order of 3 or 4 to 1 for both timerelated and temperature-related phenomena, giving an over-all ratio of the order of 10:1. Resistance The rate of ageing is affected by the surrounding atmosphere, and also depends to a large extent on the operating temperature (and hence on the power being dissipated). Most will quote life related to maximum power in various temperatures and atmospheres. Element near end of life New Element Temperature Figure 1 Resistance of Silicon Carbide Element as a Function of Temperature 2. Control requirements A control system for silicon carbide heaters should ideally provide means for: ● Dealing with the wide variation of resistance ● Keeping the power dissipated below the specified maximum at all times Control of Silicon Carbide Heating Elements using SCRs White Paper Issue 1 1 Glass 2.1 Contactor and multi-tapped transformer This is the traditional method used for controlling silicon carbide heaters. It is included here only for comparison with the SCR methods. In this system the power is switched by a contactor and the voltage applied to the heaters is adjusted manually by means of multi-tap transformers, ammeters and voltmeters. It is necessary to measure and adjust the currents and voltages regularly and frequently (by manually changing the transformer connections). This method can compensate for the change of resistance due to ageing, but it is not a practical solution to the resistance changing with temperature. Load Current 2.2 Voltage control with fixed current limit (Figure 2) This method can provide some degree of automatic comparison for variation of load resistance. The SCRs are triggered in the “phaseangle” mode, and there are two internal control loops: voltage control and current limit. The voltage control loop is designed to keep the mean square of the voltage applied to the load proportional to the control signal. The current control loop can override the voltage control loop, and is designed to prevent the RMS value of the current from exceeding a fixed level (irrespective of control signal). This has also been called “Threshold Current Limit”. Limit of load voltage (The load voltage can not increase past this point) Current Four different methods are described below: “Current limit” setting If operating point is on this line (card resistance below critical value) then unit operates as a current controller Actual load resistance Critical value of load resistance Operating point Current control point Note that the power to the load always changes as control signal varies Voltage control If operating point point is on this line (card resistance above critical value) then unit operates as a voltage controller Volts Supply volts Figure 3 Voltage control with Proportional current limit 2.4 True-power control with current limit (Figure 4) The SCRs are triggered in the “phase-angle” mode, and there are two internal control loops: power control and current control. The power control loop is designed to keep the mean power (volts x amperes) supplied to the load at a level corresponding to the control signal. The current loop can override the power control loop, and is designed to prevent the RMS value of the current from exceeding a fixed preset level (irrespective of control signal). Load resistance Current limit setting Operating point Current In this region the power to the load does not charge as control signal varies Load resistance Load voltage changes as control signal varies Supply volts Load Volts & Control Signal “Current limit” setting “100%” power level Figure 2 Voltage control with Fixed current limit 2.3 Voltage control with proportional current limit (Figure 3) The SCRs are triggered in the “phase-angle” mode and there are two internal control loops: voltage control and current control. The voltage control loop is designed to keep the mean square of the voltage applied to the load at a level corresponding to the control signal. The current control loop is designed to keep the RMS value of the current at a level corresponding to the control signal. The transition from voltage control to current control occurs at a particular value of load resistance, which is determined by the setting of the “current limit” potentiometer. This has also been called “V/I Transfer” control and “Linear Current Limit”. Power level corresponding to control signal Operating point Supply volts Volts Figure 4 True Power Control 3. Choice of Control Method: The choice of which method to use depends on several factors and, of course, it probably requires a compromise between performance and price. 3.1 The ”Contactor and Transformer” method has little to recommend it. The initial cost of the multi-tap transformer and wiring is high and it requires considerable time, effort, and skill to maintain the correct adjustment manually. It compensates for only the resistance change due to ageing, so the system must be designed to provide enough heat when the resistance is maximum 2 Control of Silicon Carbide Heating Elements using SCRs White Paper Issue 1 Glass Current 3.2 “Voltage Control with Current Limit” appears to be the simplest SCR method, however it requires great care and several difficult choices to be made in the system design. Figure 5 illustrates the problems. It shows “load lines” corresponding to the maximum and minimum resistances of a typical silicon carbide element on a current versus volts graph, with a power curve corresponding to the maximum permissible power specified for the element. In order to prevent excessive power, the operating power must be below and to the left of the “Heater power limit” curve at all times. Therefore the current limit must be set to the values corresponding to the power limit at the supply voltage (shown as point A in Figure 5). If the current limit and supply voltage are set to give full power (heater power limit) at the maximum resistance (point B in Figure 5), at all other values of resistance the available power will be less than the power limit and so larger heaters will be needed to reach the required temperature. Heater resistance at normal operating temperature Avg C Old Q Current limit E A Heater maximum resistance B D 0 Supply volts Operating point lies within this region Volts Figure 6 Voltage Control with Current Limit showing silicon carbide element at normal operating temperature 3.3 Choice of which type of current limit to use Either type of current limit may be used in the system described in 3.2, but proportional current limit is much better than fixed current limit. The following is an explanation of why this is so. Heater minimum resistance E Operating point Heater maximum lies in this region resistance A B D 0 New Heater power limit C Current limit Heater minimum resistance Heater power limit Current without over-powering the elements when the resistance is minimum. Incorrect adjustment (due to human error or forgetfulness) can cause the heaters to dissipate more than the permitted maximum power or less than the required power, resulting in shortening of element life or inability to achieve the required temperature. Supply volts Volts Figure 5 Voltage Control with Current Limit used to limit heater power A similar problem exists if the minimum resistance is chosen to be “full-power” value (point C in Figure 5). (In this case, of course, current limit would be unnecessary.) The best solution (using voltage control with current limit) will be compromise (such as A in Figure 5) which will minimize the size of heater required while still providing enough power to reach the required operating temperature. The operating point will always be within the area denoted by 0EAD in Figure 5. Point A should be as close as possible to the maximum operating temperature (assuming that this temperature requires maximum power) but that resistance changes during the life of the element! So the point chosen should represent the mean resistance at maximum operating temperature over the expected life of the element. In practice the available supply voltage or transformer voltage will probably not coincide with this chosen point (A in Figure 6) and so a different point, close to A, will be used. This is shown as Q in Figure 6. Fixed Current Limit works well with those types of heaters whose resistance increases with rising temperature, such as tungsten, because the current limit operates only when the temperature is low and the controller is calling for maximum power. Such a system should be designed so that the supply voltage and current limit setting interact at the point on the maximum power curve corresponding to the maximum resistance (point B in Figure 5). When the resistance of those heaters is low, so is the temperature and hence the heat loss so that the power available (reduced by current limiting action to a fraction of the power limit) is still sufficient to raise the temperature. As the temperature increases, the available power increases and so automatically compensates for the increasing heat loss. By the time the operating temperature is reached and the temperature controller is reducing the power demand, the current limit is no longer being used. When fixed current limit is used with silicon carbide elements (at least when new) it is likely that the resistance will be close to the minimum when the load reaches operating temperature, so that the current limit will be operating as the temperature approaches setpoint. This means that there will be a discontinuity in the proportional band at the point of transition from voltage control to current control, and the point of transition changes with changing signal. Within this region the current-control signal has no effect (until the point of transition reaches the operating point). This will be certain to cause “overshoot” when setpoint is reached. Also the reduction of resistance causes an increase in loop-gain, so that if the control loop was tuned when the resistance was cold it may begin oscillating as it heats up. Unfortunately, any increase in proportional band to compensate for this will increase the overshoot. Thus proportional current limit is better than fixed current limit because proper control action is maintained throughout the proportional band. The operation simply transfers between voltage and current control as the load resistance passes the critical value (represented by the 0Q in Figure 6). There is no discontinuity in the proportional band, and the variation in loop-gain is much less than fixed current limit. Control of Silicon Carbide Heating Elements using SCRs White Paper Issue 1 3 Glass It should be noted that voltage control, with either fixed or proportional current limit, suffers from the disadvantage that the maximum permissible power dissipation can be achieved at only one value of load resistance (represented by 0A in Figure 5 and 0Q in Figure 6). At any other value of load resistance the maximum power available must be lower, so that the heater required is larger than that implied by the specified power limits. 3.4 “True-power Control with Current Limit” True-power control has the ability to reach the maximum permissible power level at all values of load resistance. This enables smaller heaters to be used in many applications. Current Heater power limit Heater minimum resistance New Current limit Heater resistance at normal operating temperature Heater maximum resistance Avg C Old Q Operating point lies within this region A B D 0 Supply volts Volts Figure 7 Power Control with Current Limit showing silicon carbide element at normal operating temperature As illustrated in Figure 7, the supply voltage and current limit setting can be set at or near the limits of the resistance range, thus allowing full power (i.e. maximum permitted power) to be dissipated at all possible values of resistance. Note also that current limit is not necessary for normal operation; it serves only to protect against faults such as incorrect connections when changing elements. 4. Design Procedure To optimize the design of a system using silicon carbide elements it is likely to be necessary to repeat the calculations with different elements, different supply voltages, etc. Thus by a process of iteration the best combination for the particular application can be found. Eurotherm has developed software tools to assist engineers in the optimization of power control systems, the calculation of top voltage on transformer and thyristor current ratings. Appendix 1 shows a table with examples of designs for several different applications. Warning Elements connected in series and/or parallel will not dissipate equal amounts of power unless their resistances are identical. Therefore such elements should be replaced as a set. It is unlikely that these elements will age, or heat up, at the same rate, and therefore the life of the set may be reduced due to over-powering of one element. This problem can be avoided by providing a separate power controller for each element. 4 Control of Silicon Carbide Heating Elements using SCRs White Paper Issue 1 Glass Appendix 1 Power required (Watts) Maximum power per element(Watts) Supply volts Wreq Hmax Vsup FOR EACH ELEMENT Minimum resistance (Ohms) Maximum resistance (Ohms) Hot resistance. New (Ohms) Hot resistance. Old (Ohms) Rmin Rmax Rtmin Rtmax Hot resistance. Average (Ohms) Point A volts Point A current (Amps) Point B volts Point B current (Amps) Point C volts Point C current (Amps) VOLTAGE CURRENT Number of elements in series Point Q volts per element Point Q current per element Maximum power, hot, new Maximum power, hot, old Worst case power hot Number of parallel paths Current limit setting (Amps) Number of elements Total power available at Rmax Total power available in Rmin Point E Volts (total) Conduction angle at point E (radians) Sine of conduction angle at point E Maximum peak current Total current at point C if no limit Application 1 Application 2 5000 5000 1000 1000 120 240 Application 3 5000 1000 480 2 10 3 6 2 10 3 6 2 10 3 6 Rtavg Va la Vb Ib Vc Ic 4.50 67.08 14.91 100.00 10.00 44.72 22.36 4.50 67.08 14.91 100.00 10.00 44.72 22.36 4.50 67.08 14.91 100.00 10.00 44.72 22.36 Svc Vq Iq Hnew Hold Hmin Pvc Clvc Nvc 2 60.00 16.67 833.67 600.00 600.00 5 83.35 10 4 60.00 16.67 833.67 600.00 600.00 3 50.01 12 8 60.00 16.67 833.67 600.00 600.00 2 33.34 16 3600.00 5557.78 66.68 1.26 0.95 201.53 111.80 4320.00 6669.33 133.36 1.26 0.95 120.92 67.08 5760.00 8892.44 266.72 1.26 0.95 80.61 44.72 5 1 5 5 111.80 5 2 3 6 67.0 5 5 1 5 22.36 5000.00 0.92 0.80 339.41 6000.00 0.56 0.53 134.92 4608.00 0.35 0.34 23.08 Wvrmax Wvrmin Ve Øvc SinPkvc Ipkvc TRUE POWER CONTROL Number of elements needed Number of elements in series Number of parallel paths Actual number of elements Current limit setting (Amps) m Spc Ppc Npc Clpc Total power available at Rmax Conduction angle at point C (radians) Sine of conduction angle at point C Maximum peak current Wprmax Øpc SinPkpc Ipkpc Control of Silicon Carbide Heating Elements using SCRs White Paper Issue 1 5 Glass 6 Control of Silicon Carbide Heating Elements using SCRs White Paper Issue 1 Glass ENERGY SOLUTIONS Eurotherm® Energy Solutions for the Glass Industry Power Control and Energy Management Solutions Power Limiting on Multi Zone Furnaces using Thyristors Cost of Electrical Energy Lambda Control Reducing NOx Emissions Glass Catalogue Part No. HA029511U004 Iss. 1 Printed in England 10.07 i Glass ii Energy Solutions contents Issue 1 Glass Eurotherm® Energy Solutions for the Glass Industry Eurotherm is a principal supplier of control systems for energy applications in the glass industry and has a global reputation for innovative fossil fuel and electrical energy delivery solutions. The extensive range of thyristor products and fuel control devices from Eurotherm is supported by control algorithms and energy software solutions, which bring benefits across the whole business for the efficient use and management of energy. Thyristor products Robust design for hot and cold end applications. Complete range of single, dual and three phase devices from 10 Amps to 10,000 Amps. Suitable for firing into all type of heater materials including: ● Standard resistive materials ● Silicon Carbide ● Molybdenum Di-Silicide ● Graphite ● Molybdenum and Tungsten Wire ● Shortwave Infrared lamps and Quartz tubes ● Transformer coupled loads including Scott wound and unbalanced transformers Built for control system integration with features including: ● Inbuilt alarms with supply and load protection. ● Alarms for system and heater element diagnosis ● Digital communications ● Routines for power sharing, load shedding and load management Please contact Eurotherm for more information on firing modes and the use of thyristors with specific heater materials. Fossil fuel control systems An extensive range of control strategies and algorithms including: ● Simple On-off and high low fuel control ● Specialist burner control algorithms ● Bounded and boundless fuel valve control algorithms ● Single and multi zone pulse burner control systems ● Simple fuel-air ratio systems ● Lead-Lag fuel control systems ● Special dual fuel-air with excess air trim ratio control systems Energy management A selection of energy monitoring and management features and capabilities: ● Single and three phase electrical power, plant monitoring solutions ● Management software systems for energy recording and reporting ● Gas usage and fuel flow monitoring ● Furnace energy optimisation routines ● Batch process energy profiling ● Electrical power maximum demand avoidance solutions ● Furnace and batch process energy consumption recording ● Bath and lehr electrical load sharing techniques Please contact Eurotherm for more information on the efficient use and management of energy. Eurotherm Energy Solutions for the Glass Industry Issue 1 1 Glass 2 Eurotherm Energy Solutions for the Glass Industry Issue 1 INDUSTRY Power Control and Energy Management Solutions Electrical heating White paper Glass Glass The debate over increasing energy cost has caused suppliers in the glass production and glass processing industry to look at control refinements for heating systems. Reducing energy costs remains a key area of focus and successful companies are finding ways to improve their competitiveness by concentrating investment in this area of their business. This paper aims to highlight further savings, which can be made by paying careful attention to the way electrical energy is used and distributed around thermal processing equipment. Energy monitoring Since energy use in glass production and glass processing is a major cost factor, there is a need to record and store energy usage data. With the advent of simple communicating power metering equipment it is a natural extension of the control system to embed plant energy usage in to the stored records. Having access to energy data in real time and historic format allows users to evaluate the following: ● Instantaneous overall power demand ● Instantaneous power demand for individual processes ● Energy usage against pull ● Energy usage against plant utilisation ● Plant priority for load shedding Using wireless technology as a cost effective way to acquire and distribute energy information over Ethernet allows the data to be shared in real time around groups of internal management and engineering clients. Experience has shown that where users have access to energy data it has always been possible to define areas of savings. Electrical energy switching methods Except for the most complex heater loads i.e. those element materials which have resistance change with temperature or complex transformer coupled loads, it is recommended that simple whole cycle switching methods are employed to control electrical energy with thyristors. The continuing use of Phase Angle (Cycle Chopping) for simple heaters including modern Silicon Carbide causes disadvantages to users through poor power factor, harmonic disturbance on the supply and RF interference around the installation. Figure 1 shows typical harmonic disturbance associated with phase angle firing for single and 3 phase loads. It can be seen from the diagrams that when switching the sine wave at 90 degrees a high proportion of odd harmonic current is reflected into the supply. Power Control and Energy Management Solutions White Paper Issue 1 1 Glass Advanced single cycle can be particularly effective for shortwave infra-red loads or for loads where it is desirable to minimise the effect of long bursts of power on the elements. 100 Percent of Maximum 80 For element materials, which have a positive resistance/temperature coefficient, it is also possible to use intelligent thyristors to switch from phase angle firing to whole cycle firing when the element resistance increases to allows full mains volts to be impressed across the load. 60 Fundamental Total RMS Fundamental Total RMS 40 3rd 5th 20 5th 7th 0 30 60 Information is available from Eurotherm® on the benefits of alternative thyristor switching methods for particular heater materials. 7th 9th 150 90 120 Delay Angle 0 180 20 40 60 80 100 120 140 160 180 Delay Angle Harmonics in single phase (4 wire) loads Load sharing and load shedding techniques Harmonics in three phase 3-wire loads Figure 1 Poor power factor associated with phase angle firing is the principal concern for energy cost. Since most electrical installations are designed to operate at around 50% output power at the nominal operating setpoint, the supply mains cycle will be chopped at the worst case of 90 degrees when operating in PA mode. Under these conditions the resultant power factor could be as low as 0.72 instead of above the desired level of 0.95. Dependent on the metering type and the supply impedance, this could have a very detrimental effect on the billing value - adding 7-10% cost with no benefit to the process. Two simple solutions can reduce or overcome the disadvantages associated with phase angle thyristor control: 1. Where a glass processing shop has a large installed base of electrically heated thermal processing equipment, it is often desirable to sequence the firing of individual loads to minimise the supply fluctuation. By using intelligent thyristor firing methods it is possible to limit the power surge and instantaneous supply loading associated with any installation through a selectable combination of firing patterns. In this mode none of the zones are switched on simultaneously and individual load power demands are synchronised to give a very even loading on the factory supply. The following figures show a zone sequencing pattern and the overall effects on the supply by evening out the load on the plant. The benefits enable clients to operate higher installed equipment base from the existing supply. For installations where phase angle control cannot be avoided, using an electronic supply tap changer will automatically keep the power factor and supply disturbance to a minimum. Figure 2 shows typical response from a .4- tap change control system. Notice how the power factor is above 0.9 for most tappings at the critical 50% demand level compared to the fundamental curve which shows 0.72 for 50% demand. Zone sequencing 1.000 5 0.900 4 0.800 4 3 0.700 4 4 5 5 3 2 3 2 0.600 Power Factor 0.500 1 0.400 0.300 0.200 0.100 0.000 Supply switching pattern before and after load sharing 0 10 20 30 50 40 60 70 80 90 Power (%) Figure 2 2). For non complex heater loads it is possible to use any of the whole cycle firing modes, including single cycle and advanced single cycle switching methods, to satisfy the watts density loading and thermal mass characteristics of most common heaters - whilst eliminating the poor power factor and harmonic problems. 2 A further benefit can be obtained from this solution by setting a threshold on the smoothed power level to trap excursions of energy use through the site maximum demand point. Setting alarms on the threshold level can trigger prioritised load shedding and thus avoid costly excess-tariff penalties. The same principle would be applicable to tinbath roof heating and Lehr heating. Power Control and Energy Management Solutions White Paper Issue 1 Glass Out of hours furnace setpoint control Using the intelligence of modern control systems, it is possible to automate out-of-hours setpoint control for thermal processing equipment. In the example shown below, the control systems understand the dynamics of the furnace and can recognise the power required to maintain the standby setpoint and the power required to achieve the operating setpoint. The controller has a user screen which allows the operator to enter the required duty setpoint and time for the furnace to be back at temperature. The controller uses the furnace tuning information and an internal real time clock to ensure the furnace is back at the duty setpoint as required for work. Benefits enable much more consistent and repeatable energy savings through the use of out-of-hours furnace turn down. SP = 850 SP = 850 SP = 600 10:00 Real Time Clock Loop Alarm SP Select 05:00 Eurotherm supply control systems are specially designed to incorporate their unique energy saving routines. Power Control and Energy Management Solutions White Paper Issue 1 3 Glass 4 Power Control and Energy Management Solutions White Paper Issue 1 INDUSTRY ● Power limiting ● Tariff band cost saving ● Generator protection Power Limiting on Multi Zone Furnaces using Thyristors Purpose 1: To prevent Power Bursts White paper Glass Glass Purpose 2: To limit the Power usage when there is insufficient supply On multi-loop furnaces the installed power can be rather high compared to the available supply. In cases when the supply is limited or the power is supplied by e.g. Emergence or a Load Power Transformer, methods should be available to control the amount of supply used. Also, when the supplier is monitoring, the demand and penalties/fines are raised when the usage exceeds certain limits or is peaking. When the furnace is turned on all control loops will want to start firing and a sudden power burst can occur running up to or over 100% of power. The sudden draw of current will cause a supply voltage to drop (noticeable by the dimming of lights), fuses can be blown or supply transformers damaged. A generator cannot handle the increase of this demand instantaneously and needs some time to run to that power. It is even possible for the generator to stall. These situations occur when the power lines are not designed for this amount of power. It is also possible that there is a general lack of available power. Another consideration is the investment required for this higher power demand. When the furnace is at temperature the control loops need less power. A well designed furnace will run around 50% of its installed power. Frequently, due to construction limits or other restraints, the furnace will run at less than 30% of its power. To control the instantaneous maximum power usage is not easy. Most methods apply on an averaging basis over time. With Analogue/Communication controlled thyristors the input signal can simply be limited, but this has other impacts depending on the firing mode: 1. Analogue fired thyristors modulate their firing over time. It is a matter of coinciding firing since thyristors are unsynchronized units and they all can fire at the same moment. Each thyristor adds its demand to the total on a Sine Wave Level (Superposing). When the firing mode is burst firing the thyristor can syncopate; noticeable due to oscillations in the current by either light or sound. 2. When the firing mode is Phase Angle the effects are noticeable by humming of transformers but this has a drastic/catastrophic affect on the wave form. 3. With Logic driven thyristors one has to disable units or even complete groups over time. Doing this Manually or Hardware wise has a very course effect on the heating up. Power Limiting on Multi Zone Furnaces using Thyristors White Paper Issue 1 1 Glass Controlling the maximum power: 1. Calculate the installed power by summing the individual power of each loop. 2. Continuously calculate the power usage by summing the actual output times the loop power. This figure is an average for analogue fired thyristors and actual for logic fired thyristor. 3. Set the maximum output of each loop to the maximum allowed percentage. This is not an absolute limitation but gives feed back to the loops that they are limited in output and can prevent integral windup and output bursts if power limitation is no longer needed. 4. An individual loop basis checks if that loop wants to fire the thyristor and that the loop power added to the power usage does not exceed the maximum allowed power to enable the firing. If it does exceed the limitation, disable the firing. Doing exactly this creates a variation in firing all thyristors. 5. By applying a positive ramp rate (Ramp Up) on the maximum allowed power, a gradual demand increase can be simply achieved e.g. at startup. 6. Depending on the mechanism used, the above can lead to situations that certain loops are never allowed to fire at all. More variations have to be brought in: Incremental: Allows only one loop to switch each cycle. Sequential: Follows a strict order in switching. Rotational: The first loop disabled is the first one to be enabled again. Time wise: Firing allowed for a certain duration. Priority: First firing high priority loops then lesser priorities. Deviation: The lowest deviation is the first to be turned off. Priority changing: Change priority when needed, e.g. on a time base. The above technique requires powerful mathematical capabilities within the control system. The Eurotherm EPower thyristors have been developed to incorporate power limiting calculations - Predictive Load Management. These units can be arranged in a networked group to communicate with each other and manage the multizone plant load requirements. Setting the Maximum Power limitation mode will enable the group to behave as a single unit. They will configure themselves as to how and which thyristor is allowed to fire depending on parameters set in the instruments. 2 Power Limiting on Multi Zone Furnaces using Thyristors White Paper Issue 1 INDUSTRY ● Energy cost reduction ● Load sharing ● Load shedding Cost of Electrical Energy Energy cost is one of, if not the most important issue in the glass industry at the moment and improvements in efficiency of use or reductions in energy cost would have a substantial influence on the operational result of any glass producer. White paper Glass Glass In applications where an electrical energy user has to control multiple loads the Predictive Load Management features of Eurotherm EPower controllers will give better control over Peak Power Demand. In many countries the monthly Peak Power Demand is a critical factor in the cost that industrial users have to pay for electrical energy. The Predictive Load Management* function of EPower controllers offers two features that can lead to a reduction in Peak Power Demand and therefore a reduction in cost. The features are: ● Load sharing ● Load shedding In many applications the installed power capacity exceeds the required power during normal operation. Predictive Load Management uses this overcapacity by distributing loads on/off switching over time in such a way that the power required from the network is at any moment in time lower than the installed power capacity. Load sharing The load sharing feature takes care that a group of loads is switched on/off in such a way that the average power demand is flattened out as shown in the following diagrams. In the first diagram the loads are switched on in a synchronised fashion. The moment the furnace is switched on all loads will be switched on at the same time causing a peak demand equal to the installed power. * patent pending Cost of Electrical Energy White Paper Issue 1 1 Glass The second diagram shows the effect of desynchronising the switching of the loads and the effect on the peak demand. Load shedding With load shedding a user can define a maximum allowable peak demand. Because this feature will actively reduce the power applied to certain loads it cannot be used under all circumstances. The possible effects of load shedding on the behaviour, the dynamic stability of control and accuracy of control should be taken into consideration before load shedding is applied. It is particularly useful when large thermal masses such as a lehr are controlled. When all the signs are at green a user gets real dynamic control over its peak power demand. The result is a decreased Peak Demand and flattened average power use. By switching on EPower controllers “Efficient Power” features the result becomes even better. In this case for instance the power demand during normal operation could be reduced by 20% to 1433kW without harming process dynamics. The limit of 1433kW is set in the Eurotherm EPower master controller and Eurotherm patented load shedding feature takes care that the limit is never exceeded. So rather than a peak demand that is unpredictable and could be as high as the installed power of 3138kW load shedding in this case takes care of a controlled maximum peak demand of 1433kW. The average power demand shows an almost flat line, which results in less flickering and a reduced peak. The efficiency of the use of power can be characterised by the Power Efficiency Factor K, a value between 0 and 1. The closer to one the more efficient the use of power is. K is calculated with the following equation: K= Installed Power - (max power - min power) Installed Power In this example the installed power is 3138kW with a total power per modulation period of 1792kW. The Power Efficiency Factor goes from 0 in the synchronised case to 0.84 in the desynchronised case and 0.97 by the use of “Efficient Power” However, although Peak Demand is reduced significantly, it is not limited to a certain level. To limit the peak demand we can use the load shedding feature of EPower controllers. 2 To be able to predict the cost benefit for the user we would have to know how electrical energy costs are calculated and invoiced by the power company. The tangle of rules, regulations, rates and conditions Before the liberalisation of the power market life was easy. As a power user one had the choice out of a list of one power supplier, the power supplier active in the region and that was it. In each country all power suppliers applied comparable conditions and prices. That one company was responsible for generating and delivering the power at the user’s doorstep. So how have things changed? The energy market in many areas is completely liberalised and a user can buy power from any supplier all over Europe, with power suppliers being totally free in setting their conditions and prices. Rather than dealing with one supplier responsible for the complete supply chain, a user now has to deal with three companies and a tangle of rules, regulations, rates and conditions. Cost of Electrical Energy White Paper Issue 1 Glass These three companies are: ● The energy supplier. The company from which a user buys the actual kWh’s - a highly competitive market. ● The network operator. The company that transports the actual energy from the generator to the customer. This company owns the grid in a region and often has a monopoly in that region. ● The metering company. An independent company that meters the actual energy use, the monthly peak demand and the power factor. ● Annual connection maintenance cost: an annual fee depending on the range of the connection. i.e. typically, Eneco Netbeheer charges €1,272 for a connection in the range of 400KVA to 2.4MVA and €6,804 for a connection in the 2.4MVA to 10MVA range. A difference of €5,532/year. ● A fixed annual transport charge: i.e. typically, Eneco Netbeheer charges €0 for a connection in the range of 400KVA to 2.4MVA and €2,760 for a connection in the 2.4MVA to 10MVA range. A difference of €2,760/year. ● A fixed cost for transport of the “Contact Power” (see energy supplier). The charge per kW per annum also varies with the power range. i.e. typically, Eneco Netbeheer charges €14.16 per kW of contract power per annum for a connection in the range of 400KVA to 2.4MVA and €20.16 per kW for a connection in the 2.4MVA to 10MVA range. This again could be big money. i.e. If it would be possible to go down from 3200kW contract power to 1800kW it would also be able to reduce the connection range. A cost saving of €39,024 would be possible. ● A variable monthly charge for transport based on the actual monthly peak demand. i.e. typically, Eneco Netbeheer charges €1.96 per kW of peak power per month for a connection in the range of 400KVA to 2.4MVA and €2.03 per kW for a connection in the 2.4MVA to 10MVA range. A reduction in average peak demand of 700kW in the >2.4MVA range saves 700*12*€2.03 or €17,052. ● A variable charge for the actual kWh transported could be applicable but in the case of Eneco this only applies for the lower ranges of the connections. ● A variable charge for reactive power when the power factor of the connection is lower than a certain value. For Eneco this value is 0.85 and the charge is €0.00102 per kVARh for additional reactive power. Energy supplier The four main variables used to fix the price of a kWh for an energy contact are: ● Contract power in kW: the maximum power expected to be used at any moment i.e. equal to the total installed power ● Annual use during off-peak hours: i.e. between 23.00 and 07.00 and weekends ● Annual use during peak hours ● Duration of a supply contract: in most cases a minimum period of 1/2 a year is applicable The higher the contract power or the longer the contract duration, the higher the price per kWh will be. Eurotherm EPower controllers may reduce the peak demand and therefore a lower contract power could be agreed reducing the cost per kWh. Example by supplier Oxxio: Contract Power 3200kW 1800kW Peak hour use kWh 7,072,000 kWh 7,072,000 kWh Off-peak hour use 6,944,000 kWh 6,944,000 kWh Contract duration 12 months 12 months 7,86 ct/kWh 7.56 ct/kWh €1,101,573.60 €1,071,896.80 Average price/kWh Total annual cost Annual savings by reducing the contract power on the basis of a lower peak demand are €29,676.80. Metering company It is assumed that the metering costs are marginal compared to the cost of energy and have therefore, not been taken into consideration. Conclusion Load sharing and load shedding could allow substantial cost savings for industrial electricity users. A proper calculation of the savings however can only be made when details of the rates and conditions of the different parties in the supply chain are known. Note: All figures are based on rates applicable in December 2006. Network operator An energy transporter charges for: ● Connection costs: a one-off cost for connecting a customer to the grid, this includes transformers, cables and junction boxes. The charge is depending on the maximum capacity of the connection. This is about big money! i.e. typically, Eneco Netbeheer charges 40k€ for a connection in the range of 1MVA to 2.4MVA and 220k€ for a connection in the 2.4MVA to 10MVA range. A difference of 180k€. These costs only have to be taken into consideration when a new factory is to be erected or when connection capacity has to be increased because of an extension of existing facilities. Cost of Electrical Energy White Paper Issue 1 3 Glass 4 Cost of Electrical Energy White Paper Issue 1 Glass Glass Lambda Control Reducing NOx Emissions White paper This application note describes the operation of the Lambda control to a glass melting furnace. Purpose INDUSTRY Lambda control is applied to optimise combustion, reduce emissions and save energy. Application Measuring oxygen percentage in the exhaust of a glass furnace with a Lambda probe gives a good indication of the efficiency of the combustion process. A too high percentage indicates that too much air or oxygen is fed to the burners. The excess of air/oxygen will not be used for combustion but will be heated up before it leaves the furnace through the exhaust, causing loss of energy. Also the excess of oxygen could react with nitrogen in the air and cause additional NOx emissions. A too low value indicates incomplete combustion with (natural) gas leaving the exhaust unburned. By using the Lambda value in a closed loop control system one can optimise combustion in such a way that at any moment the exact required amount of air/oxygen is fed to the gas burners to obtain a stoichiometric process. Lets look at an example of oxy fuel furnace. In the air/gas furnace the ratio between air/gas is 10:1, so for an oxygen furnace the ratio oxygen/gas is close to 2. Because no furnace is airtight air that leaks into the furnace will contribute its part to the total amount of oxygen required for combustion. A more practical ratio of 2:1 is therefore 1.83:1. A Lambda controller will optimise the oxygen/gas ratio by multiplying the oxygen/gas ratio setpoint with a factor 0.9 to 1.1; a trim of ±10%. Refer to Figure 1 for a block diagram of a principle Lambda control application. Lambda T’ Lambda probe 1.830 0.9 1.1 X X Exhaust O2_ref O2 Temp. Thermocouple sp Gas Melt Furnace Figure 1 Basic block diagram Lambda control Lambda Control Reducing NOx Emissions White Paper Issue 1 1 Glass ● Precautions/Considerations Although Lambda control does at first glance look to be the ideal solution to optimise combustion, a number of precautions should be taken and several technical issues should be considered when applying Lambda control. ● ● For an optimum result it is required that gas is applied at a constant pressure and that gas is supplied with a constant caloric value (gas quality). If not, pressure fluctuation compensation or Wobbe fluctuation compensation should be applied. Best is to work with T and P compensated flow measurements of air, or oxygen and gas. Lambda probes do have a limited lifetime (3 - 6 years) and do need calibration at regular intervals. Nowadays Lambda probes/transmitters are available that do have an auto calibration function. Lambda probes only operate at temperatures above 650°C, which should not be a problem in most glass furnace applications. If it is a problem, probes are available with an inbuilt heating system. ● Air leakages should be avoided as far as possible. ● Lambda control should only be applied for relatively stable combustion processes. Stability could be assessed by the rate of change in the oxygen demand. Refer to Figure 2. ● A Lambda probe does need reference air/oxygen at all time. The free flow of reference air/oxygen should be controlled at regular intervals. T O2 - ref λ= O2 proc = O2 - ref . e O2 - ref - O2 proc { .-Up 0.215 T } Up = U.ln { Pproc Pref } PID λ sp ENABLE RATE OF CHANGE Lambda probe 1.830 0.9 1.1 X X FIC Exhaust O2_ref O2 T’ PID(T’) Thermocouple FIC sp Melt Furnace Gas Figure 2. Block diagram Lambda control Conclusion Lambda control will give you close to Stoichiometric control at all time, reducing energy usage and reducing emissions. Figure 3 and 4 give two examples of the use of Eurotherm controllers, indicators and control systems in Lambda control applications. 2 Lambda Control Reducing NOx Emissions White Paper Issue 1 3504/3508 λ controller Glass T O2 - ref λ= O2 proc = O2 - ref . e O2 - ref - O2 proc { .-Up 0.215 T } Up = U.ln { Pproc Pref } PID λ sp ENABLE Lambda probe 1.830 0.9 1.1 X X RATE OF CHANGE FIC Exhaust T2550 PAC O2_ref O2 T’ PID(T’) Thermocouple FIC sp Melt Furnace Gas Figure 3. Block diagram Lambda control T2550 PAC 3508 λ Lambda Indicator T O2 - ref λ= O2 proc = O2 - ref . e O2 - ref - O2 proc { .-Up 0.215 T } Up = U.ln { Pproc Pref } PID λ sp ENABLE RATE OF CHANGE Lambda probe 1.830 0.9 1.1 X X FIC Exhaust O2_ref O2 T’ PID(T’) Thermocouple FIC sp In combination with cross limited combustion control Gas Melt Furnace Figure 4. Block diagram Lambda control Lambda Control Reducing NOx Emissions White Paper Issue 1 3 Glass 4 Lambda Control Reducing NOx Emissions White Paper Issue 1 Glass CASE STUDIES Glass Fibre Manufacture Efficiency Now 95% Batch Plant Process of Asahi Glass Glass Catalogue Part No. HA029511U005 Iss. 1 Printed in England 10.07 i Glass ii Case Studies contents Issue 1 Glass Glass Our customer is an established company within the glass industry and operating in more than 50 countries worldwide, is one of the world’s hundred leading industrial corporations, and employs a workforce of over 200,000. Case study INDUSTRY Glass Fibre Manufacture Efficiency Now 95% Case Study A new patented control strategy designed for glass industry customer, increased glass fibre manufacture efficiency to 95% Customer challenge Glass fibre manufacture requires a high level of accuracy and reliability to achieve a consistent quality in the fibre produced. Manufacturing costs increase if either of these two areas does not achieve the highest levels possible. Our customer was experiencing a range of differing efficiencies across a number of their bushings plants in different parts of the world. The issues were related to fibre production reliability and recovery from fibre breakages. Our customer needed to achieve the same level of efficiency across all plants, and this level was to be at least the same as the highest achieving plant. Process analysis Working with our customer, combining their process knowledge and requirements with our control expertise and capability, the existing bushings process as a whole was investigated and analysed. The results of this activity lead to the development of a new control strategy for the control bushings process. The changes required to realise this new control strategy were implemented without the need for any costly changes to the existing control hardware installation, only an internal upgrade to the temperature controllers. Solution evaluation When the changes to the control strategy had been implemented and refined, the results proved to be beyond expectations. A repeatable efficiency of 95% was achieved, delivering increased productivity and return on investment (ROI). Efficiency = Plant Availability – Downtime = 95% Plant Availability Glass Fibre Manuafacture Efficiency Now 95% Case Study Issue 1 1 Heat Treatment How these improvements were achieved Improvements were achieved in two main areas: Firstly the improved strategy provided a more reactive and sensitive control to the bushings process, this has lead to a significant decrease in fibre breakages during processing and hence reduced downtime. The effect of fibre breakages has been further reduced by an improved recovery time. The recovery time has been reduced from an average of between two and three minutes down to 40 seconds The process to allow you to benefit from these control improvements ● Review of current operation ● Analyse results from above ● A technical evaluation of your process will be undertaken ● Eurotherm will propose the modifications to your process control to enable you to realise improved efficiency These combined savings serve to reduce overheads and increased operating profit before tax (OPBIT). HA029422U001 2 Glass Fibre Manuafcture Efficiency Now 95% Case Study Issue 1 Glass Glass Asahi India is a subsidiary of Asahi Glass Co. Ltd. with its head offices in Tokyo, Japan. Case study INDUSTRY Batch Plant Process of Asahi Glass Case Study At the fall of 2006 Asahi India celebrated “ first glass” from its 700 tonnes new float line in Roorkee. It was a spectacular moment for the Eurotherm glass team that saw its 2.800 I/O point Batch House Automation system come to life, and deliver the first batches of raw material to the melting furnace. It is from that moment that Eurotherm involvement changed from system conceptual design, detailed engineering, cabinet building, system programming, testing and installation and commissioning to actual silo and hopper filing, batch weighing, batch transport, mixing and cullet returns. The batch process of the float line has been divided into four sections. Each of the sections, or process cells, can be controlled either from the Distributed Control System (DCS) or from the Local Control System (LCS). Silo feeding This consists of feeding the raw matarial into one of eleven silos or hoppers. When unloaded from the trucks raw material is conveyed through a series of bucket elevators and conveyor belts to the silica, soda ash, limestone, feldspar or sodium sulphate silo. Each of these silos are fitted with level transmitters, pressure switches and over pressure flaps that are all mounted and controlled by the EurothermSuite DCS System. The silos have a series of dedusting units that help in trapping the excess dust, which tends to rise as the silos get filled up. These dedusting units comprise of dust collectors and blower fans. At every stage magnetic separators prevent iron impurities finding their way into silos. Batch weighing and transport This section deals with the weighing, dosing and transport issues of the batch plant. Dosing into the weigh scales is either through screw feeders, pneumatic feeders or vibrating feeders. Both coarse and fine dosing from the feeders into the weigh scales is controlled by Eurotherm AC inverters. The time and sequenced dosing of the raw material is completely controlled by the EurothermSuite System. The conveyors are again controlled by Eurotherm AC inverters. Batch Plant of Asahi Case Study Issue 1 1 Glass Mixers The plant is equipped with two mixers each driven by a 110kW motor that is controlled with a Eurotherm flux vector AC drive. Raw material is fed to the mixer that has to be filled through a swivel pipe. The EurothermSuite System also controls the elaborate water and oil feeding options that are used to ensure that the mix reaches the desired consistency before it is fed on to the main conveyor belt. Cullet is added to the mix on the conveyor belt to get the final mixture that is ready to be loaded in the furnace. When the final mix is not of the desired quality it is rejected and fed to a waste hopper. A four compartment batch charger takes the final mix to the furnace silo from where it is fed into the melting furnace. Cullet and cullet return The process to allow you to benefit from these control improvements ● Review of your requirements ● A technical evaluation of your process ● Analyse results from above ● Eurotherm will prepare economically and technically attractive systems Road Map to a Flexible Solution Review of Requirement Analysis of Results As with almost every glass producer, Asahi is using cullet from external suppliers or cullet that is returned from its own production line. The cullet handling part of the control system deals with the loading of the cullet silo with material of the cullet yard as well as the cullet crushing and return from the float line. Eurotherm AC inverters control the operation of line crushers, water crushers finger drops and breakers as well as the conveyor belts that transport the cullet directly back into the batching process or to the cullet yard. Implement Project Technical Evaluation Project Proposal Incoming cullet from external sources is loaded into a hopper that feeds the cullet to a series of crushers. On its way to the cullet silo the cullet passes magnetic detectors and magnetic separators that keep iron parts away from the silo and finally from the raw glass melt. Safety From a safety point of view the systems supplied are in compliance with all the relavant safety and machine directives. Emergency stop switches, pull cord switches zero speed detector units and belt sway detectors secure to bring the plant into a safe state when an emergency does arise. Eurotherm supply Eurotherm has been responsible for the design, delivery, installation and commissioning of the DCS System and the motor control systems. The EurothermSuite DCS System comprises of: 5 off T940X Process Supervisor (redundant) 33 off Model 2500 Process I/O units for 2,800 I/O signals 2 off Operator workstations - EurothermSuite Operation Servers 5 off Local operator stations The model 2500 I/O units communicate with the T940X Process Supervisors via Profibus DP, whilst communication between the T940X’s among each other and the Operator workstations uses a redundant fibre optic Ethernet ring. The motor control system comprises of 10 Eurotherm 690 Series AC inverters in a range of 10kW to 110kW. The inverters are fully integrated with the PCS system Process Supervisor using a Modbus RTU connection. 2 Batch Plant of Asahi Case Study Issue 1 Glass System architecture Batch plant of Asahi Case Study Issue 1 3 Glass 4 Batch Plant of Asahi Case Study Issue 1 Glass KNOWLEDGE A Glossary of Terms International Colour Codes for Thermocouples Compensating Cables Glass Catalogue Part No. HA029511U008 Iss. 1 Printed in England 10.07 i Glass ii Knowledge contents Issue 1 Glass Glass INDUSTRY A Glossary of Terms Glass definition The following terms are used in the Glass industry. A more comprehensive list is available on the internet at www.glassonline.com A Reference Acid etching This process for the decoration of glass involves the application of hydrofluoric acid to the glass surface. Hydrofluoric acid vapours or baths of hydrofluoric acid salts may be used to give glass a matt, frosted appearance (similar to that obtained by surface sandblasting), as found in lighting glass. Glass designs can be produced by coating the glass with wax and then inscribing the desired pattern through the wax layer. When applied, the acid will corrode the glass but not attack the wax-covered areas. Acid polishing A process used in the production of cut crystal to remove the opacity of etched surfaces where decoration has been applied. Items to be polished are immersed in a mixture of demineralized water, sulphuric acid and hydrofluoric acid, and then rinsed. There may be a single short immersion in a stronger solution or, alternatively, a series of immersions in a weaker solution. Acid stamping The process of acid etching a trademark or signature into glass after it has been annealed, using a device that resembles a rubber stamp. Air trap, air lock An air-filled void, which may be of almost any shape. Air traps in stems are frequently tear-shaped or spirally twisted. Alkali-borosilicate glass A special glass used for glass-to-metal seals, particularly suitable when electrical qualities are not important. Alumina-silicate glass (1) Alumina (aluminium oxide Al2O3) is added to the glass batch in the form of commonly found feldspars containing alkalis in order to help improve chemical resistance and mechanical strength, and to increase viscosity at lower temperatures. Alumina-silicate glass (2) A special glass used for glass-to-metal seals, particularly suitable when operating temperatures of electrical components are high (up to 750°C). Annealing Under natural conditions, the surface of molten glass will cool more rapidly than the centre. This results in internal stresses which may cause the glass sheet or object to crack, shatter or even explode some time later. A Glossary of Terms Issue 1 1 Glass The annealing process is designed to eliminate or limit such stresses by submitting the glass to strictly controlled cooling in a special oven known as a "lehr". Inside the lehr, the glass is allowed to cool to a temperature known as the "annealing point". When the glass reaches this point, the lehr temperature is stabilized for a specific length of time (depending on the glass type, its thickness, its coefficient of expansion and the amount of residual stress required) to allow stresses present in the glass to relax. This phase is followed by a period of cooling with a pre-defined temperature gradient. Armour plate glass Laminated glass, resistant to mechanical shock, composed of at least four panes of glass and usually at least 25 mm thick. Autoclave A strong vessel used for the lamination of glass under hugh pressure and controlled temperature conditions. See laminated glass. bubble. During blowing, a vacuum is applied through the mould to suck any trapped air or other gases from the bottom of the mould. A takeout mechanism then lifts the container from the mould. Blowpipe An iron or steel tube, usually about five feet long, for blowing glass. Blowpipes have a mouthpiece at one end and are usually fitted at the other end with a metal ring that helps to retain a gather. Borosilicate glass Glass made from silica and boric oxide. Such glass is highly resistant to chemical corrosion and temperature change (thermal shock) and is particularly suitable for laboratory ware (test tubes, etc.), domestic cooking ware (oven dishes, etc.), high-power lamps and other technical glass ware. It is also used when glass has to be bonded to metal and low expansion is a key characteristic. Bottle-making machine see I.S. machines AZS refractories Refractory blocks or tiles in varying proportions of alumina-zirconiasilica; initially used for areas where corrosion resistance was important but now used in most parts of the furnace. B Banding The application of decorative bands of enamel or precious-metal compounds, normally by machine, to containers such as tumblers, cups, cosmetics bottles, etc. Barium crown glass Barium crown glasses contain larger proportions of boron oxide and barium oxide with a relatively low SiO2 content. The glass can be stabilised against devitrification and weathering by adding small amounts of substances such as aluminium oxide Batch A term used to refer to the raw materials required to produce the desired type of glass once they have been weighed and mixed, and are ready for melting. Boudin process A glass rolling process in which glass flow is controlled by the speed of the machine and fed directly onto the rollers over a refractory sill. As the ribbon of glass passes from the forming rollers, it is supported by an air cushion. The process can be adapted in order to introduce wire mesh into the glass ribbon. (See also "Pilkington double-pass wired glass process" and "wired glass). Bubbles Gaseous inclusions in the glass melt which are removed by refining (see "fining"). Fining agents are introduced to encourage the formation of larger bubbles which rise more rapidly to the surface of the melt, attracting smaller bubbles on their way. Larger bubbles which are not removed by fining are known as "blisters", smaller ones as "seeds" and longitudinally stretched bubbles as "air-lines". Bubbles in glass are generally considered as defects but may also be intentionally created and used as a form of decoration (see "air twist") Bulletproof glass Armour plate glass which is more than 60 mm thick and which resists penetration by bullets. Bending A process used widely in the production of bowls, plates, ashtrays, etc., whereby the shaped glass article (which may be pre-printed) still in sheet form is placed on a stainless steel, sheet steel or cast iron mould coated with talc or powdered chalk. The temperature is increased until the glass sheet sinks into shape in the mould. Bevelling The production, by abrasion, of a sloping edge on the glass sheet. Commonly used on mirror glass. Blow-and-blow process A production process used for glass container manufacturing with forming machines. The elongated gob of molten glass formed by the gob feeder falls into the inverted parison (blank) mould. It is blown down into the mould (settle blow) before being blown from below (counter blow) back up into the now closed mould. The inverted parison is transferred to an upright position in the blow mould where it is reheated before compressed air is introduced into the parison 2 Burners Used to heat glass in furnaces of all sizes, burners mix air (or oxygen) and gas (natural gas or liquid petroleum gases) for efficient combustion. Bushings Platinum alloy electrically-heated boxes with numerous nozzles in their bases used as furnaces for the forming of continuous glass fibre. Glass can be fed into the heated bushing either in its molten state from a forehearth (direct melt) or, alternatively, as marbles to be melted (re-melt process) C Cast glass Glass produced by 'casting', in other words by pouring molten glass into a mould or by heating glass already contained in the mould until the glass melts and assumes the shape of the mould. A Glossary of Terms Issue 1 Glass Centrifuging process A relatively new method for the production of hollow ware such as borosilicate glass columns in chemical plants, funnels, television tubes and other non-rotationally symmetrical items by spinning. Molten glass is fed into a steel mould which rotates at the required speed. At high speeds, the glass can assume almost cylindrical shapes. When the glass has cooled sufficiently, rotation stops and the glass is removed. Chalcogenide glass Gauging or measuring checks: height, diameter and verticality; choke (inner and outer dimension of the neck); dips and saddles in the finish area (mouth/seal of the container); wall thickness. Inspection for specific faults: cracks (also known as checks); stones; foreign material (tramps); spikes; birdswings; thin spots. Proof testing: simulated impact; vertical load. Crown glass Coating 1. Window glass blown into a crown or hollow globe that is flattened and cut before use. This is produced by reheating and spinning out a bowl-shaped piece of glass (bullion) that causes the glass to extend into a flat disk by centrifugal force. The glass is then cut into the size required A thin layer which covers the surface of an object. Coatings may be applied to glass in order to alter the appearance or performance of the product in question e.g. anti-reflective coatings applied to auto mirrors to aid vision, coatings with photocatalytic and hydrophilic properties to make self-cleaning windows. 2. One of the two principal types of optical glass used in the production of compound lenses. The Crown glass, which is an alkali-lime silicate optical glass, has a low index of refraction and low dispersion (its Abbe v-value is larger than 50 or 55, depending on its index). Cold end Cutting The name given to the stage in glass production involving processing when the glass is cold. Cold end processes include grinding, engraving, cutting, etc. The technique whereby glass is removed from the surface of an object by grinding it with a rotating wheel made of stone, wood, or metal, and an abrasive suspended in liquid. Conductive coating Cylinder glass A glass coating which is electrically conductive. Conductive coatings have been used to produce frost-free windscreens, and in a range of electro-optical applications. One way of producing a conductive coating is by depositing tin salts onto the glass. A technique for producing sheet glass dating from the 11th century. By blowing a hollow glass sphere and swinging it vertically, gravity pulls the glass into a cylindrical "pod" measuring up to 3 metres long, with a width of up to 45 cm. While still hot, the ends of the pod are cut off and the resulting cylinder cut lengthways and laid flat. Glass with electrical conductivity characteristics made with the addition of the chalcogen elements (sulphur, selenium and tellurium). Containers, defects Defects in automatically produced containers are categorized as very critical (Group 1), main faults (Group 2) and secondary (Group 3). Group 1 defects make the container dangerous and unusable; Group 2 defects make the container unusable; containers with group 1 or group 2 defects must be discarded. Group 3 defects represent a lowering of the quality of the container but do not affect the functionality of the container. Dalle glass Coloured glass produced in pot furnaces and cast in moulds to form plates in thicknesses of approximately 25 cms. Dalle glass ("dalle" is French for "tile") is used in church and decorative glazing, as well as for furnishings such as door handles. D Containers, enameling Danner process The application of enamel as a means of applying decoration and/or labeling to containers. Enamel patterning or labeling is typically applied by automated silk screening; all-over color can be applied by spraying. See also Enamel A widely used method for the production of glass tubing. The process was developed by an American engineer, Edward Danner, in 1912. Containers, forming The process of turning a gob of molten glass into a hollow container was first mechanized towards the end of the 19th Century. Fully automatic machines were developed during the first quarter of the 20th Century, principally in the USA, using the blow-and-blow process for narrow-neck ware and the press-and-blow process for wide-neck ware. The landmarks in the development of automatic forming of containers were the gob feeder in 1923, which automated delivery of consistently sized gobs of glass, and the individual section bottle making machine in 1925. The equipment in use today is descended from these innovations. See also gob feeder, press-and-blow, blow-and-blow, I.S. machine, mould In the Danner process, the glass flow falls onto a rotating, slightly downward pointing mandrel. Air is blown down a shaft through the middle of the mandrel, thus creating a hollow space in the glass as it is drawn off the end of the mandrel by a tractor mechanism. The diameter and thickness of the glass tubing can be controlled by regulating the strength of the air flow through the mandrel and the speed of the drawing machine. Day tank A glass-containing vessel made from refractory blocks mainly used for the melting of batch for coloured glass, crystal glass and soft special glasses. Day tanks are refilled with batch daily, with melting usually done at night and glass production the following day. Used for producing larger quantities of glass than is possible with pot furnaces (see "pot"). The type of glass to be melted can be changed at short notice. Containers, inspection Inspection of glass containers includes the following: gauging or measuring; inspection for specific faults; proof testing. A Glossary of Terms Issue 1 3 Glass Doghouse The name used to describe the batch feeding compartment within the furnace. The molten glass is covered with the batch material as it flows through the compartment. Also known as "felspar". Any of a group of aluminium silicates of potassium, sodium, or calcium. Used in the batch as a means of adding alumina to the molten glass. Fibre glass Dolomite A raw material compound (CaCO3 + MgCO3) of calcium carbonate and magnesium oxide, which helps lower the melting temperature in the production of flat glass. Domestic ware Very fine strands of glass (normally with a high boric oxide and content) used in the form of glass wool for insulation, glass fibre for matting, etc., and also for the reinforcement of plastics. The principal production process involves blowing jets of steam or air onto molten glass as it emerges from a tank furnace through very small diameter nozzles. The collective term for glass containers used in the home (oven dishes, bowls, jars, etc.). Fining Drawn glass The process by which gaseous inclusions are removed from the glass melt after all batch materials have been added. Fining agents induce the formation of large bubbles which collect smaller bubbles as they rise to the surface. A process for making sheet glass by drawing the molten glass as a sheet directly from the furnace. The thickness of the glass is determined by the drawing rate. E Firing The process of bringing a glass furnace up to its operational temperature and then maintaining the temperature. Edging The shaping or finishing of the edges of a glass surface, usually by grinding with an abrasive wheel. Flat glass All types of glass (rolled, float, plate, etc.) produced in a flat form, regardless of the method of production. Electrode A metal conductor through which electricity enters or leaves an electrolyte, gas, vacuum, etc.). Embossing Carving or moulding in relief. The forming or application of figures or patterns to an object so that they stand out from the surface. Float process A method for the production of high-quality sheet glass whereby a ribbon of molten glass is fed across a bath of heated liquid, usually molten tin, in a carefully controlled atmosphere. The process was developed by the UK firm Pilkington Brothers. Flue Enamel A vitreous substance made of finely powdered glass colored with metallic oxide and suspended in an oily medium for ease of application with a brush. The medium burns away during firing in a low-temperature muffle kiln (about 965-1300°F or 500-700°C). Sometimes, several rings are required to fuse the different colors of an elaborately enameled object. A duct or channel for conveying heat or exhaust gases. Flux A substance that lowers the melting temperature of another substance. For example, a flux is added to the batch in order to facilitate the fusing of the silica. Fluxes are also added to enamels in order to lower their fusion point to below that of the glass body to which they are to be applied. Potash and soda are fluxes. Engraving The production of a design in glass by cutting into the glass surface. Engraving methods include copper wheel engraving, diamond or tungsten point engraving, acid etching and sand blasting. Extrusion A process for the production of continuous strips or rods of material such as glass and also the butyl used in the sealing of insulating glass units. The material, molten in the case of glass, is forced through a die and cut to the required length. F Feeder A mechanism mounted on the casing of the forehearth which delivers the glass in gobs. The rate of flow of the molten glass is regulated by the use of different sized orifices in the feeder spout and by a plunger which pushes the glass through the orifice. Shears for the cutting of the glass flow into gobs are operated through the same cam system as that of the plunger to ensure constant gob size. Foam glass Glass with a high bubble content, produced by adding additional gases or gas forming substances to the glass melt. The resulting glass has a very low density but a high compressive strength and dimensional stability, making it particularly suitable for thermally and acoustically insulating construction materials. Forehearth A refractory tank whose function is to receive glass from the furnace, reduce its temperature to the desired level and discharge it to the feeder mechanism at a uniform temperature. The forehearth usually consists of two sections: a cooling section with burners and cooling ducts which allow the cooling process to be regulated, and a conditioning (equalising) section generally equipped only with burners which ensure uniform temperature distribution through the glass flow as it enters the feeder. Feldspar 4 A Glossary of Terms Issue 1 Glass Founding Gob The initial phase of melting batch. For many modern glasses, the materials must be heated to a temperature of about 2450°F 1400°C). This is followed by a maturing period, during which the molten glass cools to a working temperature of about 2000°F (1100°C). A drop of still molten glass formed by the cutting of the stream of glass as it flows from the forehearth through a feeder into a spout/orifice of variable diameter; the greater the diameter, the larger the gob. The gobs are fed into the forming machine to be moulded into bottles and other glass objects. Frosting Gob feeder The process of giving a glass surface a matt finish, thus reducing transparency. Frosting may be by means of acid treatment (pouring hydrofluoric acid onto the glass), sandblasting, special glue application and subsequent removal, or mechanical etching with a grinding wheel. Furnace An enclosed structure for the production and application of heat. In glassmaking, furnaces are used for melting the batch, maintaining pots of glass in a molted state, and reheating partly formed objects at the glory hole. Furnace, pot A pot furnace consists of a melting chamber lined with refractory brick, a vaulted roof or "crown" of silica brick, and external walls made of insulating brick. Below the upper chamber in which there may be as many as twelve melting pots, there is a lower section for the pre-heating of the fuel gas. Pot furnaces are used today in the manufacture of mouth-blown glass objects and special glasses. Furnace, tank see Tank Fusing (1) The process of founding or melting the batch; (2) heating pieces of glass in a kiln or furnace until they bond (see casting and kiln forming); (3) heating enameled glasses until the enamel bonds with the surface of the object. Fusing glass-to-glass Glasses of different compositions can be fused together for decorative purposes and also in the sealing of electrical, medical and industrial components. The fusion temperature for soda-lime glasses is generally between 760°C and 820°C. Particular attention must be paid to the thermal expansion coefficients of different glass types. G Glass A homogeneous material with a random, liquidlike (non-crystalline) molecular structure. The manufacturing process requires that the raw materials be heated to a temperature sufficient to produce a completely used melt, which, when cooled rapidly, becomes rigid without crystallizing. Glass-ceramics Materials produced from glass which have a polycrystalline structure. Most offer advantages of low thermal expansion, making them suitable for uses such as cookware. Others have high physical strength and can be machined like metals. Glory hole A hole in the side of a glass furnace, used to reheat glass that is being fashioned or decorated. The glory hole is also used to fire-polish cast glass to remove imperfections remaining from the mould. A Glossary of Terms Issue 1 A machine mounted at the end of the forehearth that dispenses gobs of molten glass of consistent size and weight for forming into glass containers. From the spout of the forehearth the molten glass flow out through an orifice, the size of which influences the flow rate of the glass. A cylindrical plunger moves up and down to accelerate or slow the flow of molten glass through the orifice. Linked to the motion of the plunger is a shear that cuts the molten glass into gobs at the correct point in relation to the plunger action. The gobs are then fed down chutes to the forming machine. Grinding The removal of glass with abrasives or abrasive (grinding) wheels in order to shape, polish or otherwise finish both flat and hollow glass. Grinding processes include milling, sawing, edging and drilling. H Heat resistant glass Glass which has a low coefficient of expansion and which is therefore less liable to thermal shock. Borosilicate glass is the most common type of heat resistant glass. Heating up Raising the temperature within the furnace to the required operating temperature under strictly controlled conditions, ensuring the homogenous expansion of refractory materials. Hollow ware Made generally of soda-lime glass, but also of crystal, lead crystal and special glasses, hollow ware includes a wide variety of containers and receptacles: container glass (bottles, jars, medical and packaging glass), tableware (drinking glasses, bowls, etc.), construction hollow ware (glass building blocks, etc.), medico-technical glassware (laboratory equipment, tubing, etc.) and lighting glass (lamps, bulbs, etc.). Hot spot Inside the furnace, the hot spot is that area on the surface of the melt which has reached the maximum temperature (at which batch reactions have been completed and dissolved gases have been reduced to acceptable levels). Also known as the "spring" or "source". I I.S. machine I.S. (independent/individual section) container forming machines are made up of individual but identical sections placed side by side in line. Each section comprises an arrangement of mechanisms with gears enabling the sections to be started or stopped independently of the others, making the I.S. machine more flexible than continuous- or intermittent-motion rotary machines. Infrared lamp An incandescent lamp working at a low filament temperature and consequently emitting relatively high amounts of infrared radiation. Infrared bulbs are usually made of borosilicate glass with molybdenum or tungsten wires. Inleakage The unwanted entry of air into a furnace through expansion-created 5 Glass gaps in the furnace superstructure or through other areas such as burner ports, regenerators and exhaust flues. Inleakage can result in decreased efficiency and increased fuel costs. K Kiln Limestone A sedimentary rock composed mainly of calcium carbonate which is added to the batch to provide calcium oxide. Low emissivity on Low-E glass Kiln forming Commonly known as "low-E" glass and often used in double and triple glazing units, this window glass has a special thin-film metallic or oxide coating which allows the passage of short-wave solar energy into a building but prevents long-wave energy produced by heating systems and lighting from escaping outside. Low-E glass thus allows light to enter while also providing thermal insulation. The process of fusing or shaping glass (usually in or over a mould) by heating it in a kiln. M An oven used to process a substance by burning, drying, or heating. In contemporary glassworking kilns are used to fuse enamel and for kilnforming processes such as slumping. Melt L The fluid glass produced by melting a batch of raw materials Laminated glass Laminated (or compound) glass consists of two or more sheets of glass with one or more viscous plastic layers "sandwiched" between the glass panes. The solid joining of the glasses takes place in a pressurised vessel called an autoclave. In the autoclave, under simultaneous heating of the already processed layers of glass and special plastic, lamination occurs. Mirror When laminated safety glass breaks, the pieces remain attached to the internal plastic layer and the glass remains transparent. The transfer of the various ingredients of the batch into the mixer by means of hoists, buckets and conveyor systems. Lathes Mould Two distinct types of lathe exist, although both basically consist of a horizontal shaft rotated by a motor. The first type uses the shaft to spin an abrasive wheel (often at high speed) in order to cut, score or polish glass; the second type uses the shaft to rotate a piece of glass so that it can be heated and manipulated. A form, normally made of wood or metal, used for shaping and/or decorating molten glass. Some moulds (e.g., dip moulds impart a pattern to the parison, which is then withdrawn, and blown and tooled to the desired shape and size; other moulds are used to give the object its final form, with or without decoration. Lead crystal Mould, block The type of glass produced when lime in the batch is replaced by lead oxide. The composition of lead crystal is 54-65% silicon dioxide (SiO2), 18-38% lead oxide (PbO), 13-15% soda (Na2O) or potash (K2O), and other oxides. Such glass has a high refractive index and is particularly suited for decoration by cutting. A particular type of mould produced in a single piece of cast iron, hollowed into a specific shape using a cold-deformation process. Used in the production of pressed glass hollow ware. Mould, dip Lehr A cylindrical, one-piece mould that is open at the top so that the gather can be dipped into it and then inflated. A special type of oven or kiln used specifically for annealing glass (see "annealing"). In industrial production, it usually has a moving belt to carry the glass through at controlled speeds, and is divided into different areas each with its own heat source, making it possible to carefully regulate the temperature gradient to which the glass is submitted. In smaller workshops, the lehr may be a simple kiln with a shelf for the glassware rather than a moving belt, and with electronic controls to programme the temperature cycle required. Polished glass with a reflective coating of silver deposited on the back. Mixed feed Mould, optic An open mould with a patterned interior in which a parison of glass is inserted, then inflated to decorate the surface. Muffle kiln A low-temperature kiln for refiring glass to fuse enamel, fix gilding, and produce luster. See Kiln. Libbey-Owens process N A method for the production of sheet glass by means of a continuous drawing process. Devised by the American, Colburn, and further developed with the support of the US glassmaker Libbey-Owens, the process was patented in 1905, and was first used for commercial production in 1917. Narrow-neck ware The glass ribbon is drawn vertically from the tank for about 70 cm by a metal "bait" before being bent over a roller into the horizontal plane ready for cutting and annealing. The drawing speed with the Libbey-Owens process is twice that of the Fourcault process. 6 Glass containers, such as bottles, whose opening is tapered and of smaller diameter than the body of the vessel. Neck-ring In the production of glass containers, the tool coupled with the blank mould (parison) which gives the shape to the neck of the container. During the shaping process in the IS machine, the neck ring transports the glass container into the blow mould (or finishing mould). A Glossary of Terms Issue 1 Glass O Owens-Illinois coating techniques Techniques developed by the Owens Illinois company for the surface treatment of glass containers. The two main types are stearate- and polyethylene-based. Stearate treatment using polyoxyethylene monostearate gives good lubricity and reduced friction. It is water-soluble and not waterrepellent, facilitating the application of labels. Stearic acid is of vegetable origin, making this type of coating also suitable for kosher foods. However, since the stearate is destroyed by firing or any subsequent processing, the treatment needs to be repeated after the firing of applied colour labels. Polyethylene coatings are deposited from a water emulsion but are not water-soluble and can thus withstand washing and pasteurising. Although they are slightly water-repellent, most glues used ensure satisfactory adhesion. Polyethylene coatings are transparent and give high lustre and lubricity to the glass surface. P The means of verifying the bursting strength of a glass container during automatic inspection. Push-up The base of a glass bottle (particularly of a wine bottle) which is pushed upwards inside the bottle during the forming process. Pyrometer An instrument used to measure the temperature inside the furnace or kiln. R Raw materials, for basic refractories Basic refractories are made up of various mixes of periclase (magnesium oxide), chromite (chrome ore) and forsterite (olivine). Bonding agents can also be added so that refractories can be shaped. Pellet Redox A small block of compressed matter. Pre-weighed and mixed batch materials are available in the form of pellets. The abbreviated form of "reduction-oxidation". The term "redox equilibria" is used to refer to the balance between reduction and oxidation in the glass furnace. Pelletising The preparation of materials, e.g. batch ingredients, in pellet form (see also "pellet"). Phial See "vial". Redox equilibra Used to refer to the balance between reduction and oxidation in the glass furnace. Refining A variation of the Schuller up-draw process (patented in Germany in 1931) for the mechanical manufacture of glass tubing and rod. Refining ensures that a homogenous glass is produced during founding by eliminating bubbles (see also "bubbles"). Refining is achieved through the action of certain chemicals (refining agents) added to the batch recipe and also by keeping the glass above the liquidus temperature so that the bubbles rise to the surface. Plate glass Refractive index Flat glass made by the casting or rolling of molten glass which is then mechanically ground and polished to produce a smooth and transparent sheet. A standard of measurement used particularly to establish the qualities of optical glass. The index is the ratio of the sine of the angle of incidence of a ray of light to the sine of the angle of refraction (the change in direction when a ray of light passes from one medium to another) by the glass. The second medium normally used to establish the index is a vacuum. Philips process Plunger A tool used in the production of glass containers during the first stage of shape forming in the IS machine. The task of the plunger is to help give the glass container its final shape inside the parison (or blank mould). Pot A fire clay container placed in the furnace in which the batch of glass ingredients is fused, and kept molten. The glass worker gathers directly from the pot. Pressed glass Glassware formed by placing a blob of molten glass in a metal mould, then pressing it with a metal plunger or "follower" to form the inside shape. The resultant piece, termed "mould-pressed," has an interior form independent of the exterior, in contrast to mouldblown glass, whose interior corresponds to the outer form. The process of pressing glass was first mechanized in the United States between 1820 and 1830 Preston test A Glossary of Terms Issue 1 Refractories Material capable of withstanding extremely high temperatures and thus used in furnaces for industries such as glass and steel where raw materials have to be heated to a molten form. Regenerative heating As in recuperative heating (see "recuperative heating"), waste heat from the furnace is used to pre-heat combustion air. Regenerative heating is a cyclic process whereby exhaust gases pass over and thus heat up refractory blocks in one of two pre-heating chambers. Once the first chamber has been heated up, exhaust gases are diverted to heat the second chamber, while cold combustion gas is introduced into the first chamber to be pre-heated by the hot refractory blocks. Continuous reversal of this process provides a permanent flow of pre-heated gas for combustion. Rolled glass Rolled (or cast) glass is a translucent glass with 50-80% light transmission, depending on its thickness and type of surface. It is used where transparency of the glass sheet is not important or not desired. 7 Glass To produce rolled glass, molten glass pours from the melting tank over a refractory barrier (the "weir") and onto the machine slab where it flows under a refractory gate (the "tweel"), which regulates the volume of glass, and then between two water-cooled rollers. The distance between the rollers determines the thickness of the glass S Safety glass Glass which does not disintegrate into sharp and potentially dangerous splinters when it is broken. Safety glass may be produced by laminating (see "laminated glass") or by tempering (see "tempering"). Sand The most common form of silica used in making glass. It is collected from the seashore or, preferably, from deposits that have fewer impurities. For most present-day glassmaking, sand must have a low iron content. Before being used in a batch, it is thoroughly washed, heated to remove carbonaceous matter, and screened to obtain uniformly small grains. Screen printing A process for the decoration of glass whereby coloured ink is forced by a flexible "squeegee" through a fine-mesh screen, or "mask", (traditionally made of silk, now also made of nylon, polyester and stainless steel) onto the glass surface. A separate mask is used for the application of each colour. Considerable automation of the process has been developed, thus allowing extremely high printing speeds for even complex designs Sheet glass processes See the definitions for the following processes, listed in order from oldest to most recent: "crown glass" (definition 1), "cylinder glass", "drawn glass", "Fourcault process", "Libbey-Owens process", "Pittsburgh process", "float process". The float process is now the standard method of producing sheet glass world-wide. Silica Silicon dioxide, a mixture that is the main ingredient of glass. The most common form of silica used in glassmaking has always been sand. Soda Sodium carbonate. Soda (or alternatively potash) is commonly used as the alkali ingredient of glass. It serves as a flux to reduce the fusion point of the silica when the batch is melted. Soda ash Sodium carbonate (Na2CO3), or 'soda ash', is the main source of sodium oxide (Na2O), or 'soda'. This anhydrous, white powder is added to the glass batch, with sodium oxide becoming part of the glass and carbon dioxide being released. Soda-lime glass The most common type of industrially produced glass. A typical soda-lime glass is composed of silica (71-75%), soda (12-16%) and lime (10-15%), plus small amounts of other materials to provide particular properties such as colour. Spinning, hollow ware A relatively new method for the centrifugal production of hollow ware such as borosilicate glass columns in chemical plants, funnels, television tubes and other non-rotationally symmetrical items. Molten glass is fed into a steel mould which rotates at the required speed. At high speeds, the glass can assume almost cylindrical shapes. When the glass has cooled sufficiently, rotation stops and the glass is removed. 8 Staple fibre Short lengths of glass fibre, usually U-shaped, which intertwine and are used, in particular, to create insulation materials. Stemware The collective term given to drinking glasses whose body is connected to the base by a thinner column of glass. Suck-blow process A process used for glass container manufacturing with forming machines. Glass is sucked from the tank of molten glass into the parison mould and then cut by shears. A plunger inside the mould produces a hollow space in the glass which is then enlarged by blowing. Following this initial blow, and then reheating, the parison is transferred to the finishing mould for the finishing blow. Suction cup A semi-spherical cup of flexible material such as rubber. By pressing the cup onto a glass surface and removing air from inside the cup, the vacuum thus created holds the cup and glass together. Suction cups are used in both the manual and automatic handling and conveyance of glass. T Tank A large receptacle constructed in a furnace for melting the batch.Tanks replaced pots in larger glass factories in the 19th centry. Tempering see toughening Thermal conductivity The passage of heat through a material. Insulation materials are defined as having 'low' thermal conductivity whereas metallic materials generally have 'high' thermal conductivity. Thermal shock testing Assessing the effects on a material of rapid temperature change. In glass, the shock may derive from the external surface of glass expanding or contracting more rapidly than the interior surface as a result of heating or cooling. Any such difference may lead to cracking or shattering. Thermocouple A pair of different metals in contact at a point, generating a thermo-electric voltage which can serve as a measure of temperature. The wires are encased in a protective sheath that can be introduced as a probe into the glass furnace or kiln. Toughening Special process of solidification of a glass sheet in order to make it particularly resistant to breakages. The process may be physical (thermal) or chemical. In the former, the glass sheet is heated to a temperature just below its softening point and then immediately cooled by special jets of cold-air. These harden the surface of the glass, giving the inside more time to cool. This allows the external layer to crystallize into a wider lattice while the inside solidifies with greater compression than in the crystal lattice. The result is a sheet of glass which is two or three times stronger than untempered glass and which, upon breakage, shatters into tiny pieces with blunt edges (the most common applications are for automotive glass). The chemical process, on the other hand, is based on the so-called ion-stuffing technique. Different chemical elements possess different ionic radii and therefore different densities. Hence, if glass containing sodium is cooled slowly in a salt bath of molten potassium, the sodium ions will migrate from the glass to the salt, while the A Glossary of Terms Issue 1 Glass potassium ions will move to the surface of the glass where, due to their wider radium, they create a denser and therefore stronger surface layer (of no less than 0.1 mm). Glass sheets which have been chemically tempered are five to eight times stronger than those which have not undergone any tempering process. Furnace gas testing may be performed with Orsat equipment (gases are absorbed selectively as they pass through a series of specific solvents) or by means of instrumental analysis. Paramagnetic detection may be used for oxygen analysis, and infrared absorption for carbon dioxide analysis. Mass spectrometry or gas chromatography are also used to analyse gas mixtures. Tube-drawing process Waste-heat recovery see danner process An economy measure whereby the heat of exhaust gases is used in a cyclic process to pre-heat combustion air and/or fuel-gas. (see "regenerative heating"). Tubing Hollow rods of glass used especially in the production of laboratory/medical equipment (ampoules, vials, etc.) and fluorescent lighting. V Vapour deposition of thin fims The term covers a wide range of techniques for applying a thin film on the surface of the glass to change its technical or aesthetic properties e.g. scratch resistance, solar control. The methods employed to deposit the film include spraying onto hot glass, condensation in a vacuum and evaporation of the film material by heating. Vello process Weathering Changes on the surface of glass caused by chemical reaction with the environment. Weathering usually involves the leaching of alkali from the glass by water, leaving behind siliceous weathering products that are often laminar. Wired glass Flat rolled glass reinforced with wire mesh and used especially for glass doors and roofing to prevent objects from smashing through the glass and also to hold pieces of broken glass together. By holding the glass together, it can also protect against break-in and the spreading of fire. Wired glass is produced by continuously feeding wire mesh from a roller into the molten glass ribbon just before it undergoes cooling. A drawing process used for the production of glass tubing. Glass from the furnace forehearth flows down through an orifice (ring) within which is a rotating conical-ended shaft (or mandrel) over and around which the glass flows. The tube-shaped glass is pulled from the end of the shaft by a tractor machine and turned through 90° into a horizontal position ready for cutting. Venturi tubes Short pieces of narrow tube between wider sections of tube, used for exerting suction or measuring flow rates and invented by the Italian physicist G. B. Venturi, who died in 1822. Vial A small cylindrical glass vessel especially for holding liquid medicines. Viscosity The quality or state of being viscous; the physical property of a liquid or semi-liquid that enables it to develop and maintain a certain amount of shearing stress dependent upon the velocity of flow and then to offer continued resistance to flow. W Waste gas analysis Gases emitted by the melt in the furnace can be analysed either in the furnace itself (in order to assess melting efficiency, for example) or as they are discharged from the furnace stack (above all, for pollution control purposes). A Glossary of Terms Issue 1 9 Glass 10 A Glossary of Terms Issue 1 Glass International Colour Codes for Thermocouple Compensating Cables E J K EXISTING COLOUR CODES Extension and compensating Leads BRITISH BS1843:1952 AMERICAN ANSI/MC 96.1 GERMAN DIN NICKEL CHROMIUM/CONSTANTAN –200ºC to 850ºC (Nickel Chromium/Copper-Nickel, Chromel/Constantan, TI/Advance, NiCr/Constantan + – + – IRON*/CONSTANTAN 0 to 850ºC (Iron/Copper-Nickel, Fe/Konst, Iron/Advance, Fe/Constantan, IC) + – + – + – NICKEL CHORMIUM/ NICKLE* ALUMINIUM –200ºC to 1100ºC (NC/NA, Chromel/Alumel C/A, T1/T2, NiCr/Ni, NiAL) + – + – + – N NICROSIL/NISIL –200ºC to 1300ºC + – + – T COPPER/CONSTANTAN –200ºC to 400ºC (Copper/Copper-Nickel, Cu/Con, Copper/Advance) + – + – + – COPPER/COPPER-NICKEL Compensating for Platinum 10% or 13% Rhodium/Platinum (Codes S and R respectively, over Range 0-50ºC) (Copper/ Cupronic, Cu/CuNi, Copper/No.11 Alloy) + – + – + – COPPER/CONSTANTAN (LOW NICKLE) (Cu/Constantan) Compensating for “K” over Range 0-80ºC (CU/Constantan) + – + – + – RCA SCA KCB *Magnetic ( ) Alternative and Trade Names For thermocouple connectors, body colours are as outer sheath colours above For thermocouple connectors, body colours are as outer sheath colours above EXTENSION /COMPENSATING CABLES Extension cables are designated by the suffix X (eg JX') and compensating cables by the letter C (eg NC). Different alloys may be used in certain circumstances and these are distinguished by additional letters (eg KCB) + – EX + – JX + – KX + – NX + – TX + – RCA SCA + – KCB Reference CODES CONDUCTORS (Operating ranges vary with wire size and application) +/– NEW IEC584-3: 1989, Mod BS4937. Part 30. 1993 For thermocouple connectors, body colours are as outer sheath colours above THERMOCOUPLE CONNECTORS New colour coded connectors are marked IEC and have a grey body with a clearly visible colour coded area (with exceptions of the fascia/panels sockets). This is to prevent any confusion regarding the use of the new and old colour coded connectors International Colour Codes Issue 1 1 Glass 2 International Colour Codes Issue 1