Transcript
Outline
Keys to Laminating Success: Web Handling Advice for Laminators
• • • • •
Timothy J. Walker
Lamination Process Options Curl & Other Laminate Defects The Ideal Laminator in 22 Steps Compliant Rollers Nip Deflection Compensation (Not covered – Materials & Chemistry)
TJWalker+Associates, Inc. 164 Stonebridge Road Saint Paul, MN 55118 (651) 686-5400 Fax (866) 572-3139
[email protected] www.tjwa.com
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Lamination Defined
Laminate Properties
Lamination is… The process of combining two or more substrates, creating a product of combined properties not found in any layer individually.
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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• • • • • •
Moisture Barrier Light Barrier Vapor Barrier Oxygen Barrier Abrasion Resistance Heat Sealability
• Gloss/Matte Finish • Aesthetics • Strength > Tear Resistance > Break Strength > Modulus
• Release
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Laminated Products
Lamination Methods Gaskets
• • • • • • • •
Flexible Packaging Cartons Heat Sealable Insulation IDs (passports, licenses) RFID Tags LCD Displays High-Tech Fabrics Reflective Sheeting
• • • • • • • •
Labelstock Trash Bags Flooring Medical Pouches Batteries Adhesives Book Covers, Maps In-Process “Carriers”
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•Wet Lamination •Dry Lamination •Thermoplastic Lamination •Reactive Lamination •Extrusion Lamination Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Lamination Micro-View
Dry Lamination
Coat:
Laminate:
Applying the bonding layer to A, forcing intimate contact, excluding air at A interface.
Applying substrate B to the bonding layer, forcing intimate contact, excluding air at B-interface.
Bonding Layer
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• • • •
Solvent (or water)-based adhesives Solvent is removed prior to lamination Lamination is typically integrated with coating / drying. Common for products with adhesive end-use (e.g. labelstock)
Substrate B Convection Drying
Substrate A Coating and laminating processes are dependent on a material’s response to pressure, temperature, and time.
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Wet Lamination • • • •
Thermoplastic Lamination
Water or solvent based adhesives One of the laminates is absorbent Bonding fluid is applied cold then dried in laminate form Common for bonding paper, non-wovens, and fabrics. Convection Drying
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Cooling may be needed after any hot process.
Thermal Pre-Heat
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Reactive Lamination Externally Initiated Cure
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Don’t wind hot!
Chill
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Extrusion Lamination
Material Cure
• Solvent free coating between • Two-part adhesives or epoxies substrates. form chemical bond over time. • Coating cured via UV, E-Beam, • Coating and laminating must be moisture (or other reaction completed within limited “pot-life”, initiator) in laminate form. the time between mixing and hardening. • For light-based cure, one web is transparent. UV, E-Beam, or Cure Reaction
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• Thermoplastic film softens when heated and hardens when cooled. • The thermoplastic film is pre-heated to soften, then combined with the second web. • High nip loads required to flow high viscosity material. • Commonly have heated nip rollers. (Laminate should be cooled prior to winding.)
Extrusion lamination combines extrusion coating and laminating in one step.
Extrusion Coating
Extrusion Lamination
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Extrusion Lamination
Internal Print Lamination
• Bonding material is thermoplastic heated above its melt temperature. • Slot dies apply the heated material and control the final coating temperature. Slot dies may be used in either drop or knife mode. • Advanced slot dies have rotating rods to smooth the coating.
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Protect printing from abrasion and UV degradation…
Dry or Thermoplastic Lamination
…by reverse printing on the inner surface of a clear film, then laminating the printed side to a second substrate.
Extrusion Lamination
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Curl
+ Printing
+ Printing
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Elastic Curl
Many web products have a flatness specification. Web curl describes lack of flatness.
The most common cause of curl is mismatched strains at lamination. A
εA > εB B
Flat under tension.
Curled when tension is removed. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Elastic Curl
Tension = Stretch and Neck For solid materials, tension and compression stresses do not significantly change density.
1. Materials are laminated under tension. T>0
Therefore, dimensional increases in one direction cause decreases in other directions.
2. When tension is removed, materials return to unstrained dimensions.
STRETCH: Tensioning Increases Length
T=0 NECK: Thickness & Width Decrease
3. Non-uniform recovery creates curl. T=0 T0 = 0 Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Measure Laminate Curl
r
MD TD
TD
1. Cut strips in machine and transverse directions. 2. Measure orientation and radius of curvature. 3. If MD curl is high, try lowering inside radius web’s tension.
r
4. If TD curl is high, look for cause in coating or web dimensional change. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Web Elasticity
Quantify curl magnitude and direction with MD and TD strips.
MD
T1 > 0
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Material properties modulus (E) and Poisson’s ratio (ν) determine how a stretches under tension. Webs respond to tensile stress, defined as both force over area. In tensioning, the important area is the cross-section: thickness x width. z
Stress, σ = Load / X-Sectional Area
z
Strain, ε = Stress / Modulus
z
Web strains are commonly < 1%.
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σ = ε =
F tw
σ E
Tensile Stress
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KEY CONCEPT
!
KEY CONCEPT
Stress
Strain
Stress and pressure are both defined in units of force per areas. To better understand any web process, convert forces into stresses by dividing the load by the cross-sectional area it is exerted over. Use: Machine tension is commonly set in units of force, such as lbf, kgf, or N. For an “apples-to-apples” comparison of different products or processes, calculate tensile stress by dividing tension load by product thickness and width. Example: 50 lbf creates higher stress if exerted over a smaller area. Across a 50” wide and 0.010” thick web, the tensile stress is a low 100 psi. For 50” by 0.001”, the stress is 1000 psi. Loaded on 1” by 0.001”, the stress is 50,000 psi!
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
KEY CONCEPT
Strain is dimensional change in a solid material in reaction to stress. For positive stresses, materials will elongate in the direction of the stress. For negative stress or pressure, materials will compress. Strain is calculated as the change in dimension divided by the original dimension. Use: When a web is forces to conform around variations in roller parallelism or diameter, the web’s response will begin by determining the web strain. Example: If a roller diameter varies from 5.00” to 5.05”, the web develop a 1% strain differential to conform to roller. WWW.WEBHANDLING.COM 22
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
!
Web Spring Constant
Web Spring Constant
Spring
Web
An elastic web has a spring constant, k, proportional to thickness X width X modulus. Use: Calculating the web stretch created by tension Example: Matching strains of different webs at laminating to prevent curl. Use: Calculating tensile stress created by web strain Example: Determine the tension variations created from the web conforming to roller diameter variations.
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
!
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The web’s spring constant is the product of its thickness, width and modulus.
F=0
F=0 F
F
F =k
∆L = k∆ε L
F =k
∆L = (twE )∆ε L
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Modulus Defined
Web Pressures
Modulus is defined as the slope of the initial linear portion of the elastic stress-strain curve. It describes a web’s “stretchability.” Stress
σ
(psi)
σ
Brittle Break
Yield Point
x
P=
High modulus: Foils Papers Polyester
x Ductile Break
BOPP HDPE
Ε=∆σ/∆ε
Low modulus:
Elastic strain
Strain, ε
Unnipped systems are dependent on web tension and roller radius.
PE, Vinyl, PU
ε
(%)
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Delaminating Compliant Roller
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
1 PLI, 2” radius = 0.5 psi
Nips create 10-1000x more pressure.
N P= bw
Example:
10 PLI, 0.5” footprint = 20 psi
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Tensioning Recommendations Tensioning
Nipping
Wrinkling
Example:
Nipped systems can focus high load over a small area, creating high pressure, independent of tension and radius.
The Ideal Laminator in 25 Steps? Tensioning
T r
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1•
Driven steel roller and idling or torque driven rubber roller.
2•
Minimize curl by tensioning each web match pre-laminating strains.
3•
Exit tension set equal to the sum of the input tensions.
4•
Minimize accumulation wrinkles by pulling out bagginess with tension.
5•
Drive the compliant roller with a torque-assist, if needed to avoid shearing thick, soft adhesives or substrates.
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Laminating Drive Options
Idling Nip Torque Idling Rubber Roller Driven Steel Roller
Most Common
Neither Roller Driven
What drives the idling nip roller?
Driven Steel Roller
Direct-Driven Steel Roller
Idling Rubber Roller
Torque-Driven Rubber Roller WWW.WEBHANDLING.COM 29
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
tweb = web thickness δrubber = rubber indentation
If tweb < δrubber
If tweb > δrubber
Steel roller and web drive the idling nip.
The web drives the idling nip.
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Laminating Drive Options
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Rule #1 of Laminating Match Strains of Incoming Webs. To prevent elastic curl, set input tension ratio proportional to web spring constants.
ε A = εB
Most Common
TA σA EA
For low tension laminating, often leads to problems from drag and inertia.
Good for most products, but may have too much shear thicker laminates
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
One in tension mode, one in torque, most advanced laminating. WWW.WEBHANDLING.COM 31
TA t A E A = TB t B E B εA =
σA EA
=
TB
TLAM
TA t AEA
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Rule #1 of Laminating Example Strain Calcs: εA =
σA EA
=
TA t AEA
Rule #2 of Laminating Set Laminate Tension to Sum of Input Tensions.
TA
To reduce in-nip shear and allow minimum nip load without slippage.
TLAM
TB
TA TLAM = TA + TB
TA=0.5 PLI
TB=0.5 PLI
tA=0.001”
tB=0.0005”
EA=40,000 psi (OPP)
EB=500,000 psi (PET)
Stress = (0.5)/(0.001) = 500 psi
Stress = (0.5)/(0.0005”) = 1000 psi
Strain = (500)/(40000) = 1.25%
Strain = (1000)/(500000) = 0.2%
Strain / PLI = (1.25%)/(0.5 PLI) = 2.5% per PLI
Strain / PLI = (0.2%)/(0.5 PLI) = 0.4% per PLI
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
∆TLAM = 0
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TB
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Tensioning Baggy Webs The ideal web carries tension uniformly across the web width. T1 > 0 T0 = 0
T2 > T1
T0 = 0
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Compliant Roller Recommendations
For an imperfect web, tension stretches the short lanes first. When short lanes are stretched to equal the long lanes, the web appears taut. T1 > 0
TLAM
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6•
Lamination processes should be design to achieve a desired pressure, not by total load or load per width.
7•
Rubber rollers should have 10-30 mils deflection under anticipated process pressures.
8•
Both rollers should have sufficient diameter and wall thickness to keep deflection under process conditions to be less than 20 percent of rubber roller indentation.
9•
Default should be cylindrical roller. A crowned roller can offset pressure variations from deflection, usually only needed in extremes of high width to diameter ratio or high nip loads.
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Why Measure Pressure Variations?
Average Pressure vs. Indentation
For consistent product quality, you need:
Pressure vs Indentation
80.0
Uniform pressure across nips of sister process lines.
70.0
?
P
P width
4 T 2 Req ho N = 4ηV + ho 3π Rwr Req
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30.0
Req =
Small relative to first term
Rwr Rnip Rwr + Rnip
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0.005
0.01
0.015
0.02
Indentation, in. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Nipping Recommendations
ho N
40.0
0
width
Req Req
50.0
0.0
Simple Nip & Air Model
ho = 4ηV
P vs δ is independent of radius.
t=1.00-in
10.0
P
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
N = 4ηV
t=0.50-in
P vs δ is directly proportional to cover thickness.
20.0
?
? width
t=0.25-in
60.0 Pressure, psi .
Uniform pressure across a nip.
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10•
Avoid gapped or indentation controlled nipping.
11•
Load should be delivered by pivoting rubber roller via pneumatic or hydraulic pressure limited to 50% above maximum process load requirements.
12•
Both rigid and articulating nipping systems can be successful. Rigid systems must close and hold their parallelism to the non-moving roller. Misalignment should be less than 5-10% of rubber indentation. Articulating nipping rollers (where each side can move independently) should have even flow control to close squarely.
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Nipping Recommendations (cont’d) 13 •
Use nip footprint measurements to verify crossweb nip uniformity.
14 •
Use flow control to prevent nips from slamming shut or flying open, but don’t overly restrain or cut off flow.
15 •
Sufficiently guard nip rollers for safe operations. Nip roller should quickly open to a gap of over 4-inches.
16 •
Nip point should be well-lit and easily viewable.
17 •
Avoid wedging nips.
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Nip System Comparison
Advs.
P ind. Rubber, thickness Direct relation of N = f(P, psi)
Disads.
Added complexity
Many processes require high pressure nipped rollers:
Pneumatic Loaded
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Pneumatic
Nipped Rollers Load Options
Engagement
Gravity Loaded
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Ensure Nipping Alignment
Gravity
Simple
Simple
Can control thickness (gap mode)
Load is uniform vs width (top)
P is NOT independent Rubber, thickness, speed
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Engagement Loaded
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1. Ensure all rollers and shafts are cylindrical, concentric, and straight. 2. Level and tram fixed roller. 3. Level and tram nipping roller’s pivot shaft. 4. Transfer shaft parallelism to nipping roller, through parallel and equal length arms. 5. Close nip and ensure good alignment through footprint measurement. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Wedging Nips Farm
Fnip
θ
Froller
When the nip is closed, if the nip arm angle is not parallel to the nipping tangent line, then the nip load is magnified by a wedging factor.
Nip Deflection Compensation Farm
Fnip
Froller θ
Increase Diameter
D
For nips, L/D<5
Fnip = Froller / cos θ
L
Compliant Covering
θ
θ Fixed Crowned Roller
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Wrinkling Recommendations
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Worst Case: Baggy Web + Nips
18 • Avoid pre-nip wrinkling with a spreader and/or skewing
rollers/bars immediately upstream of the nip point. 19 • Entry rollers for each web should create short spans (<18”) and
small pre-nip point wrap angles. 20 • If your product often has extreme left-right bagginess (defined
as bagginess not resolved by tension or spreading), wrinkles can be avoided by using a 90-degree wrapped entry roller that pivots parallel to entry span and twists in pre-entry span.
VWEB = 100
21 • Avoid larger wrap angles on all rubber nip rollers. 22 • Avoid 90-degree wrap angle on nipping rollers to prevent
deflection-induced tracking wrinkles.
Baggy Edge
VWEB = 101
23 • Use large wrap angles on steel nip rollers only if needed for
pre-heating. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Adjustable Roller: Best Practice 24 •
Set up entry roller with 90o wrap.
Angle entry roller parallel to entry span, lengthening baggy side.
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Compliant Roller Benefits
z
Roller hardness or diameter variations,
z
Hysteresis, a differing response in the compression-recovery cycle, creates internal heat… …which can lead to significant elastomeric degradation or melting.
Web thickness variations
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Elastomeric roller covers deform, elongating near the nip point and bulging before and after.
Compliance is needed to compensate for: Roller deflection,
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Elastomer Nip Deformation
Lamination nips usually include at least one compliant roller.
z
After laminating, avoid small diameter rollers in handling thick laminate with weak bond. 25 • To prevent defects associated with build up of delamination or bubbles ahead of rollers, use laterally ridged rollers, as needed. 26 • Avoid post-nip wrap on nipping rollers. Pull the web straight out.
Bonus: New this week…
Baggy Edge
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Delaminating & Curl Rec’s
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Elastomer Nip Deformation What is the surface speed of a rubber nip roller driven by a steel roller?
Equivalent Radius
Vrub., unnipped
Vrub. nipped Vrub., unnipped < Vrub., nipped = Vsteel
Vsteel
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Footprint vs. Engagement b
r
No Footprint
2
The equivalent radius, req, of a nip formed by two rollers is the same as one roller twice as small pushed against a flat plate.
req =
1 1 1 + rA rB
Engagement Creates Footprint
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
δ r-δ
r-δ
Example: Ra=6”, Rb=6” Req=3”
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Footprint vs. Engagement
= 8 r eq δ
r-δ1
δ
Smaller diameter = Smaller footprint
r-δ2
More Engagement = More Footprint
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r
No Footprint
r-δ1
Engagement Creates Footprint
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
r-δ2
More Engagement = More Footprint
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Footprint vs. Engagement
Calculate Nip Load Given Machine Settings: Nip Air Pressure (psi)
t
Convert to Process Condition: Nip Load (lbs/in)
rA
δ
b = 8reqδ
req =
r-δ
1 1 1 + rA rB
LCYL
Calc. cylinder force from pressure and area
FCYL = nPA = nP (2πr ) 2 cyl
LNIP A=Area of Cylinder
Calc. leveraged nip force
b
δ = Engagement b = Footprint rA = Rubber Roller Radius rB = Steel Roller Radius
rB
For vertical nips, include roller weight effect
FNIP = FCYL (LCYL LNIP ) ± WNIP
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Nip Pressure Equations F 2 (1 −ν ) Eo N= N = w 3 1 − 2ν 1 −ν 2 2
N = FN / w w
F1
WNIP=Weight of Nip
N = FNIP w
Nip Force per Width (N) FN = F1 + F2
N=Number of Cylinders
Calculate Nip Load:
For small pentrations, δ/t<0.07 Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
P=Pressure
FNIP = FCYL (LCYL LNIP )
F2
2r 32 δ t
Contact Mechanics by KLJohnson, Cambridge University Press, 1989, pp 139-140. (According to Dr. JKGood, this can be used for rubber strains up to 7 percent.)
E o ( psi ) = 20 . 97 e 0 .0564 ( ShoreA ) E o ( kPa ) = 145 e 0.0564 ( ShoreA ) Modeling Rubber Covered Nip Rollers in Web Lines, J.K. Good, Oklahoma State University, Stillwater, OK, Proceedings of the Sixth Annual Conference on Web Handling, 2001 pp. 159-177. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Rubber Modulus vs. Durometer (27)
Modulus, psi
3500
2
E o ( psi ) = 20 .97 e 0.0564 ( ShoreA ) E o ( kPa ) = 145 e 0 .0564 ( ShoreA )
3000 2500 2000
F 2 (1 −ν ) Eo N= N = w 3 1 − 2ν 1 −ν 2
Modulus vs. Shore A
(MPa) 4000
Nip Pressure Equations
(14)
1500 1000
2r 32 δ t
Reversing this equation to get indentation from nip load:
δ =
Assuming a Poisson’s ratio of 0.46 simplifies to:
0.23Nt 3 δ = 0.5 Eoreq
500 0 30
40
50
60
70
80
90
Shore A
Modeling Rubber Covered Nip Rollers in Web Lines, J.K. Good, Oklahoma State University, Stillwater, OK, Proceedings of the Sixth Annual Conference on Web Handling, 2001
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Nip Pressure Equations
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Pressure vs Indentation
)
Then find the footprint, b, from the indentation and equivalent radius.
b=
2 3
8 req δ
70.0
t=0.25-in
60.0 Pressure, psi .
(or use simplified ν=0.46 equation from last slide)
(
80.0
3 tN 1−ν 2 1− 2ν 2 E 2 ( ) − r 2 1 ν o eq
δ =
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Average Pressure vs. Indentation
If you know nip load, N, and want pressure, P… First, find indentation from t, N, req, E0, and ν.
)
t=0.50-in
P vs δ is directly proportional to cover thickness.
P vs δ is independent of radius.
t=1.00-in
50.0 40.0 30.0 20.0 10.0
Average pressure is simply nip load, N, divided by footprint, b.
PAVG = N / b
0.0 0
0.005
0.01
0.015
0.02
Indentation, in. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
2 3
2
IWEB 01
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
(
3 tN 1−ν 1− 2ν 2 2 2r Eo (1−ν ) 2
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Nip Load (PLI) vs. Indentation
Nip Roller References • Calculations of the Behaviour of Rubber Covered Pressure Rollers, Parish, GJ, British Journal of Applied Physics, Vol 12, July 1961. • Air Entrapment and Residual Stresses in Roll Wound With a Rider (Nip) Roller, JKGood and SMCovell, , Oklahoma State University, Stillwater, OK, pp 78-92, Proceedings from the Third International Conf on Web Handling, 1995 • Entrained Air Films in Center Wound Rolls - With and Without the Nip, RMTaylor and JKGood, Oklahoma State University, Stillwater, OK, pp 189-202, Proceedings from the Fourth International Conf on Web Handling, 1997 • Modeling Rubber Nip Rollers in Web Lines, JKGood, Proceedings of the 6th International Conf on Web Handling, June 10-13, 2000. • Contact Mechanics, K.L. Johnson, Cambridge University Press, 1985
Nip Force/Width vs Indentation 50.0 0.25, 1.5 0.5, 1.5
Force/Width, PLI .
40.0
1, 1.5 0.25, 3 0.5, 3
30.0
1, 3 .25, 6 0.5, 6
20.0
1, 6 10.0
0.0 0
0.005
0.01
0.015
0.02
Indentation, in.
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Two Rules of Elastomer Nips
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Elastomeric Roller Covers Important Characteristics of Elastomer Coverings: • Elastic • Durable • Non-Porous • High Coefficient of Friction • Chemically Resistant • Moldable • Conductive?
#1 Maximize elastomer hardness, but enough compliance to ensure full width contact and minimize pressure variations.
#2 Minimize Load, but enough to squeegee air and ensure line contact. Both reduce hysteresis and increase life.
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Eccentricity: • • •
2.
Cleaning: • • • • •
3.
Clean with isopropyl alcohol or MEK on a lint free cloth. Do not clean hot rollers. Clean once per shift. Clean before storing. Clean the entire exposed surface, including the ends.
Degradation / Damage: • • •
4.
Always rest rollers on their journals to avoid flat spots or surface damage. Open nips when web line is stopped. Periodically rotate roller in long-term storage.
Avoid UV exposure (including sunlight, cure lamps, and florescent lights). Avoid ozone exposure (from motors and corona treaters). Never use a razor near the elastomer surface.
Typical end-loaded nipping rollers will deflect away from each other, reducing pressure and contact at the nip’s center.
Y, width
Pressure
Replacement: • •
Pressure
1.
Nip Pressure vs. Width
Y
Change out rollers when damaged or worn. Periodically measure for uniform footprint and hardness.
Contact Area
Elastomer Roller Care
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Nip Variations vs. Load
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Nip Deflection Compensation Increase Diameter
Nip deflection is directly proportional to load. Pressure
For nips, L/D<5
D L
Compliant Covering Y, width
Contact Area
Excessive nip loads lead to increase variation and associated problems.
Y, width
Fixed Crowned Roller
Y, width Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Skewed / X Nipped Rollers
Skewed / X Nipped Rollers
To end-loaded rollers will bow away from each other.
(
y = r 2 − x2
Skewing the rollers, so their deflecting shape wraps slightly around the opposing cylinder reduces pressure variations.
∆y = 2 r − r 2 − x 2
)
Wrap vs Skew 0.006
Vertical Wrap, in
This technique has a subtle, but sometimes significant effect, especially with steel-on-steel nips.
r=2 in
0.005
x y
r=3 in r=6 in
0.004 0.003 0.002 0.001
Note: Ensure you don’t have this misalignment in your nips if you don’t want it. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
0.000 0
0.05
0.1
0.15
0.2
Skew, in
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Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Addendum
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Measure Nip Gap
• Measuring Nips
•
For a fixed gaps, use a feeler gauge to measure the space between rollers.
•
For a fixed interference, use a known spacer (S) and set the gap (G). Removing the spacer will create the fixed interference (G-S)
Some nips are set using a fixed opening or interference dimension.
S
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Measure Nip Load
Nip Footprint Measurement 1 Measure nip contact area using a series of sticky notes.
Method 1 (lower nip loads) 1. Wrap a rope around the nipping roller.
1. Close the nipping roller and apply full load (with nip not rotating).
2. Attach the rope to a handheld force gauge.
2. Place a series of Post It™ notes on one roller, pushing them as far into the nip point as possible and stick them in place. 3. Open the nip and measure the gap between opposing notes.
3. Measure the force at various input pressures. 4. Divide the sum of the forces by web width to convert to pounds per inch load.
4. Look for MD contact length variation as a sign of non-uniform nip pressure.
Method 2 (higher nip loads) 1. Insert two compression force gauges on either side of a nip. 2. Close the nip and load at various levels. 3. Divide the sum of the forces by web width to convert to pounds per inch load.
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Nip Footprint Measurement 2
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Nip Footprint Measurement 3
Measure nip contact area using knurled foil. 1. Open the nipping rollers 2. Place a strip of knurled foil across the nipping area.
EZ-Nip - $300 / 200 ft.
3. Close the nip with the desire force.
A single sheet pressure sensing film.
4. Open the nip and inspect the area where the knurl was flattened.
Thickness Humidity Range Pressure Minimum
5. Look for MD contact length variation as a sign of nonuniform nip pressure.
15 mils (0.076 mm) 10-90% RH 300 PSI (20.8 kg/cm2)
Contact: Stowe Woodward - Neenah, WI www.sensorprod.com/nip.php
Junille Hintz 920-729-7000 Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Nip Footprint Measurement 4
Nip Footprint Measurement 5
P-Nip - $2000
Sigma-Nip - Depending on the length of the chain and how many sensors, cost is from $8k to $16K.
Sensor Products Inc. 300 Madison Avenue Madison, NJ 07940 USA
For 60“ around $10K Phone: 1.973.884.1755 Fax: 1.973.884.1699 Toll Free (U.S. Only): 1.800.755.2201 Email:
[email protected] www.sensorprod.com/nip.php
www.sensorprod.com/nip.php Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Nip Pressure Measurement 1
Folded Brass Sleeve 0.001” (25 µm) thick
N=
F 2 µwS
µ N F ws
F F
= Brass-Steel Friction Coefficient (use 0.25) = Nip load per width (lbs/in or N/m) = Frictional force to slide steel vs. brass (lbs or N) = Width of steel strip
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Nip Pressure Measurement 2
Insert a steel-brass ‘hot dog’ into the loaded nip and measure the force to slide the steel strip. Calculate the nip load from the measured frictional force, COF, and geometry.
Steel Shim Stock 0.002” (50 µm) thick
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Tekscan’s sensors detects pressure changes as a electrical resistance drop though a conductive ink. The array sensor is 0.005” thick and read every 0.1” over a 1” by 16” area. Tekscan® 307 West First Street South Boston, MA 02127-1309 800-248-3669 www.tekscan.com System Cost ~$25000 Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Nip Pressure Measurement 3
Nip Pressure Measurement 4 Stowe Woodward’s Smart Roll™ Technology is a batterypowered, fiber optic measurement sensor set embedded in the roller covering to measure load and temperature, with wireless communication to your PC.
AutoNis XP - The complete system with scanner, and software is $4000 www.sensorprod.com/nip.php Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
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Laminate Defects Common defects associated with laminate products and processes include:
The Smart Roll system adds $30,000 to the price of a 200”wide rubber or polyurethane covered roller. Narrower application should be significantly less.
Stowe Woodward 1 Technology Park Drive Westborough, MA 01581 508-616-9458 www.stowewoodard.com
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Curl Causes:
Curl
Differential dimensional change of one layer vs. another. Mismatched elastic strains at laminating. Dimensional change from aging or external factors (long term cure in coatings, heat stability and films, hygroscopic expansion of papers).
Bubbles
Cures: Delamination
Understand and control dimensional stability of all materials. Balance strains using tension ratio based on spring constants (thickness x width x modulus) Control humidity and other external factors.
Tunneling
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Laminating Film Options
Bubbles
How Material Selection Affects Curl Defects:
Causes:
Example: Film for book cover lamination Polyester (PET)
Polypropylene (OPP)
Nylon
PET features excellent scruff and scratch resistance, durability and good folding characteristics.
OPP has a good combination of cost and overall characteristics. It is the clearest and brightest of these films. Because of its softness, OPP folds extremely well.
Nylon is a durable product with excellent scuff- and scratchresistance.
PET has high tensile, tear and impact strength and retains these outstanding properties and remains tough and flexible once applied. It is a popular choice for book covers and dust jackets, presentation folders and video cartons.
Applications include writeon/wipe-off calendars, posters, presentation folders and labels.
Nylon laminating film is popular particularly for book covers and dust jackets, due to its ability to absorb moisture from the air at about the same rate as the paper substrate. RESULT: Significantly less curl!
Nylon is the film of choice for most book manufacturers.
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Tunneling
Gasses emitted from internal layer’s residual solvent or cure byproduct.
Cures: Improve nipping system to eliminate squeegee error source. Change to porous substrate Improve drying or curing.
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Delamination Causes:
Causes: Gross failure to squeegee air continuously in a lane from nip deflection, nip diameter variations, nip hardness variations, or caliper variations Accumulation of bubbles ahead of a nip, roller, or winding roll. Laminates contacting ahead of nip point due to bagginess or sagging.
Poor laminate bond. Shear on bond interface from roller curvature. Shear stresses increase with small diameter. Worsens with thicker layer on roller contact side. May be triggered by bubble accumulation upstream of roller.
Cures:
Cures: Improve nipping to eliminate squeegee error. Install a laterally ridged roller to pulse-feed bubbled web, avoiding accumulation. Increase entry angles and increase tension to pull baggy web taut, preventing early contact. Gasketing/Converting Expo ’08 Seminar: Keys to Laminating Success, TJWalker – April 2008
Failure to squeegee air from nip deflection, nip diameter variations, nip hardness variations, not enough nip compliance, web bagginess, or caliper variations
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Improve laminate bond before wrapping rollers. Increase roller radius to reduce laminate shear. Eliminate bubbles Install a laterally ridged roller to pulse-feed bubbled web, avoiding accumulation.
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