mechanics of creping in tissue making€¦ · mechanics of creping in tissue making kui pan a....
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Mechanics of Creping in Tissue Making
Kui Pan A. Srikantha Phani & Sheldon Green
Department of Mechanical EngineeringUniversity of British Columbia, Vancouver, BC
Outline
Background
Research Objectives
Methodology and Results
Conclusion
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Background
Research Objectives
Methodology and Results
Conclusion
3
H.F. Jang, FPI, 2013SEM cross-sectional image of tissue
Schematic of tissue structure
𝜆2𝐴
Wavelength: 𝜆 ~ 0.3mmAmplitude: A ~ 0.1mm
Creping Influences Tissue Properties
Creping: a de-densification process
MD: machine direction; CD: cross direction.
Before
After
Dry-Creping Process
DoctorBlade
CleaningBlade
Adhesive Spray Nozzle
Felt
PressureRoll
Wet Web
DryerHoods
DryerHoods
Reel
Yankee DryerDiameter ~3m
Velocity~1500 m/minCrepedTissue
20℃, SC: ~20%
SC: ~40%
100℃, SC: ~94%
𝑉𝑖𝑛
𝑉𝑜𝑢𝑡
Crepe Ratio=𝑉𝑖𝑛−𝑉𝑜𝑢𝑡
𝑉𝑖𝑛
SC: solid content
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5
Creping Regimes
W. McConnel, The science of creping. 2004.
√
Governing Parameters Typical Control Parameters: Yankee surface speed
𝑉𝑖𝑛(1000~2000𝑚/𝑚𝑖𝑛)
Creping angle 𝛿 (80°~100°)
Crepe ratio 𝑉𝑖𝑛−𝑉𝑜𝑢𝑡
𝑉𝑖𝑛(10%~30%)
Adhesion 𝐺𝑐 (50~400 𝑁/𝑚)
Blade Friction (0.25~0.35)
Current situation: trial and error.
Fundamental study is necessary.Guide the choice of adhesive chemicals,process parameters, blade type and so forth.
𝛿: Creping angle
𝑉𝑖𝑛
𝑉𝑜𝑢𝑡
𝛿
Crepe Ratio=𝑉𝑖𝑛−𝑉𝑜𝑢𝑡
𝑉𝑖𝑛
quality, runnability and productivity
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Creping Mechanism
Micro-fold to Macro-fold Transition
High Speed Imaging Study
Limited surface speed: 140 m/minNo further validation about the mechanism.
H. Hollmark, STFI 1972
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Creping ratio: 32%
Outline
Background
Research Objectives
Methodology and Results
Conclusion
8
Research Objectives
Experiments:
Observe the creping process under high speed to reveal relevant
phenomenon and understand the mechanism.
Modeling:
Develop mechanistic creping model to study the effects of process
parameters (adhesion, creping angle…) and dynamic effects (creping ratio,
surface velocity…) on tissue structure.
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Outline
10
Background
Research Objectives
Methodology and Results
Conclusion
Methodology: High speed imaging
11Goal: reveal creping mechanism at high speed
Creping testing rig based on Lathe
Edge-on view of set-up
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Laser informationPower: 500mW; Fan angle: 5°;Length: 20mm; Thickness: 0.1mm.
Disk informationRadius: 89mm; 𝜔𝑚𝑎𝑥: 1500 rpm;Maximum surface speed: 838 m/min.
Doctor bladeCreping angle 𝛿: adjustable;Blade thickness: 1.2 mm.
𝛿
Surface speed: 𝑉𝑖𝑛=217 m/min
Creping angle 𝛿 =45°
No creping ratio: 𝑉𝑜𝑢𝑡 ≈ 0
Micro-fold to macro-fold transition is observed.
Creping Video
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1 mm
45°
1 mm
Increase Creping Angle
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Surface speed: 𝑉𝑖𝑛=195 m/min
Creping angle 𝛿 = 90°
No creping ratio: 𝑉𝑜𝑢𝑡 ≈ 0
Transition mechanism still exists, when we increase creping angle.
90°
1 mm
Creping Ratio by Hand Pulling
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Surface speed: 𝑉𝑖𝑛=217 m/min
Creping angle 𝛿 = 90°
Creping ratio: 𝑉𝑖𝑛−𝑉𝑜𝑢𝑡
𝑉𝑖𝑛≈ 25%
Micro-fold to macro-fold transition disappeared Indicating creping ratio is important.
1 mm
𝑉𝑖𝑛𝑉𝑜𝑢𝑡
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Summary of Current Experiment
Lathe creping experiment
Relative high speed 800 m/min; System is stable;Creping process is clearly recorded;Verified micro-fold to macro-fold transition mechanism.
Limitations: Creping ratio not well-controlled; Non-uniform adhesion.
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Yankee
web adhesive
CZM CZM CZM
web
adhesive
Methodology: Discrete Particle Model
Particle’s mass: 𝑀 = 𝜌𝑎0ℎ𝑤.
ℎ is thickness, w is width of paper, 𝑎0 is initial spacing, 휂𝑎 is damping coefficient,𝑘𝑎 is axial stiffness.
axial elastic force : 𝒇𝑎 = 𝑘𝑎 𝒓𝑖−1 − 𝒓𝑖 − 𝑎0 𝒆𝑖,𝑖−1 + 𝑘𝑎 𝒓𝑖+1 − 𝒓𝑖 − 𝑎0 𝒆𝑖,𝑖+1damping force: 𝒇𝑑 = −휂𝑎 𝒓𝑖 − 𝒓𝑖−1 ∙ 𝒆𝑖,𝑖−1 𝒆𝑖,𝑖−1 − 휂𝑎 𝒓𝑖 − 𝒓𝑖+1 ∙ 𝒆𝑖,𝑖+1 𝒆𝑖,𝑖+1
bending force and viscous bending force: 𝒇𝑏 , 𝒇𝑣
Spring damper coefficients are related to paper layer properties.
𝛿
𝑖
𝑖 𝑖+1
𝑖+1
𝒇𝑐
𝒇
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traction vs. separation
Nonlinearsprings
Yankee
web
D. Xie, A.M. Wass, Engng. Fract. Mech., 2006
Normal tractionShear traction
Cohesive Zone Model
Cohesive force applied on particle: 𝒇𝑐 = −𝜎𝑎0𝑤𝒆 − 𝜏𝑎0𝑤𝒆
𝒆 and 𝒆 : normal and tangential unit vectors
𝜎𝑐: normal strength; 𝜏𝑐: shear strength;𝐺𝐼𝐶: mode I fracture toughness; 𝐺𝐼𝐼𝐶: mode II fracture toughness. (adhesion)
CZM parameters are related to adhesive layer properties.
Newton’s equations ∶ 𝒇𝑡𝑜𝑡 = 𝒇𝑎 + 𝒇𝑑 + 𝒇𝑏 + 𝒇𝑣 + 𝒇𝑐 = 𝑀𝒂
A
B
C
𝑑𝑡: threshold distance. 𝑑𝑡 = ℎ/100.
When 𝑑𝑠>= 𝑑𝑡, no contact force 𝐹𝑐1 = 0.
When 𝑑𝑠 < 𝑑𝑡,
New function: 𝐹𝑐1 = α[𝑒𝛽
𝑑𝑠 −1]. 𝛼, 𝛽 are constants
𝑑𝑡
𝑑𝑠𝐹𝑐1
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
1000
2000
3000
4000
5000
6000
7000
8000
9000
ds/h
Fc
Self-Contact Model
Motivation:
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8 8.5 9 9.5 10 10.5 11 11.5 120
1
2
3
4
5
6
7
8
x/h
Deflection
/h
8.5 9 9.5 10 10.5 11 11.50
1
2
3
4
5
6
7
8
x/h
Deflection
/h
No self-contact Include self-contact
𝐿
𝐿′
∆𝐿 = 𝐿 − 𝐿′ = 0.87𝐿
Self-Contact Model
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휀∗ = 𝜋2ℎ2 12𝑎2
maximum deflection:
휁 = ℎ4
3
휀0휀∗− 1
The experimental data comes from: “Atomic force microscopy of in situ deformed nickelThin films”, C. Coupeau et. al., 1999, Thin Solid Films.
휁
Validation of Model
Buckle-delamination
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Creping Simulation
Schematic of creping model
𝑉 is Yankee surface speed, 𝛿 is creping angle.
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Radius of Yankee (~1.5𝑚) ≫ Paper thickness (~0.1𝑚𝑚)Surface can be considered as flat
Single Fold Simulation
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𝑉 = 1200𝑚/𝑚𝑖𝑛, 𝛿 = 80°.
Single Fold Simulation
Three stages: delamination propagation (Mode I) buckle initiation; buckling-driven delamination. (Mixed-mode)
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Mixed-mode fracture toughness
0 5 10 15 20 25
2.5
3
3.5
4
4.5
Mixed-mode GIIC
/GIC
Wavele
ngth
/h
0 5 10 15 20 252800
2850
2900
2950
3000
3050
Mixed-mode GIIC
/GIC
Cre
pin
g F
orc
e (
N/m
)
(a) (b)
𝐺𝐼𝐶 is varied to change the mixed-mode.
Creping wavelength is dependent on both
𝐺𝐼𝐶 and 𝐺𝐼𝐼𝐶;
Creping force is determined by 𝐺𝐼𝐼𝐶 .
𝜎
𝜎𝑐
𝛿𝑐 𝛿𝑚
𝛿
𝐺𝐼
𝐺𝐼𝑐
𝐺𝐼𝐼
𝐺𝐼𝐼𝑐
𝜏
𝜏𝑐
0 0 𝑐 𝑚
(a) (b)
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Periodic Folding Simulation
FFT analysis:𝜆 = 0.35𝑚𝑚𝐴 = 0.052𝑚𝑚
26Schematic of tissue structure
𝜆2𝐴
Wavelength: 𝜆 ~ 0.3mmAmplitude: A ~ 0.1mm
Creping angle: 85°;V_in=20m/s;
V_out=0.7*V_in
Creping angle: 85°; V_in=20m/s; V_out=0
A few micro-folds evolve into a macro-fold.
Self-Contact Simulation
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Parametric Study
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Larger modulus results in larger creping wavelength; Larger adhesion results in smaller creping wavelength.
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Limitation of Current Model
Currently one-dimensional model.
Plastic deformation of fiber is not included.
Outline
Background
Research Objectives
Methodology and Results
Conclusion
31
Conclusion
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Lathe creping experimentRelative high speed 800 m/min; System is stable;Clear view of creping process;Micro-fold to macro-fold transition mechanism is verified and it is found to be affected by creping ratio.
Conclusion
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Discrete particle model has been developed.One-dimensional dynamic, creping-ratio included.Process parameters included.
Simulation of creping process.Single fold formation shows three typical stages.The periodic creping process is successfully simulatedand simulation results are close to experimental values.
Parametric studies.Effects of modulus, adhesion, and creping angle. Need to be compared with experimental data.
Future Work
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Extend current model to microscopic level to account forfiber properties and explosive bulk.
Pilot Tissue Machine, FPInnovations, Montreal.
Maximum Yankee surface speed: 1500 m/min;Able to process parameters and furnish. 34
Future WorkCompare simulations with experimental data from
commercial machine.
Thank you!
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