Recent Advances in Rubber Roll Covers for Improved Paper Machine Performance and Reduced Energy Requirements
Dilip De, Ph.D. – Research Manager, Rubber Ch l H t Ph D R h M P l thCharles Hunter, Ph.D. – Research Manager, PolyurethaneBill Butterfield – Vice President of Research & Product Engineering
Stowe Woodward, Xerium Technologies Inc.Stowe Woodward, Xerium Technologies Inc.P.O Box 575 Middletown, VA 22645, USA
PaperCon 2011 Page 2660
Topics
• Rubber Chemistry/Physical Properties• Applications• Applications
- Press Rolls- Size Press Rolls- Yankee Pressure Rolls- Coater Backing Rolls
• ConclusionsConclusions
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Structure of a Cured Rubber
• Long polymer chains• Mainly synthetic• Have sites for crosslinking • Different chemicals are incorporated for optimum physical p p p y
and mechanical properties
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Types of Rubbers
• NBR - Resistant to aliphatic and aromatic solvents. Best combination of physical properties and solvent resistance.physical properties and solvent resistance.
• HNBR - Resistant to aliphatic and aromatic solvents. Ozone resistance. Higher temperature rating than NBR.p g
• CSM – High temperature applications. Excellent resistance to strong chemicals and natural aging. Resistance to oils, solvents, and ozone. Excellent release behavior.
• EPDM - Good aging properties. Good resistance to steam and d l H ioxygenated solvents. Heat resistance.
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Rubber Formula Ingredients
• Rubber matrixFill C b Bl k Sili Cl fill fib t• Filler - Carbon Black, Silica, Clay, nano-fillers, fibers etc. -Reinforcement
• Antioxidant - Prevents oxidation of the rubber so it does not ( )degrade (crack or harden).
• Plasticizer - Different kinds of oils – Helps processing and softens rubber.
• Crosslinking agent - Peroxide or Sulfur – controls hardness and improves the properties of the rubber.
• Other Misc AdditivesOther Misc. Additives
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Compounding and Mixing
2-roll mills to blend rubber componentsp
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Physical Property Testing
• P&J – Pusey and Jones H dHardness
• Abrasion resistance• Tensile and elongation at• Tensile and elongation at
break• Tear strength• Compression set• Hysteresis• Dynamic modulus• Chemical resistance
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Press Rolls
• Typically 15 to 25 P&J high performance rubber covers- Engineered Dri-Press® venting
• Required cover properties• Required cover properties- Superior wear resistance to maintain crown profile and hole geometry- Low hysteresis to run cool
S i t h t ith t d i t t hi h l d ith t- Superior toughness to withstand impacts at high loads without cracking
- Superior bonding system- Excellent chemical resistance- Excellent chemical resistance
Press Section
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Press RollsHysteresisHysteresis
• Hysteresis is the amount of heat generated by a material as it is y g ycyclically loaded and unloaded
• Calculated by area of the hysteresis loop (MTS)• Lower hysteresis is desirable• Lower hysteresis is desirable• Used in material development• Results in materials that run at lower
temperatures
Compression
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Press RollsTear StrengthTear Strength
60
80
100tr
engt
h
20
40
60
elat
ive
Tear
St
0Standard Press
Roll CoverNew Press Roll
Cover
Re
High tear strength of new cover technology withstands high impactsand avoids hole to hole cracking in drilled rolls
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Case History- Press RollNA Pulp MachineNA Pulp Machine
Press Line Load, Speed Current conditions, water cooled
Proposed, non- water cooled Water savings
1st press 96 kN/ m,183 m/min
0 PJ Steel top/ 20 PJ Rubber cover 70 PJ top/ 20 PJ 12 L/min
2nd press 149 kN/ m,183 m/min 20 PJ/20 PJ Rubber 30 PJ/30 PJ 14 L/min
3rd press 280 kN/ m,183 m/min 18 PJ/18 PJ Rubber 21 PJ/ 21 PJ 16 L/min
Press Roll Conditions and Water Savings
Nip Width Nip Intensity
3456789
cm
2000
3000
4000
5000
6000
kPa
0123
1st Press 2nd Press 3rd PressExisting 3.6 3.73 7.13Proposed 6 68 7 03 8 78
0
1000
2000
1st Press 2nd Press 3rd PressExisting 3569 5325 5257Proposed 1942 2831 4272
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Proposed 6.68 7.03 8.78 Proposed 1942 2831 4272
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Case History Results- Superwear Xtreme ®
• Removal of water cooling: Savings in water and maintenance of $55 000/ year$55,000/ year
• Increase in nip intensity and dwell time provided 1% dryer sheet entering the dryer
d i f 10%- steam reduction of 10% - $200,000/ year savings
• Much longer runtimeg- 6 months vs 3 years
• No hole to hole cracking• No chemical attack on the roll s rface• No chemical attack on the roll surface
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Case History: A Soft Press Case History: A Soft Press
Problem / Opportunity- Decrease cover hardness to increase press loading- Improve sheet solids- Improve sheet bulk
Resolution – Install 40 P&J new technology cover with gy
Dynamic nip technology in 1st press bottom– Increase press loading– Use Dynamic nip technology® Roll to
flatten nip at increased load.
Machine Type: TrinipGrade: Bleached BoardSpeed: 365 mpm (1200 fpm)Load: 45 Kn/ m (250 PLI)
pValue
– Increased sheet bulk– Reduced fiber usage by 3-4%
Impro ed CD moist re and caliper profile Load: 45 Kn/ m (250 PLI)– Improved CD moisture and caliper profile– $700,000 sign off
PaperCon 2011 Page 2672
Size Press Rolls
• Soft size press rolls typically 20 to 45 P&J rubber covers• Hard size press rolls typically 0-1 P&J rubber covers • Required cover properties
High ear resistance to maintain s rface profile and longer r n- High wear resistance to maintain surface profile and longer run time
- Chemical resistanceH d t bilit- Hardness stability
- Minimal thermal crown growth- Mark Resistant
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Size Press Rolls
• Roll Cover Design- Sheet follows hard roll with smooth or 0.8 – 1.6 µm (20-40 µ-in) Ra
finishfinish• Smoother finish maintains more intimate contact• Soft roll deformation results in surface velocity change in the nip• Hard roll deforms less thus maintaining more constant contact• Hard roll deforms less thus maintaining more constant contact
- Soft roll ground to or 1.2 – 2.0 µm (30-50 µ-in) Ra. - Adequate wetting balance between sheet and size
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Film Press Case History – Misting Study
Misting test: LWC, 1800 m/min, 8 g/m²
Paper top side to the right Paper top side to the left
Old Technology cover(left) / New Technology cover(right); 50/50 P&J
Paper top side to the right Paper top side to the left
Misting stays onMisting stays on Old Technology cover side
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Film Press Case History – Misting Study Supersize XL®
Misting test: LWC, 1800 m/min, 8 g/m²New (left) / New (right); 50/50 P&J
Supersize XL®
Paper top side to the right Paper top side to the left
New (left) / New (right); 50/50 P&J
Paper top side to the right Paper top side to the left
No misting with two gNew Technology covers
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Tissue Pressure Rolls
• Typically- 30 to 45 P&J high performance rubber covers- Engineered venting
• Required cover properties- Superior wear resistance to maintain crown profile and hole geometry- Excellent chemical resistance- Superior bonding system- Hardness stability
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New Tissue Pressure Roll Covers
- Suction pressure roll and blind drilled pressure roll
- Excellent abrasion resistance - Excellent hardness stability- Superior bonding systemSuperior bonding system- Cooler running covers able to run
non-water-cooled
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Structure of Cured Rubber and Causes of HardeningCauses of Hardening
• Oxygen/ Ozone• T t• Temperature• Loss of Processing aids• Chemical Attack
Double bonds,Site for further crosslinks
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Hardness Stability- Hyperpress X ®
H d St blit
30
35
Hardness Stablity
20
25
30
PJ H
ardn
esss
New cover
Standard
15
20
0 7 14 21 28 56Elapsed Time ( days )
5.0 cm thick samples, 100 °C Oven
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Case History – Xtreme TS ®
NA Tissue MachineNA Tissue Machine
Material Cover Max Max RequiredMaterial Cover Thickness
(cm)
Max Stress(kPa)
Max Temp.,
bond line(°C)
Required cooling water
Standard 2.54 2032 89 24L/ minNew 2.54 2108 76 none
Water Cooled
Non-Water Cooled
Load 79 kN/m (450 pli)Machine Speed 1860 m/min (6100 fpm)Machine Speed 1860 m/min (6100 fpm)Cover Diameter 76.2 cm (30”)Cover Face Length 3.25 m (128”)Surface Temperature 49 °C (120 °F)Felts 1
Significant drop in operating temperature
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Coater Backing Rolls
• Typically- 45 to 95 P&J rubber covers
• Required cover properties- High wear resistance - Excellent resiliencyExcellent resiliency - Chemical resistance- Mark resistance
H d t bilit- Hardness stability- Crack and tear resistance- Surface release properties
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Coater Backing RollsAbrasion ResistanceAbrasion Resistance
100
120ta
cne
60
80
100
sion
Res
ist
20
40
elat
ive
Abr
as
0Rubber #1 Rubber #2 New Cover
Re
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Case Histories- Hypercoat ®
Coater Backing RollCoater Backing Roll
Improved Run Times
• Board Mill - Increased run time 90 to 180+ daysy- Edge cracking eliminated
• LWC MillIncreased r n time 90 to 200 da s- Increased run time 90 to 200 days.
• Coated Paper- Mill increased run time from 45 to 75+ days
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Base Technology for High Performance Base Technology for High Performance Applications
• base technology –base technology high performance, non-water-cooled applications
Excellent hardness stability– Excellent hardness stability
– Superior bonding system
– Cooler running coversCooler running covers
– All press roll applications
– Advantages• Water and energy savings• Lower maintenance cost• Avoid water diffusion related failures
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An Example: Coated Board Machine
Mill Problem• Water diffusion related cover
failuresfailures• 70 gpm water cooling rate for 2
rolls• Temperature controlled to 130 F• Water cooling required constant
maintenanceSolution
• Apply new non-water cooled base technology
Results• 1.5 roll cover savings
annualized• Machine downtime minimized• $200K li d i• $200K annualized savings
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Conclusions:
• The improved performance of several rubber covers in Press, Size Press Yankee Pressure and Coater Backing rolls haveSize Press, Yankee Pressure, and Coater Backing rolls have been illustrated
• Improved covers are running longer in the machine C• Covers with low hysteresis along with high temperature base system allow roll to run under non-water cooled conditions. It saves energy, maintenance, and the cost of water.
• Case histories were discussed regarding energy savings
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