1

What Type of Cover Should I Use to Optimize my

Process?

By Stephen HuffDirector of Engineering & Technology

Imperial Rubber Products, Inc.

AIMCAL Roll to Roll Conference 2017October 17, 2017Tampa, Florida

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• Releases From the Web

• Holds Up to Process Heat

• Holds Up to Process Pressures

• Resistance to Process Chemistries

• Has Proper Finish

• Has Proper Geometry

Process Determines What is NeededThe Needs of the WEB Control Everything!

(Rough or Smooth)

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Roller Cover Operational Questionnaire• What Type of Operation Does This Roller Perform?

• What Temperature Does the Roll Face See During Operation?

• Is the Roll Body Chilled or Heated?

• What Chemicals are Present On or Near the Roll Cover?

• Is the Roller in a Nip? If So What Pressure Does the CoverExperience in PLI (Pounds per Linear Inch)?

• What Durometer is Desired?

• What Type of Surface Finish or Ra is Desired?

• What Geometries (TIR, Taper, Steps) Are Required for Your Cover?

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What Rubber Compound Should I Use?

Why Isn’t There One Type of Rubber That Works For Everything?

• There Are Over 20 Major Rubber Families

• Two Types of Rubber Structures- Crystalline- Amorphous

• Molecular Structure of Compound Determines Physical Properties

• There Are Elastomeric Alloys (Blends) EPDM/SI

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What Properties Should be Optimized?The Properties of a Rubber Cover Are Controlled by the Formula or Compound. Compounding is the Method that a Particular Formula is Mixed.

• Chemists Choose Physical Properties to Optimize When Formulating

- A 50 Duro Compound From One Supplier ≠ A 50 DuroCompound From a Different Supplier

• Choose Wisely Which Property to Optimize

• Compounding Will Vary the Performance Between Formulas Made with the Same Base Polymers

- Covers Don’t Fail Due to Tensile Strength

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Imagine a Small Square Table with a Round Tablecloth that is Just a Little Too Small.

• Each Corner Represents a Physical Property That is Desired for the Application.

One Type of Cover Will Never Meet All of the Desired Requirements

• If You Cover 3 Corners of the Table, The Fourth Corner is Exposed.

• As the “Tablecloth” is Moved Around to Optimize Coverage, Other Edges and Corners (Physical Properties) Are Exposed or Given Up.

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Hot Melt Example• Hot Melt Adhesive Working Temperature is 360° F

• 360° F Eliminates Most Rubber Compounds Except the Silicones and Fluoroelastomers (Viton type)

• Silicone Works Great With Heat But Wears Out Easily, Fluoroelastomers Are Very Expensive and Easily Damaged

• Does the Roll Cover Really See 360° F ? NO !

• Process Web and Chilled Core Carries Off Heat

• Surface Cool Enough to Utilize Many Different Rubber Compounds

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What About Hypalon?

Hypalon Softens With Heat and Pressure

Hypalon is Chlorosulfonated Polyethylene

All Compounds Soften In Use and with Increased Temperature!

Hypalon Looses 40% - 60% of Its Properties at 300° F.

Works Great Under the Right Conditions

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What About Nitrile?

Nitrile Comes in 3 Different Forms• Each Form Has Differing Properties

- Hydrogenated Nitrile (HNBR)

- Carboxilated Nitrile (XNBR)

• Molecular Structure Determines Physical Properties

- Nitrile (NBR)

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What About Urethane?

Castable & Millable

• Great Abrasion Resistance & Elasticity

- Can Revert @ Temperature (Sticky)

- Expensive

- Relatively Low Operating Temperature ( < 150° F)

- Difficult to Machine

- Not Optimum for Water Resistance

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What Durometer Should I Use?

What Does Durometer Measure?

• Durometer is an Indicator of a Compound’s Modulus

• Durometer is Measured While the Rubber Is In a Non-Stressed Condition (Static)

• Rubber Covers Are Used In a Stressed Condition (Dynamic)

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What Is Modulus?

Modulus, Or Stress, Is Used To Express The Amount of Pull Needed to Stretch A Test Piece to a Given Elongation.

• Modulus Expresses the Stiffness of the Compound

• Modulus is a Dynamic Measurement

• Modulus Indicates How Much a Rubber Cover Will Move in a Nip

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Modulus Curves

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8

ε

σ, M

Pa

Strain or Extension

Stre

ss Crystalline

Amorphous

Chart3

00

11

22

33

44

55

Crystalline

Amorphous

e

s, MPa

0

0

1

3.5

1.25

6

1.5

14

2

21

2.25

25

Sheet1

ExtensionCrystallineAmorphous

000

113.5

21.256

31.514

4221

52.2525

6

7

8

s

s, MPa

Sheet1

Crystalline

Amorphous

e

s, MPa

Sheet2

Sheet3

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Which Is Stiffer: A 95 Durometer HNBR Or a 95 Durometer Urethane?

HNBR Is Stiffer Because of Its Higher Modulus Number!

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90 100

ε (% Elongation)

σ, M

Pa

HNBR

Urethane

Chart1

00

1010

2020

3030

4040

5050

6060

7070

8080

Urethane

HNBR

e (% Elongation)

s, MPa

0

0

0.75

1

1

1.5

1.5

2

2

2.5

3

5

4

6

5

8

6

10

Sheet1

ExtensionUrethaneHNBR

000

100.751

2011.5

301.52

4022.5

5035

6046

7058

80610

90

100

s

s, MPa

Sheet1

Urethane

HNBR

e (% Elongation)

s, MPa

Sheet2

Sheet3

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Can Modulus Be Modified In a Compound?

Yes!• EPDM Cover Needed Due to UV Cure

Chemistry

• Existing EPDM Compound is “Too Soft”

• Different Binding Agents & Cure System Change Modulus and Make it “Harder”

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Why Is My Cover Cracking?

• 75 Durometer Silicone Cover on Heated Embossing Line

• Cover Starts to Crack Along Web Edge

Web

Embossing Roller

Silicone Roller

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Web

Embossing Roller

Silicone Roller

Solution to Cracking

• Step Cut Cover Just Wider Than Web

• Stress Along Web Edge Drastically Reduced

• Cover Stopped Cracking

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Conclusion• Process Dictates The Type of Cover Needed

• Durometer Widely Used to Specify Covers But Unfortunately Doesn’t Tell the Whole Story

• End User Must Understand Process Needs in Order to Properly Specify a Roller Cover

• Modulus Describes a Compound’s Behavior Dynamically

• Modulus Can Be Altered Through Mixing

Questions?

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