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Polymer Extrusion

of: Chris Rauwendaal

Carl Hanser Fachbuchverlag, 2014

ISBN: 9781569905395 , 950 Pages

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Polymer Extrusion


 

Preface to the Fifth Edition

6

1 Introduction

18

1.1 Basic Process

18

1.2 Scope of the Book

19

1.3 General Literature Survey

20

1.4 History of Polymer Extrusion

23

Part I – Extrusion Machinery

28

2 Different Types of Extruders

30

2.1 The Single Screw Extruder

30

2.1.1 Basic Operation

32

2.1.2 Vented Extruders

33

2.1.3 Rubber Extruders

34

2.1.4 High-Speed Extrusion

39

2.1.4.1 Melt Temperature

39

2.1.4.2 Extruders without Gear Reducer

40

2.1.4.3 Energy Consumption

40

2.1.4.4 Change-over Resin Consumption

40

2.1.4.5 Change-over Time and Residence Time

41

2.2 The Multiscrew Extruder

41

2.2.1 The Twin Screw Extruder

41

2.2.2 The Multiscrew Extruder With More Than Two Screws

42

2.2.3 The Gear Pump Extruder

44

2.3 Disk Extruders

45

2.3.1 Viscous Drag Disk Extruders

45

2.3.1.1 Stepped Disk Extruder

45

2.3.1.2 Drum Extruder

47

2.3.1.3 Spiral Disk Extruder

48

2.3.1.4 Diskpack Extruder

48

2.3.2 The Elastic Melt Extruder

52

2.3.3 Overview of Disk Extruders

53

2.4 Ram Extruders

53

2.4.1 Single Ram Extruders

54

2.4.1.1 Solid State Extrusion

55

2.4.2 Multi Ram Extruder

58

2.4.3 Appendix 2.1

59

2.4.3.1 Pumping Efficiency in Diskpack Extruder

59

3 Extruder Hardware

66

3.1 Extruder Drive

66

3.1.1 AC Motor Drive System

66

3.1.1.1 Mechanical Adjustable Speed Drive

67

3.1.1.2 Electric Friction Clutch Drive

67

3.1.1.3 Adjustable Frequency Drive

68

3.1.2 DC Motor Drive System

70

3.1.2.1 Brushless DC Drives

72

3.1.3 Hydraulic Drive System

72

3.1.4 Comparison of Various Drive Systems

75

3.1.5 Reducer

76

3.1.6 Constant Torque Characteristics

77

3.2 Thrust Bearing Assembly

78

3.3 Barrel and Feed Throat

81

3.4 Feed Hopper

85

3.5 Extruder Screw

87

3.6 Die Assembly

89

3.6.1 Screens and Screen Changers

89

3.7 Heating and Cooling Systems

92

3.7.1 Electric Heating

92

3.7.1.1 Resistance Heating

92

3.7.1.2 Induction Heating

93

3.7.2 Fluid Heating

94

3.7.3 Extruder Cooling

94

3.7.4 Screw Heating and Cooling

97

4 Instrumentation and Control

102

4.1 Instrumentation Requirements

102

4.1.1 Most Important Parameters

103

4.2 Pressure Measurement

104

4.2.1 The Importance of Melt Pressure

104

4.2.2 Different Types of Pressure Transducers

105

4.2.3 Mechanical Considerations

109

4.2.4 Specifications

110

4.2.5 Comparisons of Different Transducers

113

4.3 Temperature Measurement

113

4.3.1 Methods of Temperature Measurement

114

4.3.2 Barrel Temperature Measurement

117

4.3.3 Stock Temperature Measurement

119

4.3.3.1 Ultrasound Transmission Time

122

4.3.3.2 Infrared Melt Temperature Measurement

123

4.4 Other Measurements

124

4.4.1 Power Measurement

124

4.4.2 Rotational Speed

126

4.4.3 Extrudate Thickness

127

4.4.4 Extrudate Surface Conditions

131

4.5 Temperature Control

133

4.5.1 On-Off Control

134

4.5.2 Proportional Control

136

4.5.2.1 Proportional-Only Control

136

4.5.2.2 Proportional and Integral Control

140

4.5.2.3 Proportional and Integral and Derivative Control

141

4.5.2.4 Dual Sensor Temperature Control

142

4.5.3 Controllers

143

4.5.3.1 Temperature Controllers

143

4.5.3.2 Power Controllers

143

4.5.3.3 Dual Output Controllers

145

4.5.4 Time-Temperature Characteristics

145

4.5.4.1 Thermal Characteristics of the System

145

4.5.4.2 Modeling of Response in Linear Systems

147

4.5.4.3 Temperature Characteristics with On-Off Control

150

4.5.5 Tuning of the Controller Parameters

152

4.5.5.1 Performance Criteria

152

4.5.5.2 Effect of PID Parameters

153

4.5.5.3 Tuning Procedure When Process Model Is Unknown

154

4.5.5.4 Tuning Procedure When Process Model Is Known

155

4.5.5.5 Pre-Tuned Temperature Controllers

156

4.5.5.6 Self-Tuning Temperature Controllers

157

4.6 Total Process Control

157

4.6.1 True Total Extrusion Process Control

158

Part II – Process Analysis

164

5 Fundamental Principles

166

5.1 Balance Equations

166

5.1.1 The Mass Balance Equation

166

5.1.2 The Momentum Balance Equation

167

5.1.3 The Energy Balance Equation

168

5.2 Basic Thermodynamics

170

5.2.1 Rubber Elasticity

174

5.2.2 Strain-Induced Crystallization

176

5.3 Heat Transfer

177

5.3.1 Conductive Heat Transfer

177

5.3.2 Convective Heat Transfer

178

5.3.3 Dimensionless Numbers

178

5.3.3.1 Dimensional Analysis

178

5.3.3.2 Important Dimensionless Numbers

180

5.3.4 Viscous Heat Generation

185

5.3.5 Radiative Heat Transport

186

5.3.5.1 Dielectric Heating

188

5.3.5.2 Microwave Heating

190

5.4 Basics of Devolatilization

192

5.4.1 Devolatilization of Particulate Polymer

197

5.4.2 Devolatilization of Polymer Melts

198

Appendix 5.1

202

Example: Pipe Flow of Newtonian Fluid

202

6 Important Polymer Properties

208

6.1 Properties of Bulk Materials

208

6.1.1 Bulk Density

208

6.1.2 Coefficient of Friction

211

6.1.3 Particle Size and Shape

217

6.1.4 Other Properties

218

6.2 Melt Flow Properties

219

6.2.1 Basic Definitions

219

6.2.2 Power Law Fluid

225

6.2.3 Other Fluid Models

230

6.2.4 Effect of Temperature and Pressure

231

6.2.5 Viscoelastic Behavior

235

6.2.6 Measurement of Flow Properties

237

6.2.6.1 Capillary Rheometer

237

6.2.6.2 Melt Index Tester

240

6.2.6.3 Cone and Plate Rheometer

244

6.2.6.4 Slit Die Rheometer

245

6.2.6.5 Dynamic Analysis

247

6.3 Thermal Properties

250

6.3.1 Thermal Conductivity

251

6.3.2 Specific Volume and Morphology

253

6.3.3 Specific Heat and Heat of Fusion

256

6.3.4 Specific Enthalpy

258

6.3.5 Thermal Diffusivity

259

6.3.6 Melting Point

262

6.3.7 Induction Time

262

6.3.8 Thermal Characterization

264

6.3.8.1 DTA and DSC

264

6.3.8.2 TGA

264

6.3.8.3 TMA

265

6.3.8.4 Other Thermal Characterization Techniques

265

6.4 Polymer Property Summary

265

7 Functional Process Analysis

272

7.1 Basic Screw Geometry

272

7.2 Solids Conveying

275

7.2.1 Gravity Induced Solids Conveying

276

7.2.1.1 Pressure Distribution

279

7.2.1.2 Flow Rate

282

7.2.1.3 Design Criteria

283

7.2.2 Drag Induced Solids Conveying

285

7.2.2.1 Frictional Heat Generation

299

7.2.2.2 Grooved Barrel Sections

301

7.2.2.3 Adjustable Grooved Barrel Extruders

313

7.2.2.4 Starve Feeding Versus Flood Feeding

319

7.3 Plasticating

322

7.3.1 Theoretical Model of Contiguous Solids Melting

323

7.3.1.1 Non-Newtonian, Non-Isothermal Case

333

7.3.2 Other Melting Models

343

7.3.3 Power Consumption in the Melting Zone

347

7.3.4 Computer Simulation

349

7.3.5 Dispersed Solids Melting

350

7.4 Melt Conveying

357

7.4.1 Newtonian Fluids

360

7.4.1.1 Effect of Flight Flanks

365

7.4.1.2 Effect of Clearance

367

7.4.1.3 Power Consumption in Melt Conveying

370

7.4.2 Power Law Fluids

373

7.4.2.1 One-Dimensional Flow

373

7.4.2.2 Two-Dimensional Flow

378

7.4.3 Non-Isothermal Analysis

384

7.4.3.1 Newtonian Fluids with Negligible Viscous Dissipation

384

7.4.3.2 Non-Isothermal Analysis of Power Law Fluids

391

7.4.3.3 Developing Temperatures

404

7.4.3.4 Estimating Fully Developed Melt Temperatures

421

7.4.3.5 Assumption of Stationary Screw and Rotating Barrel

428

7.5 Die Forming

436

7.5.1 Velocity and Temperature Profiles

437

7.5.2 Extrudate Swell

446

7.5.3 Die Flow Instabilities

448

7.5.3.1 Shark Skin

448

7.5.3.2 Melt Fracture

449

7.5.3.3 Draw Resonance

451

7.6 Devolatilization

452

7.7 Mixing

458

7.7.1 Mixing in Screw Extruders

459

7.7.1.1 Distributive Mixing in Screw Extruders

464

7.7.2 Static Mixing Devices

474

7.7.2.1 Geometry of Static Mixers

477

7.7.2.2 Functional Performance Characteristics

481

7.7.2.3 Miscellaneous Considerations

485

7.7.3 Dispersive Mixing

486

7.7.3.1 Solid-Liquid Systems

486

7.7.3.2 Liquid-Liquid System

488

7.7.4 Backmixing

500

7.7.4.1 Cross-Sectional Mixing and Axial Mixing

500

7.7.4.2 Residence Time Distribution

502

7.7.4.3 RTD in Screw Extruders

504

7.7.4.4 Methods to Improve Backmixing

505

7.7.4.5 Conclusions for Backmixing

507

Appendix 7.1

508

Appendix 7.2

509

Appendix 7.3

510

8 Extruder Screw Design

526

8.1 Mechanical Considerations

527

8.1.1 Torsional Strength of the Screw Root

527

8.1.2 Strength of the Screw Flight

529

8.1.3 Lateral Deflection of the Screw

531

8.2 Optimizing for Output

536

8.2.1 Optimizing for Melt Conveying

536

8.2.2 Optimizing for Plasticating

547

8.2.2.1 Effect of Helix Angle

549

8.2.2.2 Effect of Multiple Flights

549

8.2.2.3 Effect of Flight Clearance

551

8.2.2.4 Effect of Compression Ratio

553

8.2.3 Optimizing for Solids Conveying

554

8.2.3.1 Effect of Channel Depth

554

8.2.3.2 Effect of Helix Angle

555

8.2.3.3 Effect of Number of Flights

556

8.2.3.4 Effect of Flight Clearance

556

8.2.3.5 Effect of Flight Geometry

556

8.3 Optimizing for Power Consumption

557

8.3.1 Optimum Helix Angle

558

8.3.2 Effect of Flight Clearance

560

8.3.3 Effect of Flight Width

561

8.4 Single-Flighted Extruder Screws

565

8.4.1 The Standard Extruder Screw

566

8.4.2 Modifications of the Standard Extruder Screw

567

8.5 Devolatilizing Extruder Screws

570

8.5.1 Functional Design Considerations

571

8.5.2 Various Vented Extruder Screw Designs

575

8.5.2.1 Conventional Vented Extruder Screw

575

8.5.2.2 Bypass Vented Extruder Screw

576

8.5.2.3 Rearward Devolatilization

577

8.5.2.4 Multi-Vent Devolatilization

578

8.5.2.5 Cascade Devolatilization

579

8.5.2.6 Venting through the Screw

580

8.5.2.7 Venting through a Flighted Barrel

581

8.5.3 Vent Port Configuration

582

8.6 Multi-Flighted Extruder Screws

585

8.6.1 The Conventional Multi-Flighted Extruder Screw

585

8.6.2 Barrier Flight Extruder Screws

586

8.6.2.1 The Maillefer Screw

589

8.6.2.2 The Barr Screw

592

8.6.2.3 The Dray and Lawrence Screw

595

8.6.2.4 The Kim Screw

596

8.6.2.5 The Ingen Housz Screw

597

8.6.2.6 The CRD Barrier Screw

598

8.6.2.7 Summary of Barrier Screws

599

8.7 Mixing Screws

601

8.7.1 Dispersive Mixing Elements

601

8.7.1.1 The CRD Mixer

619

8.7.1.2 Mixers to Break Up the Solid Bed

633

8.7.1.3 Summary of Dispersive Mixers

635

8.7.2 Distributive Mixing Elements

636

8.7.2.1 Ring or Sleeve Mixers

638

8.7.2.2 Variable Depth Mixers

639

8.7.2.3 Summary of Distributive Mixers

640

8.8 Efficient Extrusion of Medical Devices

641

8.8.1 Introduction

641

8.8.2 Good Manufacturing Practices in Medical Extrusion

642

8.8.3 Automation of the Medical Extrusion Process

642

8.8.4 Minimizing Polymer Degradation

643

8.8.5 Melt Temperatures Inside the Extruder

643

8.8.6 Melt Temperatures and Screw Design

644

8.8.7 Molecular Degradation and Screw Design

647

8.8.8 Conclusions

651

8.9 Scale-Up

652

8.9.1 Common Scale-Up Factors

652

8.9.2 Scale-Up for Heat Transfer

655

8.9.3 Scale-Up for Mixing

656

8.9.4 Comparison of Various Scale-Up Methods

657

8.10 Rebuilding Worn Screws and Barrels

659

8.10.1 Application of Hardfacing Materials

661

8.10.1.1 Oxyacetylene Welding

661

8.10.1.2 Tungsten Inert Gas Welding

662

8.10.1.3 Plasma Transfer Arc Welding

662

8.10.1.4 Metal Inert Gas Welding

663

8.10.1.5 Laser Hardfacing

663

8.10.2 Rebuilding of Extruder Barrels

663

9 Die Design

670

9.1 Basic Considerations

671

9.1.1 Balancing the Die by Adjusting the Land Length

672

9.1.2 Balancing by Channel Height

676

9.1.3 Other Methods of Die Balancing

679

9.2 Film and Sheet Dies

680

9.2.1 Flow Adjustment in Sheet and Film Dies

681

9.2.2 The Horseshoe Die

684

9.3 Pipe and Tubing Dies

685

9.3.1 Tooling Design for Tubing

688

9.3.1.1 Definitions of Various Draw Ratios

689

9.3.1.2 Land Length

690

9.3.1.3 Taper Angles

691

9.3.1.4 Special Features

693

9.4 Blown Film Dies

693

9.4.1 The Spiral Mandrel Geometry

696

9.4.2 Effect of Die Geometry on Flow Distribution

697

9.4.3 Summary of Spiral Mandrel Die Design Variables

701

9.5 Profile Extrusion Dies

701

9.6 Coextrusion

703

9.6.1 Interface Distortion

707

9.7 Calibrators

709

10 Twin Screw Extruders

714

10.1 Introduction

714

10.2 Twin versus Single Screw Extruder

716

10.3 Intermeshing Co-Rotating Extruders

718

10.3.1 Closely Intermeshing Extruders

718

10.3.2 Self-Wiping Extruders

721

10.3.2.1 Geometry of Self-Wiping Extruders

722

10.3.2.2 Conveying in Self-Wiping Extruders

730

10.4 Intermeshing Counter-Rotating Extruders

737

10.5 Non-Intermeshing Twin Screw Extruders

747

10.6 Coaxial Twin Screw Extruders

760

10.7 Devolatilization in Twin Screw Extruders

762

10.8 Commercial Twin Screw Extruders

766

10.8.1 Screw Design Issues for Co-Rotating Twin Screw Extruders

770

10.8.2 Scale-Up in Co-Rotating Twin Screw Extruders

773

10.9 Overview of Twin Screw Extruders

775

11 Troubleshooting Extruders

780

11.1 Requirements for Efficient Troubleshooting

780

11.1.1 Instrumentation

781

11.1.2 Understanding of the Extrusion Process

781

11.1.3 Collect and Analyze Historical Data (Timeline)

782

11.1.4 Team Building

783

11.1.5 Condition of the Equipment

783

11.1.6 Information on the Feedstock

784

11.2 Tools for Troubleshooting

785

11.2.1 Temperature Measurement Devices

785

11.2.2 Data Acquisition Systems (DAS)

786

11.2.2.1 Portable Data Collectors/Machine Analyzers

786

11.2.2.2 Fixed Station Data Acquisition Systems

787

11.2.3 Light Microscopy

789

11.2.4 Thermochromic Materials

790

11.2.5 Thermal Analysis

792

11.2.6 Miscellaneous Tools

792

11.3 Systematic Troubleshooting

793

11.3.1 Upsets versus Development Problems

793

11.3.2 Machine-Related Problems

793

11.3.2.1 Drive System

793

11.3.2.2 The Feed System

795

11.3.2.3 Different Feeding Systems

795

11.3.2.4 Heating and Cooling System

795

11.3.2.5 Wear Problems

797

11.3.2.6 Screw Binding

814

11.3.3 Polymer Degradation

820

11.3.3.1 Types of Degradation

820

11.3.3.2 Degradation in Extrusion

824

11.3.4 Extrusion Instabilities

837

11.3.4.1 Frequency of Instability

838

11.3.4.2 Functional Instabilities

845

11.3.4.3 Solving Extrusion Instabilities

850

11.3.5 Air Entrapment

851

11.3.6 Gels, Gel Content, and Gelation

853

11.3.6.1 Measuring Gels

856

11.3.6.2 Gels Created in the Extrusion Process

857

11.3.6.3 Removing Gels Produced in Polymerization

858

11.3.7 Die Flow Problems

860

11.3.7.1 Melt Fracture

860

11.3.7.2 Die Lip Build-Up (Die Drool)

862

11.3.7.3 V- or W-Patterns

863

11.3.7.4 Specks and Discoloration

863

11.3.7.5 Lines in Extruded Product

868

11.3.7.6 Optical Properties

870

12 Modeling and Simulation of the Extrusion Process

878

12.1 Introduction

878

12.2 Background

879

12.2.1 Analytical Techniques

879

12.2.2 Numerical Methods

881

12.2.2.1 Finite Difference Method

882

12.2.2.2 Finite Element Method

883

12.2.2.3 Boundary Element Method

884

12.2.3 Remeshing Techniques in Moving Boundary Problems

885

12.2.4 Rheology

887

12.3 Simulating 3-D Flows with 2-D Models

888

12.3.1 Simulating Flows in Internal Batch Mixers with 2-D Models

888

12.3.2 Simulating Flows in Extrusion with 2-D Models

894

12.3.3 Simulating Flows in Extrusion Dies with 2-D Models

898

12.4 Three-Dimensional Simulation

902

12.4.1 Simulating Flows in the Banbury Mixer with Three-Dimensional Models

902

12.4.2 Simulating Flows in Extrusion Dies with 3-Dimensional Models

904

12.4.3 Simulating Flows in Extrusion with 3-Dimensional Models

909

12.4.3.1 Regular Conveying Screw

909

12.4.3.2 Energy Transfer Mixer

910

12.4.3.3 Twin Screw Extruder

912

12.4.3.4 Rhomboidal Mixers and Fluted Mixers (Leroy/Maddock)

918

12.4.3.5 Turbo-Screw

923

12.4.3.6 CRD Mixer

925

12.4.4 Static Mixers

927

12.5 Conclusions

929

Conversion Constants

936

Length

936

Volume

936

Mass

937

Density

937

Force

937

Stress

938

Viscosity

938

Energy/.Work

939

Power

939

Specific Energy

939

Thermal Conductivity

940

Temperature

940

Index

942