Polymer Extrusion

Preface to the Fifth Edition

1 Introduction

1.1 Basic Process

1.2 Scope of the Book

1.3 General Literature Survey

1.4 History of Polymer Extrusion

Part I – Extrusion Machinery

2 Different Types of Extruders

2.1 The Single Screw Extruder

2.1.1 Basic Operation

2.1.2 Vented Extruders

2.1.3 Rubber Extruders

2.1.4 High-Speed Extrusion

2.1.4.1 Melt Temperature

2.1.4.2 Extruders without Gear Reducer

2.1.4.3 Energy Consumption

2.1.4.4 Change-over Resin Consumption

2.1.4.5 Change-over Time and Residence Time

2.2 The Multiscrew Extruder

2.2.1 The Twin Screw Extruder

2.2.2 The Multiscrew Extruder With More Than Two Screws

2.2.3 The Gear Pump Extruder

2.3 Disk Extruders

2.3.1 Viscous Drag Disk Extruders

2.3.1.1 Stepped Disk Extruder

2.3.1.2 Drum Extruder

2.3.1.3 Spiral Disk Extruder

2.3.1.4 Diskpack Extruder

2.3.2 The Elastic Melt Extruder

2.3.3 Overview of Disk Extruders

2.4 Ram Extruders

2.4.1 Single Ram Extruders

2.4.1.1 Solid State Extrusion

2.4.2 Multi Ram Extruder

2.4.3 Appendix 2.1

2.4.3.1 Pumping Efficiency in Diskpack Extruder

3 Extruder Hardware

3.1 Extruder Drive

3.1.1 AC Motor Drive System

3.1.1.1 Mechanical Adjustable Speed Drive

3.1.1.2 Electric Friction Clutch Drive

3.1.1.3 Adjustable Frequency Drive

3.1.2 DC Motor Drive System

3.1.2.1 Brushless DC Drives

3.1.3 Hydraulic Drive System

3.1.4 Comparison of Various Drive Systems

3.1.5 Reducer

3.1.6 Constant Torque Characteristics

3.2 Thrust Bearing Assembly

3.3 Barrel and Feed Throat

3.4 Feed Hopper

3.5 Extruder Screw

3.6 Die Assembly

3.6.1 Screens and Screen Changers

3.7 Heating and Cooling Systems

3.7.1 Electric Heating

3.7.1.1 Resistance Heating

3.7.1.2 Induction Heating

3.7.2 Fluid Heating

3.7.3 Extruder Cooling

3.7.4 Screw Heating and Cooling

4 Instrumentation and Control

4.1 Instrumentation Requirements

4.1.1 Most Important Parameters

4.2 Pressure Measurement

4.2.1 The Importance of Melt Pressure

4.2.2 Different Types of Pressure Transducers

4.2.3 Mechanical Considerations

4.2.4 Specifications

4.2.5 Comparisons of Different Transducers

4.3 Temperature Measurement

4.3.1 Methods of Temperature Measurement

4.3.2 Barrel Temperature Measurement

4.3.3 Stock Temperature Measurement

4.3.3.1 Ultrasound Transmission Time

4.3.3.2 Infrared Melt Temperature Measurement

4.4 Other Measurements

4.4.1 Power Measurement

4.4.2 Rotational Speed

4.4.3 Extrudate Thickness

4.4.4 Extrudate Surface Conditions

4.5 Temperature Control

4.5.1 On-Off Control

4.5.2 Proportional Control

4.5.2.1 Proportional-Only Control

4.5.2.2 Proportional and Integral Control

4.5.2.3 Proportional and Integral and Derivative Control

4.5.2.4 Dual Sensor Temperature Control

4.5.3 Controllers

4.5.3.1 Temperature Controllers

4.5.3.2 Power Controllers

4.5.3.3 Dual Output Controllers

4.5.4 Time-Temperature Characteristics

4.5.4.1 Thermal Characteristics of the System

4.5.4.2 Modeling of Response in Linear Systems

4.5.4.3 Temperature Characteristics with On-Off Control

4.5.5 Tuning of the Controller Parameters

4.5.5.1 Performance Criteria

4.5.5.2 Effect of PID Parameters

4.5.5.3 Tuning Procedure When Process Model Is Unknown

4.5.5.4 Tuning Procedure When Process Model Is Known

4.5.5.5 Pre-Tuned Temperature Controllers

4.5.5.6 Self-Tuning Temperature Controllers

4.6 Total Process Control

4.6.1 True Total Extrusion Process Control

Part II – Process Analysis

5 Fundamental Principles

5.1 Balance Equations

5.1.1 The Mass Balance Equation

5.1.2 The Momentum Balance Equation

5.1.3 The Energy Balance Equation

5.2 Basic Thermodynamics

5.2.1 Rubber Elasticity

5.2.2 Strain-Induced Crystallization

5.3 Heat Transfer

5.3.1 Conductive Heat Transfer

5.3.2 Convective Heat Transfer

5.3.3 Dimensionless Numbers

5.3.3.1 Dimensional Analysis

5.3.3.2 Important Dimensionless Numbers

5.3.4 Viscous Heat Generation

5.3.5 Radiative Heat Transport

5.3.5.1 Dielectric Heating

5.3.5.2 Microwave Heating

5.4 Basics of Devolatilization

5.4.1 Devolatilization of Particulate Polymer

5.4.2 Devolatilization of Polymer Melts

Appendix 5.1

Example: Pipe Flow of Newtonian Fluid

6 Important Polymer Properties

6.1 Properties of Bulk Materials

6.1.1 Bulk Density

6.1.2 Coefficient of Friction

6.1.3 Particle Size and Shape

6.1.4 Other Properties

6.2 Melt Flow Properties

6.2.1 Basic Definitions

6.2.2 Power Law Fluid

6.2.3 Other Fluid Models

6.2.4 Effect of Temperature and Pressure

6.2.5 Viscoelastic Behavior

6.2.6 Measurement of Flow Properties

6.2.6.1 Capillary Rheometer

6.2.6.2 Melt Index Tester

6.2.6.3 Cone and Plate Rheometer

6.2.6.4 Slit Die Rheometer

6.2.6.5 Dynamic Analysis

6.3 Thermal Properties

6.3.1 Thermal Conductivity

6.3.2 Specific Volume and Morphology

6.3.3 Specific Heat and Heat of Fusion

6.3.4 Specific Enthalpy

6.3.5 Thermal Diffusivity

6.3.6 Melting Point

6.3.7 Induction Time

6.3.8 Thermal Characterization

6.3.8.1 DTA and DSC

6.3.8.2 TGA

6.3.8.3 TMA

6.3.8.4 Other Thermal Characterization Techniques

6.4 Polymer Property Summary

7 Functional Process Analysis

7.1 Basic Screw Geometry

7.2 Solids Conveying

7.2.1 Gravity Induced Solids Conveying

7.2.1.1 Pressure Distribution

7.2.1.2 Flow Rate

7.2.1.3 Design Criteria

7.2.2 Drag Induced Solids Conveying

7.2.2.1 Frictional Heat Generation

7.2.2.2 Grooved Barrel Sections

7.2.2.3 Adjustable Grooved Barrel Extruders

7.2.2.4 Starve Feeding Versus Flood Feeding

7.3 Plasticating

7.3.1 Theoretical Model of Contiguous Solids Melting

7.3.1.1 Non-Newtonian, Non-Isothermal Case

7.3.2 Other Melting Models

7.3.3 Power Consumption in the Melting Zone

7.3.4 Computer Simulation

7.3.5 Dispersed Solids Melting

7.4 Melt Conveying

7.4.1 Newtonian Fluids

7.4.1.1 Effect of Flight Flanks

7.4.1.2 Effect of Clearance

7.4.1.3 Power Consumption in Melt Conveying

7.4.2 Power Law Fluids

7.4.2.1 One-Dimensional Flow

7.4.2.2 Two-Dimensional Flow

7.4.3 Non-Isothermal Analysis

7.4.3.1 Newtonian Fluids with Negligible Viscous Dissipation

7.4.3.2 Non-Isothermal Analysis of Power Law Fluids

7.4.3.3 Developing Temperatures

7.4.3.4 Estimating Fully Developed Melt Temperatures

7.4.3.5 Assumption of Stationary Screw and Rotating Barrel

7.5 Die Forming

7.5.1 Velocity and Temperature Profiles

7.5.2 Extrudate Swell

7.5.3 Die Flow Instabilities

7.5.3.1 Shark Skin

7.5.3.2 Melt Fracture

7.5.3.3 Draw Resonance

7.6 Devolatilization

7.7 Mixing

7.7.1 Mixing in Screw Extruders

7.7.1.1 Distributive Mixing in Screw Extruders

7.7.2 Static Mixing Devices

7.7.2.1 Geometry of Static Mixers

7.7.2.2 Functional Performance Characteristics

7.7.2.3 Miscellaneous Considerations

7.7.3 Dispersive Mixing

7.7.3.1 Solid-Liquid Systems

7.7.3.2 Liquid-Liquid System

7.7.4 Backmixing

7.7.4.1 Cross-Sectional Mixing and Axial Mixing

7.7.4.2 Residence Time Distribution

7.7.4.3 RTD in Screw Extruders

7.7.4.4 Methods to Improve Backmixing

7.7.4.5 Conclusions for Backmixing

Appendix 7.1

Appendix 7.2

Appendix 7.3

8 Extruder Screw Design

8.1 Mechanical Considerations

8.1.1 Torsional Strength of the Screw Root

8.1.2 Strength of the Screw Flight

8.1.3 Lateral Deflection of the Screw

8.2 Optimizing for Output

8.2.1 Optimizing for Melt Conveying

8.2.2 Optimizing for Plasticating

8.2.2.1 Effect of Helix Angle

8.2.2.2 Effect of Multiple Flights

8.2.2.3 Effect of Flight Clearance

8.2.2.4 Effect of Compression Ratio

8.2.3 Optimizing for Solids Conveying

8.2.3.1 Effect of Channel Depth

8.2.3.2 Effect of Helix Angle

8.2.3.3 Effect of Number of Flights

8.2.3.4 Effect of Flight Clearance

8.2.3.5 Effect of Flight Geometry

8.3 Optimizing for Power Consumption

8.3.1 Optimum Helix Angle

8.3.2 Effect of Flight Clearance

8.3.3 Effect of Flight Width

8.4 Single-Flighted Extruder Screws

8.4.1 The Standard Extruder Screw

8.4.2 Modifications of the Standard Extruder Screw

8.5 Devolatilizing Extruder Screws

8.5.1 Functional Design Considerations

8.5.2 Various Vented Extruder Screw Designs

8.5.2.1 Conventional Vented Extruder Screw

8.5.2.2 Bypass Vented Extruder Screw

8.5.2.3 Rearward Devolatilization

8.5.2.4 Multi-Vent Devolatilization

8.5.2.5 Cascade Devolatilization

8.5.2.6 Venting through the Screw

8.5.2.7 Venting through a Flighted Barrel

8.5.3 Vent Port Configuration

8.6 Multi-Flighted Extruder Screws

8.6.1 The Conventional Multi-Flighted Extruder Screw

8.6.2 Barrier Flight Extruder Screws

8.6.2.1 The Maillefer Screw

8.6.2.2 The Barr Screw

8.6.2.3 The Dray and Lawrence Screw

8.6.2.4 The Kim Screw

8.6.2.5 The Ingen Housz Screw

8.6.2.6 The CRD Barrier Screw

8.6.2.7 Summary of Barrier Screws

8.7 Mixing Screws

8.7.1 Dispersive Mixing Elements

8.7.1.1 The CRD Mixer

8.7.1.2 Mixers to Break Up the Solid Bed

8.7.1.3 Summary of Dispersive Mixers

8.7.2 Distributive Mixing Elements

8.7.2.1 Ring or Sleeve Mixers

8.7.2.2 Variable Depth Mixers

8.7.2.3 Summary of Distributive Mixers

8.8 Efficient Extrusion of Medical Devices

8.8.1 Introduction

8.8.2 Good Manufacturing Practices in Medical Extrusion

8.8.3 Automation of the Medical Extrusion Process

8.8.4 Minimizing Polymer Degradation

8.8.5 Melt Temperatures Inside the Extruder

8.8.6 Melt Temperatures and Screw Design

8.8.7 Molecular Degradation and Screw Design

8.8.8 Conclusions

8.9 Scale-Up

8.9.1 Common Scale-Up Factors

8.9.2 Scale-Up for Heat Transfer

8.9.3 Scale-Up for Mixing

8.9.4 Comparison of Various Scale-Up Methods

8.10 Rebuilding Worn Screws and Barrels

8.10.1 Application of Hardfacing Materials

8.10.1.1 Oxyacetylene Welding

8.10.1.2 Tungsten Inert Gas Welding

8.10.1.3 Plasma Transfer Arc Welding

8.10.1.4 Metal Inert Gas Welding

8.10.1.5 Laser Hardfacing

8.10.2 Rebuilding of Extruder Barrels

9 Die Design

9.1 Basic Considerations

9.1.1 Balancing the Die by Adjusting the Land Length

9.1.2 Balancing by Channel Height

9.1.3 Other Methods of Die Balancing

9.2 Film and Sheet Dies

9.2.1 Flow Adjustment in Sheet and Film Dies

9.2.2 The Horseshoe Die

9.3 Pipe and Tubing Dies

9.3.1 Tooling Design for Tubing

9.3.1.1 Definitions of Various Draw Ratios

9.3.1.2 Land Length

9.3.1.3 Taper Angles

9.3.1.4 Special Features

9.4 Blown Film Dies

9.4.1 The Spiral Mandrel Geometry

9.4.2 Effect of Die Geometry on Flow Distribution

9.4.3 Summary of Spiral Mandrel Die Design Variables

9.5 Profile Extrusion Dies

9.6 Coextrusion

9.6.1 Interface Distortion

9.7 Calibrators

10 Twin Screw Extruders

10.1 Introduction

10.2 Twin versus Single Screw Extruder

10.3 Intermeshing Co-Rotating Extruders

10.3.1 Closely Intermeshing Extruders

10.3.2 Self-Wiping Extruders

10.3.2.1 Geometry of Self-Wiping Extruders

10.3.2.2 Conveying in Self-Wiping Extruders

10.4 Intermeshing Counter-Rotating Extruders

10.5 Non-Intermeshing Twin Screw Extruders

10.6 Coaxial Twin Screw Extruders

10.7 Devolatilization in Twin Screw Extruders

10.8 Commercial Twin Screw Extruders

10.8.1 Screw Design Issues for Co-Rotating Twin Screw Extruders

10.8.2 Scale-Up in Co-Rotating Twin Screw Extruders

10.9 Overview of Twin Screw Extruders

11 Troubleshooting Extruders

11.1 Requirements for Efficient Troubleshooting

11.1.1 Instrumentation

11.1.2 Understanding of the Extrusion Process

11.1.3 Collect and Analyze Historical Data (Timeline)

11.1.4 Team Building

11.1.5 Condition of the Equipment

11.1.6 Information on the Feedstock

11.2 Tools for Troubleshooting

11.2.1 Temperature Measurement Devices

11.2.2 Data Acquisition Systems (DAS)

11.2.2.1 Portable Data Collectors/Machine Analyzers

11.2.2.2 Fixed Station Data Acquisition Systems

11.2.3 Light Microscopy

11.2.4 Thermochromic Materials

11.2.5 Thermal Analysis

11.2.6 Miscellaneous Tools

11.3 Systematic Troubleshooting

11.3.1 Upsets versus Development Problems

11.3.2 Machine-Related Problems

11.3.2.1 Drive System

11.3.2.2 The Feed System

11.3.2.3 Different Feeding Systems

11.3.2.4 Heating and Cooling System

11.3.2.5 Wear Problems

11.3.2.6 Screw Binding

11.3.3 Polymer Degradation

11.3.3.1 Types of Degradation

11.3.3.2 Degradation in Extrusion

11.3.4 Extrusion Instabilities

11.3.4.1 Frequency of Instability

11.3.4.2 Functional Instabilities

11.3.4.3 Solving Extrusion Instabilities

11.3.5 Air Entrapment

11.3.6 Gels, Gel Content, and Gelation

11.3.6.1 Measuring Gels

11.3.6.2 Gels Created in the Extrusion Process

11.3.6.3 Removing Gels Produced in Polymerization

11.3.7 Die Flow Problems

11.3.7.1 Melt Fracture

11.3.7.2 Die Lip Build-Up (Die Drool)

11.3.7.3 V- or W-Patterns

11.3.7.4 Specks and Discoloration

11.3.7.5 Lines in Extruded Product

11.3.7.6 Optical Properties

12 Modeling and Simulation of the Extrusion Process

12.1 Introduction

12.2 Background

12.2.1 Analytical Techniques

12.2.2 Numerical Methods

12.2.2.1 Finite Difference Method

12.2.2.2 Finite Element Method

12.2.2.3 Boundary Element Method

12.2.3 Remeshing Techniques in Moving Boundary Problems

12.2.4 Rheology

12.3 Simulating 3-D Flows with 2-D Models

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

12.3.2 Simulating Flows in Extrusion with 2-D Models

12.3.3 Simulating Flows in Extrusion Dies with 2-D Models

12.4 Three-Dimensional Simulation

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

12.4.2 Simulating Flows in Extrusion Dies with 3-Dimensional Models

12.4.3 Simulating Flows in Extrusion with 3-Dimensional Models

12.4.3.1 Regular Conveying Screw

12.4.3.2 Energy Transfer Mixer

12.4.3.3 Twin Screw Extruder

12.4.3.4 Rhomboidal Mixers and Fluted Mixers (Leroy/Maddock)

12.4.3.5 Turbo-Screw

12.4.3.6 CRD Mixer

12.4.4 Static Mixers

12.5 Conclusions

Conversion Constants

Length

Volume

Mass

Density

Force

Stress

Viscosity

Energy/.Work

Power

Specific Energy

Thermal Conductivity

Temperature

Index