Polymer Extrusion 5e

This book bridges the gap between theory and practice in the extrusion field. Now in its fifth edition, the best-selling Polymer Extrusion continues to provide valuable, up-to-date information for polymer engineers and chemists who need both theoretical and practical tools for successful extrusion operations. Since the last edition in 2001, there have been many new developments in the field and are incorporated in this edition. New, Updated Content •Chapter 2: A discussion on high speed single screw extruders has been added. •Chapter 7: An innovative theory is presented that allows prediction of melt temperatures without having to result to numerical techniques and computer simulation. •Chapter 8: Now includes information on the efficient extrusion of medical devices; this section discusses optimal manufacturing practices, screw designs, and processing conditions. •Chapter 11: The section on gels has been expanded and now includes information on discolored specks, how to predict their occurrence and frequency, as well as instruments to detect defects in pellets. •New information has been added throughout and references have been updated Cover Half Title Polymer Extrusion Copyright Preface to the Fifth Edition Contents 1. Introduction 1.1 Basic Process 1.2 Scope of the Book 1.3 General Literature Survey 1.4 History of Polymer Extrusion References 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 References 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 References 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 REferences 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 References 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 References 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 References 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 References 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 References 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 References 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 References 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 References Conversion Constants Length Volume Mass Density Force Stress Viscosity Energy/ Work Power Specific Energy Thermal Conductivity Temperature Index Initially published "to bridge the gap between theory and practice in extrusion," this 5th edition of Polymer Extrusion continues to serve the practicing polymer engineer and chemist, providing the theoretical and the practical tools for successful extrusion operations. In its revised and expanded form, it also incorporates the many new developments in extrusion theory and machinery over the last years. Contents · Different Types of Extruders · Extruder Hardware · Instrumentation and Control · Fundamental Principles · Important Polymer Properties · Functional Process Analysis · Extruder Screw Design · Die Design · Twin Screw Extruders · Troubleshooting Extruders · Modeling and Simulation of the Extrusion Process