Analyzing and Troubleshooting Single-Screw Extruders

Preface

Acknowledgements

1 Single-Screw Extrusion: Introduction and Troubleshooting

1.1 Organization of this Book

1.2 Troubleshooting Extrusion Processes

1.2.1 The Injection Molding Problem at Saturn

1.3 Introduction to Screw Geometry

1.3.1 Screw Geometric Quantitative Characteristics

1.4 Simple Flow Equations for the Metering Section

1.5 Example Calculations

1.5.1 Example 1: Calculation of Rotational and Pressure Flow Components

1.5.2 Example 2: Flow Calculations for a Properly Operating Extruder

1.5.3 Example 3: Flow Calculations for an Improperly Operating Extruder

1.5.4 Metering Channel Calculation Summary

Nomenclature

References

2 Polymer Materials

2.1 Introduction and History

2.1.1 History of Natural Polymers

2.1.2 The History of Synthetic Polymers

2.2 Characteristics of Synthetic Polymers

2.3 Structure Effects on Properties

2.3.1 Stereochemistry

2.3.2 Melting and Glass Transition Temperatures

2.3.3 Crystallinity

2.4 Polymer Production and Reaction Engineering

2.4.1 Condensation Reactions

2.4.2 Addition Reactions

2.5 Polymer Degradation

2.5.1 Ceiling Temperature

2.5.2 Degradation of Vinyl Polymers

2.5.3 Degradation of Condensation Polymers

References

3 Introduction to Polymer Rheology for Extrusion

3.1 Introduction to the Deformation of Materials

3.2 Introduction to Basic Concepts of Molecular Size

3.2.1 Size Distribution Example

3.2.2 Molecular Weight Distributions for Polymers

3.3 Basic Rheology Concepts

3.4 Polymer Solution Viscosity and Polymer Molecular Weight

3.4.1 Sample Calculation of Solution Viscosity

3.5 Introduction to Viscoelasticity

3.6 Measurement of Polymer Viscosity

3.6.1 Capillary Rheometers

3.6.2 Cone and Plate Rheometers

3.6.3 Melt Index and Melt Flow Rate

3.7 Viscosity of Polymers as Functions of Molecular Character, Temperature, and Pressure

3.8 Models for Non-Newtonian Flow

Nomenclature

References

4 Resin Physical Properties Related to Processing

4.1 Bulk Density and Compaction

4.1.1 Measurement of Bulk Density

4.1.2 Measuring the Compaction Characteristics of a Resin

4.2 Lateral Stress Ratio

4.2.1 Measuring the Lateral Stress Ratio

4.3 Stress at a Sliding Interface

4.3.1 The Screw Simulator and the Measurement of the Stress at the Interface

4.4 Melting Flux

4.5 Heat Capacity

4.6 Thermal Conductivity and Heat Transfer

4.7 Melt Density

Nomenclature

References

5 Solids Conveying

5.1 Description of the Solid Conveying Process

5.2 Literature Review of Smooth-Bore Solids Conveying Models

5.2.1 Darnell and Mol Model

5.2.2 Tadmor and Klein Model

5.2.3 Clarkson University Models

5.2.4 Hyun and Spalding Model

5.2.5 Moysey and Thompson Model

5.3 Modern Experimental Solids Conveying Devices

5.3.1 Solids Conveying Devices at Clarkson University

5.3.2 The Solids Conveying Device at Dow

5.4 Comparison of the Modified Campbell-Dontula Model with Experimental Data

5.4.1 Solids Conveying Example Calculation

5.5 Grooved Bore Solids Conveying

5.5.1 Grooved Barrel Solids Conveying Models

5.6 Solids Conveying Notes

Nomenclature

References

6 The Melting Process

6.1 Compression Ratio and Compression Rate

6.2 The Melting Process

6.2.1 The Melting Process as a Function of Screw Geometry

6.2.2 Review of the Classical Literature

6.2.3 Reevaluation of the Tadmor and Klein Melting Data

6.3 Theory Development for Melting Using Screw Rotation Physics

6.3.1 Melting Model for a Conventional Transition Section Using Screw Rotation Physics

6.3.2 Melting Models for Barrier Screw Sections

6.4 Effect of Pressure on Melting Rate

6.5 One-Dimensional Melting

6.5.1 One-Dimensional Melting Model

6.6 Solid Bed Breakup

6.7 Melting Section Characteristics

Nomenclature

References

7 Fluid Flow in Metering Channels

7.1 Introduction to the Reference Frame

7.2 Laboratory Observations

7.3 Literature Survey

7.4 Development of Linearized Flow Analysis

7.4.1 Example Flow Calculation

7.5 Numerical Flow Evaluation

7.5.1 Simulation of a 500 mm Diameter Melt-Fed Extruder

7.5.2 Extrusion Variables and Errors

7.5.3 Corrections to Rotational Flow

7.5.4 Simulation of the 500 mm Diameter Extruder Using Fc

7.6 Frame Dependent Variables

7.6.1 Example Calculation of Energy Dissipation

7.7 Viscous Energy Dissipation and Temperature of the Resin in the Channel

7.7.1 Energy Dissipation and Channel Temperature for Screw Rotation

7.7.2 Energy Dissipation and Channel Temperature for Barrel Rotation

7.7.3 Temperature Increase Calculation Example for a Screw Pump

7.7.4 Heat Transfer Coefficients

7.7.5 Temperature Calculation Using a Control Volume Technique

7.7.6 Numerical Comparison of Temperatures for Screw and Barrel Rotations

7.8 Metering Section Characteristics

Nomenclature

References

8 Mixing Processes for Single-Screw Extruders

8.1 Common Mixing Operations for Single-Screw Extruders

8.1.1 Common Mixing Applications

8.2 Dispersive and Distributive Mixing Processes

8.3 Fundamentals of Mixing

8.3.1 Measures of Mixing

8.3.2 Experimental Demonstration of Mixing

8.4 The Melting Process as the Primary Mechanism for Mixing

8.4.1 Experimental Analysis of the Melting and Mixing Capacity of a Screw

8.4.2 Mixing and Barrier-Flighted Melting Sections

8.5 Secondary Mixing Processes and Devices

8.5.1 Maddock-Style Mixers

8.5.2 Blister Ring Mixers

8.5.3 Spiral Dam Mixers

8.5.4 Pin-Type Mixers

8.5.5 Knob Mixers

8.5.6 Gear Mixers

8.5.7 Dynamic Mixers

8.5.8 Static Mixers

8.6 Mixing Using Natural Resins and Masterbatches

8.7 Mixing and Melting Performance as a Function of Flight Clearance

8.8 High Pressures During Melting and Agglomerates

8.9 Effect of Discharge Pressure on Mixing

8.10 Shear Refinement

8.11 Direct Compounding Using Single-Screw Extruders

Nomenclature

References

9 Scaling of Single-Screw Extrusion Processes

9.1 Scaling Rules

9.2 Engineering Design Method for Plasticating Screws

9.2.1 Process Analysis and Simulations

9.3 Scale-Up from a 40 mm Diameter Extruder to an 80 mm Diameter Machine for a PE Resin

9.4 Rate Increase for an 88.9 mm Diameter Extruder Running a HIPS Resin

Nomenclature

References

10 Introduction to Troubleshooting the Extrusion Process

10.1 The Troubleshooting Process

10.2 Hypothesis Setting and Problem Solving

10.2.1 Case Study for the Design of a New Resin

10.2.2 Case Study for a Surface Blemish

10.2.3 Case Study for a Profile Extrusion Process

10.3 Equipment and Tools Needed for Troubleshooting

10.3.1 Maddock Solidification Experiment

10.4 Common Mechanical Problems

10.4.1 Flight Clearance and Hard Facing

10.4.2 Barrel and Screw Alignment

10.4.3 Extruder Barrel Supports

10.4.4 First-Time Installation of a Screw

10.4.5 Screw Breaks

10.4.6 Protection from High-Pressure Events

10.4.7 Gearbox Lubricating Oil

10.4.8 Particle Seals and Viscoseals

10.4.9 Screw Cleaning

10.5 Common Electrical and Sensor Problems

10.5.1 Thermocouples

10.5.2 Pressure Sensors

10.5.3 Electronic Filters and Noise

10.6 Motors and Drive Systems

10.6.1 Motor Efficiencies and Power Factors

10.7 Typical Screw Channel Dimensions

10.8 Common Calculations

10.8.1 Energy Dissipated by the Screw

10.8.2 Screw Geometry Indices

10.9 Barrel Temperature Optimization

10.10 Screw Temperature Profile

10.11 The Screw Manufacturing and Refurbishing Process

10.12 Injection-Molding Plasticators

10.12.1 Calculations for Injection-Molding Plasticators

10.13 New Equipment Installations

10.13.1 Case Study: A Large Diameter Extruder Purchase

10.13.2 Case Study: Extruder and Line Purchase for a New Product

10.13.3 Summary for New Equipment Installations

Nomenclature

References

11 Contamination in the Finished Product

11.1 Foreign Contaminants in the Extrudate

11.1.1 Melt Filtration

11.1.2 Metal Fragments in the Extrudate

11.1.3 Gas Bubbles in a New Sheet Line

11.2 Gels in Polyolefin Resins

11.2.1 Protocols for Gel Analysis

11.3 Resin Decomposition in Stagnant Regions of a Process

11.4 Improper Shutdown of Processing Equipment

11.5 Equipment Purging

11.6 Oxygen Exclusion at the Hopper

11.7 Flight Radii Size

11.8 Drying the Resin

11.9 Color Masterbatches

11.10 Case Studies for Extrusion Processes with Contamination in the Product

11.10.1 Intermittent Crosslinked Gels in a Film Product

11.10.2 Small Gels in an LLDPE Film Product

11.10.3 Degassing Holes in Blow-Molded Bottles

11.11 Contamination in Injection-Molded Parts

11.11.1 Splay Defects for Injection-Molded Parts

11.12 Injection-Molding Case Studies

11.12.1 Injection-Molded Parts with Splay and Poor Resin Color Purge

11.12.2 Black Color Streaks in Molded Parts: Case One

11.12.3 Black Streaks in Molded Parts: Case Two

11.12.4 Silver Streaks in a Clear GPPS Resin Injection-Molded Packaging Part

11.12.5 The Injection-Molding Problem at Saturn

Nomenclature

References

12 Flow Surging

12.1 An Overview of the Common Causes for Flow Surging

12.1.1 Relationship Between Discharge Pressure and Rate at the Die

12.2 Troubleshooting Flow Surging Processes

12.3 Barrel Zone and Screw Temperature Control

12.3.1 Water- and Air-Cooled Barrel Zones

12.4 Rotation- and Geometry-Induced Pressure Oscillations

12.5 Gear Pump Control

12.6 Solids Blocking the Flow Path

12.7 Case Studies for Extrusion Processes That Flow Surge

12.7.1 Poor Barrel Zone Temperature Control

12.7.2 Optimization of Barrel Temperatures for Improved Solids Conveying

12.7.3 Flow Surging Due to High Temperatures in the Feed Section of the Screw

12.7.4 Flow Surging Due to High Temperatures in the Feed Casing

12.7.5 Flow Surging Due to a Poorly Designed Barrier Entry for GPPS Resin

12.7.6 Solid Blockage at the Entry of a Spiral Mixer

12.7.7 Flow Surging Caused by a Worn Feed Casing and a New Barrel

12.7.8 Flow Surging for a PC Resin Extrusion Process

Nomenclature

References

13 Rate-Limited Extrusion Processes

13.1 Vent Flow for Multiple-Stage Extruders

13.2 Screw Wear

13.3 High-Performance and Barrier Screws for Improved Rates

13.4 Case Studies That Were Rate Limited

13.4.1 Rate Limitation Due to a Worn Screw

13.4.2 Rate Limitation Due to Solid Polymer Fragments in the Extrudate

13.4.3 Rate Limited by the Discharge Temperature for a Pelletizing Extruder

13.4.4 Large Diameter Extruder Running PS Resin

13.4.5 Rate Limited by Discharge Temperature and Torque for Starch Extrusion

13.4.6 Vent Flow for a Two-Stage Screw Running a Low Bulk Density PS Feedstock

13.4.7 Increasing the Rate of a Large Part Blow-Molding Process

Nomenclature

References

14 Barrier and High-Performance Screws

14.1 Barrier Screws

14.2 Wave Dispersion Screws

14.2.1 Double Wave Screw

14.2.2 Energy Transfer Screws

14.2.3 Variable Barrier Energy Transfer Screws

14.2.4 Distributive Melt Mixing Screws

14.2.5 Fusion Screws

14.3 Other High-Performance Screw Designs

14.3.1 Stratablend Screws

14.3.2 Unimix Screws

14.4 Calculation of the Specific Rotation Rate

Nomenclature

References

15 Melt-Fed Extruders

15.1 Simulation Methods

15.2 Compounding Processes

15.2.1 Common Problems for Melt-Fed Extruders on Compounding Lines

15.3 Large-Diameter Pumping Extruders

15.3.1 Loss of Rate Due to Poor Material Conveyance in the Feed Section

15.3.2 Operation of the Slide Valve

15.3.3 Nitrogen Inerting on Vent Domes

15.4 Secondary Extruders for Tandem Foam Sheet Lines

15.4.1 High-Performance Cooling Screws

Nomenclature

References

Appendix A1 Polymer Abbreviation Definitions

Appendix A3 Rheological Calculations for a Capillary Rheometer and for a Cone and Plate Rheometer

A3.1 Capillary Rheometer

A3.2 Cone and Plate Rheometer

References

Appendix A4 Shear Stress at a Sliding Interface and Melting Fluxes for Select Resins

A4.1 Shear Stress at a Sliding Interface for Select Resins

A4.2 Melting Fluxes for Select Resins

References

Appendix A5 Solids Conveying Model Derivations and the Complete LDPE Solids Conveying Data Set

A5.1 Channel Dimensions, Assumptions, and Basic Force Balances

A5.2 Campbell-Dontula Model

A5.2.1 Modified Campbell-Dontula Model

A5.3 Hyun-Spalding Model

A5.4 Yamamuro-Penumadu-Campbell Model

A5.5 Campbell-Spalding Model

A5.6 The Complete Dow Solids Conveying Data Set

References

Appendix A6 Melting Rate Model Development

A6.1 Derivation of the Melting Performance Equations for a Conventional Channel

A6.2 Effect of Static Pressure on Melting

References

Appendix A7

754

A7.1 Transformed Frame Flow Analysis

A7.1.1 x-Directional Flow

A7.1.2 z-Directional Flow

A7.1.3 z-Directional Flow for Helix Rotation with a Stationary Screw Core and Barrel

A7.1.4 z-Directional Flow Due to a Pressure Gradient

A7.2 Viscous Energy Dissipation for Screw Rotation

A7.2.1 Viscous Energy Dissipation for Screw Rotation: Generalized Solution

A7.2.2 Viscous Energy Dissipation for Screw Rotation for Channels with Small Aspect Ratios (H/W < 0.1)

A7.3 Viscous Energy Dissipation for Barrel Rotation

A7.3.1 Viscous Energy Dissipation for Barrel Rotation: Generalized Solution

A7.3.2 Viscous Energy Dissipation for Barrel Rotation for Channels with Small Aspect Ratios (H/W < 0.1)

References

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