Table of Contents
The Design of Food Extrusion Dies
Preface
1. Introduction 3
2. Basic Principles of Extrusion Cooking 9
2.1 What is Product Quality?
2.2 A Review of the Extrusion Process
2.3 Flow Components in an Extruder Screw
2.4 The Extrusion System
2.5 The Role of Energy Input
2.6 A Simple Analogy for Extruder Performance
3. Role of Rheology in Extrusion Processing 25
3.1 A Definition for Fluid Viscosity
4. Understanding Visco-Elastic Behaviour 35
4.1 What is visco-elasticity?
4.2 Visco-elasticity during extrusion
4.3 Modelling visco-elastic behaviour
4.4 Visco-elastic flow and die swell
4.4 Mathematically describing visco-elasticity
Tutorial # 1 - Elastic Phenomena
5. Die Design & Extruder Operating Curves 47
5.1 The Pipe Flow Analogy
5.2 The Die Characteristic
5.3 Extruder Operating Curves
5.4 Derivation of the Die Conductance Equation
5.5 Technical Considerations for Die Design
5.6 Determination of Equivalent Radius for Non-Newtonian Fluid Die Flow Analysis
Worked Example # 1 – Calculate the Die Conductance for Newtonian and Non-Newtonian Cases
Worked Example # 2 – Die Design for Smaller Product Size
5.7 An Alternative Approach to Pressure Drop Estimation
5.9 Influence of Fluid Rheology upon Die Flow
5.10 Interaction with the Extrusion System
Worked Example # 3 – Comparison of Newtonian vs. Non-Newtonian Flow in Dies
Tutorial # 2 - Basic Conductance Calculations
Tutorial # 3 - Equivalent Die Conductances
Tutorial # 4 - Die Machining Accuracy
Tutorial # 5 - Conductance vs. Open Area – Which Applies?
6. The Die Entrance Effect 83
6.1 The Effective Die Land Length
6.2 The Bagley Entrance Correction
6.3 Determination of the Effective Inlet Diameter
6.4 Experimental Validation of the Die Conductance
Tutorial # 6 - Entrance Effects
Tutorial # 7 - The Bagley Entrance Correction
Tutorial # 8 - The Cone Angle Effect
7. Evaluation of Extruded Product Curvature 97
7.1 Theoretical Background
Tutorial # 9 - Product Curvature Analysis
8. Product Expansion During Extrusion Processing 107
8.1 The Product Expansion Process
8.2 Elastic Effects and Die Swell
8.3 Bubble Growth Theory and Bubble Structure
8.4 Process Control and Product Expansion
8.5 The Relative Effect of Temperature and Pressure upon the Product Expansion
Worked Example – Effect of Temperature and Pressure on Expansion
9. The Design & Operational Characteristics of Primary Dies 121
9.1 Transition Section
9.2 Breaker Plates
9.3 Insert Dies incorporating Primary Dies
9.4 Flared Die Plates
9.5 Modelling the Performance of a Primary Die
Tutorial # 10 - Design of a Primary Die
10. The General Extrusion Die Design Procedure 132
10.1 Simple Design for a Homologous Series
10.2 The General Design Procedure
Tutorial # 11 – Conductance Matching
Tutorial # 12 – Multi-Component Die Development
11. The Design & Performance of Pasta Dies 139
11.1 The Basics of Dies for Pasta Extrusion
11.2 Analysis of the Melt Velocity Profile
11.3 Process Effects during Pasta Extrusion
Tutorial # 13 – Analysis of the Flow through a Pasta Die
12. Die Plate Wear & Its Influence on Product Quality 158
12.1 Background
12.2 Die Plate Wear Mechanisms
12.3 The Die Plate Life Cycle
12.4 Extending the Operational Life of Extrusion Dies
13. Mechanical Considerations in Die Design 171
13.1 Material Selection for Extrusion Dies
13.2 Mechanical Stress Analysis of Die Plates
13.3 Attachment of the Die Assembly to the Extruder
13.4 Mechanical Failure of Extrusion Dies
14. Extruder Cutter Assemblies & Knife Design 181
14.1 Die Face Cutting
14.2 Post-Extrusion Cutting
14.3 Influence of the Cutter on Product Quality
14.4 Cutter System Design Calculations
14.5 Summary of Design Procedure
15. Post-Die Forming Operations 189
15.1 Twisted Profile Manufacture
15.2 Coiled Products
15.3 Sheeted Products
15.4 Dies for Two-Stage Shaping
16. Design of Dies for Specialty Applications 195
Part 1 – The Design of Dies for Co-Extrusion Technology
16.1 Considerations for Co–Extrusion Process Design
16.2 Process Instabilities
16.3 Process Design for Co-Extrusion Dies
Part 2 - Design of Long, Cooling Dies for High Moisture Extrusion Cooking
Part 3 - Design of End-Fed Sheet Forming Dies
Part 4 – The Design of Monolith Dies
Tutorial # 14 – Design of a Monolith Die for a 3G Snack Pellet
17. Obtaining Rheological Data from Extruders 215
17.1 Introduction and Background
17.2 Equipment Required & Applying the Method
18. Use of Dimensional Analysis in the Design and Evaluation of Extrusion Dies 227
18.1 Introduction
18.2 Primary and Secondary Criteria
18.3 The Buckingham π Theorem
18.4 The use of Dimensional Analysis for the Study of Extrusion Dies
Tutorial # 15 - Application of the Resistance Factor Method
18.5 The Scale-up of Extrusion Dies
Appendix 1 – The Golden Rules of Die Design 243
Conductance Calculations for Multiple Die Assemblies
Appendix 2 – The Four Golden Rules of Extrusion Technology 245
Appendix 3 - Recommendations for the Manufacture of Extrusion Dies 247
Appendix 4 – Conductance Equations 251
Appendix 5 – Miscellaneous Data for Die Design 253
Appendix 6 – Worked Solutions for the Tutorials 255
Tutorial # 1 – Elastic Phenomena
Tutorial # 2 - Basic Die Conductance Calculations
Tutorial # 3 – Equivalent Die Conductance Calculations
Tutorial # 4 – Machining Accuracy
Tutorial # 5 – Conductance vs. Open Area
Tutorial # 6 – Entrance Effects
Tutorial # 7 – The Bagley Entrance Correction
Tutorial # 8 – The Cone Angle Effect
Tutorial # 9 – Product Curvature
Tutorial # 10 – The Design of a Primary Die
Tutorial # 11 – Conductance Matching
Tutorial # 12 – Multi-Component Die Development
Tutorial # 13 – Analysis of the Flow through a Pasta Die
Tutorial # 14 – Design of a Monolith Die for a 3G Snack Pellet
Tutorial # 15 – Die Pressure Drop [Resistance Factor]
Nomenclature & Symbols 299
Technical References 309