Practical Guide to Rubber Injection Moulding

Practical Guide to Rubber Injection Moulding
John A. Lindsay
Contents
Preface ix
1 Market Leader: Introduction . 1
1.1 Perfection of the Process 1
1.2 Historical Background . 1
1.2.1 Practical Considerations 2
Reference . 4
2 Setting the Parameters: Initial Stages . 5
2.1 The Quality System . 5
2.2 Shape . 5
2.3 Polymer Compatibility . 5
2.4 Production Volume 6
2.5 Start of Production 6
2.6 Component Design 6
2.6.1 The Enquiry Stage . 6
2.6.2 Finalising the Component Shape . 7
2.6.3 Compound Design 7
2.6.3.1 Oils and Solvents 7
2.6.3.2 Gases 8
2.6.3.3 Water 8
2.6.3.4 Temperature . 8
2.6.4 Engineering Requirements . 8
2.6.4.1 Resilience or Damping 8
2.6.4.2 Fatigue Resistance 9
References . 9
Contents iv
Practical Guide to Rubber Injection Moulding
3 The Rubber Compound . 11
3.1 Specification 11
3.2 Selection of Polymer 11
3.3 Hardness or Modulus 12
3.4 Compound Design and Cost 12
3.5 Factors that Adversely Affect Processing 12
3.5.1 Scorch . 12
3.5.2 Effect of Temperature 14
3.5.3 Compound Viscosity . 15
3.5.4 Moisture . 18
3.5.5 Gel 18
3.6 Mixing . 18
3.6.1 Weighing of Ingredients . 18
3.6.2 Mixing Cycles . 19
3.7 Compounding Ingredients . 20
3.7.1 Polymers . 20
3.7.1.1 Natural Rubber . 20
3.7.1.2 Synthetic Polymers . 21
3.7.1.3 Peptisers 21
3.7.1.4 Zinc Oxide 21
3.7.1.5 Stearic Acid and Activation . 22
3.7.1.6 Fillers . 22
3.7.1.7 Process Aids . 23
3.7.1.8 Process Oils . 23
3.7.1.9 Accelerators . 23
3.7.1.10 Sulfur . 24
3.7.1.11 Anti-ozonants 24
3.7.1.12 Masterbatching of Compounds . 24
3.7.2 Characterisation of Materials 24
3.7.3 Example Compound Formulations . 24
3.8 Stock Presentation . 25
3.9 Storage of Uncured Rubber . 26
References . 26v
Contents
4 The Injection Machine . 27
4.1 The Parts to Understand 27
4.2 The Pre-plasticising and Injection Unit 27
4.3 The Press Unit . 31
4.3.1 Horizontal or Vertical Opening? . 32
4.3.2 Hydraulic or Toggle Clamp? . 32
4.4 Hydraulic Power 33
4.4.1 Oil Cooling . 33
4.4.2 Clean Oil 33
4.5 Heating and Cooling . 34
4.5.1 Platen Heating 34
4.5.2 Cavity Temperature . 35
4.6 Control Systems . 35
Reference . 36
5 Mould Design 37
5.1 Sizing of Moulds 37
5.2 Runner System . 38
5.2.1 The Sprue Bush . 40
5.2.2 Injection Gates 40
5.3 Air Removal 41
5.4 Modelling Software . 42
5.5 Ejector Systems 42
5.6 Flashless Mouldings . 42
5.7 Mould Monitoring Points 43
5.8 Mould Materials 43
References . 45
6 Moulding 47
6.1 Purging 47
6.2 Single Cavity Tools 48
6.3 Initial Process Set-up 48
6.4 Problem Solving . 51vi
Practical Guide to Rubber Injection Moulding
6.4.1 Recognition . 51
6.4.2 Classifying the Fault 51
6.4.3 Identifying Causes . 51
7 Mould Fouling, Cleaning and Management 55
7.1 Mould Management 57
7.2 Platen Condition 57
8 Mould Release Agents . 59
8.1 Sacrificial Mould Release Agents . 59
8.2 Internal Mould Release Agents 60
8.3 Semi-permanent Mould Release Agents . 60
8.4 Method of Application 60
9 Maintenance 63
9.1 Routine Matters 63
9.2 Routine Maintenance 64
9.3 New Job Start-up Procedures . 64
9.4 Reworking . 65
10 Bonding of Rubber to Substrates . 67
10.1 Introduction 67
10.2 Compound 67
10.2.1 Polymer . 67
10.2.2 Curing System . 68
10.2.3 Rubber Presentation at the Press . 68
10.3 Inserts 68
10.3.1 Condition 68
10.3.2 Metal Inserts . 68
10.3.3 Plastic Inserts 69
10.4 Insert Preparation 70
10.4.1 Solvent Degreasing 70
10.4.2 Aqueous Degreasing 71vii
Contents
10.5 Surface Preparation . 71
10.5.1 Grit Blasting 72
10.5.2 Wet Processes 73
10.6 Bonding Systems 73
10.6.1 Control of the Bonding Agent . 75
10.6.2 Application Methods 75
10.6.3 Storage and Handling of Prepared Inserts . 76
10.7 Moulding . 76
10.7.1 Preheating the Inserts 76
10.7.2 The injection Cycle . 77
Appendix 1 . 79
Appendix 2 . 85
Appendix 3 . 89
Appendix 4 . 93
Appendix 5 . 95
Appendix 6 . 97
Appendix 7 . 99
Appendix 8 . 101
Abbreviations 103
Index . 105
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