كتاب Rotational Molding Technology

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Rotational Molding Technology
Roy J. Crawford
The Queen’s University of Belfast
Belfast, Northern Ireland
James L. Throne
Sherwood Technologies, Inc.
Hinckley, Ohio

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Contents
Preface . V
About the Authors . Ix
1. Introduction to Rotational Molding 1
1.0 Introduction . 1
1.1 the Process 2
1.2 the Early Days . 4
1.3 Materials . 6
1.4 Advantages and Disadvantages 9
1.5 General Relationships Between Processing Conditions
And Properties 11
References . 14
2. Rotational Molding Polymers . 19
2.0 Introduction . 19
2.1 General Characteristics of Polymers 19
2.2 Polymers as Powders and Liquids . 21
2.3 Polyethylene Types 22
2.3.1 Low-density Polyethylene . 22
2.3.2 Medium-density Polyethylene . 23
2.3.3 High-density Polyethylene 24
2.3.4 Linear Low-density Polyethylene 25
2.3.5 Ethylene Vinyl Acetate 27xii Contents
2.4 Polypropylene . 28
2.5 Pvc – Plastisols, Drysols, and Powdered Flexible
Compounds 30
2.6 Nylons . 31
2.7 Other Polymers . 33
2.7.1 Polycarbonate . 33
2.7.2 Cellulosics . 34
2.7.3 Acrylics . 35
2.7.4 Styrenics . 35
2.8 Liquid Polymers 36
2.8.1 Pvc Plastisols 38
2.8.2 Polycaprolactam . 39
2.8.3 Polyurethane . 41
2.8.4 Unsaturated Polyester Resin . 42
2.8.5 Silicones . 43
2.9 in-coming Material Evaluation . 43
2.9.1 Melt Index and Melt Flow Index . 44
2.9.2 Sieving 46
2.10 Product Testing Protocols and Relationship to Polymer
Characteristics 47
2.10.1 Actual Part Testing – Protocol . 47
2.10.2 Actual Part Testing – Entire Parts . 49
2.10.3 Actual Part Testing – Sections 50
2.10.3.1 Molded Part Density . 51
2.10.3.2 Drop Tests 51
2.10.3.3 Astm Tests for Mechanical
Properties . 54
2.10.3.4 Color . 55
2.10.3.5 Chemical Tests 56
2.10.3.6 Environmental Stress Crack Test . 57contents
2.10.3.7 Chemical Crosslinking and the
Refluxing Hexane Test . 58
2.10.3.8 Weathering . 61
2.10.3.9 Odor in Plastics 62
2.10.3.10 Fire Retardancy 62
2.11 Desirable Characteristics of a Rotational Molding
Resin . 64
References . 65
3. Grinding and Coloring 69
3.0 Introduction . 69
3.1 General Issues Relating to Grinding 73
3.2 Particle Size Distribution . 75
3.2.1 Particle Size Analysis 77
3.2.1.1 Dry Sieves 77
3.2.1.2 Elutriation . 78
3.2.1.3 Streaming . 78
3.2.1.4 Sedimentation 78
3.2.1.5 Fluidization . 79
3.2.2 Presentation of Psd Data . 79
3.3 Particle Shape 81
3.4 Dry Flow 83
3.5 Bulk Density 84
3.5.1 Packing of Particles . 85
3.6 Factors Affecting Powder Quality . 88
3.6.1 Gap Size . 89
3.6.2 Number of Mill Teeth . 90
3.6.3 Grinding Temperature . 90
3.7 Grinding Costs 91
3.8 Micropelletizing . 93xiv Contents
3.9 Polyvinyl Chloride . 96
3.10 Coloring of Plastics for Rotational Molding 96
3.10.1 Dry Blending . 97
3.10.2 High Speed Mixing (Turbo Blending) . 99
3.10.3 Compounding 101
3.10.4 Types of Pigments 101
3.10.5 Aesthetics of Rotationally Molded Parts 104
3.10.6 Other Types of Additives . 105
References . 108
4. Rotational Molding Machines 111
4.0 Introduction . 111
4.1 Types of Rotational Molding Machines 112
4.1.1 Rock-and-roll Machines . 113
4.1.2 Clamshell Machines 115
4.1.3 Vertical Machines 116
4.1.4 Shuttle Machines 116
4.1.5 Fixed-arm Carousel Machine 117
4.1.6 Independent-arm Machine 118
4.1.7 Oil Jacketed Machines 119
4.1.8 Electrically Heated Machines 120
4.1.9 Other Types of Machines 121
4.2 Machine Design Considerations 122
4.2.1 Mold Swing . 122
4.2.2 Mold Speed . 125
4.2.3 Speed Ratio 126
4.3 the Oven 127
4.3.1 Oven Design . 129
4.3.2 Heat Transfer in Oven . 131
4.3.3 Oven Air Flow Amplification 135contents
4.4 Cooling 137
4.5 Process Monitors 138
4.5.1 Internal Air Temperature Measurement in
Rotational Molding 140
4.5.2 Infrared Temperature Sensors 144
4.6 Servicing . 144
4.7 Advanced Machine Design . 145
References . 147
5. Mold Design . 149
5.0 Introduction . 149
5.1 Mold Materials 151
5.1.1 Sheet Steel . 151
5.1.2 Aluminum 152
5.1.3 Electroformed Nickel . 154
5.2 Mechanical and Thermal Characteristics of Mold
Materials . 156
5.2.1 Equivalent Mechanical Thickness . 156
5.2.2 Equivalent Static Thermal Thickness 157
5.2.3 Equivalent Transient Thermal Thickness . 159
5.3 Mold Design 160
5.3.1 Parting Line Design . 161
5.3.1.1 Butt or Flat 161
5.3.1.2 Lap Joint . 162
5.3.1.3 Tongue-and-groove . 162
5.3.1.4 Gaskets 163
5.3.2 Mold Frame . 165
5.3.3 Clamping . 166
5.3.4 Pry Points . 167xvi Contents
5.3.5 Inserts and Other Mechanical Fastening
Methods 168
5.3.5.1 Self-tapping Screws . 168
5.3.5.2 Mechanical Fastening 169
5.3.5.3 Postmolded Insert 169
5.3.5.4 Molded-in Insert . 169
5.3.6 Threads . 171
5.3.7 Cut-out Areas 172
5.3.8 Kiss-offs 172
5.3.9 Molded-in Handles 173
5.3.10 Temporary Inserts . 173
5.4 Calculation of Charge Weight . 174
5.4.1 Methodology . 174
5.4.2 Maximum Part Wall Thickness for a Given
Mold 180
5.5 Venting 183
5.5.1 Simple Estimate for Vent Size . 186
5.5.2 Types of Vent 193
5.5.3 is a Vent Necessary? 195
5.6 Mold Surface Finish 196
5.7 Mold Releases 196
5.7.1 Spray-on Zinc Stearates . 197
5.7.2 Silicones . 197
5.7.3 Disiloxanes . 197
5.7.4 Fluoropolymers . 197
5.7.5 Mold Surfaces to Be Coated 198
5.7.6 Controlled Release 199
5.7.7 Mold Release Cost 199
References . 200contents
6. Processing . 201
6.0 Introduction to Heating . 201
6.1 General Anatomy of the Rotational Molding Cycle 201
6.2 General Process Description 204
6.3 Powder Behavior 205
6.4 Characteristics of Powder Flow 207
6.5 Rheology of Powder Flow 210
6.6 Heat Transfer Concepts Applied to Rotational Molding . 213
6.7 Heating the Mold . 213
6.8 Heating Powder 215
6.8.1 Transient Heating of an Individual Particle 215
6.8.2 Heating the Powder Bed . 217
6.9 Tack Temperature 219
6.10 Mold Cavity Air Heating Prior to Powder Adhesion to
Mold Surface . 221
6.11 Bed Depletion . 222
6.12 Particle Coalescence 223
6.13 Densification . 234
6.14 Phase Change During Heating 243
6.15 the Role of Pressure and Vacuum 244
6.16 Mathematical Modeling of the Heating Process 245
6.17 Total Oven Cycle Time . 251
6.18 Cooling and the Optimum Time for Removal From
Oven . 259
6.19 Some Comments on Heat Transfer During Cooling 259
6.20 Thermal Profile Inversion 262
6.21 Cooling and Recrystallization 266
6.22 Air Cooling – Heat Removal Rate 274
6.23 Water Cooling – Heat Removal Rate . 275
6.24 Pressurization . 276
6.25 Part Removal 276
6.26 Effect of Wall Thickness on Cooling Cycle Time . 277
6.27 Overview and Summary of Thermal Aspects of the
Rotational Molding Process 278
6.28 Introduction to Liquid Rotational Molding . 278
6.29 Liquid Polymers 278
6.30 Liquid Rotational Molding Process . 279
6.30.1 Liquid Circulating Pool 280
6.30.2 Cascading Flow 281
6.30.3 Rimming Flow . 281
6.30.4 Solid Body Rotation . 281
6.30.5 Hydrocyst Formation . 282
6.30.6 Bubble Entrainment . 284
6.30.7 Localized Pooling 285
6.31 Process Controls for Liquid Rotational Molding . 285
6.32 Foam Processing 287
6.32.1 Chemical Blowing Agent Technology 288
6.32.2 Single Layer Vs. Multiple Layer Foam
Structures . 295
6.32.2.1 One-step Process 295
6.32.2.2 Two-step Process 296
6.32.2.3 Drop Boxes – Inside or Out? 297
6.32.2.4 Containerizing Inner Layers . 298
References . 299
7. Mechanical Part Design 307
7.0 Introduction . 307
7.1 Design Philosophy 307
7.2 General Design Concepts 310
7.3 Mechanical Design . 314
7.3.1 Three-point Flexural Beam Loading 315
7.3.2 Cantilever Beam Loading 316
7.3.3 Column Bending 317
7.3.4 Plate Edge Loading . 318
7.3.5 Hollow Beam With Kiss-off Loading 318
7.3.6 Creep 322
7.3.7 Temperature-dependent Properties 323
7.4 Design Properties of Foams . 324
7.4.1 Uniform Density Foams . 324
7.4.2 Multilayer or Skin-core Foams 329
7.5 Computer-aided Engineering in Rotational Molding 330
7.5.1 Cad/cam in Rotational Molding . 332
7.5.2 Computer-aided Stress Analysis . 332
7.6 Some General Design Considerations . 335
7.6.1 Uniformity in Wall Thickness . 336
7.6.2 Shrinkage During Cooling . 337
7.6.3 General Shrinkage Guidelines 339
7.6.4 Effect of Pressurization . 340
7.6.5 Draft Angles and Corner Angles 341
7.6.6 Warpage Guidelines 344
7.6.7 Corner Radii – the Michelin Man 345
7.6.7.1 Right-angled Corners . 345
7.6.7.2 Acute-angled Corners 346
7.6.8 Parallel Walls 348
7.6.9 Spacing and Bridging 348
7.6.10 Internal Threads, External Threads, Inserts,
And Holes 349
7.7 Process Effects on Porosity, Impact Strength 350
7.8 Trimming . 354xx Contents
7.9 Surface Decoration . 357
7.9.1 Painting . 358
7.9.2 Hot Stamping 358
7.9.3 Adhesives . 358
7.9.4 in-mold Decoration 359
7.9.5 Postmold Decoration . 359
7.9.6 Internal Chemical Treatment . 359
7.10 Troubleshooting and Quality Assurance 360
7.10.1 Coordinate Measuring Machine . 360
References . 362
Appendices . 367
Appendix a. Troubleshooting Guide for Rotational Molding 367
Appendix B. Conversion Table . 375
Author Index . 379
Index

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كتاب Rotational Molding Technology 761752

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طريقة التنزيل من المنتدى خطوة بخطوة

الهارد الشامل والمتكامل لقسم ميكانيكا

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