A Practical Approach to Scientific Molding

by Gary F. Schiller

Overview

This easy-to-understand guide provides the necessary information to implement a scientific molding program. It is a hands-on reference for people on the molding floor, including those previously lacking theoretical background or formal education.

The book covers how the injection molding machine prepares the plastic and understanding of plastic flow. The functions of the main machine components are explained and understanding of correct procedures and testing is developed. Each step of the process is clearly explained in a step-by-step manner, and simple examples of important calculations are provided. The practical approach is augmented by useful guides for troubleshooting and machine set-up.

An Excel spreadsheet with a process test and a machine performance test is available as bonus material.

Product Details

ISBN-13:	9781569906880
Publisher:	Hanser Publications
Publication date:	05/01/2018
Sold by:	Barnes & Noble
Format:	eBook
Pages:	190
File size:	9 MB

About the Author

Gary Schiller is a Certified Master Molder I, II, & III with 35 years of experience in the plastics industry, including as an instructor for RJG. He is an Advisory Board member for the American Injection Molding Institute.

Table of Contents

Preface v

About the Author vii

1 Injection Unit: Screw 1

1.1 Prepares the Melt 1

1.2 Flows the Melt 2

1.3 Pressurizes the Melt 3

1.4 Sections of the Screw 3

1.4.1 Feed Zone 3

1.4.2 Transition or Compression Zone 4

1.4.3 Metering Zone 4

1.5 L/D or Length/Diameter 4

1.6 Compression Ratio 4

1.7 Profile 6

1.8 Injection Pressure 6

1.9 Injection High Limit Fill Time 7

1.10 Injection Pack Pressure/Time 7

1.11 Injection Hold Pressure/Time 7

1.12 Non-return Valve Function 8

1.13 Different Styles of Non-return Valves 9

1.14 Decompression/Pull Back/Suck Back 10

1.15 Screw Rotate Delay 10

1.16 Mixing Head on a Reciprocating Screw 11

1.17 Barrier Screws 11

2 Injection Unit: Barrel 13

2.1 Barrel 13

2.2 Thermocouples 14

2.3 Heater Bands 17

2.4 Spacing of Heater Bands 19

2.5 Wattage 19

2.6 Worn Barrel 20

2.7 Feed Throat 21

2.8 Venting of the Barrel 21

2.9 Hopper 22

2.10 Hopper Dryer Diagram 23

2.11 Filter Packs/Dispersion Disks/Screen Packs 24

3 Clamping Unit 27

3.1 Hydraulic 27

3.2 Toggle 28

3.3 Weakness 28

3.4 Tie-Bar-Less 28

3.5 Single Point 29

3.6 Platen Wrap 30

3.7 Mold Coverage Area 31

3.8 Cleanliness of the Platens 31

3.9 Care of Bolt Holes 32

3.10 Proper Bolt Location 33

3.11 Weight of Mold Calculations 34

3.12 Mold Height 35

3.13 Calculating Clamp Tonnage for a Press 35

4 Ejectors/Controllers, Human Machine Interface (HMI) 37

4.3 Ejector Pattern and Spacing 37

4.2 Ejector Spacing 37

4.3 Controllers 40

4.3.1 Open Loop 40

4.3.2 Closed Loop 40

4.4 Key Pads 41

5 Machine Performance Testing 43

5.1 Rear Barrel Zone Optimization 43

5.2 Load Sensitivity 44

5.2.1 Purge Disk 45

5.3 Pressure Response 46

5.4 Dynamic Non-return Valve Test (FILL) 48

5.5 Static Non-return Valve Test (PACK/HOLD) 49

5.6 Injection Speed Linearity 50

6 Process Development Test 53

6.1 Tonnage Calculation/Projected Area 53

6.2 On Machine Rheology Curve (Viscosity Carve) or Fill Time Study 56

6.3 Construction of Viscosity Curve Graph 57

6.4 Least Pressure Curve 60

6.5 Plastic Flow Rate (Qp) 60

6.6 Shear Rates 60

6.7 Gate Freeze, Gate Seal, or Gate Stabilization 64

6.8 Runner Weight Study 67

6.9 Range Finding for Gate Seal 68

6.10 Manifold Imbalance and Balance of Fill Analysis 68

6.11 Cooling Optimization Study 70

6.12 Pressure Loss Study 71

7 Plastic Temperature 73

7.1 Molecular Structure of Common Materials 73

7.2 Morphology 74

7.2.1 Amorphous Resin Morphology 74

7.2.2 Semi-Crystalline Resin Morphology 74

7.3 Glass Transition Temperature (Tg) 75

7.4 Melt Transition Temperature (Tm) 75

7.5 Shrinkage 76

7.5.1 Isotropic Shrinkage 76

7.5.2 Anisotropic Shrinkage 77

7.6 Melt Density versus Solid Density 78

7.7 Advantages/Disadvantages of Hot Runner versus Cold Runner 79

7.8 Induced Shear through a Hot or Cold Runner System 80

8 Plastic Flow 81

8.1 Fountain Flow 81

8.2 Flow of Plastic 82

8.3 How to Calculate Flow Rate (Op) 82

8.4 Calculating Volume of Shot Size 83

8.5 Blocking a Cavity 84

8.6 Flow through a Mold 85

8.7 Orientation 85

8.8 Transfer/Cut-Off Position 86

8.9 Viscosity Changes 86

8.10 Intensifying Ratio (Ri) 87

8.11 Pressure Limited Process 88

8.12 Safe Start-Up Shot Size 89

8.13 Runner Sizing 91

9 Plastic Pressure Pack/Hold 93

9.1 Plastic Pressure 93

9.2 Dynamic versus Static 93

9.3 Viscosity Changes 93

9.4 End of Cavity Pressure Loss 94

9.5 Part Shrinkage versus Cavity Pressure 94

9.6 Maximum Average Pressure at Parting Line before Flashing 95

10 Cooling 99

10.1 Plastic Cooling 99

10.2 Turbulent versus Laminar Flow 99

10.3 Reynolds Number 101

10.4 Water Lines 102

10.5 Area of Water Line 103

10.6 Series/Parallel 103

10.7 Cooling Rate 105

10.8 Ineffective Cooling 106

10.9 Cooling Time 106

10.10 Depth, Diameter, and Pitch 106

10.11 Baffles/Bubblers 108

10.12 How a Thermolator/Mold Heater Works 108

11 Benchmarking the Injection Molding Process 111

12 Process Troubleshooting 115

12.1 Black Specks 115

12.2 Blush 117

12.3 Brittleness 118

12.4 Burns 119

12.5 Burns in Gates 121

12.6 Cloudy Parts 121

12.7 Color Streaks 122

12.8 Deformation: Ejector Pin Marks 123

12.9 Degraded Polymer 124

12.10 Design 124

12.11 Fish Hooks 125

12.12 Flash 126

12.13 Flow Lines 128

12.14 Hot Tip Drool 129

12.15 Jetting 130

12.16 Long Gates 131

12.17 Nozzle Drool 133

12.18 Parts Sticking in Mold 133

12.19 Pulls 134

12.20 Shorts/Non-Fills 134

12.21 Sinks 135

12.22 Splay 137

12.23 Sprue Sticking 138

12.24 Surface Imperfections 139

12.25 Voids 140

12.26 Warpage 141

12.27 Weld Lines 143

13 What is Important on a Set-Up Sheet? 145

14 Commonly Used Conversion Factors and Formulas 149

14.1 Conversion Factors 149

14.2 Common Formulas for Injection Molding 150

15 Machine Set-Up 153

16 Things That Hurt the Bottom Line of a Company 157

17 Terms and Definitions 159

18 Reference List for Further Courses and Reading 173

18.1 Courses 173

18.2 Reading 173

Index 175