Scientific Molding Pocket Guide
Scientific Molding Pocket Guide
Fourth Edition
Routsis Training
Hands-on. Online. Ongoing
Contents
• Understanding Plastics
• Plastic Materials Overview
• Properties, Additives & Preparation
• Establishing a Scientific Molding Process
• Seven Steps to Scientific Troubleshooting
• Molded Part Defects
• Purging Materials and Techniques
• Basic Mold & Part Design Guidelines
• Units and Conversions
• Frequently Used Calculations
• The Importance of Training
1 Understanding Plastics
1.1 General Classification of Polymers 1
1.1.1 Thermoplastics vs. Thermosets 1
1.1.2 Amorphous vs. Semi-Crystalline 1
1.2 Hygroscopic vs. Non-Hygroscopic 2
1.3 Understanding Variability in Plastics Processing 2
1.4 Understanding Viscosity 3
1.4.1 Capillary Rheometry 3
1.4.2 Melt Flow Index 4
1.4.3 Spiral Flow Test 4
1.4.4 In-Mold Rheology 5
2 Plastic Materials Overview
2.1 Table of Plastic Material Properties 6
2.2 General Information About Common Materials 8
2.2.1 ABS (Acrylonitrile Butadiene Styrene) 8
2.2.2 Acetal or POM (Polyoxymethylene) 8
2.2.3 Acrylic or PMMA (Polymethyl Methacrylate) 8
2.2.4 CPVC (Chlorinated Polyvinylchloride) 9
2.2.5 HDPE (High Density Polyethylene) 9
2.2.6 HIPS (High Impact Polystyrene) 9
2.2.7 Ionomer 10
2.2.8 LDPE (Low Density Polyethylene) 10
2.2.9 LLDPE (Linear Low Density Polyethylene) 10
2.2.10 PA-11 (Nylon-11) 11
2.2.11 PA-12 (Nylon-12) 11
2.2.12 PA-4/6 (Nylon-4/6) 11
2.2.13 PA-6 (Nylon-6) 12
2.2.14 PA-6/10 (Nylon-6/10) 12
2.2.15 PA-6/12 (Nylon-6/12) 12
2.2.16 PA-6/6 (Nylon-6/6) 13
2.2.17 PAEK (Polyaryletherketone) 13
2.2.18 PBT (Polybutylene Terephthalate) 13
2.2.19 PC (Polycarbonate) 14ii
2.2.20 PC/ABS (PC/ABS Alloy) 14
2.2.21 PC/PET (PC/PET Alloy) 14
2.2.22 PEEK (Polyetheretherketone) 15
2.2.23 PEI (Polyetherimide) 15
2.2.24 PES (Polyethersulfone) 15
2.2.25 PET (Polyethylene Terepthalate) 16
2.2.26 PETG (Polyethylene Terepthalate Glycol) 16
2.2.27 PP (Polypropylene) 16
2.2.28 PPO (Polyphenylene Oxide) 17
2.2.29 PS (Polystyrene) 17
2.2.30 PVC (Polyvinylchloride) 17
2.2.31 SAN (Styrene Acrylonitrile) 18
2.2.32 TPC-ET (Thermoplastic Copolyester Elastomers) 18
2.2.33 TPE (Thermoplastic Elastomer) 18
2.2.34 TPO (Thermoplastic Polyolefin) 19
2.2.35 PPS (Polyphenylene Sulfide) 19
2.2.36 PSU (Polysulfone) 19
2.2.37 PUR (Polyurethane) 20
3 Properties, Additives & Preparation
3.1 Common Fillers and Fibers 21
3.2 Heat Resistance 24
3.3 Hardness 25
3.4 Burn Characteristics 26
3.5 Feed Zone Temperature Study 26
4 Establishing a Scientific Molding Process
4.1 1st Stage Filling 27
4.2 1st Stage to 2nd Stage Transfer 27
4.3 2nd Stage Pack 27
4.4 Screw Delay or Decompression before Recovery 28
4.5 Screw Recovery 28
4.6 Screw Decompression after Recovery 28
4.7 Cooling 28iii
Table of Contents
5 Seven Steps to Scientific Troubleshooting
5.1 STEP 1: Develop a Scientific Molding Process 29
5.1.1 1st Stage Injection 29
5.1.2 1st to 2nd Stage Transfer 29
5.1.3 2nd Stage Packing Pressure 29
5.1.4 2nd Stage Time 29
5.1.5 Screw Delay or Decompression before Recovery 29
5.1.6 Screw Recovery 29
5.1.7 Screw Decompression after Recovery 29
5.2 STEP 2: Properly Document the Process Outputs 30
5.3 STEP 3: Examine Defective Part and Rule-Out Obvious Causes 30
5.4 STEP 4: Compare Current Process with Documented Process 31
5.5 STEP 5: Return the Process to the Documented Standard 31
5.6 STEP 6: Verify the Part and Process 32
5.7 STEP 7: Document All Changes Made 32
6 Defects
6.1 Visual Defects 33
6.1.1 Flash 33
6.1.2 Sinks and Voids 33
6.1.3 Short Shots 34
6.1.4 Jetting 34
6.1.5 Gate Blush 34
6.1.6 Burning 35
6.1.7 Flow Lines 35
6.1.8 Weld and Meld Lines 35
6.1.9 Poor Surface Finish 36
6.2 Dimensional Defects 37
6.2.1 Large Dimensions Overall 37
6.2.2 Small Dimensions Overall 37
6.2.3 Larger Parts at the Gate 38
6.2.4 Smaller Parts at the Gate 38
6.2.5 Warpage 38
6.3 Material Defects 39
6.3.1 Splay, Bubbles, and Blisters 39
6.3.2 Brittleness, Cracking, and Crazing 40
6.3.3 Delamination 41iv
6.3.4 Contamination 41
6.3.5 Poor Color Distribution 42
6.4 Cycling Problems 42
6.4.1 Part Sticking and Ejector Pin Marks 42
6.4.2 Occasional Part Hang-Up 43
6.4.3 Nozzle Freeze-Off 43
6.4.4 Drool and Stringing 44
6.5 Molded Part Defects Troubleshooting Chart 46
7 Purging Materials and Techniques
7.1 Purpose of Purging 48
7.2 Purging Materials 48
7.2.1 Resin-Based Purging Compounds 48
7.2.2 Mechanical Purging Compounds 49
7.2.3 Chemical Purging Compounds 49
7.3 The Four Phases of Purging 50
7.4 Purging Techniques 51
7.4.1 Large Shot Purging 51
7.4.2 Small Shot Purging 51
7.4.3 Continuous Purging 51
7.4.4 Closed Mold Purging 51
7.4.5 Dry Purging 51
7.4.6 Wet Purging 51
8 Basic Mold & Part Design Guidelines
8.1 Uniform Wall Thickness 52
8.2 Corner Radii 53
8.3 Ribs and Gussets 53
8.4 Draft Angle 53
8.5 Undercuts 53
8.6 Surface Finish 53
8.7 Tool Steels 56
8.8 Basic Heat Treatment 59
8.9 Common Surface Treatments 59
8.10 Common Surface Coatings 60
8.11 Wear Considerations 60
8.12 Porous Metals 61v
Table of Contents
9 Units and Conversions
9.1 Time 62
9.2 Rotation 63
9.3 Temperature 63
9.4 Length 64
9.5 Speed 64
9.6 Area 65
9.7 Volume 65
9.8 Volumetric Flow Rate 66
9.9 Mass 66
9.10 Mass Flow Rate 67
9.11 Pressure 67
9.12 Tonnage 68
9.13 Common Conversion Tables 68
10 Frequently Used Calculations
10.1 Intensification Ratio 71
10.1.1 Machine Pressure Graph Method 71
10.1.2 Machine Specifications Method 71
10.1.3 Hydraulic Cylinder Method 72
10.2 Drying Calculations 72
10.2.1 Material Consumption 72
10.2.2 Dryer Residence Time 73
10.2.3 Dryer Capacity 73
10.3 Part Shrinkage 74
10.4 Tolerances 74
10.5 Chiller Requirements 75
10.5.1 Cooling Time 75
10.5.2 Total Amount of Heat to be Removed 75
10.5.3 Required Cooling Power 75
10.5.4 Cooling Power Per Line 76
10.5.5 Required Volumetric Flow Rate 76
10.6 Determining Screw and Barrel Wear 76
10.7 Barrel Residence Time 77vi
11 The Importance of Training
11.1 Training and the Plastics Industry 79
11.2 Success Factors for Employee Training 80
11.3 Available Training Options 80
11.3.1 Printed Materials 80
11.3.2 Video Training 80
11.3.3 Seminars 81
11.3.4 Online Training 81
11.3.5 On-the-Job Training 81
11.4 Structured In-House Training 82
11.5 Training Room Setup 82
11.6 Program Implementation
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