The Basics of Troubleshooting in Plastics Processing
Contents
1. Antioxidants Anti block Agents Antistatic Agent Clarifying Agents Slip Additives Processing Aids Antifogging Agents Antiblocking Agents Heat Stabilizers Lubricants Plasticizers Coupling Agents or Surface Modifiers Release Agents Flame Retardants Pigments Light Stabilizers Impact Modifiers Blowing Agents Nucleating Agents Biocides Fillers Fundamentals References 4 Plastics Processing 4 1 4 2 Focus on Plastics Processing Injection Molding 4 2 1 Injection Molding Machine 4 3 4 2 2 4 2 3 4 2 4 4 2 5 4 2 6 4 2 1 1 Ram Injection Molding Machine 4 2 1 2 Screw Injection Molding Machine Injection Unit 4 2 2 1 4 2 2 2 4 2 2 3 4 2 2 4 Mold 4 2 3 1 4 2 3 2 4 2 3 3 4 2 3 4 4 2 3 5 4 2 3 6 4 2 3 7 Injection Molding and Parameters 4 2 4 1 4 2 4 2 4 2 4 3 4 2 4 4 4 2 4 5 4 2 4 6 Injection Molding Processing Barrel Screw Clamping Unit Hydraulic Unit Gate Runner Sprue Cavity Nozzle Vent Ejection System Temperature Pressure Time Cooling Velocity Part Design Process Variables 4 2 6 1 4 2 6 2 Cushion Shot Size 4 2 7 Advantages 4 2 8 Shortcomings Extrusion 4 3 1 Extrusion Basic Requirements 4 3 2 Extruder 4 3 2 1 Single Screw Extruder 4 3 2 2 4 3 2 3 4 3 2 4 4 3 2 5 Twin Screw Extruder Feeder Screw Die 4 3 3 Polymer Melt 4 3 4 Extrudate Swell 4 3 5 Extrusion and Process Parameters viii CONTENTS 4 3 6 4 3 7 4 3 82. Demand for engineering plas tics will rise by 3 1 per year to reach 5 4 billion lbs by 2012 Polycarbonate nylon and ABS will continue to be the largest volume engineering plastics accounting for more than 75 of total demand by 2012 7 Polymer demand has been driven by high levels of invest ment particularly in packaging appliances consumer elec tronics and automotive 8 However in the modern global market quality is a key issue to remain competitive in busi ness Quality can no longer be simply the result of an inspection INTRODUCTION 3 process but very much part of the strategic planning process of successful companies 9 1 2 Importance of Plastics Plastics are increasingly important in the manufacture of materials due to their significant higher strength to weight ratio and stiffness as well as impact strength The main driv ers for the rapid increase in their use are low cost and the pos sibility of achieving total recyclability But the large scale and widespread use of plastics is due to its low density and ease of processing Plastics are macromolecules derived from monomers also called polymer The word poly meaning many and mer des ignating the nature of the repeat unit 10 11 Polymers are from synthetic or naturally occurring material which can be used with modification to suit with respect to processing The term polymer is these days known as plastics when referring to m
3. Extrusion Processing Advantages Shortcomings 4 4 Blow Molding 4 4 1 4 4 2 4 4 3 4 4 4 4 4 5 Blow Molding and Process Parameters Extrusion Blow Molding Injection Stretch Blow Molding Advantages Shortcomings 4 5 Thermoforming 4 5 1 4 5 2 4 5 3 4 5 4 4 5 5 Thermoforming and Parameters Processing Mold Advantages Shortcomings 4 6 Rotational Molding 4 6 1 4 6 2 4 6 3 4 6 4 4 6 5 4 6 6 Rotational Molding and Parameters Mold Processing Pigmentation Advantages Shortcomings 4 7 Fundamentals 4 7 1 4 7 2 4 7 3 4 7 4 4 7 5 References Injection Molding Extrusion Blow Molding Thermoforming Rotational Molding 5 Troubleshooting Problems and Solutions 5 1 Troubleshooting Requirements 5 2 Injection Molding Troubleshooting 5 2 1 ieee 5 2 3 5 2 4 5 29 5 2 6 Part Sticking in Cavities Part Sticking in Core Discoloration Burnt Marks Diesel Effect Part Sticks During Ejection Jetting 100 104 104 105 106 107 110 110 110 111 112 112 113 114 114 116 116 118 119 119 119 119 120 120 121 122 122 133 135 136 140 141 141 143 143 144 CONTENTS ix 5 2 7 Dimensions Out of Specification 144 5 2 8 Bubbles 146 5 2 9 Internal Voids 146 5 2 10 Flash Over Substrate or on Periphery of Part 147 5 2 11 Poor Weld Line 149 5 2 12 Low Gloss Gloss Difference 150 5 2 13 Overmold Breaks Impinges Through Hollow Substrate 151 5 2 14 Warpage or Wa
4. self lubricating and does not require any external lubrication during operation INTRODUCTION 5 Table 1 1 Materials properties comparison Wood Mechanical Better Good Poor Poor properties Chemical Good Better Poor Poor Properties Water resistance Corrosive 5 Shock and Good Better Poor Poor vibration resistance 6 Microbial resistance Good Poor Poor Poor Difficult 1 2 2 Plastics vs Paper and Paper Board Paper and paperboard are widely used as food packaging materials and have been used with a number of chemicals such as slimicides bleaching agents and inks during the production process Virgin paper and paperboard products produced by pulping bleaching and treatment processes undergo severe chemical treatment and it is impossible to eliminate the chemical residue present 15 17 Hence migra tion of chemicals from paper packaging to the food is quick resulting in toxicity to humans as being the main concern 1 3 Plastics Processing Plastics processing requires the knowledge fundamentals of the raw material additives process control and finally the product properties required to the finished end product Today polymer contains a package of ingredients to modify its properties while processing or at its end product stage to create a new one In thermoplastics processing techniques can be classi fied into either batch or continuous process Batch processes 6 THE BASICS OF TROUBLESHOOTING IN PLA
5. 1 Chemical Week 171 No 16 8th 15th June 2009 p 22 26 International Bottler and Packer 83 No 5 May 2009 p 12 13 McKeown P 1992 Implementing quality improvement pro grammes Robotics amp Computer Integrated Manufacturing Vol 9 No 4 5 pp 311 20 10 Mark H and Whitby G S eds Collected Papers of Wallace Hume Carothers on High Polymeric Substances John Wiley amp Sons New York 1940 Oo CON OD O1 11 12 13 14 15 16 17 INTRODUCTION 7 PJ Flory Principles of Polymer Chemistry Cornell University Press Ithaca NY 1953 H Staudinger From Organic Chemistry to Macromolecules John Wiley amp Sons New York 1970 H Staudinger Chem Ber 1924 57 1203 Throne J L Adv Polym Technol 1987 7 4 347 Nu ez A J Sturm P C Kenny J M Aranguren M I Marcovich N E Reboredo M M Mechanical characterization of polypropylene wood flour composites J Appl Polym Sci 2003 88 6 1420 8 Ozaki A Yamaguchi Y Fujita T Kuroda K Endo G Chemical analysis and genotoxicological safety assessment of paper and paper board used for food packaging Food and Chemical Toxicology 42 2004 1323 1337 Arvanitoyannis LS Bosnea L Migration of substances from food packaging materials to foods Crit Rev Food Sci Nutr 44 2004 63 76 Vitrac O Mougharbel A Feigenbaum A Interfacial mass transport properties which control the migration of packaging constitu
6. 6 5 Low Density Less Than Estimated 208 5 6 6 Poor Mold Filling 211 5 6 7 Poor Properties 211 5 6 8 Rough Inner Surface 211 5 6 9 Surface Pitting 213 5 6 10 Uneven Wall Thickness 213 5 6 11 Warpage 213 5 7 Fundamentals 215 References 215 6 Future Trends 217 6 1 Productivity 217 6 1 1 Reactive Approach 218 6 1 2 Proactive Approach 218 6 2 Automotive Applications 218 6 3 Medical Applications 219 6 4 Environmental Issues 219 6 5 Fundamentals 220 References 220 Index 221 This page intentionally left blank Preface Plastics processing is a core technology in major sectors of the plastics industry In spite of the growing importance of the field of plastics processing a clear and uniform practical guide covering the entire field of troubleshooting of plastics processing has not been presented until now The Basics of Troubleshooting in Plastics Processing An Introductory Practical Guide will appeal to all those who are involved in the plastics production sector The material in the book covers both fundamental and practical aspects of plas tics processing and attempts to provide the necessary back ground to understand the factors that constitute successful plastics manufacturing In an effort to mirror the goals of the plastics industry the scope of the book emphasizes the importance of the high quality production of end products processing while delib erately restricting coverage of machine details to the main processing t
7. Poor Gates Fish Eyes Flash Tails etc 185 5 4 2 2 Poor Gates 185 5 4 2 3 Rocker Bottoms 186 5 4 2 4 Incomplete Thread 186 5 4 2 5 Pig Tails 186 5 4 2 6 Short Shots 188 5 4 2 7 Parison Flashing 188 5 4 2 8 Neck Folds Shoulder Cuts 188 5 4 2 9 Plastic Sticking to Core Rods 188 5 5 Troubleshooting Thermoforming 191 5 5 1 Blisters or Bubbles 191 5 5 2 Incomplete Forming or Poor Detail 191 5 5 3 Sheet Scorched 191 5 5 4 Changing in Color Intensity or Blushing 191 5 5 5 Whitening of Sheet 192 5 5 6 Webbing Bridging or Wrinkling 192 5 5 7 Nipples on Mold Side of Formed Sheet 195 5 5 8 Too Much Sag 195 5 5 9 Sag Variation between Sheet Blanks 196 5 5 10 Chill Marks or Mark off Lines on Part 196 5 5 11 Bad Surface Marking 196 5 5 12 Shiny Streaks on Part 198 CONTENTS xi 5 5 13 Excessive Post Shrinkage or Distortion of Part Removing from the Mold 199 5 5 14 Part Warpage 200 5 5 15 Poor Wall Thickness or Excessive Thinning in Some Areas 201 5 5 16 Non Uniform Pre stretch Bubble 201 5 5 17 Shrink Marks on Part Especially in Corner Areas Inside Radius of Molds 202 5 5 18 Too Thin Corners in Deep Draws 204 5 5 19 Part Sticking to Mold 204 5 5 20 Sheet Sticking to Plug Assist 205 5 5 21 Tearing of Part When Forming 205 5 5 22 Cracking in Corners During Service 207 5 6 Troubleshooting Rotational molding 207 5 6 1 Bubbles on Outer Wall 207 5 6 2 Discolored Part 208 5 6 3 Flash Excessive 208 5 6 4 Long Oven Cycle 208 5
8. STICS PROCESSING include injection molding thermoforming and rotomolding Extrusion of plastics is a continuous process However blow molding is available both in batch and continuous process In these days online continuous thermoforming machines are available along with extrusion process As the scientific techniques become available the plastics processing is quickly incorporating the changes However new solutions pose new problems so these continue to be challenges to overcome Troubleshooting helps to solve the problem at the root and increase the production efficiency during processing 1 4 Fundamentals e Based on recyclability plastics can be divided into thermoplastics and thermosets Knowledge of properties with respect to plastics raw material or its end product is essential to establish the trouble free plastics processing References Plastics versus Food Contamination Corrosion Technology June 1965 2 Reilly J F Doyle M Kazmer D An assessment of dynamic feed control in modular tooling J Inject Mold Technol 5 1 2001 49 59 3 Takoungsakdakun T Pongstabodee S 2007 Separation of mixed post consumer PET POM PVC plastic waste using selective flotation Separation Purification Technology 54 2 248 252 4 Burat F G ney A and Olga Kangal M Waste Management 29 2009 1807 1813 Macplas International March 2009 p 20 Plastics and Rubber Weekly 28th May 2010 p 1
9. The Basics of Troubleshooting in Plastics Processing An Introductory Practical Guide Muralisrinivasan Natamai Subramanian IP Scrivener WILEY This page intentionally left blank The Basics of Troubleshooting in Plastics Processing Scrivener Publishing 3 Winter Street Suite 3 Salem MA 01970 Scrivener Publishing Collections Editors James E R Couper Ken Dragoon Richard Erdlac Rafiq Islam Pradip Khaladkar Vitthal Kulkarni Norman Lieberman Peter Martin W Kent Muhlbauer Andrew Y C Nee S A Sherif James G Speight Publishers at Scrivener Martin Scrivener martin scrivenerpublishing com Phillip Carmical pcarmical scrivenerpublishing com The Basics of Troubleshooting in Plastics Processing An Introductory Practical Guide Muralisrinivasan Natamai Subramanian IP Scrivener WILEY Copyright 2011 by Scrivener Publishing LLC All rights reserved Co published by John Wiley amp Sons Inc Hoboken New Jersey and Scrivener Publishing LLC Salem Massachusetts Published simultaneously in Canada No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording scanning or other wise except as permitted under Section 107 or 108 of the 1976 United States Copyright Act without either the prior written permission of the Publisher or authorization through payment of the appropriate per copy f
10. acromolecules like polypropylene polystyrene etc Plastics are constructed by the covalent linking of simple molecular repeated units 12 Plastics are composed of car bon nitrogen oxygen sulfur chlorine fluorine and silicon Moreover plastics are made from petrochemical products which are a rich source of methane ethylene aliphatic and aromatics Variations in the elements make the plastic into stiff or flexible linear or branched and hard or soft Plastics are classified based on recyclability into thermo plastics and thermosets Polyethylene PE polypropylene PP polyvinylchloride PVC etc are some of the thermo plastics and phenol formaldehyde urea formaldehyde etc are examples of the thermosets Both thermoplastics and ther mosetting materials may be molded and then cooled to obtain the end product Thermoset once molded cannot be either softened or reprocessed Thermosets lead to products which are not recyclable Moreover it will form a network and it can neither be melted 4 THe BASICS OF TROUBLESHOOTING IN PLASTICS PROCESSING nor reprocessed Once shaped it can be altered by post form ing operations if required Pre polymers are to be made before processing in thermoset processing However thermoplastics soften while heating and solidify during the cooling process Thermoplastics can be recycled by either direct heating or after grinding into granules of scrap products 13 Processing technology
11. echnologies These technologies are injection molding extrusion extrusion blow molding injection blow molding thermoforming and rotational molding By includ ing fairly comprehensive details of technical information and reference material this ensures the book is suitable for class room and industry training purposes without affecting its overall usefulness as a technical and reference work It will be very suitable for research workers engineers and operators in industry students in plastics processing as well as to all those seeking an introduction in plastics processing The framework of the book underscores both the book s academic and professional aspirations Thermoplastics mate rials and characteristics are discussed in Chapter 2 A useful introduction of additives is covered in Chapter 3 The plas tics processing techniques occupy Chapter 4 which also gives xiii xiv THE BASICS OF TROUBLESHOOTING IN PLASTICS PROCESSING information pertinent to troubleshooting Chapter 5 deals specifically with troubleshooting problems and solutions and elucidates the various control measures available in plas tics processing Chapter 6 briefly presents the future trends related to plastics My major objective in writing this book was to provide a thorough background in plastics processing which is par ticularly important in order to increase the productivity and reduce wastage Additionally I hope this book will help people to dev
12. ee to the Copyright Clearance Center Inc 222 Rosewood Drive Danvers MA 01923 978 750 8400 fax 978 750 4470 or on the web at www copyright com Requests to the Publisher for permission should be addressed to the Permissions Department John Wiley amp Sons Inc 111 River Street Hoboken NJ 07030 201 748 6011 fax 201 748 6008 or online at http www wiley com go permission Limit of Liability Disclaimer of Warranty While the publisher and author have used their best efforts in preparing this book they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives or written sales materials The advice and strategies contained herein may not be suitable for your situation You should consult with a professional where appropriate Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages including but not limited to special incidental consequential or other damages For general information on our other products and services or for technical support please contact our Customer Care Department within the United States at 800 762 2974 outside the United States at 317 572 3993 or fax 317 572 4002 Wiley also publishes its books in a variety of electronic formats S
13. elop the skills necessary to solve the problems in a stepwise manner I would like to thank Dr A Thamaraichelvan and Mr A N Sapthagireesan for their encouragement In addition special thanks are due to my wife and sons for their support Iam especially grateful to Mr Martin Scrivener and edito rial staff at Scrivener Publishing for an excellent and profes sional job Muralisrinivasan Natamai Subramanian November 2010 Introduction Plastics have become an integral part of our lives Plastics are an excellent and very useful material and they are func tional hygienic light and economical Using a key polymer processing system plastics produce diverse products used in packaging automotive and industrial applications and also extensively used in medical delivery systems artificial implants and other healthcare applications water desalina tion and removal of bacteria etc Until the 1930s and in early 1940s thermoplastics were not common material Ever since the first industrial scale produc tion of plastics synthetic polymers took place in the 1940s the production and consumption has increased consider ably Although plastic materials are relatively new they have become basic and indispensable in our life with different shapes sizes and applications that can be seen daily at home office and even on the street The growth in the manufacture of thermoplastic products for various applications has been considerab
14. ents into foodstuffs J Food Eng 79 2007 1048 1064 This page intentionally left blank Plastics Materials Plastics material undergoes different and complicated thermo mechanical processes It experiences significant change in rheological mechanical and transport properties due to large variations and rapid cooling The term polymer is preferred to resin when referring to a high molecular weight substance like polystyrene or polypropylene Plastics are e Made from chemical raw material composed of atoms of carbon in combination with other elements 1 2 called monomers which are basic materials including those made from coal alcohol natural gas and petroleum e Made up by the repeated addition of one or more types of monomeric units Plastics have progressed with invention efficiently and prod ucts can be manufactured economically But various plastics 9
15. ly increased 1 2 THE BASICS OF TROUBLESHOOTING IN PLASTICS PROCESSING It includes many light engineering applications The plastics materials usage for food packaging has obvious advantages associated with the non toxic nature of these materials and their resistance to chemical and biological degradation 1 1 1 Market Trends Today the requirements are constantly changing and rising to higher levels 2 The world s annual consumption of polymer materials has increased from around 5 million metric tons in the 1950s to nearly 100 million metric tons today 3 4 The worldwide demand for plastic pipes is forecast to increase 4 6 annually through 2012 to 8 2 billion meters or 18 2 mil lion tons Demand for HDPE polyethylene pipes will benefit from use as small diameter pipes in natural gas transmission as conduit for electrical and telecommunications applications and as corrugated pipes for drains and sewers 5 The US market for plastic healthcare packaging is expected to reach 3 8 billion pounds of products in 2010 This amount is forecast to increase to nearly 5 billion pounds in 2015 PP polypropylene packaging the largest segment of the market will reach 1 3 billion pounds in 2015 after increasing by 6 3 per annum from the estimated 2010 total of nearly 1 billion pounds 6 Global demand for PE the largest volume basic polymer is expected to grow about 4 2 per year to reach about 81 million metric tons by 2013
16. ome content that appears in print may not be available in electronic formats For more information about Wiley products visit our web site at www wiley com For more information about Scrivener products please visit www scrivenerpublishing com Cover design by Russell Richardson Library of Congress Cataloging in Publication Data ISBN 978 0 470 62606 1 Printed in the United States of America 30987654321 Contents Preface 1 Introduction 1 1 1 2 1 3 1 4 Market Trends Importance of Plastics 1 2 1 Plastics vs Metal 1 2 2 Plastics vs Paper and Paper Board Plastics Processing Fundamentals References 2 Plastics Materials 2 1 Properties and Processing 2 1 1 Molecular Weight 2 1 2 Molecular Weight Distribution MWD 2 1 3 Flow Properties 2 1 4 Degree of Crystallinity 2 1 5 Surface Quality 2 1 6 Viscosity Polyethylene Polypropylene PP Polystyrene Polyvinylchloride PVC Engineering Plastics 2 6 1 Acrylonitrile Butadiene Styrene ABS 2 6 2 Polymethylmethacrylate PMMA 2 6 3 Nylon 2 6 4 Polyethyleneterephthalate PET Vv ra jmi o pie jmi ADAJO WN vi CONTENTS 2 7 2 8 2 6 5 Polycarbonate PC 2 6 6 Polyether Ether Ketone PEEK 2 6 7 Polytetrafluoroethylene PTFE 2 6 8 Polyacetal POM 2 6 9 Polyvinylidene Fluoride PVDF 2 6 10 Polyphenylene Sulfide PPS Advantages Fundamentals References 3 Plastics Additives 3 16 3 17 3 18 3 19 3 20 3 21 3 22
17. rped Parts 152 5 2 15 Splay Marks Delamination 152 5 2 16 Flow Marks Folds and Back Fills 153 5 2 17 Ejector Pin Marks 155 5 2 18 Sink Marks 155 5 2 19 Shrinkage 156 5 2 20 Silver Streak 158 5 2 21 Short Shots 158 5 2 22 Brittle Part 159 5 2 23 Poor Plasticizing 160 5 2 24 Crack During Mold Release 160 5 2 25 Nozzle Drool 162 5 2 26 Short Shots no Burn Marks 162 5 2 27 Surface Ripples and Pit Marks 163 5 2 28 Pellets not Melted 163 5 2 29 Air Entrapment in the Mold 165 5 2 30 Gate Blush 166 Troubleshooting Extrusion 167 5 3 1 Bridging at the Throat of the Feed Hopper 167 5 3 2 Brittle Braking Tearing 168 5 3 3 Contamination Black Specks and Spots 169 5 3 4 Die Lines 170 5 3 5 Entrapped Gasses Air Bubbles 170 5 3 6 Excessive Die Swell 170 5 3 7 Material Accumulation at Die 172 5 3 8 Low Gloss 172 5 3 9 Material Non Homogeneous 172 5 3 10 Variable Thickness 174 5 3 11 Variable Output Surging 174 5 3 12 Plate Out on Die Lip 176 x CONTENTS 5 4 Troubleshooting Blow molding 176 5 4 1 Extrusion Blow Molding 177 5 4 1 1 Curling 177 5 4 1 2 Hooking 178 5 4 1 3 Inconsistent Tail Length 178 5 4 1 4 Blowouts or Pin Holes 178 5 4 1 5 Poor Wall Thickness Distribution Top to Bottom 180 5 4 1 6 Asymmetric Part 180 5 4 1 7 Poor Weld 180 5 4 1 8 Poor Parting Line 181 5 4 1 9 Contamination in Parts 182 5 4 1 10 Flashing Tear 182 5 4 1 11 Holes in Pinch Offs 182 5 4 1 12 Blowouts 182 5 4 2 Injection Blow Molding 185 5 4 2 1
18. that shapes material and technology of plastics allows the manufacture of parts with lightweight precision and strength and low cost It is cheaper than metal or ceramic processing However to use plastic effectively and to have the best advantage of its application specific charac teristics or physical properties must be considered In plastics processing with technology and application advances conventional product replacement and unlimited innovation can take place Plastic raw materials are also wid ening its range of products Achieving higher performance with increased quality is the major challenge in manufactur ing today Plastics processing therefore requires constant and sometimes fundamental change Moreover as plastics have replaced many conventional materials such as metal and wood in many applications throughout the world the growth will be accelerated by the tendency to substitute plastics for metal 14 1 2 1 Plastics vs Metal When plastics are compared with metals some of the prop erties of plastics can be considered either favorable or unfa vorable depending upon the application Plastics are not so strong as metal However plastics have certain properties to be considered as advantageous for engineering applications Plastics have better chemical and moisture resistance Plastics are more resistant to shock and vibration than metals Plastics are usually easier to fabricate than metals Nylon material is
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