Rauwendaal Understanding Extrusion Chris Rauwendaal Understanding Extrusion 3rd Edition Hanser Publishers, Munich Hanser Publications, Cincinnati The Author: Dr. Chris Rauwendaal, 10556 Combie Road PMB 6677, Auburn, California 95602, USA Distributed in the Americas by: Hanser Publications 6915 Valley Avenue, Cincinnati, Ohio 45244-3029, USA Fax: (513) 527-8801 Phone: (513) 527-8977 www.hanserpublications.com Distributed in all other countries by: Carl Hanser Verlag Postfach 86 04 20, 81631 Munich, Germany Fax: +49 (89) 98 48 09 www.hanser-fachbuch.de The use of general descriptive names, trademarks, etc., in this publication, even if the former are not especially identi- fied, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. 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No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or by any information storage and retrieval system, without permission in writing from the publisher. © Carl Hanser Verlag, Munich 2019 Editor: Dr. Julia Diaz-Luque Production Management: Jörg Strohbach Coverconcept: Marc Müller-Bremer, www.rebranding.de, Munich Coverdesign: Stephan Rönigk Typesetting: Kösel Media GmbH, Krugzell Printed and bound by Kösel GmbH, Krugzell Printed in Germany ISBN: 978-1-56990-698-9 E-Book ISBN: 978-1-56990-699-6 Preface to the Third Edition The first edition of Understanding Extrusion was published in 2000 and the second edition in 2010. Since the second edition was issued several important develop- ments have taken place. As a result, it makes sense to have a third edition of Under- standing Extrusion. Most of the new material is incorporated in Chapter 2. Topics included in this chapter are interpretation of extrusion process data, dimensional variation by melt temperature fluctuations, efficient extrusion, and more. Chapters 7 and 8 have also been extended and now cover topics such as analysis of shrink void formation and grooved barrel extruder technology. I would like to thank Dr. Mark Smith for his encouragement to work on this third edition. I also want to thank my wife Sietske for her continued support and for put- ting up with me despite these time-consuming projects. Chris Rauwendaal September 2018 Contents Preface to the Third Edition ........................................ V 1 Extrusion Machinery .......................................... 1 1.1 What is an Extruder? .......................................... 1 1.2 Different Types of Extruders .................................... 2 1.2.1 Single Screw Extruders .................................. 2 1.2.2 Twin Screw Extruders ................................... 2 1.2.2.1 Co-Rotating Twin Screw Extruders ................. 2 1.2.2.2 Counter-Rotating Twin Screw Extruders ............ 3 1.2.3 Ram Extruders ......................................... 4 1.3 Components of an Extruder ..................................... 5 1.3.1 The Extruder Screw ..................................... 5 1.3.2 The Extruder Barrel ..................................... 5 1.3.3 The Feed Throat ........................................ 6 1.3.4 The Feed Hopper ....................................... 7 1.3.5 Barrel Heating and Cooling .............................. 7 1.3.6 Screw Heating and Cooling ............................... 9 1.3.7 The Breaker Plate ....................................... 9 1.3.8 The Screen Pack ........................................ 10 1.3.8.1 Screen Changers ................................ 11 1.3.9 The Extrusion Die ...................................... 12 1.3.9.1 Coextrusion Dies ............................... 14 1.3.10 The Extruder Drive ..................................... 14 1.3.10.1 Coupling between Motor and Gearbox .............. 15 1.3.11 The Speed Reducer ..................................... 16 1.3.11.1 Thrust Bearing Assembly ........................ 16 1.3.12 The Gear Pump ......................................... 17 2 Instrumentation and Control .................................. 19 2.1 Instrumentation .............................................. 19 2.2 Most Important Process Parameters .............................. 19 2.2.1 Melt Pressure .......................................... 20 2.2.2 Pressure Transducers ................................... 21 VIII  Contents 2.2.3 Temperature Measurement ............................... 22 2.2.4 Melt Temperature Measurement .......................... 23 2.2.5 Barrel Temperature Measurement ......................... 24 2.3 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.3.1 On-Off Control ......................................... 26 2.3.2 Proportional Control .................................... 26 2.3.3 Fuzzy Logic Control ..................................... 28 2.4 Collection and Interpretation of Extrusion Process Data ............. 29 2.4.1 Introduction ........................................... 29 2.4.2 Vital Signs of the Extrusion Process ....................... 29 2.4.2.1 Melt Pressure .................................. 30 2.4.2.2 Melt Temperature ............................... 35 2.4.2.3 Training ....................................... 44 2.4.3 Examples of Extrusion Problems Solved by Using a Data Acquisition System ................................. 44 2.4.3.1 Variation in Stock Temperature ................... 44 2.4.3.2 Variation in Feed Housing Temperature ............ 46 2.4.3.3 Variation in Melt Pressure ........................ 48 2.4.4 Process Optimization .................................... 50 2.4.5 Temperature-Induced Dimensional Changes of Extrudate ..... 50 3 Complete Extrusion Lines ..................................... 53 3.1 Tubing and Pipe Extrusion Lines ................................ 53 3.2 Film and Sheet Lines Using the Roll Stack Process ................. 54 3.3 Film Lines Using Chill Roll Casting .............................. 55 3.4 Combination of Materials ....................................... 56 3.4.1 Coextrusion ........................................... 56 3.4.2 Extrusion Coating ...................................... 57 3.4.3 Extrusion Lamination ................................... 58 3.5 Blown Film Lines ............................................. 59 3.6 Extrusion Compounding Lines .................................. 59 3.7 Profile Extrusion Lines ......................................... 61 4 Plastics and Their Properties Important in Extrusion ............. 63 4.1 Thermoplastics and Thermosets ................................. 63 4.2 Amorphous and Semi-Crystalline Plastics ......................... 64 4.3 Liquid Crystalline Plastics (LCPs) ................................ 66 4.4 Elastomers ................................................... 66 4.5 Flow Behavior of Plastic Melts ................................... 67 4.6 Melt Index ................................................... 68 4.7 The Effect of Shearing ......................................... 69 4.8 Shear Thinning or Pseudoplastic Behavior ........................ 69 Contents  IX 4.9 Effect of Temperature on Viscosity ............................... 70 4.10 Viscous Heat Generation ....................................... 71 4.11 Thermal Properties ............................................ 71 4.11.1 Thermal Conductivity ................................... 72 4.11.2 Specific Heat and Enthalpy ............................... 72 4.11.3 Thermal Stability and Induction Time ...................... 73 4.11.4 Density ............................................... 74 4.11.5 Melting Point .......................................... 76 4.11.6 Glass Transition Temperature ............................ 76 5 How an Extruder Works ....................................... 77 5.1 Solids Conveying .............................................. 78 5.1.1 Gravity Induced Conveying ............................... 78 5.1.2 Drag Induced Conveying ................................. 81 5.1.3 Starve Feeding ......................................... 82 5.1.4 Grooved Feed Extruders ................................. 83 5.2 Melting ...................................................... 85 5.2.1 Contiguous Solids Melting ............................... 85 5.2.2 Dispersed Solids Melting ................................ 86 5.3 Melt Conveying ............................................... 89 5.3.1 Melt Temperatures ...................................... 90 5.4 Mixing ...................................................... 93 5.4.1 Distributive Mixing ..................................... 93 5.4.2 Mixing Sections ........................................ 98 5.4.2.1 Distributive Mixing Sections ...................... 98 5.4.2.2 Dispersive Mixing Sections ....................... 102 5.5 Degassing ................................................... 108 5.6 Die Forming .................................................. 110 5.6.1 Size and Shape Changes ................................. 111 5.6.2 Tubing and Pipe Dies ................................... 114 5.6.3 Flat Film and Sheet Dies ................................. 117 5.6.4 Profile Dies ............................................ 119 6 How to Run an Extruder ....................................... 123 6.1 Introduction .................................................. 123 6.2 Before Start-up ............................................... 123 6.3 Getting Ready for a Run ........................................ 124 6.4 Starting the Extruder .......................................... 126 6.5 Actual Operation .............................................. 128 6.6 Shutdown .................................................... 129 6.6.1 Purging ............................................... 129 6.7 Safety Issues ................................................. 131 6.7.1 Heat .................................................. 131 X  Contents 6.7.2 Moving Parts .......................................... 131 6.7.3 Electrical .............................................. 132 6.7.4 Weights ............................................... 132 6.7.5 Pressure .............................................. 132 6.8 Inspection and Training ........................................ 133 7 How to Troubleshoot Extrusion Problems ....................... 137 7.1 Objectives ................................................... 137 7.2 Prerequisites ................................................. 137 7.2.1 Good Instrumentation ................................... 137 7.2.2 Good Understanding of the Process ........................ 138 7.2.3 Collect and Analyze Historical Data ....................... 138 7.2.4 Teamwork ............................................. 138 7.3 Main Types of Problems ........................................ 139 7.3.1 Output Problems ....................................... 139 7.3.1.1 Low Extruder Output ............................ 139 7.3.1.2 Variation in Extruder Output ..................... 141 7.3.2 Appearance Problems ................................... 144 7.3.2.1 Lines ......................................... 145 7.3.2.2 Die Drool ...................................... 145 7.3.2.3 Discoloration and Degradation .................... 145 7.3.2.4 Voids ......................................... 147 7.3.2.5 Vent Flow ...................................... 156 7.3.2.6 Air Entrapment ................................. 156 7.3.2.7 Gels .......................................... 157 7.3.2.8 Poor Mixing .................................... 158 7.3.3 Functional Product Problems ............................. 160 7.3.4 High Melt Temperature .................................. 160 7.3.5 High Motor Load ....................................... 161 7.3.6 Wear Problems ......................................... 161 7.4 Systematic Problem Solving .................................... 163 7.5 Machine Troubleshooting and Maintenance ....................... 164 7.5.1 Check the Oil .......................................... 165 7.5.2 Unusual Noises ........................................ 165 7.5.3 Drive Motors and Belts .................................. 167 7.5.4 Spare Parts ............................................ 167 7.5.5 Screw and Barrel ....................................... 167 7.5.6 Extruder Maintenance Checklist .......................... 168 7.6 Troubleshooting Lists .......................................... 171 8 New Developments in Extrusion and Methods to Increase Efficiency ........................................... 175 8.1 General Trends ............................................... 175 8.2 High-Speed Extrusion .......................................... 175