Hot Runners in Injection Moulds

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<p>Hot Runners in Injection Moulds</p> <p>Daniel Frenkler and Henryk Zawistowski English Translation by Robert Walkden</p> <p>Hot Runners in Injection Moulds</p> <p>Daniel Frenkler and Henryk Zawistowski</p> <p>English translation by Robert Walkden</p> <p>Rapra Technology LimitedShawbury, Shrewsbury, Shropshire SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.rapra.net</p> <p>First Published in English in 2001 by</p> <p>Rapra Technology LimitedShawbury, Shrewsbury, Shropshire, SY4 4NR, UK</p> <p>2001, Rapra Technology Limited</p> <p>The right of Daniel Frenkler and Henryk Zawistowski to be recognised as authors of this Work has been asserted by them in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1998. All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder. A catalogue record for this book is available from the British Library.</p> <p>ISBN: 1-85957-208-1</p> <p>Typeset by Rapra Technology Limited Printed and bound by Redwood Books, Trowbridge, Wiltshire</p> <p>Contents</p> <p>Preface ................................................................................................................... 1 Introduction .......................................................................................................... 3 1 Types of Hot Runner Systems .......................................................................... 7 1.1 Melt supply methods ................................................................................ 9 1.2 Methods of heating ................................................................................. 13 References ...................................................................................................... 19 2 Conditions for use of Hot Runners ................................................................ 21 2.1 Technical advantages and limitations of using HR ................................. 21 2.2 Initial grounds for introduction of an HR system ................................... 23 2.3 Comparative cost analysis ...................................................................... 29 References ...................................................................................................... 36 3 Links with Technology ................................................................................... 37 3.1 Impact of properties of plastics on HR system design ............................. 37 3.1.1 General impact of composition and structure of plastics ............. 37 3.1.2 Temperature window ................................................................... 41 3.1.3 Properties of plastics in a liquid state .......................................... 47 3.1.4 Interaction between plastics in fluid state and HR components ... 61 3.2 Impact of HR on product quality ........................................................... 62 3.2.1 Shaping of internal features of product in mould ........................ 62 3.2.2 Shrinkage of moulded parts ......................................................... 65 3.3 Mould requirements when an HR system is used ................................... 67</p> <p>i</p> <p>Hot Runners in Injection Moulds</p> <p>3.4 Interaction between HR moulds and injection moulding machine .......... 69 References ...................................................................................................... 71 4 Structure of a Hot Runner System.................................................................. 73 4.1 HR nozzles ............................................................................................. 75 4.1.1 Gates ........................................................................................... 84 4.1.2 Open nozzles ............................................................................... 93 4.1.3 Tip nozzles ................................................................................ 102 4.1.4 Shut-off nozzles ......................................................................... 117 4.1.5 Edge nozzles .............................................................................. 131 4.1.6 Nozzle heating ........................................................................... 138 4.2 HR manifolds ....................................................................................... 146 4.2.1 Manifold with external heating ................................................. 148 4.2.1.1 Manifold design ............................................................ 148 4.2.1.2 Fastening and sealing of manifolds ............................... 166 4.2.1.3 Sprue bushings .............................................................. 175 4.2.1.4 Manifold heating and insulation ................................... 178 4.2.1.5 Manifold housings ........................................................ 182 4.2.2 Manifolds with internal heating ................................................ 183 4.2.2.1 Manifold design ............................................................ 184 4.2.2.2 Nozzle installation ........................................................ 189 4.2.2.3 Sprue bushings .............................................................. 191 4.3 Enclosed HR sets .................................................................................. 192 4.4 Moulds with insulated channel ............................................................. 194 4.5 Thermal expansion of HR sets.............................................................. 196 References .................................................................................................... 202 5 Thermal Balance and Temperature Control ................................................. 205 5.1 Heaters and thermocouples .................................................................. 205 5.2 Heating zones ....................................................................................... 217</p> <p>ii</p> <p>Contents</p> <p>5.3 Heat losses ............................................................................................ 221 5.4 Power consumption .............................................................................. 224 5.5 Temperature regulators ......................................................................... 228 References .................................................................................................... 235 6 Filling Balance .............................................................................................. 237 6.1 Natural balance .................................................................................... 239 6.2 Rheological balance .............................................................................. 241 References .................................................................................................... 252 7 Choosing an HR System .............................................................................. 253 7.1 Definition of HR system ....................................................................... 254 7.1.1 Type of system ........................................................................... 254 7.1.2 Heating method ......................................................................... 256 7.1.3 Heating voltage ......................................................................... 256 7.1.4 Degree of expansion .................................................................. 257 7.1.5 The melt supply method ............................................................ 257 7.2 Channel and gate selection ................................................................... 263 8 Special Injection Processes Using HR ........................................................... 273 8.1 Sequential and cascade moulding ......................................................... 273 8.2 Moulding with decorative films ............................................................ 276 8.3 Moulding with textile linings ................................................................ 279 8.4 Multi-component moulding .................................................................. 282 8.5 Injection of high-temperature group plastics ......................................... 285 8.6 Thermoplastic elastomer moulding ....................................................... 286 References .................................................................................................... 287 9 Special HR Mould Designs .......................................................................... 289</p> <p>iii</p> <p>Hot Runners in Injection Moulds</p> <p>9.1 HR in moulds for large pieces .............................................................. 289 9.2 HR in moulds for small mouldings ....................................................... 296 9.3 HR in moulds for thin-walled tubular mouldings ................................. 297 9.4 HR in stack moulds .............................................................................. 299 9.5 Moulds with HR in long cores ............................................................. 306 9.6 Moulds with HR for moulding without a weld line .............................. 308 9.7 Non-standard methods of melt distribution in HR moulds .................. 311 9.8 Modular units for moulds with HR nozzles .......................................... 314 References .................................................................................................... 315 10 Use of Moulds with HR ............................................................................... 317 10.1 Mould acceptance ............................................................................... 317 10.2 Preparation of a mould for operation ................................................. 319 10.3 Ongoing servicing ............................................................................... 321 10.4 Maintenance and storage .................................................................... 325 10.5 Work safety principles ........................................................................ 326 References .................................................................................................... 326 11 Disruptions to the Operation of HR Moulds and Typical Moulding Defects . 327 11.1 Leaking in HR systems ....................................................................... 327 11.2 Shut-off nozzle leaves vestige .............................................................. 328 11.3 Gate blocked ....................................................................................... 329 11.4 Gate stringing or drooling .................................................................. 329 11.5 Incomplete mouldings ......................................................................... 329 11.6 Sinks ................................................................................................... 330 11.7 Brown or silver streaks (burn) ............................................................ 330</p> <p>iv</p> <p>Contents</p> <p>11.8 Delamination ....................................................................................... 332 References .................................................................................................... 332 12 The Way Ahead for HR Technology ............................................................ 333 Abbreviations and Acronyms............................................................................. 335 Appendix 1 - List of Hot Runner Suppliers ....................................................... 339 Index ................................................................................................................. 343</p> <p>v</p> <p>Hot Runners in Injection Moulds</p> <p>vi</p> <p>Preface</p> <p>The technology of hot runners in injection moulds for plastics is becoming more and more widely used, and this has been accompanied by an increase in the range of hot runner systems available. This development has meant that in manufacturing practice, the user of hot runner moulds is faced with the problem of how to make an objective comparison between the systems on offer from the technical information at his disposal company catalogues and brochures. The large range of hot runner systems on the market and the complex link between their design and the result obtained in practice means that many designers and users have difficulty in making the best choice. Besides economic and technical considerations, this choice must also take into account the specific properties of the plastics. An understanding of the physical processes taking place in the mould during injection forms a basis for informed building and optimum selection of the hot runner system, and for its subsequent operation. This is an aspect to which the book gives special attention. In the meagre selection of works on the subject of the design of injection moulds, comparatively little space is devoted to hot runner systems. There is only one book exclusively addressing this subject, and that was published in 1960 [E. Moslo, Runnerless Moulding, Reinhold Publishing Corporation, 1960]. The aim of this manual is to fill that gap. It introduces a logical division of hot runner systems, illustrates the design of nozzles, manifolds and other system components, discusses the principles of selection, building, installation and use, analyses the causes of faults and suggests ways of eliminating them, and presents examples of applications. In researching this book, we made use of information that is available in the technical literature and that was provided by hot runner system manufacturers and users. With our own experience to guide us, we have tried to be objective without making evaluations of individual systems produced by specific companies. Writing a book takes a certain time, and the rapid development of hot runners has meant that by the time the book was ready for publication, some nozzle types had already been replaced by later versions. The book cannot, however, be a substitute for a companys catalogue, and the very latest illustrations are not essential for explanatory purposes. We would like to thank all those who have assisted us, and especially the manufacturers of standard hot runner systems who made their graphic material available to us. Readers</p> <p>1</p> <p>Hot Runners in Injection Moulds will find a list of these manufacturers in Appendix 1. Special thanks also to Robert Walkden who performed the difficult task of translation from the Polish, and to the staff of Rapra Technology, particularly Claire Griffiths, Steve Barnfield, Sandra Hall and Frances Powers, who all worked on the editorial aspects of the English translation. Thanks also to Clive Broadbent of Fast Heat International (UK) Ltd., who kindly proof read the fina...</p>