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Hot Runners in Injection Moulds

Daniel Frenkler and Henryk Zawistowski English Translation by Robert Walkden

Hot Runners in Injection Moulds

Daniel Frenkler and Henryk Zawistowski

English translation by Robert Walkden

Rapra Technology LimitedShawbury, Shrewsbury, Shropshire SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.rapra.net

First Published in English in 2001 by

Rapra Technology LimitedShawbury, Shrewsbury, Shropshire, SY4 4NR, UK

2001, Rapra Technology Limited

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.

ISBN: 1-85957-208-1

Typeset by Rapra Technology Limited Printed and bound by Redwood Books, Trowbridge, Wiltshire

Contents

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

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Hot Runners in Injection Moulds

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

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Contents

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

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Hot Runners in Injection Moulds

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

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