Mixing in Single Screw Extruders

Mixing in Single Screw Extruders

Author: Martin Gale
ISBN 978-1-84735-130-2 

Hard cover
Mixing in Single Screw Extruders is a must-have practical guide to the subject of single-screw extrusion. Avoiding mathematical theory, except when absolutely necessary, this authoritative handbook empowers the reader to achieve good results with their plastic mixing. Mixing in Single Screw Extrusion will be a valuable resource to all involved in the art of plastic extrusion.

A lot of plastics products are extruded and most of those products contain additives, which mean that the plastic must be mixed at some point. Mixing is generally done with a twin-screw extruder, and the single-screw extruder, which is used in product production, is generally overlooked as a device for mixing. This reference handbook, written by a former Principal Consultant at Smithers Rapra, and the inventor of the cavity transfer mixer, redresses the balance.

Extrusion is used for about half of all plastics product manufacture, mostly using single screw extruders. Very often part of their role is the incorporation of one or more of a very wide range of additives, mainly in the form of masterbatches. These range from very visible colours to the invisible traces of anti-block and slip additives. There are also continuing pressures to improve overall economics and these require increased mixing performance in many cases.

With the growing pressures to increase the amount of plastics recycling, both the limitations and success in blending the mainly incompatible polymer combinations are explained.

The development of 'add-on' cavity mixers and floating ring mixers, together with their methodology are described, whilst the associated innovative techniques using a liquid injection of colours, tackifiers, lubricants, crosslinking agents and foaming agents, (particularly carbon dioxide) are included. Developments in controlled levels of blending by 'chaotic mixing' to produce products with very specific properties such as barrier films are briefly described.
Extrusion tests for carbon black dispersion are included and the book concludes with a practical guide to the preparation of microtomed plastics specimens for evaluation by optical microscopy.  

1 The Need for Good Mixing in Single Screw Extrusion
2 Dispersive and Distributive Mixing
3 Measurement of Mixing
4 Single Screw Extruder Stages: Effects of Mixing
5 Pellet Handling: A source of Variable Composition
6 Solids Conveying in the Feed/Transport Zone
7 Melting
8 Screw Channel Mixing and the Application of Mixing Sections
9 Interacting Rotor/Stator Mixers
10 Floating Ring Mixing Devices
11 Static (or Motionless) Mixers
12 Incorporation of Liquid Additives and Dispersions by Direct Addition
13 Dispersive Mixing of Fillers and Pigments
14 Dispersive Mixing Applied to Polymer Blending
15 Compounding with Single Screw Extruders
Appendix - Preparation of Microtome Sections for Assessment of Dispersive

After graduating in chemical technology, specialising in plastics, Martin Gale's first involvement in mixing and extrusion was as the plastics technologist in a new plant being set up to produce UPVC pipes in 1959. After two years he joined the Rubber and Plastics Research Association (later to become Rapra Technology). After working on glass fibre/matrix bonding and antistatic agents, he became a member of the newly formed plastics section, eventually becoming responsible for plastics processing. The work was a mix of industrial multiclient/government projects, short and long term development contracts, product failure analysis, and factory troubleshooting, and so on. Several projects resulted in pilot scale manufacturing at the Association's laboratories using innovative techniques.

Since retiring in 2000, he has been involved in consultancy work, training courses, and advising on extrusion foaming and mixing as a visiting professor at the University of Bradford. About 100 publications bear his name as either author or co-author, whilst there are 9 patents (6 with co-inventors) including the one for the Cavity Transfer Mixer. He wrote the plastics part of the chapter on Processability Tests in Handbook of Polymer Testing (1999).