Extrusion

General Features of Single Screw Extrusion

One of the most common methods of processing plastics is Extrusion using a screw inside a barrel as illustrated in Fig. 4.1. The plastic, usually in the form of granules or powder, is fed from a hopper on to the screw. It is then conveyed along the barrel where it is heated by conduction from the barrel heaters and shear due to its movement along the screw flights. The depth of the screw channel is reduced along the length of the screw so as to compact the material. At the end of the extruder the melt passes through a die to produce an extrudate of the desired shape. As will be seen later, the use of different dies means that the extruder screwharrel can be used as the basic unit of several processing techniques.

PLASTICS

ENGINEERING

Third Edition

R.J. Crawford, BSc, PhD, DSc, FEng, FIMechE, FIM

Department of Mechanical, Aeronautical

and Manufacturing Engineering

The Queen’s University of Belfast

l E I N E M A N N

OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS

SAN DlEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO

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