Page 265 - Plastics Engineering

248 Processing of Plastics

Fig. 4.3 Typical extruder outputs for different plastics

In commercial extruders, additional zones may be included to improve the
quality of the output. For example there may be a mixing zone consisting of
screw flights of reduced or reversed pitch. The purpose of this zone is to ensure
uniformity of the melt and it is sited in the metering section. Fig. 4.4 shows
some designs of mixing sections in extruder screws.

pclra\Ie\ Interrupted mixing tWts Undercut spiral barrier-type

Ring-type barrier mixer

Mixing pins
RAPRA cavity tmnsfer mixer
Fig. 4.4 'I)lpical designs of mixing zones