Barrel and Screw Materials

The majority of barrels and screws are made from special steels (Tables 2-4 and 3-4), which are nitrided to a minimum depth by special techniques. Low alloy steels are sometimes used with wear-resistant liners. Usually the wear on these bimetallic cylinders is almost three times that of the others. In the processing of abrasive materials, feed sections are sometimes finished in hard metal or other special materials, and matched with the screws. If there is wear in the extruder, then the greatest damage is always on the screw. Often only a new screw is used as a replacement, as it is assumed that the barrel is not damaged. However, usually this assumption is a fallacy. If the screw is worn out, the barrel has been affected to some extent. It may well need complete replacement. 

The rate of wear is increased considerably when the feed contains fillers such as titanium dioxide, glass fibers, and so on. As reviewed in Chapter 2, there are many variables that cause damage to the barrel and the screw. If a problem is likely to occur frequently, protect the screw and consider using barrels with replaceable inner liners. 

A Support downstream die adaptor, etc. A Remove, clean, and re-install A Correct cause of damage (see below) or replace A Replace 

A See procedure for setting U/S body A Ensure correct screen size and installation 

A Utilize positive screen retention A Utilize hopper magnet or other metal-catching device 

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DESIGNING WITH PLASTICS AND COMPOSITES A HANDBOOK Barrel and Screw Materials... 

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