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8/3/2012

Screw and Barrel Wear

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Screw and barrel wear is critical in all plasticating applications whether is it extrusion, injection molding, and blow molding, or twin screw extrusion.  

Screw and barrel wear is critical in all plasticating applications whether is it extrusion, injection molding, and blow molding, plus twin screw extrusion.
 
Excessive screw and barrel wear can cause instable throughput or recovery on reciprocating screws, increased melt temperature and reduced plasticating rates.
 
Some of the causes of excessive wear are:
 
  • Screw straightness
  • Barrel straightness
  • Barrel alignment to the gearbox
  • Screw/barrel concentricity
  • Screw speed
  • Screw flight to barrel liner compatibility
  • Polymer being process
  • Fillers in the polymer
  • High headpressure
 
The accompanying chart shows the typical rebuilding requirement for various applications. Critical would be for a close tolerance produce and non-critical may be for a process such as making plastic lumber.
 
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Tim Womer is a recognized authority in plastics processing and machinery with a career spanning more than 35 years. He has designed thousands of screws for all types of single-screw plasticating. He now runs his own consulting company, TWWomer & Associates LLC. Contact: (724) 355-3311; tim@twwomer.com; twwomer.com