How to determine if a feedscrew is wearing too quickly?

“Screws don’t really die; they just pass away to the scrap yard. But you can learn a lot by performing an “autopsy” on your screw before you heave it.”

So says Jim Frankland in an excellent article entitled “Dead Screw Talking” written for Plastics Technology available in a searchable database here.  ( )

“Areas of high wear on the screw flights can reveal either a design issue or an alignment problem. If the flight has a burr on the trailing edge, it means the screw has a high, localized, and unbalanced pressure that is forcing the screw aggressively to one side of the barrel. This is causing the flight to gall with the barrel, and the flight is being distorted by the mechanical pressure. This usually occurs in an area that is plugging with solids, causing very high pressure on one side of the screw.”

“Plugging with solids” is a common issue and results from poor melt rate in the zone or too fast a recovery cycle, contributing to poor melt rate.  In any event, the flight OD wears and screw performance suffers.  

How to know if you are getting reasonable life from a screw/barrel system?

There are three factors to consider:  

  • feedscrew design
  • process parameter settings
  • materials of construction

These factors together make up the well-known three-legged stool analogy.  Any one factor out of balance can shorten the working life of your system.  

A screw design optimized for crystalline materials will struggle when processing an amorphous resin.  An injection process with a faster than necessary recovery cycle can wear screw flights. Incompatible materials of construction can lead to metal-to-metal galling and rapid wear of screw or barrel. 

Here are a few articles of interest:

Finally, we at USTS have a lot of experience examining worn/damaged screws to identify a root cause of wear.  We are happy to share this experience on your particular issue.  The chances are we have seen it before and can help you find a solution. Contact us today.

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