Rebuilding Feedscrews & Barrels

Questions and Answers

Question:  

How does a barrel that is reconditioned with a CPM-10V sleeve compare to a new barrel with a high abrasion bi-metallic liner in longevity and performance?

Answer:  

Barrels that are full-sleeved reconditioned by SFP that contain a CPM-10V liner should yield an equivalent life cycle to that of a new barrel with a high abrasion bi-metallic liner.  This data comes from thousands of barrels that have been in operation where both CPM-10V and bi-metallics have been interchanged. Both products will completely satisfy the needs of plastics processors under a variety of processing conditions. The only variable to consider is cost. Typically, once barrel bores exceed 50mm, a new bi-metallic barrel is more cost effective than a full-sleeved reconditioned barrel.

Question:  

Can tool steel feedscrews be rebuilt?

Answer:  

Yes. However, there are inherent risks to rebuilding tool steel feedscrews. There is a chance that tool steel feedscrews can break during the rebuilding process.  Should breakage occur, Services for Plastics, Inc. does not assume any responsibility for replacement of the feedscrew, and will not issue an invoice for work done to that point.

Also, in order for the feedscrew to become a solid candidate for rebuilding, the following conditions must not exist in excessive forms:

• Excessive wear of O.D.

• Broken tip assembly stud remaining in threads

• Severe undercutting of flights, thinning of flights, or missing flights.

SFP has the capabilities to repair feedscrews that show signs of damage as listed above, even to extreme damage conditions. However, from an economic standpoint, it would not be cost justifiable.

Question:  

Should new and existing worn components be matched?

Answer:  

Simply put, wear is wear.  When a new OEM specification injection unit is assembled, the tolerance between barrel I.D. and feedscrew O.D. is critical. The purpose of the barrel is to contain the feedscrew and to ensure that plastic material stays within the flights of the feedscrew to be: 

• Conveyed
• Compressed
• Melted
• Mixed

As the components wear, the tolerance is increased and consequently plastic shears over the tops of the flights.  As the material travels over the flights, it will carry fillers inside the plastic as well (i.e. glass fillers, metal, talc). This leads to the normal wear of the barrel and feedscrew.

When mating a new component (feedscrew, barrel, or tip assembly) with a worn component, the improper tolerances that increased the rate of wear still exist. The new component will not be able to compensate, and consequently will wear out much sooner. When replacing the components of an injection unit, ensure that all components are within acceptable tolerance limits before re-assembly.