The Problem:

This process suffers an extreme wear rate. Fifty mm, CPM-9V screws last three to five months running a polyamide based material with up to 60% glass fiber fill. This is a metal replacement material used to make structural automotive Class A parts.

A combination of high glass fiber filler and large shot utilization shorten screw and barrel life. The facility has more than 50 machines operating around the clock and process conditions are monitored closely to determine when a wear condition exists. Loss of cushion leads to a tip assembly replacement. Increased recovery time means a worn screw and barrel and typical preventive maintenance consists of removing the old barrel and screw as one piece and depositing them whole in the dumpster. New screw, barrel and tip are then installed to reduce down time and keep producing.

Their 300 ton Van Dorn machines were using 90% of the available shot size which reduced polymer residence time and greatly accelerated system wear. The customer increased screws and barrels from 50 to 57 mm to increase shot size and improve residence time. They also decided to evaluate carbide encapsulation as the price of CPM-9V tool steel was high and larger screws required 30% more material to manufacture.

The Solution:

Standard 4140 HT screws were supplied with .010” of XC1000 tungsten carbide and a mirror polish finish. Tool steel screws wore heavily on the push side of flight which eventually undercut the upper edge of the flight. After one year in process the carbide screws were examined and found to be in excellent condition. No measurements were taken but there was no flight side erosion as with past screws.

Benefits:

Historically this process has required two to three screw replacements per barrel. Given six months life for past screws, this translates into 18 months of barrel life. Our carbide encapsulation and improved residence time may now provide 18-20 months of screw life and 24 to 36 months of barrel life.

All screws at this facility will be carbide encapsulated and installed in carbide lined barrels. This customer has determined that a small investment for high quality components, more than pays for itself in process consistency and predictability.

More than double feed screw life expected. Significantly longer barrel life. Overall cost savings from longer life of components and better process consistency.