Purge compound and tool/die cleaning
Vol. 22 #2, September 1995
A good purge compound that is ready available and cleans a screw real well is fractional melt HDPE (.35 MI) bottle grade. The temperature profile is set at approximately 400 F. across the board and the processing resin is run out until no extrudate is evident. The HDPE is then added and processed through the extruder until the extrudate appears to be clear. This is done with the die on. The die or tooling can be removed from the extruder and cleaned easily. After the die is removed turn the screw rotation on and operate the screw at about 15-20 rpm. until the extrudate stops. Now the screw can be pushed out and easily cleaned with a wire brush and copper gauze.
Die cleaning can be a long, labor intensive process. It is also a time when many dies are damaged from improper cleaning, tools, and/or procedure. Maintain an adequate supply of brass scrapers and a stable work surface.
If HDPE fractional melt resin is used to purge an extruder and die, the die can be pulled apart easily. A pair of needle nose pliers and an air blowgun are useful in cleaning flow channels. By taking the air blowgun and starting at a corner of the die and freezing a small portion of resin on the die or tooling, and then using the pliers to pull the material away from the die surface, the cooled material will clean the die surface as it pulls away. Use the blowgun to freeze the material as it is being pulled away from the die/ tooling surface. Once the HDPE is removed, the hot die and tooling surface and can be cleaned with stearic acid and copper gauze.
- T. Womer, Spirex
See also:
- Cleaning dies
- Extrusion dies
- How effective are purge compounds
- Pelletizing die cleaning
- Purging of extruders
- Purging of extruders (1993)
- Screw cleaning
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