Purging, Componds, Techniques

Hints & Tips

Hints & Tips

Purging should be a part of your production process which enables your company to reduce downtime and increase production.
Purging often accompanies changeovers of colors and resins. Purging should be done at startup or shutdown, and is even beneficial as a regular maintenance procedure.
The more often you purge the better the results. Procedures vary with type of purging compound. What you have to do first is read the instructions.
It is usually recommended that the screen pack be removed before purging. Few products don't require removing the screen pack, but the quantity of discarded resin remaining in the machine will be the determing factor.
It is usually recommended that the screw be run until all possible material has been removed before the purge is added. With all but the chemical type of purge, a slow screw speed is the usual recommendation.
Purging into water is recommended for the cast-acrylic scouring type, and also with some resins such as ABS. The temperature should be that of the following material, or a little below. Lower temperature will stiffen the purging compound, which is beneficial. Observe the temperature of the purging compound; some won't handle resins that process above 600F.
Note that running a purging compound may not be the end of the clean up operation. Don't expect miracles. It may still be necessary to pull the screw...but by using the purge first you will have eliminated a good deal of the heavy clean up chores. Or, to put it another way, any time your planning to pull the screw for whatever reason; run a purge cycle first.
How long will purging take? A lot less time then pulling the screw and having at it with the tools of the scraping trade.
Case histories are plentiful and inspiring, saving hours and hard labor. Some compounders of an experimental bent, faced with a tough clean-out, or perhaps just impatient, will run first one type of purge, then another. Some even combine two or three and run them together, and occasionally stumble onto synergy.

larsan