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4/1/2009 | 2 MINUTE READ

Better Purging Saves Money, Material and Time

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How much money can a better purging compound save even a small molder? Ask Garlock Sealing Technologies, Palmyra, N.Y., an injection molder of thermoplastic fluid seals, which saves $38,710 a year since changing purging compounds on its four injection machines. The company molds clear and black seals from TPU, other TPEs, and nylon. “Whenever we changed from black to clear urethane, we experienced an excessive amount of material degradation, which caused an unacceptable level of scrap from the changeover, as well as prolonged downtime,” says Jeffrey Johncox, senior production planner.

The company traced the problem to the HDPE-based purging compound it had been using for more than 10 years, which did not clean Garlock’s production materials from the press efficiently, and was itself difficult to purge from the machine. Garlock purged its machines an average of six times a week, at a cost of $170.85 per purge. This amounted to $53,305 in annual purging costs.



Garlock met with the Dyna-Purge div. of Shuman Plastics and selected one of its most successful products, the Dyna-Purge M engineered purging compound. This is a three-part compound designed for purging at temperatures from 350 to 600 F, says Tim Cutler, Dyna-Purge business manager. The polyolefin compound contains non-abrasive “scrubbing granules” of about 0.003 in. diam. that soften but do not melt as they move through the injection press. The compound also contains smaller “scrubbing fines” that contribute non-chemical “dual-action cleaning” with no mixing or soak time required.

Use of Dyna-Purge M reduced Garlock’s purging costs from $170.85 to $46.78 per purge. That includes the cost of wasted resin, purging compound, machine time, and labor. Purging six times a week for 52 weeks now costs $14,595, a savings of $38,710 a year or 73%. Post-purging—elmination of the purge compound after the previous production material had been purged—previously required 18 lb of TPU material (at around $4.50/lb).

All told, purging used to take 90 min before good parts were made. Since Dyna-Purge M uses polyolefin, Garlock was able to displace the purging compound and all of the contaminants using just 2 lb of TPU and 20 min before good parts were made. Garlock eliminated the scrap parts due to contamination during changeover, saving $13,500 worth of TPU resin. And saving 70 min per purge resulted in a gain of 364 hr of additional production time, says Johncox.

Dyna-Purge M, at $2.55 lb, is more expensive than the $1.50/lb HDPE purging material previously used, but Garlock uses less of it, says Johncox.