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July 4, 2006
2 Min Read
By John Pizzo, technical service and development manager, Asaclean-Sun Plastech Inc.
With savings often more than 75% on material changeovers for injection molding operations, it?s easy to see why commercial purging compounds have quickly gained favor in the industry. A brief explanation clarifies the factors that figure into these savings: the minimized downtime, the amount of resin replacement, and the total cost per purge.
In some cases, use of purging compounds can reduce machine downtime nearly 90% as compared to resin or cast acrylic purges, especially when production runs call for frequent mold, color, or material changes. Typical application time for a commercial compound purge on a 500-ton machine is 15-20 minutes. The use of purging compounds also means less scrap and fewer rejects.
Purging Compounds at a GlanceA purging compound is a resin-based formulation designed to clean plastics processing machinery and tooling. Purging compounds are called for when it takes 30 minutes or more from the last good part of the previous resin to the first good part of the new resin. Specks and streaks that reappear after a job is paused also indicate the need for purging compounds.
Purging compounds act primarily by mechanical or chemical means. Commercial purging compounds are available as premixes or concentrates that are added to resin.
The price of commercial purging compounds ranges from $2-$5 per pound. The main benefits of purging compounds over resin purging are reduced machine downtime and materials expense.
Purging Compounds vs. Scrap Resin
At first blush, purging compounds may seem expensive. Also, scrap resin is sometimes thought of as being cost-free, since the material is already paid for.
However, the cost per pound is only a minor factor in calculating the actual cost-to-benefit ratio of commercial purging compounds, especially when increased productivity is considered. In addition, using natural resin such as polypropylene or polyethylene will not completely clean the machine or molds, resulting in internal buildup and longer-term contamination.
One must take into consideration estimated machine running cost, machine downtime, the amount and cost of purge material used, and the cost of replacement resin, to determine the total cost savings from using commercial purging compounds. See the table above for an example.
A Matter of Dollars and Sense
Purging with commercial compounds rather than with resin not only features an attractive price-to-performance ratio, but the compounds are also safe, easy to use, and applicable to virtually any purging scenario likely to present itself.
For molders, with frequent changes in mold, color, or material as the norm, purging compounds deliver substantial benefits that can have immediate and lasting effects on efficiency and profitability.
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