Purging Myths Busted: What Actually Works

(and What Just Costs You Time)

There are many misconceptions regarding the purging process in injection molding which involves cleaning various system parts of one material or color before starting the next run. Let’s explore some common myths and what works to help make this procedure productive and cost-effective.

The Myths and Truths

Myth: Purging is just an extra cost and an unavoidable expense.

Truth: Efficient, strategic purging is a savings opportunity but inefficient purging increases expenses in scrap, downtime, quality control and wear.

Myth: Purging compounds are one-size-fits-all.

Truth: Various grades are available and quality differentials are formulated for specific production conditions, temperatures and resin types. Use of an improper product reduces efficacy and can even damage equipment.

Myth: Virgin resin or regrind can clean like a commercial compound.

Truth: These materials are not designed to purge. Although they are less expensive per pound, dedicated commercial formulas result in a lower cost per purge with decreased waste and faster transitions.

Myth: Dry purging by running the barrel empty is necessary.

Truth: This poses the risk of leaving a layer of material on the mold components that can lead to carbonization and contamination. The barrel should be kept full to prevent baking of residue.

What Actually Works Effectively

1) Use Commercial Purging Compounds (CPCs)

These are the most appropriate tools – whether you decide to use a mechanical grade (scrubbing technique) or chemical grade (foaming/expanding) formulation. It’s critical to select a CPC that is compatible with your processing temperatures and material.

2) Stick with a Strategic Procedure

Don’t think generically – follow the CPC provider’s explicit instructions. They will include steps detailing optimal temperatures, screw speed, back pressure and complete displacement to prevent cross-contamination.

3) Prevention

Yes, back to the old “an ounce of prevention…” saying. Be sure to schedule regular maintenance purges even during normal production cycles. When doing an extended shutdown, seal the machine with a heat-stable purging compound to prevent oxygen from getting in the barrel. Oftentimes, the best purge could be the one you didn’t need!

Slide Products’ collection of high-quality purging compounds likely includes the perfect solution for your individual application. Our factory experts and distributor partners are always available to answer questions and provide guidance. Or schedule a free purging consultation through our Top Tier Service program.

Read more about calculating the true cost of purging, and try Slide’s purging calculator for your specific procedure.

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