The Plastic Molding Source

Find what you need in machines, equipment and manufacturers


Plastic Purging Compounds, Mechanical, Chemical And Combinations

Today's plastic technician has a wide range of plastic purging compounds to choose from; this article can help to decide which is best for each requirement. Whether it is for injection molding, extrusion or a hot runner system, there are products that use mechanical, chemical and a combination of the two to purge material.

plastic purging compounds

Plastic processors around the world all have the same problem: What is the best way to purge the barrel, screw and hot runner system? Obviously, there is no one size fits all product that works perfectly for every machine and material; there are just too many variables to account for.

Mechanical purging compounds

This type of compound scours the machine to clean it of all residue. Often manufacturers use a base resin and add various abrasive agents, such as calcium carbonate, ground cast acrylic or some other material to scrub the machine.

The mechanical purging compound is generally highly effective and is quite popular. However, not all products are suitable for hot runner systems because the scouring agent does not fully melt.

Chemical purging compounds

In the past chemical agents had a bad reputation due to the very strong, caustic odor produced during the purging process. Ammonia was a favorite chemical and was very effective, but became obsolete due to the objectionable odor and health concerns.

Today's chemical compounds are very effective and do not suffer from the same odor problems. In fact, some even have pleasant scents added to the formula to make the process somewhat more pleasant.

Basically, the compounds break the polymers down into smaller chemical chains and use a foaming type agent to purge the broken down plastic from every part of the machine.

Depending on individual requirements, it is possible to buy FDA approved chemical purging agents. This alone demonstrates just how far these compounds have come since the harsh chemicals of the not-so-distant past.

Chemical/Mechanical compounds

Just as the name implies, these are a combination of the two methods. This process can be highly effective on the most stubborn or neglected injection molding or extruding machine.

See how purging works


JIT, Just-In-Time, Lean Manufacturing

One of the tenets of a lean manufacturing initiative is keeping little or no inventory as a way of reducing costs. Another concept is a quick response to change and adapting to the changing needs of the customer.

This is a great way to win clients and keep them happy, but it can make life quite challenging for the molder, who must keep changing materials in the molding machine. Some runs are very short and change-overs can happen on an almost daily basis.

In a perfect world, each machine would be dedicated to a specific type of plastic, making the need for purging almost non-existent. The real world experience is very different, as any molding technician can attest to.

This constant purging of material can create a great deal of scrap, especially if inferior methods of purging are used. Some molding companies report that their single largest scrap expense is due to the material lost during the purging process.


Individual cases require unique solutions for purging plastic material from injection mold and extrusion machines. Variables such as material type, machine type, use of hot runner systems, budget, and melt temperature all contribute to make the decision making process more complicated.

Choosing the correct plastic purging compound can greatly affect the profitability of a project, making an intelligent decision imperative.

More great ideas on plastic processing







"Thank you for contributing your recent articles for our AMBA newsletter. They are well thought out, informative, helpful and written with a no-nonsense, common sense approach."

The Editors of The American Mold Builder, the official publication of the American Mold Builders Association

American Mold Builders Assoc.


Click here to get started with Lean Mfg.

Lean manufacturing

Minimize stress