Purging compounds are used in injection molding, blow molding, and extrusion molding machines as a transition material from one product to another. They remove residue from color or resin changes and are used to clean screws, barrels, and hot runners.
Purging compounds are available as concentrated liquids, powders, or pellets. Many have a cast acrylic base and can remove residue from thermoplastics such as nylons, polycarbonates polyesters, and polyvinyl chloride (PVC). Some products can be poured directly into a hopper or the throat of a molding machine. Others are combined with a base resin or used as part of a multi-product system. Pre-mixed purging compounds are more expensive than raw materials, but reduce the amount of setup and cleanup time required.
Selecting Purging Compounds
Selecting purging compounds requires an analysis of product specifications and features. Factors to consider include cleaning method, operating temperature, and shipping weight. Purging compounds that scrub screws, barrels, and hot runners remove residues via mechanical action. Heat-activated products do not require pre-soaking and may use steam and foam to remove accumulated resin deposits. Operating temperature, another important specification, can range from 160 to 600 degrees Fahreheit. Shipping weight is measured in pounds (lbs.). Liquid purging compounds ship in containers that weigh 5, 10 or 20 lbs. Pellet-based products ship in cardboard drums, heavy paper bags, or plastic barrels that weigh 50, 100, or 250 lbs.
In terms of features, purging compounds may be heat-stable, non-toxic, non-corrosive, or non-flammable. Low-odor products are also available. Purging compounds and purging compound suppliers differ in terms of approvals and certifications. In the United States, products that are FDA compliant meet guidelines from the Food and Drug Administration (FDA). In Europe, the containers in which purging compounds are shipped may bear the CE Mark to indicate compliance with relevant European Union (EU) directives for health and safety. Suppliers of purging compounds may also adhere to quality standards such as ISO 9000, which provides an internationally recognized framework for quality management systems.