Injection molding is the most ubiquitous and scientific of all of the plastic forming processes. But, even in light of the advances made in the industry, many molders are still using virgin resin or a homemade concoction such as resin mixed with laundry detergent to purge screws and barrels during color or resin changes. These purging methods may work eventually, but after how many pounds of scrap are molded? It is not uncommon for a color change, from dark to light, to take 1 or more hours. However, mechanical purges with good material affinity and good detergent power can offer drastic reductions in changeover times by scrubbing the first material of screw flights and in nozzles. Chemical purges can be used to reach hard-to-clean areas in the screw/barrel or hot runner, especially if they are not optimally designed. Since mechanical and chemical purges clean in different manners, it makes sense to look at them separately where applicable. Commercial purging compounds (CPCs) are gaining widespread acceptance in the injection molding community for an array of reasons.
The main CPC applications for injection molders include:
- Cleaning screws and barrels
- Assisting with screw pulls
- Purging hot runners
- Injection molding-specific tips