Tips for the Effective Use of Purging Materials
By John Pizzo
Sun Plastech
1. How do we know which type of purge is best for our facility?
These days, there are a number of commercial purging compounds (CPCs) to choose from, and they can all be grouped into several types or categories based upon the way they work. The most popular types are mechanical or chemical, and there are some newer "hybrids" that incorporate mechanical and chemical traits. Mechanical purges seem to be the best all-around type of purge when a processor is looking to perform color changes or material changes and remove contamination. They have an advantage over chemical purges since they don’t require any soak time. However, in some applications where machine dead spots are an issue, this soak time could help as it allows the purge greater time to address these hard-to-clean areas. Hybrid purges may call for smaller volumes of purge initially, which is great for simple changeovers, but may require multiple purges for more heavily-contaminated machines. Ultimately, the best purge for any facility is one that has been tested and is proven to be the most effective. CPC suppliers offer free samples, so processors should be sure to test as many different purges as possible.
2. How can we tell if a purging compound is saving us money?
A good purge supplier can and should help you with this! Many suppliers have forms which calculate purging costs and savings when using their products. Some go a step further and compare the cost of the current purge method versus any other method or product the processor is testing. The supplier then can extrapolate to determine what the total savings could be in the course of a year. ASACLEAN has a Cost Savings Analysis calculator on its website in which the processor inputs its numbers and the system calculates the costs and savings.
3. We use our purging compound for color changes and material changes. Are there other uses for purging material?
Absolutely! Purging compounds should be used proactively as a part of a "preventative maintenance" program. For example, purge can be used to shut down and seal an injection molding or extrusion barrel. The benefits are two-fold: 1) providing further cleaning during shutdown; and 2) preventing carbonization, which often appears on start-up. And, while purging regularly is a great way to prevent screw-pulls, sometimes they are mandatory. If this is the case, a more aggressive grade of purge can facilitate the screw-pull by providing maximum cleaning, thereby reducing the amount of time and effort required.