In my career in plastics processing and working for Asaclean, I've run into many examples of plants that were hesitant to use purge because they only processed black resins. It's an incredibly common process, but one that can lead to serious issues down the line. It's perfectly logical. In many areas of life, if people can't see something being bad for them in real-time, then they discount or brush off the potential long-term consequences. This is the case when it comes to skipping purge when using black resin.
There is a false belief that there are far fewer defects in black parts. If the part looks good, why should you purge? Blemishes and processing issues that wouldn't be accepted in other colors are overlooked in black parts. But just because a defect is hidden, that doesn't mean it isn't there.
This idea is present in all industries that process plastic parts: automotive, household appliances, industrial product, electronics, etc. The process and quality engineer must not forget that there are materials that are sensitive to heat. There are resins like PVC and POM that burn easily. In the same way, some ingredients such as flame retardants, waxes and couplings can degrade as well. Fiberglass resins or other fillers can break down leaving residue on the screw and tooling.
Regardless of whether the process is injection, blow extrusion, profile or sheet, I will list two benefits of cleaning the machines, even in this case of black resins:
1. You Will Always Guarantee Good Parts
If you purge regularly, your machine will be clean and free of residue/contamination of any kind. Otherwise, the degradation will occur and simply will blend into the part. In the best of cases, it will generate a visible defect that can be observed. If you don't notice the defects, you may start having parts that will functionally fail on the market. The worst thing about degradation waste-related defects is knowing the root cause. This can be a real headache for both the your business and your customer. If your parts start failing, vendors will stop trusting you with their contracts.
The loss of material due to out-of-specification parts, even whenrecycled, always implies a cost: energy, waste, labor, or even storage.
2. Your Downtime Will Reduce Significantly
A quick purge that avoids contamination means you will have quicker changeovers and fewer teardowns. Now consider downtime as any cause that makes you unable to take advantage of the machine to obtain the desired amount of parts in the desired time.
So why let layers of degradation build up on the screw?
This can lead to longer fill cycles that are reflected in fewer shots per hour in injection and blow extrusion, or slower production speeds that mean fewer meters or kilograms per hour in sheet, profile or blow extrusion.
If we accumulate the seconds lost for each cycle in the machines that are not filled at the desired speed in a year, we can have cases in which the total loss can be from days to weeks. Then the Production and Plant Manager must be attentive to implement good cleaning practices that ensure the greater efficiency of the equipment. When running black resins, keep the big picture in mind.
Working below the efficiency for which the process was designed is wasting money: labor, buying unnecessary extra machine capacity.
Ready to reduce your production downtime to protect your profits? Learn more about how purging compounds and process efficiency work in tandem.