It is well known in the plastics industry by process, quality, and management engineers that post-weekend start-ups increase downtime and scrap. This causes downtime, and unnecessary strain on the adjusters. In addition, there is an increased risk of contaminated parts reaching the customer leading to complaints and rejections. In some cases, the scrap in the early hours of the start-up day, usually on Mondays, reaches up to 90% of the production.
So we will mention 4 tips that are part of a purge program. Especially when there are heat-sensitive polymers like PVC, Acetal, flame retardants, and other complex resins like PBT, nylon, acrylic, polycarbonate, etc.
- 1.)The use of purging compounds must be preventive, avoiding the degradation of the resin and its additives or pigments. Use purging compounds that can be loaded in the barrels, molds, dies, and generally in the system. Thus, we will avoid oxygen entry that promotes degradation, leaving a thermally stable material that can withstand the residual heat while the machine cools down or heats up.
- 2.)It is common to leave resistors on or stand by. As a general rule, no machine should be left on. Degradation can be so great that it may force the disassembly of the screw or worse, it can reach the ignition point of the plastic and cause flames. If sometimes it’s left at a very low temperature, consider that this will eventually cause the formation of layers that will come off in the form of black spots. The ideal is to leave the system off, so the "time savings" you believe to have to reach operating temperature is regularly lost when you have to spend hours cleaning the machines manually or sorting out the contaminated parts. Turn off the resistors, because in some cases the purging compound will have a contraction that can help in the removal of some contaminants that were forming.
- 3.) The first thing to do at the end of the production of the last part before moving on to another batch or stopping a machine is to purge the barrel and mold. I considered that if the machine was produced with quality and we purged it immediately and correctly there was no reason for it to get dirty and it can start with any urgency. An important advantage if you want to keep your customer happy, don't you think?
- 4.)On the start-up day, turn on the machines in an orderly manner, starting with those that have the most urgent production and secondly with those that will work at a lower temperature. Machines that have very high operating temperatures will have to raise their temperature. Keeping a machine on for hours above 230°C without producing will promote the formation of scabs and black spots.
Learn more about how to reduce production downtime and protect your profits with a purging compound.