I was recently at a molder’s facility who was having a complication with one part…
Even though this polypropylene part has a curve, we have a problem with it curving too much thus causing a complication with assembly.
note: when discussing the troubleshooting process, they have investigated most aspects of the process, but it turns out they never considered trying differential mold temperatures.
Although I try to avoid using differential coolant temperatures when possible, it would be a good option to investigate for this mold/process combination. Since PP has a high degree of crystallinity, decreasing the temperature of one side will cause a tendency to bow towards the opposite side due to differential shrinkage. In this case, the coolant temperature differential between one side and the other might only be 5 or 10 degrees, but it might be enough to counteract the bowing.
Before using differential heats, it would be beneficial to measure both the coolant temperature entering and exiting the mold as well as the temperature of the mold steel. In many cases, you may be using differential coolant temperature, but the result may be similar mold surface temperatures.