Problem

I got a call from a new client that had problems with one of their extruded PVC products. The parts had been fine for years but they had started to get customer complaints about the PVC warping in hot weather and sagging. They wanted to know what was happening and why. They had two samples of good products from previous production runs and a sample of the newest production run that was causing the issues. They had already run a lot of analytical tests and were still  not sure whether the problem was due to a change in material formulation or maybe due to improper compounding. They needed to fix the problem and find QC methods to prevent future problems.

Action

They overnighted me the three samples to examine. As soon as they arrived, I measured Shore hardness to see whether the new material was softer than the two good material batches from the past. The new PVC parts were substantially softer meaning that the PVC formulation had been changed without the client’s knowledge. This was causing the PVC to soften when heated in direct sunlight because a material that is harder / stiffer at room temperature requires a higher temperature before it softens. I also measured the gloss of the samples and found very large differences. The new, bad batch of PVC had a lower gloss which often indicates poor mixing or improper extrusion conditions. All testing was performed in one morning whereas all the prior testing had taken weeks at substantial cost.

Solution

Now that we knew that the PVC formulation had been changed and was unsuitable, we created a new formulation and specified that it could not be altered. In addition we implemented two new quality control methods, Shore Hardness and gloss, to be performed on every production run. That was to ensure that customers would not experience PVC warping in the future. The customer was very impressed with the fast and comprehensive solution.

More information:

Raising the Softening Point of PVC

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