Part Sticking and Machine-Independent Documentation…

I received a detailed request for help from a blog reader last month. Below if a distilled rendition of the discussion…

The mold has run without issues for years. Now the parts stick in the mold almost every shot, there is more flash, and the cushion is much lower than recollection. All the machine and temperature settings are the same, but the result is much different. Could this be a check ring issue?

My Response
The check ring is more commonly an issue if the sticking is intermittent… which this seems not to be the case. My initial suspicion is that there is too much material being injected or packed into the mold. Second, the mold or melt temperature might be higher than usual. There are a wide host of items which could contribute to this problem… but investigating these first might give a good idea as to the cause of the defect.
Additional Thoughts
This could also be chalked up as a documentation issue. Since we don’t know the melt temperature, 1st stage fill time, part weight, or other machine-independent parameters during the good runs, we cannot quickly identify ‘what changed’ between then and now. 
If you or anyone you work with would like to learn more about process documentation… we have some free multimedia webinars on scientific molding which can be viewed at

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