Hot Runner/Tolerance Issues

Hi all,

I’m currently running a 16 cavity hot runner mold with acetal. We ran the first lot of material and all the QC came back good. We swapped to another lot and now we’re having parts coming out way smaller than before. I’m also getting a cavity that’s coming out decently larger than all the others.

I’ve never run a hot runner mold before, thus I’m not sure how sprue, manifold, or cavity temps would play a role in some of the issues I’m having. We have not adjusted anything from the last lot of materials. I’m also having an issue with getting consistent parts from the same cavities as well.

For information sake, currently running the barrel from (Rear) 375-400 (nozzle). Sprue - 450. Manifold - 450. Cavities – 470. This information is per our customers setup sheets as well. Leaving around 6.75 mm of cushion during holding.

Any and all suggestions would be greatly appreciated. I’m at a loss here (probably mostly from frustration).

I run a few 48 cavity acetal molds. Your temps are kind of high but that might be necessary due to deficiencies of the hot runner. Can you split the hot runner plates to remove the solidified tip on the drops to the cavities?

Are you seeing any other defects?

What you use for cleaning of hot-runner? Similar i have similar problem with PA6.6 GF30, solved by proper tool maintanace with compound for cleaning and after production inside of hot-runner is PP.
Because of that later i was able to reduce a bit temperatures and get more stability in process and less scrap rate. Now for all tools i have regular maintanance by number of shots and scrap is down from 5% to 0.3-0.7%, dimensions all the time in tolerances.