Plastics processors' peer-to-peer forum: How do I avoid PC/ABS strings?

04/14/2011

It is not an uncommon issue. An injection molder notices strings of hardened melt hanging from his molding machine's nozzle when the gate pulls away from it. How to beat this problem? Ask your peers.

That's what one molder did in our online forum, and we decided to bring the helpful feedback he received here to the front page to help other processors facing the same issue. The comments have been mildly edited for clarity; you can skip to the original string here.

Starting the string of comments was this problem:

"Ok, help me out here as I've got some stringing issues. When the gate pulls from the nozzle, there is some plastic string hanging there; this naturally is not optimal.

The material is ABS and PC and PC/ABS for now. What I tried so far is to lower the nozzle temperature from 10 deg. to 50 deg. (Fahrenheit) and also raised them as well so they'd suck back less, then more. I switched from a full taper nozzle tip to a GP tip, and lowered the mold temperature. We also tried adjusting the back pressure-reducing it as well as increasing it, and done the same with screw rpm speeds (faster and slower).

My head has a dent in it from banging it on the mold; that did not help. The most problematic material is an ABS, gray in color. Thanks for any help."...
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