Material wrapping around the screw

One more thing is when your doing your barrel / screw checks make sure they have cooled to room temp. Measuring them hot will give you a false reading

YES. It is a good idea when you have a unit opened up, check ALL of the components before putting it back into service.
Rick.

Here is a little info to preface my issues. We were having problems keeping the part weight consistent. pulled screw, found broken screw tip and barrel. replaced with all new, started up and continued to have the same problem with part weight inconsistency , pulled mold ran wire wheel through hot runner system, new gate bushing on mold. Still experiencing the same problem. Cleaned screw of wrap(always in one location) it was on top of screw flight and also at base of flight. Found a bad heat zone and fixed. Ran for 10 minutes, pulled screw back and still, wrapped at same location. Is it possible my barrel is worn?

The big giveaway is your struggle to keep sizes. This is telling you the barrel / Check ring system is worn and leaking. Also Rick's analysis is correct.

You can't make good parts on worn equipment. Pull the screw, check the barrel and Screw diameter's per the manufacturer's specifications. Also check the non-return valve sizes. 90% of the time , there's your problem.

Hope this helps

Bill Tobin

Thanks for the feed back. The machine is a Negri Bossi. This happens while it is running. It is especially bad when running PC it still happens with PP. I have a feeling for a long time that a the screw/barrel/or checkring are worn but can't seem to get anyone to listen. I run parts on this machine that have extremely close tolerances and struggle daily to keep size :(

Excessive barrel temp settings, worn injection unit resulting in enough room for the melt to stick to the screw instead of being sheared off the barrel wall, folks cleaning the screw with Emory cloth versus a brass brush; these are the biggest reasons I have had this issue. I have also seen this happen predominantly with one brand of IMM's. Do you perchance have one of these machines? By the way-Does this happen while running or after a shut down? That could make a differance as to the root cause.
Rick.