how to clean PVC extrusion die

I have, in the past, successfully used some purge compounds to restart PVC lines (flexible PVC). One that comes to mind is

You may also want to look at your die design to ensure there are no spots, especially reverse. Also, look into some coatings for the die to reduce the co-eff of friction like:

The "corrosion" of the machine depends on the material of construction. If it is a bi-metallic liner, it would need to have a nickel content backing, which I believe would be the corrosive resistant Xaloy 309 or similar from another vendor. If your screw is only of the 4140 flame hardened chrome plated variety, when reheating, you could have damage to the screw. Leaving it full may be more beneficial only in that you may be able to get material moving in the system immediately upon start-up. Extended heat soak time can/will cause huge problems.

PVC will burn if it is left inside the extruder regardless if it is a rigid or flexible formulation. The proof is the burnt material you find when you disassemble it.

When I was running f-PVC sheet for automotive instrument panels, we would typically shutdown during the afternoon on Friday; the evening crew would then come in and pull the screw and clean it and the die. Then they would button everything together for the 11-7 shift to heat up (empty) on Sunday night. Typically we would have some small amount of burnt material in the adapters and around the breaker plate unless we were running very hard. Then it was not uncommon to have a burn up during the middle of the week and we would have to purge the extruder and clean the adapters and dies. For a purge compound we would use a PVC formulation with about 50 phr of calcium carbonate, 1.5 times the lubricant level and about 2 times the stabilizer level. The idea was that the high level of calcium carbonate would scrub the extruder screw and barrel. It worked fairly well and was a good alternative to pulling the screw.

Larry Effler

Thank both of you. Your former suggestion are very helpful. I am going to let our material supplier to provide the purging compounds or buy from NOVACHEM or make some by ourselves. The screw supplier came in and measure our 2" barrel. He said the barrel was 10 thou down already and needed to replace. Next step I am going to change extrusion and die temperature setup and speed up our machine. Thank you again.

I saw your posts on plastics.com, and now I can understand what you were trying to say (I can be a little thick at times).

You should see a big difference in the process with the new barrel without any other changes.

replying to Larry Effler, Morgan Mccorkle wrote: I had a similar question. We typically have to shutdown and clean our dies every

2-3 days because of plate out issues. Running foamed PVC sheet. We had issues with burning, but since adding more processing aid, and a little more lubricant that issue is not as bad. However we have build up on the lips and behind the restrictor bars that cannot be cleaned without opening. Is there a way to clean, or "scrub" the dies without shutdown and during a run without breaking the sheet?