Restarting extrusion of PETG

Plasticizing Screw Extrusion Filament Extrusion
1

Hi there!

The problem.
In different sources I read that PETG does not mix with other materials. Scew and barrel must be clean before introducing PETG. Otherwise material can stick to the screw. But for small factory that does not work 24/7, but want to make PETG filament quiet often cleaning of the screw each sutdown is a nightmare and economically unprofitable.

I want to find solution how to properly shutdown the mashine with PETG and continue work next day.

What I do now.
I have filament extrusion line. I am using material Selenis Bondz GG 074. When I start the mashine first time after cleaning the screw - everything works fine. I dry pellets 65 degrees for 6 hours. Then I heat mashine to temperatures 255, 250, 250, 245, 235, 225. Then start screw rotation at speed 10 RPM. Once extrusion is stable I start winding and gradually increase speed from 10 to 40-50. When material is over in the hopper I change speed to 10 RPM and introduce mix of LLDPE-based clean compound + 50% of PETG pellets. Wait for clean compound to start extruding, stop motors, turn off heaters. Part of the compound remains in the throat.

Next day I start mashine in the same way. There is 50% chance that it will work. Third day - nothing works. Once purge material is over in the barrel - screaming noises occurs in the barrel, then extrusion speed is slowly going down up to zero. PETG is sticking to the screw in the feed section. Then only clean compound can remove PETG from the barrel.

What I tried.
I thought maybe I am setting too hot temperature in the feed zone. So I tried the same process with modified temperatures: 255, 250, 249, 239, 228, 217. The same result. I was able to work only 2 days. Third day it did not work and I had to clean the screw and barrel again.

Possible solutions
I am going to try to change my purge material to HDPE. Also currently I am using universal screw, so I am going to buy another screw designed for PETG. But all this experiments cost me a lot of time and money. I don`t want to reinwent the wheel. If someone know what I am doing wrong, please help! There must be a way to work easier with this material so it will stop sticking to the screw.

2

Buy a Teflon auger from here: Industrial Poly Straight Auger Pricing | Lundell Plastics

3

Or try Teflon lubricant

4

Thanks, but my screw looks completely different. Yellow is PETG residue.

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5

I would try to electroplate it first with maybe graphene, make your screw the negative electrode and a chunk of graphite the positive in a solution of potassium sulfate and water at 12 volts for 3 days. I guarantee nothing will stick to that screw when its done. let me know and i’ll send you the materials do it with free of charge. I must be something to do with the surface finish. Or check the PH of the material. This should be an easy fix

1 Like
6

Thanks! Is it common procedure for screws? Did you do it before? I am afraid to do such manipulations for now.

Now I suspect another problem. It can be that my screw cannot generate enough of pressure on this material and backflow occurs. It explains why during restart when purge material is replaced by PETG - extrusion speed is going down up to zero. It started happening recently, but I don`t understand why. Screw looks good. Maybe I damaged my barrel when tried to push clogged material…

Now I am considering to buy screw specially designed for PETG. Also to inspect the barrel somehow. Maybe it also should be replaced.

7

Awesome, its sounds logical to me. Yes I manufacture graphene

8

Issue is solved. There is a water belt around the feed zone before first heater. It is important to make sure water pump is enabled together with starting heating.