posted June 06, 2001 09:03 PM            

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Originally posted by closkey:
The company I work for extrudes PVC onto a braid for a customer. We are having problems running a smooth product. Our screw has just been rebuilt and a new barrel is on it's way. Both had 12 years of wear on them.

Question: If the barrel is worn beyond recommended tolerances, will this cause raw material to get to the head of the screw faster than before? What might I try to get the compound to breakdown better until the new barrel comes in? Finer breaker plate/screen packs/etc.?

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Bigger barrel = more slip = longer residence time. And usually a little more heat and mixing. You may get a less homogenous mix with a new barrel, but that depends on the screw design and temperature profile.

What exactly do you mean by SMOOTH product? Can you describe what it looks like?

posted June 08, 2001 08:13 PM            

quote:

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Originally posted by closkey:
When I say "smooth", I mean extrusion over the wire without any bumps. I was out yesterday, but supposedly, the new barrel is in. It will be interesting to see how it affects our process.

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What do the bumps look like - unmelted material? Burned material, contamination?

A picture would be worth a thousand words . . .

louis

posted June 11, 2001 06:29 PM            

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Originally posted by closkey:
Before we put the new barrel in, the bumps WERE unmelted material. We could do a cross-section and see white material. We were running black colorant. Now, with the new barrel in, the extrusion is running just fine. Only problem is that the screw is rebuilt to run AVS instead of PVC, so the line speed is down a little from what we were running, which should be the other way around, we should be able to run faster.

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Not sure what AVS is, but if you are running PVC you should have a screw "designed" for PVC. The output for an extruder depends on the proper conveying and melting capacity of the screw. That is one reason why the clearance between the barrel and screw is important. The compression ration should be anywhere from 2.5 to 1 up to and over 3 to 1 depending on the type of PVC used.