Posts: 1
From:San Antonio, Texas, US
Registered: May 2003

posted May 30, 2003 04:03 PM               

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hi,

I am a student in electrical engineering, I designed an extruder single screw. I started trouble shouting with acrylic and with a temperature of 315 F. The screw turn for a couple of seconds and then it stop. I can move or take the screw off, it is completely glued to the barrel. Can you direct me with some information? I try using higer temperatures but that did not work.

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Posts: 148
From:Wharton, NJ, USA
Registered: Jun 2001

posted May 31, 2003 06:59 AM               

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What is the MI of the acrylic?

What is the materials of construction of the screw, barrels, and throat.

How tight is the screw to barrel clearance in the throat area, and the remainder of the extruder?

First vacuum out all of the pellets from the feed throat.

Take the head off and clean off any material you find.

Then I would let the extruder soak at 450F for about 2 hours before trying to turn the screw. Turn the screw backwards slowly if possible a few turns to take additional material out of the throat. Stop if the screw begins to move out of the gear box. Then try turning the screw in the normal direction to purge the screw.

There are more steps to solving these problems, but please report on the questions above and how things go first.

Tom C

[This message has been edited by Tom C (edited May 31, 2003).]

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Posts: 17
From:bethesda MD USA
Registered: Sep 2001

posted May 31, 2003 11:00 AM            

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I agree with Tom but add the following alternate:
Find a suitable solvent for acrylics (call supplier of your material). At this time, too, make sure you got an extrudable grade of acrylic. That's why Tom asked you for MI (a measure of viscosity). Some acrylics are so high in molecular weight that they can't be extruded.
I assume your machine is small enough to tip in such a way that the barrel is angled downward. Put the whole assembly over a large pan and take it out into the Texas sunshine where you won't breathe solvent vapors. Clear the hopper, remove the die and put solvent into the hopper, soak until screw turns and can be disassembled. Then, before you start up again, talk with whomever gave you information on screw and barrel design (maybe you did this already) or with Tom or me or someone who knows about barrel clearances, thermal expansion, horsepower, grades of resin, etc. And try the next run with polyethylene; it's much less likely to give you trouble.
This project is in electrical engineering? Sounds more mechanical. Extrusion electrics mostly deal with controls or power/heat input/output. You might learn more about extrusion by doing analyses of power consumption on a real extruder in a factory, especially if you relate power cost to total mfg costs.
Good luck and be careful
Allan Griff

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Posts: 165
From:McHenry, IL USA
Registered: Nov 2002

posted June 01, 2003 06:41 AM               

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Solvents for acrylics (in order of preference)are Xylene, and Toluene. However, there's a chance that the acrylic you've tried may be slightly crosslinked.

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Posts: 1
From:Thomasville Ga USA
Registered: Apr 2003

posted June 13, 2003 06:06 AM            

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just a note any chance of metal getting into the barrel or possiably piece of a flight breaking off

this is happened to me in the past where a piece of broken flight came of and shear welded itself to the screw and barrel

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