Wednesday, March 08, 2006

A note on polymer fouling of the auger...

I disassembled the polymer extruder for the first time since it was assembled and tests began. As usual the auger, whose extreme end resides in the heated extruder barrel was frozen. Turning on the heater for the extruder barrel I was able to get the auger to rotate freely after a few minutes. Extracting it from the device proved, however, to be surprisingly hard.

When I recovered the auger I discovered that molten polymer had migrated through between two and three flights of the auger back towards the polymer pump of the mechanism. This melting was restricted to the PTFE thermal barrier part of the mechanism. Cleaning the auger was a trivial exercise. No polymer remained in the PTFE thermal barrier barrel.

This mechanism may explain why the extrusion of filament has been somewhat irregular during the tests carried out on the extruder. During the tests I've been rather cavalier in leaving the extruder barrel heated with the polymer pump turned off. I suspect that this is when the molten polymer migration occurred.

It would appear to me that extracting and cleaning the auger before making filament would be considered a good practice rule for operating this device.


vik-olliver said...

Might it be possible to block off the retreat of the polymer down the drill? I'm not sure if epoxy and a neoprene 'O' ring are appropriate, but it might be worth a shot?

Vik :v)

Forrest Higgs said...

Um, if we did that how could we use the drill to pump polymer into the extrusion barrel in the first place?