anti gravity material?

I've just re-setup my nozzle, changing it for a new one with a G555 thermistor (before I using the classic 100k with large glass bead, not sure the brand). Clearly, I changed the Sprinter's thermistor setting.

Before I was processing PLA at 200C, now it came out in droplets at the same temp so I imagine the two different thermistor are measuring incredibly different temperatures. I dropped the temp 5C each time and arrived at a decent extrusion at 170C (30C difference!!).

However, if I try some extrusion "in the air" (not on the bed) the material flowing out of the nozzle goes up!!!!! Why this happens? I thought lowering temp would avoid that but at 170C still does it.

Is there a physical explanation?
Thanks again for your knowledge sharing.

It curls up if the hole is not perfectly round (hair curls for the same reason) but it is of little consequence when building because it sticks to the layer below and does not get chance to curl. It is a nuisance during warm up because it tends to stick to the outside of the nozzle and burn.

I think longer nozzle holes make the plastic less turbulent and so less likely to curl, but the downside is it takes more pressure to extrude.

ABS seems to run straighter than PLA.

Edited 1 time(s). Last edit at 11/11/2011 11:25AM by nophead.

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[www.hydraraptor.blogspot.com]

Fantastic answer Nophead, thank you!

It can also be cause by large burrs on the inside lip of the nozzle, also. In this case it might obstruct flow enough to cause a problem at higher flow rates.

Also, it sometimes creates alignment issues with bridges and can cause some unruly behavior with overhangs.

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www.Fablicator.com

I'm running PLA and when I tried to run home made nozzles it had a tendency to curl up. In the end I believe that its due to a poorly built nozzle that probably has some internal restriction. The factory built nozzle flows great and doen't have a chance to curl up.