How to prevent PLA from sticking to the outside of the nozzle?

[aidtopia 0]

A lot of my print failures stem from the extruded filament sticking to the exterior surface of the nozzle instead of the previous layer (or the build plate).  Is there something I should be doing to the nozzle on my Ultimaker 2 to prevent the extruded plastic from sticking to the nozzle?

 

Sometimes, during the initial extrusion at the beginning of a print job, the filament will make a mid-air u-turn (driven by the fan?) and attach to the side of the nozzle.  Sometimes the skirt or brim lines will go down perfectly, but the filament starts to accumulate on the nozzle when putting down the first layer of the actual object which might have sharper corners and tighter radii than the skirt or brim.  Sometimes it starts much later, often when there's a retraction before a travel move, or when the nozzle touches a bit of stringing that sticks up from a lower layer.

 

Whenever it starts, the problem quickly becomes catastrophic.  Once you have a tiny bit of plastic on the outside surface of the nozzle, all other plastic in proximity will stick to it.  Before I know it, it's infiltrated the fan bracket and encased the heater block in plastic.

 

I've tried heating up the nozzle and brushing off residual plastic with a brass brush and even replacing the nozzle a couple times.  But it continues to happen frequently.  Is there some lubricant or solvent I should apply to the exterior of the nozzle?

 

[ahoeben 1,770]

Some people experimented with "socks" around the nozzle in the past:

Having said that, it has never really been a problem with any of my Ultimaker printers sofar, but maybe I am just lucky.

Edited March 24, 2022 by ahoeben

[aidtopia 0]

Those nozzle socks are interesting, but I think the real gem in that thread is wiping the nozzle with a little silicone lubricant before printing.  So thanks for pointing me to that!

[aidtopia 0]

The silicone oil made a world of difference.  I got 2 hours into a 4 hour print without any filament sticking to the nozzle!

 

Unfortunately, that's when the temperature sensor failed.  I'm sure it's unrelated, but I think it's final sign that it's time for me to give up on this printer.

[ahoeben 1,770]

1 hour ago, aidtopia said:

I think it's final sign that it's time for me to give up on this printer.

That's sad to hear. If you do, be sure to offer it up as a "semi-working 3d printer", as I am sure someone will be able to make it work still.