Question about Hotend cooling

[Igi82m 0]

Is it possible that if the Hotend fan cools poorly, ozzing can occur?

[GregValiant 1,044]

The hot end fan is there to remove the heat from the finned aluminum heat sink.  If there was no fan then eventually the heat sink would get hot enough to severely impact printing.  In that case it would cause more oozing as retractions wouldn't be as "crisp" because the filament up above is too soft and is stretching rather than pulling the melted material back from the nozzle.

I went to a 4015 hot end fan on my Ender 3 Pro.  That required a 3mm shim to move the hot end housing outboard.  I printed a little baffle that fits into the housing.  It aims the airflow at the heat sink.

 

 

Edited May 21 by GregValiant

[Igi82m 0]

I replaced the original hot end fan with a Noctua 40x10mm. I'm not sure, but I think that after changing the fan, it started to ooze a lot more. If with retraction distance 8.0mm on direct drive and temperature 180C with PLA filament there is still a little ozzing, then I don't know what to do anymore.

[Torgeir 217]

Hi @Igi82m,

 

You never said what printer you have?

I thought a direct drive feeder stepper is mounted close to the extruder, right?

If so, 8mm retraction is by far too much.. Would not (2-3) mm be something a direct drive use?

Typical retraction for an Ultimaker printer is 6.5 mm and thous printer's are using a bowden tube.

If you just changed the printer "hot end" fan, -make sure this new fan deliver same CFM (cubic feet per minute or better) at same voltage as the original fan.

 

-just my 5p.

Thanks

Torgeir

 

 

[GregValiant 1,044]

Most direct drives I've seen have retraction distances in the range of 0.8 to 2.0.  Are you sure you are retracting 8mm?  I can't retract that much on my bowden setup or I have problems with clogging.

I think the Noctua's are 12volt fans and require a buck converter to work with the 24v circuit.  They are about 20% less CFM so yes, that could be a problem.

[Igi82m 0]

I have an Anycubic Kobra. Yes, it should be 1-3mm. But with this retraction distance ozzing is worse. I tried again with the original fan, no luck. I will try to replace the hotend. 

[Torgeir 217]

Hi @Igi82m,

 

Almost forgot this, the nozzle is worn over time, it might be more like 0.6mm instead of 0.4mm.

Pressure would not build up, but "no" sign of under extrution -but lots of stringing...

Further, a little to high nozzle temp can have "same" effect ish..

 

But, you're going to change this part, so we'll see.

 

Thanks

Torgeir

Edited May 21 by Torgeir
Typo.

[Igi82m 0]

I replaced the original hotend set. This did not solve the problem. To get a good retraction test print without ozzing, I have to print, for example, PLA Silk filament much below the recommended temperature. This means that I have to print only with 190 C instead of the lowest recommended 210 C.
Same with normal PLA filament, no more than 190 C.
The retraction distance is 2.5mm, if I increase it, nozzle starts popping and leaving gaps in prints.

Is this normal or something wrong with the printer?

 

 

[Torgeir 217]

Hi @Igi82m,

 

If a filament is left without any protection as into sealed airtight bag or container, it might attract water directly from the air.

This is very important if you're living at places with high humidity.

Printing with filament containing water, will make extrusion uneven and sometimes pops out hot vapor damp that makes dents into your object during printing.  Most plastic filaments attract water moisture, some more and some less.

 

To remove water from filaments, people use food dehydrators to "refresh" dry out water from a roll of filament.

Between 50-60 degrees Celsius for 8 - 10 hours. If you go higher than this temperature, the coil will start to degrade/deform.

 

Also, if filaments are contaminated with water, it may oze and more as temperature increase.

 

Thanks

Torgeir

 

Edited May 31 by Torgeir
More info.