Black gunk staining prints  

RE: Black gunk staining prints

My guess would be that Since you've been printing PC blend in the 275C + range, that some of the leftovers from the lower temp filaments that you have printed with finally cooked off and past through the nozzle, and yes I think a cleaning filament would help with regular cleanings.

however there are several ways to handle this some folks like to get the nozzle really hot (290's) and push Nylon through (same as cleaning filament basically) and yet others like to use damp Nylon to get a bubbling action. some do a small purge after the use of each filament based on the service temperatures of the filaments they are using at the time, these are all ways that folks use to keep the inside of the extruder clean to prevent blockages and big discolored strains in their prints.

Looks to me like you just cleaned yours out real good :  )

RE: Black gunk staining prints

I've seen this where small blobs of scorched filament 'boogers' remain on/in the nozzle area and drop off onto the current print.

I'm in the habit of brushing off the nozzle area before (most) every print.

I've also heard of this happening when a nozzle was replaced and not tightened properly, resulting in a leak.

RE: Black gunk staining prints

Inspect the gap between the heater block and heatsink. If there's filament oozing out the top, your nozzle is not sufficiently tightened.

RE: Black gunk staining prints

@lvet

May be I'm mistaken, but I was understanding you to say, It's not a leak, but rather the offending color is coming out with the extruding filament. is this correct?

RE: Black gunk staining prints

Hi @swiss_cheese,

Yes the offending gunk is coming out with the extruding filament.

I left a strand of 50cm of nylon filament in water for few hours, and then I slowly pushed it through the extruder. The nozzle was at 290C.

After the expected popping and  and hissing, two big lumps of brown gunk came out and then nothing.

I just launched another print and I will see if there are still problem.

If this is failing, I will open the extruder and tighten the nozzle. When I change nozzle, I always follow the E3D V6 procedure to the letter, tightening the nozzle with a dynamometric key. I cannot see any leaks, but better check it again just in case.

RE: Black gunk staining prints

I forgot to mention an important detail.

I opened the extruder where the Bowden gears are located and it was full of PLA dust coming from another print (of course I cleaned everything).

My present theory is that each gunk lump is a particle of PLA that was dragged by the PC filament inside the PTFE tube and got charcoaled in the high temperature nozzle.

RE: Black gunk staining prints

Posted by: @lvet

I forgot to mention an important detail.

I opened the extruder where the Bowden gears are located and it was full of PLA dust coming from another print (of course I cleaned everything).

My present theory is that each gunk lump is a particle of PLA that was dragged by the PC filament inside the PTFE tube and got charcoaled in the high temperature nozzle.

 

 

That can happen,

when I'm doing maintenance I tend to leave a piece of filament in the PTFE tube, to keep the hole blocked and I give a quick shot or two of canned air to clean that debris out of the chamber, then pull the blocking piece of filament out, and load the filament I'll be printing or cleaning with. I normally don't see a lot of build up in there unless I've been printing Hard filaments, I've also seen it after a jam when the Bondtech gear have been grinding away on a filament hard or not, but I can count the number of jams I've had in the past 3 years with two fingers :  ).

Hopefully you have it all cleaned out now.

RE: Black gunk staining prints

Two days of printing without a single stain.

I suspect it was the cleaning of the area around the Boden gears that solved the problem eventually.

😀

RE: Black gunk staining prints

Very good I'm glad it's all worked out, 😀  till next time 🤣 .