I just had a very clogged right nozzle in my H2D. when I removed the nozzle the plastic in the tip felt rock hard. The filament last used in the right nozzle was PLA.
In the left nozzle for a few days I was attempting to print Nylon PA-6 with the chamber temp set at 65.
after printing I tried to print ABS in the right nozzle and it would not feed. It had to use a hex wrench heated and attached to the harden PLA to get it out. Could the chamber heat going up and down for a few days cause the PLA in the right nozzle to become rock hard? that is the only thing I can think of to why it was that way. If so, I know now to do a cold pull on the the opposite nozzle if PLA is present to make sure this doesn’t happen in the future.
A 65C chamber temperature for a prolonged period will soften the PLA in the cold section of the hotend, since it is above the Glass Transition Temperature of the PLA.
I was a while ago afraid that, what happened to you, would also happen to me during a 6hr ASA print, but I was lucky and my right nozzle containing PLA didn’t clog.
I think a warning could be introduced by the printer when the last used filament in one of the nozzles was PLA, that the user might want to check if he removed that nozzle from the tool head.
I basically see the same issue for the H2C, where there might be multiple nozzles in the rack that still contain PLA while the chamber is heated to 65C for a prolonged period.
I am not sure if the H2D can remember the last used filament if it has been switched off.
The H2C has definitely a history of the filament in the nozzles.
This is also why INDX / Multi toolhead WITHOUT AMS like system is a bad idea in general, because it sucks to be required to manually unload 4 or 8 toolheads, just because you want to make an abs print.
PLA would not harden / anneal at 65C, but it would melt and potentially fully fill the heatbreak, and because it’s in the heatbreak that makes it harder to melt smoothly afterwards. So a higher than normal temperature to get out.
I did not with ABS, but the prints were shorter than the one I did with PA-6. I also ran the chamber at 60 and not 65 so maybe that 5 degrees was enough to now vulcanize the PLA. LOL
thinking about it, I ran ABS out of the right nozzle and my AMS and not the left so it wouldn’t be an issue. I am running the PA out of the left because that is where my AMS-HT is at.
I bet that was it. I tried to use a needle to unclog it and it bent when it got most of the way into the nozzle. I was able to heat up and hex keep and melt it into the PLA and then heat the nozzle to remove it.
Just as a side note:
The glass transition temperature is working fine as a reference for PLA in this case where the softening temperature and the glass transition temperature are close.
But for many materials it doesn’t say anything at all about the material softening or not.
But to be sure, the temperature to look out for is the temperature where the material actually gets soft, looses its form, which is the vicat softening temperature. This can be very far away from the glass transition temperature, especially for materials where the amorph part is low.