Mid print colour change risks cooking the nozzle?
I've recently been experimenting with mid print colour changes (with PLA) and I am having great fun doing it. However, I am paranoid about ruining my nozzle if I take too long to change the filament. The hot end remains heated after the first reel is automatically unloaded and I am worried that the residual plastic in the nozzle might be cooked if left for too long. I've been very careful to do the swap promptly up until now, but what if I am held up somewhere or gone to the toilet or something and left the printer hanging for several minutes, or hours! How likely is it that this would damage the nozzle?
RE: Mid print colour change risks cooking the nozzle?
No guarantee, I have done filament swaps a long time after unload.
If I recall correctly, the nozzle heater times out, but the hetbed remains heated, then when you return to change the filament, the hot end, re heats,
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Mid print colour change risks cooking the nozzle?
It's been awhile since I've done one, but as I recall when you get to ca color change the print head parks over the right front corner of the bed and beeps every few seconds to get your attention. You then push the knob to retract the filament and it patiently waits for you to insert the next color, purges it, asks if the color is correct, you push the knob, it purges a little more then continues the print.
When I was doing this a lot I would leave the printer unattended and sometimes would go an hour or more before answering the beep. Now, I don't recommend that, and I do try to change filament quickly, but I have let it go. I want to say Joan is right if you wait too long that the nozzle goes cold, but I can't recall. I do know that on my Ender 3 it does that because almost the moment it parks the print head it shuts off the nozzle.
In any case I don't think you're going to have nozzle damage. The temperature the nozzle is at is just enough to keep the plastic in a semi fluid state, little bits of it get stuck to the heat block while printing and it takes quite a long time for that stuff to discolor. 
Here's one of the fun ones I did with this technique.
Cheers
-Bob
Prusa I3 Mk2 kit upgraded to Mk2.5s, Ender3 with many mods, Prusa Mini kit with Bondtech heat break, Prusa I3 Mk3s+ kit