Burn marks and layer issues

[Rosebud635 1]

Hello everyone,

 

I change the teflon coupler of my Ultimaker2+ with the one by 3DSolex because I couldn't finish even the first layer without clogging and now it works like a charm.

But now some weird burn marks appears from time to time and I've never seen that.

I use the same setting as usual with PLA and tried to reduce the temperature from 210° to 200° with no effect.

Also I have layer issues with some not bonding so well but not all of them. As you can see in the picture the bottom layers are not so clean but the top layers are fine.

It's a 0.3 layer height print with a 0.4 nozzle.

Any of you knows about these issues? Especially the burn marks which are just weird.

 

[geert_2 557]

In my UM2 (non-plus) the thick light brown blobs and burn marks come from material accumulating on the outside of the nozzle. Then this sags and gets deposited somewhere on the print, and then gets smeared out. These often appear when there is a bit of overextrusion, for example if the layer contains lots of short infill lines where the head has to slow down and change direction. Little, thin black flakes come from the inside of the nozzle, and they often appear after a cold start, thus in the beginning of a print. If I carefully watch while printing, I can see it happen. Some materials and some colors are more susceptible to this than others.

 

[mnis 11]

White is ideal for detecting burned material ?
This will be visible if the filament is in HotEnd for too long. Many retractions in a small space also cause this effect, as well as slow high temperature printing and too much water in the filament. Concerning water content, I'm not sure if it will eventually lead to burned filament.

 

And of course, problems with constant filament movement are responsible for combustion residues. Therefore, the entire path from the filament roll to the material exit from the nozzle must always be examined for the smallest problems.

 

When assembling, ColdEnd's (the Teflon parts) must fit snugly in the coupling, so much so that the compression spring can always manage to push the ColdEnd through the coupling onto the neck of the HotEnd. But very often new Teflon couplings are far too tight in the coupling and can not be moved by the pressure of the spring. This can cause extreme disturbances in the filament flow. Then, the ColdEnd has to be made manually accurate with grinding tools. Otherwise, there may be a gap between the neck of the HotEnd and the lowest point of the ColdEnd, where material accumulates and is slowly roasted.

 

In the most harmless case, some of the roasted material is always being conveyed out, and the risk of nozzle clogging is increasing. If the gap is too large, however, material may also leak out through the threads of the hot-end and clutch. Then the exiting material runs slowly over the hot end down over the nozzle and finally even to printed areas.

Edited May 28, 2018 by mnis