Filament 'deforming' in hotend

[humorlessclown 0]

A few weeks ago I replaced the heating block on my Ultimaker 2+ Connect (accidentally snapped the nozzle when changing it and the thread got stuck inside the old one). Since then, I have been having this issue where the filament deforms, creating a lip inside the head that prevents it from retracting/extruding (see image of the end of the filament). This makes me think the bowden tube is not fully inserting, and the material is oozing out between it and the heating block, but the tube will not go in any further.

 

I suspect I have made a mistake when re-assembling, but I'm not entirely sure what the issue is. Has anyone experienced this before? I can supply a photo of the machine if necessary.

[gr5 2,247]

I think maybe you are right that this is where the bowden touches the teflon part.  This region should be far enough from the hot end that it doesn't do this so I'm thinking your 3rd fan isn't spinning.  Whenever the nozzle is > 60C the rear fan should start spinning - please check that this occurs by manually heating the nozzle to e.g. 100C and checking the rear fan.  I'm not talking about the side 2 fans.

 

You may have pulled the wire a bit or maybe you unplugged the fan and forgot to plug it back in.  Usually fan wiring issues happen in the 2 inches (5cm) or so above the print head or inside the print head.

 

Alternatively maybe the fan is in backwards.  It should blow towards the teflon part.

[gr5 2,247]

Also maybe take a photo of your hot end as sometimes people assemble it wrong.

[humorlessclown 0]

Thanks for your reply! After posting here I found out about heat creep, which seems to be what is happening.

 

I tested the fan as you suggested, and it was spinning when the material heats up, however it was rattling a bit so I suspect it was not working as it should. Conveniently I had a spare so have replaced it. Hopefully that has done the trick!

[gr5 2,247]

One thing I don't like about the um2+ is that the aluminum cylinder hides from view if the bowden is properly in the teflon part.  The bowden is never perfectly straight and tends to hit the tiny vertical wall in the teflon part.  In the UM2 "regular" there is no aluminum cylinder but instead a spring which you can see through so you can tilt the bowden above the print head while sliding it in.

 

This reminds me - you want to tighten that round nut just the right amount so that the aluminum cylinder is just barely loose.  This is a more serious issue as then there can be a gap where the teflon white part touches the heater block.

 

By the way - having a gap just at the bottom of the bowden isn't normally a cause for jams like yours unless the fan isn't working.  I suppose it could also be a problem if your room temp is unusually high (>75F), or you print PLA hotter than recommended (>210C).  This isn't a problem for other materials as only PLA gets soft at such a low temp (52C).  Despite this (or maybe because of this), PLA is still the easiest material to print.