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ParCan Mk2 Hot End Leak

Posted by PeterBunyan 
ParCan Mk2 Hot End Leak
March 13, 2012 09:25AM
Hello All

Firstly a big thanks to everyone on the forum as reading all of your advice has gotten me this far with my first reprap (a longboat prusa)

After having the PTFE based hot end that was supplied with my Longboat Prusa break I invested in a ParCan Mk2 Hot end. The first time I used this hot end I had not screwed the nozzle tight enough into the PEEK rod and suffered quite a bad leak. After cleaning out the hot end I put the hot end back together and tightened it up, brought the hot end to operating temperature and made sure it was still tight. Since then I have had much success printing many objects, but nothing that took longer than an hour/hour and a half. After printing an object that took two and a half hours I noticed that the top layers of the object didn't have as much plastic as the bottom/middle layers, and that a small amount PLA had leaked from the joint between the nozzzle and the PEEK rod again, as per these pictures:




I haven't had time to disasemble the hot end yet but I believe the PTFE tube is not being held securely by the threaded rod/PEEK junction, and as the top of the hot end warmed up it came loose. I do have a fan pointed at the hot end to cool the PLA as it comes out (pictured below), but the positioning does not really help to cool the PEEK rod.




This may also have something to do with the recent addition of a heated bed (run at 60 degrees for PLA) and my move to an extrusion temperature of 210/220 for PLA. This was because I wasn't able to extrude fast enough at 195 degrees on anything other than the first slowed down layer, as evidenced by the extruder stepper skipping steps. According to a thread on here a while ago the faberdashery recommends 210 for their plastic, but I think i was probably pushing it too far with 220 degrees. These things combined with any PLA that may be left from the last leak probably mean that after an hour or two the melt zone has moved up into the PTFE tube and is getting forced out of the joint. It could also be that the thread gets loose at 220 degrees and doesnt hold the PTFE tube as tight as at 195/210.


I was wondering if anyone could help me out with some questions I have about this experience:

1. The last time I got a leak I used a hot air reflow tool to blow air at ~250 degrees inside the PEEK thread and around the nozzle to try and clean out as much PLA as I could, but it was very hard to clean it out. Are there and better ways of doing this?

2. Should I run my hot end cooler? Is 220 degrees ok for PLA?

3. I was thinking i could maybe add some metal clips around the PEEK rod to act as a heatsink, and make a duct for my fan. Would this be a worthwile thing to try?

4. Another idea I had was that maybe the PTFE tube was stretched by the first PLA leak, and so isn't gripped as tightly now that it is asssembled correctly. would It be worth trying to ass a small ring of PTFE tape around the joint so that when I re-assemble it the PTFE tube is held more tighty between the nozzle and the PEEK rod


One more thing I need to do is move the heater block as close to the nozzle as possible, as at the moment it is screwed on as far up the nozzle as I can get it, which in hindsight probably causes more heat to go to the cold end. this also may have been why I needed the higher temperature to extrude properly at higher speeds (30mm/s and over).


Lastly I would like to mention that I am very impressed with this hot end and these problems are due to my assembly skills. I would not hesitate to recommend this hot end to anyone!
Re: ParCan Mk2 Hot End Leak
March 13, 2012 11:06AM
Possibly you could dissolve the PLA out with warm caustic soda in an ultrasonic cleaner the same way BfB remove there support materiel. They say hot water works a well but takes longer.

I find the best way to stop it leaking is to seal the thread with silicone sealant.

Yes 220C is OK for some types of PLA. If it is too hot it runs out like syrup.

The entrance must be below about 55C. If it gets hotter than that then yes you need to cool it.

Yes I think the heater is better close to the nozzle but with that relatively short nozzle it shouldn't be too critical.


[www.hydraraptor.blogspot.com]
Re: ParCan Mk2 Hot End Leak
March 13, 2012 11:46AM
Hello nophead, thanks for the reply

Unfortunately I don't have access to an ultrasonic cleaner. Do you think boiling water will work as well? If I don't get anywhere with my hot air tool I think I will try that, unless it would adversly affect the PEEK?

I have now disassembled the hot end, and unfortunately the flange on the end of the nozzle which holds the PTFE liner in place has split (visible in the attached picture), so I have contacted parcan and asked if I can purchase a new nozzle and PTFE liner separately. Any ideas on what could have caused this? I'm leaning towards me tightening it too much when hot, possibly cracking it when it cooled down?



While writing this I recieved a reply to my email saying that he would send me a new nozzle free of charge. I would just like to re-iterate that his is a great hot end with great support!
Attachments:
open | download - 2012-03-13 18.01.08.jpg (450.2 KB)
Re: ParCan Mk2 Hot End Leak
March 13, 2012 11:50AM
Hi Peter

My Hot Ends should simply not fail in that way.
There will be a new one in the post to you tomorrow.

220 seems very warm to me for PLA.
Can I suggest with a heated bed you drop to about 180 C and work up in 3 or 5 C increments from there.
I would expect you to settle below 200 C

Thankyou for the feedback.

Alex.
AKA ParCan
Re: ParCan Mk2 Hot End Leak
March 13, 2012 12:12PM
Thank you again Alex.

When I get up and running again I will try lowering the temperature as per your suggestion. I think I will find lowering the heater block will help keep temperatures lower as the heat will be concentrated where it is needed. Im not sure why I didn't put it lower to begin with!
Re: ParCan Mk2 Hot End Leak
March 13, 2012 01:03PM
The only way I can imagine the flange breaking like that is unscrewing it with solid plastic in there.


[www.hydraraptor.blogspot.com]
Re: ParCan Mk2 Hot End Leak
March 13, 2012 01:59PM
That is a possibly, although before unscrewing it I heated it up to operating teperature, and it didn't take much effort to unscrew. There was also no PLA stuck to the metal in the area of the split, most of it stayed in the PEEK rod. I would have thought that if it was stuck to the metal enough to tear it it would still be on there after fully removing the nozzle but I could be wrong. Maybe the PLA was stuck even more to the PEEK, but in that case would it have pulled the metal off entirely or not?

My theory was that I over-tightend it while the hot end was at operating temperature and the nozzle cracked due to either the over-tightening itself or the subsequent hot/cold cycles causing the PEEK to expand/contract at a different rate and compress the end. I dont think PEEK suffers from much expansion or contraction at these temperatures though?
Re: ParCan Mk2 Hot End Leak
March 17, 2012 12:44PM
Just to update everyone, the new hot end is working perfectly, and lowering the temperature to 195 throughout the whole print works great too. I printed a new x carriage (total time just under 2 hours) and measuring the top of the PEEK rod it stayed around 33/34 degrees, which seems fine.

In the near future I would like to add a shroud for my fan to direct air onto the top of the PEEK rod and just below the nozzle, and a temperature sensor for the cold end. The extra temperature sensor may be a bit overkill, but I would like the peace of mind it will offer.


Thanks again for helping me get this sorted!
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