Should I circulate air inside a temperature controlled enclosure?
 
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surfacenormal
(@surfacenormal)
New Member
Should I circulate air inside a temperature controlled enclosure?

Hi all! I'm modding/building a temp controlled enclosure so that I can precisely manage ambient temp for ABS and PC Blend printing.

Assuming I can safely get everything to ideal ambient temps (ABS @ 60C, PC Blend @ 80C), should I design the enclosure so that the air circulates, or should i design it so that the ambient air is as still as possible?

I assume you don't want temperature variation, where the bottom of the print is at bed temp, and the top of the print is much cooler, correct? So you should circulate the lower temp ambient air, right?

Or do I have that wrong, and blowing a bunch of sort-of-hot air over the previous layer will cause layer adhesion issues?

What's the correct way to do this?

 
 
Posted : 14/10/2021 12:43 am
towlerg
(@towlerg)
Noble Member
RE: Should I circulate air inside a temperature controlled enclosure?

I believe the main object of an enclosure is to prevent drafts ie rapid changes of temperature, I would say no. Nevertheless however you heat the enclosure you are going to get convection, hopefully the gradient and velocity will be so small as to be disregarded.

Perhaps you could split the difference, measure the gradient and if excessive run a carefully deflected fan slowly, just to even things up a bit.

I suspect the next post in this thread will suggest the exact opposite. True to tell FDM printing is not a science.

This post was modified 5 days ago by towlerg
Posted : 14/10/2021 1:50 pm
surfacenormal
(@surfacenormal)
New Member
Topic starter answered:
RE: Should I circulate air inside a temperature controlled enclosure?

Yeah that makes sense. thanks for your take.

As far as I know, there's three bits to this problem:

1) The very top layer needs to be hot enough that  that the heated filament has no trouble getting it to its melting point of 230. No airflow would help that for sure.

2) Temperature delta across the object should be as consistent as possible. Airflow might help that, but there might also be better options like heat reflectors above the print volume.

3) Entire print is above tg (120c for PC), so that it can anneal and relieve tension as it goes. Yeahhhh... there's all SORTS of failures that will happen if I try for those ambient temps.

So perhaps the best solution is to heat the chamber to around 80c (my max safe ambient temp). Then, to keep airflow out of the print volume and raise print volume temps further, I might add an aluminum foil reflector setup directly on the sides and above the print volume.I wonder if anyone has tried IR reflection before to keep temps up on larger prints that are further from the bed like this? Seems like it would help get the heat from the bed on to the upper parts of the print where it needs it the most...

 
Posted : 14/10/2021 3:04 pm
BogdanH
(@bogdanh)
Reputable Member

So perhaps the best solution is to heat the chamber to around 80c....

-that's a typo I guess? Because at this temperature PETG (MK3's printed parts) will become quite soft 😉 

Mini+ with Bondtech upgrade & modified firmware...
Posted : 14/10/2021 6:40 pm
fuchsr
(@fuchsr)
Noble Member

Sounds excessive to me. I print ABS and PC Blend in Lack enclosures (which are anything but airtight) with no problems. I do put a draft shield around PC Blend. 

Sometimes I preheat to operating temperature and wait for 20 minutes, sometimes I don't. I have never seen temperature in the Lack's go beyond 36 degrees. 

Posted : 14/10/2021 6:49 pm
BogdanH liked
surfacenormal
(@surfacenormal)
New Member
Topic starter answered:
RE: Should I circulate air inside a temperature controlled enclosure?

Thank you for the replies!

@BogdanH Not a typo. I've replaced all petg with polycarbonate. The issues after that are eventual extruder heatsoak (peltier cooling can get it back down), and electronics/PSU stress (put it outside the enclosure). I'm definitely not the first nerd down this road 😀 

@fuchsr The issue really only crops up with taller PC parts that get further from the bed. The internal tension builds up, the ambient temp gets cooler as you go up, and boom... delamination 6 inches up into a functional print. 😑 Ambient temps are almost certainly a lot higher near the bed, so small prints... yeah I agree no issue there.

Posted : 14/10/2021 9:49 pm
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