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How variable does air cooling need to be?

Posted by leadinglights 
How variable does air cooling need to be?
March 16, 2023 11:36AM
Can I pick some brains about the need for variable cooling? Previously I have rarely needed cooling, even when printing PLA. When I needed some cooling I delivered this from a diaphragm air pump, through a 6mm I.D. silicone tube to an air ring similar to a Berd Air Ring. Where there has been a need for more air I have used a bank of four 25mm fans in addition to the above arrangement.

The option I now have is to use two Nitto Kohki DP0102S 24VDC BLDC Air Pumps, which will allow me the options of:-
  • No Air
  • Some Air
  • More Air
The question is, is it useful to have an airflow that can be controlled in smaller steps? e.g., 10%, 25%, 50%, 75%, etc?

Re: How variable does air cooling need to be?
March 16, 2023 01:00PM
Hi Mike,

... eventual of interest would be a "kraken-type" tubing structure with segmentet hoses (as used for CNC-coolant), where you can direct air-flow direct on special spots ... or too, attached to the print-head, if the printer can handle the aditional weight ...

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Re: How variable does air cooling need to be?
March 19, 2023 06:25PM
I use two 12 volt blowers in series on the 24 volt PWM signal. This gives me control from 5-100% PWM. Although PETG is often advertised as needing no cooling, I find that the difference between 15% and 20% cooling speed can make or break bridges.

So yes, fine control is very useful, and why would you Mike, of all people, think otherwise?

There should be pico-Pascal control of the air flow versus plastic viscosity, and I expect you to jump on this ASAP ;-)
Re: How variable does air cooling need to be?
March 20, 2023 03:30PM
@rq3. The reason I have little knowledge of the art of 3D print cooling is that most of my printers had little need for it. This, in turn, was caused by most of my prints being designed not to need bridges: In the more extreme situations, I made things to be screwed or glued together thus eliminating the need for bridges. When I did need extra cooling I either directed the cooling air from the hot-end over the print or used the bank of fans mentioned above.

The diaphragm pumps that I have got have near-constant speed motors, and PWM would not be of much use. Since these pumps are very well-made I will try them out with various bridge torture tests before dismissing the idea.

Re: How variable does air cooling need to be?
April 20, 2023 02:45PM

This may, or may not be of some use but some time back, I investigated the effect of deflected part cooling air on the temperature inside the nozzle. The issue being that deflected part cooling air can affect the actual nozzle temperature but that the sensor inside the hot block is somewhat isolated from that deflected air so does not react to it. So I guess my answer to your question is that the positioning of the cooling air is much more important than the flow volume. My blog write up can be found here [somei3deas.wordpress.com]


Re: How variable does air cooling need to be?
April 24, 2023 02:41PM
Thank you deckingman. I have found over the years that steel anywhere in the path from the heater element to the nozzle was really bad news. I have followed your investigations and got very much the same sort of temperature drops with a very short stainless steel tube between the copper heater block and the brass nozzle.

I have managed to avoid too much cooling of the nozzle as my various annular and "Berd Ring" type coolers are directed away from the nozzle.

The problem of how to get a variable speed with supposedly constant-speed BLDC diaphragm pumps has gone away though as they do seem to have about the same voltage/speed characteristic as a BLDC fan.

I have nearly finished the auxiliary box holding two of these BLDC diaphragm pumps and hope to report on how they do in my rebuildlog on this forum in the next week or two.

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