Blowers v. fans for cooling PLA

I was playing with a friend's Replicator and we tried printing a 1/2" hollow ball - we just used all the default settings (no support, brim, raft, etc.) and the thing came out perfect. My typical experience with the hot-end spending so much time over a small area would produce a lot of curling and otherwise make a gooey mess. Two things I noticed: the Replicator default temp is rather high (230C) but it also has a pretty wicked amount of air blowing on the part - it nearly whistled as it moved over the part. It seems that most people use a fan for blowing on the part rather than a squirrel-cage type blower. Fans have more airflow but at a lower pressure differential. This is good for blowing a broad swath of air across the part in general. However, if you try ducting a fan to concentrate the airstream, the actual CFM is reduced dramatically. Blowers, however, can produce a much higher pressure differential and hence when ducted can produce a high velocity focused air stream.

I tried printing the same ball with my setup with a traditional ducted 40mm^2 fan, and I got lots of curling and gumminess. I then switched to a ducted blower and it printed like a dream. You can hear and feel that much more air is blowing over the part. As a bonus, I also cut a small port in the top of my duct to blow on the cold-end heatsink plate. Is there any reason why people tend to use fans over blowers?

With PLA, the more air movement, the better as far as I've seen. A blower is in the plan for my printer.

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Possibly the first thing people think of is a CPU / graphics card cooling fan, when it comes to cooling something. Blower fans aren't seen as often so don't come to mind.

I use generic cooling fans for the heat sink on the hot end, but a separate blower fan for cooling filament as it's laid down.

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I am using two blower fans on mine. They work good but could be better on the opposite side of the nozzle. I plan to make a duct to get some cooling on all sides.

I tried to print a 1/2" ball with my old setup and it did not work. I then made the duct to get cooling on all sides and I was able to print it. It is not perfect but it worked.

I use one of these currently with a duct:
[www.dx.com]

Edited 1 time(s). Last edit at 10/15/2014 05:14AM by Ralph.Hilton.

I think the correct way of stating the question would be:

Radial fan vs Axial fan

For me, the radial fan has way more air-displacement with the same power consumption. Besides that, the air-flow is easier to guide in a certain direction. Therefor I prefer the Radial fan. I have noticed that when you cool a too-large area, even with PLA, you will get cases of warping, especially when printing objects with large surface areas. When you have a radial fan with a small nozzle blowing mostly on the area directly underneath the hotend nozzle, you don't cool too much of the surrounding material and keep warp to a minimum.

It's a bit about balancing out the heat provided from your heatbed vs the cooling of the freshly deposited filament. You don't want to cool down too much, just so that the bridges stay tight and don't hang, and so that the small printed areas are hard enough to print the next layer on, but soft enough to prevent massive warping and eventually failure of a complex part.

Not sure, but I believe this is what I ordered:
[www.ebay.nl]

The only drawback that I noticed, is that when you run the fan at low speeds, sometimes it doesn't start to rotate, so it needs a minimal power input to get it started. PWM values ranging from 1-255 in my firmware, I found out that I at least need to set the PWM to >80.

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http://www.marinusdebeer.nl/

One thing I've noticed in a lot of duct designs is an attempt to blow air at the nozzle tip equally from all sides. If you were able to blow exactly equally from all sides, by symmetry, the air velocity at the nozzle would be exactly zero - most of the air would actually end up going upwards rather than across the surface of the freshly laid filament.

In early trials with air directed close to the nozzle I discovered the effect that LoboCNC mentions - there is actually not much cooling where you want it and there can be parts that get no cooling at all. A later design used an air ring which sent air directly down onto the print and was much more succesfull. I would have to admit though that it is only about the same as any good fan. I have attached a sectioned drawing to explain what I mean by an air ring.

As far as the discussion about the relative merits of axial versus centrifugal blowers, the axial blowers are lighter for any given air flow but the centrifugal type can deliver its flow against a greater back pressure - so is better when connected to duct work.
One observation in passing, the small heatsink cooling fan on the left is directed against the very square and blocky body of the extruder. This creates a lot of turbulence and gives very even and effective cooling. I am more pleased by this than by the air ring which was a lot of hard work.

Edited 1 time(s). Last edit at 10/15/2014 02:30PM by leadinglights.