Forge Blower

by vik, published

Forge Blower by vik Mar 26, 2011
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Forge Blower by vik is licensed under the GNU - GPL license.

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This is a parametric design for a centrifugal fan. I wanted one that could take a knock or two to blow air into my forge with, so I designed one with parametric wall thickness, fan clearance, diameter, height, output nozzle and inlet hole diameter etc. It can be printed entirely without support material and the two halves are held together with 3xNo.8 screws.

The sample fan is 70mm in diameter and 45mm high. It uses a small 12V motor I salvaged, but can easily be modified (physically or programmatically) to suit a range of motors.

The forge now has an RP'd 110mm diameter blower, and that blows plenty of air into the tuyere. The motor I chose does not have a very high RPM. It can only just reach white heat with one fan, but does not melt even in PLA due to the high airflow. A much faster motor on a smaller printed blower produces a higher flow, so I'm sure I can get more out of it later.

If you want one with a handle on, see http://www.thingiverse.com/thing:8096


Print case, impeller and lid. Attach motor to lid with 2 x M3 screws or similar. Warm motor shaft and insert into hole in base of impeller. Do not trim printing goo strands off the interior of the impeller.

Ensure that:

a) Impeller clears motor mounting screws, and
b) Impeller is fitted centrally on the motor shaft.
c) Impeller will rotate in the right direction to "brush" air out of the outlet.

Fix the lid to the case with 3 x small countersunk woodscrews. Hook motor up to relevant volts.

A nozzle may be made of any convenient tube or sheet metal and fixed to the outlet with duct tape. Hey, it's a ducted fan so this is a legitimate use.

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What kind of machine did you salvage a high-speed 12V DC motor from? I've got a few DC motors out of old inkjet printers but they have quite odd power supplies like 35V, so I don't think I'd get much speed out of them without loads of batteries.
I have a large and medium-sized motor from a washing machine, but I think either of those would be over-kill for this, assuming they run on 12V. Going to use the larger one for a lathe project and not really sure what to do with the medium one yet.

I just melted bronze in the forge and cast it, using the 110mm fan and some charcoal. It works!

Didn't come close to melting the fan, I'm glad to say. The recycled car battery is holding out too.

how do you balance this rotor? I guess it would be pretty noisy if left unbalanced, and probably deliver less air/wear more.

I balance it by hand, just manually turning the impeller round on the motor driveshaft and looking for wobble. As the heated driveshaft cools off, the plastic gets firmer and this makes minor corrections easier.

The first one I made was not well balanced and packed with paper tape etc. Sounds like a hairdryer. But the second time with the 110mm blower I knew I had to heat the shaft up and it all just worked beautifully.

(Hmm, had to type that in twice.)

Despite my continued protestations that PLA is somewhat fire resistant, I have no illusions that PLA will melt catastrophically.

Please to be being careful with plastics, beer cans convey heat too! ^.^

I put the sample fan in front of the forge tuyere and cranked it over for a couple of hours on slow. I only just went to yellow heat. The blower's exit hole felt a little warm but was nowhere near melting. Given that there will be a thin metal tube giving it more distance from the tuyere, I doubt it's going to melt. Unless I really stoke the forge up and cut the power.

A shiny beer can tube with air rushing down it tends to stay pretty cool. I've used tubes made of even thicker aluminium on plastic-bodied, hand-cranked centrifugal blowers, and they don't conduct the heat back to the fan. As long as air goes down the tube. I've seen some awesome disasters caused
by old-style bellows where the outlet flap has failed or not been put back in and they started sucking!

Oh, scrap bits of PLA are great for lighting the forge with :)

The aluminium would act as a heat sink wouldn't it?

Well, sort of. Fortunately beer can is very thin and the air flow past it quite high, so it acts like a fan-cooled heatsink :)