An LPG burner for the foundry.

June 12th, 2012

Tonight I came home and decided I shouldn’t be working on the car due to a sore wrist (aggravated by all the sawing and hand filing) so instead I looked at building an LPG burner to use in my foundry.  I had spent some time looking into different designs and basically decided to chuck something together with what I could find in my garages. I liked the idea of using a MIG welding tip as the gas jet as in a lot of the ones you find online. I knew I had some spares at home too. I made the rest from things I had lying about.

I found a brass hose barb that the MIG tip happened to slide into perfectly.

IMG_2414_1 IMG_2416_1 MIG tip and hose barb.

The MIG tip is a 0.6mm one and the thread on it is M6 x 1mm. I simply tapped the inside of the hose barb so I could screw the tip in. I didn’t even need to drill the hole, the existing one was the right size already.

IMG_2417_1 Tapping for MIG nozzle.

I then looked for some suitable tube. What I needed was something about 5/8ths of an inch (16mm) or so. Now it just so happens I have a ton of it since that’s what I am making my Austin 7 body frame from. I also happened to have some scraps of tube that would slide over that tube. I cut some suitable lengths.

IMG_2423_1 Tubes.

The tube I use is 1mm wall thickness but by mistake I happened to once buy several lengths of 1.5 wall thickness. This was perfect for me to tap to take the brass hose bard. The thread on that is 1/4 inch BSP and I have a tap for that. Again no need to drill, I just tapped the inside of the tube.

IMG_2429_1 IMG_2430_1 Tapping for hose barb.

The shorter of the rusty tubes is the choke for controlling air flow. The longer was to make a nozzle. I heated the end of that red hot with my gas torch then bell mouthed it with a ball pein hammer. In the main burner tube I drilled, milled (using a milling cutter on my drill press and cutting VERY slowly)  and filed four air slots.

IMG_2434_1 IMG_2436_1 Air slots.

I just guessed at the length. That was basically the burner done well enough to test. This was a quick hack job. If I was being nice I would have machined the ends of all the pipes on the lathe and taken more care over construction but I just wanted to throw together a proof of concept.  Next I made up a manifold from pipe fittings, a 1/4 turn ball valve and a gauge. All these things were left over from the last time I played with LPG burners. That was the jet powered beer cooler and that was over 10 years ago now!

IMG_2439_1 Manifold.

Now it turns out that regulator is only 2.8kPA which is a pathetic 0.4 PSI so I soon ditched that and hooked to the gas bottle directly (as in my jet building days).

The burner did work! Well sort of. It definitely needs some tuning. The nozzle is too small I think and the flame prone to blowing out. I was able to get the burning running from about 1 to 30 PSI but I don’t think it is burning properly yet. I think perhaps I don’t have enough air so I may lengthen the slots. I also found that at 10 PSI the flame would only stay lit over about a 5mm adjustment range on the nozzle so the length it critical. I seem to have a lot of orange in the flame and the blue part is not well defined. Choking the air off produces more orange. I think I need more air to get a better flame.  I also tried a bigger nozzle (from an aluminium can taped on!) and the flame holds much better in that. I think if I make a proper 1 in 12 taper nozzle it might be a bit more stable. The flame was a bit rough but I think smoothing off all the cut and filed edges will help there.

IMG_2441_1

Since it was burning I thought why not bung it into my furnace and see what happens. I did manage to melt some aluminium but the flower pot furnace isn’t really ideal for this burner. I also started with the crucible just sitting on the bottom of the furnace floor with the burner pointed at it. The sides got red hot but not the base. So I quickly made a steel plinth to sit it on. That helped. I did manage to melt 2 cupcakes of aluminium. I didn’t want to add more since I didn’t think I could get enough heat in to keep it all molten. As it was a lot of metal remained in the crucible after the pour since it was a bit too cold.

With the burner in the furnace I didn’t need a nozzle and was able to get it burning from 1 to over 30psi but with lots of orange flame. With the lid on flames were coming out everywhere (much to the amusement of my neighbours teenage son watching me over the fence).

IMG_2442_1 IMG_2444_1

The burner does work. I have plenty more tube so can make more to play with. I will try making my air slots longer or perhaps drill extra holes between them. I also need to build a better foundry. I might go this weekend to get some Pyrolite fire bricks. I rang about them today and they are reasonably cheap. Only $2-3NZ a brick. They also do different sizes of them as well as sheets.

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