Author Topic: My new foundry  (Read 17619 times)

Offline NormanV

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Re: My new foundry
« Reply #50 on: October 07, 2013, 07:37:33 AM »
It is certainly worth bearing in mind the idea of casting it in two halves if I can't manage it in one piece.

Offline NormanV

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Re: My new foundry
« Reply #51 on: October 13, 2013, 08:51:38 AM »
I did my first firing yesterday using charcoal and was pleased to find that I had molten aluminium within 20 minutes and cast 2 ingots weighing a total of 1.75kg 30 minutes after lighting the fire.
I did find that it was very smoky for the first few minutes, I need to hurry up with a propane burner.
My next task it to cut up all my aluminium and cast ingots in order to produce some clean aluminium ready for casting parts for my milling machine.
Norman

Offline NormanV

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Re: My new foundry
« Reply #52 on: October 14, 2013, 10:34:57 AM »
I did another firing today. I must get a propane burner made as soon as possible, when I switched on the air blast I had smoke pouring out of the furnace. God knows what they put on B & Q charcoal, it is supposed to make it easy to light! It's appalling! I lived in Kenya for 10 years and used charcoal a lot, the locally made stuff was easy enough to light and clean burning. In fact it was smoke free and the Masai people used it inside their houses (never mind the carbon monoxide).
The smoke died down after about 10 minutes and then a huge flame burnt from the hole in the lid for another 10 minutes, after that it was fine, except that I had to recharge it twice and had to go through the whole business again.
Anyway, I produced 2 large ingots that weigh a total of 7.5kg. Two loaf tins full, now I can't make any bread until I buy some new tins!
Cutting up the big lumps of scrap is not too bad with an angle grinder, I read somewhere that I should use a stone cutting disc. I tried both stone and metal cutting, the metal cutting disc clogged immediately but the stone cutting disc worked well until it was worn down. 
Norman
The smoke is leaking from under the lid as it is jammed up by aluminium in the crucible, it stopped once the aluminium melted a bit.

Offline awemawson

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Re: My new foundry
« Reply #53 on: October 14, 2013, 11:37:07 AM »
All very good  :thumbup:

But have you tried the beach sand yet!
Andrew Mawson
East Sussex

Offline NormanV

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Re: My new foundry
« Reply #54 on: October 14, 2013, 12:07:57 PM »
Thanks Andrew, I haven't tried the sand yet. I can only do one thing at a time, money!!!!
Norman

Offline vtsteam

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Re: My new foundry
« Reply #55 on: October 14, 2013, 04:47:13 PM »
The reason for the smoke is most likely that the upper coals weren't hot, while the lower ones were. This usually occurs when someone adds a large amount of fresh charcoal on top of burning coals and turns up the blast. Smoke issues until the upper coals reach ignition temperature. Once the upper coals are glowing, the smoke (unburned fuel gasses) will burn cleanly, with as you mention, a large flame issuing from the port in the lid.

True charcoal, made from wood, burns very differently than compressed briquet type charcoal, which may contain wood waste, low grade coal, and petroleum waste products. I've used both.

The briquets will work well for aluminum melting but must be started properly, starting with a low layer, making sure that is glowing, and gradually addling layers bringing them to ignition with no blast and the lid off until all briquets are well lit. They do produce a lot of ash, and in a big melt will require replenshing during the melt. The frequency of replenishing will be proportional to the amount of fuel you can fit in the furnace compared to the crucible size. Obviously, a big melt volume requires more fuel, but reduces the fuel capacity of the furnace barrel at the same time, so has a doubly negative effect.

A furnace can also smoke if the volume of fuel is disproportionately large compared to the air supply. As the fuel is used up, the proportion of fuel reduces, and a smoky burn can clear up that way, as well.

I love it when a Plan B comes together!
Steve
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Offline NormanV

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Re: My new foundry
« Reply #56 on: October 30, 2013, 09:19:19 AM »
Well, I've made a propane burner and tested it on a small melt. It works ok but seems a bit slow compared to charcoal but the convenience it offers far outweighs the time factor. Anyway, I'm retired, my time is my own and I can always find something to do whilst the metal if melting.
I did a few calculations, it took 4.5kg of charcoal to melt a load of aluminium. Charcoal produces 29,600 Kilojoules/kg, which means 29600x4.5=133,200kj were used. Propane produces 49,500kj/kg therefore 133,200 divided by 49,500 equals 2.69kg of propane to deliver the same energy. The charcoal cost me 89pence per kilo, total cost £4. 2.69kg of propane at 1.42 pence per kilo equals£3.82. I am amazed that propane works out cheaper and is cleaner and easier to use. Have I got it wrong?
Anyway here is my burner, I made it from a 10" length of 1" galvanised water pipe, I drilled 3 10mm holes each side a short distance from one end. I then turned a steel plug, with an eight mil threaded hole through the centre. One end of the plug I turned down for a 1/2" compression fitting and attached a ball valve. The jet screws into the 8mm hole and has a 1mm through hole.

Offline NormanV

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Re: My new foundry
« Reply #57 on: October 31, 2013, 03:49:53 PM »
I need some advice from someone who is familiar with using propane as a fuel.
Today I melted 5.5kg of aluminium scrap to make ingots. It took two and a half hours! That is far too long. As I said in my previous post, I used a 1mm drill for the burner jet. If I increased the size to 1.2mm or 1.5mm would that give me a more powerful flame or would it reduce the velocity of the gas so that it would not draw enough air? Can anybody help who has experience messing around with gas jets?
Thanks, Norman