Stevious said:
That's basically what I've been using for years except the air and gas are switched. I could probably set it up for $40. Just a few pipe fittings.
building a melting furnace
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That's basically what I've been using for years except the air and gas are switched. I could probably set it up for $40. Just a few pipe fittings.
goldsilverpro said:
There 'ya go... $40 beats %360 any day. A glass furnace probably needs a ceramic burner outlet, but a gold melting furnace doesn't. Now we know where to buy the gas/air mixers from! Indeed all it really is is an orifice of the right size and a piece of iron pipe connected with another at a T.
Ever though of making a small (~50 oz or less) furnace? Seems like there is a need.
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I built a small furnace that accommodated #1 crucibles. It served the intended purpose perfectly well. I even made a lifting and pouring shank that fit the crucibles properly (I am a retired machinist/toolmaker with a shop). Those I still have, along with a number of new crucibles. They were retired when I discovered that a #1 was too small for the business I had at hand. I ended up building a second furnace that accepted a #8 crucible. It turned out to be an excellent fit for my needs in that one needs considerable volume when melting cement silver. I used to pour anodes that ran 200 ounces, ±.Stevious said:
There's absolutely nothing wrong with a small furnace. In fact, it's wise to size the furnace in keeping with the work you intend to do. Crucibles are much more reasonably priced in small sizes, plus it makes no sense to fire a large furnace when the task at hand can be handled by a small one. It's also a great way to save space, and to minimize the amount of heat you dump in your work area. (I had a dedicated room, equipped with a hood, for running my various furnaces).
Harold
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My design was just opposite that of GSP's. Both work. My logic was it was easier for traces of natural gas to make a 90° turn than the large volume of air involved. So long as the blower can deliver more air than is needed, it makes no difference. I used a gate valve to control air flow, as well as natural gas flow in all of my designs. Never a moment's trouble, and all of them fired well.
Harold
Harold
Looks perfect to me. Joppa's real cost is the ceramic burner head. Since firing times in a kiln can be maintained up to 2400f for up to 20+ hours, it makes sense that it is the expensive part. Remove that cost, and essentially that is what you have the only problem that I see is sizing the proper orifice and making a rheostaticlly controlled fan to adjust air input. The iron pipe will never be exposed to 2400f except at the very tip, and even there it can be protected by being slightly recessed. I'll post those pics eventually.
In the burner sketch above, for a #20 crucible furnace, which was about 20" in dia x 20" tall, the gas pipe was definitely 1/2" and I am almost sure the larger pipe was 1-1/2". The outlet tip of the gas pipe MUST BE at least 2"-3" beyond the air supply tee. I don't remember exactly how I did the pipe reducers, where the gas pipe enters the larger pipe, but it shouldn't be too hard to figure out. I'm thinking that either I had about 6"-8" of the end of the gas pipe threaded or the pipe was in 2 pieces. I used an old upright vacuum cleaner for the air supply - I used the same one almost daily for 3 or 4 years without failure.
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Chris, like you, I used a vacuum cleaner for my air supply, in spite of reading that that isn't a good idea (they are not designed for continuous usage). The only failures I had were related to brushes and bearings. Maintenance stuff, really.
In my case, thanks to having a machine shop, I modified the motor and fan housing such that it would mount directly on the furnace feed pipe. Barring the good fortune to find a different blower, I expect I'll use one for the non-ferrous furnace I hope to build in the future. Frankly, they're a great way to get the needed air. I don't recall paying any more than $5 for those I used.
Harold
In my case, thanks to having a machine shop, I modified the motor and fan housing such that it would mount directly on the furnace feed pipe. Barring the good fortune to find a different blower, I expect I'll use one for the non-ferrous furnace I hope to build in the future. Frankly, they're a great way to get the needed air. I don't recall paying any more than $5 for those I used.
Harold
