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Dual Fuel Metal Melting Furnace

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Picture of Dual Fuel Metal Melting Furnace
I got such a great response from the Easy Dual Fuel Furnace Burner that it only made sense to follow it up with the rest of the furnace.

This furnace will be able to handle melting aluminum and bronze with no trouble. In theory it should be able to melt iron too but that's probably pushing it.

I've been using my furnace for a couple years now and it has worked out quite well. My design is based on information I picked up from the backyard metalcasting forum. It's a great resource and community. There are a bunch of furnace builds there exploring a variety of ideas. I recommend checking it out. I'd also read this comprehensive guide for a general overview of metal casting and furnace design.
 
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Step 1: General Plan

The basic concept is that we are making an insulated container that can withstand temperatures of up to 2600 degrees. The dimensions don't need to be precise but you will have better results if you stick with the general program. I wanted a furnace that would let me cast a decent amount of metal, about 5 lbs aluminum.  It needs to be sturdy but as inexpensive as possible to make and run.

The furnace is really simple. It's just a metal container with a lid, a drain and a hole for the burner. It is filled with high temperature insulation to retain the heat and a sturdy inner lining (hot face) to withstand the flame from the burner.

I based my design around a small metal barrel that I got from a salvage place. The sheet metal was thick enough to weld to (pretty much) and not galvanized. The zinc coating on galvanazed metal containers will burn and make a noxious smoke so don't use it. Otherwise any metal container should make a serviceable shell for the furnace. I used bits of pipe and angle iron from my scrap pile for the rest of the metal parts.

I made my own insulation because it was substantially cheaper than buying commercial insulation and I just wanted to try it. I did buy a bag of high temperature refractory cement for the hot face.

The shell is filled with insulation leaving an airspace of roughly 2" on all sides between the crucible and the inside of the furnace.
nreed410 months ago
Is there any substitute for fire clay in this ible?
spike3579 (author)  nreed410 months ago
You could try a different clay but I would make sure it can handle high temperatures without breaking down.
nreed4 spike357910 months ago
Did you get the clay online, or do you have a supplier near you. Great 'ible by the way.
sparhawk7 nreed42 months ago

you can get a 95lb bag of fireclay at home depot, free shipping to store, if you can't find it anywhere else.

spike3579 (author)  sparhawk72 months ago
Great tip!
Thanks
spike3579 (author)  nreed410 months ago
I went to a ceramics supply house. Look for the kind of place that professional potters go for their supplies.
ivver1 year ago
You also can get clay stronger with adding some pig hair (belive or not) , I use that method when I need to repair broken clay in furnace. It holds pretty well, try and see at your self. :)
spike3579 (author)  ivver1 year ago
Great idea but where does one get pig hair?

paintbrushes?

weish2 months ago

do you think this furnace design could handle glass? that would require around 2-3000 degrees at most. I'm interested in learning primitive glassworking so a furnace that's easily home built would be very valuable

spike3579 (author)  weish2 months ago
I used to be a glass glassblower so I've given this some thought. The short answer is yes. In fact it's on my list to set up a small glassblowing studio at some point. That said It will take some work to get there from here.

Generally for glassblowing you don't need to go higher than 2000 f. The refactory materials will tolerate the heat. In theory my burner will generate enough heat but in practice I don't think it does. I've seen glass furnaces that run quite happily on waste oil though.

The set up for a glass operation requires more equipment than this furnace which is basically a hot can. You need a place to reheat the glass (glory hole) as well as a place to cool it down (annealer). Most small furnaces have a dome over the tank for reheating and then run the exhaust gasses through a secondary chamber for the annealer. You will also need to come up with a crucible to hold the glass in which is very corrosive when molten.

Check out this movie for a very primitive but effective set up and this one for a more modern take.

Good luck on your project. PM me if you have more specific questions. I've built a couple glass furnaces and would love to see a low cost glass blowing set up get built.
weish spike35792 months ago
For a crucible, i had seen post by a guy who was making his own pots from hand mixed clays and whatnot, so I've at least got a recipe for that. My thought on annealing was that once the work is done and the furnace is shut off, place a simple wire rack with multiple levels into the hot furnace to pee heat, then shut in the glass pieces on the rack, maybe with a small wood or charcoal fire in the bottom to keep everything warm, but not hot enough to slump the glass. Then just let the insulated burn chamber slowly cool to anneal the contents. The glory hole is a design element I hadn't thought of yet. My first thought though would be to basically take another matching barrel cut to half height and turn that into a topper lined with refractory and with a hole or door for reheating parts. I'll have to continue my research, ultimately I'd like to end up with a furnace I can use for metal casting, and then reconfigure for glass working. Of course for me, the fuel of choice is charcoal, gas is just too expensive compared to hardwood lump charcoal, and naturally that would have been the fuel of choice for centuries before modern processes and fuels were available.
spike3579 (author)  weish2 months ago

The glass needs to go right into the annealer after it is formed. You can't cool it down and then anneal it later. I would make an oven that sits above the furnace and gets heated from the exhaust of the furnace. You use a damper to control the temp of the annealer and then seal it up when you are done. For the glory hole you can cast a dome top like a wood fired pizza oven. Use that when you are melting glass and just a ring when you are melting metal. The rocket mass heater seems like a good approach for wood firing a furnace. Here's another couple links to some old school glassblowing for inspiration.

http://www.romanglassmakers.co.uk/index.htm

ivver1 year ago
well, I don't know how is in your country, but here by me we sometimes slaughter a pig (to make sausages, bacon and other) so it left behind. I don't know where else would you find hair, try to deal with some local butcher, he could have one. :)
instead of using the clay you could also use refractory cement that is rated up to 3000 degrees F
spike3579 (author)  x3wayassassin2 years ago
The clay is $12 for a big bag and the refractory cement is $95 for a small bag. I did try it with some left over refractory cement and it just made crumbles rather than holding together. There are other lower temp refractories that would work but they too are awfully expensive.
static2 years ago
Great instructable, saved it for future reference. On the 100 W. light bulbs, LOL. I'm certain that 100 W. incandescent bulbs that meet the energy efficiency standards are available
spike3579 (author)  static2 years ago
I don't know....
I think I might start stockpiling a few. Can't get much heat out of a led :P
hag2 years ago
I was just wondering what you used for a burner. The only thing that comes to my mind is a propane blow torch, but I doubt that gets hot enough.
spike3579 (author)  hag2 years ago
I used this burner.  Works great :)
Ace1932 years ago
This is a great 'ible. Your eye for detail in writing this one made it very useful. Keep up the good work!
lewster2 years ago
Looks awesome, great 'ible
pj632 years ago
What a Great Instructable....I've been waiting for a while for this to come up...I have Bricks,Fire Cement and a 25kg bag of Fire Clay to try to build a Smelting/Foundry in my Garden..I needed some final information and your Instr was Brilliant..Thanks and well done very informative...
spike3579 (author)  pj632 years ago
Sounds like you're ready to go!
PM me or put any questions that come up in the comments
Post some pics of your project.
We want to see....
robotjim2 years ago
thanks for the tips, been wanting to try melting
and casting metal for ages...this looks easy enough
I've got no excuse not to !
wasabi2372 years ago
Gold melts at around 1800. Whoo Hoo!
kenwork2 years ago
Loved this instructable on creating a metal melting furnace! Thank you!

BTW, your website address is incomplete at the end of the instructable, it is missing the .com.

Here is the complete link for people that want to see Mike and Molly's house :)
http://mikeandmollyshouse.com/
PS1182 years ago
Do you think it would help with the cracking to dry the insulation before pouring the liner?
spike3579 (author)  PS1182 years ago
Probably some. The trouble is that the clay is going to shrink no matter what. The commercial stuff is formulated with parts that expand and contract for a zero net change but it costs more. I don't think a few cracks will really affect the performance of the insulation in this application. You could fill the cracks with mortar if you wanted too.
drewgrey2 years ago
Awesome, looks like fun!
soul_eater2 years ago
it looks Great , Im going to make plans to build this one
rimar20002 years ago
GENIAL, thanks for sharing.
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