Plans for building a home made furnace

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lazersteve

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All,

I'm looking for the best plans for a homemade electric furnace. I want to make a video of this project and also need a furnace for my shop. I have one set of plans and most of the materials to complete it. I want to get your feedback before I start. Maybe someone has a better set of plans than I found on the internet. To keep costs down the plans will have to be free. The furnace will be for melting gold and silver.

Thanks in advance,

Steve
 
Do you want a box furnace or a pot (crucible) furnace? IMHO, the only thing a box furnace is good for is fire assaying. To me, when melting gold or silver, you need to be able to chemically flux the metal, in order to improve the purity. This is very inconvenient (if not impossible) to do in a box furnace. It is very easy to do this in a pot furnace. Also, in a pot furnace, improving purity is probably 10 times more efficient than it is in a torch melt. With a pot furnace, you can also see what's happening.

If you do want a pot furnace (which I think is what you need), why, oh why would you want to go electric? Building a small gas pot furnace is much more simple (and cheaper) to build than an electric furnace. You also don't have corrodeable elements or expensive controllers to worry about. You can use natural gas, propane, etc.
 
I'm definitely after the pot furnace. I want to design it around a small crucible that I have. Gas is not not a problem, the only reason I said electric is that is what the plans I have called for. It would be great to have a propane powered pot furnace to melt small amounts of gold and silver. Can I use standard grill burner parts or will I need special high temperature parts? What is the maximum temperature I can expect from a gas powered furnace?

Steve
 
Steve,
Have you checked ot backyardmetalcasting.com?

http://www.backyardmetalcasting.com/

http://www.backyardmetalcasting.com/gallery.html

You should be able to get alot of ideas from
some of their setups.
I like this one, as I have 2 boxes of firebricks, and
the rest looks easy;
http://www.backyardmetalcasting.com/guest_martin.html

Jim
 
Hi

I have been collecting plans for different types of furnace / forge types lately.

The one is a coffee type forge says it gets up to 2,000 degrees. (gas)

Also information on the blowers, all home made.

If interested let me know.

I got them scattered around my hard drive as I haven't organized them yet!
 
Jim,

I'm going to use castable refractory cement to make mine. I want it as small as possible. I'm building it around a small 50 oz crucible. I would like it to be able to tilt for easy casting.


Steve
 
Steve,
Have you seen the one that action mining sells?
It looks like it is made from a small freon type
bottle. Jim
 
Dgoldboy,

I'm game! Please send them to me via PM when you locate them.

Thanks and welcome to the forum,

Steve
 
Jimdoc,

I like the furnace on your last link. The burner set up is very simple and is very similar to what I used, when I used propane. You just put a piece of burning paper in the chamber and turn on the gas. After a few minutes, you slowly open the air. After a few more minutes, you close the lid and adjust the air and gas until you get about a 2" plume (tail) of flame coming out the exhaust hole in the lid. I used an old upright vacuum cleaner for an air supply.

I hate the way the lid works. I could see myself getting burned. How would you lift the lid without having your arm over the 2200 deg F. chamber? I much prefer a lid that pivots to the side. This can be simply made by welding two short lengths of pipe, one to the lid and the other to the top of the body. A smaller diameter pipe is inserted into these and acts as a pivot pin. Very simple and works as well or better than those common, complicated, lever arm lid raisers that you see on a lot of furnaces.

I would probably use a large diameter piece of pipe (scrap yard) for the body and the lid. I would weld a plate to the bottom. I would use refractory cement instead of bricks. I would weld 4 crossed pieces of rebar inside of the lid ring to hold the cement. To determine the inside diameter of the pipe that is needed, add about 10" to the widest diameter of the largest crucible you will be using. This will give a 3" refractory thickness and a 2" spacing all around between crucible and refractory. The pipe ring is also 3" thick. Some sort of mold must be used to cast the refractory in the chamber. The best is round thick walled tubing made of cardboard. I think they use it for molding round sections of concrete bridges. That way, you can cut the cardboard to remove it. Don't use a metal mold or, you never get it out. When casting the lid, use a tin can to mold the exhaust hole in the center. I prefer at least a 3" lid hole.

Somewhere, in one of my early posts, I went into this in more detail. It is, by far, the simplest furnace to make, maintain, and use that I have seen.
 
GSP,
I have the kit that Lionel sells on the backyardmetalcasting site, I just need the refractory. I also would like a smaller one like Steve is looking to make. I have a bunch of empty 134 freon bottles that I plan on trying.
But since I already have 100 firebricks, I am definately going to try to
build that one. You are right about the lid should swivel though. That site is interesting to see how other people have built their equipment on the cheap. You just have to redesign a little to your own liking or needs.
Jim
 
Are the bricks the light weight, soft, insulating type or the heavy, hard, refractory type? If they are the soft type, you can't use a flame directly on them. You can line them with about 1", or so, of refractory cement.

I always liked to have 2 furnaces. A small one, about a #4 or #6, for only pure metals and a larger one, about a #16, for whatever. A #16 is about the largest that one man can safely handle with only a standard pair of crucible tongs, without breaking the side out of the crucible.
 
They are the soft refractory ones.
I can also get the ones that they build
fireplaces with, they are harder, but
I was under the impression that the softer
ones are better for high temps. You are
talking about handling direct flame though,
so would the fireplace bricks work? They are
only 75 cents each, the soft ones are a few
bucks each, usually $5-$7, but I got the boxes
cheaper. I probably have enough of each to
build a furnace like the one we are talking of.
I was also under the impression that the harder
ones may pop or explode from the moisture at
very high temps. Jim
 
I just found about 6 commercial crucible furnaces, for copper, gold, and silver, on the net. All of them used a hard firebrick lining with a 2" insulating (probably soft firebrick) layer underneath it.

Every furnace I made was out of mixed refractory cement. I have never used firebrick. A number of pros have told me never to line a furnace with soft insulating firebrick. They said it wouldn't stand up to the direct flame and, I definitely know that it won't stand up to the fluxing chemicals or molten metals.

On this forum, there are two threads that prove this. In one case, someone was melting and fluxing metal, in an electric box furnace, that somehow escaped into the soft firebrick lining. Everywhere it landed, the flux and metal ate big holes in the soft firebrick. The guy posted photos of it. In another thread, someone was trying to flux melt metal, with a torch, in a dished out area on a soft firebrick. The flux and metal melted down through the firebrick and he had to dig it out.

No matter how good you are, you will always get flux spills in the furnace. Crucibles will wear thin and get holes in them. Melts will foam over, especially when using stuff like standard hydrated borax. Most all furnaces have clean out holes at the bottom for this purpose.

Soft firebrick is called insulating brick and that's what it is used for - not lining high temp corrosive melting furnaces.
 
For the ones who might want to make the refractory from the one in the doc. Most of those items are easy to find. Don't let them names fool you. lol
 
Great info everyone!

As a side note I want to point out to everyone that refractory dust is not good for you. Be sure to read the MSDS on the refractory material you are working with. Typically a good filter mask is a minimum requirement.

Steve
 
http://pacificcoast.net/~kerslake/BronzeSite/Studio/MetalCastingFurnace.html Sorry didnt check the original link posting the first time.
 
This is something like i was talking about but smaller and you drop it in from the top. No lid removal. Note the static air pressure i was talking about. The flames just naturally push their way out with ease. Notice the rushing sound, but little push.

:arrow: http://www.youtube.com/watch?v=QNm4Kb0wCsw
 
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