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Building My Foundry Furnaces

WARNING!!!: You got a brain... USE IT! Building and working with a foundry furnace is "NOT" child's play. It can be very dangerous and if 'you' screw-up don't come crying back to me! If you don't know what you're doing and didn't take the time to read and study all the safety procedures that are available on the net, as well as your local library and you get hurt that's your problem. You are responsible for yourself and your own actions and safety.

--- "NOT ME!" ---

What you'll be seeing below are two types of furnaces being built at once.

One thing you should know is that building a furnace is 'NOT' a weekend project..... You can figure on spending at least a month putting one together, (The right way.)

Of course if you're loaded with extra bucks just burning a hole in your pocket there are shortcuts you can do.

Doing my research on the net, I've found 100's of designs. Some were just fire brick stacked into a circle on a steel rack another was nothing more than refractory jammed into nothing more than a cut in half milk jug. :-(

My designs are not new... just modified the basic concepts to my own ideas and I think improvements.

I can say without a doubt I've LEARNED ALLOT!!! Of what NOT to do and things I FORGOT to do; as well as things I should have done!!, so if you try to do this understand right off that it's a learning process and you WILL make mistakes.


the tank

I have a friend in the "Heating and Cooling" business and I get his empty freon tanks. They make great bodies for furnaces. But I did find out the hard way that you need to reinforce the side walls and use plenty of nails to hold the refractory in place.

What I will do for all future furnaces is weld a 1/2" or 3/4" wide by 1/8" band around the tank above and below the cut line... then do my cut. If you can hold a steady gap of say an 1/8" or 3/16"; then just drill a few holes, enough to get a jigsaw or saber saw blade into it and you'll have a perfect cut.



tank with bands

I cut the tank at about the 70-75% mark and with a 6" diameter pot this has given me about a half a gallon per pour.

"How much is that?" Well you can see for yourself on the other pages... I poured a 11-1/2" by 13-1/2" by 3/4" plate of aluminumn.



spout cut

Here's a front view of the tank with the pour spout cut and bent out.... After doing a couple of pours it was clear that I should have made this spout higher, (Bent at the weld seam), and about 3" longer and then modified the compound hinge. (You can see the changes I made on the Furnace Rebuild pages.)



The Furnace base

Here's the base for a standard crucible type furnace with the burner tube welded in place.
TIP: Double check your alignment in all directions, because I was welding 2 cylinder shapes at just over the 90 mark; as it turns out after this cooled down it had pulled to the left, (I had welded it 'right to left' causing it to draw.), and I didn't catch it till after I had put in the refractory cement.



refractory in and drying

Here is the top of the reverberating furnace after I filled it with refractory. For the mold I simply used pink Styrofoam glued together with a hot glue gun to get the height I need and sanded it into shape.
Side Note: One thing you find out if you get into this is.. You can never have enough Styrofoam or hot glue sticks... Stock up on both 1" and 2" thick sheets. For bulk supplies of hot glue sticks, (go for the 10" sticks), try You'll also wind up building a hot wire foam cutting table as well.... Food for another webpage.. ;-)



Used a bent nail to hold the refractory in place

To hold the refractory in place I just took a clip of nails for my framing nail gun and bent them to 90 and welded them in.




Here you can see the nails welded in at 2" spacing. After the pic was taken I added several to the top of the dome as well.


This is how far it tips before the compound hinge takes over and starts to lift the furnace.


hinge 2 hinge


One of the biggest problems with a reverberating type furnace is that you start to pour at one point but as you lift the furnace the spout swings "BACK" into the frame. So you either have to pour into a crucible and then into your mold or make a compound hinge like this. As you can see here there's only about a 1/4" to 'maybe' 3/8" swing back of the spout.


A couple of close-up shots of the compound hinge... I've modified this design in a later rebuild. (See the pages on rebuilding)




With a crucible type furnace you have to plan for the time that your crucible fails and spills hot metal inside your furnace... This is the drain channels and hole for when that happens.
Once you have this in place you fill in the refractory level with the top of it ramming it down then smoothing it off and insert your chamber mold on top, (Making sure as you ram in the refactory that the mold doesn't pull away from your burner feed tube.

The black pipe is a 1-1/4" for the burner inlet.


Here is the base being setup with a mold to form the chamber.
The picture doesn't show it very well --- The yellow box is the burner inlet.
This is going to be a standard crucible type furnace, and 'YES' I'm building more than one.
In fact I'm building 3 now and a forth one is being planed.



The mold for the top vent was just a 1-1/4" pipe and coated with vasoline. Then the mold for the chamber is aligned to the pipe.
You first have to add in about 2" of refractory around the pipe and ram it down, then insert your mold and ram in the refractory around it.

NOTE: When you do this watch carefully as you ram it in, so your mold doesn't shift off center. It's extremely hard to get back on line without digging out a bunch of the refactory.


You'll have to put some weight on it as the refractory likes to try and lift your mold when you're packing/ ramming it in. When I was relining the other furnace, (See the rebuild pages), I had to actually stand on it, (225 pounds), to get it back down. Notice how it goes uphill toward the center... that's so you can file and sand the top and bottom halves to be a perfect fit. Some builders leave this cone shape and cut out the bottom half to fit. Basically locking the two halves together for a better seal.


firing it up




"AND WE HAVE FIRE!!!" But as good as this looks there were problems to come. As Paul

Harvey would say: "And THAT'S THE REST OF THE STORY!!"

The burner is a Reil type and I made out of galvanized pipe --- WRONG!--- the galvanizing flakes
off on the inside of the tube plugging the orifice. I should used a 1/4" ream on the inside of the
pipe to remove the galvanizing. This mistake cost me a 20# tank of LP gas and destroyed the
furnace pot/ chamber .
Notice the bracing on the bottom half to support the lift handle?
I forgot to do the same to the top.
Notice the orange and yellow flames coming out of the spout?
---WRONG! --- I didn't know it at the time, but this means the refractory blend/mix was wrong.
To much sand and not enough fireclay. The entire lining was turning to glass beads as the
sand melted.
You see what I mean about a learning process?!?!?
YES! It was just a few simple mistakes, but I had to knock out all the refractory and rebuild/
reline it all over again, PLUS rebuilding the burner as well.

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