Box furnace... Might happen

So in other threads you may see that it is time for me to build a rather substantial furnace.

So now I have some materials:


175x 3000°F bricks, junk refractory cement, and not in the picture I have 50#'s of 3k clay morter.

The bricks are tapered, boo. I got most of them for under 2$ a brick and I can get more too! Yay!

I want to construct a two chamber box furnace. Think first chamber really hot for bronze, second chamber is a large warmer(if 1700°f is just a little warm) for the vitrification or warming of shells. The first boxes exhaust would flow into the second box. I have a couple old metal working books that have some insite, but everything is rather a large application. So there needs to be some evil geniuss blueprints. I got the largest two shelf wheeled metal cart from chinafreight, I am thinking using it as the base frame.

So before I start the 'cut bricks in half party'... The only herringbone patter I know is for a domed cathedral. Anyone have pictures of herringbone patterns?

Am I crazy for not making a kegg?

 

Yes and No. Let's see what ya do with it. $2 a brick is a bargain. I saw someone, somewhere that had a 2 stage furnace like what you are kicking around. I have no clue where I saw it. Might have been over at AA. I think it's going to come down to how you fire this thing. I would think you need to run forced air to it and will need to keep in mind the flow of exhaust through the 2 chambers.

I would be more inclined personally to go with a conventional furnace and use your bricks to design a kickass dewax/burnout chamber. You can melt bronze in a hole in the backyard, but dewax can be tricky with the best of equipment. My recent pour was done with boil out and I didn't get all the wax out. I loaded the shells into the kiln and smoked us out of our house. OMG did that wax stink! So there really isn't a perfect system yet that I have seen without dropping 20grand. And that's not happening. Barry from www.outbackfoundry.com has the slickest dewax/burnout setup I've seen. I should build a scaled down version for myself.

 

Those 3,000 F bricks are very expensive around here, perhaps $6.00 / brick in the non-tapered form.

Did you decide on a layout?


Edit:
New 3,000 F non-tapered 9"x6.75"x3" bricks are $20.00/brick when you include shipping (one supplier on ebay).

I found some tapered 3,000 F bricks for $3.00/brick, but the shipping cost is far more than the cost of the brick.

 

Ho ware the bricks tapered? I can't see it from the photo.

 

I'm with Jason on using the square burnout chamber for lost wax. I'm making one of those 24x24x20" interior. I've seen many commercial foundries use square burnout chambers.

For furnaces I think the spiraling action of the flame around the crucible on the smooth walls provides an efficient and even heating action to the crucible. That's likely why all the larger foundries use it. Less fuel better heating to all parts of the crucible. That said I think your square one will probably work but the turbulence from flames hitting flat walls and not being directed in any specific path might cause uneven heating and lead to earlier crucible failure or cold spots that won't melt as easily. This probably won't matter for aluminum or even bronze but iron might be out of reach.

 

I think it is a pretty slight taper on them.
You can see it on ebay if you look closely.

Seems like if the taper were on the sides only, then the bricks could be alternated up/down.
If the bricks were going to be used for a circular furnace, then the sides would be cut anyway, so the taper would not matter.

 

I can see that.. I talked to paragon about some replacement bricks for my cat pizz kiln and they were 12bucks a pop. I've still got 3 out of the 4 coils running, so I'm not screwing with it until another one shits the bed.

 

Just don't buy bricks and concrete online

You can find insulating firebrick suppliers around.

 

Lowes sells it. You can put in an order and have it delivered to the store. Fairly cheap bricks too.

 

Lowe's has 2,400F firebrick.

 

The only fire bricks I see at Lowes are these:
https://www.lowes.com/pd/US-Stove-Company-Sand-Ceramic-Firebrick/3775895

and they are hard fire bricks, and I don't think they are considered insulating.

Two different types of fire bricks bricks are manufactured, which are hard fire bricks, and insulating fire bricks (IFB's), and they are not the same thing.

A soft fire brick can easily be cut by hand using a hacksaw.
A hard fire brick can only be cut using something like a diamond masonry blade.

.

 

Is Barry from outbackfoundry a member of this site?

I want to see pics of the burners he has feeding into the de-wax furnace he has. Also more pics of inside and the floor contraption he has. His pics online give little hints of what is going on but not much solid detail. I've already bought half the stuff I need to make a box dewaxer but need to see how the burners are set up for peace of mind.

 

I think he is, but that's the busiest 60something I have ever known. That man runs circles around people a third his age. I'll text him for ya if we need to, but let me try...

I've been to his foundry and bs with him for hours there. His dewax box is run on natural gas and uses 2 (HIGHLY reliable FREIGHT reasonable priced foreign made) weed burners with modified orifices to shoot flames in that box. Shell shouldn't be dewaxed with direct flame impingement. Now if you want to know about his furnace burner... It too is natural gas. He has a 2" ng line and he had them up his gas pressure. He is in an industrial area after all. His furnace floor build reminds me of Mark's latest cast plinth using foam. Brothers from another mother perhaps.

that help?

 

Somewhat but still doesn't help me figure out what materials would work. I'd rather not buy weed burners if I can make do with pipes.

Do the flames come up the walls and radiate inwards? How large are the burner holes?

 

He has 2 inch pipes welded on the sides of that box. Then he stuffs the end of the burner in that pipe and tightens it down with a set screw. No blower, just a pressurized flame.
Didn't you see his tour of this thing?

 

Bingo that's the money video I needed. I haven't seen it before.

Pretty interesting. Only 2 ports for fire. I had planned to put in 6 or so, 3 on each side for even heating. I might still do that so there is even heating.

I like his idea about a viewing port and the hinged door rather than the sliding door. I'll be using fiber board + satanite coating to protect the surface. I like the swivel bottom doors. Though I wonder why he didn't just poke holes in his refractory floor and not make the swivel bottom doors? Why is it important to open the bottom like that. Seems weird. He even said refractory floor was on his list of things to do.

He didn't really explain the pyrometers. Are they just taking a temperature or actually controlling the temperature inside?

Looks like a lot of welding and fab work. I'll see if I can organize the materials over xmas and make one. I've already got some 1/4" L frame steel for the general box shape.

 

He has gone to hell and back with that floor. Save yourself some headaches. Do it the way its shown today. There was a thread over at AA. Remember he gets it hot, opens the bottom doors and inserts the shells for dewax. Once its complete, he closes the bottom doors and adds the new floor. So it really doesnt need the swinging doors anymore. It was originally a good idea except the heat kept destroying the floor.

 

What was his solution? He mentioned he might want to use refractory in the future but has been repairing the grate over and over. Didn't seem like it was solved unless I missed something?

 

I was following along when he was building it. It seemed to me at the time he was putting carbon steel in an area that was too hot.

 

Andy is right. He has a steel grate in it again, but covers it up after dewax to protect it.