Firebrick furnace

[petersenj20]

I am building a small furnace for casting Al and brass. I also frequent backyardmetalcasting. I am looking for your help because they don't seem to want me to use anything but perilite or castable.

I want a square firebrick furnace. The bricks won't degrade and now I have a better reason. Because people seem to tell me it can't be done. I found a refractory mortar on the net- Heat stop. Looked at the list of suppliers here in Atlanta and what do you know they show Boral Brick where I bought the bricks. I called back and they keep offering fireclay. Apparently they don't carry heatstop and someone should tell the website. The first time I called they said I need to talk to a brick mason.

Here is what I have done that hasn't worked. I bought Quickrete Type N masonry cement at Home Depot. Followed the instructions 1 part cement, 3 parts sand. I built the furnace with about 1/4 inch joints. (This next part may be the problem) I am using a Reil burner and fired up to cure. It crumbled.

The second time I used 1 cement, 2 fireclay, 3 sand like another stone supplier said. Same problem. Did heating instead of letting air cure cause the problem? The last furnace I made was rammed fireclay and sand and was cured by firing and sintering.

Long story short, does anyone have suggestions for what to assemble the brick with. At this point I am not real worried about the endurance of the joint, I just want it to have strength.

Thanks

[yesteryearforge]

I was told by someone that if you mix the mortar with salt water that wont happen
dont know if thats true or not nor do i know how much salt
just read your post and had a flashback
sometimes thats good
sometimes thats not so good

[Tyler Murch]

Georgia red clay will work in a pinch, and what about fireplace cement?

[sdalcher]

Why not make an angle iron frame/stand to hold it all together? Then you dont have to worry about a joint.

Thanks
Steve

[petersenj20]

I have decided to try the build again, and am hoping that if I leave it alone for a few days it will air cure. (Maybe I was just rushing things). I made it up last night around 11:00. It is killing me to leave it alone. I looked at it a little while ago and it doesn't seem to have dried at all, but will wait and see.

I used 1 part cement, 2 parts fireclay, and 3 parts sand.

I read elsewhere to use straight fireclay and water. Add enough water to get the consistency of pancake batter. Dip the brick in it and lay as normal. Make joints that are 1/8 thick. It doesn't seem like this would have any strength though. Will try if this recent one fails.

[Nomad]

Well, a couple quick points.....

The bricks and joints don't have to hold anything but heat. As long as the insulate, they are doing their part. Build a frame (as was sugested) or put another layer of brick and real morter around the outside.

Second...slow cure is way important. You ought to cover it with plastic and leave it alone for a couple days. Then couple more with no cover. Then reallly low heat. Water expands somewhere in the neigborhood of 1600 times it's size when it becomes steam. That's why concrete explodes in a fire, it's the moisture inside.

Well, let us know how it goes....

BTW- my current furnace is made of garden clay, perilite, and sand inside a shell from a 40# propane tank. Not the best but something to play with.....


Nomad

[ThomasPowers]

Don't expect anything that will thermal cycle as much as a hobiest furnace to be structurally sound. You are basically just stacking the firebrick up and should expect the frame to hold everything together---ant that frame should deal with expansion and contraction too. For big industrial furnaces things like tapered firebrick arches are used so that they hold up just like drystone arches do.

[petersenj20]

I'm still letting my last assembly dry out a bit to see if it will work. I can make an angle iron frame if need be. The little sucker is a lot heavier than I expected it to be.
This does make me curious though. I have been to an old pre-civil war furnace at Red Top Mountain here in Kennesaw. It is about 4 stories high and the center is lined with what looks like standard sized firbricks. Makes me wonder how they have stood the test of time with no one servicing the thing over the last 130 or so years.
Granted rock it does have a limestone outer shell, but I wonder what the adhesive for the bricks was.

[Bentiron1946]

I have made my melting furnaces out of old gas fired water heater bodies for years. I use the the bottom of a 30 gallon heater and cut it off at a height of two fire bricks high with a sawzall using a metal cutting blade. Next cut off a four inch high section of the tank body. Now line the bottom of the tank with fire brick, just use regular fire bricks, nothing special. Now lay up the wall by splitting the fire bricks in half lengthwise and using a mortar of fire clay and sand set them in place. The top row will be about half a brick high. Make a plaster of fire clay and sand and make the lining level with top of water heater body and paint the inside of the furnace with it. Well I forgot one step, the hole for burner. I usually use a 1-1/2" set at an oblique angle to produce a swirling flame around the crucible. Set one half fire brick in the center of the bottom for the crucible to set on. Now to make the top I take fire brick and all of the scrap brick pieces I have left and crush them up to pea size pieces and make a thick mixture of them sand and fire clay. Make handles before pouring in the clay/sand/ fire brick mixture out of "U" bolts. Then I get a 1 lite soda bottle and fill it with water and set it in the middle of the 4" high ring of water heater body and put re-mesh wire around it to support the clay/sand/fire brick mixture. Cover the whole thing, both furnace and lid with plastic and let it dry out slowly, patch any cracks with a fire clay/sand mixture. For the first fire I usually build a wood fire and let it burn for a couple of hours to drive out and residual moisture. I would then bring it up to the first melt very slow. This fire brick furnace should last about 5 years with moderate use, that is about three or four melts a week.

[ThomasPowers]

BentIron; what were you melting in that? Al, brass, cast iron, steel?