Burnout oven construction question

[Sandiapaul]

Sorry this may be a stupid question but here goes.

I'm going to build a burnout oven, have the bricks and an old electrical box to put them in to.
How do you attach the bricks to the "ceiling" of the box so they dont' fall down? Is a refractory cement all that is needed? I just fear that the cycling of the hot to cool will destroy the bond and the bricks will fall.

Thanks,

Paul

[hammermill]

if the top is metal t rails that stick inside the brick thru the sides would be what i suspect would work and could be attached to the roof with thru pin or such

[Sandiapaul]

Hey thats an idea...never thought of it! Makes it a bit more complicated to build but they would never fall down that way.

Thanks!

[steamin10]

First off, if you are using hard bricks, why? The use of lightweight materials like Fiberfrax and carvable Bricks have cut the weight of process ovens, and one of the issues is fallout of insulation. Low temperature ovens often use a highway mesh to hold the insulation above it. I am unsure of higher heat treat ovens as the heat exceeds the steels yield point.

You should consider, for small scale a rendering oven, that will capture the bulk of the wax for reuse. The temp is driven up to 5-600 degrees to 'dry out' the molds, evaporating the remaining wax.

I should be mentioned that molding wax burns like Diesel fuel at any heated stage, and the vapors can condense and cause problems in the shop, smoking everything up, or catching fire in the last stages of heating.

[Sandiapaul]

Dave,

thanks...I'm aware of the dangers of the wax. I'm also building a steam dewaxer to get the bulk out.
And also using lightweight firebrick. But still the question remains...how do the ceiling brick stay in place. The screen idea is good too, had not thought of it. THe thing is in the ovens I have seen on the web there does appear to be any kind of support which led me to think there is some sort of bonding agent(refractory cement, or...?)

for example, take a look at this one:
http://www.backyardmetalcasting.com/for ... a4e9423b98

there is some sort of bonding between the brick, but what keeps them up?

Paul

[steamin10]

I am not all-knowing here, so get out the salt.

In the thread that popped up, the soft brick went half way across, and does not completely bridge the opening. I would guess that rods of 1/4 inch or similar were pushed through to give some back bone to the top. There is no arch, and I dont know of a refractory cement that will last with the heat and cool cycles of the oven that will provide a lasting bond. Most often those materials are made so one piece goes across the span, and being ridged but liight weight they fair pretty well in small areas. In the large furnaces I have worked around, support rods and washers in the seams go to the outside shell, to hold the roof liner. Mostly stainless, they sacrifice very slowly in a neutral atmosphere. One cheap solution is putting hiway wire in to hold the roof, and it is replaced when needed, actually new layer over old, in the long term maintenance cycles.

Beyond that I cant say much, being a home thing, you do what works and is handy. That in itself may be a design flaw, that is seen on the web, if it fails quickly, they may not tell on themselves. So it is buyer beware.

I did not mean to insult your labors, just throwing some ideas out, that may help.

[Sandiapaul]

Dave,

No insults taken!
Good ideas all around...now I have to get to the design stage, the bricks are sitting here waiting!

[rrnut-2]

The main question is, how hot do you plan to run the oven?

If it's going to be under 1000deg f, then weld .25" rod shaped into an "L" so the leg is sticking down, to the top of the oven.

If it's going above 1000deg F, then cut off the top of the oven, and make an arch.
Personally, I would use Kaowool and not brick. The oven will heat up quicker and take less energy to run.

Jim B

[steamin10]

When I refer to insulating brick, in this case it is the light weight spun fiber type, that weigh mere ounces, compared to firebrick, ladle brick and that ilk. Really diferent animals. Often rods of steel are pushed through multiple bricks to form panels, that are independant of each other. and if thinned or damaged, are changed as a unit, for quick turn around. Given that thought, it would be easy to craft whole sides of the unit at one go, and give it a thin sheet skin, and bolt /weld these assemblies into a box.

Food for thought.

[rrnut-2]

The investment casting foundry that I worked in, had lots of ovens. All of the new ones, we spec'ed the fibre block insulation. The main thing to remember is, that once its heated, any repairs to the insulation should be done with a breathing mask. Never mind the the stuff iches like hell if you don't wear a suit.

We had 4 ovens that were all brick, but they were scrapped about 6 years ago.

Jim

[jpfalt]

I used to design waste fired burner cells and have built three small heat treat ovens similar to what you are talking about. The easiest way to support the ceiling bricks is to get a large brick tile that will bridge the top and rest on the side and back walls. Tiles are available from refractory suppliers up to at least 24 x 24 inches. If you can't bridge, the method we used was to cement anchors into the back of the tile, run the anchors through the case and tack weld the anchor to the case. Another approach was to cut a groove into the side of the brick and use an "L" shaped metal clip to plug into the groove and then get welded to the case. Gaps were filled with trowelable refractory patch.

I would recommend 25# per cubic foot insulating tile for the refractory in the furnace and put a stainless steel liner pan inside the bottom with a drain lip for the wax to collect and drain out of the ffurnace. That way it doesn't turn into a flaming ball of burning wax during the burnout.