Heat Treat Furnace Build

[scwhite]

I have come to a point with a couple of projects that have parts that will need to be heat treated so it is time to build a furnace. This will be my version of the many examples out there on the interweb.

Specifications:

Heat chamber is 7" x 7" x 16"
Dual heating elements wired in series, 240v, 3100w
PID / SSR controller.
k-23 firebrick heat chamber wrapped with three layers of 2300 degree 1 mm ceramic paper.
1" angle iron frame & door skinned with .060 sheet metal

Here is the concept in CAD.

Heat chamber.

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With frame and door.

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Before I can finalize the frame dimensions I need to get the heat chamber assembled. Today I cut all the bricks in preparation for assembling.

To cut the side and back bricks with the heating element grooves I made a jig out of 3/4" plywood. Time to put the CNC router to work.

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Bricks in the Jig ready to cut. The bricks are clamped with screws against plastic shims. I put several coats of shellac on the edges of the plywood to firm up the wood a bit. The jig only needs to last for 10 bricks so this should be fine.

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Cutting was done with a hacksaw with a carbide grit blade. It makes short work of the soft bricks. Unfortunately the length of the brick combined with the 3/4" plywood took almost all the blade length leaving a very short stroke. 1/2" or 3/8" ply would have been better.

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The jig is also setup to cut the rabbits. Here is the second op on the back bricks.

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The way the bricks are laid out there is a 1.5" x 1.5" filler on the corners. I need 16 at 9" long and 8 at 1.5" long. Fortunately I still have the tile saw from my construction business. The bricks cut like butter on the wet saw.

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Here are all the bricks cut.

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Last thing to do before assembly is drill the holes for the heating element and the thermocouple and make the recess pockets for the bolts that the elements terminate to.

I have to say this is a first. Machining bricks!. I used a damaged 1/2" 4 flute carbide end mill for the pockets. Holes wire drilled with regular drill bits.

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Hopefully tomorrow I will get the heat chamber assembled and mortared.

I have a question I like your build by the way
My question is die you cut the bricks dry or
Run water .
I was thinking not to run any water
Because it would suck up the water like a sponge

 

[jbolt]

Most of the bricks I cut dry by hand using a hacksaw with a carbide grit blade. That would not work at all if they were wet. It would load up the saw and make it useless.

The corner pieces I cut wet on my tile saw because I had it and saved me a lot of time. I washed all the bricks after cutting to get rid of the loose grit plus I wanted the bricks damp for mortaring. Its not necessary but if you use mortar on a bone dry brick it will quickly suck the moisture out of the mortar making it more difficult to work with and it can affect the cure strength. Cement products cure better damp. The bricks do soak up a tremendous amount of water.

I chose to use mortar on the joints to create the best seal I can to contain the heat as much as possible. I have read some reports of builds where no mortar was used along with no additional insulating layers which lead to overheating of the outer shell. I'm hoping my strategy of using mortar and multiple thin layers of insulating material will result in acceptable heat limit of the outer shell.

By the time I build the frame and control box I figure 3-4 weeks will pass and a lot of that moisture will have evaporated. The rest will come out during the break in.

If I were to mortar dry bricks I would first apply a thin layer to each face to be mortared together, scrape that tight and then apply another thin layer to one side and then assemble. Scraping a thin layer on each face forces a mechanical bond and puts a little moisture into the brick. This will help the thin bond layer to better adhere and not dry out as fast.

If you do not use mortar then there is no reason to get them wet.

 

[Groundhog]

jbolt,
Please keep us posted (as to heating of the shell and anything else). I want to build a heat treating oven and don't know the first thing about masonry or most of the talents necessary to build a good one. Your thread has been very helpful and seems to be a good plan to follow. Thanks!

 

[kvt]

Jbolt, Mine is the electrical side of it, I can do basic electrical and could prob figure some of the other stuff out but would take a while. Moisture can be a killer, as I did not get enough out of my small home made foundry the first time and it did pop a bunch of chunks and crack because of the moisture expanding . I need to build a bigger one, along with a forge and a heat treat oven Just more projects, At this rate I will never reach the end of my list.

 

[ezduzit]

...At this rate I will never reach the end of my list.

This used to trouble me until I realized that there will always be a list of things to do, and that one must take pleasure in simply actively working on the list of projects.

 

[jbolt]

This used to trouble me until I realized that there will always be a list of things to do, and that one must take pleasure in simply actively working on the list of projects.

Projects breed projects.........

 

[jbolt]

Jbolt, Mine is the electrical side of it, I can do basic electrical and could prob figure some of the other stuff out but would take a while. Moisture can be a killer, as I did not get enough out of my small home made foundry the first time and it did pop a bunch of chunks and crack because of the moisture expanding . I need to build a bigger one, along with a forge and a heat treat oven Just more projects, At this rate I will never reach the end of my list.

Yes sir on moisture. At a house I built for a client we built a huge beautiful Rumford outdoor fireplace. My mason was really proud of it. He gave the owner all kinds of warnings and instructions on how to season it properly by building several small fires over a period of time. They ignored him and at their house opening party they built a huge fire in it. Cracked the firebox, blew out the throat and damaged the chimney. One expensive party.

 

[jbolt]

Very nice work, Jbolt! This should be an awesome addition to your capabilities.

This has been on my wish list for a very long time. Not sure where the heck I'm going to put it though.....LOL

 

[scwhite]

Most of the bricks I cut dry by hand using a hacksaw with a carbide grit blade. That would not work at all if they were wet. It would load up the saw and make it useless.

The corner pieces I cut wet on my tile saw because I had it and saved me a lot of time. I washed all the bricks after cutting to get rid of the loose grit plus I wanted the bricks damp for mortaring. Its not necessary but if you use mortar on a bone dry brick it will quickly suck the moisture out of the mortar making it more difficult to work with and it can affect the cure strength. Cement products cure better damp. The bricks do soak up a tremendous amount of water.

I chose to use mortar on the joints to create the best seal I can to contain the heat as much as possible. I have read some reports of builds where no mortar was used along with no additional insulating layers which lead to overheating of the outer shell. I'm hoping my strategy of using mortar and multiple thin layers of insulating material will result in acceptable heat limit of the outer shell.

By the time I build the frame and control box I figure 3-4 weeks will pass and a lot of that moisture will have evaporated. The rest will come out during the break in.

If I were to mortar dry bricks I would first apply a thin layer to each face to be mortared together, scrape that tight and then apply another thin layer to one side and then assemble. Scraping a thin layer on each face forces a mechanical bond and puts a little moisture into the brick. This will help the thin bond layer to better adhere and not dry out as fast.

If you do not use mortar then there is no reason to get them wet.

We had heat treat ovens Graves I think that was the name nether one had any mortar andd was put together dry .
We used some packing white packing in all the joints we could put it in .
The dry out procedure is long it will take a week to do it . Slow procedure .

 

[scwhite]

Jbolt you did a great job on your oven .