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Heat Treat Furnace Build

jbolt

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#1
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.

Heat Chamber01.png

With frame and door.

Oven01.png


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.

20170603_113154_resize.jpg


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.

20170603_124929_resize.jpg


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.

20170603_131747_resize.jpg


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

20170603_162103_resize.jpg


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.

20170603_172638_resize.jpg


Here are all the bricks cut.

20170603_174111_resize.jpg


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.

20170603_182038_resize.jpg
20170603_184847_resize.jpg 20170603_191235_resize.jpg

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

Redmech

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#2
I'm enjoying this thread. I have a manual kiln that I'd like to put an automatic controller on to run my element. I'll be curious of he exact electrical pieces you use. Look forward to more posts.
 

jbolt

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#3
I got thinking last night I should pre-fit the heating elements before assembling. I'm glad I did. I had to make some adjustments where the element turns back on itself and my calculated length was short.

Here are the heating elements from Budget Casting Supply. Un-stretched the coils are 31".

20170604_082118_resize.jpg


I attached a board to my workbench and marked it at the length it needed to be stretched. The opposite end is clamped in a vise at the end of the bench. It takes some force for the initial stretch but after that you don't need to pull as hard to make it stretch more so it would be easy to overshoot the length if your not careful. The supplier says you can cut the pigtails but not the coils otherwise overheating may occur.

20170604_082835_resize.jpg


Hear is the element pre-fitted. I used a small flat bladed screw driver and a 1/2" wide wood chisel to hand carve the cutouts where the coils turn. washed the brick last night and they soak up a tremendous amount of water. The firebrick is very easy to carve when damp as there is no dust. Having the bricks damp also helps with the mortar application and curing.

20170604_085836_resize.jpg


For assembly is screwed a couple of boards to my workbench using a framing square. I also attached a couple of 8" squares the the table as a guide to keep the first three course square. The bricks were assembled from front to back so the back could be installed at the same time. I only got two pounds of refractory mortar which was exactly enough. I plan on picking up another pound to make a slurry and detail all the outside joints. I will let the assembly cure for a couple of weeks while I work on the frame. Once it has had some time to cure I will block sand the sides and back to address any high spots.

20170604_103221_resize.jpg 20170604_111830_resize.jpg


Once the ceramic paper arrives next week. I can cut some samples and stack it with the sheet metal to finalize the frame dimensions. I'm still debating adding a thicker insulating layer. Not sure yet. I have seen a number of builds with just a sheet metal skin over a single layer of bricks and other builds with a second thick layer of ceramic board or insulation. I suppose the worst case is if the outer shell gets unacceptably hot I could add a second skin with a layer of insulation in between.
 

jbolt

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#4
Hmmm... seems I missed a "R" in the thread title. Makes it sound like a medieval torture device....LOL
 

mikey

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#5
Very nice work, Jbolt! This should be an awesome addition to your capabilities.
 

terrywerm

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#6
Title issue fixed.

Nice project! Right up my alley also, so I will be following this one closely and hope to built a similar oven in the future.
 

kvt

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#7
I know a brick layer that use to wet all his bricks prior to use, Ask why and it was so the mortar would stick better. Quick question how long do you have to wait for the bricks to dry out before heating it fully.
 

jbolt

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#8

Silverbullet

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#10
This is an excellent build for us on this sight. I'm looking forward to doing one eventually. I enjoyed doing heat treatment and case coloring long ago.
Thanks
 

scwhite

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#11
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.

View attachment 234775

With frame and door.

View attachment 234776


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.

View attachment 234777


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.

View attachment 234778


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.

View attachment 234779


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

View attachment 234781


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.

View attachment 234782


Here are all the bricks cut.

View attachment 234783


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.

View attachment 234786
View attachment 234784 View attachment 234785

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

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#12
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

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#13
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

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#14
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

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#15
...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

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#17
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.
 

scwhite

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#19
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

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#21
Jbolt you did a great job on your oven .
What controller did you buy ? I don't think I seen one in the pictures .
 

jbolt

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#22
Jbolt you did a great job on your oven .
What controller did you buy ? I don't think I seen one in the pictures .
For the PID I got the SYL-2352P from Auberins on the recommendation from others. I don't know much about these yet.
 

Eddyde

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#23
Awesome Build!
I have some experience around pottery kilns that are constructed similarly, fire brick with a metal skin. They get blazing hot on the outside, you may want to consider adding a couple of inches of mineral wool insulation between the brick and casing, if excessive radiant heat is a concern.
 

jbolt

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#24
Thanks for the heads up Eddy.

I think I am going to continue with my current plan and if it ends up not being acceptable I can modify it to add another insulating layer.
 

jbolt

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#26
A little more progress on the build.

After much reflection I decided to do a redesign on the frame to accommodate a 1" layer of ceramic blanket. I would prefer to be able to use the oven inside my shop and with the limited space I have I'm hopeful it will keep the outer shell temps acceptable.

In addition I added a sub frame to the firebrick assembly. I had some concerns about braking the joints of the firebrick when handling and the way I assembled the bricks I wanted additional support on the bottom row.

The sub-frame is made form some surplus 1 x 1 angle I had. The sub-frame is held together with 3/16" rods that I single point threaded on each end for a 10-32 nut. I could have used all-thread but what is the fun in that.

Between the sub-frame and firebrick is a single layer of ceramic paper and a layer of steel mesh on the sides and top to provide some support. A piece of 22 ga. sheet metal on the bottom. I used the mesh to help with the break-in to let moisture out.

20170617_140117.png 20170617_140129.png 20170617_140141.png
 

mark_f

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#27
I notice the heating elements are too long in the picture once they were stretched. Can you cut the excess off or do you have to use the full length? ( I would think the length must be kept original). Also, how did you terminate the ends of the elements for connection? My questions are because this is on my short list of things to build.
 

jbolt

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#28
I notice the heating elements are too long in the picture once they were stretched. Can you cut the excess off or do you have to use the full length? ( I would think the length must be kept original). Also, how did you terminate the ends of the elements for connection? My questions are because this is on my short list of things to build.
The coils of the elements are not supposed to be cut, the pigtails can be trimmed. The extra length you see will turn along the back wall before the pigtails are run out the rear.

The pig tail will be run out a small hole and then terminated on a stainless steel bolt. It is recommended to make the termination on the outside. Repeated heat cycles can loosen the connection if made on the interior side. I have also heard it is recommended to double back and twist the pigtail to reduce the amount of heat at the element termination.
 

jbolt

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#29
A little more progress this weekend.

I'll start by saying I really dislike flux core wire welding. I can stick weld, tig weld and gas weld but for some reason I have a hard time seeing the weld joint with flux core wire. Nor does it help to not have a proper welding space and table. Working on a HF folding table out in the driveway stinks. I long for the day when I have a decent shop.

I got the frame mostly welded up and the door partially made and hinged. I also test the fit of the heat chamber to the frame. So far so good. My local metal supplier gave me some aluminum diamond plate cutoffs to use for the frame sides. Can't argue with free. 20170625_090213.png 20170625_090225.png 20170625_135205.png 20170625_135213.png
 

jbolt

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#30
Slowly but surely progress is being made.

I have the heat chamber installed in the frame. The heat chamber is centered in the outer frame with jacking screws on the sub frame. I installed the diamond plate top and bottom and the 1" layer of Inswool ceramic blanket first and then used the jacking screws which are accessible through the open sides to center and lock the heat chamber in place. Once that was done the side insulation and panels were slid in place. The door was a little more complicated since I wanted to be able to service the innards if necessary so I didn't want to weld everything permanently inside. A smaller frame made from 1-1/2" angle slips inside the outer door fame from the front and is held in with screws from the side. Two jacking screws through the bottom of the door frame center and adjust the height of the door firebrick in the opening. It took a little more work but everything is adjustable so it fits together very well.

Next is getting the rear closure done and the control box wired and installed.

20170704_085043.jpg 20170704_120715.jpg 20170704_121126.jpg 20170704_121149.jpg
 
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