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Heat treat oven

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  • Heat treat oven

    I'm at the point now where I'm going to cut some bricks for my oven. Just thought I'd lay out my plan here in case anyone wanted to share some ideas.

    First step was to see if I could cut the bricks easily. Turns out a carbide blade does the job so easily that at first I thought something was wrong- I couldn't even hear the blade cutting as I pushed the brick through. It does an absolutely beautiful cut. So- where I'm at now- because most of my bricks have angled ends so they would fit around in a circular pattern, I'm thinking to make an arched top on this thing- kind of like a quanset hut. I will have to change the angle, making it steeper so three bricks can come together in an arc before setting down on top of the walls. This means the top brick on the walls will also be angled to suit. Because of the arched top I'll make the walls a little less high than I might have otherwise.

    The rest of the structure will be assembled with rectangular bricks. Once I prep the bricks for the roof and walls, I'll have a dimension for the width and length of the oven. I plan to cut pieces of cement board for the bottom, sides, and back, probably gluing the corners together with Sika Anchorfix. One of my motivations for this is that I also plan to use that to fasten my granite pieces together for another project- might as well glue it all up at once so I can get the most out of the epoxy before wasting the opened tube. Anyway, I also want to 'beef up' the front of the oven and the door so the brick material doesn't crumble away too quickly with repeated opening and closing of the door. I thought to use the cement board on the front and door as well, but insetting it into the brick, leaving a half inch or so of brick around the opening. The remaining brick edges will still be vulnerable, but the facing where the door closes will not be brick on brick, it will be cement board on cement board.

    I plan a lift-up door like a commercial dish washer, so as you open it, the door swings outwards slightly as it rises. Pretty sure I can rig up a spring on each side so the door will stay upwards when open, and also spring closed to some degree when it's closed.

    The whole structure will be wrapped in aluminum once assembled, since I still have the original aluminum wrapping that was on the kiln I got the bricks from.

    The bricks almost all have a channel where the heating elements lay. For a more even heating, I'd like to pass some of the element across the ceiling- most of it will lay in the floor and walls. Going across the ceiling is going to require some means of holding it in the channel. Perhaps I could arrange to terminate the ends of the heating elements in the ceiling so it can be held by its own wire, and perhaps also I can just use some other pieces of element wire to support it.

    I mentioned some time ago that I would put a slab of stainless steel in the bottom as a floor and as a heat moderator. Because the brick itself is so light it won't hold much heat, so I thought this would be a good idea.

    I don't know how hot the outside will get with extended operation, so I might re-think the idea of putting the pyrometer directly onto the structure itself. I do want to keep this all together as one piece, so it would be nice if the only 'loose' piece was the power cord. I want to mount the meter and controls on the back piece facing forwards (the back cement board would extend upwards enough to handle this) so it's all one unit. I'm hoping that with the aluminum wrapping the outside temperature will remain touchable- or I isolate the control area with its own wrapping- a separate heat sink as it were. With an aluminum cover over the back of the back board, I should be able to keep that area cool enough.

    Enough for now. I'm going to load up my bricks and go cut them to suit. When it comes to assembly- well I wish that AnchorFix was not so fast-acting so I wouldn't have to rush it. In some ways it's a blessing, but otherwise- the tube does come with two mixing nozzles, so at least I can divide the work into two stages.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Sounds like a fun project. I'd be careful about breathing any dust from the bricks. Not sure but I would suspect that the dust is pretty bad for you.






    • #3
      I have a good mask that I'll use when cutting, and during the clean-up. I know it's not good to breathe in any silica or alumina.

      Here's another thought- during the build process I have the option to include a means to purge the interior of the oven with nitrogen or CO2 or whatever. I wonder if this would make sense, and where to introduce the gas- at the top, the bottom, or doesn't matter-
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


      • #4
        Sounds like an interesting project. I am all a dither.

        Do take and post pictures.
        Paul A.
        SE Texas

        Make it fit.
        You can't win and there IS a penalty for trying!


        • #5
          Well I took about 50 bricks to the shop and cut them to suit. I have the walls, roof, and floor. Tomorrow I take more bricks in and cut enough to build the back wall and the door- and cut cement board pieces. The tricky ones will be the door area where I'll have to saw out the openings in two of the pieces. I want them to be one piece, not assembled from multiple pieces.

          The sawing I did today went well. I wore my face mask and ran the dust collector the whole time. I was happy to see that I didn't create any visible dust in the shop. As I was checking angles, I made two cuts on a chop saw, and that made dust. As one part of the testing I sanded one piece on the belt- that sure made a lot of dust in a hurry.

          Only two mistakes today- two bricks pretty much wasted. Small price to pay to have it all done to my satisfaction. I will take pictures.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


          • #6
            Do an aluminum sheet metal enclosure around it with standoffs, so that the enclosure is not touching the bricks walls. Leave the bottom open and top too or use vent holes up the top. This way when the oven heats up, it heats the air between the brick wall and the outer shell and creates a chimney effect, which keeps cool air moving between the enclosure and the wall and thus the enclosure stays cool.
            Amount of experience is in direct proportion to the value of broken equipment.


            • #7
              I used fiberglass reinforced cement board as an insulator for the speed coils on a golf cart. The original was mica, I think. Any way, I recall looking into the properties of the board before buying it. IIRC, it had a max temperature of 1200 or something like that. Perhaps due to the binder used. I think plain cement can handle 2500+ depending on what it's mixed with. When cement gets too hot, it turns to a calcium powder. You might want to coat the cement board with foundry wash or something.


              • #8
                Well that's a couple of interesting ideas. I really have no idea how warm the cement board will get. It is on the outside after all- but not knowing the rate of heat transfer or how long the oven will be on at various times, I'll just have to wing it. I'm at the point now where I'll be gluing the cement board pieces together prior to laying the bricks into place. There's a bottom, back, and two sides- one side will be left off until all the bricks are placed, then it gets glued on. Not sure what foundry wash is, but I do have some glaze. Wouldn't hurt to paint the inside with that. Pretty sure it can take the heat

                As far as the aluminum skin, I had planned on a fairly tight wrap, but I could easily leave a gap and cater to air flow for cooling. As the basic structure is already wrapped in cement board, there really wouldn't be much need for further skinning. In the original kiln, there was nothing but the aluminum wrap to keep the structure together. Perhaps I can just reinforce the corners and get the thing working before I do the outer skin. And this reminds me- I need to mount some tee nuts into the sides before fitting all the bricks.

                I'm off to the shop again right now- with my camera, the anchorfix, and some tee nuts.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                • #9
                  last time I made an arch out of bricks I cut some sheets of Styrofoam insulation into arch shaped supports to hold the brick until the mud set. Then cut out the foam.
                  Might work for you as well.


                  • #10
                    My top bricks will sit together without problem, no support required, but that's a good idea. As far as styrofoam, I plan to do some lost foam casting- that should be interesting.

                    I got a few of the pieces fastened together a while ago. The anchorfix pretty much set up, but I thought it would be best to leave it longer, so I went for a beer. I took some pics- before I start setting the bricks in place I'll take another few photos. It won't take long to assemble it from this point, so I'm sure I'll have a pic or two of it assembled by mid tomorrow. The door will be interesting- it's the last piece that will need dados cut in the bricks, and it will need a complete assembly including the aluminum skin before it can be handled, since it won't have a cement board back- just a front. I goofed on the dados on the front of the oven- made them too deep for the cement board that's left. Not a big deal, it just means I may have to sand the exposed part of the bricks to be level with the cement board piece that nests onto it. Wouldn't you know it- my second piece of board is thinner than the first piece I used.

                    Down at the pub someone asked me what I'd been doing- well you know how that goes, you start in on it and then have a lot of 'splaining' to do. We started talking about gold, silver, 'lunimun, palladium- Iphones are on the net looking up melting points, etc. Nobody said anything about me being crazy- hm.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                    • #11
                      Originally posted by darryl View Post
                      I really have no idea how warm the cement board will get. It is on the outside after all.
                      Ok. I misunderstood. I thought you were using the cement board for doors. If it's not exposed to the internal heat, it should be good.

                      Can't wait to see pictures. Be sure to include something to give the picture scale. (Yard stick, beer can, etc.)


                      • #12
                        DARRYL: one of your posts spoke of using stainless for the floor. That reminded me of a little story. Years ago, in the big shop where I spent my apprenticeship, we had a Lucifer brand heat treat furnace. The floor of the oven got in bad shape, so a foreman instructed a couple of mechanics to cut a piece of stainless for a new floor for the furnace. The new floor plate was about 24" x 30"lg x 3/4" thick. They did a nice job of fitting the plate. Too nice, it turned out. When we tried to use the oven to do some annealing, the oven would come up to about 350 degrees and then the oven would shut off. The Pyrometric people called in, said the plate was so close fitting, that the plate was shoving against the door and the micro switches (safety switches) would shut the oven off, working just like a thermostat. The lesson learned was that stainless is given to expand a lot when heated. So, if you use stainless for the floor, leave it a bit loose on the sides and end. Good luck.


                        • #13
                          Nice story on the stainless oven floor. Yes, I'll be leaving quite a bit of space around it.

                          If all went well with the picture upload, here's some- first couple show the cement board pieces and some of the bricks. Last pic shows the box assembled with the back row of brick pieces in place.

                          Last edited by darryl; 01-11-2016, 01:06 AM.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                          • #14
                            A few more- another view of the box. The dark marks on the side are where two tee nuts have been embedded from the inside. These will carry the control bars that hold the door. Two more are on the other side.

                            Last edited by darryl; 01-11-2016, 01:14 AM.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                            • #15
                              And some more- the roof bricks are just sitting there for now. I think it might be good to glue them in place, but since the glue lines will be at least partially exposed to the inside heat, I'll want to use a furnace cement or similar.

                              This is a close-up of the front, showing the recessed area where the front cement board piece nests into. The door will be made with the same detail, so when the door is closed it will be brick against brick. The inside edges of the cement board are thus not exposed to the inside of the oven. I expect the edges of the brick will soon become a bit eroded as the door is opened and closed, but from the moment when the cement boards begin touching each other this erosion will stop. The fit should be pretty much good at this point.

                              I have to do some real work tomorrow, but after that I'll be on to cutting out the center of the front board and the door board, then laying out the bricks for the door and basically making it a mirror image of what you are seeing here.

                              For the door itself I want to avoid putting cement board on the front, or outside of it, as that will add more weight- instead I plan on facing it with aluminum, which will also wrap around the top, bottom, and sides of the door. This might be a mistake since aluminum will expand a lot as it warms and possibly allow the door bricks to become loose. I'll think more on this. Perhaps I'll find a thinner board that won't weigh as much-
                              Last edited by darryl; 01-11-2016, 01:39 AM.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-