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heat treatment oven - question

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  • heat treatment oven - question

    All the homemade heat treat ovens that I have seen are narrow so the bricks for the roof can sit on the side bricks. My thought was to use a stainless steel strip placed into a slot in the bricks and a couple of stainless steel bolts to support the strip so the oven can be 12" wide (inside dimension).

    Has anyone else done something like this?


  • #2
    You could also go two layers on top, with the bottom layer of two bricks crosswise to support a vaulted brick across the gap above. Run lots of insulation in either case on top.

    Also note that you could make a true vaulted ceiling for your oven using refractory mortar and make a very roomy oven if desired. That's how pizza ovens are made. The mortar is the same stuff fire bricks are made of, but you can use it as mortar between the bricks. It is good to 1250C = 2200F. Oughta work!

    A 25lb bag is available for $35 from this source:

    I got interested in pizza ovens and realized at some point there was crossover value for a heat treater. Worth Googling the pizza oven world--lots more pizza ovens being made than heat treat ovens. LOL

    Mamma Mia, at's a spicey meatball!


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    • #3
      I use a fiber or kao-wool block for the top and half of the sides. Brick the bottom and half way up the sides then use the thermal ceramic fiber blocks for the rest. Lighter and will last longer than the brick. They come in different shapes and sizes and density for higher temperatures.

      They come with a threaded rod to attach to the metal Shell of your furnace/oven. The manufacturer I used last was Vesuveus.

      Good Luck

      The Worm


      • #4

        Marinite is probably a better choice than bricks. Comes in up to 4' x 8' sheets, so you can make a large oven.


        • #5
          JPR, I can't imagine why your plan won't work. Just make sure and try to use the firebrick mud to seal it off a bit.
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          Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

          It is true, there is nothing free about freedom, don't be so quick to give it away.


          • #6
            I have the lid off an old ceramic oven at work,those bricks are just keyed together and the whole top is wrapped in a thin stainless steel band which is pulled tight with screws like a hose clamp.

            BTW,I sold a ceramic kiln three weeks before I saw one being used to heat treat some big blocks of D-2.Sometimes you can find old ceramic kilns in the FS ads for $100-200.
            I just need one more tool,just one!


            • #7
              You should be able to just glue the bricks together with sodium silicate firebrick cement. If you cross laminate two layers it will be plenty strong.


              You could also use one layer of bricks glued to a piece of high temp mineral board.
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              • #8
                I had not thought of looking for a used kiln. I did a search on Craigslist last night and now the proud owner of a small 12" wide x 8" deep x 8" high kiln. The bricks on the door are chipped and need some minor repair. Also planning to install a newer thermostat.

                Faster and cheaper than building one, plus I can use it today. I forgot the k.i.s.s. part. Now off to try Evan's tandem vacuum idea while heating a part.


                • #9
                  I was given a small ceramic kiln, about 8" X 8" x 8" inside. A digital temperature controller was found on eBay, brand-new, for about $70.00, including thermocouple and power contactor. Didn't take long to lash things together, and it has worked well for heat-treating purposes. The controller reads in degrees C instead of F, but conversion is no big deal.

                  It's slow to warm up to hardening temperature, and slow to cool to tempering ranges, but works great otherwise.


                  • #10
                    Originally posted by Evan
                    You should be able to just glue the bricks together with sodium silicate firebrick cement.

                    Ugh, I wish I knew about that site. I bought the same refractory cement from McMaster for around twice the price when I fixed the crack in my muffle furnance/heat treat oven...
                    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


                    • #11
                      you have the right idea however what temp are you thinking of operating at?? if thats standard brick size your anchor is only 2" from the hot face?
                      we use 309 s.s. for anchors, for the price its good enough. our heatreat ovens are good up to 1800 deg. F. which covers all heat treating except forging temps.
                      most all "metal" anchor mterials will fail over time due to carborizing. the heat cycling from cool to hot over time will scale them away.
                      we use a light weight brick call IFB 2300. you can get from ALAN REFRACTORY. somewhere in Pennsylvania. i can get you details if interested. brick will cost you 1/3rd the price over ceramic fiber.. hoever fiber is better.
                      electric element is your better source for heat. less problems, and no excess oxidation problem caused by combustion types like natural gas.
                      Most important issue with building a heat treat furnace.. "UNIFORMITY".
                      equal heat all around is key.. limit warping, bending, uniform hardness. most furnaces you need to "spike" the temp to get the part temperature to correct temp if critical hardening. if you heat one side, well then its trial and error.. furnace of this type is infrared radiant heating. "line of site". convection is too slow..anything else is thermal transfer through the piece.

                      As i stated above if you can use electric elements you need to put them on as many walls as possible to heat the piece in all directions..

                      i built a small furnace just a short while ago, used 2" thick ceramic fiber board from Vesuvious Refractories comes in 36" x 48" x 2". i embedded Cromalox electric elements on the surface. i cut grooves in the board to press fit the elements. i put them on all 4 walls, excluding back and front door. furance was 16" square. Cromalox specified 6 elements wired in series max. so we had several banks wired then powered individually.. works real well. used a cheap temp controller to pulse it on/off using a type "k" thermocouple.. Ebay is a good source for the controller and thermocouple..

                      my 2cents
                      good luck.


                      • #12
                        Does the pulsed output controller make that much of a difference?


                        • #13
                          Hmm. It shouldn't be too hard to make a controller. A thermoelectric generator from an old gas furnace, an op amp and a 20 amp solid state relay about covers it.
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                          • #14
                            You can try most firebricks in your kiln but be warned that some will not take very kindly to temperature cycling as they are designed to work at very high temperatures by a phase change and have to be replaced if they cool down.
                            In copper refineries the furnace was rebuilt when they switched them off for the holidays and so were rebuilt twice a year I think the same goes for blast furnaces etc
                            I have tools I don't know how to use!!


                            • #15
                              I put a piece of 3/16 stainless between my top bricks to tie them .
                              I believe they are light weight 2600 degree bricksThey are very light weight. at 2000 degrees you can place your hand on top and it is not tooo hot.