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  • darryl
    replied
    JT you're probably right. Thought about it a bit more- the hood I plan to use for the paint booth is plastic. Might not be the best place for an oven.

    Looked at both ideas more- the vent I wanted to use for the paint booth is not where I thought it was. My option has always been to remove a basement window and fill in the bottom 2/3 or so with plywood, using the remaining opening above that for the vent. I think I'll do that for the oven, and use a second basement window in another room for the paint booth. For that one I'll just make the glass shorter so I still have light coming in. Most of the time the window will be exposed anyway, so that will be better than just blocking it off. Where the oven will now be it won't matter if you can't see outside. I'll keep the windows and just put them back in when I sell the place.

    The plan is coming together-

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  • J Tiers
    replied
    Originally posted by darryl View Post
    Somebody asked me about this project a few days ago, and made the suggestion that 'you're gonna need ventilation'. Now I'm thinking to build the paint booth bench and make it long enough to set this oven on one end. Then I can just slide it over when I'm using it and the fans will vent whatever fumes are generated.
    ...
    Yeah, it's going to stink some, I bet.

    And I'd not normally think of a heat treat oven right next to a painting area. It will probably stink worse as residual fumes get partly burnt in it.

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  • darryl
    replied
    Somebody asked me about this project a few days ago, and made the suggestion that 'you're gonna need ventilation'. Now I'm thinking to build the paint booth bench and make it long enough to set this oven on one end. Then I can just slide it over when I'm using it and the fans will vent whatever fumes are generated.

    This thing has gotten heavier, but I think as much weight is in the cement board as in the bricks. It will be heavy, but I can still carry it.

    As far as the door, I could make it swing open- but I thought it would be safer and probably seal better if it moved outwards and upwards, staying parallel to the oven face. Its own weight would tend to pull it tight when lowered, plus there wouldn't be a hot surface (the inside of the door) right at my elbow as I'm accessing the contents. I've also been thinking of using stainless steel strapping around the door perimeter.

    One of my reasons for epoxying the cement board pieces together is to make the containment box airtight. And if the door fits well, there should be very little air infiltration. This should make the job of maintaining a suitable atmosphere easier, and if I use a gas from a bottle, it should last a good while. At the same time, the less outside air that can get in, the less heat will escape and the better the chance that it will reach the highest temperature it's capable of. An airtight box should also let the thermocouple sense the actual temperature more accurately, and a further bonus is that air in the gaps between bricks won't be able to move and conduct heat to the box.

    All in all I'm taking pains to ensure that the inside of the oven keeps its trapped atmosphere. The stainless floor that I would put in is there partly to protect the floor and keep things away from the heating elements, but mostly for thermal mass.

    More pics to come as I progress. I wanted to work on this more after my working day, but here I sit at home now with a touch of the flu. Something going around again, so they say.

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  • Seastar
    replied
    That's very good looking.
    It makes my heat treat toaster oven look pretty wimpy.
    Bill

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  • ironmonger
    replied
    Looking good! If the slots you spoke of concern you they could be filled with koawool, but I doubt that you would need to. You might hold the door together with a strap of stainless steel wrapped around the perimeter. I don’t know what the expansion rate of your insulating firebrick is, but this source says .6%. around .1" for 18"

    I friend of mine had purchased a large commercial heat teat furnace and they used a stainless steel box inside the furnace proper to maintain a inert atmosphere. It was, of course, smaller than the furnace interior. The box had a piece of stainless steel tubing that exited the furnace though the fire brick and was fed with argon.

    You could flood the entire furnace with gas as well, but wrapping the parts in stainless steel foil would likely be more cost effective. Commercial brazing furnaces can use exothermic atmospheres to protect the parts form oxidation... kinda overkill for a furnace your size :>) You could toss some lump charcoal inside to scavenge the free oxygen... as long as your shop is well vented...

    I have a much smaller furnace, about 8"X6"10" interior, and had to stress relive a block of steel... no inert atmosphere and no foil wrap = lots of scale. If it was outside I would have used the charcoal...

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  • CCWKen
    replied
    Dang, that's slicker than a fresh cow patty! I see that a lot of foresight went into the design and construction. Brilliant!

    Perhaps an angle iron frame would allow for a swinging door with captured brick. And allow it to be moved as a unit. (With a crane?)

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  • Sim
    replied
    Beautiful work. It will be very interesting to see the finished oven, and the temperatures you will achieve with it.
    Looking forward to more pictures.

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  • darryl
    replied
    In the second last pic you can see a groove going front to back in the middle of the oven floor- this is not a design feature, but is a consequence of having to cut the bricks to a length that didn't let me get rid of all the original angles on the ends of the bricks. Not a big deal, but well, there it is. You can see that on one of the bottom bricks in the lower picture.

    Also in the last pic you can see the groove 'feature' in the two bottom outside bricks. Again a consequence of not having enough unaltered full bricks to build with. The groove is the same in the bricks inside, and is where the heating elements used to be, and will be again in this oven. I did manage to get the grooves lined up in the final assembly It's a bit hard to tell, but the two front grooves inside the oven are closer together than the rest. I don't know yet but I might put elements in both front grooves, then skip a groove, then fill both back grooves. It's a matter of how much element coil I have, how long they will end up being, where will I place the lead in and lead out wires, and to what extent I can have the coils go across the roof. Basically, where do I want the heat to be made- and how much power do I have available to run it. I'm thinking I'll have to branch off from the dryer wiring and mount a second dryer receptacle, or perhaps just a 20 amp, 220 outlet. There is not more room in my panel for another dual breaker, so I'm kind of stuck with doing it this way. Hoping to arrive at a figure of 3000 to 3500 watts for the oven.
    Last edited by darryl; 01-11-2016, 02:58 AM.

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  • darryl
    replied
    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.

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  • darryl
    replied
    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.

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  • darryl
    replied
    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.

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  • sarge41
    replied
    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.
    Sarge

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  • CCWKen
    replied
    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.)

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  • darryl
    replied
    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.

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  • 1-800miner
    replied
    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.

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