Handle or knob for ceramic insulating block for heat treatment furnace?
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  1. #1
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    Default Handle or knob for ceramic insulating block for heat treatment furnace?

    I recently got a new heat treatment furnace and the manufacturer recommends using an insulating block in the front of the furnace compartment. The door has a built in insulation block, but basically the idea is that you are supposed to also insert a fairly tight fitting block behind the door as well to maximize insulation.

    They supply a block which is about 1 x 4 x 4 and fits the opening closely. The problem is that it is incredibly fragile. It appears to be made from pressed ceramic fiber and it crumbles under even pretty slight pressure. The block has two depressions in it which are intended to be finger holds, but in practice the block just crumbles more every time I try to put it in or take it out of the furnace.

    It seems like some kind of knob needs to be built into the block to allow it to be manipulated successfully. Anybody have experience with this kind of thing?

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    A photo or two would help. Is the furnace door swinging on hinges? Is the supplied block supposed to go inside or outside the door? How is it supposed to mount to seal what the built-in door insulating block does not? Just where is the knob going?
    Since the oven is new, presumably the mfr has answers to what you are asking. No?

    -Marty-

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    sounds ridiculous that you need to be involved that way.
    this sounds like a small furnace...

    you shouldn't need to dick around with a block to seal it.. unless it's an open long type furnace.. then I get it.

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    Well, the manufacturer just recommends putting the block in the mouth of the furnace compartment and the block they supply, like I said, is pressed ceramic fiber with two finger holes, not a knob. It is very fragile and just crumbles anytime I touch it.

    One option would be to use regular firebrick. I could just mill out an inset knob in the firebrick and cut it to size. This would definitely work, but firebrick does not have the same insulating qualities as ceramic fiber. Also, the firebrick would be in contact with the sides of the furnace chamber which are insulated with more ceramic fiber, so the fiberbrick might gouge that lining.

    Ceramic fiber has about 1/3 to 1/4 the thermal conductivity of firebrick, so it definitely would reduce the efficiency of the furnace to use firebrick (or use nothing). This would be more of factor when the furnace would be at higher temperatures 1600-2000F.

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    When you refer to firebrick, do you mean "insulating fire brick", aka IFB? They are the ones that are very light and porous, and pretty fragile.

    For the ceramic fiber, maybe you could make a cage from high temp wire to enclose it, with a loop for a handle

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    Well, I guess I could use insulating firebrick as a compromise between the ceramic fiber that was supplied and hard firebrick.

    I don't know. The bottom line is that I need some way to pull it out of the opening, so there needs to be a knob of some kind. The problem is how to make such a knob. Actually I probably need two knobs because to pull it out evenly with just one knob might be difficult.

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    Would rock wool stand up to the temperatures you're working with? I think it melts at around 2,000*F? It comes in bulk so you can just grab a fresh chunk whenever you need. Just poke it with a stick and pry it out of the furnace.

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    What about two holes and a loop of wire for a handle?

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    PHOTO of the unit and ceramic brick.

    or link to the product you bought...

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    Quote Originally Posted by crossthread View Post
    What about two holes and a loop of wire for a handle?
    Two holes and a BBQ fork?

    Ed.

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    Can you butter up/ coat inside of the finger holes with some refractory cement? This would glue all the fibers together in the finger holds, reinforcing them. You can get this where they sell wood stoves or hardware store.

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    This comment certainly doesn't help with the original question, but I built a heat treating furnace for my shop and the door is thicker than the sides..more insulation than the sides, so it baffles me why one would need a secondary piece of insulation put in place every time you charged the furnace. Seems like it should have been built with a door thickness/insulated to preclude that monkey motion...but there's probably lots I don't know about the deal.

    Is this furnace you have electric or gas fired?

    Stuart

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    Paint the block with hardener for ceramic blanket,
    Mark

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    They probably figure the door seals leak so they have you place some extra insulation inside the door to prevent drafts and cold spots.
    Bill D

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    HVAC suppliers sell fiber ceramic premade combustion chambers for oil furnaces. They come wet and flattened in a sealed plastic bag. They are very workable until set up and fired when the material hardens. A source of replacement material. Yes it is better insulation, but say twice the same thickness of fire clay equals the same insulating value.

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    Aac blocks are fireproof. Cheap. A bit stronger. Easy to get your hands on. Easy to cut to size

    Peter

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    if hardener for ceramic blanket is not available use water glas. melts at 1100°c.

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    Perhaps coat the outside with something like this?

    Ceramic Fiber Rigidizer, coating and High Tempearture Adhesive


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