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Thread: New Furnace Lid - Refractory Issue

  1. #1
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    New Furnace Lid - Refractory Issue

    I am making a new lid for my furnace. Despite lots of tamping/shaking for several minutes after pouring, I ended up with a very rough bottom. The top is nice and smooth, though. This happened on my last lid, which I used for a few years anyways. I am wondering, can I mix up some more refractory and layer it over the bottom? Or, will it it not bond and be likely to separate after firing? I am using Allied Mineral Products' Minro Fire-Cast F80. I just pulled the wet rags and plastic off, so it hasn't dried yet, if that matters.
    IMG-0288 (1).jpg

  2. #2
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    I have not worked with this material but: People patch old refractory so this should work. I expect the initial setting may be over. Apply filler to the bottom ASAP because the wet top will pull less water out of the patch. Let it air dry a few more days. It may be that firing will help the patch bond with the top.

    Not sure how thick to make the patch coat. I'm guessing thin as possible to get the best bond due to heating. If that sort of bonding happens.

    Howard

  3. #3
    Senior Member Zapins's Avatar
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    It doesn't bond well. I tried patching my lid and it fell off almost immediately. Its different inside the furnace where it can gain a purchase on the wall and sort of sit there rather than hang.

  4. #4
    Quote Originally Posted by RyanMark View Post
    I am making a new lid for my furnace. Despite lots of tamping/shaking for several minutes after pouring, I ended up with a very rough bottom. The top is nice and smooth, though. This happened on my last lid, which I used for a few years anyways. I am wondering, can I mix up some more refractory and layer it over the bottom? Or, will it it not bond and be likely to separate after firing? I am using Allied Mineral Products' Minro Fire-Cast F80. I just pulled the wet rags and plastic off, so it hasn't dried yet, if that matters.
    IMG-0288 (1).jpg
    Depending on the refractory used, I think if you sieve a batch of powder only and mix up a slurry (no large media) to fill in the gaps, it will work out ok. I agree with Zapins that if you try to add thickness using refractory mixed straight from the bag, it may not bond properly.

    I fixed up the tuyere on my furnace with wet slurry and it seems to have done a good job.

    This is how I would try it, best of luck.

  5. #5
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    What's the worst that can happen? It will crack and fall off. So what? It won't hurt your melt if it falls in the crucible. Just skim it off.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  6. #6
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    Thanks, everyone! I put the wet rags back on while I waited for answers. I think there's enough crevices to "cling" onto, so I'll go ahead and sieve some grog out of the mix, then patch it with that.

  7. #7
    Senior Member Tobho Mott's Avatar
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    Sounds like a plan, good luck! I bet that will work ok.

    You say you had 2 lids come out like that? Did you ram them up in layers or all in one shot? No matter, you say you got good use out of the last one right? I used a vibration tool similar to the one in myfordboy's furnace build videos when I cast refractory parts for my furnace and was amazed at how it made a very dry mix flow like a liquid! Here's my under-lid pic:

    Attachment 16633

    Just something to consider for later if you ever end up having to to make another lid. Mind you, I only built my lid a couple years ago too... I remember when researching my build it seemed like a lot of people were saying lids are the trickiest to build so they won't fall apart eventually. If/when mine falls apart I will probably borrow a page out of Rasper's book of tricks and replace the castable bottom half with some kind of rigidized ceramic fiber blanket that can be easily replaced.

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

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    If its not creating a functional problem i wouldnt bother with it

  9. #9
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    I cant tell the shape/profile of the lid, but if the "tops" come out nice and smooth maybe you can pour them upside down next time?

    Cheers Phil
    So, whats your Plan B?

  10. #10
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    Update: I finally got around to using the lid the other day, and it seems to have held up fine. I sieved the refractory through a pasta strainer to get the really big pieces out. Then I did it again through a window screen. I decided that was maybe too fine so I mixed a little of the pasta-strained bits back in. Mixed with water and filled in my lid bottom. Covered with damp rags and plastic for a day, then let air dry until this week (over a month). The day before casting, I put the lid in my oven on low, slowly ramping up over 12 hours but only to 300F. Then I turned it off while I slept because I don't trust my oven. On casting day morning I warmed it back up on low while I made coffee, did morning stuff. Then I placed it on the furnace with a crucible inside and set the burner on low, ramping up over about 3 hours until the crucible glowed a dull red. I then cranked up the burner and melted, and poured some bronze. No cracks or pieces missing but I guess time will tell how long it lasts. Thanks everyone!

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