Wool vs I.F.B.

Discussion in 'Furnaces and their construction' started by dennis, Jan 4, 2021.

  1. dennis

    dennis Silver

    I have bricks on the brain, it seems.

    I hope to build a Gingery-style lifting-body furnace (zinc, aluminum, perhaps occasionally cuprous alloys) some time in the future, and for some reason, I cannot wrap my mind around wool - either Kaowool, or the (marginally???) Less hazardous Super-Wool.

    I have a brick fixation. Is it because I'm more familiar with Insulating/soft bricks?(I've used them in the past) Is it because of the fond recollections - in my life, rare indeed - of the soft-brick kilns in my first stint in college? Is it because there's something I cannot yet name that makes wool "too noxious"?

    I've seen wool but once in the solid. Somehing about it rubs me the wrong way, and I don't know what it is. Is the stuff like fiberglass for itching? (Whole body barrier-cream time?)

    Note: I live within 6 miles of High-Temp, Inc. so no shipping worries. I've checked their prices, and wool (Super-Wool) is slightly cheaper. I'd need to buy a roll of it - 50 square feet - or two cases of k-23 brick. (I'd have a few bricks left over). I've heard wool is a better insulator, but 3 inches thick of Satanite-slathered brick, topped with ITC-100 ...

    Oh, and the outer portion of the planned furnace needs to look a (fair) bit like a propane BBQ - it needs to be square - which really pushes things into the brick camp. I can do a round 7.5 inch inside hole in a 13.5 inch square outside easy then.

    At least, it does to my crazed mind.

    Is it time to call the bin-keepers and await their nets?
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    K23 IFB is a good insulator but wool is much a much, much, better insulator......or lower thermal conductivity as we say. In general refractories with higher density are more thermally conductive but stronger.

    Soft IFB is easy to work but you would be mistaken if you think they are any less of a respiratory hazard than wool at least when you are working the brick.....not so in furnace use. They are quite friable and the fines can become easily airborne. Use common sense, respirator, and wash yourself and your clothes after working with it. Don't use saws and sanders in confined spaces with IFB. I moved mine outdoors. If you do so indoors it will deposit fines all over your shop which can become airborne many times after the fact. If you use hand tools much better and brush up the fines, do not vacuum.

    My first furnace was IFB with very thin mortar hot face, and ceramic wool outer insulation. I really liked it. I coated the inner surface with a very thin layer of mortar which dramatically increased the surface strength, but it will peal and sluff off with repeated heats due to differing thermal expansion. If I was going to build a fuel fired furnace I'd lean toward K26 IFB. They are a good compromise of mechanical strength and insulating qualities. There's a reason kilns are built out of brick.

    Oldironfarmer has an IFB furnace that has provided much faithful service for him in all kinds of duty. You should check his out.

    Best,
    Klely
     
    dennis likes this.
  3. dennis

    dennis Silver

    This was/is the electric one, correct? Was just reading about the bricks crumbling and needing replacement with castable...

    I do plan to build up a few (thin) layers of Satanite on the bricks, and then an ITC-100 finisher. High-Temp has k-26 bricks, also.

    The base is planned to be Kast-o-lite30.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes it was/is electric, and very thin, only 1/2" thickness at the root of the heating coil groove. The bricks were glued together with mortar and after many heat cycles there were micro fractures at the joints. Like wool, IFB's mechanical properties will change after time at temperature and weaken somewhat. If your design contains the brick I don't think it will be much of a problem, especially if it doesn't get moved jostled around often. If I hadn't dissembled that furnace and handled it carelessly, I may still be using it.

    The dense refractory version was my least favorite of the three. I still have it. It is indestructible but takes much longer to come to temp, and conducts more heat to the shell. The current low mass molded ceramic fiber and ceramic wool incarnation is by far my favorite. -Non-ferrous duty.

    Best,
    Kelly
     
  5. dennis

    dennis Silver

    The outer shell - .032 stainless, or similar - will coral the bricks. (Lots of stainless BBQs out there...) Plan is to anchor them to the shell if needed.

    The usual will be zinc, aluminum, and below-1800 heat-treating, e.g. case-hardening. Will be running a small, low-speed blower and propane.
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    If you build a furnace to melt iron, bear in mind that iron eats its way through refractory at a rate inversely related to the refractrory density. A drip of iron on IFB will travel through 2 inches of brick in a single melt. Iron on wool is worse. A few coats of Satanite provides marginal resistance to iron and fair resistance to reactive atmosphere (the wild chemical chaos in fuel-fired furnaces.) Kelly uses resistance wire so he does not have to deal with all the crazy chemical combining and recombining of oxygen with combusting fuel and his IFB holds up very well for aluminum service. Castolite is pretty sensitive to iron too. Dense castable is less so, but not immune. Rammable refractrory is as immune to iron and slag as anything I've seen to date. Iron can still erode it. But it resists quite well.

    The temperature ratings of refractories must be for still-air environments. Add in fuel and swirling hot gases and they melt to glass beads pretty quickly if not covered in something like Satanite. When I ran an IFB lid, if the Satanite failed, the brick could melt full thickness in the failed area in an hour where it was washed over by hot gas. In dead-end areas where gas did not wash over it but just impacted it (big difference) it could resist fairly well.

    It is sort of like making cowboy toast on the gas stove like I do from my grandkids. Take a piece of white bread. Put a hole in it with your finger. Use a fork to hold it flat over the lit burner. Where the flame/exhaust impacts the bread it will brown gradually. But where the flame/gas passes through the hole the bread burns away rapidly. Same thing in the furnace. The stream of gas is much much more corrosive than the same material impacting refractory.

    Denis
     
    Last edited: Jan 4, 2021
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I have no doubt about MS' experience with those materials. Most of the manufacturers of IFB and Wool aluminosilicate refractories say they will be reduced by the gases present in fuel fired furnaces. They don't like fluxes either. I can attest that even molten aluminum will rapidly penetrate IFB which was another reason for the mortar coating. There were plenty of examples at degraded fiber and IFB at AA. The one that seems to fair much better is OIF. He has a loose IFB furnace that is exclusively fuel fired fueled by about anything he can find to burn, but I believe he may have a coating and not sure it's seen iron but a time or two....maybe he'll chime in.

    Best,
    Kelly
     
  8. dennis

    dennis Silver

    Thanks for the replies. I've been trying to figure out 1) why wool is so popular, and 2) why some would think me a fool or worse for not using it. Nearest I can think is most people don't live 5 miles from a major-level place that sells refractory, and hence they might well be getting lit up by the shipping fees. (Ups, FedEx. One person quoted me 95$(!!!!) For shipping a modest number of bricks!)

    Wool endures "rugby-handling" by shipping firms better than brick, too.

    Then there's something akin to "fashion" - something I've Never understood.

    Wool might well insulate better, but I'm wondering how much better? I'm thinking to try it in a small core/powder-coat/tempering oven, where it gets stainless steel sheet on both sides to supply a degree of rigidity. I think that's an issue - brick is easier to handle that way.

    I'm currently dealing with an insulating material a bit like wool - climashield - in making a pair of insulated bags for perishable foods. The feel of this stuff on the hands is unpleasant at best!
     
    Last edited: Jan 4, 2021
  9. dennis

    dennis Silver

    Hence using kiln wash in the kilns of recollection?
     
  10. dennis

    dennis Silver

    Another reason, which I just (re)learned: the feeling of fibrous insulation, be it glass, ceramic, or polyester - is beyond my capacity to describe adequately. "Awful" is the best I can do, and that word is hopelessly inadequate!

    It's as if I'm combing the crystalline "hair" of a Lovecraftian "deity" - and said deity is currently sorely irked, and becoming exponentially more so by the second, by my blundering mistreatment of his/its/??? integument.

    It wants to make my hands turn into mushrooms and then have both fungal nightmares run off while screaming.
     
    Tobho Mott likes this.

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