Re: [hobbicast] Re: Refractory blanket how-to for welding forges.
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"You should note that, even after the rigidizer has penetrated ceramic fiber products to a desired depth, it remains somewhat porous, so adherence of the toughening layer presents no problem." Instead of "it" I should have written "they," for obviously the ceramic fiber products remain "somewhat porous"--not the water glass coating rigidizer leaves behind.
Neither my writing, nor your reading is faulty. I think you're just suffering a little bit of anxiety for lack of an installation plan. The folded rectangles are placed side by side through the expedience of compression on either side of two plates. One plate can be welded in place, and the other moved by means of a handle, or both plates can be moved in unison by scissors action (pinning extending handles together), or you can have a second person help you by holding one plate by its handle while you use both hands to push the second plate and place extra folded rectangles in place. The only "form" you need is supplied by the furnace or forge's steel outer shell
Adding rigidizer into compressed fiber blanket parts is quite simple; it still penetrates the material just fine, just not as quickly (this actually improves control of penetration depth). Ceramic fiber board is simply a highly compressed form of fiber blanket, and it accepts rigidizer just fine (but slowly compared to blanket products). Once the rigidized layer is fired and becomes permanent, the thin toughening layer is added and fired. You should note that, even after the rigidizer has penetrated ceramic fiber products to a desired depth, it remains somewhat porous, so adherence of the toughening layer presents no problem.
I don't have a drawing and am not set up to draw at this time (I make book drawings and take photographs all at once, over a period of months between writing text and the first edit of each book; otherwise I don't make drawings at all). You can see relevant drawings in Giberson's book, which is so full of drawings and valuable equipment building instructions that it will become a permanent part of your technical library; I wouldn't consider loaning my own copy anymore (having had to replace it twice).
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Recently someone on one of the casting groups commented that there was no such thing as a cement that can have all of the water baked out of it; I believe this was done in defense of the use of Portland cement in a homemade castable refractory. The official answer would be that the chemically locked portion of water in lime based cement cannot be baked out, but the chemically locked portion of water in refractory cements can be. I have always accepted this official version as the only reality...in the past. The limiting factors on "baking out all the water" are that the refractory must be taken to yellow heat in the first place, and that over time, water content can recollect in refractory if you're not careful to seal the refractory surfaces against water vapor in ambient air.
However, truth of any kind is seldom found effortlessly; including technical "truths". I suspect that a healthy debate, with both sides airing their views, might adjust what the majority of us accept as practical reality--to our mutual profit; this could be important for people wanting to make insulating refractories as secondary layers. Homemade refractory as an insulating secondary layer might be quite forgiving of official standards; standards useful for hot-face layers may constitute a waste of money in secondary refractory layers.
While casually dismissing the Portland cement idea, I have noted both resentment, and a strong hint of "I'll match your official facts with personal experience" in passing (heated) comments from the other side of this issue. Isn't it time they had a FAIR hearing; something open minded, maybe?