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## Re: [hobbicast] Re: Refractory blanket how-to for welding forges.

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• Mikey:I don t know if it is your writing or my reading but I still don t understand. Best I can tell you are saying to squeeze 1 thick ceramic fiber into a
Message 1 of 40 , Sep 3, 2013
Mikey:I don't know if it is your writing or my reading but I still don't understand. Best I can tell you are saying to squeeze 1" thick ceramic fiber into a 1/2" thick space (or smaller) to compress it so it won't shrink as much after heating. In other words: to fill a 2" space you would use 4 (or more) layers of 1" thick blanket. I still don't understand how these "rectangles" would be arranged.                                                 As I said before I don't see how this could be done without a form. In your first post on this topic you said "Rigidizer, and toughening coats work best when the surface beneath them is itself highly stable." How would it be possible to add rigidizer or toughening coats (Satanite) while the blanket is tightly squeezed between two forms? Do you have a way to make a drawing? Thanks Carl

________________________________
From: "michael.a.porter@..." <michael.a.porter@...>
To: hobbicast@yahoogroups.com
Sent: Monday, September 2, 2013 2:12 AM
Subject: Re: [hobbicast] Re: Refractory blanket how-to for welding forges.

Carl,

You wrote. "I assume you mean he" (Giberson) "cuts the blanket into rectangles and then folds them in half to make squares. How big are the squares? To highly compress the squares I assume some type of form is needed. My interest is how to do this in a furnace rather than a forge."

My "squares" are more precisely called rectangles (as you did), for their lengths are whatever the builder finds convenient for the space they fill, while their widths are to be twice that of the desired thickness of the wall they are to form; this isn't likely to turn out well for them to be termed "squares" as I called them.

The genius in Giberson's method lies in the ability to easily place the folded rectangles beside each other until the space of a kiln's arch or within the tubular form of forge and/or furnace. After a complete wall is formed, extra folds are deliberately placed between existing folds until the builder is satisfied that much or all the springiness, which has allowed folded layers to be forced aside is used up (or as close to this point as is wished in order to more than overcome shrinkage).

Because this "sandwiching" tends to move all the folded parts more or less equally (especially as pressure builds), it isn't necessary to place the additional folds in different areas; thus, a couple of wooden or metallic plates can aid installation of the additions greatly (serving as "wedges"). Also, the folded parts can be used to shape the internal surfaces of a forge (by varying their widths), so that they can become support for a kiln shelf "floor". I realize this point is of no importance to someone wanting to construct a casting furnace, but others are reading these emails, too.

The springiness of new ceramic blanket material, and its tendency to "take a set" after a few heats can be used to make superior internal structures, if kept in mind, or can become a source of irritation if ignored during construction; this is especially true in the light of this material's tendency to shrink after a few heats. The lighter (less dense) the ceramic fiber layers the more extensive shrinkage will be, and the corollary is also true.

Mikey

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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
Message 40 of 40 , Sep 15, 2013

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?
Mikey
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