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Post by jkirk3279 on Feb 7, 2017 20:24:25 GMT -8
Hi.
I've been studying the batchbox archive.
The model of a Five part casting was interesting.
Now, I'd like to ask about refractories and reinforcement.
I like the "water glass" recipe but I'm concerned if it can be waterproofed or not.
And I instinctively think that the refractory should be reinforced.
The simplest way is chicken wire.
Will it survive in a batch box?
Will it expand in the heat and cause cracking?
My latest sketch suggested that a skeleton of rerod would be perfect for mounting stainless carriage bolts.
They would protrude through the walls of the batchbox and allow mounting and weight support.
The head of the bolts would be embedded in the refractory.
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Post by ronyon on Feb 7, 2017 21:30:33 GMT -8
The chicken wire would not survive. I would add rock wool fibers. Stainless needles might survive. Harder to come by. Stainless steel scrubbies might serve, but I still favor the rock wool.
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Post by peterberg on Feb 8, 2017 1:08:48 GMT -8
Any metal parts embedded in refractory castable will lead to cracks. Simply because the metal will expand faster than the refractory. One exeption are the stainless steel needles, when mixed through the castable. I seem to remember there happened to be one type which incorporated polypropylene fibres. When heated, those melted and left miniature cavities with less cracks as the net result. Mind you, it was only done by that one type with good results, no conclusions about any other product with the same fibres.
All those refractory materials are designed products consisting of very carefully balanced components. Whatever you add to it, it will influence the end result in a negative way, the SS needles as a notable exception.
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Post by jkirk3279 on Feb 8, 2017 9:59:44 GMT -8
Excellent.
That confirms my expectations.
I have seen the stainless steel needles on eBay at a very fair price.
I think it was $21 for ten POUNDS.
I will have to consider castings with holes in them to use stainless steel bolts and large washers.
They should survive the heat while providing support.
Now, does anyone have a favorite water glass recipe for firebrick?
I repeat, I loved the five-part casting model.
I can whip up the forms. I can build a kiln from rusty barrels and mineral wool, and power it with a Babington burner.
I just need a recipe for the refractory so if we've got a thread on that please let my know.
I'll try to search for it.
I worked for a Ceramics teacher in college; recipes are everything.
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Post by drooster on Feb 8, 2017 10:38:32 GMT -8
I will have to consider castings with holes in them to use stainless steel bolts and large washers. I recently dismantled a dead washing machine. I recommend doing just that to learn something about casting with holes and bolts, and as a byproduct you get a nice garden brazier ...
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grga
Junior Member
Posts: 76
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Post by grga on Feb 10, 2017 1:43:16 GMT -8
Any metal parts embedded in refractory castable will lead to cracks. Simply because the metal will expand faster than the refractory. One exception are the stainless steel needles, when mixed through the castable. I seem to remember there happened to be one type which incorporated polypropylene fibres. When heated, those melted and left miniature cavities with less cracks as the net result. Mind you, it was only done by that one type with good results, no conclusions about any other product with the same fibres. All those refractory materials are designed products consisting of very carefully balanced components. Whatever you add to it, it will influence the end result in a negative way, the SS needles as a notable exception. Probably the use of polypropylene fibres that leaves miniature cavities as you said helps the redundant water to remove from concrete easily. Regarding stainless steel needles usually they sell type 304 or 340 which tend to loose their strength if constantly exposed to temperatures above cca 700 C athough its mellting is much higher. So after a year of use the inox inside maybe is gone or of no use - but it still can prevents initial cracks due to inproper drying and curing... Better to find inox 310 or some other.
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Post by jkirk3279 on Feb 11, 2017 11:53:34 GMT -8
The PVA fibers make total sense.
When they burn out they leave micro-cavities.
Leftover moisture expands into the microcavities instead of building pressure and exploding.
Gradually, the moisture cooks out leaving a refractory with tiny worm holes.
In theory, dry sawdust would also work. I've seen it suggested,
It burns to char and leaves a cavity with moisture absorbing charcoal in it.
For that matter, shredded styrofoam "peanuts" might leave the right size cavities.
I hate to beg, but searching the forums on this iPad is slow.
Are there any vital threads on using high temp cement and Waterglass?
I'll build a prototype kiln and do experiments this Spring, I just need some specifics to start with.
"Magnesium" cement? Portland cement?
Would any PVA ribbons work?
I like the idea of cutting up SS "scrubbies" at least for experimental tiles.
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Post by coisinger on Feb 15, 2017 10:18:05 GMT -8
Jkirk,
Even stainless will expand and contract to some degree, thus it is discouraged to use metal in most applications. (To quote a wise man: "All Metal is Doomed!!!"). Use perlite, it has natural voids and will make any casting lighter and have a greater insulation value.
Some have suggested instead of using standard cement (Portland, which is not suitable at all for refractory purposes) is to try using a calcium aluminate cement.
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Post by Vortex on Feb 16, 2017 10:12:09 GMT -8
Stainless seems to have a higher thermal expansion than mild steel: www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.htmlMaybe you could paint the needles or wire to give a layer to burn out and give a little expansion room. I know it's shunned by some people but the roof of my firebox I cast 9 years ago with chicken wire in it is still as good as new. Probably been fired 2,500 times since then, but maybe I've just been lucky.
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