Machining Lava (or ceramic)

Anybody have experiencing machining lava? I need a plate that can be easily drilled, and can withstand high temperature (annealing iron in a kiln). Are there gotchas I need to know about drilling lava? Do I need special tools (there could be up to about 100 holes in the piece)? Does it crack easily?

Here's a web page on a lava I'm considering:

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The same company offers a partially fired alumina bisque that might work, but it shrinks

15 to 18% on firing. That seems like a lot to me, and I'd be worried it would distort.

If anyone has experience with another favorite material that takes high temperature (at this point, I can't say exactly how high -- dull red heat, maybe, for a few hours), I'd like to hear any recommendations. Must be electrically non-conductive. Must be non-magnetic (in the usual sense -- i.e. weakly diamagnetic). Cost is not a big deal (it's a one-of-a-kind prototype -- labor cost will be high, so saving a few bucks on material won't matter). Must be available in small quantity (like one, plus a few extras to break, if it cracks easily).

I'd like it to be as thin as possible, which would imply high strength, but I wouldn't want to use a ceramic if it's going to distort when fired. If it shrinks very uniformly and predictably, maybe I could use it, but I can't afford to go through several rounds of redesign and learning curve to understand how to work with the material. It's got to be cut it, fire it, and it works.

Reply to
Mark Thorson
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contact any refractory or firebrick supplier

EVERYTHING undergoes phase changes/expansion and contractions when heated - even lava

don't buy partially fired ceramics as they will shrink more

the shape WILL effect how much movement you get on firing i.e. plates won't expand/contract as uniformly as a cube

select the material to best suit your needs

Al2O3 - SiO2 - MgO - ....

your temp range is probably only 1100F - 1500F based on your description

depending on the material i.e. except for things like silicon nitride, you can generally use concrete drill bits for making holes

what are you trying to do?

Reply to
Portly Stout

You did a nice job of describing your needs but I'm not sure what sort of dimensions you are envisioning.

Rather than machining a ceramic plate you might consider using a refractory cement like "High-Temperature Refractory Cement" sold by

You could punch the holes in it before it cures. These cements don't shrink when fired.

Almost any fired ceramic or slab of rock (like granite from a monument maker) will work for your application. Think of things like saucers designed for large flower pots, etc.

Diamond tools to drill the holes are prefered but you might get away with carbide if the ceramic is soft enough (like the terra-cota used for flower pots.)

You might consider very porous ceramics like insulating firebricks that you could simply punch holes in.

Reply to
dave martin

Go to

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and check out RS-100. It can be machined with ordinarly workshop tools. I have used it and works just like they say in the spec.s!

Watch out for silicon carbide kiln furniture - it is a passable electrical conductor at your temperatures.

Thin sheets of refractory (castable or otherwise) will be much more prone to breaking than RS-100.

If you want to cast your own, don't use burn-out plugs to form the holes: most candidate materials will expand while the castable is undergoing firing shrinkage, which will split the piece. Use lubricated posts and pull them out as soon as possible - most castable refractories shrink on drying.

Reply to
Alan Walker

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