Subject: [Q] Look for simple high temp (1800 C) rated refractory

From: C++ Freak <[email-masked]>
Date: 1 Jul 1996 13:01:18 GMT

Currently I use YTONG (air-spaced gypsum inner wall blocks, normally
not designed to be used as refractory, but it works excellent) as
refractory for a furnace holding a crucible for melting metals like
copper, silver, etc. It works well until 1350 C. I just carve out a block
which is the space where the torch heats the crucible.
But heating it up till 1450 C (melting cast-iron) or higher (using
carbon arc instead of propane torch) the inner wall melts down to a white hot
slurry of molten CaSO4 with dissolved CaO (and silica ?) which is very
sticky and attacks Hessian (alumina) crucibles.
Chamotte is no option, as it is *very heat-soaking*. It 'costs' about
200 degrees in maximum temperature.
I look for a 'refractory' like 'YTONG' which is *very* insulating but which
can withstand 1600-1800 C without sticking to the crucible. Or can one make
it yourself by mixing crushed/powdered gypsum with magnesia and then
're' baking it ?
Even lining the inner walls of a carved YTONG block (which I use now) 
with this 'refractory suffices.

Any help would be appreciated.

Klaas

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From: [email-masked] (Alan Walker)
Date: 1 Jul 1996 23:20:36 GMT

In article <[email-masked]>, C++ Freak <[email-masked]> says:
(snip)

>with this 'refractory suffices.

See http://www.zircar.com  There you will see a 
reference to an American company called Zircar.  They have an office in 
Europe.  They make a range of light weight refractory insulating boards 
that can be used at 1800 deg C.  It is quite simple to assemble a small 
kiln using their boards on the hot face, and some sort of lower rated, 
lower cost material behind that.  Use the Zircar board to take the first 
300 - 500 deg, then a cheaper material in the lower temperature zone.

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From: Uncle Al Schwartz <[email-masked]>
Date: Mon, 01 Jul 1996 12:06:43 -0700

> Any help would be appreciated.

Expanded zirconia is available as felt sheets and shaped blocks.  
It is >tremendously< insulating.  If that won't take the heat you 
have big troubles.  Have a look around in http://www.search.com/ 
and especially http://www.thomasregister.com/

You could always go the conventional route and look up kiln 
furniture.

-- 
Alan "Uncle Al" Schwartz
[email-masked] ("zero" before @; 24 hour delay)
http://www.netprophet.co.nz/uncleal/
 (Toxic URL! Hazardous to children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?"  The Net!

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From: mike vest <[email-masked]>
Date: Tue, 02 Jul 1996 15:51:32 -0600

> Any help would be appreciated.

As mentioned Zircar is probably the best supplied of oxide type 
refractories.  They can be expensive and the oxides will mechanically 
degrade.  There is another oxide insulation outfit in Augusta GA, but I 
can't remember their name.  E-mail me and I'll look for it.  Don't 
forget the grafite fiber insulations.  These are quite good under 
reducing conditions, or vacuum.  They are also cheap.  One company is 
Great Lakes Carbon.  A final note is heat shields.  Try using these 
metals or alloys of, molybdenum (sp?), tungsten, and tantalum (softens 
at high T, but does not  melt).  Heat shields are sturdy and can be used 
to cut the temperature down to one suitable for insulation.

Mike

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From: Thomas Hamling <[email-masked]>
Date: Wed, 03 Jul 1996 04:11:51 -0700

> Any help would be appreciated.

check out our home page at http://www.zircar.com for information 
regarding high temperature insulating products. for the range of 
1600-1800 c alumina fiber insulation. It retains its strength at those 
temperatures betterthen fibrous zirconia.

I hope this helps.

thom