From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: sci.chem,rec.crafts.metalworking,sci.engr.metallurgy
Subject: Re: Does SO2 attack Kanthal heating wire ?
Date: Sun, 13 Dec 1998 01:33:01 GMT

On Sat, 12 Dec 1998 20:34:11 GMT, billaryclinton@hotmail.com wrote:

>In a small furnace I use Kanthal A1 (or AE ?) wire and the refractory is
>air-spaced gypsum (YTONG building blocks). I used this refractory because
>of their very good insulating properties and resistivity to about
>1400oC. The refractory however *slowly* decomposes above 1200oC and
>SO2 is released.
>After a few uses the Kanthal wire (which is heated to at most 1300oC,
>more often not more than 1200oC) is still functioning, but is brittle.
>Attempts to bend results in breakage. Is this due to SO2 attack or is
>it normal aging ?

I hope you have a good (necessary) reason for bending any furnace wire
once in place. They are subject to all kinds of heat treatments most
of which are not well documented and Murphys law probably will
prevail.

You  are pushing Kanthal a bit at 1400 C.
>Is there a possibility to seal them by e.g. alundum cement ?

Alundum cement will not make a  gas tight seal. In addition the
temperature cycles would probably produce cracks in the alundum which
will allow direct contact to the furnace atmosphere.

I question the use of gypsum. There should be better ceramics but you
didn't list any special requirements.

From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Make your own Insulating Castable Refractory...
Date: Sun, 13 Dec 1998 01:33:00 GMT

On Sat, 12 Dec 1998 17:21:16 GMT, "Kurt Bjorn" <pyroware@flash.net>
wrote:

><Excellent post snipped>
>
>Thanks John, this is great stuff!
>
>In the jewelry trade, there is a rather expensive little device that looks
>just like a coffee pitcher which is used to melt small quantities of metal,
>maybe a few ounces at best.  It uses I'm sure nichrome wire to approach 2000
>degrees.  I have always wanted to make one, and your recipe might be the
>ticket. I was thinking of molding a shell inside a SS pitcher, then wrapping
>the nichrome around a form of some kind, then lining it.  A small graphite
>crucible would hold the melt.  I could add a thermocouple and use a variac
>for control.

I assume 2000 degrees F. Brought back memories when I was gainfully
employed and working with both metallurgists and chemists. When they
came through the door you needed to know their field expertise to know
what temperature scale they were using.

I would suggest that you give some thought to upgrading to Kanthal.
The maximum temperature in comparison to nichrome is not a big deal.
The advantage is that Kanthal will take more temperature cycles at a
somewhat higher temperature than nichrome before failure.