[TheForge] Question for Tom, Strengthening castable refractory

Mon Aug 25 10:53:00 2003

A few years ago I built a Gingery charcoal-fired crucible furnace, using
castable refractory poured between metal forms.  After the refractory
had set thoroughly, I built a wood fire in the thing to cure it at
moderate temperature.  No air blast, just natural convection.  Worked
fine.  The outer metal shell has since rusted partly away, but the
refractory is as good as new, though I'd build another wood fire inside
before using it at high temp again, as I'm sure there's lots of water
seeped into it.

Bruce
NJ

>>> [email protected] 08/22/03 03:45PM >>>
Tom,

In building furnaces using castable refractory -- how have you done a
"dry
out" before going on to use under high fire?  What has worked for you? 
How
long have you let it air cure etc.?

In industrial practice for large aluminum melting furnaces we
developed
rather complex dry out schedules -- then went to work with an aluminum
producer in China and found they just built a wood fire in the furnace
and
let it burn itself out.  They would limit the draft at the start, so as
not
to overheat but then would open up the draft more as the "burn"
progressed.

Dave Smucker

----- Original Message ----- 
From: "Thomas A. Troszak" <[email protected]>
To: <[email protected]>
Sent: Friday, August 22, 2003 3:27 PM
Subject: [TheForge] Strengthening castable refractory

> > Date: Fri, 22 Aug 2003 12:07:26 -0500
> > From: [email protected] 
> > Subject: Re: Subject: [TheForge] Strengthening castable refractory
>
> > Another thought. Someone else mentioned using bricks. I've already
got
the
> > castable, but now I'm thinking of putting in expansion joints.
When
casting, I
> > could insert some thin cardboard dividers running the entire length
of
the
> > shell. The cardboard would just burn out during the curing.
> > Would that even be necessary with the needles?
>
> Dear Marc,
>
> I hesitated to mention this because, well, I seem to stick my foot in
my
> mouth (or keyboard) every time I attempt to reply to someone on this
list.
>
> My personal recommendation is that separation between the roof and
walls
(to
> allow expansion) is a good thing, regardless of the size of the
furnace.
The
> cardboard should work fine.
>
> I would suggest using the needles either way. Refractory blocks that
are
> properly mixed, reinforced, cast, and fired will be tough enough to
survive
> even a medium blow with a sledge hammer. Even after a LARGE blow,
the
blocks
> with the needles stay together even when cracked, which is the whole
point.
>
> I have built more than 100 industrial furnaces since 1985, including
the
> ones I mentioned with the slab roofs, bunches of pottery kilns, etc.
and
my
> recommendations come from that experience. I know what has worked (or
not
> worked) for me, what works well for others may be different.
>
> Most of my furnace designs are based on the concept that refractory
linings
> should be allowed freedom to move when heating and cooling, and this
comes
> from my experience repairing and maintaining the settings for large
steam
> boilers, etc, where the expansion from cold to hot can be measured
in
> inches.
>
> I now expect we will hear from ALL of the guys who made their (1)
forge by
> casting a refractory liner in a five gallon bucket with no needles,
or
> expansion joints, or anchors, and how they never even measured the
water
> when they mixed the cement and how their forge has been working for
15
plus
> years with no cracks... and I'm sure that they are telling the
truth.
>
> I am just attempting to share from my experience, I hope it is
helpful.
>
> Let me know if you can't find the needles, I can get them for you.
>
> Tom Troszak
>
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