[TheForge] Strengthening castable refractory

[Thomas A. Troszak]

> Date: Fri, 22 Aug 2003 12:07:26 -0500
> From: marc@ironringforge.com
> 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