[TheForge] Castable Refractory

[Andrew Vida]

larbooks@impulse.net wrote:
> 
> I know this has been discussed before on theforge but I didn't pay
> enough attention.  I have an atmospheric forge that works well and is
> lined with 2" of kaowool and then covered with ITC 100.
> 
> Now I want to make a forge that is lined with Mizzou castable
> refractory 3000 degree.

	Curious as to why.  AFAICS, unless you're looking to keep
	the forge running for extended periods (days?  weeks?)
	and/or are planning to be handling heavy objects in a 
	rough fashion that would tear up wool, I see no reason
	to use a solid refractory liner.  They take a hell of a
	lot longer to get up to heat, which if you're forging for
	just a few hours here and there is very wasteful of fuel.

	Just an observation.

> What I'm wondering is:
> 
> Does it help to put a short metal rods, screws, or whatever through
> the sides of the forge to help hold the lining in place once dry?
> What's the best thing to use?

	I don't think so.  I have yet to see any such arrangement in
	a commercial forge.  First, it should not be necessary.  Second,
	they will serve as a conductor of heat to the steel shell, and
	third, the continual expansion and contraction inside the
	cement may cause gradual failure around the steel inserts,
	possibly reducing the servicable life of the liner.
> 
> What's the best way to make a removable form to fit the inside of the
> forge to shape the inside opening?

	Cardboard or plastic that burns out the first time you
	fire the forge.  If you have not received directions,
	I would strongly recommend you obtain them for several 
	reasons.  One, if you season the liner incorrectly, the
	usable life may be greatly reduced or you may even ruin it
	the first time out, though perhaps unlikely.  Second, there
	is the safety consideration.  There may be special precautions
	one must take with a given product to ensure the lining
	doesn't dunt or blow, the latter which can prove very dangerous,
	steam being what we all know it to be.
> 
> What are the disadvantages and advantages of using castable
> refractory as opposed to kaowool or durablanket type insulation?

	Economy.  Cast liners eat a lot of heat on startup.
	Advantage is they retain a lot of heat on shutdown.
	They are generally far more durable.  A good solution
	is a hybrid.  Line with wool, cast in a hard floor and
	wash with ITC-100.  Or line with castable, then a layer
	of wool, cast in a floor, ITC wash... a little rube-ish,
	but would give an additional layer of insulation.

	Really, the only reasons to use castable, AFAIK, is for
	durability and heat retention.  If you want something
	strong or need to anneal a lot, then such a beast may
	be the ticket.  If you're a typically broke smith, then
	perhaps cost savings in fuel would be your greater concern
	in which case washed wool is definitely the way to go.
> 
> Does Mizzou type material make a good floor for  a forge?

	Sorry, dunno... though probably it does.
> 
> I plan to make the forge out of about a 10" or 12" pipe with about a
> .09 wall and form a flat place in the pipe for the bottom of the forge.
> 
> Been thinking about making the thickness of the insulation
> somewhere between 1.5 and 2 inches.  Will this be adequate?

	Depends on the refractory.  It is fine for the two brands
	of wool I have used.  The only type of cast refractories I
	know of are all high density.  They are not as good at
	insulating as low-density.  Consider the difference between
	hard and soft refractory bricks.  The soft (low density) are
	far better insulators than the hard.  I had four cast 
	refractory forges and they all had liners about three to four
	inches thick as I recall.

	One of the methods of manufacturing low density bricks is to
	mix the clay with fine sawdust.  After set up, the bricks are
	fired normally and the sawdust burns out, leaving large numbers
	of very tiny voids and thus raising the insulating value
	sharply.  You might want to query the manufacturer to see if
	you could do this with their castable, in which case you could
	do, say, a 1.5" LD outer liner and a .5" thick inner liner as
	a protective layer and floor.
>