Sifting Refractory?

[a456bt]

I haven't seen anywhere online that people have castable refractory like mine, but the stuff that was recommended to me by my local refractory supplier and I inevitably bought comes with gravel mixed in to it. I imagine this is to increase strength much like in concrete, but I wonder if this is needed. The gravel makes it much harder to cast and work with, essentially removing much of it's structural integrity while wet and can fall apart easily without a mold to tamp and pack it in to. Perhaps the gravel can help with thermal properties as well? I suppose it must be there for some kind of reason, the question is whether or not that reason is beneficial to me.

[Exo313]

What's it called?

[Lou L]

I just did a quick search for refractory and aggregate and found a hydraulic refractory mortar.  I suspect t that the stone aggregate in your mix means that it is a mortar.  If that is the case, the guy who sold it to you doesn’t understand what a forge does.  I’d be curious to know the name of the product and what it is rated for.  Offhand and with limited information I would guess the stuff you have is not suitable for a forge.  That would be the reason you haven’t seen people building forges using it.  If you search for information on building fireplaces you will likely find it.

[ThomasPowers]

Sounds seriously off to me.  I'd double if not triple check!

[JHCC]

Got a photo of the packaging?

[a456bt]

The guy seemed to be pretty convinced he knew what he was doing. Said he had helped many people build forges before. That, coupled with the fact that this guy ran a company that specialized in this stuff, is what initially gave me the confidence to take his word. I hope I wasn't too wrong haha.

The stuff is called Uni-Cast 3000 and it's made by a company called United Refractories Co. I tried looking up information about the company and the product but their website just lists the product and no real information on it. All I really know about it is that it's rated for 3000 degrees (as you could guess by the name) and how it is currently working in my paint can forge -- which is actually pretty well.

I know it's not a long time, but I've ran my forge for a total of about 20 hours and the refractory seems to be holding up great. There is a crack in it but that's because I had to chip away at it after not putting mold release on the glass bottle I used to form the inner chamber. As well it has taken on an ashen grey color since the first firing. Other than that it looks the way it did when I cast it.

The only problem I have with it so far is that gravel. Here are some photos of the packaging--

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[HojPoj]

Is it true gravel, or is the aggregate all the same color?  What you're thinking is gravel may actually be grog (smashed up bits of already- fired refractory).  This actually helps with the refractory performance and reduces shrinkage.   It may be the kind that needs to cast or rammed into a form, and not painted onto a surface. 

[Lou L]

It’s interesting.  Perusing the manufacturer’s website, It appears to be a product with high thermal shock resistance and is intended for use in an iron foundry.

here is its chemical makeup.  I post it so that the gurus can tell more.  I know noth8ng about the chemical makeup of refractories...

AI2O3 51.6%

SiO2 40.9%

CaO 4.6 %

Other 2.9%

To be honest, high thermal shock resistance sounds like a refractory that will last a lot of heat cycles.  No idea if it can stand up to flux or being bumped while hot.  You just may have turned into an experiment for the gas forge gurus.

 

Edited to add:  WOW HojPoj, that is one heck of an insightful first post on IFI.  It is an idea that could hold promise for this refractory.

[DWH]

I've used a castable refractory that has gravel in it.  Its called Tex Kast HS made by Wesco.  "HS" stands for high strength.  Its rated for 2700 degrees.  I used it originally to make a wood fired pizza oven.  I formed my 2" thick dome over a 30" yoga ball and it turned out great.  I had no trouble smoothing it with a trowel.  No cracks after 4 years of use.  I've also made some blocks that sit just outside my forge and are flush with the forge floor.  I didn't use it inside my forge.  I used Kastolite 30.  Here's a picture of the gravel after screening out the fine particles.  I wouldn't remove the gravel.  I think all refractory needs something for strength.  If you run Kastolite thru a screen, you'll see a lot of fibers.

[HojPoj]

I spent a lot of time in metal casting forums (alloy avenue), one of the moderators had extensive ceramics knowledge and shared it freely.  There's some interesting chemistry that goes on in the refractory and heat- much like the right combination of alloying agents and heat treatment gives the intended properties to a metal. 

[a456bt]

UPDATE! Looks like it isn't grog. Here are some photos of the aggregate sifted and washed.

[HojPoj]

Huh... try hitting one of those chips with a hammer to be sure they're rocks?  Grog could be from a myriad of sources.   Regardless, I wouldn't advise pulling out what the company puts in without talking to one of their application engineers.  They can tell you the function of the aggregate as well as provide end-user information (minimum recommended thickness,  for instance).  Fortunately the application Lou L mentioned (high heat foundry applications,  likely a direct-melt furnace) sees a lot of abuse and should resist fluxes for quite awhile. 

[ThomasPowers]

How insulative is it?  For hobby use I find I'm more concerned with saving propane and speed of heating the forge up to using temp than if the inside is rated for steel foundry use.

[HojPoj]

ThomasPowers, that's the dense (non-insulative) type.  It'd only be practical for a hotface application (cast to the thinnest shell practical) and backed with something like Kaowool for insulation.  Even then it would still add appreciable thermal mass, but would stand up a lot better to fluxes and carelessness with insertion/removal of stock.  Only really relevant if you do a lot of fluxed forge welding, I'd imagine.

Of the United refractories products, you'd need the stuff that has 'LW' in the name for the lightweight insulating refractory.  Compared to the fiber blankets, though, they're still sizeable heatsinks.

 

 

[a456bt]

So from what I gather I may be able to sift it out at the expense of some physical strength?

[Frosty]

Only sift out the larger aggregate and you'll be okay. Without aggregate there will be problems with thermal cycling, besides crusher run keying it provides room for expansion/contraction without heat checking. Cracking. If refractories didn't need aggregate they wouldn't put it in.

A #20 sieve should leave enough aggregate for strength and still be fine enough for easy casting. 

Frosty The Lucky.

[a456bt]

Thanks Frosty, makes sense

[stevomiller]

And remember “gravel” just means small chunks of minerals, which come in almost unlimited compositions/ combinations.

I’m very sure this isn’t gravel from some dried riverbed as used in aggregate concrete, although part of the intent is the same.

Many refractories are or were originally made of said materials and reprocessed by milling, etc into the shapes ore sizes wanted. Ytrium isn’t agate etc. You get the point.