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Refractory Concrete Recipe


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#1 ToolSteel

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Posted 20 January 2011 - 05:15 PM

I would like to build a small propane-powered foundry. I plan to melt plumbing/flashing copper scrap, combine it with tin and produce bronze to use later in lost wax castings.
I'm looking for a recipe for refractory concrete... not refractory cement. I've read that I'm not to use Portland cement in the concrete mix because it will break down under the intense heat. But then, I've talked to guys who've been putting in fireplaces and chimneys for decades and they tell me they use Portland cement all the time. I live in Atlanta and for the life of me, I can't find anyone who's ever heard of calcium aluminate cement... which I've read is what I should be using. I have ready access to fire clay and hydrated lime... and, of course, Portland cement and sand. Does anyone have a reliable recipe for refractory concrete?
Thanks in advance for your time.

ToolSteel

#2 lostunderhood

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Posted 20 January 2011 - 06:29 PM

Hi ToolSteel, you may look over at backyardmetalcasting.com/forums/. You will find a lot of info and help!! :)

#3 Rich Waugh

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Posted 20 January 2011 - 06:38 PM

Lemme see.... a fireplace MIGHT hit a thousand degrees Fahrenheit. A foundry WILL hit TWO thousand or more. D'ya think there might be hint there why Portland cement is really bad idea for a foundry? I do. :-)

You can get high-temp rammable or castable refractories from a number of manufacturers. Between fifty and a hundred bucks will get you plenty enough to make a foundry that will handle a 20# or larger crucible. Those companies have spent hundreds of thousands of dollars, maybe millions, on research and development of these products. There is simply no way that you can hope to achieve the results they get by making your own homebrew concoction, even if you have a recipe and access to the raw materials. Why re-invent the wheel? You need a high-temperature alumina based refractory, which is not something you just whip up in your garage. Check out A.P. Green or one of the other refractory manufacturers and save yourself the headache of building a foundry and then having it crap out on you because you you used an inappropriate refractory. I won't even go into the dangers associated with refractory failure in a foundry - just imagine a river of molten metal flowing toward your feet.

Rich
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#4 ToolSteel

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Posted 21 January 2011 - 07:57 PM

Rich,
You're absolutely right. I must have tried a different search string today because I immediately found a refractory supply place within 10 miles of my home. It sells all types of refractory products. I spoke briefly with a very knowledgeable and helpful salesperson. I'll probably go with the KAST-O-LITE 30 LI. A 55 pound bag costs less than $70.
lostunderhood... thanks SO much for the link. I had no idea one site could contain so much information.
I appreciate the two of you for taking the time to respond.
ToolSteel

#5 Rich Waugh

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Posted 26 January 2011 - 06:36 PM

You're very welcome, Toolsteel. One of the main reasons I come here is to pass on some of the lessons I've learned in over forty years of working with metal. Over that time a lot of people passed on information to me and I'm just passing along to others in turn. Paying it forward, as it were.

Rich
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#6 AKAMetal

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Posted 22 August 2012 - 12:44 AM

Also, Foundry101.com sells a "backyard kit" that is fully functional and will give you the ability to start melting the day it arrives. I think they are based out of Oregon so this is only helpful if you are stateside. I have used one of their furnace setups literally to death and had great results. I have also reverse engineered one of these and found that I couldn't build the set as cheap as they sell it.

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#7 nobodyspecial

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Posted 05 August 2013 - 08:16 AM

I've used the backyardmetalcasting recipe with Portland for casting up to bronze/brass temps with no real issues. Takes patching once in awhile.

 

On the other hand, why not get the good stuff if you've got the money? 

 

On the other other hand, I line the bottom of my forge with the stuff. Upside down lawnmower, brake disc on bottom where the engine goes, pipe tuyere. Homemade refractory filling the outer bits and then forming a funnel  for a firepot, down to the grate i put on the middle of the disc.

 

Biggest problem was early on the closest part of the funnel to the middle would slag a little and clinker would stick to it. But once I made it wider (by knocking out said clinker, and a little refractory) so it's out of the worst of the heat? Works fine. B)






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