The Shop > Metal Stuff
Foundry Furnace for the Tiny Shop
MetalMagus:
Hi
While googling the plaster of paris. I came across this concrete designed for making furnaces.
http://www.specialplasters.co.uk/index.php?_a=product&product_id=244
Might be of some interest.
Cheers
Sean
vtsteam:
Thanks Oz, Andrew, Will, MM.
Oz, Plaster of paris is a different mineral compound than spackle or wallboard compound (which is what I think we call what you are referring to). Chalk vs Gypsum, carbonate vs sulphate. And they have very different characteristics. The most valuable of which in poP is its ability to set without drying (water evaporation). Spackle will take very long to dry even if 1/4" thick on a wall, and if trapped between forms in a 2" thickness would never dry. It also shrinks on drying, unlike poP and would develop cracks in any thickness. The usual wallbord compound/spackle contains starch, as well as calcium carbonate.
poP cures, rather than dries -- it goes through a chemical change that liberates heat. And a thicker section will actually cure faster than a thinner section due to this heat. It doesn't shrink, which is why it is used for molding fine details.
MM, that castable refractory with that temp rating seems very reasonable in price, and if had been locally available here I might have used it. My guess is, you'd need 2 bags for a furnace this size.
Will I'm sure there are better grades of poP for the purpose. The problem for me is that there are NO castable refractories available cllose enough to me to be able to pick up. I would have to ship anything in that line, and the shipping costs can double the cost.
If I were going to pay big money for shipping a refractory my ultimate choice would be a fiber mat and zircon coating exactly as ironman uses -- as the highest insulating vaue, and a proven iron melting capability. And I do hope to some day do that if I can find the materials. But if it comes down to a castable with lesser temperatuure capabilities, I think this plaster and sand combo, available to me for $20 and local pickup at my hardware or builder's store makes good sense, and I'll be saving my pennies as a result for the ultmate refrac, some day.
RobWilson:
Good to see you got the furnace fired up Steve :thumbup:
Rob
Will_D:
As this is the "goto" foundry thread at the moment:
The refractory: PoP+Sand seems to work well. So thats my furnace lining sorted.
I like the look of the gas bottle for the body and lid - we have a lot of these in Ireland
How much sand and PoP was needed/ 25 kg of each or more?
What would the max crucible size be: A4 or larger?
Next problem:
Casting Sand:
Nowhere to buy it in Ireland! Talked to a few foundries and they all import from UK.
So yes I could drive 100K and 'try' to blag 25 or 50 kgs, however:
I can get 'play' sand in 25 kg bags (basically its a very clean, silica sand, for kiddies sand pits)
I need to add some 'clay' - I can get Koalin and Bentonite (both clays)
What is a recommended mix?
I know I can do it the old way (squeeze and shear the sausage [oops - off on a wrong thread fantasie :bugeye:] ) but I need to know if its 100 parts sand to 1 part Clay additive or is it more like 10 to 1?
Its just I need to know how much to order!
vtsteam:
Rob, thanks! :beer:
Will, I have only fired this furnace once, and it is experimental, so I can't say it is proven yet. I'd know better after ten melts how it will hold up.
The propane tank I used was larger than our usual BBQ tank here. The smaller ones are called 20 lb tanks. This one, I believe is a 30 lb tank. The cylinder body was approximately 18" tall (not including valve or sheet metal guard/handle), and 12" in OD.
I used up a 25 lb bag of poP, and nearly a bag of sand (50 lb, I believe)
Interior open space chamber is 12" high by 8" diameter.
It would definitely fit an A-6 crucible. I went with 8" diameter because I like to fit charcoal briquets on edge around the cast iron plumber's pot I use as a crucible. If a gas or oil furnace was contemplated, probably a larger crucible would be do-ablein my furnace -- however you do need space for tongs, so I don't want a smaller diameter. There are rules of thumb for bore size vs crucible sixe on other sites. I'm used to an 8" bore charcoal melter.
Seems like you could get sand from the foundries you mention if you are able to talk to them. I don't live near any foundries. Ceramics suppliers/pottery supplies often have silica sand, and fire clay ( I've used fireclay and sand for both building furnaces and casting) In fac my greensand for aluminum today is still made from fireclay and sand, not Bentonite. My Gingery lathe and accessories were all made with that. I do have silica and Bentonite for my iron sand. The fireclay I've used is called Hawthorn.
I strongly recommend getting Dave Gingery's book on the Charcoal Foundry for all the info on foundry building, firing, greensand from clay and sand, moulding, etc.
Also I'd severely miss my two Terry Aspin foundry books if they were gone -- and they are published in the UK. All three are small but jam-packed paperbacks, and a tremendous bargain. I've read them all through several times over the years, and in my opinion they beat most online sources hands down -- but then I'm a reactionary when it comes to casting!
Don't be shy about opening a thread and asking lots of questions there -- you'll get a lot of differing opinion, this one isn't the go-to furnace thread or shouldn't be -- I'm a nutcase who generally does what you're not supposed to do and occasionally gets away with it, and this is an experiment that may not work out -- just finding out if I can push an envelope for cheapness! :beer:
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