Instructables

making a (more) permanent mold from cement/concrete for aluminum castings?

Hey
I've been looking into aluminum casting for a while now (done it once or twice with different "furnaces") 
Now I'm reading alot about lost foam casting (sounds interessting too)

But I was thinking; do you think (/have experience) that I could make some kind of "permanent" mold out of some kind of cement/ concrete/ fireclay mixture for casting similar pieces several times??

I was thinking, when you make the furnace(s) you make a cement/ concrete/ fireclay mixture that can withstand the temperature, so shouldn't it be able to withstand the temperature of the aluminum being poured into it also?
(and therefor be able to make the mold out of)
- I was thinking to use a special type of cement ment for use around a fireplace.

What do you know/ think of the idea?
- and also; is there any (other) cheap/ "easy" way to make permanent molds for several similar castings? (at home/ the backyard)

PS. not important but I've made/ used a coal fired furnace, a gas (butane) fired furnace and now I'm about to build an electrical furnace (for the sake of expence and time of heating up)... I'm trying to make some casting sand/ green sand, but the ingredients looks to be rather difficult for me to gather (In Denmark Europe)

lordl9999 (author) 2 years ago
it's simple parts I want to make, a normal 2part mold would be working with no "trapped" parts so a solid mold should work, the reason I'm asking is because I don't have easy/direct acces to casting sand and would like to reuse the mold to produce simmilar parts. and cement is fairly easy/cheap for me to get :)
Think I'll give it a shot, just think it's important to make enough " air vents".
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canucksgirl2 years ago
Is it possible to make a permanent mold? Yes, but it depends on what you want to make.

For example, the sand casting process uses a mold only once, because of the type of cast they are making. For something like an engine block, they use a sand mold. The sand is held together with a special adhesive. The aluminum is heated and poured into the sand mold and once its set the mold is heated to breakdown the adhesive in the sand so that the sand can be poured out of the cast aluminum. (Otherwise you can't get the mold out of the cast).

AFAIK, in large productions, they have a process where they use one mold to make the sand mold, and then they create the aluminum cast, and reuse the sand for additional molds.

By using a positive mold and a negative mold, I think you could achieve similar results, but again, it all depends on what you are making.

I hope that helps.
Making a permanent mould depends a lot on the shape - Casting is most used fro complex shapes which would be hard to machine.

Their complexity makes a multi part mould difficult to make so you can get it off.
Silicone may be used and be released because it is flexible to some degree but sand is simple, works and is no problem at all to remove.

Even then the shape of the pattern has to be considered so it can be removed from the mould unless the lost foam is used.