Metal Casting Zone

Hi

I'm a complete beginner armed with that most danagerouss of things "a little knowledge".

I make kit cars for a living and I need aluminium bumpers that I can polish up and chrome.

I'm looking for the easiest way to make them for as little money as possible. I'm considering a permanent concrete mould. I know this is likely to ring alarm bells but I'll paint a picture and hopefully someone can guide me down this road or steer me onto another.

At work we have a large wood burning stove 900c. Its easily big enough to have a permanent concrete mould housed inside along with the wood that feeds it. I'm considering a steel hopper permanently installed to be filled with aluminium first thing in the morning just after the fire is lit. It would then be allowed to melt and fill the mould during the day. The next morning the mould gets emptied and reset.

I've read about the explosive expansion of water in concrete being a problem on sudden contact with melted alloy but I'm hoping that any water will be boiled off well before the alloy melts. Also are there problems with this direct fill aproach, or with the metal being molten within the mould for several hours before it cools overnight?

All comments would be greatly appreciated.

Welcome to the forum!

I don't know how the concrete would react to this. I imagine it would crack and splay and have a very rough surface. You may have to test out different types of material for the mold.
How large a bumper and what will it weigh?

im not sure you will be able to "hold" aluminium in a molten state for too long... low melt alloys work fine in a big pot on the stove but aluminium???? it needs a very high heat to melt it! at once. not a slow "big to the boil" approach.

High, thanks for the initial thoughts.

The bumpers are likely to weight 1kg each or there abouts. They only protect the corners of the car, like those found on a Ferrari Dino.

I've had a short trial by putting a few bits of aluminium into a cup placed within the bail burner, it melted but the cup cracked. Its note conclusive enough to say the concrete permanent moulds would work or fail as yet but it indicate that the heat may be sufficient. However before I go much further I'm going to get a couple of prices for having the casting done by someone else, just to be sure the chaise is worth the biscuit before I embark on the chaise.

I'll let you know if I get any further with my idea though. Thanks again for the responses.

Tom

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