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Aluminium casting

Hi Can anyone help this old codger trying his first casting please. What I am trying to make is an aluminium block, 150mm square by 52mm thick with a 100mm hole in the centre, hopefully with a decent finish as I am short on finishing equipment. I am planning to weld angle iron into a square to make the sides, use a section of 100mm steel tube for the centre hole and tack weld them onto a steel plate to make the mould. I also want to fill the tube to make a disc. Does this this sound feasible please, also will the aluminium, as it shrink as it cools, get stressed by the centre steel tube. When I have poured the aluminimium into the moulds, do I slide a scraper across the top to get a reasonable finish. Many thanks Keith

axus4 (author) 8 years ago
Hi Thank you, sorry about posting in the wong section, wasn't sure which to use. I will take your points on board. What worried me was because the aluminium cannot shrink inwards as it cools, it might stress or crack. One further question though. I need to get the gap between the inner casting in the hole and the outer casting as tight as possible. The only tube I have found so far, the steel is about 4mm thick, I can get it out by hacksawing it through in two places but if the tube prevents the outer casting from shrinking inwards and the inner hole casting shrinks say 2%, then I will finish up with a 6mm gap all round. If I used a bean tin or similar, would the molten metal deform it. If a tin would work, I could possible get away with a 3mm gap. Thanks Keith
_soapy_8 years ago
Erm, you've posted this to the bugs section. To answer: Yes, you can make a mould out of angle iron, or indeed anything heatproof. Personally, I'd use something that was less conductive of heat, but it won't hurt. The central hole will also shrink, so you will need a way to get the steel form in the hole out. The whole thing should drop out of the mould without issue if you make the central form loose, as you correctly point out, the aluminium will shrink further than the steel. Make very sure your mould is clean and dry (heat it to above 100 degrees just before you pour to make damned sure there is no water waiting to flash into steam!) before you start pouring. The better the finish on the mould, the better your casting will turn out. Finishing aluminium is easy, you can just use a hand or power file. It is quite soft.