Re: Advice on Casting Small Components in Aluminium


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Posted by Rob Frink on April 23, 1999 at 20:29:02:

In Reply to: Advice on Casting Small Components in Aluminium posted by Phil B on April 19, 1999 at 15:43:30:

Hi Phil,

As I learned just recently, its kinda difficult to fully explain all the specific details about your setup without photos. However I've got a couple of opinions that I hope can help.

I feel that your pouring temp is good, maybe a touch hot though. I figured it at ~1400 F or so. Aluminum can just-start to gas at this temp and hotter depending on the alloys. I wouldn't go hotter. In aluminum, gassing can be used to reduce shrinkage but this is probably not good practice for structural stuff or air/water tight requirements.

As far as venting, I really favor vents. I use them often in green sand to reduce any pressure from steam/gas in the mould which may prohibit cavity fill. I call the vents "whistlers" and I make them by simply poking a wire thru the sand. After pouring and cooling, the whistlers are snipped off the casting with side cutters.

I don't have any experience with investment methods but I have some thoughts on BP's note about chills. If a chill is used, I'm thinking that you should reduce the temp of the mould before pouring. A hot mould will have a hot chill and if the heat capacitance of the chill is greater than that of the mould, the chill may have the opposite affect by keeping the metal hot rather than sinking the heat away.

Now for an area that I do have some experience ...centrifical casting. Maybe this will help with the short-fill problem. I've used my lathe for this, casting aluminum in simple 2 piece steel dies. I fix the mould/die to a face plate and spin it. To feed the metal while spinning, I mounted a stationary feed tube centered and parallel to the bed ways. This horizontal feed tube was made from good old black iron pipe with an elbow turned up to pour into. The mould/die was mounted offcenter on the face plate. I made sort of a cylindrical reciever which was mounted in the center of the face plate and revolved around the stationary feeder tube. The reciever had a sprue connecting it to the mould/die. When hot metal was poured into the stationary feeder tube it would run out the other end into the spinning reciever and centrifical force would push it into the mould/die via the sprue. The receiver has to have an internal groove or recess and internal flanges to prevent liquid metal from slinging out. If you over fill too much you'll sling liquid metal around. Spindle speed was slow....130rpm. If you don't understand, let me know and I'll draw a sketch and post it.

One last thought. I don't mean to be trivial, but....are you using good raw material for melting? Pop cans, aluminum siding, extruded structural shapes...etc are not really good for casting (my opinion). If your using scrap or recycled stuff, junk aluminum engine parts are my 1st choice. In particular, small engine cylinder heads, pistons, rods, housings...etc. If it was cast from aluminum it is probably a good alloy that lends itself to casting.

Well, thats my 2 cents. I hope there is something here that can help. Your project sounds exciting and good luck with it.


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