Casting stainless

The only process I know of for casting stainless steel is ceramic shell casting. Not something easily done at home.

Hi Ernie, how's the hand?

That sounds like just exactly what I want, thanks.

It doesn't seem to be that hard to do at home though, just needs a suitable furnace*, and something to make the ceramic shells** out of.

Am I missing something?

melting stainless requires a controlled atmosphere furnace.

A lot of handgun frames are ceramic shell castings.

While you are at it may I suggest making 12" adjustable wrenches. Every boat would want one.

What's the difference between ceramic shell casting and investment casting?

What I had in mind was making a wax, spruing it, and adding a wax crucible on top. Dipping the whole in slurry, then refractory flour/sand, repeating. Dry shell. Heat shell to melt out wax, heat shell in air, red hot, till strong and clean. Cool a bit.

Add broken metal to the crucible part, put the shell + metal in vacuum furnace, heat the whole thing past the metal melting point. When hot enough, pressurise the crucible top with argon (the metal will have melted into the mould by this time, and the argon pressure will act on the molten surface, which should be halfway up the sprue at this point, pressing the molten metal into any remaining crevices of the mould). Switch the furnace off, and cool.

This is a bit unlike the normal investment casting process, in that all the metal stays molten inside the shell rather than forming a solid skin on the outside as soon as it is cast (the shell usually being cooler than the metal in investment casting, eg shell 1100 C, metal 1500 C, at the moment of casting). In this case both the shell and the metal would be at ~1500 C, and the metal could flow slowly into place rather than a fast casting.

Anyone forsee any difficult problems?

I have vacuum, and argon, and 240 Volts as I am in the UK. I can do the waxes myself, I hope and expect.

As I see it the two areas of uncertainty are the investment/ceramic shell material, and the furnace (I am thinking of modifying a {pair of} microwave oven{s}, or an induction ring from an electric kitchen hob, or perhaps both. I can't afford the £1,000's+ for a ready-made 1500C electric furnace). Any ideas, comments?

The reason why usual sites are about casting aluminum (and not stainless steel) is because you need an induction furnace to melt the stainless and few if any home foundries would have that type of equipment.

What type of furnace do you have (pounds size, kW rating, high medium frequency, etc.). What type of stainless steel do you intend to melt?

Your crucible supplier would be able to help you select the right type crucible. The choices are usually Magnesite, Spinel, Alumina, Zircon and Silica.

I always had best results with Silica crucibles when melting 316S stainless. We were casting into shell molds, about 75-100 pound pour weight.

Mark

I don't have a furnace for metal casting. I will buy one, or make one from a microwave oven or perhaps an induction cooker. Any advice?

The casting (singular, I want to cast one at a time) will weigh at most a hundred and fifty grams/ 6 ounces. It will have lots of undercuts, but won't be very large, say 60mm/ 2 1/2 inches in any dimension maximum.

304/316. It's for the impellors and casing of a small liquid oxygen/kerosene turbopump for model rocketry.

Perhaps 321 for non-rotating parts of the turbine, and inconel 718 for the turbine wheel. I'll probably buy the turbine wheel ready-made though.

About 1450 C max melting point, 1500 C/ 2700 F max casting temperature.

Any idea what the shells were made of? I'm thinking alumina with a silica sol binder, any comments? Do I need zirconia?

Thanks,

Ceramic Shell requires a bigger investment. :)

[And I don't think regular investment will take the temp you need]

The wax expands as it heats, before it melts and frequenlty [In my limited experience] results in cracks in the investment. The metal will exert a fair amount of pressure towards the bottom of the shell.

Your metal and the silica will be in contact for a relatively long time, I would worry about possible reactions forming a skin.

jk

Peter,

You should look into the Jewelry industry. Investment (or "Lost-Wax") casting is used by jewelers to make rings, etc. mostly in Silver and Gold, but they also make them in Platinum (which has a higher melting point than Stainless). They use the flask method (which works well for small pieces) with centrifugal or vacuum casting machines. Here's just one of many sites to tell you a bit about this:

There are companies dedicated to selling investment material, injectable wax, casting machines, induction furnaces, etc. for small investment castings by jewelers. There are casting machines and furnaces dedicated to do Platinum casting (which can be adapted to Stainless). Here are a few of the main players:

Hope this helps.

Regards, Alex P.

Check into what goes on in the dental laboratory industry. The alloys that go into many partial denture castings are in the family known as stellites. They are cast day in and day out in dental laboratories. Mostly, they melt the alloys by induction but an oxyacetylene torch will do well in a pinch.

bob g.

James H. wrote: