I'm trying to do some casting using 304 Stainless Steel. Has anyone here used an oxy-acetylene torch (or any other type of torch) to melt Stainless Steel? If so, can you tell me how long it would usually take to melt about half a pound (250 grams) of Stainless using this torch.
I hate to toss cold water on your plan, but I have serious doubts about you achieving success. You have a high enough temperature to melt stainless use an AO torch, of that there's no doubt, but it may be hard to contain enough of it to do you any good. I've melted platinum with an AO torch. By the time you've melted a troy ounce, it gets difficult to keep it all molten. Granted, it melts at a higher temperature, but not enough to make a significant difference. The other problem you're likely to encounter is destroying the alloy and creating gasses in the heat. It's safe to say you'd have some serious oxidation with which you'd have to contend. In general, I'd say the idea isn't sound, but I'd be interested in hearing from anyone that has had success. Such materials are generally melted by induction, where there is no direct contact of the molten metal with a flame.
You can melt and weld stainless steel with an oxy-acet torch, but it has risks.
To achieve a molten puddle you have to use a carburizing flame. The carbon feather should be about 3-4 times as long as the inner cone.
The problem with this is that is imparts carbon into the stainless steel, which can bond with the chromium to form chromium carbides, which cause cracking in stainless steel welds and can also be a seed for corrosion.
I don't know about stainless Harold, but at least 50 years ago I melted platinum (well, 10% irridium - 90% platinum alloy) in open crucibles using a torch running oxygen/city gas, while centrifugally casting stuff in "lost wax" molds at my dad's jewelry manufacturing shop. The crucibles had a nipple on one side fitting into the sprue (gate) hole in the mold. The metal rose up the side of the crucible and flowed into the mold when the casting machine spun.
The platinum melted at a white heat and I had to wear very dark glasses for that job. Can't remember the total weight of the "shots", but we usually "treed up" quite a few pieces of jewelry off one sprue so I'm pretty sure I was melting well over an ounce each time.
I remember the molds were kept quite hot in an furnace until just before the casting operation, to reduce chilling of the molten metal. I don't recall the specific furnace temperature, but IIRC it was just short of a red heat.
The molten platinum was so hot it changed the "plaster" molds into a glassy material about a millimeter thick coating every surface of the cast pieces. That didn't happen when we were casting gold alloys.
We had to soak the pieces in hydroflouric acid (nasty stuff) for several hours to eat away the glassified stuff. The acid didn't do anything to platinum.
To be brutally honest, I, too, used city (or "natural") gas when I melted platinum. In my case, I was melting sponge from the refining process, in order to end up with a button of pure platinum. The recommended fuel when doing so is hydrogen, but I was not so equipped.
Rarely did I encounter anyone that did their own platinum casting when I refined, and my list of customers numbered over 60. Quite a few of them worked platinum, but didn't cast it. As I recall, there is a vertical centrifuge used in place of a horizontal one for casting platinum.. Why, I don't know.
Not only are the molds kept hot, but the recommended investment used is different from that used for gold and silver alloys.
Makes me wonder if, perhaps, you may have been using the gold investment, although I never witnessed any of the castings as they came from the molds when the recommended investment is used. . Could be that the proper investment does that as well. Dunno.
I, too, had to pickle my button (which I still have after all those years) even though it was melted in the proper melting dish. The problem with platinum is that it melts at the same, or very near the same temperature as silica, which is used to make the dishes. It's difficult to melt the platinum and not get some of the silica involved.
Yep, sort of a nice walk down memory lane for me, too. I sold the refining business more than ten years ago. Don't miss it!