Not really, as I do it nearly every day. Certain alloys are a little more difficult to cast than others, because they have to be poured at just above the melting point, which makes them rather thick and syrupy, rather than watery. We don’t treat the molds any differently than we do those used for other types of steel, bronze, or aluminum. We even cast “thruster” props for Navy ships using stainless steel, and a considerable number of civilian boat parts out of it as well. The toughest parts of casting stainless steel are getting the mix and the temp right, the machining can also be a bit of a bear as well.
I believe you’re confusing a “chloride environment” - IE, chlorine, bleach- with a “saltwater environment”.
The prop, as I said, is Naval Bronze (or a similar variant.) And I’m quite certain I wasn’t buying Monel or Titanium bolts at the hardware store for ninety cents apiece.
Most of what we used was labelled 303 or 304 Stainless Steel, pretty standard stuff, with some specialized pieces being 316 SS.
Strength wise, the 303/304 bolts were largely rated at Grade 2, with some of the 316 SS ones as good as Grade 5. We could have special-ordered 316 (or similar- stainless anyway) in Grade 8, but at five times the cost (which was already roughly twice that of plain steel.)
Even Grade 2 was sufficient for noncritical bits- for things like the handrails or reels, we just bumped up a size or two; 3/4" instead of 5/8", or 1/4-20 instead of 10-32, and so on. As I said, we used standard steel of the proper grade on the engines- they were protected by the clouds of oil vapors anyway. 
But all the electrical stuff was either a stainless bolt/nut (like the battery teminal clamps) or brass (like on the battery-cutoff switch terminals) and even then slathered with some copper never-seize.
The prop shafts are stainless steel- probably a good alloy, but a close cousin to 316. I have what’s left of a bent one we replaced years ago- I’ve been sawing it up to machine stainless parts from for many years. I haven’t had it metallurgically analyzed, but it looks, cuts, turns, taps and work-hardens just like stainless.
It’s definitely not Titanium, Monel, Inconel, Cupronickel, brass, Naval Bronze, white metal, silver steel, drill rod or cast iron.
How about that. Live and learn - maybe.
Tuckerfan meet andy_fl about “wetted parts” and stainless steel.
Hey, Doc, if you want, I can have a small hunk of that steel run through our spectrometer and give you a definative answer as to what it is. (No charge, BTW.) All I’d need is a piece roughly the size of a plastic bottle cap.
The alloys you mention are pretty much the same ones we pour for the various boat parts, there might be one or two others, I don’t know. I’m more worried about not getting a leg singed off than I am what kind of metal we’re pouring when it comes down to it.
The oxidation layer on iron and plain carbon steel (not stainless) doesn’t “fit” very well on the surface of the metal - the oxide tends to lift off and flake away at an atomic level, allowing oxygen to continue to reach the unreacted metal. In contrast, the crystal dimensions of stainless steel and aluminum are a better “fit” with the oxides, so they stay stuck to the surface to form a protective layer, called a “passivation layer.”
I think that nickel behaves like aluminum and forms a passivation layer (although I’m not certain of that). I believe that gold and platinum do not oxidize at normal atmospheric conditions, although they can be made to form oxides under high temperatures and/or oxygen activities.
(IAAMetallurgist by education, but I haven’t done much metallurgy for the past ten years or so, and I didn’t look up any oxidation potentials for this post - I’m working on memory here).
No I am not confusing anything here, besides bleach does end up us chlorides. Have been long there, designing desalination plants, sea-water cooled heat exchangers, etc. Just because you use an alloy and dont “see” any corrosion does’nt imply its not corroding. All it implies is that you dont “see” any mark of it on the surface - but the material loses its tensile properties - maybe not so important for a bolt or a railing.
Like I said before, stainless steel is vulnerable in chloriDE environments - its more prominent at higher temperatures . You can do a google search on Stainless Steel and Stress Corrosion Cracking or pitting corrosion or crevice corrosion. Here’s a ready cite for you.
I’d just like to add to the discussion that my Naval vessels (DDGs, for anyone who cares) have CRES all over 'em. Read that “corrosion resistant” steel. It’s pretty good, even where it’s sprayed all the time with seawater.
What kind of containers do you use when you are casting steel? Are the molds ceramic? And how do you machine or press steel?
Like the OP, I feel nearly embarrased about how little I understand about working with steel.
I’m not even sure how to ask my question so please bear with me. If I were working with candle wax, I know that I could melt it and pour it into steel molds, because of course wax melts at a lower temperature than does steel. And if I wanted to carve my initials in the resulting candle, again I could use steel because steel is harder than candle wax.
But when I try to think through how you work with steel, it seems to my naive brain that there is some kind of ‘prime mover’ problem when you get to steel. Ok, so you pour the steel into a mold. I’m assuming that whatever material the mold is made out of, it must have a higher melting temperature than steel. Well, ok, but then how do you make the mold? And when I see people machine steel, do they use steel tools, or do the tools have to be made of diamond or something? And if diamond can be used to grind steel, how can it also be the case that diamond cutters use steel chisels?
Could some expert out there please try to divine a sensible question from the muddled ones I just asked and try to shed some light on this?
Ask something simple, whydon’cha.
I’m no expert on casting, but generally, yes, a ceramic is used. Ruger (the gun maker) uses a “lost wax” process, where a wax object is cast or machined, stuck together with rods to form a “tree”, then dipped in some sort of ceramic slurry, like thin clay paste. After repeated dippings, the clay is quite thick, and often built up even further with heavier, coarser pastes.
Then, like “firing” any clay cup or bowl, the tree is put in a kiln (furnace) where the heat melts and burns away the wax, and cures the slurry into true ceramic.
Then, usually while the now-hollow mold is still hot, it’s filled with molten metal, and the whole mess set aside to cool. Once cooled, the clay is chipped off and broken away, then the metal parts- duplicates of the original wax parts- are sawed off the “tree” and readied for further finishing.
As far as machining goes, there are various grades, or alloys, of steel. Mild steel (not much carbon, fairly soft, can’t be heat-treated) carbon steel (obviously, more carbon, somewhat stronger, can be heat-treated and tempered) tool steel (more carbon and other alloys, like nickel or chromium, can be heat-treated, wears better) and other even more exotic alloys.
There’s always something harder; Have a bar of mild steel you need to cut? Use high-speed steel. Have a piece of high-speed steel you need cut? Use carbide or cobalt steel. Have some cobalt you need cut? Then we get into high-end exotics like cubic boron nitride. How do we cut CBN? Typically with abrasives- diamond saws, specialized grinding wheels,etc. What if we need to cut a grinding wheel? Use harder abrasives- for example, Aluminum oxide (the particles that are pressed together into a grinding wheel as you’d see on any shop bench grinder) tends to be softer than silicon carbide.
I could go on, this is the stuff of a hundred textbooks, and even then you’d have just scratched the surface. Suffice to say, we have industrial alloys in a wide range of “hardnesses” up to closely appoaching that of diamond- and we make industrial quantities of that too, for cutting purposes. There is very little these days, that we can’t machine or form in one way or another.
It is the most abundant metal in the Earth’s crust.
Doc pretty much nailed everything as far as casting and machining steel goes, but I’ll fill in a few nitpicky things.
For common metals like steel, aluminum, copper, bronze, etc., there’s four main ways that they’re usually cast:
[ul]
[li]Green Sand Casting: This is probably the oldest method of casting metal. You take lightly moisted sand, shape a pocket into the form you wish the metal to take, and then simply pour the metal into that pocket. When it cools, you simply shake the part free from the sand. Common things cast using this are engine blocks and cast iron cookware.[/li]
[li]Lost Wax Casting: Doc nailed this one pretty much on the head. Our proceedures are slightly different, in that we run the dried molds through a giant autoclave to melt the wax out, instead of burning the wax out. Nearly anything can be cast using this method. Generally you use it when you want a lot of fine detail in the final casting or you want a fairly smooth surface without having to do a lot of machining to clean up the final part. We cast things like propellers, parts for automated chicken gutting machines, and numerous military components. (I’ve handled so many military parts, that if Osama ever gets sent to his final reward, odds are I’ll have made parts of whatever it was that did it.)[/li]
[li]Lost Foam Casting: This is similar to green sand casting and was developed by the Saturn division of GM for casting engine blocks. With this method you take a block of styrofoam which has the final shape that you wish the metal to take. You bury this block in green sand, cut a hole in the sand leading to the foam, and pour the metal in. The high heat of the metal, vaporizes the foam instantly, leaving a pocket in the sand that the metal then occupies.[/li]
[li]Die Casting: If you’ve ever heard of injection molding, this is the same thing, only the material being injected is metal. You have a metal mold (though I think that some ceramics are now being used as well) and into this mold, metal under pressure is injected. Obviously, you either have to have a mold with a melting point that’s higher than the metal that’s being injected into it, or the mold has to be cooled rapidly to prevent it from melting.[/li][/ul]
As for machining, well, the only common things that Doc missed are the varities of EDM. (EDM stands for “Electro Discharge Machining”.) This can be done in two different methods. The first is by using an electrode which shoots a high voltage spark into the metal to erode a pocket into the metal. This is really handy when you need to put a hole in a piece of steel after you’ve hardened it. The second method is called “wire EDM.” This uses a wire as the electrode and lets you cut complicated patterns into metal parts.
There’s also laser cutting and water jet cutting, and probably a couple of others that I missed, but AFAIK, they’re not all that common, but their use is growing.
An excellent source for books on machining and casting (also a few other odd ball subjects) is Lindsay Publications. Great catalog, great service, and the owner of the company would make a great Doper, IMHO. (He can be quite snarky in his comments. )
I’m a bit confused about this. The my primary experience with lightly moistened sand involves building sandcastles at the beach. Considering how tough it is to make sandcastle that doesn’t collapse, much less form a shaped hole in the sand, I don’t see how one could form an engine block shaped pocket in moist sand. And when a wave comes at my sandcastle, it quickly washes it away, so I don’t see why pouring molten metal into the form wouldn’t immediately wipe it away.
What am I missing?
A couple of things. It’s a bit more complicated than I posted. The sand is a very clean fine grain silica sand and has a small amount of fire clay mixed in with it (there’s other possible combinations of ingredients, but they’re used for really large scale industrial operations and I’ve no experience with them, so I can’t say much about them), and depending upon how large the casting is, the sand might be moistened with a binder other than water. (Again, the only experience I have with green sand casting is as a hobbiest, and not on a large, industrial scale.) When you’ve got everything mixed correctly (sand, fire clay, water or other binding agent), the sand will clump in your hand, but can still be broken apart fairly easily.
Also, the metal is generally not dumped straight into the form, but poured into a sprue, which is a channel cut into the sand, the metal will run through the sprue, and then into the mold. You also don’t dump the metal into the form as fast as you possibly can, it has to be poured in at a certain rate. This prevents the metal from splashing about and burning your leg off, also, it saves on metal, since any metal which doesn’t make it into the form is wasted.
The mixing of the sand and the other ingredients is a bit more art than science. You have to get it just right if you want the casting to come out correctly. Too much water, and when the metal hits the sand, the water will flash to steam and cause an explosion (If you’re the guy holding the pot of molten metal, you’re screwed at this point, because the metal’s going to come right at you. If you’re not the guy holding the pot, you’ll get to find out exactly how fast you can run. I’m not kidding, I’ve seen a pot of molten steel “burp” when it had a load of wet steel shoveled into it. If you don’t run, you will get burned.) too little water, and the form falls apart, no matter how gently you pour the metal in.
Playing with molten metal in any form is not something to be careless with. I work with people who’ve done it for a living for over a decade in some cases, and nobody is reckless with the stuff. Even if no one got burned, you can bet that the joker would have his ass hauled outside and completely stomped by everyone around. Paradoxically enough, I feel safer pouring steel than I have in any other job, because I know that if there’s a problem, there’s not going to be any arguments with anyone about it. The time I got burned (it happens to everyone, no matter how careful you are), I shouted for someone to take over for me, immediately, one of my coworkers grabbed my end of the shank, I moved out of the way, stripped off my protective gear, dug the hunks of burnt flesh and metal out of my back, suited back up and then took back over for my coworker. The only question I was asked during this was, “You gonna be able to do this?” Management afterwards only asked if I needed to go to the hospital for treatment, they didn’t try to pin the blame for what happened on me, or imply that someone was at fault. They knew that if I had gotten hurt, that everyone had done everything they could do to prevent it from happening.
If you want a good idea of what the inside of a foundry looks like check out this site. It’s not my employer, but it’s nearly an identical set up.
I’m glad you brought that up, [nit] but I’ll only agree if you’re talking about the Earth’s crust. Mantle and core are different beasts.[/nit]
There are different alloys that are all called “stainless steel”. Some are very “impervious” others are harder, etc. Thus, perhaps stainless steel for naval usage is more impervious than other alloys. I know that you’ll sometimes see cheap “stainless flatwear” rust.
There are also different bronze alloys- again, some more resistant than others. That’s why the call the bronze used in props “naval bronze”.