You can melt metal right in the furnace (I do it a lot for large pieces), but once it melts it drips to the bottom, and unless you have a specially designed furnace, this is pretty useless. (In my large furnace, it usually goes down and out the drain hole as intended.) So you need a container to hold the metal - a crucible - and the tools to use it.
Pictured at left is the old style crucible that I used for my first few melts. It consists of a soup can (actually Mandarin Oranges but who cares ;) with some sheetmetal wrapped around it and riveted on, plus a handle on top, and a hole for a tilting hook at the bottom.
A standard crucible style for the backyard metalcaster is a 3 or 4" dia. steel pipe nipple with an end cap screwed on tightly for the bottom. This is very heavy and slow to heat, so if there is access to a welder, the other customary crucible type can be had - a 4" dia. schedule 40 steel pipe with a 1/4" thick plate welded to the bottom. Naturally, I have access to neither (g), so I use tin cans. Being made of thin steel, they only last a melt or two (whereas the heavier crucibles last practically forever), but with Dad cooking up a storm in the kitchen, I have no shortage of suitable cans.
The best crucible, when it comes to keeping the alloy constant (aluminum dissolves iron, both metallic and oxidized (scale); the latter can easily flake off and fall into the melt, be dissolved, and increase the iron content) is one made from ceramic. This is usually a clay-based material, with graphite added for heat conductivity. Crucibles are also made of graphite-bonded silicon carbide (SiC).. don't ask me how they manage to do that! A ceramic crucible won't be dissolved by the metal inside (except for iron alloys, which dissolve carbon from the surface of either type, except clay-graphite which leaves a layer of graphite-free clay).
First required piece of equipment is something to move the crucible. I use pliers (see above) for my cans, but ceramic types require special lifting tongs to apply an even lifting force - lifting with pliers from around the rim will most likely crack the crucible. Photo at left is what I made, two bent strips of iron brazed to some EMT conduit.
Second piece, which is almost required (read: if you want to do good work, you need it) is a dross skimmer, to pull up the dirt and grime that gets in the melt. Right now, my skimmer is just a coat hanger, coiled flat for the active part, and the rest is bent into a handle. Skimming is very easy, the molten metal flows out the gaps while the dross sticks.
Made these in 2004 for my new crucible furnace. Actually, I made these for my #6 SiC crucible and designed the furnace to fit around the tongs! The double jointed setup is very nice to use. These are HRS brazed with brass filler.
Made this today (3-14-2005) to degas some really messed up metal. It's just a 5/16" dia. rod with an inch of EMT conduit welded onto the end. The diameters are, shall we say, a bit different, so there's about one 1/8" welding rod caked on there.
To use, you put a quarter teaspoon of pool chlorine (I have some 65% calcium hypochlorite "Pool Shock") in a piece of tin foil, roll it up tight and tuck it in the end. When the hypochlorite passes 350°F or so, it decomposes, releasing chlorine gas, which bubbles through the metal, reacting with any hydrogen present to form hydrogen chloride (HCl) and any magnesium in the alloy (forming magnesium chloride, molten at aluminum temperatures). You need to hold the tool at the bottom of the melt, so the bubbles break up and so they bubble through the full height of the melt.
A crucible allows you to hold the molten metal - but once it's all melted, then what? You have to pour it off somewhere. If I'm melting scrap, I'll usually cast ingots first; this cleans the metal a bit, making for better castings, plus the pride in having a bigger heap of bright ingots to stare at. ;) Pictured at left is the current ingot mold, made from a strip of 3 1/2" wide 22ga. sheet steel bent in a zig-zag, with two flat strips clamped to the side. Since it gets as hot as the metal coming in, the clamp is protected from the mold with two strips of wood, which just char in use.
See molding section for info on casting metal into something other than ingots...
2004-2005: FYI, I mostly use an old, rusty angle iron for ingots. I stand it up between two other pieces and pour; holds about 6 pounds, which is enough for anything I've got, besides the large reverb., which can hold the extra until the mold is ready for use again.
Dad said the basement HAS TO BE CLEANED UP. (...) Then, he said I can't use the basement unless I clean it up.....so I'm moving my casting stuff to these shelves. I know, stacking, order, alignment, it's an ugly, terrifying sight, but I don't have much choice. :^)
Well anyway, as long as you're here I'll show you around.
The green table on the left is going to be the molding bench, it's way too damn rough right now so I'll have to put some plywood on it before I can use it for molding. Under it is my sand in the two pails.
Behind the bench (behind the riddle and under the shelves) are two white pails, one is for spare wood ash (that I usually use for insulation in refractory), the other is sand for lost-foam casting. To the right, under the shelves are two more pails, these have a brand-new old item in them: I broke up the 10' of well-used (*cough cough*) cast iron sewer pipe (which was "hiding", snaked behind the shelves) with a sledge - so I have about 80lbs. of quality cast iron scrap ready for melting. Behind these you can barely see a basket, this (and another pail) are holding my steel scrap.
On the far right of the bottom shelf, the rightmost milk jug - this has the scrap lead that came from the joints in the sewage pipe. I'll melt that into neat ingots soon... Proceeding to the left, I have a jug of maybe 5lbs. of zinc ingots and scrap (pennies ;). Left of that are two jugs (soon to be three or four) of melted popcan aluminum in varying states of cleanliness (a lot of the raw stuff has slag still stuck in it). The next row is generic scrap, mixed aluminum. The single jug, from this angle hiding behind the shelf support, is engine casing alloy, it casts real nice and drills almost like butter. To the left of that is my copper alloy: wire, brass and bronze parts, older pennies, whatever. I figure I'll melt the whole thing together, then add some zinc to the pot and make a nice yellow brass. The small bucket at the end has the rust and crap (ahem) that fell off the iron pipe as I was busting it up. I'm going to grind it up fine and use it for thermite. ;->>
On the next shelf up, I keep some molding supplies - flasks and molding tools, while on the other side I have the variac and blower, plus the minifurnace/oil burner and the crucible and tongs behind there. On the 2nd-from-the-top shelf, right to left, I have a box of charcoal - Real Charcoal - that I've pulled from the furnace to save for other uses; the ingot mold (see above), spare milk jugs (for ingots, etc.), molding patterns, and the basket I fill with wood chunks for the big furnace. On the very top shelf I keep spare stock (rod, angle, etc.) and other odds and ends.