Metal casting is an inherently difficult and daunting activity to get into, because of the high temperatures involved, the dangers posed by the molten metals, and the special construction needed for molds to withstand said high temperatures. Here I present a way to experiment with casting using a relatively inexpensive and accessible alloy which can be compounded using common tools, in one's kitchen. The alloy, commonly known as 'Rose Metal' has a melting point low enough that it can be melted safely and cast into molds of simple construction.
Standard disclaimer: This project and others available on this site uses heat, tools, chemicals, and open flames. You are responsible for taking all applicable safety precautions, and applying common sense. Since I have no control over how you do things in your own shop, or what precautions you choose to use or not use, and I'm not there to hold your hand, it's not my fault if you hurt yourself.
The constituents of Rose Metal are Bismuth, Lead, and Tin. Bismuth is available as lead free casting sinkers or lead free shotgun shot from sporting supplies, or can be bought from metallurgy suppliers. Lead is available as casting sinkers, decoy weights for shotgunners, or bullet casting supplies. Tin is available as a pewterer's supply, or as plumber's lead free solder. Here I have non-lead fishing sinkers, a section of heavy lead wire from a decoy weight, and a roll of tin wire intended for use as lead free solder.
Here's a closeup of the bismuth fishing sinkers. They're covered in a shrunk-on plastic cover to protect them, as pure bismuth is a brittle, fragile metal. This covering is easy to peel off with a razor blade, scissors blade, or such. I conveniently took a chunk out of my fingertip at this point, but it's not a PROJECT unless you leave some blood on it...
Here are the sinkers without their covering. The next step in compounding an alloy is to determine the weight of the primary constituent, and for that we'll need a scale.
This is an inexpensive reloader's scale. I have a couple of these kicking around, but I also could have constructed one, or borrowed one. This particular scale weighs in 'grains', and is accurate to one tenth of a grain, or about 6 milligrams. I'll do my calculations in grains, and as long as I do ALL my weights in grains, everything will come out right. If I was constructing a balance, such as a simple pan balance, I could use any convenient and consistant system of units. I'm especially fond of the weight of a penny, not to be confused with 'pennyweight'. As long as the pennies used for scale weights are new, unworn, and uncorroded, they're close enough to serve as scale weights.
Here's the balance sheet where I recorded the weights of the individual sinkers. It's also the printout from a file where I keep various alloy formulas. Rose metal is second from the bottom, and its IDEAL formula is the bottom entry. Adding the weights of the individual sinkers, we find that there are 1705.2 grains of bismuth. We divide that by the proportion of bismuth in the finished alloy, in this case .5253, to get the total weight of the finished ingot, in this case 3246.1 grains. We multiply the weight of the finished ingot by the proportions of the other ingredients to get the weights of them that will be needed. In this case, the weight of lead is 3246.1 grains multiplied by .3255 to give 1056.6 grains, and the weight of tin is 3246.1 grains multiplied by .1492 to give 484.3 grains. As a check of the calculation, we add the weights of the constituents together and find that 1705.2 plus 1056.6 plus 484.3 is 3246.1, the correct total weight. The picture shows the lead and tin already weighed out, by setting the scale to the desired weight and then cutting sections of wire into the balance pan until the scale balances.
After getting the proper amount of each constituent, it's neccesary to melt them together. The melting dish shown here is a failed attempt to raise a hemisphere of steel for an air tank. The board its sitting on is a piece of ceramic tile I use for soldering. The heat source is a hobby torch. The one shown in the picture is a bit underpowered for the job, as it makes a pinpoint flame, so I used a plumber's blowtorch instead. The metals only take a moment to melt. One anomaly from normal metal casting is that the individual components of this alloy melt at about 400 degrees Celsius. The finished alloy melts at less than 100 degrees Celsius. Thus once the metals are melted together, they're WAY above their normal melting point, and the alloy takes a long time to solidify.
Here I'm using a scrap of steel rod to skim the oxides off of the molten metal. You can see the larger torch too. Lead and tin both begin to oxidize at a relatively low temperature, and this leaves some powdery yellow residue floating on the melt. I like to skim this off as the metal cools, leaving a nicer surface.
Behold the shine of the skimmed metal. It's cooled to below where it oxidizes, but it's still molten. About five minutes later, this solidified, and I turned the bowl over to dump it out. At this point, the metal is too hot to handle comfortably, but not hot enough to make the nasty burns that molten iron would.
Here's my high-tech proof of concept melting set up. A pot of water, the ingot of alloy, and a dixie cup to cast into. This isn't how one would use the metal when making an actual cast, but it makes a cool demo, and I've found that people think the pool of metal in water is awfully cool.
Here's a nice shot of a pool of molten alloy underneath some simmering water. I use a teflon pan because the alloy doesn't stick to it.
Here's the finished cast. I dumped out most of the boiling water, then poured the remaining metal and water into the dixie cup, where it solidified. It was nowhere near hot enough to melt the cup, which can be used for coffee. After a few minutes, I poured the water off, and shredded the cup to get the metal out of the bottom.
Casting from water leads to a lot of defects in the casting, so while it makes a cool demo, if you're actually hoping to make a useful part, you'll want to heat the metal without water. Small quantities can be melted in a steel spoon, over a stove burner. A butane lighter is enough flame to melt this stuff too. Molds can be paper mache', plastic, plaster, or just about anything that could be boiled without melting.
Other uses of fusible alloys:
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