#semitutorial

[talopeiros]

Learning to Smelt - 2

Part 2! The main goal of my second smelt was to A: Figure out how the sand casting worked B: Try mixing copper and aluminium together to make Aluminium bronze! TLDR: Here was how it went down:

Now into the details! The whole reason I got into smelting was to cast metal into cool items and the like, and to do that I needed a casting flask and some casting sand. All a casting flask is is a wooden or metal box that comes in two sections that you can pack sand and your design into. You want to be able to clasp the box shut so that the heat and pressure of the liquid metal doesn't cause it to pop off. Part of the reason the box in the vid burst into flames at the mid point is because we only clamped down one side of the box, thinking it would be enough (IT WASN'T) For the casting sand we made a mix of bentonyte (bentonite?) clay and yellow bricklayers sand in a volume ratio of 2:8. A lot of other casting vids and forums suggest a similar combination. Bentonyte clay is super fine so use a mask when handling it. With the sand part, you can't use regular sand since the grain shape of that does not lock together too well and will fall out of the vessel really easily (trust me I tried and it was impossible to hold anything in it). Once it's been mixed, you then need to put in 2 or 4 stroke motor oil into it and mix it thoroughly. Don't really have any specific measurements/amounts but what you're going for is to use a little oil as possible for it to be "wet" all throughout. Best way to test is to mix in a bit of oil, clasp a chunk of the sand mix in your hand and, if it can hold its shape, you're good. otherwise, MOAR OYLE

Now a quick heads up, the sand mix we used didn't work so well. best volume mix of sand-clay we used (which I'll go into a bit in the next post) was 6 sand for 4 clay.

Once you have your template, sand and flask, you start loading up the sand into the flask, and packing it in as tightly as possible. If it's not, then there's a chance that some of the sand could fall into the gaps and cause the design to be a bit scuffed.

Once you get to the halfway point of your flask (i.e. 1 of the two sections, the second section should not be on top yet) you press your design into the sand and keep it in there. Once you're satisfied it's evenly at the halfway point, get some talcolm powder or some other separating powder and coat your design/exposed sand in it, using a brush to spread it evenly (YOU NEED TO DO THIS IF YOU DON'T WHEN YOU TRY AND REMOVE THE DESIGN IT WILL NOT SPLIT AT THE HALFWAY POINT EVENLY)

After that, lock your top half on (with the design still in there) and start filling in the sand and really packing it in there as best you can. Once you're done you simply separate the 2 halves and voila! You have your negative space for the metal to FLOW LIKE FINE WINE. (Also sorry I didn't have many pictures in my second smelt, probs should've taken more photos over this part) Of course for it to flow (like fine wine) you need to then carve channels into the sand so you can pour it in in the first place. You NEED to take special care when carving because, even if the sand is packed in tightly, too much force may dislodge the whole thing. You'll need either a drill or a sharpened section of pipe to allow you to make a hole in the top piece for the fluid to flow. Make sure it's large enough for the metal to pour. You also need to make one (or more) vent holes. These holes you aren't pouring down there but they need to be there to make sure there's a place for the gases to vent out. Probably a sharp piece of wire coathanger would be best for these (and of course make sure they connect to your design.

Speaking of your design, you never want to pour directly onto it! Make sure your pouring hole if off to the side a bit with a channel that leads into the main design. This is mainly so you don't damage if from the inital collision of the liquid metal onto the sand.

In the end, you should have something that looks like this! (Hopefully better than it though since again, this one did NOT go according to plan)

There were a couple of reasons this one didn't go well.

The sand composition. 2 Clay for 8 sand was not a good ratio, it needed more clay

More talcom powder as a separation layer. You can't see it but that middle layer was very uneven since some parts of the top layer fused to the bottom layer and it was a whole thing)

The end result of the above pour was this! Another attempt at the channel emblem:

Yeah not too good, looks like really bad aluminium bronze. Plus there are a few holes in it, where I'm guessing the mold began to break down while the sand was burning.

Another reason this one didn't work too well! We used almost exactly the amount we needed! Because we didn't put too much in the crucible, I believe that too many impurities got poured out with the molten metal which caused it to look like a mess. Still, not too shabby! And I can certainly say the next one went a lot more smoothly too! On a side note, make sure if you want to do this that you don't have a crazy uncle nearby. After we had poured out the aluminium bronze, he wanted to "take advantage" of the hot crucible/smelter and put some scrap brass he had into it. Certainly sounds like a good idea if you like efficiency, but of course mixing metals you don't want to mix is a very bad idea. When poured, the brass ended up looking really bad since it was mixed with the leftover aluminium bronze already in the crucible and also I could not use the bronze crucible again until I filed out all the traces of brass I could find. More to come!