Here is a little story about how easy it can be to cast parts from an aluminum alloy. Particularly – at home.

I’m going to tell you about the method, which I use when casting aluminum parts and, of course, I’ll give you a description of my muffle mini-furnace and its equipment. I should note that I work with a high-power electric heating equipment and molten alloy. Both can cause serious burns, so please, follow safety requirements. Avoid electric shock when using the furnace. If you use your head and be a good boy, you'll be all right)

I can say it was an utterly makeshift contraption. Financially, it has cost me about $10. Well, the whole thing started when I had to test-cast several aluminum parts – tracks for a tank, which I was designing. I had tried to craft something resembling those tracks using different methods, but one day I realized I could not make one without casting. Both Runet and, particularly, the RC design website’s tank construction topic bear tons of information, except they tout expensive and bulky solutions. For instance, there was a description of a furnace and a handful of methods of heating aluminum to the fusioning point (700°C), but none of them was good for home use, except a muffle furnace. Second, I'd have to have a mold cast, and casting one, I found out, would be a hooo-ma-gawd investment. I did solve the issue in my own way. This is how I did it…

Miniature muffle furnace.
First I thought I was going to have to melt only a tiny amount of aluminum (at most 150-200 gr), so I studied tons of articles and forum posts, picked out a template and made it unabashedly simple. The furnace was all makeshift. I also bought fechral (ferrum-chromium-aluminum) wire at an electrical shop.

I also brought 4 fire-clay bricks (I had repeatedly heard that exposure to heat caused usual bricks to deteriorate quickly), which I cut apart with an angle grinder using a diamond blade. I cut out 5 thin tiles with angled edges and fixed them as side walls of the furnace, plus two more ones as the bottom and a removable lid. I cut grooves in the outer side of each wall tile for the wire and, even though I reckoned that the total length of the grooves would leave me a bit of excess wire, it proved exactly to a T. The grooves were to prevent the wire from short-circuiting. Heated fechral wire grows loose and expands, and it will definitely sag if you simply wind it around the furnace without cutting the grooves.

How long a piece of fechral wire do you need? Moot question. It took me quite a while to figure out how to calculate power, plus the wire I had purchased turned out to be mismatched, and it is better to buy 0,6-0,8 gauge wire. I assumed that power would not exceed 2kW. Using formulas and Ohm’s law (quite superlatively and with little reference to factors like resistance change due to heating – it was less than a spaceship that I was building!), I concluded that the resistance level had to be about 30 Ohm to provide 1,5-2kW power. I calculated the required wire length based on resistance level, which I measured using a portable multimeter, and, I reckoned, it had to be 3-4 meters long. I made a 2-minute test-launch and, though I’m not sure whether or not I really hit the 2kW mark, there was not a single fuse blowing in the extension piece that I was using. So, power was all right.

I drilled two holes in the bottom of an old enamel pot for the power cord, which I used as a case. The glow wire is connected to the mains cords via two 2mm copper wires isolated by aid of two obsolete thermoset ceramic fuse plug sockets.

I filled the pot in the following order: I perched the furnace itself onto two pieces of brick placed at the bottom of the pot and laid the cords in such a way as to keep them safely away from each other, from the wall and from the furnace. Then I filled the space between the furnace and the wall with fractured brick, placed quadrangular brick plates to isolate the fechral wire, and topped the plates with evenly cut brick cubes. Once again, I used what I had close at hand, because I was too busy to look for a basalt slab, chamotte clay (although there were construction material stores in the area, where I could have purchased clay in 5kg packages, as well as mortar, etc.); besides, brick shards in the pot could perform the same insulator function in brief operations. After two hours of functioning the upper part of the pot will get too hot to touch, but you can easily hold in by the bottom.

To make a lid handle, I drilled the lid brick plate (at a low speed and using water) and attached an axis to it.

I made a melting pot out of a 57mm steel pipe; then I heated a portion of the rim up with a gas cutter and pulled it off to make a nozzle, and then I welded the bottom. The handle won’t slip should the melting pot topple over.

I used old garage junk as raw materials – a few tap nuts, some car engine parts and a huge gauge of some measurement device. It should be noted that it takes a special kind of alloy to cast an item, so please, be careful when choosing an alloy type. There are tons of detailed information online, and I can brief you on where you can extract the alloy: most car engine parts (carburettors, boxes, etc.), aluminum wheels, pump bodies, etc. Well, take a look at the part and find out how it was manufactured and pay attention to seams, if any. If it was really cast, it will be ok. Check it with a sledgehammer. If it breaks easily and fracture face looks rough and scratchy, it is duralumin. I should also note that aluminum wire is not good, because it has poor fluidity and it won’t fill a cast properly.

I cast my parts using a plaster mold. Using pure plaster casts is not always advisable because they never dry completely, not even after lengthy drying. They say, it is better to use mixes containing sand, etc. Personally, I’m quite satisfied with pure plaster. I buy casts at Lerua Merlen (no ad work meant!) at about $2/5kg. I should note that plaster is quite reactive: the thicker the mix, the sooner it hardens. It starts hardening in 2 minutes, and a chemical reaction causes it to heat up as it hardens. I use a screw gun and a head of a kitchen machine to mix it (my wife kicked up an Armageddon-class temper tantrum party when she found out I had stolen part of her Moulinex device)))).

After about 30 minutes, the melting pot got cherry red hot, and the pieces of aluminum junk began to fuse together. I had no home thermometer to measure how hot it got, and the heat sensor, which came with the multimeter, began to burn when the temperature reached 700°C. As far as I know from the Internet, the cherry red signifies a temperature of about 1000°C.

I’ll focus on casting molds and the casting process itself in my next post. In brief, it is nothing less than gas molding in a very simplified fashion. What I do is cast a mold for a track, fix a polystyrene input tube and leave it to dry for 3-5 days and put it in the oven for a while. Before pouring in the metal, heat the mold up to 300°C. The molted metal burns out the styrene template and fills in the space inside the mold. Cut off the excess plaster.

To ensure safety, place the furnace on a tray and check your ventilation systems, because the oils and paint on the aluminum scrap being molted will smell pretty bad. The furnace and fire-proof materials should be arranged in the following order: place a piece of gypsum plasterboard on the floor (to minimize damage from spilled aluminum); shield the walls around your workplace using this material. Put a baking tray on it, then, a metal tray for hot dishes, two pieces of brick and the furnace itself. Fill a bucket with water in case you spill molten aluminum (do not pour the water into the furnace!) and place it close at hand. Make sure you have a fire extinguisher. I’m always there to control your work (handling the furnace, heating and cooling). Better safe than sorry!

In summer, my little furnace will move happily to my rural residence, thank God it is less than a heavyweight object. No more campfires or blowtorches))). Here are a few photos of tracks from my first lot (so far I’ve cast almost a hundred). My SU 101 shall be built!

This is the translated version. You can read the original Russian article here.