Smelting – 1st Run

It looks like one of the parts that will be needed for the mower will be a couple of spacers for the rear wheels. The idea is to fit new wheels to the 17mm axle the only issue being that the ID of the new wheel is much larger at approx 25mm.

A search on Trademe didn’t produce any results for an appropriately sized section of aluminum billet so after some though I figured why not cast some. A bit of research on the subject confirmed that on a small-scale it is a relatively simple affair, make a really hot fire, chuck some aluminum bits in a tin can, wait until it’s liquid and then pour the molten result into some form of mold.

A week of ferocious can collecting ensued (and is still ongoing) along with a quick whip around the house looking for any no longer used aluminum things.

On Saturday Matt, Bill and I fired the lot up. An old bouncy castle blower connected to a length of air conditioning ducting provided the air supply whilst a bag of charcoal in a brazier was used as fuel and container. A couple of crucibles (old fruit salad cans) were heated up initially to burn off the label and any rubbish inside before the scrap aluminum was added to the larger of the two cans.

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The results were quite promising, the scrap aluminum heated and melted quickly and so a couple of drinks cans were added to the mix. These didn’t go quite as well however and instead of melting they just oxidized creating a lot of slag that then needed to be scraped off.

Aside from that the pouring went well, A muffin tray formed a mold with 4 and a half aluminum muffins being the result.

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We decided that there must be a better way of melting everything down that addressed the major issues encountered;

  1. The fuel burned through too quickly and released a lot of ash that then landed in the molten metal
  2. The size of the tin made it hard to effectively scrape off the slag
  3. The drinks cans oxidized as opposed to melting

On Sunday we reconvened for a second attempt after refining the technique and equipment. Firstly the charcoal was swapped initially for cedar and then once there was enough heat in the fire, for coal. The can was swapped for a larger metal pot which we figured would allow us to more easily remove the slag and also dunk crushed cans under the surface so that they would melt and not oxidize.

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The larger size of the pot meant that more fuel was needed to get the aluminum to melting temperature but once it did it was a lot more stable and less affected by the addition of new material. Overall the amount of fuel used to produce each muffin was about the same but the lower cost of coal made it slightly more cost effective. End result for the day, 11 muffins and one uncast chunk of solid aluminum for next time (we ran out of fuel before we could get it to a decently flowing state)

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Next step looks like it will involve the manufacture of some form of furnace. It looks like you can mix cement, crushed kitty litter and something called Perlite (apparently available from gardening centers) together and then form it inside a metal cylinder to make a rudimentary furnace (if anyone has an old gas bottle that has expired / not passed re-certification then I can get rid of it for you?). You then have the option of either using charcoal / coal or propane to heat the furnace which should work a lot better due to the greater amount of insulation. Hopefully this should be the only step up that is needed to turn what is really a once off procedure (due to the inefficiency) into something that is feasible long-term. With that will also come the final stage of recasting the aluminum into the final shape.