The Foundry: Molding Sand

Let's see what we got in the trailer today... Oh it looks like we're making some molding sand for the foundry! Now that we got the furnace working at a decent level, it's time for some real casting action!

Details on the trailer now available!

For over a week I was compulsively checking the free section on Craigslist hoping for a free bathtub which I was going to store the sand in, but the Scrap Alchemists had something better in mind. Instead of letting me have a bathtub, they intentionally withheld all free bathtubs in the area for those two weeks until I could find this: the turtle sandbox. I know this for a fact because as soon as I got the sandbox, free bathtubs started appearing all over the place. With that notion, I decided that bathtub dodging was very necessary. Not in a gypsy sort of way. Actually, yes.
Anyways, we gave the turtle a lift by attaching some trashpicked castors onto a pallet. There were a few small holes in the bottom of the sandbox, but I just put duct tape over them.

The internet couldn't give me a straight answer as to the formula for green sand, so I just took the average of all the suggestions. I used 100 pounds of silica sand and 10 pounds of ~~Belafonte~~ bentonite clay (not pictured). When I went to the ceramics supply store to get the clay, from their website, I thought the price was going to be >$1/lb, but that turned out to be the price for one pound only. If you bought more than one pound, it was 17¢/lb. At this, I decided to buy 35 pounds. The sand was from a building supply place which claimed that 60 grit was the finest they had, so I decided to take a chance even though all the unreliable sand formulas I read said use 100 or something. At that point I really didn't care because the sand was so much less expensive compared to the 5 bags of refractory cement I needed to build the furnace, so I figured it was not really worth worrying about. The bag of sand had a warning label saying something about inhalation hazard and not allowed for indoor blasting. For some reason I misinterpreted it as "THIS IS NOT A MATTRESS".

For my first mold, I decided to try the Runescape ingot again. In the picture is a sieve fashioned out of part of an oil jug with window screen stapled on it. I found a spent fire extinguisher on the side of the road. It said one of the ingredients in the powder formula was talc, so I opened it up and used it as parting compound.

Here's a close up of my flask alignment mechanism, though I only used one half of it for the "open face" mold.

Let's see what we got in the crucible to melt this time: a housing from a terrible bench grinder, the old soap dish attempt, and an aluminum sprocket! Because I just looooooooove aluminum sprockets!

The swirling action of the flames was more pronounced than ever this time!

The glow.

Two molds after pouring the aluminum. They took quite a bit of metal!

I have to admit, the sand was still a bit moist when the molds were made, but there were no steam explosions fortunately. I also noticed less shrinkage in the metal compared with last time. That is to say, the bottom of the ingot wasn't caved in, for all I know there could be a huge air pocket in the middle.

All that heat and moisture has got to go somewhere when the molten aluminum starts flowing. This is the bottom of the mold, and given that there was about less than an inch of sand between the cavity and the wood board, something's gotta give.

It turns out the wood started smouldering from the heat, and that stain was the result. Also all the moisture seemed to permeate into the surrounding wood as it escaped the hot metal.

Did I mention the moisture had to go somewhere? Here's what happened to one of the flasks during shakeout. The wood got so wet that the screws no longer could hold it together! That's what I get for building flasks out of terrible particleboard furniture.