Friday, April 3, 2015

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!
bike trailer with bag of sand
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. 
turtle sandbox on pallet with wheels

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".
turtle sandbox with greensand
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.
making a sand mold
Here's a close up of my flask alignment mechanism, though I only used one half of it for the "open face" mold.
casting flask alignment mechanism
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!
some scrap aluminum in crucible
The swirling action of the flames was more pronounced than ever this time!
swirly flames from the furnace
The glow.
glowing radiation from the furnace
Two molds after pouring the aluminum.  They took quite a bit of metal!
molds with aluminum poured
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.
mold of runescape ingot
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.
mold stain
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. 
wood board smouldering from heat
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.
flask destroyed by moisture
More detail of shakeout.  I think the 60 grit sand worked well.
shakeout of molds
The finished products.  So luxurious! Now I have enough bars to smith some aluminum platelegs!
some runescape aluminum bars





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