So you started melting metal and you feel like making something other than cupcake pan ingots? Here’s everything you need to know to get started sand casting.
A pattern is covered in talc or another parting powder. Greensand is rammed around the pattern in the top half of a flask, and this forms what is known as the “cope”. The top half is flipped over, and the cope is covered in parting powder. The bottom half of the flask is then locked to the top half. Sand is rammed into this half as well. The flask is unlocked and the pattern is removed. A gating system is carved into the sand and gas vents are added. The cope and drag are reassembled, and aluminum is poured into the sprue. Seems straightforward enough. Are you ready to watch me fail… repeatedly? Because, this is Ten Tries.
Click Below to Watch the Video!
Materials:
Commercial Casting Sand:
Teton-Black Olivine Fine-Mesh Water-Bonded Foundry Casting Sand, 10lb: Amazon
DIY Casting Sand:
Kitty Diggin’s Fragrance-Free Cat Litter, 7 Lbs: Walmart
Quikrete Premium Play Sand, 50lb: Home Depot
Mesh Strainer: Dollar Tree, Walmart
Food Processor: Thrift Store, Walmart, eBay
5 Gallon Buckets: Home Depot
Sifting Pan, 20 Mesh: Amazon
Sifting Pan, 50 Mesh: Amazon
Fire Proof Wood Flask:
Sodium Silicate (Water Glass): Amazon
Other Supplies:
Ornament Patterns: Dollar Tree, Amazon, eBay
Silicon Metalloid Lumps: eBay
Parting Powder (Talc): Kroger, Amazon
Full-Face Respirator: Amazon
Try 1:
Casting sand can be pricey to buy online, so I made my own. I bought some cheap, unscented cat litter at Walmart, for about $2, and Quikrete play sand at Home Depot, for about $3. Then, I sifted the sand with a kitchen strainer then an exfoliating cloth, both from Dollar Tree. I ground up the clay cat litter with a cheap food processor. Keep in mind, this may break it, so you’d want to use an old one from a thrift shop. Then, I mixed together 10 parts sand to 1 part clay. I added water with a spray bottle and mixed, repeating until it passed the break test.
To do a break test, you just squeeze a handful of casting sand to form a clump, then you break it. If it breaks in two pieces, there is enough water in the mix. If other pieces fall, it needs more water. Stop adding water when the sand just passes the break test. You don’t want to add too much water.
In a previous video, I showed how to treat wood to make it fire resistant. I made a box out of the fire resistant wood by cutting 4 inch wide pieces of three quarter inch thick wood. Four of them were 7.5 inches long for the longer sides, four more were 4 inches long for the shorter sides, and the final four were 1.5 inches long for the alignment blocks. These were then sanded, fire proof treated, and screwed together as shown. The fireproof treatment isn’t really necessary, but it’s nice to have as you’ll see later. I then formed the sand mold as shown earlier. I melted Aluminum and now it’s time to pour.
The texture was pretty rough. Surface quality wasn’t very good, and the metal shrunk causing this dip. Still, it’s not bad for a first try.
Try 2:
Let’s compare the DIY casting sand to a commercial one. I used 140 mesh commercial casting sand, prepared the mold in the same way as Try 1 and poured.
The surface quality was a lot better but it still has shrinkage issues.
Try 3:
For the third try, I flipped the pattern and added a riser on the top of the cavity. Since the pattern was on the bottom half of the flask, I printed and painted a sprue. This saves time and helps keep the pouring basin consistent. It looks like I set the cope down on the coffee can too hard while preparing the mold, which caused these lines in the back of the result. That also allowed Aluminum to flow out of the sand and out of the flask. The good news however, is that the treatment applied to the wood of the flask worked flawlessly.
Other than that, the result looks pretty good and the dips are almost completely gone. The surface texture is better, but appears more dull than I would expect for how smooth the sand is.
Try 4:
After a little research, I found that aluminum is normally alloyed with Silicon (the element, not to be confused with silicone, the caulking). I used the same process as the last try, but I added 8% by weight Silicon from eBay. To get the silicon to dissolve in aluminum, I had to crush it nearly to a powder with a scrap of steel, and sift it. This process was actually pretty fun. The dust is not good to breathe, so a ventilator is a must. Then, I heated the mixture to 1000 degrees Celsius for three hours and stirred it a couple times. The addition of silicon to aluminum makes it more fluid, which, together with its relatively low cost, makes it a very good casting alloy.
I believe the dots forming in the molten metal are silicon precipitating out as the alloy cools.
The lower surface tension and viscosity of the molten aluminum allowed it to take the shape of the cavity more easily. This resulted in a much shinier surface finish.
Try 5:
Alright, Try 4 looked pretty good, so let’s complicate it a bit. I made a two sided pattern by using two symmetrical star patterns. All of these patterns are available right now at Dollar Tree, by the way. And no, they don’t sponsor me, they just have really cheap stuff.
Well, the sprue was too small and it appears that the aluminum froze before enough of it flowed into the cavity. I’ll have to revisit two part pattern sand casting sometime.
Try 6:
The results of the DIY casting sand were a little disappointing. So, I made more casting sand, but with two changes.
- I was more careful about grinding and screening all of the clay, and
- I sifted the sand with a 50 mesh screen.
Then, I dry mixed it, added water, and wet mixed the casting sand.
The result was much better! For larger castings that need to look professional, and aren’t decorative, the DIY V2 sand will work well. Plus it’s… “dirt” cheap.
After a little cleanup, it’s pretty enough to go on the tree!
To see how I made my flask fire resistant, click the link here! What should I try next? Let me know in the comments below!
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