Oil Bonded Sand Cating Large Aluminum Skull

In this aluminum casting I made a replica of a decorative plastic skull that I bought for €10. For the sand moulding I used petrobond and carved around the pattern. The main problem with the skull was its shape. I used filler to smooth "problematic" angles of the skull so that way it would be easier to remove the pattern without breaking the sand impression.

For this casting I also built a new wooden Flask because of the large size of the skull. I decided to reduce the weight of the aluminum skull by creating a hollow core. To form the core I just used an empty can of corn instead of making the traditional sand core.

The casting turned out well the only mistake is did was placing the corn can too high in the sand and that caused holes in the casted skull eye sockets.

I made a short video just showing how I removed the can of corn from the skull casting. It's a very easy proccess all that is needed is some sort of pliers to cut and pull the can out of the aluminum skull casting.

Video of me removing the can:

Green casting sand VS oil bonded sand

I decided after using oil bonded sand (petrobond) to test some homemade green sand. I got some play sand and after doing a bit of Internet research I started making the green sand. My goal was to make it at minimum cost and to achieve semi good casting quality ;-).
I started experimenting with small quantities measuring first 1KG of sifted and dry play sand. I used a mixer to grind the cat litter (clay) to a powder stage and then sifted 100gr (10% of clay), mixing both together and after just adding small amounts of water at a time. The process was very quick and the sand mix was ready after performing the squeeze test.

My first casting was an aluminum eagle. This was the 12th aluminum eagle I have casted and the result was very promising. No difference in the quality of the casting from the oil bonded eagle castings.

I decided to cast a bigger aluminum object this time so I casted my 3rd aluminum sun. The quality of the casting in this case was not the same. The oil bonded sand sun casting was with almost zero defects and the green sand casting was with a lot of defects mostly porosity. Perhaps from not ramming the play sand hard enough or from the lack of vent hole but again it's not the worst sand casting. I hung the sun on a garden wall and the defects aren't even noticeable it just needs a bit of sanding and polishing.

How oil bonded sand VS green sand:
Oil bonded sand produces a better quality casting but is much more expensive then green sand. Green sand is cheap, easy to make and re-usable. Oil bonded sand is stinky, smokey and stains everything it comes in contact with. Green sand is clean with no smell. Oil bonded sand is much more sticky then green sand. Green sand is alot more fragile then oil bonded sand.
If you are looking for amazing finishing on your casting use oil bonded sand. If you want a cheap solution for casting, for example some heavy machinery parts green sand will do just fine.

Here is a 5 min' demo video I made of how to make casting green sand.

Aluminum Spoon and Chicken Sand Casting

In this post I will show two castings that I made in one flask. I used two of my children's toys: a spoon and a toy chicken so I could engrave them as souvenir for them for years from now. I started by making the impression in the sand, I think I mentioned it before but the easiest type of pattern to duplicate for sand mould is a flat pattern. All that is needed is a bit of patience when digging out the sand after flipping over the drag part. It is important to carve around the pattern as far is its parting line to prevent breaking the sand when lifting the pattern out of the sand.

As I did mention before it is good practice to pre-heat any ingots or scrap aluminum before throwing it into the crucible molten aluminum. Two reasons, one: cold metal will "freeze" the molten metal in the crucible and second: to eliminate moisture coming in contact with molten metal if ingots where left in the wet. You can see in my foundry I used mesh on the top of the lid hole that works perfect for me. Very important to work safe with foundry gloves and pliers when lifting and placing hot ingots into the crucible and also face shield protection.
In one of my visits down the beach I found a pressure cooker lid washed ashore so that happily got a new "life" in my crucible and I also melted my sons broken scooter ;-)
The last image is scrap aluminum from my old electric router and sander. What ever scrap is to big to fit into my crucible it ends up chopped up or broken with a heavy hammer but they all end up as nice ingots ready to become a new object.....

In the next images you can see the aluminum spoon and chicken turned out very well and all the left over aluminum turned back into ingots.

The sprue and riser did their job and you can see in the image that the casting was "feeding" from it while it was in the solidifying stage. After cutting off the sprue and riser I gave the casting a bit of cleaning with a metal file. Then some light sanding and polishing on the buffing wheel.
Now its ready for custom engraving.

Oil Bonded Sand, Molding Aluminum Sun

Its been 3 months since my last post so I am back now with a few new aluminum castings and more tips and images. In this post I am showing my casting of an aluminum sun. This is a link to my first aluminum sun casting. The pattern I used for this casting was a clay sun that I varnished so it would be easier to remove it from the sand mould and to achieve a good finishing. For this large casting I made a new timber flask as you can see in the images. The flask dimentions are 390mm x 390mm x 80mm. Because it's a large flask this is a good tip to keep in mind: when working with such a big flask it is good practice to create inner "ribs" for the flask or just to make a few grooves with an electric router, any way is good. It is very annoying when you work hard on your sand moulding and just as you are about to place the cope on top of the drag all the sand falls out.

The sand moulding was very easy to make and I was able to lift the sun pattern without damaging the sun impression in the sand. The inner ribs also worked very well and the petrobond didn't fall out of the flask. I also got another bag of petrobond and in the images you can see the differance in the color. After many uses petrobond turns dark brown vs orange color for new petrobond.

My first sand mould was perfect but when I was finishing it I got distracted and forgot a very important thing, I didn't place my clamps on the flask. Here is a very important tip: The clamps or just a weight on top of the flask will prevents the molten metal from lifting the cope part (Hydrostatic pressure) and resulting in a pool of molten metal on the floor also burning the flask if it's constructed from timber. This causes a casting defect called FLASH (see flash image circled in red).
I made a lot of castings till this day and never forgot the clamps, so this can easily happen and can be very dangerous if you don't keep safety in mind. Because I always cast in the open on dry sand no harm was done. The only annoying part was to cut off, file and grind the casting FLASH. *** In the future I will post info explaining in more detail the most common casting defects***

My second casting was very sucessful, I didnt forget the clamps this time... :-)

On the top image 3rd from the left you can see the two sun castings. On the left is the sun from my first casting after cleaning the flash defects and giving it a bit of a polish and the right sun is the second casting which turned out to be a very good quality casting with zero defects. I drilled two holes in the sun and attached it on my garden wall with my eagle castings.