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.