Aluminum diving plaque, foundry sand casting

This is a casting I made a few months ago as a gift for my sister. She is very passionate about scuba diving so I thought she might like this aluminum casting. I decided to make a round pattern for this casting and I used 9mm MDF as a base for the images and letters.
I started by using my electric router shaping an accurate radius from the 9mm MDF.
For this pattern I was trying to create a maritime/diving theme so for the plaque frame I used some plastic rope glued around the pattern.
After the rope was in place I used a filler to create a "draft" (angle), draft in sand casting means to create an angle so the pattern will not break the sand mould when lifting it out of the flask.

After the pattern base was ready I started designing the layout of the letters and images. For the letters I used children sticky foam letters, the letters works very well I used them before when I made my FlamingFurnace plaque casting. The images I got and printed are from the Internet, I glued them to 3mm cardboard and cut out the shape after glue dried. I live near the sea so from time to time my son collects shells on the beach so I used a few of them for this casting. The "challenging" shell was the spiral shape shell because I had to create the draft around it. I had to grind the base nice and flat to achieve that so I used my light-duty grinder and it was perfect for the job. At this stage it was just a case of re-arranging and marking every item to the exact location on the plaque. Gluing all the parts, creating a draft around each item with filler and finally and most important thing was to give the plaque pattern two coats of clear varnish. The varnish will prevent the sand from sticking to the pattern during the sand moulding process.

The sand moulding part was easy and successful without any sand breaking issues or other moulding problems. For this moulding I used Petrobond sand because I wanted to achieve a fine finishing for this specific plaque casting.

I used a large wooden flask with inner support ribs for this casting. As always I add a sprue and riser extension as it works very well and prevents aluminum casting shrinkage issues.
After opening the flask and removing the moulding sand I was really blown away at how great and detailed the plaque turned out.

The next part was to cut off the sprue and riser and clean a bit of "flash" (excess aluminum) around the pattern with a metal file. This is an important tip: aluminum alloy is soft metal and can be scratched and damaged very easily so when working with a vice its always a good idea to place the aluminum casting in a cloth and not directly in the vice, a cloth will prevent ruining your hard work. The only casting part that I polished was the letters, diver images and I semi polished the shells. The image with the spirit level below is just to show how flat the back of the casting plaque is with zero shrinkage thanks to the large sprue and riser.

The last and final part was to drill two wall mounting holes and paint the aluminum plaque dark blue.

Bell Replica Foundry Project

This aluminum bell casting project is relatively easy. As a pattern I used a small brass bell that is hanging on my workshop door for the last few years .

Making the mould is a very easy process but the tricky part is getting all the aluminum to fill the mould cavity. The bell pattern is about 3mm thick and as I thought it didn't fill properly the first pour.

The second pour I carved some of the sand off the cope part of the mould. This time the sand mould was filled properly. I like the contrast between the aluminum silver shine and the brass. Now I plan to make a back mounting plate for both of the bells.

Using my gas burner for the foundry it takes about 35-45 min for the aluminum to melt. I use all the scrap sprue and risers from the other castings, No aluminum goes to waste ;-)

Aluminum bell casting video:

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.