Lost PLA casting

The simplest foundry process to use is sand casting foundry. Of course, not just any type of sand should be used.

Casting sands are a mixture of sand (silica) with a binder. This binder can be natural or chemical. The binder is there to hold the mold to the shape of the part until the solidification of the metal, but thereafter the mold must be easily destroyed to extract the part.

In homemade use, the most common is green sand (sand + clay + water) but there are also sands whose binder is oil.

It is also possible to use soda silicate as a binder, in this case the binder is chemical and the hardening of the mold or the core is done by gassing the sand/silicate mixture with CO2. This last technique is very useful for cores but, of course, can be used for the complete mould.

The recipes that are given in this article are recipes that I have tested until bronze casting.

Green sand

Green sand is a sand that takes shape without chemicals and is used directly for casting metal, it is possible to buy it in the specialized trade, but it is much more interesting to make it yourself with ingredients found in DIY superstores.
The cost of this type of sand is ridiculous but it does not allow to make very complex parts and with too thin walls.
For casting, the mold remains at room temperature, which again limits the parts thickness.

Fine sand, I use sand with grains of 0.5mm

Bentonite, it is a clay which is used, among other things, as litter for cats...
It must be crushed (coffee grinder) and sieved.

And of course water.
My recipe:
8 parts of fine sand
2 parts bentonite
Just enough water to hold the sand together.

I also add a bit of powdered charcoal as the color change helps ensure the mixture is good, this should remain a negligible percentage.

A small sprayer is perfect for adding water gradually
Make the mix dry, then add the water in the form of a mist, then mix well and test the hold, add a little water at a time so as not to have too wet sand.

Regularly test the holding of the sand by squeezing it in the hand, the sand must hold without crumbling and the hand must remain almost dry.

If the sand does not hold together, water must be added.
If the sand sticks in the but, it is too wet and will stick to the model when casting.
When you judge that your sand is ready, you have to do a last test by breaking the clod that you have just squeezed in your hand. The clod must break frankly without bursting.

If, despite adding water, your sand does not hold together enough, you must add a little clay to bind the sand better.

The optimal dosages are to be tested because they vary according to your clay and the grain size of the sand. The finer the sand, the more clay you will need to add.
Here, you now have a batch of green sand, it will have to be kept if possible in a sealed box so that it better retains its humidity. Before each use, it is advisable to redo the resistance and breakage tests because it will be necessary to adjust the humidity before starting the mold making.

After casting, the green sand can be reused, it is necessary to add a little water and possibly clay. It is best not to mix new sand with recycled sand.
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A Youtube channel with lots of top casting, not to be missed
La fonderie
Casting sand, many interesting things. In french.
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Youtube chanel with many diy castings
La fonderie
Casting sands. French
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