Metal Mold Making With Sodium Silicate

Sodium silicate or – water glass or liquid glass as it is informally known – is quite a multipurpose and functional compound. It is formed by the reaction of sodium carbonate with silicon dioxide in molten form. The aqueous solution is used as an adhesive, sealer, binder or deflocculant in ceramics, cements, textile, lumber and automobiles.

The most common use of water glass emerges in foundry metal mold making applications in the manufacturing industry. The metal casting process involves pouring molten metal in sand molds. These molds are made with fine grained sand that has been sieved with a 100 grade mesh.

While making sand molds sounds simple, the question that arises is – how will the sand particles bind together? And this is where water glass enters the picture!

Indeed, sodium silicate works as a high strength binder that enables the sand to bind to form strong and durable molds.

How is it used?

Take dry, clean sand that has been strained properly. Add 3% to 4% (by weight) sodium silicate to the sand. While you can try mixing small amounts by hand, larger quantities require mixing with a sand mill.

Now pack the sand and water glass mixture in or around the object to capture its shape and details. Most manufacturers prefer to compact the mix in a core box to form the required shape.

At this point, you may be worried that the sand will just spread out everywhere without retaining any shape. Well, the sodium silicate has to be activated for it to be able to glue the sand particles together. This becomes possible when it is exposed to carbondioxide gas.

Attach a hose or nozzle to a low pressure source of carbondioxide gas and apply it all over the core. The gas should pass through the entire core mold -from one end to the other – so that all the molecules of water glass get activated. Alternatively, you can even place the core sand mold in a plastic bag and flood it with oodles of carbondioxide gas.

As the stimulated compound binds the sand, the sand particles start hardening and the mold gets cured. The core sand mold is ready to use as soon as it has solidified. You can proceed to pouring the molten metal into the mold without the risk of any leaks or the metal flowing out completely!

Apart from working as an effective sand binder, sodium silicate also functions as a sealer and adhesive. It is regularly used to seal stucco, concrete and plaster by reducing their porosity. Just a thin coat of sodium silicate is sufficient for the job, and they also become water repellant in the process.

Similarly, when a thin layer of water glass is applied between any two materials, it can efficiently join both of them by forming a tough bond.

In sum, the simple water glass is certainly quite versatile and useful!

Michael Ortiz

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