Green Sand.

The all time favourite moulding medium is green sand for its simplicity, initial low set up cost, ease of use and predictable results. Properly stored in a plastic bin, conditioned green sand will last for several weeks. Green sand is the most efficient, low cost way for the hobby worker to begin metal casting.

The only downside with green sand is the need for a Muller to make your first batch. But a very efficient hobby Muller can be built that will mull and prepare small amounts of moulding sand. Green sand does require maintenance and looking after to get the best results, but a small batch will last for many, many, years for hobby use.

The Sodium Silicate Co2 Gas Injection Process.

Moulding sand is mixed with sodium silicate and the mould is gassed (injected) with Co2 (Carbon Dioxide) gas to set the silicate mould or core. Co2 is an easy system for anyone to use, trade schools use it to demonstrate foundry practice, as only basic equipment is required which enables small batches of moulding sand to be quickly prepared.

This system is straightforward to use, and it will give repeatable results. However there is one aspect that can be detrimental to the Co2 performance and that is if excess moisture is contained in the sand, anything above 0.5% moisture could impair the performance and give poor results.

Another drawback with Co2 is the rental payments on the gas bottles, plus the purchase expense of gas cylinder regulators, required to deliver the correct line gassing pressure. The mould has to be broken apart to retrieve the casting and is generally discarded after each use, presenting a sand waste disposal problem.

The Self-Set Process.

The self-set system is also very easy to use; the only requirement is good clean sand of the required grade. A special silicate is mixed with the sand and a catalyst is also added and the sand is thoroughly mixed again to create the hardening reaction in the silicate chemical, which takes around ten minutes on a warm day.

Equipment required:

A basic mixer such as a small power drill fitted with a paint mixer tool, an accurate digital kitchen scale to measure the chemicals. The chemistry is expensive to buy, and is supplied in 20 litre or 200 litre drums. To acquire smaller amounts, you may need to cultivate' a friendship with your commercial foundry in your area.

There are many different systems for creating sand moulds, to choose the best one for your purpose, contact suppliers for product info sheets to learn how to use the products. The chemicals are generally quite safe to use as long as you follow the manufactures safety instructions, as you always should.

The Lost Foam System.

This process closely resembles investment casting in that a single-part flask is used, so that no parting lines-and hence, no fins appear on the finished casting. It is essentially a 'one-off' process, since the consumable pattern is carved from expanded polystyrene. A polymer derived from benzene and ethylene, and in its expanded form it contains only 2 % actual solid polystyrene.

This is virtually the same substance used in the manufacture of ceiling tiles, and packaging material for fragile equipment. An expendable pattern, complete with runners and risers, is cut or assembled from expanded polystyrene, and is completely surrounded with sand. The molten metal is then poured on to the pattern, which vaporises instantly, leaving a cavity, which is immediately filled by the molten metal. No solid residue is formed, and the carbon dioxide and water vapour evolved in the combustion of the polystyrene escapes through the loose permeable sand.

A mould can be prepared by pouring clean, dry beach sand around the foam pattern, rapping compacts the sand around the pattern. As the foam pattern burns, it produces a tacky bond between the sand grains just long enough for a skin of metal to form.

This moulding system is used extensively in the engineering industries; the process is used to manufacture small items of just a few ounces, to large press-tool die-holders. Casting tolerances almost match that of the investment casting technique. This system has many applications for the experienced hobby metal caster, and is being used more frequently by hobby foundry workers to create intricate shaped one off castings. Which can save many hours of making a traditional timber pattern.