Green sand is an efficient, economical means of making moulds. But one problem is that you require a Muller to make the first batch. Green sand needs maintenance and care if you wish for best results, but it lasts for years and can be reused many times for hobby purposes.
CO2 gas systems and dry sand: The CO2 process is an easy process for hobby use. It is regularly utilized in technical schools and colleges for giving practical training in foundry practices and due to basic equipment needs small batches of moulding sand may be easily made up.
Normally it is easily usable and repeatable results are easily achievable. But there is one thing which might harm its results and i.e., if there is more moisture in sand say above 0.5% it will lead to poor moulding results.
Another minus point is rental costs of gas bottles and expenditure of cylinder regulators needed for proper gas pressure. Sand used in moulding is useless after every use, which creates a problem if casting is continuous.
The self set moulding system: The self set system is easily usable; all that you require is clean foundry grade sand, a silicate resin for mixing with sand and a catalyst to induce reaction in silicate, which will take about 10 minutes on a hot day.
The equipment needed is: A mixer for this a small handheld power drill with a point mixer will do it, and an accurate scale to measure chemicals being used.
The silicate is a costly item which comes in drums of 20 or 200 liters. The hobby foundry worker will need to be on friendly terms with a commercial foundry operator of your area.
There are many separate processes which might be used, but they are rather complex to give details here. Suppliers like Foseco have their free guidelines for using their products and you can use chemicals quite safely so long as you follow their producers instructions.
The EPS or Full mould system: EPS means Expended Poly-Styrene it is similar to investment casting because a single part flask is utilized with result that no lines appear on final casting. It is necessarily a one off system, because the consumable design is made from expanded polystyrene.
This is a polymer taken from benzene and ethylene and in its expanded form it has only 2% real solid polystyrene. Readers may know this substance as it is utilized in producing ceiling tiles, and as packaging for audio and electronics equipment.
An expendable design, complete with runners and risers, is cut from expanded polystyrene and is totally surrounded with clean dry sand in a box or can. The melted metal is then poured on the design, which melts and burns fast and leaves a cavity which is occupied by melted metal. No residue is formed; the carbon dioxide and water vapor evolved by burning of polystyrene don t dissolve in the melted metal, but escape via the permeable mould sand as gas. The EPS system produces a very strong smell.
Moulding may be done by pouring dry sand around the pattern. As the polystyrene burns it makes a tacky land among the sand grains long enough for metal s skin to be formed.
This moulding process is largely used in engineering companies. It is used to make press-tool die holders and small parts in one off category. Casting tolerance is about same as that of investment casting. This process has extensive range of uses for experienced hobby caster.
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