< GREEN & DRY SANDS
AIR SET/ RESIN/ OIL (PETRO) BONDED (HOT & COLD SET)
Air set, oil (PETROBOND), and resin bonded systems are usually (though not exclusively), activated through the addition of an organic based catalyst added in controlled proportions to a silica sand. In most cases the treated sand then hardens under ambient conditions without further intervention. The air set FERROSILICON powder process described earlier (see SODIUM SILICATE), is one such example of of an air set medium. Other hot or cold setting systems require the sand/binder mixture to be exposed to a HEAT SOURCE, or GAS TRIGGER to initiate hardening.
An air set process relies upon the moulder selecting an optimum binder to sand ratio to achieve a balance between working time and sufficient mould strength (lower binder/catalyst ratios lengthens working times, but invariably reduces the adhesion of sand particles). Sand to binder proportions are initially determined by experience, the moulding operative then confirms this through TEST SAMPLING.
The cost efficiency of these processes varies with the circumstances and needs of each particular job. The founder takes into account the desired standard of finish, and balances the quality benefits against the cost of the materials used in the mould. Both hot and cold setting processes are very well suited to the ordered production systems in place at many commercial foundries. When combined with modular master patterns, and the benefits of industrial scale processing, the resulting high productivity rate and fast turn-round times makes sand casting a very effective means of producing mass produced designs in metal. Some moulding sands, such as the Petrobond (oil based) system offer both high quality results and the recycling of reconditioned sand for better economy. Despite their effectiveness within the commercial founding environment, few of these alternative systems are better suited to the slower, more labour intensive moulding techniques used in art foundries than the CO2 process.
SHELL (CORNING) PROCESS >
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