REFRACTORY SANDS & BINDERS
Sands for foundry piece moulding and casting are selected for their high refractory content – SILICA and ZIRCON type sands are ideal in this respect. Coastal beach sands are not usually sufficiently refined and are generally considered unsuitable. Prior to use in the foundry, the sand product will undergo extensive refinement, including washing and grading to a predetermined particle size. Most foundry sands are silica based (comprising 95-99% pure silica). The non-silica sands (zircon, olivine, and chromatic), are normally reserved for specialist applications, in particular the casting of special steel alloys.
Moulding sands are normally supplied to the founder as a dry, free running grain material. Small scale foundries may take delivery of bagged sand, however large operations with volume high volume requirements have the sand 'blown' from bulk transport tankers into storage hoppers of 10 ton + capacity.
Dry sand is prepared for moulding by combining it with one of a number of possible BINDERS. Some of these binders also contain an integral CATALYST component to promote setting and hardening of the sand. Binders and catalysts are selected for use according to various factors such as the working time required, the type and overall design of the master pattern, the quality of ‘as cast’ finish desired and cost considerations. The following pages describe some of the more common binder and setting systems used in sand casting.
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