< COMMECIAL PATTERN MATERIALS & CONSTRUCTION
REFRACTORY SANDS & BINDERS
The sands used for foundry piece moulding 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, a sand product will undergo a significant refinement process, 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 sand is normally supplied to the founder as a dry, free running grain material. Small scale foundries may take delivery of bagged sand, though bigger operations requiring much larger quantities have the sand blown from bulk transport tankers into storage hoppers of 10 ton + capacity.
Dry sand is prepared for moulding by mixing 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 for sand casting.
SODIUM SILICATE BONDED PROCESS >
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