< ELECTROFORMING, RESIN CASTING & ETCHING
SAND CASTING – A SUMMARY
• As with LOST WAX casting, master patterns destined for sand casting fall into one of two basic categories: LOST PATTERNS and PERMANENT PATTERNS.
• Lost patterns for sand casting are nearly always made from EXPANDED POLYSTYRENE (EPS), or a similar lightweight material. This process is also sometimes known as EVAPORATIVE or LOST FOAM casting. When lost pattern casting with higher melting point metals (copper or iron alloys), the EPS pattern should be first coated with a protective refractory barrier. This coating prevents SAND BURN faults on the finished cast.
• Permanent patterns for sand casting must be formed in a substantial material to survive workshop handling and sand compaction in the moulding flask. Patterns for sand moulding should be designed with an awareness of the processes limitations, in particular the potential problems caused by undercuts, irregular and deep surface textures and other awkward pattern features.
• Permanent patterns for a commercial sand moulding process are often designed on a modular system. Features like parting lines, ingates, feeders, and the design itself, are incorporated into a number of separate pattern parts, which are moulded separately. A core may also be formed remote of the rest of the mould, then later set into the flask with other sections to create a hollow cast.
• Sands for moulding are primarily composed mainly of high refractory materials such as SILICA and ZIRCONIUM. A BINDER consolidates the sand into a mouldable medium which can later be bonded into a hard refractory mass. If needed, an additional CATALYST or TRIGGER can be added into the binder. This accelerates the setting and hardening of the mould.
• Sodium silicate bonded sand (also known as the CO2 process), is one of the most common methods of sand casting; it is widely used within both commercial and fine art foundry environments.
• For the most part, artists and designers are advised to use fine art founders for casting their work. Direct use of commercial founders may be appropriate, provided all the potential implications of using an industrial operation have been well researched and understood.
SAND CASTNG KEYWORDS >
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