5. other expendable and permanent mold casting
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Different types of sand moulding
Green sand mold:most common, evolved from manual to mechanized process;Rough finish poor dim accuracy
Dry sand mold:Strengthening of the mold by heating and subsequent bakingAlthough the previous problems can be minimized it is not cost effective
Skin-dry sand mold
• An compromise between the two, drying the mold adjacent to the mold• refractoriness is increased by silica wash, zircon sand and also by using additional binders
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Sodium silicate-CO2 mouldingNa2SiO3 (water glass) added to sand acts as a binder when exposed to CO2
Strong hardening of the entire mold leads to • poor collapsibility• poor shake out • poor core removal
Solution: • skin-treatment approach• alternative binders like room temp-cured resins.
NO-BAKE, AIR SET, CHEMICALLY BONDED SANDS
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OTHER EXPENDABLE-MOLD CASTING PROCESSES
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• Expensive metallic pattern, hence suitable for large batch production
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Full mold casting
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Lost foam process (similar to lost-wax technique)
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