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In casting, a pattern is a replica of the object to be cast, used to form the sand mould cavity into which molten metal is poured during the casting process. Once the pattern has been used to form the sand mould cavity, the pattern is then removed, molten metal is then poured into the sand mould cavity to produce the casting. The pattern is non ...
The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture to the surface, and this makes them easy to identify. Castings made from fine green sand can shine as cast but are limited by the depth to width ratio of pockets in the pattern.
The final pattern is approximately 97.5% air and 2.5% polystyrene. The finished patterns can be hot glued to pre-made pouring basins, runners, and risers to form the final pattern. [1] The pattern is then coated with a refractory material. The coated pattern (2) is placed in a flask and packed carefully with green sand (4) or a chemically ...
This allows the entire mold to be made from green sand and from removable patterns. The disadvantage of this is more mold-making operations are required, but it is usually advantageous when the quantities are low. However, if large quantities of casting are required, it is usually more cost effective to simply use a core. [6]
The pattern is a model of the desired casting. Talcum powder is often dusted over the pattern to aid in the removal of the pattern. Sand is sifted over the pattern until the model is covered by a few inches of sand. More sand is then dumped into the drag, and rammed with a wooden wedge, or mechanically vibrated to pack the sand down. The sand ...
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The most common evaporative-pattern material used is polystyrene foam. [1] The two major evaporative-pattern casting processes are: [1] Lost-foam casting; Full-mold casting; The main difference is that lost-foam casting uses an unbonded sand and full-mold casting uses a bonded sand (or green sand). Because this difference is quite small there ...
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