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Sample Essay on Sand Casting vs Lost-Foam Casting
Sand casting is still used in the industry because of its advantages and benefits in contrast to lost-foam casting. Taking into account technological characteristics it is possible to say that sand casting has high metal content in contrast to lost-foam one.
Sand Casting vs Lost-Foam CastingBest casting results are obtained when the mold is used hot, just from the oven, and the metal poured into it relatively cold. The plaster mold is a much poorer conductor of heat than a sand mold and for this reason, if the metal is too hot, large and undesirable crystal development may occur because of the slow heat loss. In pouring, the two halves of the mold are blown clean with compressed air, fitted together, clamped between two plates of steel provided with the necessary opening for the sprue and any required risers. The clamping should be done carefully so as not to crush the mold at any point, and yet it should be tight enough to prevent metal leakage at the joint between the halves of the mold. Metal casts in a plaster mold remain fluid for a longer period of time than metal casts in a sand mold (Huffman, 2001). For some types of metal this, of course, is unsatisfactory as there is no chilling effect obtained. In the majority of cases casting will be completely normalized since there is no chilling action involved on one surface and no internal strain within the casting created by uneven cooling. For instance, Toyota Differential Pressure Process shows that sand casting is more effective in car production: “Toyota pulls a vacuum on its core boxes when making the lacy cores required in cylinder heads.
The main problem is that a plaster silica mold can only be used once. After removal of gates, risers and sprues, the casting may be cleaned by any suitable pickling solution, or by wire brushing, which will develop a bright metal surface. In casting bronzes or other alloys, where a patina is to be developed and chasing or finishing, if started, must be completed over the entire face of the casting, it is preferable to arrange the gating in such a way that the face will not have to be trimmed.
The cast plaster back should be scraped to a smooth level surface with a straight edge before it is completely set. In casting the second half, the first half is inverted and the forms built high enough so that the second half may be cast to the proper thickness. The second half also is scraped to a level surface. In gating a mold all high parts of the casting should be vented in such a way that no entrapped air will occur. The sprue is preferably led into a small skim gate and from this gate sufficient numbers of gates to feed metal uniformly into the casting should be cut into the plaster. This gating can be done with the ordinary molder’s tools when the plaster is wet, just after it has been removed from the pattern. This plaster composition is mixed in a ratio of nine to eleven parts with ten parts of water, which will give the consistency generally used in metal casting (Shaiken, 1994). The material is added like plaster, and is slowly sifted into the water with constant agitation. After the compound is added to the water, the slurry is mixed further for an additional forty-five seconds so that it is absolutly free from lumps of the dry material. This can easily be determined by placing the hand in the slurry and noting its condition. The case of CADIC shows that the company can successfully use Convert Mold Process.