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The cope and drag (top and bottom halves, respectively) of a sand mold, with cores in place on the drag. Two sets of castings (bronze and aluminium) from the above sand mold. Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand—known as casting sand—as the mold material. The term "sand ...
The history of molding sand is difficult to study, as much of the origins of the practice predate writing. Molding sand was used exclusively for bronze casts, which was pioneered by the ancient Chinese. The next major advancement came in India in 500 B.C. when cast-crucible steel was created.
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 direct molding method is to make the wax material into the same wax mold as the casting by hand or other tools; the indirect molding method is to make the wax mold through the mold. The direct molding method requires craftsmen to have a high technical level; otherwise, the quality of castings cannot be guaranteed.
In the simplest sand casting procedure, the drag is placed upside down on a board, around a pattern of the part to be cast. 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.
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]
A molding sand mixture, usually green sand or bentonite, is blown into a rectangular steel chamber using compressed air. The molding sand is then squeezed between two patterns, which are on the two ends of the chamber. After squeezing, one of the chamber plates swings open and the opposite plate pushes the finished mold onto a conveyor.
The pattern is made of wax, wood, plastic, or metal. The molds are constructed by several different processes dependent upon the type of foundry, metal to be poured, quantity of parts to be produced, size of the casting, and complexity of the casting. These mold processes include: Sand casting – Green or resin bonded sand mold.