Combined loose piece pattern for a complex job

Abstract

Casting is one of the earliest metal-shaping methods known to human being. It generally means pouring molten metal into a refractory mold with a cavity of the shape to be made, and allowing it to solidify. When solidified , the desired metal object is taken out from the refractory mold either by breaking the mold or by taking mold apart. This process is also called founding. A pattern is a replica of the object to be made by the casting process, with some modifications. The main modifications are addition of pattern allowances like shrinkage allowance, machining allowance, draft allowance etc., the provision of core prints and elimination of fine details. Loose piece pattern is used when the contour of the part is such that withdrawing the pattern from the mold is not possible. Hence during molding, the obstructing part of the contour is held as a loos piece by a wire. After molding is over, first the main pattern is removed and then the loose pieces are recovered through the gap generated by the main pattern. A safety valve which is generally manufactured by complex forging method , can be easily manufactured by sand casting method which is more economical the forging method. In the sand casting method, the two wedge shaped portions of the safety valve create problem during removal of pattern, so these two portions are taken as loose pieces and held as loose pieces by a wire or pin. Once the main pattern body is removed, these loose pieces are recovered through the space vacated by main pattern body. So this project work deals with manufacturing of safety valve using sand casting with split pattern which consists of multi loose pieces (combined loose piece) and its advantages over complex forging method