The idea of employing centrifugal force to make castings had been known for a long time, it was A. G. Eckhardt's original patent of 1809 which revealed understanding the basic principles involved. Centrifugal casting has greater reliability than static castings. They are relatively free from gas and shrinkage porosity. Many times, surface treatments such as case carburizing, flame hardening and nitriding have to be used when a wear resistant surface must be combined with a hard tough exterior surface.
One such application is bimetallic pipe consisting of two separate concentric layers of different alloys/metals bonded together. Such pipes can be economically used in many applications and can be produced by centrifugal casting process. Typically, in centrifugal casting, the following structure or zones may occur, Chill Zone - This layer is of fine equiaxed structure which forms almost instantaneously at the mould wall, Columnar Zone - This is next to chill zone. It consists of directionally oriented crystals approx. perpendicular to the mould surface, Equiaxed zone - this region may occur next to columnar zone characterized by large number of uniformly grown crystals. Centrifugal casting is suitable for the production of hollow parts, such as pipes. The process is suited for producing structures with large diameters - pipes for oil, chemical industry installations and water supply, etc.