:ربتخم هكابس
Introduction:
Centrifugal casting consists of producing castings by causing molten metal to
solidify in rotating moulds. The speed of the rotation and metal pouring rate vary
with the alloy and size and shape being cast. The following operations include in
centrifugal casting - rotation of mold at a known speed, pouring the molten metal,
proper solidification rate, and extraction of the casting from the mold. 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
