Centrifugal Castings : Manufacturing Process

Manufacturing Processes:


Centrifugal Castings are produced by pouring molten metal into a permanent mold that is rotated about its axis at high speeds (300 to 3000 rpm). The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The axis of rotation may be horizontal or inclined at any angle up to the vertical position. The speed of rotation and metal pouring rate vary with the alloy and size and shape being cast. The casting is usually a fine grain casting with a very fine-grained outer diameter, the inside diameter has more impurities and inclusions, which can be machined away. 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 uniformity and density of centrifugal castings approaches that of wrought material, with the added advantages that the mechanical properties are nearly equal in all directions. Since no gates and risers are used, the yield or ratio of casting weight-to weight of metal poured is high. The mold may be made of cast iron or steel, copper, graphite, ceramic, or dry sand. Only symmetrical shapes can be produced with this process. Size limits are up to 3 m diameter and 15 m length ranging from few kilograms to 22 tons.

 

Centrifugal force acting on a rotating body is,

C.F = mv2/r

where, m – mass (kg), v – peripheral speed (m/s), r – radius (m).

Gravitational force,

G.F = mg

where, g = acceleration due to gravity (m/s2).

G factor = CF/GF = mv2/r.mg = v2/rg

 

Solving, further we get,

N = 42.3 √G factor/D



 

Characteristics of Centrifugal Casting:


1) The casting is relatively free from defects.
2) Non metallic impurities which segregate toward the bore can be machined off.
3) Less loss of metal in tundish compared to that in gating and risering in conventional sand casting.
4) Better mechanical properties.
5) Production rate is high.
6) Can be employed to manufacture bimetallic pipes.
7) Centrifugal casting process can be used for fabricating functionally gradient metal matrix composite material.