Simple analytical calculations from the first principle can show the desired minimum rotational speed of molds in centrifugal, in particular, horizontal centrifugal casting process. The centrifugal force (F) experienced by molten metal (cast) when rotating in a horizontal mold in horizontal centrifugal castingcan be given as:

where, m refers to the mass (in kg), v refers to the tangential velocity (in m/s), and R refers to the internal radius (in m) of the mold. The force due to gravity of the motel metal rotating along with the mold can be estimated as “mg”, where m is the mass (in kg) and g is the acceleration due to gravity (in m/s²). A typical G-Factor, often referred to as ‘GF’, is defined as the ratio of the centrifugal force experienced by the rotating cast metal divided by its weight as

where, N refers to the rotational speed (in rev/min) of the mold. If the “GF” is too low resulting in smaller values of N, the liquid metal (cast metal) will rain inside the cavity rather than remaining forced against the internal wall of the horizontal rotating mold during the upper half of the circular path. In general, values of ‘GF’ in the range of 60g to 80g are found to be appropriate in horizontal centrifugal casting, although the same also depends on the type of material being cast.

Continuous casting

Continuous casting process is widely used in the steel industry. In principle, continuous casting is different from the other casting processes in the fact that there is no enclosed mold cavity. Figure 3.2.10 schematically shows a set-up for continuous casting process. Molten steel coming out from the furnace is accumulated in a ladle. After undergoing requisite ladle treatments, such as alloying and degassing, and arriving at the correct temperature, the ladle is transported to the top of the continuous casting set-up. From the ladle, the hot metal is transferred via a refractory shroud (pipe) to a holding bath called a tundish. The tundish allows a reservoir of metal to feed the casting machine. Metal is then allowed to pass through a open base copper mold. The mold is water-cooled to solidify the hot metal directly in contact with it and removed from the other side of the mold. The continuous casting process is used for casting metal directly into billets or other similar shapes that can be used for rolling. The process involves continuously pouring molten metal into a externally chilled copper mold or die walls and hence, can be easily automated for large size production. Since the molten metal solidifies from the die wall and in a soft state as it comes out of the die wall such that the same can be directly guided into the rolling mill or can be sheared into a selected size of billets.