Significance of fluidity
Fluidity of molten metal helps in producing
sound casting with fewer defects. It fills not only the mold cavity completely and rapidly but does not allow also any casting
defect like “misrun” to occur in the cast object.
Pouring of molten metal properly at correct temperature plays a significant
role in producing sound castings. The gating system performs the function to
introduce clean metal into mold cavity in
a manner as free of turbulence as possible. To
produce sound casting gate must also be designed to completely fill the
mold cavity for preventing casting defect such as misruns and to promote
feeding for establishing proper temperature
gradients. Prevent casting defect such as misruns without use of excessively
high pouring temperatures is still largely a matter of experience. To fill
the complicated castings sections completely, flow rates must be high but not so high as to cause
turbulence. It is noted that metal
temperature may affect the ability of molten alloy to fill the mold, this
effect is metal fluidity. 1t include alloy analysis and gas
content, and heat-extracting power of the
molding material. Often, it is desirable to check metal fluidity before pouring
using fluidity test. Fig. illustrates a standard fluidity spiral test
widely used for cast steel. “Fluidity”
of an alloy is rated as a distance, in inches, that the metal runs in the spiral channel.
Fluidity tests, in which metal from the furnace is poured by controlled vacuum
into a flow channel of suitable
size, are very useful, since temperature (super-heat) is the most significant single variable influencing the
ability of molten metal to fill mold.
|Fluidity spiral test
temperature. The use of simple, spiral test, made in green sand on a core
poured by ladle from electric furnace steel melting where temperature
measurement is costly and inconvenient. The fluidity test is same times less
needed except as a research tool, for the lower melting point metals, where
pyrometry is a problem. In small casting work, pouring is done by means of ladles and crucibles.