A study has been made on the cooling rate, eutectic cell structure and mechanical strength of round, square and triangular castings of different forms having the same sectional area. It was found that the cooling rate, even for the same sectional area, varied according to their forms and that it became greater in the order of round, square and triangular castings. The same was true with the number of eutectic cell and the mechanical strength. On the basis of these results, the following theory was established.
(1) The cooling rate of castings can be determined by the ratio of volume to surface area.
(2) A linear relationship, by the logarithmic graph paper, can be established among the nth power of modulus (M) of castings of different forms, the lapse of time (t), the cooling rate (Vs) and the number of eutectic cell (N). The relation can be expressed as t=AMnf, Vs=BM-nf, N=HM-nf where A, B and H are constant and f value in each case becomes f≈1. The values of n obtained were 2.0 for a round bar, 2.3 for a square bar and 2.5 for a triangular bar.
(3) Among the cooling rate, the mechanical strength (tensile strength σB, Brinell hardness HB) and the number of eutectic cell, the relationships σB=C1Vsf, HB=C2Vsf, N=GVsf were obtained.
(4) Between the number of eutectic cell and mechanical strength, σB=J1Nf and HB=J2Nf, where C1, C2 G, J1 and J2 are constant, were obtained.
