Equation 26 Equation 27


Where; • for flake graphite cast iron: 3,4


Equation 28 Equation 29 • for ductile cast iron:1,2 Equation 30 Equation 31 Equation 32 In the above equations: α is the wedge angle, Ncr


and n is the wedge size coefficient which accounts for the influence of wedge size on the chill width.


are the critical cell and nodule counts at the temperature T ≈ Tc


dex, CT and of the width of the chill in flake graphite iron is shown in Figs. 19a, & b. Similar examples are given for nodular cast iron (see Figs. 19c and d). In general it can be observed that the higher the cell and nodule count, the lower the chilling tendency index as inferred from these figures (notice that the gray cast irons are less sensitive to CT when compared with nodular irons).


An example of the effect of Ncr


Influence of Cell and Nodule Count on Shrinkage Porosity and Contraction


Figure 20 shows the effect of carbon saturation, Sc expansion of ductile and flake graphite iron.6


a given Sc on the Notice that for


flake graphite iron has nearly the same amount of graphite as nodular graphite iron. Since casting expansion is due to the presence of graphite, it is difficult to explain the large expansion differences in these irons. An approach into this problem is to consider the internal pressure generated during solidification. From the work51


it is found that as the cell or nodule count, Nx and as the width of the mushy zone, International Journal of Metalcasting/Summer 10


nodule, Nn,cr densities on the chilling tendency index, .


Figure 19. (a, b) Influence of the critical cell, Ncr


Continuous lines are predictions based on Eqns. (26, 27, 29 & 31) and Table I, experimental point.50


CT, width of chill, W and critical wall thickness, scr 49 and (c,d) on the chilling tendency in- and Nn,cr (c)


(a)


(b)


(d)


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