(a) Figure 16. Maximum degree of undercooling, ∆Tm
is 3.18 %C, 1.91 %Si and a Ti = 1239o 2.68 %Si and a Ti = 1252o
C (2286F).
Equation 22 Equation 23
Using Eqn. 23 as well as the data23 1.60 x 105
cm,-3
ure that the number of active nucleation sites increased from 2,916 to 20,312 sites/cm3
through inoculation (shaded fields in
Fig.14). Further calculations yield cell counts, N = 298 and Ni = 1085 cm-2
= 897 cm2 ).
for the base and the inoculated iron, respectively. These cell counts are in agreement with experimental deter- minations of N values (N = 324 and Ni
Cooling Rate Effects
From Eqns. 15 and 16, it is found that the cooling rate in- creases as the ability of the mold to absorb heat, a increases and the casting modulus, M decreases. The cooling rate of flake graphite iron is also dependent on the φ parameter (Eqn. 18) while in ductile iron it depends on the B2 eter (Eqn. 19) and hence on the initial temperature Ti
param- of the
cast iron just after pouring into the mold. Additionally, for flake graphite iron the cooling rate at the eutectic tempera- ture, Ts ite, Tl
is related to the liquidus temperature for the austen- (see Table 1).
International Journal of Metalcasting/Summer 10
C (32.76F) the size distribution function n(l) given by Eqn. 4 can be determined and plotted as shown in Fig. 14. From this figure, it is found that inoculation essentially in- creases the number of all sites, Ns of active sites, n(l) where lm
oculated cast iron Ns,i = 18.2°
cm,-3 bi
C (36F) and for in- = 104C and ∆Tm,i
and as a result the number l
b = 76.8C and ∆Tm = 6.10 x 106
for a base cast iron Ns = 20°
= Table 4. Reported Values for Mold Materials46-48
thicknesses, s as a function of (a) cell and (b) nodule count. Continuous line predictions are based on Eqns. (24), (25) and Table 1 for a = 0.10 J/(cm2 o
and ∆Tm,n C s1/2
C (2262F). In (b) melt composition is C = 3.62 %C,
(b)
for plates of various ). In (a) melt composition
• The mold’s ability to absorb heat—this property depends on the type of molding sand (Table 4) and its influence on the cell or nodule count as shown in Figs. 15a & c. From this figure it is apparent that as the molding material heat coefficient a increases, the cell, N and nodule, Nn
count also increase.
• Casting modulus—an example of the influence of the casting modulus, M on the cell, N and nodule, Nn
count is shown in Figs. 15b & d. From this fig- ure is it can be observed that both, the cell and nod- ule counts decrease as the magnitude of the casting modulus increases.
47
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