Stream of molten metal changes its direction by 90° at sprue base where it becomes confused and the flow velocity is lowered. The shape of the sprue base is, therefore, desired to be such that the stream smoothly changes its direction with little resistance. It has been tried, in this study, to obtain a proper shape of sprue base by means of hydrodynamically analyzing the flow resistance of various sprue bases. Suitabilities of the shapes of sprue bases were evaluated by comparing the velocity coefficient or the loss coefficient due to bend calculated from the following equations :
v=C√2
gh ········(1)
C=velocity coefficient, v=flowing velocity, h=metal head
C=1/√(1+K) or C=1/√{1+K+λ(1/d)}····(2)
K=loss coefficient due to bend, λ=coefficient of fluid friction,
l=length of stream, d=diameter of stream
Experimental Procedures : CO
2 moulds with a fixed metal head (h=205mm) were made of which the sprue bases were variously altered. Metal was poured into the mould, the weight of metal flowed out and the flowing time were measured, thus the flowing velocity v was obtained by the following equation :
v=W/a·
ρ·t ········(3)
a=sectional area of outlet of sprue base,
ρ=density of metal
Thus obtained values of v were inserted into the equation (1) and the values of C or K were calculated from the equation (1) or (2)
Metal used for the experiment was ordinary commercial grey cast iron of which density
ρ was assumed to be 7.0g/cm
3. Pouring temperatures were adjusted to 1,380-1,400°C.
Experimental Results :
(1) When metal is poured into mould cavity through the gate directly from the sprue, a rounded inside corner of the connecting area of sprue and gate is extremely effective. Deep bottom of the sprue base also gives a favourable effect.
(2) When a runner is connected to the sprue, it is effective to decrease the flowing velocity of the metal just entering the runner by widening the sectional area of the runner. To choke the gate or half way of the runner is also effective. Rounded inside corner of the connecting area also gives more favourable effect in this case, however, even when the inside corner is not rounded the unfavourable effects are somewhat relieved.
(3) When the length of runner increases, the friction of runner decreases the loss due to the sprue base of no rounded inside corner, while in the case of rounded corner, the loss due to bend and the loss due to the friction of runner occur independently.
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