A summary of the investigation on improvement of the yield of casting.
To improve the yield of casting, following factor will be considered:
the loss due to the riser, the loss due to the gating system and the loss due to the inferiority of the products.
Among them, the loss due to the riser is the greatest, and by minimizing this loss, the yield rate of the casting will be elevated to above 80%.
Of course, such effort should not cause the wrong effect to the economical conditions.
In many case the shape of the raise is cylindrical, and its diameter is equal to its height.
In this case, the time required for solidification of the metal is given by;
[Written in non-displayable characters.] ⋅⋅⋅⋅⋅⋅⋅⋅ (6)
where,
t
s : the time required from the pouring, to the beginning of the solidification,
t
c : the time required from the beginning to the end of the solidification,
γ : specific gravity of the molten metal,
c : heat capacity of the molten metal,
q : latent heat of solidification of the metal,
θ0 : the pouring temperature of the molten metal,
Ⓗ : solidificating temperature of the metal,
X=V⁄(S)=Volume of the feeder head⁄(Surface area of the riser)
B : heat diffusion rate of the mold.
The term X
2/B
2 is only concerned with the mold, and the term inside of { } is only concerned with the characteristics of the molten metal.
Now, consider two cases using different material for the mold of the raise: the one, using ordinary casting sand, shown by the symbol Rf, the other, using the heat insulating matarial, such as ceramics.
In these two cases, if the same condition of the molten metal is adopted, the terms inside of { } are the same, then from the eq. (6),
Rf solidification time : Rd solidification time
=X
f2⁄(
Bf2
) : X
d2⁄(
Bd2
)
If the time required for solidification in these case are the same,
X
f⁄(
Bf
)=X
d⁄(
Bd
) ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ (9)
And if the shapes of the raises are similar each other, consequently X=V⁄(S) ∝d, then eq. (9) becomes;
Bd
⁄(
Bf
)=d
d⁄(d
f) ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ (10)
Jf
Bd
⁄
Bf
=x, then d
f/d
f=x, consequently
Volume R
d⁄(Volume R
f)=x
3 For example, if
Bd
⁄
Bf
=X=½, the equation above becomes 1/8.
This fact induces following conclusion;
“A heat insulating material is essentially effective for the mold.”
The formulae of B is expressed;
B=√
γ•C•
λ λ : heat conductivity of the mold material.
To decrease the value B, a material having low value of
γ must be chosen.
Considering economically, we chose the material No.083 for the mold of raise.
The practical datas using this material were well brought in line with the theory above mentioned.
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