This set of Metal Casting Multiple Choice Questions & Answers (MCQs) focuses on “Solidification with Predominant Resistance in Mould”.
1. In continuous casting technology, solidification of casting starts in a thick sand mould of a closed structure.
a) True
b) False
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Explanation: In continuous casting technology, metallic mould is generally preferred. The solidification is initiated in a water-cooled open-ended copper mould. And the casting which gets shaped in the mould includes a core of liquid metal which slowly solidifies as the strand moves through the caster during the solidification.
2. Handling of very high heat flux can be possible in continuous casting technology.
a) True
b) False
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Explanation: The solidification process starts in the mould with the secondary cooling zone using a combination of water spray and radiation cooling, which maintains high heat flux. Solidification speciality of this technology arises from the dynamic nature of the casting process which relates to handling of very high heat flux in the mould.
3. Predominant resistance in mould of casting system generally produces castings of brittle nature.
a) True
b) False
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Explanation: Due to predominant resistance in the mould of casting system, the heat transfer does not occur easily. However, it can be done forcefully, but in normal way the casting produced is of ductile nature as the heat is kept within the casting for a longer time. But, inaccurate way of solidification might cause defects in the casting.
4. In the continuous casting process, there is a strong possibility of breaking of casting parts at the initial stage of solidification.
a) True
b) False
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Explanation: Continuous casting process nurtures the initial thin and fragile solid shells for the avoidance of breakout during the solidification of casting. And it also eliminates the surface and internal defects from the cast product by having the proper solidification dynamics in the casting process.
5. Minimization of friction between the mould and casting surface can reduce the chances of tearing of thin parts of the casting.
a) True
b) False
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Explanation: During solidification, prevention of sticking and tearing of the initial thin shell of the casting is a major consideration. To minimize the shell sticking and tearing, friction between the casting surface and mould wall must be kept below a critical level which depends upon the shell strength of the casting.
6. To reduce the friction between the mould’s surface and casting, a refractory coating is done to the surface of mould.
a) True
b) False
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Explanation: Minimization of friction between the mould and casting surface and for the continuous release of the shell from the mould is achieved through the introduction of mould oscillation aided by the lubrication. Refractory coating of the mould’s surface is basically done for the finishing aspect.
7. Lubrication at the interface is arises due to the infiltration of mould slag into the gap between the mould and casting.
a) True
b) False
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Explanation: Lubrication at the interface of mould arises from the infiltration of mould slag into the air gap. The motion of the mould relative to the solidified casting gives rise to a frictional force due to the viscosity of slag film. The frictional force generated through this mechanism is termed as liquid friction.
8. Which of the following formulas is used for the determination of solid friction (fs) between the mould and casting during solidification?
a) fs = ηs-H
b) fs = ηs/H
c) fs = ηs+H
d) fs = ηs*H
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Explanation: When the relative movement occurs between the casting and the solidified mould slag, then the friction force is generated by the solid-solid contact. The resulting solid friction (fs) is expressed as fs = ηs*H, where ηs is the coefficient of solid friction, and H is the Ferro-static pressure of molten metal.
9. Due to mould oscillation to minimize friction, oscillation marks formed on the surface of casting does not affect the castings.
a) True
b) False
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Explanation: The oscillation marks itself is a surface defect and its severity may prevent hot rolling. And increased thermal resistance at the bottom of mark reduces the local cooling rate which retards shell growth and coarsens the local microstructure, this can disturb the whole casting by inducing defects in the casting.
10. Analysis of frictional concept at the interface is very important and necessary for the increase in casting speed.
a) True
b) False
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Explanation: The friction concept is very useful in explaining the increased tendency of breakout with the increase in casting speed. Analysis of friction at the interface of mould and casting is done to specify the speed of the casting process or it can also be adjusted by maintaining the amount of lubrication at the gap.
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