This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Forces Acting on Cores and Mold”.
1. Cores generally experience a single force called gravitational force in the mould.
a) True
b) False
View Answer
Explanation: When the core is placed in the mould, mainly two types of forces are present, one is the gravitational force acting on the core and another is buoyancy force which tries to lift the core in an upward direction due to the density difference between the core and metal. Core is generally lighter than the metal, which is used for the casting process.
2. In the mould, the heat experienced by the core is much severe than that of experienced by the mould wall.
a) True
b) False
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Explanation: In the mould, the core is surrounded by the molten metal, so it experiences more thermal load as compared to the mould wall. The mould wall experiences the heat which is exposed to the molten metal from one side only, but in the case of the core it is surrounded from all the sides. So, the heat experienced by the core is much severe.
3. The buoyancy force is generated only due to the weight of the core inside the mould.
a) True
b) False
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Explanation: In the mould, the core experiences the static pressure as well as the weight of the core. When these two worked together in combination, then there is a lifting of the core due to the force which is called as buoyancy force. This force acts onto the core because of the density difference of the molten metal and the core material used.
4. Refractoriness required in the core should be lower than that required in the moulding sand.
a) True
b) False
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Explanation: Thermal load experienced by the core is much greater than that of experienced by the mould walls. So it is required that the core is able to bear the mechanical loading as well as the thermal loading. So, refractoriness required in the core should be higher than that required in the moulding sand.
5. Coarse sand grains of the core material can improve the refractoriness of the core.
a) True
b) False
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Explanation: The coarse sand grains of the core material are used so that the better refractoriness of the core can be achieved. Sometimes special binders are also used in the core making process to induce better mechanical and thermal properties in the core like hot strength which is very important because core experiences extreme thermal load.
6. Collapsibility of the core material is not considered in the core making process.
a) True
b) False
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Explanation: Collapsibility of the core material is very important and required in the core making process because after the solidification the core is pressurized from all the sides due to contraction of molten metal in the mould. So, the core is expected to collapse under these situations. And if it does not collapse then it causes defects like hot tearing and cracks in the castings.
7. Friability and crumbling are the properties which help in removing the core material from the solidified casting.
a) True
b) False
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Explanation: Friability and crumbling are the properties of the core material which helps in breaking and removing of core from the solidified casting part. So, these two properties are important in breaking of cores. Removal of the cores becomes easier when the friability and crumbling properties of the core sand is better.
8. Green sand core is normally used for producing shallow features in the casting components.
a) True
b) False
View Answer
Explanation: In general, the strength of the green sand core is less. So it cannot be used in the production of castings with deep or complex features, means it is normally used for producing the shallow features in the casting components. Because when the castings are made with deeper features, then the cores will have tendency to get break. So for limited features, green sand cores are preferred.
9. Increase in content of the binders in the core sand always increases the porosity of the core material.
a) True
b) False
View Answer
Explanation: Increase in content of the binders in the core sand basically holds the sand grains together tightly and reduces the pore size in the core sand. So generally, there is a tendency for a reduction in the porosity of the core material. And the hardness of core sand increases continuously with the increase in the concentration of the binders.
10. Centrifugal casting is a method of casting which works on the principle of centrifugal force.
a) True
b) False
View Answer
Explanation: Centrifugal casting is a technique which works on the principle of centrifugal force. Centrifugal force is a force that draws a rotating body away from the axis of rotation. This is basically caused by the inertia of the body. In this method of casting, molten metal is poured in the horizontal mould which rotates at high speed to form hollow castings.
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