This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Solidification of a Large Casting in an Insulating Mould”.
1. During the solidification of casting in an insulating mould, the heat transfer takes place from the upside of the moulding system which might cause defects in the castings.
a) True
b) False
View Answer
Explanation: During the solidification of casting in an insulating mould, the entire casting’s thermal resistance is offered by the mould material. Hence, the analysis of freezing time is done by mainly considering the thermal resistance of the moulding material. This method usually takes more time for solidification as compared to the other methods.
2. Concave, convex and plane types of metal mould interfaces are mainly considered for the estimation of freezing time of metal.
a) True
b) False
View Answer
Explanation: During the solidification of casting material in the mould, concave, convex and plane types of metal mould interfaces are mainly considered for the estimation of freezing time of molten metal. These types of interface show the different direction of heat transfer from the casting material to the mould.
3. In solidification of large casting in an insulating mould, precise calculations are made for the analysis of freezing time of the complex contours of casting.
a) True
b) False
View Answer
Explanation: In solidification, to find out the freezing time of complex contours of casting, only observations are made without any use of calculations. This is mainly done to observe the basic features to know whether the analysis made underestimates or overestimates the actual freezing time of the casting material.
4. Which of the following metal-mould interfaces show the divergent nature of heat flow from the casting material?
a) Concave
b) Square plane
c) Rectangular plane
d) Convex
View Answer
Explanation: During the solidification of casting in an insulating mould, the divergent nature of heat flow is shown by the convex type of metal-mould interface and the convergent nature is shown by the concave type interface. And plane interface reveals the straight and parallel nature of heat flow. The nature of heat flow in all three interfaces is shown in below figure.
5. More divergence of heat flow from the interface shows consequently high solidification rate of the casting.
a) True
b) False
View Answer
Explanation: Divergence of heat flow from the interface is directly proportional to the solidification rate of the casting material. More the divergence then much faster will be the solidification rate. When the heat flow is of convergent nature then consequently it will have less solidification rate of the casting.
6. The amount of heat removed from the castings is dependent on the amount of superheating in the casting.
a) True
b) False
View Answer
Explanation: The amount of heat that should be removed from casting to make it solidify is directly proportional to the amount of superheating and also to the amount of metal present in the casting or the casting volume. Conversely, the ability to remove heat from casting is directly proportional to the amount of exposed surface area of the casting.
7. Which of the following formulas is given by Chvorinov’s rule for the estimation of total solidification time (ts)?
a) ts = B/(V/A)n
b) ts = B*(A/V)n
c) ts = B*(V/A)n
d) ts = B/(A/V)n
View Answer
Explanation: According to Chvorinov’s rule, the total solidification time (ts) is the time from pouring to the completion of solidification which can be computed by: ts = B*(V/A)n, where n = 1.5 to 2.0; V is the volume of the casting; B is the mould constant; and A is the surface area, which depends on the characteristics of the metal being casted.
8. Chvorinov’s rule is commonly used for prediction of surface finish of the casting made in the mould.
a) True
b) False
View Answer
Explanation: Chvorinov’s rule is not used for the aspect of finishing of the casting. It is mainly used to ensure that the casting made in the mould will solidify before the riser. This is very necessary if the liquid metal within the riser is to effectively feed the casting to compensate for solidification shrinkage.
9. It is very necessary to use high refractoriness of mould material for the making of insulated mould.
a) True
b) False
View Answer
Explanation: The mould material used should be of high refractoriness because the mould used for the solidification of casting is to be insulated. So the mould should be capable of maintaining all the thermal resistance to withstand very high temperature for the long duration of time until the casting is made.
10. The solidification of casting in an insulating mould produces casting of hard and brittle nature.
a) True
b) False
View Answer
Explanation: During the solidification of casting in an insulating mould, the casting made is generally of ductile nature as the heat transfer to the surrounding is restricted and the casting is kept for long time in the mould which have slow solidification rate that causes coarse grain structure in the casting produced.
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