This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Functions of a Riser”.
1. Exothermic material does not contain which of the following metal oxide?
Explanation: Exothermic materials are those which generate a lot of heat because of exothermic chemical reactions. Exothermic materials do not include oxides of magnesium.
2. Iron oxide reacts with which metal to give aluminium oxide?
Explanation: When iron oxide reacts with aluminium, aluminium oxide and free iron atoms are formed, and a lot of energy in the form of heat is released.
3. How many moles of iron oxide are needed to react with 8 moles of aluminium to form 4 moles of aluminium oxide?
Explanation: According to the exothermic reaction, when 4 moles of iron oxide would react with 8 moles of aluminium, 4 moles of aluminium oxide and 8 moles of iron atoms will be formed.
4. Up to what percent is the efficiency increased by using exothermic materials?
Explanation: The use of exothermic materials causes to increase the efficiency by around 70%. The use of exothermic materials also causes the riser to be of only one-third its regular size.
5. Heat diffusivity does not depend on which of the following?
a) Thermal conductivity
b) Specific heat
c) Latent heat
d) Density of the material.
Explanation: Heat diffusivity depends on thermal conductivity, specific heat and the density of the material, by the formula heat diffusivity = (kcp)1/2. Hence, heat diffusivity does not depend on latent heat.
6. How high can solidification rate factor be increased by metal chills?
Explanation: The solidification rate can be increased by a factor as high as 14, relative to that which is obtained in sand molds, by metal chills.
7. Chills promote only directional solidification.
Explanation: In a particular portion of casting, to speed up the process of solidification, chills are used. Chills are used for directional solidification as well as progressive solidification.
8. With an increase in the volume of castings, how would it affect the freezing time?
c) Will not change
d) No relation
Explanation: According to Chvorinov’s rule, freezing time is directly proportional to the square of the volume. Therefore, an increase in the volume of the casts will cause a lot of increase in the freezing time.
9. Which of the following materials are not used for making chills?
b) Cast iron
Explanation: For making chills, steel, cast iron and copper is widely used. But zinc metal is not used for this. Copper is used even more for chilling, as it provides the highest conductivity.
10. External chills can be used again and again.
Explanation: External chills can be used over and over again many times. But the same cannot be said for internal chills.
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