This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Furnaces for Melting”.
1. For melting of cast iron, which of the following furnace is used?
a) Rotary furnace
b) Cupola furnace
c) Pit furnace
d) Electric furnace
Explanation: Cupola is a heavy furnace and has the capability to melt down heavy metals like cast iron. Hence, the Cupola furnace is mostly used to melt cast iron for casting purposes.
2. Why is sand bed prepared for melting of metal in Cupola furnace?
a) It provides a refractory bottom
b) It soaks the moisture from the metal
c) It conducts the heat faster and uniformly
d) None of the mentioned
Explanation: A sand bed needs to be prepared because it provides a necessary refractory bottom for molten metal and coke.
3. What is the function of slag hole in a cupola furnace?
a) To tap the slag generated
b) To generate the slag
c) To allow outflow of gases
d) All of the mentioned
Explanation: Slag hole is a tapping hole in cupola furnace. Through which slag generated during the melting process is tapped.
4. Incoming air pressure and quantity in cupola furnace are controlled by which of the following element?
b) Tapping spout
c) Wind box
d) Blast pipe
Explanation: The air enters the cupola through the tuyers. But the air blowers in the wind box controls the requisite pressure and quantity of air coming inside.
5. Which of the following chemical compound, is the most common flux added to the charge in a cupola furnace?
c) Carbon dioxide
Explanation: Limestone (CaCO3) is used as Flux in cupola furnace in a proportion of about 2-4% of the metal charge.
6. Which of the following metal has a melting point of about 1537oC and latent heat of fusion 65.0 cal/g?
Explanation: Iron is the metal having melting point of about 1537oC and latent heat of fusion of 65.0 cal/g. It has a mean specific heat of 0.141 cal/g-oC and heat required for melting 1 Kg of iron is 1168 kJ.
7. Electric arc furnaces are most suitable for which of the following type of material?
c) Both ferrous and nonferrous
d) Neither ferrous nor nonferrous
Explanation: Electric furnaces are more suitable for ferrous material in larger capacity.
8. There is no direct contact of flame and metal in which of the following type of furnace?
c) Electric arc
Explanation: In Crucible furnace, metal is placed in a crucible of refractory material. The crucible is heated with electric resistance.
9. What is hearth in a furnace?
a) The electrodes are often called hearth
b) The walls of the furnace
c) The bowl shaped bottom of the furnace
d) The dome shaped roof of the furnace
Explanation: The hearth is that bowl shaped bottom of the furnace. It is made up of a high refractory material (bricked and granular).
10. Why are flux added to the charge ( parent metal to be melted) during melting of a metal?
a) To increase carbon content
b) To increase refractoriness
c) To add specific oxides
d) To remove specific oxides
Explanation: The flux is a chemical substance, added to the metal while melting it to remove oxides present in the metal.
11. In an induction furnace, mixing and melting rates are altered by?
a) Controlling the temperature ranges only
b) Controlling the number of electrodes used only
c) Controlling power and frequency of current only
d) All of the above factors
Explanation: Due to the principle of induction used, the electromagnetic fields are produced. These EMF’s are used to stir the metal. Hence, controlling the power and frequency, Mixing and melting rates can be altered.
12. Which of the following is/are the advantage(s) of an Induction Furnace?
a) Higher yield
b) Cleaner melting
c) Compact Installation
d) All of the mentioned
Explanation: Advantages offered by Induction Furnace are higher yield, faster startup, cleaner melting, natural stirring and compact installation.
13. Which of the following metal has a melting point of about 420oC and latent heat of fusion 26.3 cal/g?
Explanation: Zinc is the metal having melting point of about 420oC and latent heat of fusion of 26.3 cal/g. It has a mean specific heat of 0.101 cal/goC and heat required for melting 1 Kg of Zinc is 285 kJ.
14. Which of the following metal has a melting point of about 660oC and latent heat of fusion 92.7 cal/g?
Explanation: Iron is the metal having melting point of about 660oC and latent heat of fusion of 92.7 cal/g. It has a mean specific heat of 0.237 cal/goC and heat required for melting 1 Kg of iron is 1022 kJ.
15. Gas-Fired burner is used in which of the following furnace?
a) Induction Furnace
b) Reverberatory Furnace
c) Cupola Furnace
d) Crucible Furnace
Explanation: Reverberatory furnace use gas-fired burner, located higher in the Furnace transferring heat by radiation to the wall and roof.
16. What is inoculation of cast iron?
a) Addition of sulphur alloys
b) Addition of silicon alloys
c) Addition of oxides
d) Addition of parent metal’s ore
Explanation: Inoculation of cast iron is addition of certain silicon alloys to molten iron to produce changes in graphite distribution.
17. Why is inoculation done certain times during melting of cast iron?
a) To enhance its mechanical properties
b) To reduce the liquid shrinkage of metal
c) To enhance the surface finishing
d) All of the mentioned
Explanation: A certain amount of silicon alloys are added to the molten metal to enhance its mechanical properties and for reduction of chilling speed.
18. Which of the following is/are not used to melt material in casting(foundry) industries?
a) Cupola furnace
b) Induction furnace
c) Ladle furnace
d) Crucible furnace
Explanation: All of listed are the furnaces used by metal foundry industries to melt down metal for casting purposes, except Ladle furnace.
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