This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Electric Furnace”.
1. Which of the following is the maximum temperature limit of the electric arc furnaces?
a) 1200 ⁰C
b) 1400 ⁰C
c) 1600 ⁰C
d) 1800 ⁰C
Explanation: The electric arc furnaces can be defined as the furnaces in which charged materials are heated by the application of an electric arc. In general, these furnaces exist in all the sizes, from the smallest to the largest one having capacity of nearly about 400 tons. The electric arc furnaces can achieve temperatures up to 1800 ⁰C.
2. An air-cooled roof is used in the electric arc furnaces for making the steel metal.
Explanation: The electric arc furnaces are widely used for making steel metal, it basically consists of a water cooled roof which shapes like a section of a sphere. These furnaces also include graphite electrodes which normally enter into the furnace through the roof which can be refractory lined or water cooled.
3. Thread couplings are widely used for the addition of new segments of electrodes in the electric furnaces.
Explanation: An electric furnace mainly has three electrodes which are made round in section, and typically in segments with threaded couplings, so that new segments can be added during wearing of electrodes. Then the charged material is heated by the passing of current through the charge and the radiant energy which is developed by the arc.
4. In electric arc furnaces, the handling and maintaining of electrodes are done by manual means.
Explanation: In electric arc furnaces, almost all the processes are performed with automation. For example, a positioning system is used that automatically raised and lowered the electrodes in the furnaces. A regulating system is also used which basically maintains uniformity in electric current and power input during the melting of the charge materials.
5. Which of the following processes is known for pouring of molten metal by tilting the furnace?
Explanation: The electric furnace is generally built on a tilting plane so that the molten metal can be poured into another container for transportation. The process of tilting the furnace to pour the molten metal is known as tapping. Electric arc furnaces are widely used only where there is plentiful electricity.
6. Slag formation does not take place in the molten metal by using the electric arc furnaces.
Explanation: Slag formation does not depend on the type of furnaces; it basically depends upon the type of metal used and the surrounding gases. Slag usually floats on the surface of molten metal which consists of metal oxides. It acts as a source of oxidized impurities and can help for reducing the erosion of the refractory lining material.
7. Which of the following is the primary benefit of using the electric furnaces for melting the metals?
a) High productivity
b) Better quality of materials
c) High strength of metals
d) Less maintenance
Explanation: The primary benefit of using the electric furnaces is the large reduction in the specific energy required to produce the metal. The ratio, energy per weight of the metal is reduced by using the electric furnaces for melting the metals, which directly hikes the productivity. So this method has high productivity.
8. In electric arc furnaces, the metal loss is very less due to electrical heating.
Explanation: In electric arc furnaces, the arc produces a heating effect by the radiation and current resistance to melt the scrap materials. An essential advantage of using electrical heating is the minimum metal loss, which basically results in high productivity and better optimization of the melting system.
9. Energy losses are minimum and optimized in the electric arc furnaces during melting metals.
Explanation: Energy losses from the surfaces are large due to the large surface area to volume ratio of the electric furnaces that results in abundant energy losses during the operation of melting metals. These losses also arise through the refractory walls and roof due to the large surface area of the furnace.
10. The process of de-slagging is mainly carried out to remove the slag impurities from the furnace.
Explanation: In electric furnaces, the process of de-slagging is mainly carried out to remove the slag impurities from the furnace. During the refining process, some of the undesirable metals are oxidized and enters into the slag phase. So the furnace is tilted to pour out the slag from the furnace through the slag door.
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