This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Sintering Practice and Sintering Furnace – 2”.
1. The moisture content of the gas is determined using a _______
a) dew Jug
b) dew Cup
c) moisture cup
d) dew meter
View Answer
Explanation: Dew point analysis is an effective method of determining the moisture content of a gas. This is done using a ‘Dew Cup’. The apparatus consists of a glass thermometer, is kept directly in the path of the gas stream.
2. Which solution is used to fill the dew cup for carrying out moisture analysis?
a) Carboxylic acid
b) Propane
c) Ethyl alcohol
d) Acetone
View Answer
Explanation: The procedure for moisture content analysis includes- first, the dew cup is filled with acetone and the atmosphere gas is passed against the dew cup. After about 5 minutes, dry ice is added to the cup with stirring. Moisture or dew appears on the surface of the cup and the dew point is read from the thermometer in the dew cup.
3. In a more sophisticated type of indicator for moisture analysis (where the sample gas is both compressed and expanded) the _________ of the gas is converted to the dew point.
a) pressure ratio
b) heat conductivity ratio
c) volume ratio
d) temperature ratio
View Answer
Explanation: In a more sophisticated type of indicator for moisture analysis, the sample gas is compressed, and then quickly expanded. In the case the gas got cooled down below its dew point due to its rapid expansion, a fog is noticed in the expansion chamber. The pressure ratio of the gas is converted to the dew point.
4. The dew point measurement of a gas either entering or leaving a furnace gives an excellent indication of ________
a) specific gravity
b) moisture content
c) chemical potential
d) carbon potential
View Answer
Explanation: The dew point measurement of a gas either entering or leaving a furnace gives an excellent indication of carbon potential. Presence of excess moisture can lead to decarburizing of the parts in a non-decarburizing atmosphere.
5. The specific gravity analysis is especially sensitive to changes in _____
a) carbon dioxide
b) carbon Monoxide
c) methane
d) oxygen
View Answer
Explanation: The specific gravity of gases can be measured with reference to air. This analysis is particularly influenced by the changes in carbon dioxide. Because carbon dioxide is much heavier than the other sintering background components.
6. Carbon potential control is important during sintering of ______
a) tungsten
b) steel
c) silicon carbide
d) molybdenum
View Answer
Explanation: Carbon potential control of sintering atmosphere is important, particularly during sintering of steels. Equilibrium between the atmosphere and the carbon potential of the steel from getting carburized and decarburized.
7. Which of the following are the important temperature controls used in sintering furnace?
a) Thermocouple
b) Radiation pyrometers
c) On-off controllers
d) On-off controllers and proportional controllers
View Answer
Explanation: The various important temperature controls used in sintering furnace include: on-off controllers, proportional controllers and transformer controls. Thermocouple and radiation pyrometers are instruments used to measure temperature for low-temperature and high-temperature furnaces respectively.
8. The transformer controls employ a transformer whose AC is connected to______ and DC is connected to _______
a) mains, thermistor
b) thermocouple, mains
c) mains, thermocouple
d) thermistor, mains
View Answer
Explanation: The transformer control uses a transformer whose AC windings are connected to the mains while a DC winding present in the transformer is connected to the thermocouple. Any changes in the temperature are relayed to the DC windings, which in turn controls the input power to the furnace windings/elements.
9. The sintering furnace can be classified on the basis of _________
a) temperature
b) operation
c) type of heating, and temperature
d) operation, and atmosphere
View Answer
Explanation: The sintering furnace can be classified n the basis of- (1) Type of heating, such as fuel-fired or electrically-heated furnaces. (2) Type of operation, such as continuous or batch type furnaces. (3) Type of atmosphere used as muffle furnaces, controlled atmosphere furnace or vacuum furnaces.
10. _________ can operate at temperatures of 1350°C.
a) Mesh belt furnace
b) Walking beam furnace
c) Roller hearth furnace
d) Radiant tube furnace
View Answer
Explanation: In walking beam furnaces, parts are periodically lifted and moved by a lifting mechanism. It can operate at temperatures of 1350°C, because the lifting part is made of refractory baked by alloy steel. Mesh belt and roller hearth furnaces are limited by their service temperature (up to 1150°C), which in turn is dependent on the belt and roller material.
11. ________ atmosphere can be divided into dry hydrogen, exothermic and endothermic atmosphere.
a) Reducing
b) Oxidizing
c) Inert
d) Vacuum
View Answer
Explanation: The three types of atmospheres prevalent in sintering furnaces are the reducing, neutral, and oxidizing atmosphere. Reducing atmosphere can be divided into dry hydrogen or dissociated hydrogen, exothermic atmosphere with low or medium carbon potential, and endothermic atmosphere enriched with hydrocarbon gas.
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