This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Sintering Practice and Sintering Furnace – 1”.
1. Which of the following condition is necessary for obtaining consistent and satisfactory sintered components?
a) More labor cost
b) Long sintering time
c) High power consumption
d) Short sintering time
Explanation: For obtaining consistent and satisfactory sintered components, it is essential to make use of furnaces operating at the lowest temperatures for the shortest times using the cheapest possible sintering atmosphere with lowest maintenance and power consumption as well as the least labor costs.
2. On the basis of which of the following factors a sintering furnace is selected?
b) Furnace lining
c) Working temperature range
Explanation: A sintering furnace is selected on the basis of the working temperature range, type and purity of the sintering atmosphere during sintering, desired production rate, operation, and maintenance costs for a given production.
3. Which of the following are the essential parts of a sintering furnace?
a) Burn-on zone, sintering zone, and cooling zone
b) Burn-off zone, sintering zone, and cooling zone
c) Preheat zone and sintering zone
d) Sintering zone and cooling zone
Explanation: The essential parts of a sintering furnace include: (1) a burn-off zone or preheat zone for the removal of lubricants, (2) a controlled high-temperature sintering zone, and (3) a cooling and discharging zone.
4. The compacts entering into the burn-off zone must be heated ________
d) Any desired rate
Explanation: The burn-off zone, must be capable of working up to a temperature of 400-500°C. The green compacts on entering this zone, are heated slowly so as to avoid rapid heating which may result in the expansion of entrapped air and lubricants. The compact should be free from lubricant when it enters into the sintering zone.
5. Incomplete burnout leads to ________ and discoloration of the components.
a) Pungent smell
Explanation: Polymers used as lubricants decompose into methane, ethane, butane, propane, CO, CO2, H20 during heating. The decomposition starts at 150°C and is completed at 500°C. When burnout is incomplete, sooting may occur along with discoloration of the components. Sooting occurs because of the rapid rate of heating without sufficient oxygen or moisture.
6. The sintering zone must be ________ in length in relation to the burn-off zone.
Explanation: The second or the high-temperature sintering zone is longer in length than the burn-off zone to provide sufficient time to obtain the desired density and strength in the sintered parts.
7. The cooling zone of a sintering furnace is made up of _______
a) A short-insulated cooling zone
b) A short conductive cooling zone and longer oil jacketed cooling zone
c) A longer water-jacketed cooling zone
d) A short-insulated cooling zone and longer water-jacketed cooling zone
Explanation: The cooling zone of a sintering furnace is made up of two sections. The first is a short-insulated cooling zone, which allows the sintered parts to be cooled slowly in order to avoid thermal stresses, and second is a longer water-jacketed cooling zone to cool the sintered parts without exposure to air to prevent oxidation.
8. ________ type furnaces require large volumes of protective gases.
b) Roller hearth
Explanation: Mesh belt type furnaces require large volumes of protective gases as the doors are kept open during operation. In the case of roller hearth, the doors are kept closed during operation and consequently, heat losses are minimized.
9. By measuring _________ of effluent gas from the furnace continuously, the completeness of purge can be identified.
a) Dew point
b) Specific gravity
c) Carbon potential
d) Gas content
Explanation: Sintering atmosphere must be carefully controlled and thus it is essential to analyze the gas content, the specific gravity of the gases, moisture content and carbon potential of the sintering atmosphere as well as to control them. The evaluation of specific gravity of effluent gas, the completeness of purge can be identified. Bydew point analysis, the moisture content can be found out. Both dew point or carbon dioxide analysis can be used to measure of the carbon potential of the sintering atmosphere.
10. In _______, the analysis takes place in two phases, the absorption phase, and the burning phase.
a) Ortab type analyzer
b) Orsat type analyzer
c) Infrared type analyzer
d) Orson type analyzer
Explanation: In the Orsat type analyzer, a complete analysis of the gaseous mixture is divided into two phases, namely, the absorption phase and the explosion or burning phase. The constituents of the atmosphere such as carbon dioxide, carbon monoxide, and oxygen are determined by chemical absorption. Portable units available lend themselves to rapid spot analysis.
11. ________ works on the principle that each constituent of the sintering atmosphere absorbs infrared energy at a characteristic wavelength.
a) Infrared analyzer
b) Orsat type analyzer
c) Energy analyzer
d) Wave analyzer
Explanation: Infrared analyzer works on the principle that each constituent (methane etc.) of the sintering atmosphere absorbs infrared energy at a characteristic wavelength. Any change in the concentration of the particular constituent results in a change in the total energy of a beam passed through the gas.
Sanfoundry Global Education & Learning Series – Powder Metallurgy.
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