This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Production of Porous Bearings – 1”.
1. _______ are bearings containing bronze or iron powder mixed with graphite.
a) Hydrocarbon impregnated
b) Oil impregnated
c) Plastic impregnated
d) Metal impregnated
View Answer
Explanation: The production of porous bearings involves its infiltration with either oil or plastic. Oil impregnated bearings are typically bearings containing bronze or iron powder mixed with graphite.
2. Tin powder is made by _________
a) Atomization
b) Electrolysis
c) Reduction
d) Cold stream process
View Answer
Explanation: For the production of porous bearings of tin by powder metallurgical route involves production of tin powder by atomization. It consists of mechanically disintegrating a stream of molten metal into the fine particles by means of jet of compressed air, inert gases or water.
3. _______ base bearings, atomized or reduced powders are employed.
a) Bismuth
b) Bronze
c) Iron
d) Tin
View Answer
Explanation: For iron base bearings, atomized or reduced powders are employed. Powders of bronze base bearings use elemental copper made by electrolytic, atomized or reduction route whereas tin powder is made by atomization.
4. Mixing of elemental powder is essential prior to compaction.
a) True
b) False
View Answer
Explanation: Mixing of elemental powder is essential prior to compaction. For making bronze bearings, copper powder is mixed with tin and graphite powders and thus it is important to ensure through mixing to avoid segregation of tin particles during sintering resulting in non-uniform sintering.
5. Green density distribution is an important factor for production of porous bearings.
a) True
b) False
View Answer
Explanation: Green density distribution is an important factor for production of porous bearings because uneven green density distribution may cause non uniform sintering or poor oil impregnation.
6. What is the compaction pressure range used for bronze bearings?
a) 775-1000 MPa
b) 500-800 MPa
c) 275-480 MPa
d) 200-300 MPa
View Answer
Explanation: The mixed powders are compacted to the required dimensions using automated compaction presses. Pressures used for bronze bearings are in the range of 275 to 480 MPa. For iron parts, higher pressures are employed.
7. The microstructure of sintered copper base self-lubricating bearing consists of ________
a) pores
b) graphite particles
c) alpha phase, graphite particles
d) alpha phase, graphite particles, and pores
View Answer
Explanation: The copper base self-lubricating bearing consists of copper + tin + graphite powders. Thus, the final microstructure after sintering shows a three-phase structure consisting of homogenous alpha (copper-tin) phase with graphite particles and pores distributed uniformly in the matrix.
8. Which of the following atmosphere is used for the sintering of bronze bearings?
a) Reducing
b) Oxidizing
c) Protective
d) Vacuum
View Answer
Explanation: The sintering of bronze bearings is carried out in continuous mesh-belt furnaces under a reducing atmosphere. During sintering, the lubricants are driven off at a temperature between 400 and 450°C, and the low melting Sn powders melt and diffuse into copper matrix.
9. Iron base bearings are sintered at _______
a) 1500-1800°C
b) 900-1000°C
c) 800-850°C
d) 1100-1125°C
View Answer
Explanation: The sintering of iron base bearings is carried out in the temperature range of 1100-1125°C for 15 minutes, and bronze bearings are sintered in temperature range of 800-850°C for 5-8 minutes.
10. ______ is carried out after sintering of self-lubricating bearings.
a) Sizing
b) Impregnation
c) Plating
d) Joining
View Answer
Explanation: All self-lubricating bearings are ‘sized’ after sintering to control the dimensions within the allowed tolerances to enable smooth operation of the porous bearings, which require suitable clearance between shaft and housing.
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