This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Products – Porous Bearings and Types – 2”.
1. What is the PV value for thrust bearings?
a) 10,000
b) 50,000
c) 20,000
d) 30,000
View Answer
Explanation: The performance factor or PV value for thrust bearings is 10,000 whereas in the case of a porous bearing, a PV value of 50,000 is usually specified.
2. The load carrying capacity of bearing is expressed as the _______
a) efficiency factor
b) work factor
c) performance factor
d) capability factor
View Answer
Explanation: The performance factor is used to express the load carrying capacity of the bearings. The load carrying capacity of porous-metal bearings is usually measured based on the friction/wear criterion, which signifies the heat generated by the bearing.
3. Which of the following is not a characteristic of a P/M bearing material?
a) Ability to withstand both static and impact loads
b) Good wear characteristics
c) Good heat dissipation capacity
d) Short service life
View Answer
Explanation: The important requirements of a P/M bearing materials are: good lubrication characteristics with minimum maintenance and long service life, adequate mechanical strength, good wear characteristics, good heat dissipation capacity, ability to withstand both static and impact loads, and must not weld/seize with the mating parts (e.g. shafts) during service.
4. ________ type of porosity serves no purpose and must be minimized.
a) Moderate
b) Open
c) Closed
d) Interconnected
View Answer
Explanation: Closed porosity refers to the amount of isolated or closed pores within the material. These pores do not serve any useful purpose and must be minimized.
5. Which type of porosity is connected to one another and to the external surface?
a) Moderate
b) Open
c) Closed
d) Interconnected
View Answer
Explanation: Interconnected porosity refers to that fraction, which are connected to one another and to the external surface. The main feature of these bearings is that the presence of interconnected pores enables flow of fluids to flow through these pores.
6. _______ is obtained by subtracting the density (%) of the material from 100.
a) Hardness
b) Porosity
c) Specific gravity
d) Ductility
View Answer
Explanation: Porosity is usually expressed as a percentage and is obtained by subtracting the density (%) of the material from 100. The pores represent the open volume in a given material and can be classified as closed and interconnected porosity.
7. _________ is possible only with the help of a pump during starting.
a) Hydrostatic lubrication
b) Boundary film lubrication
c) Hydrodynamic lubrication
d) Aerodynamic lubrication
View Answer
Explanation: Hydrodynamic lubrication is one of the mechanisms through which the lubricant operates. This mechanism is possible only with the help of a pump during starting. It is highly desirable, since the hydrodynamic pressure developed by the relative movement of the bearing and the shaft will enable the bearing to carry the applied load without contact between the bearing and the shaft.
8. Under which of the following mechanisms the bearing performance depends on the ability of the lubricant to maintain a boundary film under load?
a) Hydrostatic lubrication
b) Boundary film lubrication
c) Hydrodynamic lubrication
d) Aerodynamic lubrication
View Answer
Explanation: The mechanism in which part of the entire load is also carried by the sliding contact between the bearing and the shaft furnaces, which is separated by a thin film of lubricant is known as boundary film lubrication. In this case, the bearing performance depends on the ability of the lubricant to maintain a boundary film under load.
9. The performance factor is given by ______
a) PV
b) VF
c) AV
d) FA
View Answer
Explanation: The load carrying capacity of the bearing is expressed as the performance factor given by PV. This factor is expressed in lb/in2.ft/min, is obtained by multiplying pressure (lb/in2) on the projected area (length X diameter of the bore) by the peripheral or surface or rubbing speed (ft/min).
10. Which of the following is not a type of bearing?
a) Steel backed steel
b) Teflon bearing
c) Babbit backed steel
d) Unbacked bearings
View Answer
Explanation: The various type of bearings available are: (1) Steel backed materials with non-porous sintered lining, (2) Steel backed materials with porous sintered lining, (3) Unbacked porous sintered metallic parts impregnated with oil, (4) Unbacked porous sintered metallic parts containing graphite as a dry lubricant, and (5) Teflon bearing.
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