This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Products – Testing and Applications of Bearings”.
1. The radial crushing strength of a bearing is given by _______
a) P=KLT2/(D-T)
b) P=KLT2/(T-D)
c) P=KDT2/(L-T)
d) P=KLT3/(T-D)
View Answer
Explanation: The radial crushing strength of a bearing is given by P=KLT2/(D-T) where P=radial crushing load (kg), K=strength constant, L=length of the bearing (cm), D=outer diameter of the bearing (cm), and T=wall thickness of the bearing.
2. The ratio of interference to bore closure doesn’t rely on ______
a) density of bearing
b) rigidity of housing
c) density of shaft
d) strength of bearing
View Answer
Explanation: The ratio of interference to the ‘close in‘ of the bore (or bore closure) relies on rigidity of the housing, bearing wall thickness and strength and density of the bearing.
3. ________ clearance for higher PV values are required.
a) Small
b) Large
c) Moderate
d) Nil
View Answer
Explanation: Proper running clearance for bearing depends to a large extent on the particular application. Thus, large clearance is required for higher PV values, and small clearance is employed for high speed applications of light duty bearings.
4. __________ is used in food industries.
a) P.T.F.E bearing
b) Non-porous bearing
c) Infiltrated bearing
d) Dry-lubricated bearing incorporating graphite
View Answer
Explanation: The importance of infiltrated bearings or self-lubricating bearings lies in the fact that they are useful where external lubrication is difficult or is to be avoided and thus, they are used in food industries. Other applications include fractional horse power motors used in electric fans, sewing machines, food mixers, and office equipment.
5. _________ are employed in gearboxes.
a) Copper-lead bearings
b) Lead-tin alloy
c) Self-lubricating bearing
d) Infiltrated bearing
View Answer
Explanation: Copper-lead bearings are employed in automotive applications and for low duty applications in compressor and gearboxes.
6. Overlay layer of lead-tin alloy on copper-lead alloy has reduced fatigue properties.
a) True
b) False
View Answer
Explanation: The copper-lead bearing alloys having an overlay layer of lead or lead-tin alloy are used for heavy duty applications because this overlay confers excellent fatigue properties to the bearing besides improving anti-seizure characteristics and corrosion resistance to oil.
7. _________ are used in hot water circulating pump.
a) P.T.F.E bearing
b) Non-porous bearing
c) Infiltrated bearing
d) Dry-lubricated bearing incorporating graphite
View Answer
Explanation: Dry-lubricated bearing incorporating graphite are used in hot water circulating pump. The production of such bearing involves blending the metal powder and fine natural graphite, compacting in mechanical or hydraulic presses, sintering and finally recompacting at higher temperature. Other applications include: in pumps handling styrene for chemical industry, in loom for the textile industry.
8. Which of the following is not a feature related to the P.T.F.E material for bearings?
a) Low coefficient of friction
b) Sintering temperature is 90°C
c) Sintering temperature is 900°C
d) Chemical stability from -200°C up to 300°C
View Answer
Explanation: P.T.F.E, a plastic, has an extremely low coefficient of friction (0.015), apparent density of between 0.51-0.57 g/ml, possess chemical stability from -200°C up to 300°C in the presence of most corrosive agents and is available as a powder which can be compacted, sintered or hot pressed or hot extruded or hot rolled into large piece components. The sintering is done at 90°C in air for about 90 minutes.
9. Which of the following is a drawback of the P.T.F.E material for bearings?
a) High thermal expansion
b) High thermal conductivity
c) High shear strength
d) Non-toxic
View Answer
Explanation: The major drawbacks of the P.T.F.E material for bearings are-(1) low shear strength which restricts the bearing load, (2) high thermal expansion, (3) low thermal conductivity which results in an inability to dissipate heat developed at the bearing surface, (4) toxicity of inhaled fumes or dust, and (5) the use of solid P.T.F.E bearings is limited to below 200°C.
10. Which of the following are methods for impregnating the metallic matrix with P.T.F.E, according to Blainey?
a) Hot pressing
b) Hot rolling, and aqueous impregnation
c) Hot rolling
d) Hot pressing, and aqueous impregnation
View Answer
Explanation: According to Blainey, two methods namely hot pressing, and aqueous impregnation can be commonly used for impregnating the metallic matrix with P.T.F.E. The former method consists in placing a P.T.F.E sheet on the porous metal, and extruding the plastic into the pores under the simultaneous action of both heat and pressure.
11. Which of the following is the limitation of aqueous impregnation method?
a) Easy to get a penetration depth > 0.01”
b) Suitable for flat sheets only
c) Suitable for curved sections only
d) No loss of P.T.F.E by extrusion
View Answer
Explanation: The limitations aqueous impregnation method includes: (1) It is very difficult to get a penetration depth >0.01”. (2) Suitable for flat sheets only. (3) Bulk of P.T.F.E may be lost by extrusion around the porous metal strip.
12. The performance of P.T.F.E /metal bearings largely depends on _________
a) Base material
b) Compacting pressure
c) Journal material
d) Sintering temperature
View Answer
Explanation: The performance of P.T.F.E/metal bearings is largely dependent on the journal material. The table below shows the effect of sleeve material on the performance of P.T.F.E-impregnated thrust washers which suggests that the bearing life increases with lowering of PV values.
| Sleeve Material | PV=20,000 | PV=40,000 |
| Mild Steel | 50 | 25 |
| Sintered Cu-Pb | 10 | 3 |
13. DQ and DQ2 are the two types bearings produced by Glacier Metal Co. Ltd. by dispersing brass and Pb respectively.
a) True
b) False
View Answer
Explanation: Glacier Metal CQ. Ltd. has produced bearing materials consisting of dispersed metal powder (bronze or Pb) by 20% volume within the P.T.F.E matrix which not only improves the strength and performance but thousand-fold improvement in wear resistance occurs. These are of two types- DQ (filled with bronze powder) and DQ2 (filled with Pb powder).
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