Bearing Design: Power Loss Reduction and Ceramic Bearing Recommendation

This article discusses bearing design, power loss reduction, and ceramic bearing recommendation. It covers the parameters to keep in mind while designing a bearing, the advantages of ceramic bearings, and ways to reduce power loss. The article also provides references for further reading.

Student number:
Section B: Bearing design
Solution : (a) Load (P) = 500 KN
Starup load = 0
Shaft diameter = 500 mm
Inside dia (di) = 550 mm
N = 3000 rpm
Cdmin = 0.0015
Considering ISO Grade 46
Viscosity index = 95
Bearing inlet temperature = 600c
Ra = 0.5 μm
Actual mean pressure < 2.5 MPa
Total power loss (KW) = 2 π Tr n
= 2 π x 50 x 3000 = 942.477 kw
Minimum film thickness allowed (h0) = R – (r + ε)
h0 = 275 – (250 + 0.338) = 24.662 μm
ε =0.338
Diametric clearance (Cd) = d x Cdmin
= 500 x 0.0015 = 750 μm
Cr = 0.5 Cd = 375 μm
hmin = Cr (1 -ε ¿ = 375 (1-0.338) = 248.25 μm
Actual mean pressure = P/π(R2-r2) = 500/ π (5502 -5002) = 30.315 MPa
Actual
mean
pressur
e (MPa)
Pad
insid
e dia.
(mm)
Pad
outer
dia.
(mm)
No
of
pads
Min.
film
thicknes
s (μm)
Min film
thicknes
s
allowed
(μm)
Maximu
m
allowable
roughnes
s (μm)
Max.
pad
temp
(C)
Total
power
loss
(kW)
1

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30.315 550 500 2 248.25 24.662 0.828 40 942.47
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(a) Indicate below why this design is acceptable.
Answer : This design acceptable because this is within the limit and minimum film thickness allowed
is 24.662 μm .
Answer (b) : Due to relative motion between shaft and bearing there is always a power loss occur in
overcoming the frictional resistance and also wear occurs due to metal to metal contact.
Total power loss (KW) = 2 π Tr n
Where ,
Tr = Torque in N-m
n= rpm
Eccentricity (e )= c – h0
Minimum film thickness (h0) = R – (r + e)
Radial clearance should be small to provide necessary velocity gradient and ideally c = r
1000
2

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Bearing should not be operated near critical value because slight drop in the speed or increase in the
load result in boundary lubrication.
It is having high load carrying capacity and starting friction is absent also there are no rubbing action .
The Unit bearing pressure for starting conditions should not exceed 2 N/mm2 and radial clearance
should be small to provide necessary velocity gradient.
Maximum oil fim temperature < 1200c to prevent oxidation of oil .
The following parameters you have to kept in mind while designing Bearing are :
Bearing material should have high Compression strength.
High endurance strength to avoid failure due to pitting and ability to yield and adopt its shape that of
journal called conformability .
The bearing material should be soft to allow dirt particles to get embedded in the lining and avoid
further trouble. This property is called embeddability.
Th thrust bearing is basically used to support the shaft which is subjected to load along the axis of
shaft. As a bearing design specialist we can overcome power losses for bearing on the basis of two
classifications :
(i) Foot step bearing
(ii) Collar type bearing
Power lost in Foot step bearing and Collar type bearing (P) = 2 πNT
60 watt
3

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As a specialist we can suggest to customer on the basis of design specification and on the
basis of this parameters we can overcome the power loss due to friction.
The specifications are following as :
Bearing Material Maximum Speed (DN*)
Ceramic bearing 2,000,000
Air bearing 4,400,000
Magnetic bearing 4,500,000
Foot step bearing 5,532,000
Collar Type bearing 5,800,000
Speed comparison
Ceramic type of bearing generate a very less friction and require a less maintenance than
general type of bearing .
Magnetic bearing have virtually no maintenance required and this make them specially
suitable for equipment that must be kept running.
The another parameter is Required life and it plays vital role in bearing and ceramic
bearing operates at low level vibrations and having infinite life.
In terms of costing of bearing Ceramic bearing is more expensive than steel bearing .On
the basis of above comparison we can conclude Ceramic bearing is most suitable bearing
and power loss will be minimum and in this way we can explain to client who want to
know about bearing power loss reduction so that he/she can understand which one is
having better life.
Recommendations for Ceramic bearing:
(i) High accuracy
(ii) Low or zero wear rate giving a long life.
(iii) Low noise and vibration levels.
(iv) Capability of operating at very high and very low temperatures.
(v) Little or zero need for periodic maintenance.
(vi) Nice environmental sensitivity.
(vii) Greater use of ceramic bearings in the precision machine tools can be anticipated.
(viii) High efficiency
Advantages can be taken of lower operating temperature and it is useful for low power losses.
This may be done in two ways are following as :
 By increasing the oil inlet temperature.
 By using a oil with a lower velocity grade.
Power Loss (Kw) Shaft Speed (Hz)
0 20
2 40
4

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4 60
6 80
8 100
10 120
12 140
14 160
16 180
18 200
20 220
1 2 3 4 5 6 7 8 9 10 11
0
50
100
150
200
250
Power Loss (Kw)
Shaft Speed (Hz)
References :
Iordanoff, I. (1999). Analysis of an aerodynamic compliant foil thrust bearing: method for a
rapid design. Journal of tribology, 121(4), 816-822.
Glavatskih, S. B., Fillon, M., & Larsson, R. (2002). The significance of oil thermal properties
on the performance of a tilting-pad thrust bearing. Journal of tribology, 124(2), 377-385.
Gregory, R. S. (1979). Factors influencing power loss of tilting-pad thrust bearings. Journal
of Lubrication Technology, 101(2), 154-160.
Ferguson, J. H., Yuan, J. H., & Medley, J. B. (1998). Spring-supported thrust bearings for
hydroelectric generators: influence of oil viscosity on power loss. In Tribology Series(Vol.
34, pp. 187-194). Elsevier.
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