1 書書: Essentials of Mechanical Engineeri ng Design, 1/E 書書: Shigey Mischke Budynas 書書: MX0398
Jan 03, 2016
1
書名: Essentials of Mechanical Engineering Design, 1/E作者: Shigey Mischke Budynas書號:MX0398
2
3
4
5
8-2 Bearing lifeCommon life measure:
• Number of revolutions of the inner ring (outer ring stationary) until the first tangible evidence of fatigue
• Number of hours of use at a standard angular speed until the first tangible evidence of fatigue
Rate life (90%)-minimum life, L10 life and B10 lifeMedian life is the 50% (or average life)
6
7
In above equation:
a=3 for ball bearing
a=1/3 for roller bearing
a
DDDa
RR nLFnLC /1/110 )60()60(
Catalog rating lb or kN
Rating life in hours
Rating speedrpm
Desired life
8
9
Reliability set x=L/L10 by Weibul distribution Minimum
value of the variate
Characteristic parameter
corresponding to the 63.2121
percentile value of the variate
10
11
Along a constant reliability contour (BD)
Along load line (AB)
But FB=C10
B 0
0
1/0 0
1/
1/0 0
exp
1( )(ln )
( )1
( )(ln )
b
D
bB
D
aD DB D D
bR
D
x xR
x
x x xR
x xF F F
x x xR
12
13
Equivalent load
Axial load
Radial load
V=1 when inner ring rotate
V=1.2 when outer ring rotate
V=1 for self aligning bearing
Common expression
14
C0 : basic static load rating
15
16
17
18
19
20
21
K
22
Damage done by equivalent loads Fe1,Fe2 and Fe3 is
In general form
Eq. 8-10 can be written as
→
→
23
24
33
22
11
332211
332211
332211
equals alsoK and
and
lL
Kl
L
Kl
L
KLFlFlFK
LFLFLFK
lFlFlFLF
ae
ae
ae
ae
ae
ae
ae
ae
aeeq
aeq
For continue load
0dFdDD
dFdD
a
a
25
26
27
28
29
30
31cot389.0Kαis the half the include cup angle
32
Location of reactions
33
Relating load, life and reliability
Solve for xD gives
xD=L/L10
For Weibull model: x0=0, θ=4.48,b=3/2
For roller bearing:
a
D
bDD F
CRxxx )()1)(( 10/1
00
210/3103/2 )()1(48.4D
DD F
CRx
34
35
36
Timken:
37
38
39
40
41
42
43
44
45
Outline of design assessment:
1. Bearing reliability for the load imposed and life expected
2. Shouldering on shaft and housing satisfactory
3. Journal finish, diameter and tolerance compatible.
4. Lubricant type according to manufacturer’s recommendations; lubricant paths and volum supplied to keep operating temperature satisfactory
5. Preloads, if required, are supplied
46
Bearing Reliability
For x0=0, θ=4.48, b=3/2
47
48
49
50
51
52
8-11 Lubrication
Elastohydrodynamic lubrication
Purpose of the antifriction-bearing lubricant:
1. To provide a file of lubricant between the sliding and rolling surfaces.
2. To help distribute and dissipate heat.
3. To prevent corrosion of the bearing surfaces.
4. To protect the parts from the entrance of foreign matter.
53
54
55
Preloading
Alignment
Enclosures