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bearing-2-pptx.pptx
1. How Do Bearings Work
Dr H.Salmani
Faculty Member at the Technical & Vocational University
CEO of Advanced Maintenance and Repair Company (CCARM)
Psalmani@tvu.ac.ir
@CBMR
+989113006366
2. Sam Taylor-Johnson
“I believe that life is
short, and there is too
much time wasted bearing
grudges, and I like to move
on.”
3. BEARINGS
• Introduction
• History
• Classification of Bearing
• Bearing Types
• Bearing Structure
• Bearing Mounting and
Dismounting
• Bearing Lubrication
• Bearing Selection
• Bearing Failure
5. The word "bearing" incorporates the meaning of "to bear," in the
sense of "to support," and "to carry a burden." This refers to the fact
that bearings support and carry the burden of revolving axles. The
two pictures below show the most basic bearings, known as rolling
bearings.
What is bearing?
6. What is Friction ?
Friction is resistance to movement
it opposes sliding
it assists rotation
9. How did a bearing evolve ?
Bearing history - a never-ending story
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1100 B.C.
3500 B.C.
1995
1794
40 A.D.
1869
10. How did a bearing evolve ?
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* Invention of wheel
* Wheel rotates on axle
* Wear Plate + Rollers
* Inner ring + Outerring
+ Rollers
* With introduction of
cage Rolling Bearing
was created
11. Thrust Loads
or
Axial Loads
Combined Loads
Radial loads
Combination of radial
and thrust loads
This force applied
direction in radius
of the bearing
We select Bearing based on 3
Sector
Load Direction is
perpendicular of the
radius of the bearing
12.
13. Thrust Loads
or
Axial Loads
Combined Loads
Radial loads
Combination of radial
and thrust loads
This force applied
direction in radius
of the bearing
We select Bearing based on 3
Sector
Load Direction is
perpendicular of the
radius of the bearing
14.
15. Combined
Loads
Axial Loads
Load Direction is
perpendicular of the
radius of the bearing
Radial Loads
This force applied
direction in radius of
the bearing
Combined Loads
Combination of radial and thrust
loads
18. • BASEDONNA
TUREOFCONT
ACT
• 1. Rolling Contact Bearings Balls or rollers introduced between moving and fixed
elements
and it is also known as anti-friction bearings
• 2. Sliding Contact Bearing Sliding takes place between the fixed and moving element
of bearing and its also known
CLASIFICATION OF BEARING
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1
19. Rolling Element
Bearings
They are also called antifriction bearings/rolling contact bearings/rolling bearings. Load is transferred
through elements in rolling contact. These bearings locate the shaft in axial and radial direction.
Starting friction is twice as the running friction. REB is an assembly rather than single element.
There bearings are manufactured to take loads:
- Pure radial
- Pure axial (thrust)
- Combined (radial and thrust)
They are designed taking into consideration below points:
- Space limitations
- Load
characteristics
- Life fatigue
- Friction, heat
- Corrosion
resistance
- Material properties
- Lubrication 19/07/201
20. Radial + Thrust
Bearing
Axial bearings, or thrust bearings,
are designed to withstand force in
the same direction as the shaft. ...
Radial ball bearings are designed
to withstand forces that are
perpendicular to the direction of the
shaft
Thrust Bearing
A thrust bearing is a particular type
of rotary bearing. Like other rotary
bearings
between
they
parts,
permit rotation
but they are
designed to support a high axial
load while doing this
Radial Bearing
A ball bearing in which the direction
of action of the load transmitted is
radial to the axis of the shaft
The Classification of
bearing
According to the load types
21. Types of Rolling Bearings
1 Ball Bearing
A ball bearing is a type of rolling-
element bearing that uses balls to
maintain the separation between the
bearing races.
22. Types of Rolling Bearings
1 Ball Bearing
A ball bearing is a type of rolling-
element bearing that uses balls to
maintain the separation between the
bearing races.
23. Types of Rolling Bearings
1
2 Cylindrical Roller
Ball Bearing
Cylindrical roller bearings are available
in a wide range of designs, series,
variants and sizes. The main design
differences are the number of roller
rows and the inner/outer ring flanges as
well as cage designs and materials.
24. Types of Rolling Bearings
1
2 Cylindrical Roller
Ball Bearing
Cylindrical roller bearings are available
in a wide range of designs, series,
variants and sizes. The main design
differences are the number of roller
rows and the inner/outer ring flanges as
well as cage designs and materials.
25. Types of Rolling
Bearings
1
2 Cylindrical Roller
Ball Bearing
Tapered Roller
3
The inner and outer ring raceways are
segments of cones, and the rollers are
tapered so that the conical surfaces of
the raceways, and the roller axes, if
projected, would all meet at a common
point on the main axis of the bearing.
This geometry makes the motion of the
cones remain coaxial, with no sliding
motion between the raceways and the
outside diameter of the rollers.
26. Types of Rolling
Bearings
1
2 Cylindrical Roller
Ball Bearing
Tapered Roller
3
The inner and outer ring raceways are
segments of cones, and the rollers are
tapered so that the conical surfaces of
the raceways, and the roller axes, if
projected, would all meet at a common
point on the main axis of the bearing.
This geometry makes the motion of the
cones remain coaxial, with no sliding
motion between the raceways and the
outside diameter of the rollers.
27. Types of Rolling
Bearings
1
2 Cylindrical Roller
Ball Bearing
Spherical Roller
Tapered Roller
3
4
A spherical roller bearing is a rolling-
element bearing that permits rotation with
low friction
misalignment.
and permits angular
T
ypically
,these bearings
support a rotating shaft in the bore of the
inner ring that may be misaligned in
respect to the outer ring. The
misalignment is possible due to the
spherical internal shape of the outer ring
and spherical rollers.
28. Types of Rolling
Bearings
1
2 Cylindrical Roller
Ball Bearing
Spherical Roller
Tapered Roller
3
4
A spherical roller bearing is a rolling-
element bearing that permits rotation with
low friction
misalignment.
and permits angular
T
ypically
,these bearings
support a rotating shaft in the bore of the
inner ring that may be misaligned in
respect to the outer ring. The
misalignment is possible due to the
spherical internal shape of the outer ring
and spherical rollers.
29. Types of Rolling
Bearings
1
2 Cylindrical Roller
Ball Bearing
Spherical Roller
Tapered Roller
3
4
A needle roller bearing is a special type
of roller bearing which uses long, thin
cylindrical rollers resembling needles.
Ordinary roller bearings' rollers are only
slightly longer than their diameter, but
needle bearings typically have rollers
that are at least four times longer than
their diameter. Like all bearings, they are
used to reduce the friction of a rotating
surface.
Needle Roller
5
30. Types of Rolling
Bearings
1
2 Cylindrical Roller
Ball Bearing
Spherical Roller
Tapered Roller
3
4
Needle Roller
5
A needle roller bearing is a special type
of roller bearing which uses long, thin
cylindrical rollers resembling needles.
Ordinary roller bearings' rollers are only
slightly longer than their diameter, but
needle bearings typically have rollers
that are at least four times longer than
their diameter. Like all bearings, they are
used to reduce the friction of a rotating
surface.
31. BEARINGTYPES:
Can be classified according to shape of element and load type. According to the
type of element:
- Ball bearings
- Roller Bearings
According to the type of the load Some bearings can carry
both
axial and radial loads
- Radial bearings (ring bearings radial loads)
- Thrust bearings (axial loads
32. The components of a bearing
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Seal Rolling elements Innerring
Outerring Seal
Cage
35. Characteristics
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Deep g roove
ball bearing
Ang ular
contact
ball bearing
Self-alig ning
ball bearing
Ball bearings Point Contact :
Cylindrical
roller
bearing
Taper
roller
Needle
roller
bearing bearing
Spherical
roller
bearing
* Less area of contact
* Less friction
* More speed
* Less load
Roller bearings
Line Contact :
* More area of contact
* More friction
* Less speed
* More load
36. Rolling elements name the bearing
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Spherical roller
(symmetrical)
Ball Spherical roller
(asymmetrical)
Needle roller
Cylindrical roller Taperroller
40. Bearings with shields and seals
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Shields Low-friction
seals
Seals
-Z and -2Z -RZ and -2RZ -RS1 and -2RS1
Contaminant
exclusion
Silent
running
Grease
retention
Speed
capability
41. BALL
BEARINGS
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Rolling elements are balls and are used in simple bearing applications. They
have
smaller load carrying capacity when compared to similar size roller bearings.
Radial bearings:
1) Deep Groove Ball bearings (rigid, non-separable, both axial and radial
loads, highest speed limits). Both rings contain grooves and due to this
they can support high radial loads as well as some axial loads. Most
widely used ball bearings. They are not self- aligning therefore
accurate alignment between shaft and housing is required. There is a
cage to position the rolling elements
Single row deep groove ball bearings
Have continuous deep raceways.
Designed for radial loads. Can take some
axial thrust as well
44. Self-aligning
bearings
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They have 2 rows of balls with common
raceway
in the
outer ring. This enables relative positioning
of inner ring with respect to the outer ring and gives the
bearing its self-aligning property. Accommodate
misalignment due to mounting and shaft deflection.
45. Angular contact ball
bearings:
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Can support thrust loads combined with
moderate
radial loads.
The axial difference between inner
and outer rings provides the contact
angles. There are:
- Single row angular contact ball
bearings (1 directional thrust)
- Double row angular contact ball
bearings (2 directional thrust)
- Four-point (duplex) ball bearings (2
directional
thrust)
46. Thrust ball
bearing
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a) Single direction thrust ball bearings:
Carry thrust loads in one direction. They can locate shaft in 1
direction.
b) Double direction thrust ball bearing
Separable, only thrust capacity, not suitable for high speeds.
Can carry thrust loads in both directions and can locate shaft in
both directions.
47. Angular Contact Thrust Ball
Bearing
Some features of ball bearings:
-shields provide partial protection
against dirt
-seals provide better protection
against dirt
-if the bearing has seals on both
sides’ leakage is
prevented and the bearing may be
factory oiled for life
single row bearings can withstand
small amount of
shaft misalignment and deflection
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Uses same principle as its radial counterpart in terms
of raceway geometry. Capable of operating at higher
speeds due to ability to support centrifugal loads on
the balls by virtue of the inclined contact angle.
Reasonable axial load capacity and offers high
precision, typically assembled with pre-load or as
preloaded pair
48. Roller
Bearings
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In general, these bearings have greater load carrying capacity
due to increased contact surface. They require closer tolerance
on raceways and rollers. Heavier retainers are used. Some
straight roller bearings can carry NO thrust load, some can carry
thrust to a limited extend and some can carry great amount.
Radial Roller Bearings
1. Cylindrical roller bearings:
Separable, higher load carrying capacity, relatively high
rotational speeds, those with lips on inner and outer rings
can carry some thrust. Can accommodate LESS
misalignment and deflection (very sensitive to
misalignment).
Construction differs for different types where locating lips are
either present on one of the races or both. If both rings have
location lips, then axial loads can be taken. When used with
only location lips on one race relative axial movements
possible
49. Cylindrical roller bearings
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More and larger
rollers
Logarithmic contact
profile plus optimised
surface finish
Improved roller
end/flange contact
geometry
3 cage variants:steel,
polyamide, brass
NU NUP
NJ
N NJ+HJ
NU+HJ
50. 2. Needle roller
bearings
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Takes less radial space, they are long and
thin
(diameter to length ratio 2.5-
10), high load carrying
capacity.
Should not be used where misalignment
exist.
51. 3. Spherical roller
bearings
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Have two rows of rollers with a common raceway
in the outer ring. The two inner raceways are
inclined to an angle to the bearing axis.
Insensitive to misalignment. They can carry
thrust loads in
both directions in addition to radial
loads. Allowable angular misalignment
is between 1.50-30
Radial load capacity is high and high axial loads can be
accommodated with appropriate ratio of radial load, axial load
only capacity is poor and not recommended
52. Spherical roller bearings
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Symmetrical rollers
for maximum life under
any conditions
Floating guide ring
gives minimumfriction
and ensures reliable
operation
Window-type steel cages
strong and tolerant to
high temperatures
53. 4. Taper roller
bearings
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Have tapered inner and outer
raceways Suitable for
combined radial and axial
loading
They can carry axial loads in 1 direction
only (single tapered) They should be
used in pairs. Can support high loads.
54. Spherical roller bearings
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Symmetrical rollers
for maximum life under
any conditions
Floating guide ring
gives minimumfriction
and ensures reliable
operation
Window-type steel cages
strong and tolerant to
high temperatures
55. Thrust Roller
Bearings
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1. Cylindrical roller thrust bearing Carry only thrust
loads in 1 direction Locate shaft in 1 direction
Used mainly if capacity of thrust ball bearing is
inadequate. No radial loads, speed is limited
Sensitive to misalignment
2. Needle roller thrust bearing
Suitable for axial space limited application
3. Spherical roller thrust bearings
Carry radial loads in addition to thrust loads. Locate
shaft in 1 direction
Self-aligning can accommodate misalignment very
high loads and moderate radial loads
57. 4. Tapered roller thrust
bearings
Suitable for extremely high axial loads- no radial loads.
Sensitiveto face misalignment but can compensate for radial
misalignment.
Limited operating speeds, help to reduce sliding
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58. Single row and paired single row
taper roller bearings
Singlerow Face-to-face
arrangement
suffix DF
Back-to-back
arrangement
suffix DB
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60. Compact Aligning Roller Bearings
CARBTM
Safer, more optimized design
Increased service life
Lower running temperature
Lower vibration and noiselevel
Extended maintenance interval
Higher axial clearence
No internal Frictionforce
Longer life
Higher speed
Downsizing possibility
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61. CARBTM - Bearing
Compact Aligning Roller Bearing
Self-aligning as spherical rollerbearing
Permits axial displacements like a cylindrical roller bearing
Compact as a needle rollerbearing
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62. Advantages and disadvantages of rolling bearings
compared to journal bearings:
Advantages:
- Low starting friction/torque
- Ease of lubrication
- Less axial space
- Thrust and radial load
support
- Early warning against
failure
- Standard close tolerances
- Preloading is possible
- Freedom of shaft
positioning
- Special housing is available
Disadvantag
es:
- Greater radial space
- Higher initial cost
- More noise
- Possibility of early
failure
- Finite life
- Lower shock
resistance
Failure types of Rolling Element bearings:
Failure is happening due to inadequate shaft guidance,
excessive noise and vibration
1. Fatigue due to high fluctuating stresses (indications are
pitting, spalling)
2. Failure due to misalignment, unsuitable loading, lack of
lubrication, dirt/contamination
3. Outer raceway breakage due to overload
4. Cage (separator, retainer) failure- due to high centrifugal
forces at high speeds
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63. Bearings are precision products
Example:
Tolerancesfor
bore diameter
75 mm
High precision
bearing bearing
Normal Precision
T
olerance
classes
Standard P6 P5
SP
P4A
UP
PA9A
PA9B
0/-7 m 0/-2,5 m
0/-15 m 0/-12 m 0/-9 m
How much is a m
1
0,06 mm
A
human
hair
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64. Materials for rollingbearings
Bearingringsandrolling elements
1. Through-hardening steels
Carbonchromiumsteel containing approximately
1 %carbonand1,5 % chromium
2. Case-hardening steels
– Chromium-nickel alloyedsteel
– Manganese-chromium alloyedsteel
appr.0,20 % carbon
bearing steels have very highcleanliness
– thecontentof macroandmicroinclusionsis
extremelylow.
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65. Cages keep the rolling elements separated
Prevent immediate contact
between rolling elements to
minimise friction and heat
generation
Guide the rolling elements
Provide space for lubricant
Serve to retain the rolling
elements when bearings of
separable design are mounted
or dismounted
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66. Cage variants
Polyamide cage
+ lightweight
+ high elasticity
+ good sliding properties
+ good marginal lubrication
properties
- operating temperature
limit +120°C
Window-type steel cage
+ lightweight
+ high strength
+ no operating temperature
limit
+ high vibration and
acceleration resistance
- sensitive to poor
lubrication
Window-type brass cage
+ very high strength
+ very high vibration and
acceleration resistance
+ suitable for very high
speeds in connection with
circulating oil lubrication
- relatively expensive
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67. • Based on Nature ofContact
1. SlidingContact Bearing
Sliding takes place betweenthe fixedand moving elementof
bearing and its also known as plain bearing
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68. SLIDINGCONT
ACTBEARING
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• 1. Based on type of load carried
• 2. Based on type of lubrication
• 3. Based on lubrication
mechanism
Sliding contact bearings are classified in three
ways.
69. SLIDINGCONT
ACTBEARING
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• Working surfaces separated by some medium or force
• Working medium can be solids, fluids, gas or magnetic forces
(or
combination)
• Reduced local friction but can have high drag losses
•Life can become theoretically infinite due to lack of fatigue loads
and wear
• Often dependent on presence of other equipment to provide
working
media
70. BASEDONTYPEOFLOADCARRIED
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a. Radial bearings
(These bearings carry only radial loads.)
b. Thrust bearings or axial bearings
( These bearings carry only axial loads)
c.Radial – thrust bearings
(These bearings carry both radial and thrust
loads. )
71. BASEDONTYPEOFLUBRICATION
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• The type of lubrication means the extent to which the contacting surfaces are separated in
a shaft bearing combination. This classification includes
(a)Thick film lubrication
(b) Thin film lubrication
(c) Boundary lubrication
79. DESIGNATION OF
BEARINGS:
Rolling contact bearings and necessary parts used for mounting and sealing of them have been all
standardized by ISO. Bearings are designated by numbers andletters.
1. Bearing type
2. Dimension series
3. Borenumber
4. Specialshape
5. Special accuracy and clearance
Bearing type:
Numeric or alphanumeric designations are used 6- single row deep
groove ball bearings
2- spherical roller bearings 3- taper roller
bearings N-cylindrical roller bearings
….. etc
Dimension series
For each bearings size, there are standard series of outside diameter and width designations.
- The first number in the dimension series indicates the shape of the cross section of the bearings,
which is the ratio of the width to the outside diameter and called as width number.
- The second number indicates the ratio of the outside diameter to the bore diameter and called as
diameter number
Width number- 0, 1, 2, 3, 4, 5, 6
Diameter number- 8, 9, 0, 1, 2, 3, 4
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80. EXAMPL
E:
6314-ZN-C2
6- deep groove ball bearing
3- dimension series (03, 0 width is not written)
14- bore number 14x5=70mm
Z- shield (non-rubbing seal) at one side
N- snap ring groove at the surface of the outer
ring
C2- internal clearance is less than standard
6305-ZNR-P62P6+C2 closer tolerance
Bore Number
Indicates the bore diameter
of the bearing
Bore number Bore diameter
(mm)
00 10
01 12
02 15
03 17
n (n≥4) 5n
Special Shape
Numeric or alphanumeric designations are
used
Z : shield (non-rubbing seal) at one
side of bearing 2Z: Z shields at both
sides
N : snap ring groove in outside cylindrical
surface of outer ring NR: N with snap ring
F : machined cage made of steel or iron
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81. PREP
ARA
TIONFORMOUNTINGANDDIMOUNTING.
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Before mounting, all the necessary parts, tool, equipment and data need to be at hand. It
is also recommended that any drawings or instruction be studied to determine the
correct order in which to assemble the various components.
Housing, shafts, seals and other components of the bearing arrangement need to be
checked to see that they are clean, particularly any threaded holes, leads or grooves
where remnants of previous machining operation might have collected.
82. MOUNTINGMETHOD
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Depending on the bearing type, and size, mechanical, thermal and
hydraulic methods are used for mounting.
1. Cold Mounting Method.
2. Hot Mounting Method
83. COLDMOUNTING
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If the fit is not too tight, small bearings may
be driven into position by applying light
hammer blows to a sleeve placed against
the bearing ring face.
The blows should be evenly distributed
around the ring to prevent the bearing
from tilting or skewing.
The use of the mounting dolly instead of a
sleeve allows the mounting force to be
applied centrally.
84. HOTMOUNTING
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It is generally not possible to mount larger bearing in the
cold state, as the force required to mount a bearing
increasesvery considerably with increasing bearing
size.
The inner rings or the housings are there fore heated
priorto mounting.
Bearing should not be heated to more than 125c as
otherwise dimensional changes caused by
alterations in the structureof the bearing material
may occur.
Bearing fitted with shields or seals should not be
heatedabove 80c because of their grease fill or
seal material.
86. DISMOUNTINGMETHOD
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If the bearings are to be used again after removal, the force used to dismount them must
never be
applied through the rolling elements.
With separable bearings, the ring with the rolling element and cage assembly can be
removed independently of the other ring.
To dismount a bearing having an interference fit, the tools described in the following section
may be
used, the choice of tools will depend on bearing type, size and fit.
1. Cold dismounting.
2. Hot dismounting.
87. COLDDISMOUNTING
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Small bearing maybe removed from their settings
by applying light hammer blows via a suitable
drift to the ring face, or preferably by using a
puller
The claws of the puller should be placed around
the side face of the ring to be removed or an
adjacent component.
88. HOTDISMOUNTING
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Special induction heaters have
been developed to dismount
the inner ring of cylindrical
roller bearing having no
flanges or only one flange.
They heat the inner ring rapidly
without heating the shaft to any
degree, so that the expanded
ring can easily be removed.
90. Clearance
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Normal clearance Increased clearance
because of temperature
Reduced clearance
because of tight fit
Example:
6210/C3 = Deep groove ball bearing with
clearance greater than Normal
CN does not normally appear in the
bearing designation
Suffix clearance
/C1 less than C2
/C2 less than Normal
/CN Normal
/C3 greater than Normal
/C4 greater than C3
/C5 greater than C4
91. SPECIALIZED
BEARINGS:
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There are, of course, several kinds of bearings that are
manufactured for specific applications, such as magnetic
bearings and giant roller bearings.
Magnetic Bearings:
Magnetic bearings are found in high-speed devices because it has
no moving parts this stability enables it to support devices that
move unconscionably fast.
Giant Roller Bearings:
Giant roller bearings are used to move extremely large and heavy
loads, such as buildings and large structural components.
92. BEARINGLUBRICATION
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Lubrication reduces friction. It
also prevents wear and
corrosion, and guards against
solid and liquid contamination.
Theoretically, a properly
lubricated bearing operating
under ideal conditions will last
forever. This is not possible in
reality, of course. But a properly
lubricated bearing has the best
chance of achieving its maximum
service life.
93. LUBRICANTSUPLL
YSYSTEM
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Oil and grease require different types of
supply
systems.
Several oil and grease supply systems
exist that meet the needs of various
bearing applications.
Oil supply systems include: oil baths,
circulating oil systems, spray or mist
systems, and the wick feed method.
Grease supply systems include: housings
(with or without grease fittings), grease
chamber lubrication, and the grease
quantity regulator.
94. WHYLUBRICATION??
• Formation of protective film to
Reduce friction
Prevent corrosion
Remove wear particles and debris
Provide efficient cooling
Reduce wear
Shock absorption
Overall life improvement
95. LUBRICATION THEORY
• Full film
● Static
● Hydrodynamic
• Elastohydrodynamic
● Application of pressure / load
● Depends upon speeds, loads, lubricant viscosity
• Boundary layer
● Layer separation not complete
● Results from insufficient lube, incorrect lube
96. GREASE Vs OIL
When greases?
Normal speed and temp conditions
Simpler / cheaper installation
Better adhesion
Protection against impurities
Less frequent application required
When Oils?
High Speed and temp
Excellent cleaning and flushing characteristics
Can be used in recirculative systems
Can serve better in excessive dirt environment
More stable than greases
98. BEARINGLIFE
Bearing life is defined as the
Number of revolutions
that a bearing undergoes
under a constant load
( Equivalent Dynamic Bearing Load )
before
the first sign of fatigue failure occurs.
99. Calculating Dynamic Bearing Load
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G
Kr
Ka
G1
Kr1
I
II
l
a1
FrII
FrI
l
a1
a2
Kr
Ka
II
I
FrI FrII
Kr1
Stationary Electrical Machine
a2
101. Selection of bearings
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Some aspects to be considered
Available space Misalignment
Speed Life
Load/Direction Operating conditions
L10
P
= (C)p
102. Load carrying capacity
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of different bearing types having the same bore and outside
diameters
Load carrying capacity
is expressed as the basic
dynamic load rating
107. BEARING LIFE CONSIDERATIONS
VARY DEPENDING ON :
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Type of Rolling Element
1. Ball
2. Roller
a. Cylindrical
b. Needle
c. Tapered
d. Spherical
I. Symmetrical
II. Asymmetrical
108. Load carrying capacity
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L10 = basic rating life, millions of
revolutions
C = basic dynamic load rating, N
P = equivalent dynamic bearing load,N
p = exponent of the life equation
With the load P = C
the L10 life will be 1 million revolutions
0
Basic dynamic load rating C Basic static load rating C
P P0
P P0
The ISO lifeequation
s0
P0
C0
= static safety factor
= equivalent static bearing load, N
= basic static load rating, N
With the load P = C0
the static safety factor s0 will be 1
The static safety factor
s =
0
C0
P0
L =
10
P
( C
)p
110. Adjusted Rating Life
Equations:
In the basic life equation effect of bearing load on the life
is considered. However, by using adjusted bearing life
equation effects of other factors can be considered.
Index i (sometimes n) above represents difference between
100% and the required reliability (probability of a bearing to
achieve a specified life). For instance, for 95% reliability,
adjusted bearing rating life is denoted as L5a.
If bearing is operating at constant speed, it may more
convenient to express the rated life in terms of hours.
The factors a2 and a3 are independent from each other and can
be combined as a23. It is life adjustment factor for material and
operating conditions.
Lna=a1a23
L10
Lna=a1a23(C/P
)p
Reliability factor a1 – This factor modifies the calculated life
down to account for the extra level of reliability required above
90% and is based the fatigue probability principles already
applied.
Material adjustment factor a2 – For standard bearings the
factor is equal to 1. The factor addresses the potential
performance gains that can be achieved by material
processing and principally cleanliness control. For specialist
steel factors of 6 or more are quoted.
Operating condition factor a3 – This factor takes into
consideration the impact of operating conditions within the
bearing. In particular is considers the effects of the lubrication
conditions and material lubricant/environment cleanliness
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114. Example:
6208 DEEP Groove Ball bearing
is to be used in application
T=60 deg C, n=1500 rpm,
ν40=220mm2/s. P=24000N.
What is the adjusted rating life?
Solutions;
a1=1
(80+40)/2=60=dm
From fig.2 (with n=1500rpm) V1=15mm2/s
From fig.3 (with T=60C, v40=220) V=60 mm2/s
X=V/V1=60/15=4
a23=3 (from fig.4)
L=a1*a23*(C/P)^p=1*3*(32.5/24)^3=1058=
=8 million revolutions
Lh=8*10^6/(1500*60)=89 hours
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115. Equivalent bearing load (Fe
or P)
Equivalent dynamic bearing load
Used for combination of radial and
axial load. It is stationary radial
load or axial if thrust bearing, if
applied to a bearing, it will give
same life as actual loading and
rotating conditions.
A fictitious radial load is
calculated to be compared with
basic static and/or dynamic load
rating.
P is supposed to have the same
effect on bearing life as the actual
loading consisting of Fa and Fr.
19/07/2019
Combined loading P=VXFr+YFa
o P: equivalent dynamic load N
o Fr: actual bearing radial load
o Fa: actual bearing axial load
o X: radial load factor
o Y: axial load factor
o The damaged bearing fit on the shaft
o V: rotation factor
V=1 for rotating inner ring
V=1.2 for rotating outer ring (V=1
for self-aligning bearings)
X and Y depends on the bearing type
and its geometry. Plotting
116. Basic static load rating
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ISO basic load rating Co
corresponds to a stress that
gives permanent deformation
of 0,0001 of the rolling
element diameter
119. BEAR
IN
G LIFE
P
10
L = (C)p
Lnaa= a1 a SKF P
(C)p
ISO
Finite life
The SKF New Life Theory
Service life:
This is the actual life achieved by the bearing before it fails.
Infinite life
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120. Friction Under certain conditions the frictional
moment can be calculated withsufficient
accuracy
M = 0,5 . µ . F . d
M = frictional moment(Nmm)
µ= coefficient of friction
F = bearing load(N)
d = bearing bore diameter(mm)
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