151-chap 11-1 rolling bearings (11-1 to 11-7)(v2)
TRANSCRIPT
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Chapter 11-Rolling Contact Bearing 2
earings
Rolling Contact Bearings
Sliding CB
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History
1.
As far back as 1100 BC the Assyrians and Babyloniansused rollers inserted between enormous stones andground to reduce friction.
2. The wheel based on sliding motion came later.
3. Some historians mention that lubricated chariot
wheels existed before 1400 BC.4. The bicycle introduced the need for rolling elements
(1817).
Rolling Bearing
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Chapter 11-Rolling Contact Bearing 4
Bearing Types
Rolling ElementPure radial load
(Cylindrical roller bearings)
Pure Thrust load(Cylindrical and Ball)
Combination load
(Deep groove ball, Tapered roller,
Angular contact bearings)
Sliding (Journal)
Bearings
Pure radial
Pure Thrust
Combination
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Chapter 11-Rolling Contact Bearing 5
Other Types
Magnetic bearings
Fluid/Air bearings
Micro/Nano
bearings
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Chapter 11-Rolling Contact Bearing 6
Journal Bearings
Radial
(Plain Bearings, sleeves)
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Thrust Journal Bearing
Thrust
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Why Rolling-Contact Bearings?
RCB are used to minimize the friction
resulting from relative motion performed
under load.
RCB are used to describe bearings in
which the main load is transferred throughrolling elements.
Typical applications
Gear Box
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Inner and outer races are typically pressed onto shafts or hubs
with slight interference fit to make them move with shafts
(inner race) or remain stationary (outer race)
Ball
Bearing Nomenclature
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Ball Bearing Types
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Notes on Bearings
Bearings maybe obtained with shields on one or bothsides. Shields provide a degree of protection againstdirt.
Some bearings are manufactured with seals in one orboth sides. If sealed on both sides, bearings arelubricated at the factory.
Starting friction is almost twice the running friction.
Bearings are manufactured to take eitherpure radial
load,pure thrust loador a combination of both. Bearing makers usually provide manuals to describe
the various types. (www.skf.com, www.fag.com,www.timken.com )
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Ball Bearings
Angular ball bearings have higher thrust load capacity in
one direction than Radial ball bearings
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Chapter 11-Rolling Contact Bearing 13
Roller Bearings
Roller bearings have higher load capacity than ball bearings
Roller bearings require prefect geometry
Straight roller bearing (radial cylindrical) cannot take thrust loads
Tapered roller bearings combine the advantage of ball and straight
roller bearings, they take radial and thrust loadings.
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Chapter 11-Rolling Contact Bearing 14
Roller bearings: Needle Bearings
Needle bearings have very high load ratings and require less space
Needle bearings can be used with and without races
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Chapter 11-Rolling Contact Bearing 20
Characteristics of ball Bearings
Type Approximate range of
bore sizes, mm
Relative capacity Limiting
speedfactor
Tolerance
to mis-alignment
Minimum Maximum Radial Thrust
Conrad or deep
groove
3 1060 1.00a0.7 1.0 015
Maximum capacity
or filling notch
10 130 1.2-1.4a0.2 1.0 03
Self-aligning
internal
5 120 0.7b0.2 1.0 230
Self-aligning
external
- - 1.0a0.7 1.0 High
Double row,
maximum
6 110 1.5a0.2 1.0 0.3
Double row, deep
groove
6 110 1.5a1.4 1.0 0
aTwo directions
bOne direction
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Chapter 11-Rolling Contact Bearing 21
Rolling Contact Bearing Materials
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Ch i i f A l
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Chapter 11-Rolling Contact Bearing 22
Type A ppr oxima te
maximum
size mm
Rela tive ca pa city Limiting
speed fa ctor
Tolerance
to mis-
alignment
Ra dia l Thr ust
One-directionalthrust
320 b1.00-1.15 a,b1.5-2.3 b1.1-3.0 02
Duplex, back toback
320 1.85 c1.5 3.0 0
Duplex, face toface
320 1.85c1.5 3.0 0
Duplex, tandem 320 1.85a2.4 3.0 0
Two directional or
split ring
110 1.15c1.5 3.0 02
Double row 140 1.5c1.85 0.8 0
aOne direction
bDepends on contact angle
cTwo directionsdIn other direction
Characteristics of Angular
Contact Ball Bearings
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Type Approxi m at e range of
bore si zes mm
R el at i ve capaci t y Lim i t i ng
speed
factor
Tolerance
to mis -
al ignment
Mi ni m um Maxi m um R adi al Thrus t
Seperable outer
ring, nonlocating
(N)
10 320 1.55 0 1.20 05
Seperable inner
ring, nonlocating
(NU)
12 500 1.55 0 1.20 05
Seperable inner
ring, one direction
locating (NJ)
12 320 1.55 aLocating 1.15 05
Seperable inner
ring, two-direction
locating (NUP)
20 320 1.55 bLocating 1.15 05
aOne directionbTwo directions
Characteristics of Cylindrical
Roller Bearings
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Characteristics of Spherical Roller Bearings
R lli C B i
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Rolling Contact Bearings
In selecting these types of bearings, thedesigner should take into consideration the
following:
The available space
The load and its characteristics
The desired life
The required speed
The cost
Not to design rolling bearings but to select proper
bearings for the application
Objective:
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Bearing Life
Assuming perfect mounting, adequate lubricationand protection thus failure will occurby fatigue
Bearings are subjected to millions of repeatedcontact stress (Hertezian) cycles causing spalling
(flaking or pitting) on ball or raceway. (Video 1& 3
)
Failure Criteria:
1. SKF: failure happens when a pit of diameter10-4
diameter of ball or roller is observed.2. Timken Co.: failure happens when 10-2 in2 of
surface is spalled
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Simulation of progression of fatigue
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Simulation of progression of fatigue
failure
Flake
pit
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