Chapter 14
Bearings
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Bearings
Function:
• Carry load in one or several directions while
allowing frictionless motion in other directions
Fatigue = F(Pressure, Velocity)
• 3 main types of Bearings
– Rolling Element Bearings
– Sliding Bearings
– Elastomeric Bearings
www.bharatpetroleum.com
www.me.psu.edu
2 TYPES OF ROLLING
BEARINGS
I. Ball Bearings
II. Roller Bearings
I. Ball Bearing:
Outer
race
• Ball Bearing
– Incorporates hardened
steel balls
– Steel balls geometrically
contact inner and outer
race at a point
– This creates high stresses
locally
Inner race
seals
www.duratrax.com
cage
Ball Bearings
How to Assemble
-Inner race press fit onto
shaft shoulder (FN1, FN2)
-Assembly slides into
housing (RC2) between outer
race and housing
Types of Ball Bearings
• Deep Groove Ball
Bearings
– Primarily radial load
carrying
– Thrust load equal to
25% of radial load
– Can get as large as
300K radial load
capacity
http://my.ecplaza.net/nbsinobest/12l.asp
Types of Ball Bearings
• Double Deep Groove
– Increases radial load
Types of Ball Bearings
• Angular contact ball bearing
– Increased thrust load due to increase in
lateral contact area between ball and race
www.hz-bearing.com
Types of Ball Bearings
• Thrust Bearings
– Used in applications
with significant thrust
load
http://kianho.com
Types of Ball Bearings
• Super precision ball
bearings
– Nearly perfect spheres
– High surface finish
• Applications
– High speed grinding,
milling, boring, routing
– No Vibration!!
• Ceramics
www.timken.com
– Hard
– No deformation
HOW It’s MADE:
1. http://www.youtube.com/watch?v=eGyo
MuE4gDQ
2. http://www.youtube.com/watch?v=k8SH
Ky5tXbI&feature=related
II. Roller Bearings
• Roller Bearings
– Hardened steel cylindrical rollers
– Line contact deforms into areas larger then
ball bearings
– Capable of carrying higher radial loads
Types of Roller Bearings
• Needle Bearings
– 4 joint machine
applications
– As the number of rollers
goes up the greater the
contact area
– The greater the contact
area the greater the load
www.clworldwide.com
Types of Roller Bearings
• Spherical Roller Bearings
– Centers inner race about
shaft to avoid binding
www.dclcorp.co.kr/image/Nachi3.jpg
Types of Roller Bearings
• Tapered Roller Bearing
– Support high thrust
loads (wheel bearing)
– Supports radial load (car
weight) while supporting
thrust loads (cornering)
– Wheel rotates with little
resistance/friction
www.ahrinternational.com
Types of Roller Bearings
• Thrust Roller Bearings
– Used in applications
with significant thrust
load
www.timken.com
Mounted Bearings
Precision machine
elements such as
transmissions, reducers,
right angle drives usually
incorporate un-mounted
bearings
Other Types of Bearings
• Thompson linear
bearings
• Sliding Bearings
– No rolling elements
– Sleeve over shaft
where sleeve acts like
bearing (Generally
higher friction)
– Bronze good material
due to coefficient of
friction, porosity and
wear resistance
www.intbearing.com
Other Types of Bearings
• Self Lubricating
Bearings
– Low Friction
– No lubrication needed
www.garlockbearings.com
Elastomeric Bearings
http://www.polygoncompany.com/
http://www.polygoncompany.com/
Ball Joint – 3 rotational DOF
See heim overview powerpoint
HEIM Bearing
www.lordmpd.com
Drive Link
V-22 OSPREY
Hub Spring Set
Pendulum
Spring
Gimbal
Bearing
Downstop
Pitch
Change System
Pitch
Change Bearing
Inboard
Beam
Centrifugal
Bearing
Outboard Spindle
HCL Components of V-22 Osprey
Drive Link
Centrifugal
Bearing
www.lordmpd.com
Bearing Selection see sec 14.6 – 14.10:
Selecting Bearings
Load-Life Relationship:
L2  P1 
  
L1  P2 
k
P1 = load 1, L1 = life at load 1,
k = 3.00 for ball bearings
k = 3.333 for roller bearings
Example: A ball bearing lasts 3,000 hours at 500 lb,
how long will it last at 1,000 lbs? SIMPLE!
Selecting Bearings Cont’d
L2  P1 
  
L1  P2 
C
Ld  
 Pd
k
Most manufacturers specify
basic dynamic load rating, C,
which is the load that results
in 106 cycles. So, this
equation can be rewritten as:
k
 6
 10

= Design Life for your
specific application for a
design load of Pd
1/ k
 Ld 
C  Pd  6 
 10 
= Required dynamic load
rating for a design life =
Ld
Note, these are all L10 lives!!!
Which is the life for 90% reliability
“2” = 200
series
Example: A horizontal washing machine rotates at 1,100 rpm. Spec out
bearings on ends if the dynamic radial load is 400 lb and static load is 75
lb. Want machine to last 20 years @ 3 loads per day, 30 minute cycle
time/load.
Can use charts shown in 14-12 to get C. Or
equation presented earlier.
CAREFUL!
• Previous equations assumes: L10 life, and
inner race rotates and radial load only!!
1. Inner race rotates, then Pd = P = V*R where V = 1.0 if inner
race rotates and V = 1.2 if outer race rotates.
2. Lar = CR * L10
Washing machine example, what if want 99% reliability??
3. What if thrust load is present??? - iteration
P = VXR + YT
P = Load
V = Rotation Factor (1.0 – Inner Race, 1.2 – Outer Race)
X = Radial Factor (.56 if Y>0)
R = Applied Radial Load
Y = Thrust Factor
T = Applied Thrust Load
*Thrust Load Present – Deep Groove Ball Bearing
START
Usually get for shaft analysis
FIND R,T
ASSUME Y
~1.5 *Must initially guess
P=VXR+YT
C=PdfL/fN
Figure 14-12
Select Bearing
Table 14-3
Compute T/Co
Find e
T/R>e?
Table 14-5 Iterate within reason
YES
FIND Ynew
NO
Ynew=Yold?
NO
YES
P=VR
END
C=PdfL/fN
Select Bearing
END