desigen 3 bearings)
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Design 3Design 3
BearingsBearings
Hamidreza G.Darabkhani
Course Leader: A. Starr
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ContentsContentsBearings
Bearings Classification
Loads on Bearings
Rolling elements bearings
Ball bearings
Roller bearings
Needle bearings
Linear bearings
Thrust bearings
Sliding bearing
Magnetic bearings
Application of bearings
Bearing calculations
Bearing mounting
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Provides support for rotating machine elements
Bearings
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Bearings(1/2)
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Bearings(2/2)
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Bearings for Rotary Motion
Rolling ElementsMagnetic BearingsSliding Bearings
(Fluid film bearings)
Ball Roller Needle
Cy
lindrical
T
aper
B
arrel
Bearings Classification
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Ball Bearings
Radial and Axial loads
Roller BearingsRadial and Axial loads
Needle Bearings
Only radial loads
Allocated Loads on Bearings
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Rolling Elements Bearings
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Single row radial ball bearing
See the difference in the
curvature of the ball and the
race. (Point Contact)
Good Radial LoadModerate Axial Load
Very good speed
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Ball Bearings with shields
The shields are use to exclude dirt and foreign particles
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Angular contact Bearings
Balls are inserted by thermally expanding the
outer ring.
Can take greater axial load
Good Radial Loads
Good Axial loadsGood Speed
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Double row ball Bearings
Good Radial LoadsPoor Axial loadsModerate Speed
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piece inner-ring ball bearings
Advantages:
The maximum complement of
balls makes for higher load
carrying capacity.
The very deep ball raceway
shoulder makes for high thrust-
load capacity.
Thrust loads can be handled in
both directions.
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Roller Bearings
Because of the line contact, they
can take greater loads
They also have more rolling
resistance
Types of roller bearings
Cylindrical
Tapered
Barrel (Spherical)
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Are used in applications like conveyer belt rollers, where theymust hold heavy radial loads.
Line contact to handle much greater loads than a ball bearing.
Is not designed to handle much axial loading.
Cylindrical roller bearings
Very good Radial LoadsPoor Axial loadsModerate to very good Speed
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Are used in car hubs, where they areusually mounted in pairs facing oppositedirections so that they can handle thrust inboth directions.
Tapered roller bearings
Very good Radial Loads
Good Axial loadsModerate Speed
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Needle bearings(1/2)
Use large number of small diameter rollers
Usually there is no space between rollers
(needles). No cage required.
Very good Radial loads
No Axial loads
Poor to moderate speed
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Linear bearings
Are used primarily where something needs to be moved along astraight line with high accuracy. In other words, the object needsto only translate in one direction, and possibly move back to itsstarting position with high repeatability. The implications forrobotic pick-and-placeare obvious, as are uses for optical test
fixturing and calibration.
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Thrust Ball Bearings
Cylindrical roller
Spherical roller
Good Axial LoadsNo Radial Loads
Poor Speeds
Thrust bearings
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Ball thrust bearings
are mostly used for low-speed applications
No Radial Loads
Good Axial loadsPoor to Moderate Speed
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Magnetic Bearings
Magnetic bearing systems represent a completely different approach tothe support of rotating equipment.
(NON-CONTACTING TECHNOLOGY)
Magnetic Bearings are operating in:
compressors, electric motors, pumps, turbo expanders, steam turbines, gasturbines, centrifuges, etc. MACE
Magnetic bearings
Are a non-contacting technology
Negligible friction loss and no wear Higher reliability Enables previously unachievable surface speeds to be attained Lubrication is eliminated
Magnetic Bearings for High TemperatureSmart Aero Engine
Conical Magnetic Bearings Developed for Active
Stall Control in Gas Turbine Engines
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Bearing applications
Air Condition systems
WheelsGearboxes
Pumps
Mixers MACE
Bearings in flight systems
Helicopter bearing
Helicopter ball bearing
ball bearing
Piston engine propeller
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Manufacturers Data
Vendors publish theBasic Dynamic Loadrating (C) of a bearingat an L10 life of
1 million cycles.
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Stress Analysis
Contact Stress
c=300,000 psi is not unusual
Balls, rollers and races are made fromextremely high strength steel
e.g. AISI 52100
sy= 260,000 psi
su=322,000 psi
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Bearing Selection
Determine the design life (in cycles)
Determine the design load
Pd= V R
Calculate the required basic dynamicload
Select a bearing with (C > Creqd) and abore that closely matches the shaftdiameter.
kd
ddreq
LPC
1
6'10
=
V=1 for inner race rotation
V=1.2 for outer race rotation
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Equivalent combined radial load
For combined radial and thrust loads
P = V X R + Y Ftwhere:
P = equivalent radial load (lb)R = actual radial load (lb)Ft = actual thrust load (lb)
X = radial factor (usually 0.56)V = 1.0 for inner race rotating
= 1.2 for outer race rotatingY = Thrust factor( from chart)
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Thrust factors, Y
Deep -groove, ball bearings
X = 0.56 for all values of YMACE
Bearing Mounting
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Bearing Mounting
Shaft/bearing bore has a light interference fit.
Housing/outer race has a slight clearance fit.
(Check manufacturers catalog)
Match maximum permissible fillet radius. Shaft or housing shoulders not to exceed
20% of diameter.
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Typical bearing mounting
Shoulderslocate bearings
Nuts clamp innerring to shaft
Outer ring of onebearing clampede.g. cover plate
bearingfree to float
Other ways to locate bearings: retaining rings,washers, screws, cotter pins, taper pins
Ball Bearing
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X X297.5
DC
Ball Bearing Ball Bearing
Sample schematic of bearing mounting and gears
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1. Mechanical Engineering Design 7th Edition, J E.Shigley CR.Mischke and R G.Budynas
2. Rolling Bearing Analysis, 4th edition, Tedric A. Haris
3. Rolling bearings, T S Nisbet
4. http:// www.3Dcontentcentral.com
5. http:// www.skf.com
6. http:// www.dynaroll.com/bearing-selection
7. http://www.tec.nsk.com
8. http://www.colorado.edu/engineering/MCEN/MCEN3025/Lectures/1
9_Bearings2_2005_3_29.ppt9. http://www.webs1.uidaho.edu/ele/Mindworks/Machine_Desi
gn_files/1%20Posters/PPT%20Poster/bearing.ppt
Some useful references