Desigen 3 Bearings)

8/6/2019 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

Documents

Desigen 3 Bearings)