www.traxxas.comwww.continentalconveyor.com

/www2.chicago-rawhide.com

Chapter 14

Bearings

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.me.psu.edu

www.bharatpetroleum.com

2 TYPES OF ROLLING BEARINGS

I. Ball Bearings

II. Roller Bearings

• Ball Bearing– Incorporates hardened

steel balls– Steel balls geometrically

contact inner and outer race at a point

– This creates high stresses locally

www.duratrax.com

I. Ball Bearing:

cage

seals Inner race

Outer race

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– Hard– No deformation

www.timken.com

HOW It’s MADE:

1. http://www.youtube.com/watch?v=eGyoMuE4gDQ

2. http://www.youtube.com/watch?v=k8SHKy5tXbI&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

Elastomeric Bearings

www.garlockbearings.com

http://www.polygoncompany.com/ http://www.polygoncompany.com/

Ball Joint – 3 rotational DOF HEIM Bearing

See heim overview powerpoint

V-22 OSPREYDrive LinkDrive Link Hub Spring SetHub Spring Set

PendulumPendulumSpringSpring

PitchPitchChange BearingChange Bearing

GimbalGimbalBearingBearing

Outboard SpindleOutboard SpindleCentrifugalCentrifugal

BearingBearingInboardInboardBeamBeam

PitchPitchChange SystemChange System

DownstopDownstop

www.lordmpd.com

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:

k

P

P

L

L

2

1

1

2P1 = load 1, L1 = life at load 1,

k = 3.00 for ball bearingsk = 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

k

P

P

L

L

2

1

1

2Most manufacturers specify basic dynamic load rating, C, which is the load that results in 106 cycles. So, this equation can be rewritten as:

610k

dd P

CL

= Design Life for your

specific application for a design load of Pd

k

dd

LPC

/1

610

= 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 FIND R,T

ASSUME Y

P=VXR+YT

C=PdfL/fN

Select Bearing

Compute T/Co

Find e

T/R>e?

P=VR

C=PdfL/fN

Select Bearing END

FIND YnewYnew=Yold?

END

Figure 14-12

Table 14-3

YES

NOYES

NOTable 14-5 Iterate within reason

Usually get for shaft analysis

~1.5 *Must initially guess