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1 / Chapter 14 Bearings

2 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


4 2 TYPES OF ROLLING BEARINGS I. Ball Bearings II. Roller Bearings

5 Ball Bearing –Incorporates hardened steel balls –Steel balls geometrically contact inner and outer race at a point –This creates high stresses locally I. Ball Bearing: cage seals Inner race Outer race

6 Ball Bearings How to Assemble -Inner race press fit onto shaft shoulder (FN1, FN2) -Assembly slides into housing (RC2) between outer race and housing

7 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

8 Types of Ball Bearings Double Deep Groove –Increases radial load

9 Types of Ball Bearings Angular contact ball bearing –Increased thrust load due to increase in lateral contact area between ball and race

10 Types of Ball Bearings Thrust Bearings –Used in applications with significant thrust load

11 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

12 HOW It’s MADE: 1. MuE4gDQ MuE4gDQ 2. Ky5tXbI&feature=related Ky5tXbI&feature=related

13 II. Roller Bearings Roller Bearings –Hardened steel cylindrical rollers –Line contact deforms into areas larger then ball bearings –Capable of carrying higher radial loads

14 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

15 Types of Roller Bearings Spherical Roller Bearings –Centers inner race about shaft to avoid binding

16 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

17 Types of Roller Bearings Thrust Roller Bearings –Used in applications with significant thrust load


19 Mounted Bearings Precision machine elements such as transmissions, reducers, right angle drives usually incorporate un-mounted bearings

20 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

21 Other Types of Bearings Self Lubricating Bearings –Low Friction –No lubrication needed Elastomeric Bearings


23 Ball Joint – 3 rotational DOF HEIM Bearing See heim overview powerpoint

24 V-22 OSPREY Drive Link Hub Spring Set Pendulum Spring Pitch Change Bearing Gimbal Bearing Outboard Spindle Centrifugal Bearing Inboard Beam Pitch Change System Downstop

25 HCL Components of V-22 Osprey Drive Link Centrifugal Bearing

26 Bearing Selection see sec 14.6 – 14.10:

27 Selecting Bearings Load-Life Relationship: 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!

28 Selecting Bearings Cont’d Most manufacturers specify basic dynamic load rating, C, which is the load that results in 10 6 cycles. So, this equation can be rewritten as: = Design Life for your specific application for a design load of Pd = Required dynamic load rating for a design life = Ld Note, these are all L 10 lives!!! Which is the life for 90% reliability

29 “2” = 200 series

30 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.


32 Can use charts shown in 14-12 to get C. Or equation presented earlier.

33 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.L ar = C R * L 10 Washing machine example, what if want 99% reliability?? 3. What if thrust load is present??? - iteration

34 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

35 START FIND R,T ASSUME Y P=VXR+YT C=P d f L /f N Select Bearing Compute T/C o Find e T/R>e? P=VR C=P d f L /f N Select Bearing END FIND Y new Y new =Y old ? END Figure 14-12 Table 14-3 YES NO YES NO Table 14-5 Iterate within reason Usually get for shaft analysis ~1.5 *Must initially guess

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