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
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
HOW It’s MADE: 1.http://www.youtube.com/watch?v=eGyo MuE4gDQhttp://www.youtube.com/watch?v=eGyo MuE4gDQ 2.http://www.youtube.com/watch?v=k8SH Ky5tXbI&feature=relatedhttp://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 Elastomeric Bearings www.garlockbearings.com http://www.polygoncompany.com/
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!
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
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.L ar = C R * L 10 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=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