BEARINGS Rolling vs. Sliding Provides support for machine elements, while allowing smooth motion. µ = 0.001-0.005 Plain Bearings (Sliding/Hydrodynamic/ Journal/Sleeve) Rolling-Element Bearings Types Selection criteria Calculation Bearing arrangements T. Cicone- March 2006 1/27 ME&M- Mech. Trans. BEARINGS Rolling Bearing are better because: low starting and good operating friction radial and thrust loads no self-excited instabilities less space axially can seal lubricant in bearing simple and less expensive (extended standardization) Producers: SKF FAG Timken NSK NTN Journal Bearings are better because: fatigue failure is not a problem less space radially damping capabilities (low noise) more tolerant to misalignment less expensive, except for lubricating system less operating friction high speed adaptable T. Cicone- March 2006 2/27 ME&M- Mech. Trans. Bearing Selection T. Cicone- March 2006 3/27 ME&M- Mech. Trans. 1
Roller Bearing Bearing Loading Ball Bearing Load spread over larger area Can handle heavier radial loads Can t take much axial loading Most common type Balls transmit load Point contact If load is too high balls squish! Good in radial loading T. Cicone- March 2006 4/27 ME&M- Mech. Trans. Single-row Radial Ball Rolling Element Bearings - Types Angular Contact Ball Double-row Radial Ball Self-aligning Ball Radial Roller Tapered Roller Angular Roller T. Cicone- March 2006 5/27 ME&M- Mech. Trans. Spherical Roller Self-aligning Rolling Element Bearings - Types Needle Thrust Roller Thrust Ball T. Cicone- March 2006 6/27 ME&M- Mech. Trans. 2
Rolling Element Bearings - Types T. Cicone- March 2006 7/27 ME&M- Mech. Trans. Rolling Element Bearings - Types T. Cicone- March 2006 8/27 ME&M- Mech. Trans. Rolling Element Bearings - Classification Rolling Element Type Balls NUMBER Single Double 4-row Cylindrical Rollers Needles (Cylindrical Rollers) LOAD DIRECTION Axial Radial (Thrust) Radial-axial Axial-radial Spherical Rollers Taper Rollers Separable TYPE Non-Separable (Detachable rings) T. Cicone- March 2006 9/27 ME&M- Mech. Trans. 3
Rolling Element Bearings - Codes Bearing numbers Bearing Series (radial bearings except tapered-roller bearings) T. Cicone- March 2006 10/27 ME&M- Mech. Trans. Rolling Element Bearings - Components T. Cicone- March 2006 11/27 ME&M- Mech. Trans. Axial Location Bearing Fitting - Radial location Radial Location HOUSING - Close clearance fit SHAFT Transition to Interference T. Cicone- March 2006 12/27 ME&M- Mech. Trans. 4
Bearing Location - Axial location Axial Location Snap-rings Special Nut + Tab-lock washer Shoulders Mating parts (end covers, spacers, shims) T. Cicone- March 2006 13/27 ME&M- Mech. Trans. Bearing Location - Axial location Special Nut + Tab-lock washer T. Cicone- March 2006 14/27 ME&M- Mech. Trans. Axial play control Bearing Location - Axial location T. Cicone- March 2006 15/27 ME&M- Mech. Trans. 5
Integrated Bearings Pillow block Bearing is inserted into a cast housing, with base or flange slots, which can be readily attached to a machine base. T. Cicone- March 2006 16/27 ME&M- Mech. Trans. Floating mounting Bearing Arrangements Locating / Non-locating mounting Housing Housing Shaft Shaft Left bearing Right bearing Fixed (Locating) bearing Free (Non-locating) bearing T. Cicone- March 2006 17/27 ME&M- Mech. Trans. Floating mounting Bearing Arrangements Contact angle 0 O X T. Cicone- March 2006 18/27 ME&M- Mech. Trans. 6
Bearing Arrangements Locating / Non-locating mounting Housing Shaft Fixed (Locating) bearing Free (Non-locating) bearing Accommodates with large thermal expansion (long shafts) Good when one bearing is loaded much more than its pair T. Cicone- March 2006 19/27 ME&M- Mech. Trans. Bearing Arrangements Floating mounting T. Cicone- March 2006 20/27 ME&M- Mech. Trans. Bearing Arrangements T. Cicone- March 2006 21/27 ME&M- Mech. Trans. 7
Bearing Arrangements T. Cicone- March 2006 22/27 ME&M- Mech. Trans. Bearing Arrangement O arrangement X arrangement T. Cicone- March 2006 23/27 ME&M- Mech. Trans. Grease lubrication Bearing Lubrication Oil lubrication Gear Box T. Cicone- March 2006 24/27 ME&M- Mech. Trans. 8
Rating Life (Minimum Life) L 10 : Bearing Calculation The number of revolutions or hours at some constant speed that 90% of identical bearings tested under identical conditions will survive without noticeable fatigue damage Basic dynamic load rating C used for calculations of bearings which rotate under load Basic static load rating C 0 used when rotating bearings are subjected to heavy shock loads of short duration or when bearings rotate at very slow speeds, are subjected to very slow oscillations, or stationary under load. The pure radial/axial bearing load which will give a rating life, L 10, of one million revolutions The static pure radial/axial load which produces a total permanent deformation of rolling element and raceway of about 0.0001 ball/roller diameter (corresponds to a calculated contact stress at the center of the most heavily loaded rolling element/raceway contact of 420MPa for all radial and angular contact ball bearings). Equivalent applied load P Law of durability (Life Equation) p C L = P P = X V Fr + Y F a p = 3 balls p = 10/ 3 rollers T. Cicone- March 2006 25/27 ME&M- Mech. Trans. Bearing Calculation Given data (Load, speed, arrangement, operating cond.) F a - applied constant thrust (axial) load Equivalent applied load P P = X V F + Y r F a F r - applied constant radial load V - rotation factor (=1 or =1.2) X - radial factor (Tables) Y - thrust factor (Tables) < e X = 1 Y = 0 > e X Y > 0 F F r r Law of durability (Life Equation) p C L = P p = 3 balls 6 [ 10 rev ] p = 10/ 3 rollers 10 6 L h = L 60n [ hours ] T. Cicone- March 2006 26/27 ME&M- Mech. Trans. Bearing Calculation Angular Contact Bearings F ra R F a rb FrA, B sa, B = 0.5 Y A, B F asa F a F asb r r r r Ra = + sa + sb r R a direction A B (B takes thrust load) B A (A takes thrust load) F aa = F asa r r r B = + sa F ab = F asb r r r A = + sb T. Cicone- March 2006 27/27 ME&M- Mech. Trans. 9