15-16 bearings - ME250 Design and Manufacturing I Bearings...

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Bearings ME250 Design and Manufacturing I
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2 What? Why? Types of bearings Rolling contact bearings Journal bearings Summary Outline
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3 Support for rotating machine elements What? Radial load Axial load
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4 Bearings minimize friction “Sliding” friction “Rolling” friction Why? N mg F ext F frc (dynamic) moving if (static) stationary N N F d s frc Typically μ d < μ s N mg F ext F frc Typically μ r << μ d (rolling) N F r frc
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5 Journal bearings Minimize sliding friction with lubricants Types of bearings
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6 Rolling contact bearings Minimize friction with rolling elements (+lubricants) Types of bearings
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7 Magnetic bearing Support a load using magnetic levitation No physical contacts (i.e. no friction) Types of bearings
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8 Main load is transferred through rolling contact elements Pros: Low friction at start Cons: Small contact area surface fatigue Rolling elements Ball Cylinder Cone Rolling contact bearings Ball bearings Straight or tapered roller bearings F r : radial load F a : axial (thrust) load
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9 Nomenclature Rolling contact bearings http://www.youtube.com/watch?v=k8SHKy5tXbI
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10 Types of ball bearings Rolling contact bearings Deep-groove Filling-notch Angular-contact Basic form Radial load Some thrust More balls More radial load less thrust Slanted groove More thrust (unidirectional) Can double up for bidirectional thrust
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11 Rolling contact bearings Types of Ball bearings Thrust Self-aligning Very high thrust No radial load Allows mis-alignment of axis Exerts no moment (pin joint)
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12 Ball bearings with shields Each Type may be shielded or sealed for keeping lubricant + protecting from foreign particles Rolling contact bearings
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13 Types of roller bearings Rolling contact bearings Straight roller Needle roller Higher radial loads No thrust Higher friction (line contact) Smaller outside diameter
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14 Tapered roller bearings Rolling contact bearings Tapered roller Spherical roller Higher radial loads High thrust Self-alignment
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15 Bearing life Point contacts between ball and raceway cause surface fatigue (spalling or pitting) of ball or raceway Rolling contact bearings Increase noise/vibration
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16 AFBMA ( Antifriction Bearing Manufacturers Association ) Rating life (L 10 ): # of revolutions (or hours at given n ) that 90% of bearings will survive without fatigue Average (median) life: # of revolutions (or hours at given n ) that 50% of bearings will survive without fatigue Rolling contact bearings 100 90 50 L 10 life Average life ≈(4~5) x L 10 N(rev) % surviving
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17 Load ratings Strength of bearings [kN] (SI Only) Static load rating C 0 Radial load that causes permanent deformation (brinelling) in non-rotating bearings Basic (dynamic) load rating C 10 Radial load that gives L 10 life = 10 6 revolution of the inner ring Rolling contact bearings
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18 Relation between load and life Empirical equation Given F r and L 10 life, select bearings that satisfy k a > 1 : load-application factor (see Table 11-5 in course pack p 192).
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This note was uploaded on 03/21/2010 for the course MECHENG 250 taught by Professor Stevis during the Fall '09 term at University of Michigan.

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15-16 bearings - ME250 Design and Manufacturing I Bearings...

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