Provides support for machine elements, while allowing smooth motion'

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Rolling Element Bearings

• Provides support for machine elements, while
  allowing smooth motion.
• m0.001 - 0.005

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Types
Radial Roller
Single-row Radial Ball
Angular Contact Ball
Angular Roller
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Types
Tapered Roller
Spherical Roller
Needle
Thrust
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Ball Bearings
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Stress Analysis

• Contact Stress
• sc300,000 is not unusual
• Balls, rollers and races are made from extremely
  high strength steel
• ex. AISI 52100
• sy 260,000 psi
• su322,000 psi

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Bearing Load/Life

• Test (fatigue) data

Empirical relationship

• k3.0 (ball)
• k3.33 (roller)

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Example

• A bearing is mounted on a shaft rotating at 1200
  rpm. The bearing has been tested to have a L10
  life of 300 hrs, when loaded with 500 lbs.
  Determine the expected L10 life, if the load is
  increased to 700 lbs.

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Manufacturers Data

• Vendors publish the Basic Dynamic Load rating (C)
  of a bearing at an L10 life of 1 million cycles.

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Bearing Selection

• Determine the design life (in cycles)
• Determine the design load
• Pd V R
• Calculate the required basic dynamic load
• Select a bearing with (C gt Creqd) and a bore
  that closely matches the shaft diameter.

• V1 for inner race rotation
• V1.2 for outer race rotation

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Example

• Specify suitable bearings for a shaft used in an
  grain dryer. The shaft rotates at 1700 rpm. The
  required supporting loads at the bearing are
• and the minimum acceptable diameter is 2.16.

RBx589 lb RBy164 lb
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Mounting of Bearings

• Shaft/bearing bore has a light interference fit.
• Housing/outer race has a slight clearance fit.
• Check manufacturers catalog
• Match maximum permissible fillet radius.
• Shaft or housing shoulders not to exceed 20 of
  diameter.

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Mounted Bearings

• Pillow block
• Bearing is inserted into a cast housing, with
  base or flange slots, which can be readily
  attached to a machine base.

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Bearings with Varying Loads

• Compute a weighted average load based on duty
  cycle.

Fmequivalent load Fi load level for condition
i Ni cycles for condition i p exponent for
load/life
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Example

• Bearing 6211 is carrying the following load
  cycle, while rotating at 1700 rpm.
• Stage Load (lbs) Time (min)
• 1 600 480
• 2 200 115
• 3 100 45
• Compute the bearing L10 life in minutes.

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Radial Thrust Loads

• Calculate an equivalent load
• PVXR YT

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Thrust factors, Y

• Deep -groove, ball bearings

X 0.56 for all values of Y
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Example

• A bearing is to carry a radial load of 650 lb and
  a thrust load of 270 lb. Specify a suitable
  single-row, deep-groove ball bearing if the shaft
  rotates at 1150 rpm and the design life is 20,000
  hrs.