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State the difference between Anti Friction Bearing and Journal Bearing?

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DIFFERENCE BETWEEN ANTI FRICTION AKA ROLLER BEARING AND JOURNAL BEARING

Answer: Generally, journal bearings have higher friction force, consume higher energy and release more heat, but they have larger contact surface, so normally used in low-speed high load applications. In anti-friction bearings friction is less. One object just rolls over each other.

Classification of Bearings:

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Diagram source

Rolling or Anti-friction bearing

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  • Due to less contact area rolling friction is much lesser than the sliding friction , hence these bearings are also known as antifriction bearing.
  • Frictional resistance considerably less than in plain bearings
  • Rotating – non-rotating pairs separated by balls or rollers
  • Ball or rollers has rolling contact and sliding friction is eliminated and replaced by much lower rolling friction.
  • In plain bearing the starting resistance is much larger than the running resistance due to absence of oil film.
  • In ball and rolling bearings the initial resistance to motion is only slightly more than their resistance to continuous running.
  • Hence ball and rolling bearing are more suitable to drives subject to frequent starting and stopping as they save power.
  • Owing to the low starting torque, a low power motor can be used for a line shaft running in ball bearing.

The Anti-friction bearing consists of following parts:

  • Inner ring or race which fits on the shaft.
  • Outer ring or race which fits inside the housing.
  • Ball and roller arranged between the surfaces of two races. These provide rolling action between the races.
    • The radius of the track for balls is slightly greater 5 to 10 % than that of the ball themselves.
    • Note that the rotating surfaces rotate in opposite directions.
  • Cage which separates the balls or rollers from one another.
  • The disadvantage of the ball and roller bearings are high cost, they cannot be used in half, and greater noise.

The advantages of rolling bearings compared to journal bearings are:

  • Starting friction torque is about twice the running frictional torque, but still it is negligible in comparison to starting friction of a sleeve bearing (Sliding Bearing).
  • Ease of lubrication either with grease or with relatively simple systems.
  • Less axial space for a comparable shaft diameter.
  • Capable of supporting both radial and thrust loads.
  • Early warning of impending failure signaled by increasing noisiness at the same speed of rotation.
  • Standardization and close tolerances make preferable their use in precision machinery. 7. Easy to mount and erect.
  • Cleanliness.
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The disadvantages of rolling bearings as compared to journal bearings are:

  • Greater diametrical space required for a comparable shaft diameter.
  • Initial cost is usually higher.
  • Noisier in normal operation.
  • Finite life due to failure by fatigue.
  • Lesser capacity to withstand shock.

Journal bearing

A Journal bearing is a cylindrical bushing made of a suitable material and containing properly machined inside and outside diameters. The journal is usually the part of a shaft or pins that rotates inside the bearing.

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TYPES OF JOURNAL BEARING

There are basically 3 types of journal bearing :

  1. Solid journal bearing
  2. Bushed journal bearing
  3. Plummer block/Pedestal bearing

ADVANTAGES OF JOURNAL BEARING

  • It can handle high loads and velocities (less metal to metal contact due to oil film).
  • Long lasting and durable.
  • Quiet and smooth running of engine.
  • Low cost
  • Suitable only for low temperatures and speed
  • Requires large supply of lubrication

DISADVANTAGES OF JOURNAL BEARING

  • There is no provision for wear and adjustment on account of wear.
  • The shaft must be passed into the bearing axially i.e. endwise.
  • Limited load on shaft and speed of shaft is low.

DOWNLOAD ANTI FRICTION BEARING AND JOURNAL BEARING PPT

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Category: Mechanical Engineering