State the difference between Anti Friction Bearing and Journal Bearing?

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:

Rolling or Anti-friction bearing

• 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.

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.

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

More: Mechanical Engineering Questions and Answers