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.
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.
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 :
- Solid journal bearing
- Bushed journal bearing
- 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.