Test: Static and Dynamic Load Carrying Capacity - Civil Engineering (CE) MCQ

Life of a bearing is given by:

where
L₁₀ = basic life rating in million revolutions
C = dynamic load-carrying capacity
W = equivalent dynamic load
n = constant = 3 for ball bearing and 10/3 for roller bearing

Thus, The rated life of a ball bearing varies Inversely as the cube of the load.
So, option (4) is the correct answer.

Load-life relationship:
The approximate rating of the service life of a ball or roller bearing is based on the given fundamental equation.

L₁₀ = Rated bearing life (in million revolutions)
C = Dynamic load capacity.
P = Load acting in bearing.
k = 3 for ball bearing and k = 10/3 for the roller bearing.
The relation between life in million revolutions and life in hours is given by:

where, L_10h = rated bearing life in hours and N = speed of rotation in rpm.
Calculation:
Given:
N = 1500 rpm, P = 6 kN, L_10h = 8100 hours, roller bearing k = 10/3
We know that;

Combining both equations:

C = 43.34 kN

Bearing Loads

• Magnitude of Load
  • This is normally the most important factor in determining the size of the bearing.
  • Generally, roller bearings can carry greater loads than ball bearings of the same external dimensions.
  • Ball bearings are mostly used to carry light and medium loads, while roller bearings are often the only choice for heavy loads and large diameter shafts.
• Direction of load
  • Cylindrical roller bearings having one ring without flanges and needles roller bearings can only carry radial loads.
  • Other types of radial bearings can carry both radial and axial loads.

Single row angular contact ball bearing

• In angular contact ball bearings the line of action of the load, at the contacts between balls and raceways, forms an angle with the bearings axis.
• The single row bearing is of non-separable design, suitable for high speeds, and carries an axial load in one direction only.
•  In single row angular contact ball bearings, the basic static load can carry full radial and partial axial component of the load

The approximate rating of service life of a ball or roller bearing is based on the fundamental equation.

where L is rating life, C is basic dynamic load, W is equivalent dynamic load
k = 3 for ball bearing
k = 10/3 for roller bearing
The relationship between the life in revolutions (L) and the life in working hours (L_H)  is given by:
L = 60 N.L_H  revolutions
where N is the speed in rpm
Calculation:
Given: C = 35 kN, W = 45 kN