What is the static load rating and dynamic load rating of the bearing?

 

When we inquire about the bearing model, we often see two options, Cr and Cor, Cr refers to the bearing dynamic load, Cor refers to the bearing static load. So what is the static load rating and dynamic load rating of the bearing? What is the relationship and difference between the two?

The three basic parameters that are often used in the design of rolling bearings are: the basic rated dynamic load Cr (radial) or Ca (axial) that meets the requirements of a certain fatigue life; The basic rated static strength Cor (radial) or Coa (axial) that meets certain static strength requirements and the ultimate speed No, which controls bearing wear.

 

What is a bearing static load rating?

 

The basic static load rating of rolling bearings (radial Cor, axial Coa) refers to the imaginary radial load or central axial static load equivalent to the maximum load of the bearing when a certain contact stress is caused by a certain contact stress at the contact center of the rolling element and the raceway.

 

For radial bearings, the rated static load refers to the radial load, for the radial thrust bearing (angular contact ball bearing) refers to the radial component of the load that loads the raceway in the half ring of the bearing, and for the thrust bearing, it refers to the central axial load.

 

That is to say, the radial basic static load rating and axial basic static load rating of the bearing refer to the maximum load that the bearing can bear when it is static or rotating.

 

The load carrying capacity of deep groove ball bearings at a standstill or slow rotation (speed n≤10r/min) is rated static load.

 

What is a bearing dynamic load rating?

 

Bearing dynamic load rating refers to: the rolling bearing can theoretically bear a constant radial load (constant axial load), under the action of the basic rated life of 100W rpm, the basic rated dynamic load of the bearing reflects the ability of the bearing to resist rolling fatigue. The basic dynamic load rating of radial bearings and thrust bearings is also known as radial basic dynamic load rating and axial basic dynamic load, which are expressed by Cr and Ca.

 

The load carrying capacity of groove ball bearings during rotation (speed n>10r/mim) is the basic rated dynamic load.

 

Why is the rated dynamic load of the bearing greater than the rated static load?

 

The rated dynamic load refers to the load on the bearing when the rated life is 1 million rpm. The rated static load refers to the contact between the rolling element and the ring raceway that is the most loaded when the bearing is at rest, and the sum of the permanent deformation of the rolling element and the ring raceway is 1/10,000 of the diameter of the rolling element.

 

There is a certain relationship between the service life of the bearing and the rated load of the bearing, so under what circumstances do we choose the bearing by the rated load of the bearing? The main points are as follows:

 

Note: In some cases, the bearing size should be selected by the static load rating (defined as Co for ease of description) rather than the bearing life.

 

1. Under the action of continuous or intermittent impact load, the bearing is stationary.

 

2. Under the load, the bearing only makes slow reciprocating oscillation or adjustable movement.

 

3. Under the load, the speed of the bearing is very low (less than 10 revolutions per minute) and only needs a short life. In particular, in this case, for a given equivalent load P, the required basic dynamic load rating C is very low according to the life formula, so that the selected bearing may be severely overloaded in practice.

 

4. In addition to the normal working load, it also needs to bear a very heavy impact load, and the bearing is rotating.

 

In each of these cases, the load that the bearing can withstand does not depend on the fatigue of the material, but on the degree of permanent deformation of the raceway caused by the load.