Evaluation Methods of Bearing Life under Different Use Conditions
1 Introduction
Bearing is an important part of a machine and its life is an important factor in machine reliability. As many machines as possible, a bearing failure will result in a catastrophic failure of the machine and affect the normal operation of the machine. In order to evaluate the bearing life and predict the reliability of the machine, research on the evaluation methods and parameters of bearing life under different use conditions has attracted more and more attention in recent years. This paper summarizes the evaluation methods of bearing life under different application conditions.
2 Bearing life evaluation under uniform load
2.1 Basic evaluation method
(1) The basic life B, which is the basis for evaluating the bearing life, is determined by the bearings load carrying capacity. As long as the load, speed and lubrication condition of the bearing remain unchanged, and there is no cumulative fatigue damage and other external influences, it will not cause bearing wear, and the bearing life can reach the life B value.
(2) The basic life B is determined according to the following expression:
B = (C/P) n
Where C is the basic dynamic load carrying capacity of the bearing, P is the applied dynamic equivalent load, n is the exponent factor of the bearing life.
(3) To facilitate comparison, the basic life is generally expressed in operating hours.
2.2 Modification of basic life
Bearing life assessment under uniform load only takes the basic life B of the bearing as the evaluation index and does not consider the influence of other factors. In practical application, when modify the bearing life, we should take into account the influence of load, speed, installation and other conditions, and introduce multiple correction factors to modify the basic life.
2.3 Load factor
When the bearing is under a certain load, it is usually calculated by introducing the load safety factor to consider the impact of load. The load safety factor γ F is introduced to correct the basic dynamic load carrying capacity which can be expressed as follows:
{γ F}
Cb = C
{γ F max}
Where γ F is the load safety factor introduced to consider the effect of load, γ F max is the maximum load safety factor, Cb is the dynamic load carrying capacity of the bearing under the load condition.
2.4 Speed factor
When the bearing is operating at different speeds, the speed factor is introduced to consider the impact of speed on life. The speed factor γ N is introduced to adjust the basic life, which can be expressed as
{γ N}
Be = B
{γ Nmax}
Where γ N is the speed factor to consider the speed effect, γ N max is the maximum speed factor, Be is the adjusted basic life.
2.5 Installation factor
The installation factor γ m is introduced to correct the basic life, which can be expressed as
{γ m}
Be = B
{γ mmax}
Where γ m is the installation factor to consider the installation method, γ m max is the maximum installation factor, Be is the adjusted basic life.
2.6 Combined life
When the bearing is running under the condition of combining load, speed and installation factors, the combined life L is given according to the following formula.
L = {(γ F γ N γ m) / (γ Fmax γ Nmax γ mmax)} B
Where L is the combined life, γ F is the load factor, γ N is the speed factor, γ m is the installation factor, γ Fmax is the maximum load factor, γ Nmax is the maximum speed factor, γ mmax is the maximum installation factor and B is the basic life.
3 Bearing life assessment under variable load
3.1 Basic evaluation method
Basic life is not a realistic evaluation index when bearing load is variable. The dynamic equivalent load P. h can be used to calculate the basic equivalent load L 10, which is used to evaluate the bearing life under variable load conditions:
L 10 = B 10
Where B 10 is the basic equivalent load, L 10 is the equivalent load that can ensure the bearing running for one million hours under the bearing life calculation.
3.2 Equivalent dynamic load
When the bearing is running in the condition of variable load, the equivalent dynamic load P h . can be calculated according to the following expression
P h = (Pd + 0.6 Pt)1/2
Where Pd is the dynamic load, Pt is the static load, P h is the equivalent dynamic load.
3.3 Equivalent bearing life
The equivalent bearing life L 10 is calculated according to the equivalent dynamic load P h and can be expressed as follows.
L 10 =B 10 (P/ P h ) n
Where B 10 is the basic equivalent load, P is the actual dynamic equivalent load, P h is the equivalent dynamic load, n is the exponent of bearing life.
4 Conclusion
The evaluation of bearing life under different use conditions is very important for the reliability of the machine. This paper introduces the evaluation methods of bearing life under uniform load and variable load respectively, and summarizes the evaluation methods of bearing life related to load factor, speed factor and installation factor. This provides a reference for the evaluation of bearing life under different use conditions.
