The large size of large rolling bearings brings a series of problems in manufacturing, mounting, operation and maintenance: lack of systematic design and manufacturing technology, design and manufacturing accuracy is not easy to ensure, heat treatment difficulties, lubrication quality is not easy to guarantee, mounting accuracy is not easy to control, sealing difficulties, etc.; in the role of heavy loads, partial loads, variable loads, and other complex conditions, the local load carrying capacity will be significantly increased and frequent changes; bearing temperature field and lubrication flow field unevenness will further deteriorate the working condition of the bearing, resulting in early local wear and damage or even failure. The unevenness of the bearing temperature field and lubrication flow field will further deteriorate the working condition of the bearing, leading to premature local wear, damage and even failure.

The definition of rolling bearing life can be divided into 3 stages:

(1) fatigue life, refers to the bearing in a given cycle load conditions until the occurrence of fatigue spalling time, usually according to the S-N curve to get;

2) Remaining fatigue life, refers to the time when the bearing continues to operate under a given cyclic load condition after accumulating a period of operation under that condition until spalling;

(3) Failure remaining life, refers to the bearing in the actual conditions of the cumulative operation for a period of time after the occurrence of failure to continue to run until the time of failure. The failure form of large heavy-duty bearings has special characteristics, and in many cases it is due to the failure of the life termination rather than the conventional fatigue life problem, that is, the failure of the remaining life index is more important.

Typical failure modes

At present, the common failure modes of wind turbine rotor bearings in the project mainly include ring fracture, cage fracture, cage wear, seal leakage of grease, etc. The failure of the main bearing of the roadheader mainly includes tooth ring fracture, seal failure, etc.

The failure form of railway wagon bearing mainly has 2 types:

(1) due to the bearing by extrusion and friction load cyclic action, raceway surface layer of the organisation below the fatigue and produce fine cracks, with the gradual expansion of micro-cracks ultimately produce from the inside out of the spalling;

(2) due to poor sealing and lubrication degradation caused by overheating failure, accounting for about 72% of the total failure, which is the key reason for the shortening of the actual service life of railway wagon bearings, and when the failure is aggravated, it may even cause major accidents such as axle cutting.

In addition, axial cracks on the raceway and rolling element surfaces and white corrosion cracks on the subsurface are considered to be the root cause of premature bearing failure, which often occurs in wind turbine gearbox bearings, and this aspect of the research has been highly valued by researchers in multiple fields such as the bearing industry, engineering and technical circles and academia. Regardless of the way of expression, the early failure of bearings always follow the principle of short plate: when poor lubrication or contact surface is not smooth, the contact surface for the short plate, bearing failure is often caused by surface wear, etc.; when the lubrication is good, the sub-surface for the short plate, bearing failure is often caused by the sub-surface at the material defects or stress concentration. Large size bearings are prone to large local deformation, resulting in severe wear and local stress concentration, which in turn leads to bearing failure and premature failure.

Bearing life research status

Foreign related research

Foreign research on rolling bearing fatigue life began earlier, especially SKF, FAG and NSK and other large bearing enterprises and NASA and other scientific research institutions, has formed a set of relatively perfect theory. At present, the commonly used rolling bearing fatigue life theory has L-P life theory, I-H life theory, Zaretsky life theory.

Domestic research

Domestic related research is mainly to consider different factors on the fatigue life model of large rolling bearings to amend: based on statistical theory to analyse the fatigue life of large rolling bearings and its reliability, the results show that the fatigue life of large rolling bearings obeys the three-parameter Weibull distribution, which provides a theoretical guide for its life and reliability evaluation; considering bearing lubrication and clearance changes, the theory of the calculation of the life of the bearings was Modified the bearing life calculation theory by considering bearing lubrication and clearance change; Introduced the influence of yaw and pitch bearings under the joint action of axial force, radial force and tilting moment, and calculated the overall fatigue life of bearings by considering the fatigue life of inner and outer rings of yaw and pitch bearings; In view of the force characteristics of double-row four-point contact ball bearings, put forward the calculation method of stress distribution of bearings by considering axial load, radial load and tilting moment, and calculated the fatigue life of large rolling bearings under the equivalent dynamic load and the rated dynamic load based on the theory of L-P life. Based on the L-P life theory, the bearing life under equivalent dynamic load and rated dynamic load is calculated.