Research on Failure and Life of Large Rolling Bearings

Large-scale rolling bearings have a large overall structure and size, and complex working conditions such as eccentric load, variable load, and poor lubrication are common, and their mechanical properties, failure modes, and life are special. Starting from the structure and working conditions of large rolling bearings, the author reviews the representative research results of bearing structure mechanical analysis, testing and monitoring, failure mode, life and residual fault life, etc., and then discusses the follow-up research on these aspects of large rolling bearings. specific ideas. The author firstly introduces the bearing structure characteristics in typical applications of large rolling bearings (wind turbines, tunnel boring machine cutterheads, large axle load railway freight cars), and then analyzes the structural mechanics, testing and testing technology of large rolling bearings at home and abroad. status quo. Here we focus on sharing the relevant research on the failure and life of large bearings. The large size of large rolling bearings brings a series of problems in manufacturing, installation, operation and maintenance: lack of systematic design and manufacturing technology, difficult to ensure design and manufacturing accuracy, difficult heat treatment, difficult to ensure lubrication quality, difficult to control installation accuracy, difficult sealing, etc. ; Under the action of complex working conditions such as heavy load, eccentric load, and variable load, the local bearing strength will increase significantly and change frequently; the uneven bearing temperature field and lubricating flow field will further deteriorate the working state of the bearing, resulting in premature occurrence of Local wear, damage and even failure. As shown in Figure 6, the definition of rolling bearing life can be divided into three stages: 1) Fatigue life, which refers to the time from when the bearing operates under a given cyclic load to fatigue spalling, usually obtained from the S-N curve; 2) Remaining fatigue life , refers to the time that the bearing continues to run under the given cyclic load for a period of time until it peels off; 3) Remaining life of failure refers to the bearing that continues to run to failure after the cumulative operation of the bearing for a period of time under the actual working conditions. time. The failure forms of large and heavy-duty bearings are special. In many cases, the life is terminated due to the failure rather than the conventional fatigue life problem, that is, the remaining life index of the failure is more important. Fig.6 Diagram of bearing life 1. Typical failure modes At present, the common failure modes of wind turbine turntable bearings in engineering mainly include ring breakage, cage breakage, cage wear, and grease leakage of the sealing ring. shown in Figure 7. Fig.7 Typical fault mode of wind turbine slewing bearing Fig.8 Typical fault mode of main bearing for TBM railway freight car There are two main types of faults: 1) Due to the periodic action of bearing extrusion and frictional load, the surface of the raceway The underlying tissue fatigues and produces micro-cracks, and with the gradual expansion of micro-cracks, eventually peeling from the inside out; 2) Overheating failures due to poor sealing and deterioration of lubrication (Figure 9), accounting for about 72% of the total failures , which is the key reason leading to the shortening of the actual service life of railway freight car bearings. When the failure intensifies, it will even cause major accidents such as shaft cutting. Fig.9 Overheating fault diagram of railway freight bearing In addition, axial cracks on raceway and rolling element surfaces and subsurface white etching cracks (White Etching Crack, WEC) are considered to be the cause of bearing overheating. The root cause of premature failure, such failures often occur in wind turbine gearbox bearings. The research in this area has been highly valued by researchers in the bearing industry, engineering and academia and other fields. No matter how it is manifested, the early failure of bearings always follows the short-plate principle: when the lubrication is poor or the contact surface is not smooth, the contact surface is short-plate, and bearing failure is often caused by surface wear; when lubrication is good, the sub-surface is short-plate Plates, bearing failures are often caused by material defects or stress concentrations at the subsurface.