Maintenance management of large-size rolling bearings in heavy-duty machinery

Slewing bearings are one of the most important elements in the vast majority of large-size machines. They are widely used in the mining industry: tunnel cutters, bucket excavators and many other devices. In a Bucket-wheel excavator, continuous rotation of the body is most advantageous due to the technique of digging the input or coal. The rotational movement of the machine is then the basic cutting movement, and the delivery movement, carried out by driving the machine, is only an auxiliary movement. A similar kinematics occurs in tunnel cutters. Therefore, these bearings have played such a significant role and have been the subject of extensive research and continuous improvement over the years. High demands are placed on them in terms of load capacity, friction, accuracy, durability and reliability. It happens, however, that despite careful design and manufacture, the bearings do not achieve the required durability. Failures usually result in economic losses due to loss of production, damage to adjacent parts and repair costs. Premature bearing failure can occur for a variety of reasons. Each failure leaves its own special mark on the bearing. Consequently, by examining the damaged bearing, it is in most cases possible to find the root cause and define corrective actions, thus preventing further failures. This publication aims to provide basic knowledge about the factors determining the load capacity and durability of large-size slewing ring bearings and the analysis of their damage. The result of the considerations is finding the sources of errors in determining the load-bearing capacity characteristics of roller slewing bearings. For this purpose, the ISHIKAWA and FMEA methods were used and the risk level for errors was determined. Moreover, the article presents some forms of damage to raceways of slewing bearings and indicates their causes. Changes in the so-called angle of action of the rolling elements in the ball bearing due to the transferred loads. The influence of changes in this angle on the geometry of the contact zone of the rolling elements and raceways was investigated. It has been shown that the contact angles of some rolling elements increase significantly. This can damage the raceway by chipping or rolling the edge of the bearing ring. With the knowledge presented in this article, it is possible to evaluate various emergency situations and start their proper analysis.