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

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 loadbearing 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.