Slewing Bearing Guide

A slewing bearing is an important part of maintaining large swivel ring bearings in lifting equipment.

Large diameter slewing bearings are key components in many applications. Military applications include tank turrets, missile launchers, communication antennas, precision radar antennas, and weapon mounts. Typical commercial applications include aerial hoists, hydraulic excavators, booms, and tunneling machines. Large bearings for these applications are not only expensive to buy but usually require lead times from two months to a year or more.

In lifting equipment, a large diameter bearing serves as a connection between the top structure and the chassis, providing 360 degree rotation. Lifting devices usually have a complex load spectrum: a rotary ring bearing can simultaneously handle all combinations of longitudinal, radial and tilting loads. The use of a rotary ring bearing provides one more advantage:its shaftless design eliminates the need for a spindle or kingpost. The center of the bearing remains open to allow the passage of various hydraulic and control components.

Since the bearing is so critical, careful maintenance is necessary. More than 96% of slewing ring bearing failures are due to surface-originated lubrication problems, contamination, overloading, and improper installation and mounting fits. These surface failures occur much earlier than classical fatigue failures and are less predictable.

Inadequate lubrication is the most common cause of premature bearing failures. In slewing ring bearings, a heavy-duty, extreme pressure grease is required. When lubrication is inadequate, surface damage in the form of roughening or waviness occurs. Later, fine cracks develop, followed by flaking. Failures due to contamination are fairly common. Dirt or other debris within the lubrication system act as an abrasive and accelerate the wear. Usually, the bearing raceways are scratched or indented, again leading to fine cracking and, ultimately, spalling.

Assuming infinite rigidity and flat assembly structure, the service life of the rotating ring bearing is calculated. Structures that are significantly deformed and/or flat under load will apply loads to local areas instead of distributing them evenly. This can cause permanent deformation of the area, leading to early failure.

The unique design of the bearing with a rotating ring can transmit the combined load very efficiently. However, whenever a load exceeding the load capacity is applied, permanent deformation may occur, which in turn may cause premature failure.

Safety is a major problem in detecting problems with rotary table bearings. Excessive bearing clearance due to accelerated wear results in less overall rigidity in the entire system. This lack of rigidity is greatly increased in the bucket, causing a potential problem for the operator. Another security issue concerns the uneven distribution of work. This is especially common on excavators where most of the work is done in the same general area. Poor work distribution leads to uneven wear, which usually causes excessive play.

The potential costs associated with wear of the swivel ring bearing can be significant if the problem is not detected in a timely manner. A heavily worn bearing can damage other components such as pinion and gearbox.

While maintenance is critical to extending the life of large swivel ring bearings, the harsh use of heavy equipment means that eventually, any large swivel ring bearing will wear out. Detecting bearing wear makes repair a cheaper alternative to replacement. If you practice proper maintenance and pay attention to typical warning signs, a worn bearing can be considered repairable.

The swivel bearing ring allows the positioning and articulation of the carriage. The stress spectrum applied to these rotary ring bearings is very specific. Protection against pollution is extremely important (salt, sand, rain, and mud). They can also be integrated with special braking devices. Swivel ring bearings transport millions of people around the world by train, tram and subway.

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