What does the rotational bearing (swing bearing) consist of?

The rotational bearing, commonly referred to as the swing bearing, is an essential component of a crane's rotation system. It consists of several parts designed to facilitate smooth and controlled rotating movements. In this case, the correct answer highlights that the swing bearing comprises the bull gear, outer race, inner race, and rollers, which are critical for this function.

The bull gear is integral because it engages with the drive system to control rotation, while the inner and outer races provide the structural support needed for the roller elements. These rollers enable the rotational movement by minimizing friction and wear, thereby enhancing the efficiency and longevity of the crane’s operational mechanisms.

In contrast to the other options—such as bearings and pins or hydraulic fluid and motors—these components do not specifically describe the structural elements of a rotational bearing. The same applies to gear reducers and electrical connections, which relate to other mechanical aspects but do not pertain directly to the formation and functionality of the swing bearing itself. Understanding these components is crucial for anyone involved in crane operation or maintenance, as they play a vital role in ensuring stability and efficiency during operation.