What is the general fault pattern in the velocity spectrum to a ball fault?

The presence of a peak with cage rate sidebands in the velocity spectrum is indicative of a ball fault within a rolling element bearing. This specific pattern emerges due to the interaction between the ball and the cage during operation. As a bearing operates, the balls experience contact with the raceways and the cage, resulting in periodic impacts that create vibrations at frequencies related to the ball passage over these features.

When a fault develops on a ball, each time the faulty ball passes a stationary point, it can produce a distinctive vibration signature. The fundamental frequency of these impacts corresponds to the cage rate—essentially the rotational frequency of the cage that holds the balls. Therefore, the velocity spectrum exhibits a peak at this fundamental frequency accompanied by sidebands that occur at intervals reflective of the cage's rotational rate. The spacing of the sidebands can also provide insight into the nature of the fault, including its severity and specific characteristics.

This response to the fault can be distinctly different from other patterns seen in the velocity spectrum associated with different types of faults—like the harmonic sidebands present in misalignment or other defects, which wouldn't typically produce the same signature as a ball fault. Overall, recognizing this specific pattern is crucial for effective vibration analysis and helps in diagnosing faults in bearings reliably