What Causes Rolling Bearing Defects in Vibration Sensors?

What Causes Rolling Bearing Defects in Vibration Sensors?

Rolling bearing defects in vibration sensors are usually caused by mechanical stress or lubrication problems. These defects can create small cracks or flaws in the mechanical components of the bearing, leading to increased vibration.

Rolling bearings for vibration sensors can be found in virtually all rotating machinery. From large turbines to slow rotating motors, from relatively simple fans to high-speed friction spindles, they all rely on rolling bearings to operate. Bearing defects can be lubrication contamination, improper mounting, high-frequency discharge currents, or loss of system load. While there are many techniques for diagnosing bearing failures, the frequency of defects can be calculated for each bearing based on the physics behind the design of the bearing, such as bearing geometry, rotational speed, and type of defect, and then analyzed from a frequency-domain distribution plot to complete the troubleshooting.

The analysis of vibration data for a particular machine or system usually depends on a combination of time and frequency domain analyses:

1. Time-domain analysis is useful for detecting general upward trends in system vibration levels. However, there is little diagnostic information in this analysis.

2. Frequency domain analysis improves diagnostic capability, but identifying fault frequencies can be complicated by the effects of other system vibrations. Early diagnosis is important in order to reduce its complexity, but fault identification at an early stage requires the use of harmonic diagrams distributed in the frequency domain in conjunction with spectral analysis to identify early faults.

Vibration sensor specifications needed to diagnose rolling bearing failures include:

1) Low noise and sufficient resolution are essential for detecting early bearing defects. Typically, these defects are characterized by a small amplitude at the onset of the defect. Due to design tolerances, the inherent mechanical sloshing of the bearing will further reduce the vibration amplitude by distributing the amplitude information into multiple vacancies in the frequency response of the bearing. As a result, lower noise is required to detect the signal earlier.

2) Bandwidth is critical for early detection of bearing defects. Each time a defect is encountered during rotation, a pulse containing a high frequency component is generated. For these early failures, it is necessary to monitor the harmonics of the bearing defect frequency rather than the rotational speed. Due to the relationship between bearing defect frequency and speed, these early signals can occur in the thousands of Hz range, well beyond the 10kHz to 20kHz range. Even for low-speed equipment, the inherent characteristics of bearing defects require a wider frequency range. bandwidth for early detection to avoid the effects of system resonance and system noise in the lower frequency bands.

3) Dynamic range is also important for bearing defect monitoring because system loads and defects affect the vibration experienced by the system. Increased loads result in increased forces acting on the bearing and cause defects. Bearing defects also generate impulses that excite structural resonance and amplify the vibration experienced by the system and sensors. Changing speeds provide potential opportunities for system resonance as the machine increases or decreases in speed during stop/start conditions or normal operation. In some technical situations, sensor saturation can lead to loss of information, faulty diagnostics and damage to sensor components.

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