In modern industrial production, rolling bearings are the core components of rotating machinery, and their condition directly affects the stable operation of equipment and production efficiency. If a bearing fails, the consequences range from increased equipment vibration and noise to unplanned downtime, resulting in significant economic losses.

Therefore, timely and accurate fault diagnosis of rolling bearings is crucial.

Traditional “inspection, listening, questioning, and palpation”-style patrols can no longer meet the high demands of modern industry for equipment reliability. Today, experienced equipment maintenance engineers are like “master physicians” in the factory; they rely on a series of precision diagnostic instruments to “take the pulse and examine” equipment, achieving a transition from reactive repair to predictive maintenance. This article will provide an in-depth analysis of the three core “tools” in rolling bearing fault diagnosis—portable vibration analyzers, impact pulse/resonance demodulators, and online monitoring systems—and explain their working principles and diagnostic value in conjunction with practical application scenarios.

The “Stethoscope”—Portable Vibration Analyzer: Precisely Locating the Source of Failure Vibration is a direct reflection of a mechanical device’s operating condition. When damage such as wear, spalling, or cracks occurs in the inner ring, outer ring, rolling elements, or cage of a rolling bearing, periodic impact forces are generated during operation, thereby triggering specific vibration signals. A portable vibration analyzer acts as

a “stethoscope” used by a “master physician,” capable of capturing and analyzing these faint vibration signals to precisely pinpoint the source of the fault.

Working Principle

The vibration analyzer uses an accelerometer to collect vibration signals from the bearing housing and employs Fast Fourier Transform (FFT) technology to convert the time-domain signal into a frequency-domain spectrum. On the spectrum, different types of bearing faults exhibit unique “failure characteristic frequencies”

Outer Ring Fault Characteristic Frequencies: When the outer ring raceway is damaged, an impact occurs each time a rolling element passes over the damaged area. The frequency of these impacts is related to the bearing’s geometric dimensions, rotational speed, and contact angle.

Inner Ring Fault Characteristic Frequencies: The impact frequencies generated by inner ring damage also follow specific formulas. However, since the inner ring rotates with the shaft, the primary fault frequency is typically accompanied by sidebands spaced at the rotational frequency. This is a key indicator for identifying inner ring faults.

Rolling Element Fault Characteristic Frequency: Damage to the rolling elements themselves (such as pitting or cracks) generates vibration components related to their rotational frequency.

Cage Fault Characteristic Frequency: Wear or deformation of the cage induces low-frequency vibrations related to its rotational frequency.

By comparing the peak frequencies in the measured spectrum with the theoretically calculated characteristic frequencies, engineers can accurately determine which bearing component is faulty. For example, at a machining center in an automotive parts manufacturer, abnormal spindle vibration was observed. Vibration spectrum analysis revealed an excessively high 2x rotational frequency component, which was ultimately traced to misalignment caused by loose coupling bolts. After recalibration, the vibration amplitude decreased significantly.

Application Advantages

Portable vibration analyzers offer flexible operation and are ideal for rapid on-site diagnostics. They not only detect obvious failures that have already occurred but also enable trend analysis to monitor changes in vibration amplitude, predict the progression of failures, and provide a basis for maintenance decisions.

II. “Microscope” — Impact Pulse Analyzer/Resonance Demodulator: Detecting Early Micro-Damage

Fatigue failure in bearings often begins with microscopic pitting or cracks on the raceway surface. In the early stages of failure, the impact energy generated by these micro-damages is extremely weak and easily masked by background noise, making it difficult to detect with conventional vibration analysis. At this point, a “master technician” must employ a more precise “microscope”

—an impact pulse analyzer or resonance demodulator.

Working Principle

Both the impact pulse method and resonance demodulation technology fall under the category of high-frequency vibration detection techniques. Their commonality lies in their focus on capturing high-frequency stress waves (also known as acoustic emission signals) generated by microscopic defects within the bearing.

Impact Pulse Method: This method utilizes the transient impact force generated when a damaged area of the bearing comes into contact with the rolling elements. This impact force excites the natural frequencies of the bearing and the sensor system. The instrument evaluates the extent of bearing damage and lubrication condition by measuring the amplitude and frequency of the impact pulses. LR and HR values are commonly used evaluation metrics, with the LR value reflecting lubrication condition and the HR value reflecting the extent of damage.

Resonance Demodulation Technology: This technology first extracts high-frequency resonance signals containing fault information using a bandpass filter, then performs envelope demodulation to convert the high-frequency modulated signal into a low-frequency envelope signal. By performing spectral analysis on this envelope signal, the bearing’s characteristic fault frequencies can be clearly identified, even when the fault features in the original vibration signal are extremely weak.