Assessing Internal Damage of Loom Gearbox from Fault Vibration Spectrum: Problem Localization Without Disassembly

1、 Core Diagnostic Principles

The gear meshing, bearing rolling, and other movements of the loom reducer will produce fixed characteristic frequencies. When internal damage such as wear, pitting, and tooth breakage occurs, the vibration signal will exhibit abnormal amplitude changes, increased sidebands, and other anomalies at the corresponding characteristic frequency. FFT spectrum analysis can be used to reverse lock the fault location without affecting the normal operation of the equipment throughout the process.

2、 Typical Fault Spectrum Characteristics and Localization Methods

1. Gear damage

Uniform wear: The gear mesh frequency (GMF) and its 2- and 3-fold harmonic amplitude values continue to increase, with a significant increase in the number of sidebands. The overall amplitude of the time-domain waveform rises but remains periodically stable.

Localized pitting/peeling: Dense high amplitude sidebands appear on both sides of the meshing frequency, with an interval equal to the rotational frequency of the faulty gear, which can directly lock the shaft where the faulty gear is located.

Tooth breakage/root crack: The impact peak of the natural frequency of the gear or housing appears in the high-frequency band of the spectrum, and the time-domain waveform presents periodic sharp impact pulses, with pulse intervals completely synchronized with the frequency of the faulty gear.

2. Bearing damage

Inner ring damage: The characteristic frequency of bearing inner ring fault appears in the spectrum, accompanied by sidebands spaced at the shaft rotation frequency, and low-frequency vibration is significantly intensified.

Rolling element/outer ring damage: corresponding to the exclusive characteristic frequencies of the bearing rolling element and outer ring, the high-frequency components suddenly increase, accompanied by continuous high-frequency whistling vibration.

Holder damage: The characteristic peak of holder rotation frequency appears in the spectrum, and the stability of the vibration signal is significantly reduced.

3. Shaft and assembly damage

Axis misalignment: In the spectrum, the amplitude of twice the rotational frequency is significantly greater than that of one, and the proportion of axial vibration increases significantly.

Axis bending/imbalance: 1 times the rotational frequency dominates the frequency spectrum, and the vibration amplitude increases synchronously with the square of the rotational speed.

3、 On site practical steps

1. Sensor layout: The piezoelectric accelerometer is magnetically fixed to the vibration sensitive points on the input shaft, output shaft bearing seat, and side of the gearbox, with a sampling frequency set not lower than 25.6kHz, to filter out environmental background vibration interference.

2. Benchmark data establishment: Under the condition of brand new and healthy operation of the equipment, collect the standard frequency spectrum of the rated operating conditions, record the benchmark amplitude of each characteristic frequency, and use it as a reference for subsequent comparison.

3. Spectrum comparison analysis: Regularly collect operational data, compare benchmark spectra, and focus on checking the amplitude changes of meshing frequency, sideband distribution, and peak characteristic frequencies of bearings. Combined with time-domain waveform cross validation, locate faulty components and the degree of damage.

4. Trend warning: Continuously tracking the growth trend of characteristic frequency amplitude can predict potential faults 1-2 months in advance, and arrange targeted maintenance in non production windows to avoid sudden gear breakage and machine jamming accidents.

4、 Supporting auxiliary verification methods

Oil ferrography analysis: By analyzing the morphology of abrasive particles in lubricating oil, the wear type of gears/bearings can be further confirmed. Flake shaped abrasive particles correspond to tooth surface wear, while block shaped debris corresponds to peeling/tooth breakage.

Infrared thermal imaging scanning: Quickly locate the local high-temperature area of the box, cross confirm with the spectral analysis results, and lock in the most severely damaged area.