Detection and Severity Assessment of Faults in Gear Boxes from Stress Wave Capture and Analysis
COMPUTATIONAL SYSTEMS INC KNOXVILLE TN
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Many faults in gearboxes are accompanied by the emission of stress waves that disperse away from the initiation site at the speed of sound in metal. The wave propagation introduce a propagating ripple on the surface which will introduce a response, output, in a sensor sensing absolute motion such as an accelerometer. For an accelerometer at a fixed location, the wave propagation will be a reasonable short-term transient event lasting on the order of fractional to several milliseconds. The duration of the event will be dependent on 1 type of event e.g., stress waves from impacting will last longer than stress waves accompanying the release of residual stress buildup through fatigue cracking, 2 relative location of the sensor accelerometer to the initiation site, and 3 severity of the fault responsible for the stress wave emission. For a healthy smooth running machine gearbox, there generally will be no stress waves present. Therefore their presence is indicative of a defect which generates stress waves. Some common defects which generate stress waves are pitting in the races causing the rollers to impact, fatigue cracking in bearing raceways or gear teeth generally at root, scuffing or scoring on gear teeth, cracked gear teeth, and others. The challenge becomes one of detecting and quantifying relative to energy and repetition rate or lack thereof the stress wave activity. This leads to the identification of certain faults and, with experience their severity. The methodology employed by CSI per the capture and analysis of stress waves are to collect a block of data consisting of peak values in gs which occur within discrete sequential equal time intervals determined by the resolution sufficient to identify faults. The number of time intervals over which peak values are collected are consistent with that needed to invoke spectral analysis for the desired resolution and spectral band width.
- Machinery and Tools