Gear damage
Broken tooth in the dredging industry
In the dredging industry and on board dredging ships the sand pumps are intensively. These pumps are specially designed for transport of large quantities of water mixer with sand. The drives of these pumps, usually comprising an electric motor and a gearbox require a lot of power. Regarding the fact that the sand pumps and the propulsion are the most critical machinery on board, it is from the upmost importance to have a reliable Condition Monitoring program in place.
Pattern recognition
For a reliable statement about the actual condition of a gearbox detailed spectrum analysis are necessary. The monitoring of only the overall vibration values is in these cases absolutely insufficient.
Vibration analysis on one of the gearboxes on board a dredging vessel suddenly showed many harmonics of the input shaft. Analysis of the time history signal showed with repeating impacts a similar pattern. The amplitude levels however had such low values that the trend analysis of the overall values and band filtered values didn't show any indication!
Despite the low amplitude values it was recommended to open the gearbox at the next opportunity for a visual inspection of the gears. One month later, during an planned dry docking, a visual inspection did indeed uncover a partly fracturing of one of the teeth of the gearwheel.
The amplitude levels in the measurements were that low because only a part of the tooth surface had come of. Long term running with such damage can cause overloading with large consequential damages. The early detection enabled the customer to repair the damaged tooth without the need to exchange the whole gear reduction.
The performance of the detailed spectrum analysis and the proceedings based on pattern recognition has prevented almost certainly a sudden failure with large (consequential) damage to the gearbox. Overloading can cause fast progressing cracks which can lead to a full failure or jamming of the gearbox on a very short term.