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God Bless America 09/11/2001
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As the mining industry continues to look for the 100% availability of equipment, some mining companies are looking for new technologies to help them achieve their goals. Vibration analysis has been used for years for industrial applications, but only in the last few years, with the MSHA approval of the SKF data logger has the technology migrated to underground longwall mining. Vibration analysis is an excellent predictive maintenance tool, and a proactive maintenance tool that can help design equipment to last longer. Also by the use of oil analysis in conjunction with vibration analysis a new security can be realized with load changing heavy equipment, that is utilized daily in the mining industry. I will try to update the readers of this newsletter with new information as we discover and solve machine maintenance problems. I will accomplish this with newsletters that pertain to real case histories, as the one that follows. CASE HISTORY #25 (Pinion Tooth) During January 2000, while completing our monthly check on a gear case we saw a large increase in the time domain spectrum. The time domain is a good indicator of gear problems, especially broken teeth. The spectrum shown below is an overlay of the prior spectrum and this spectrum. Notice the energy peaks at running speed. This is a perfect example of a broken tooth on the input pinion gear. The normal frequency spectrum did not show excessive increases in amplitudes. The maintenance technician could also hear a slight noise from the unit.
The gear case was removed from service. With this unit the oil analysis did not show excessive contamination. This unit was a tail drive gear case on a longwall mining section. Being in such a critical location the unit would cause extensive downtime and loss of production if it would fail.
The unit was sent to a rebuild facility for inspection. The picture below shows the input pinion gear where a small portion of one tooth that was missing. This unit would have definitely failed in the near future.
This is a good example of positive predictive maintenance helping management to make good decisions that will increase production and decrease downtime. This is also positive proof that time domain spectrums must be taken on all units, which are in a vibration health care program for rotating equipment. Time domain spectrums are also useful in determining bearing defects on slow rpm machines. This is one of many examples of vibration analysis uncovering a problem before the unit failed. In the next newsletter I will illustrate a different case study of vibration analysis, that detects a problem and verification of the problem when investigated. If you have any questions contact us. Feed back is very important to us.
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