One of the best Preventative Maintenance tools you can use is a vibration meter. All a simple vibration meter does is give you a measurement of the amplitude of the overall vibration. It doesn't matter whether you measure it in velocity(in/sec), displacement(mils), or even metric(mm/sec). Each of these measurements provide you a measure of the severity of the vibration. A larger value means a higher severity of vibration.

 

In house PM programs are usually designed to measure the vibration levels at pre-determined intervals-such as weekly. The reading is then plotted on a graph each week to see how it changes from week to week. Is it a straight line(no change), or does it go up, then down, then up again, etc.... This is called vibration trending. Simply plotting the values collected over time.

 

If there is not much change in the amplitude, the intervals of data collection might be extended to monthly. Stretching the periodic testing to quarterly can also be OK, but not necessarily for all rotating equipment. A ball bearing can be worn and not show high overall vibration. It can then fail, and show high vibration only a day or two before a catastrophic failure would occur. The frequency of collecting data will vary with all types of equipment in many different applications.

Analyzing the vibration data collected is not necessarily simple either. There are many different parameters that could vary. The data should be collected under the same operating conditions each time. Is it under normal load, or no load? Most important, is it running at the same speed when the vibration is collected? Vibration levels can vary from day to night. From sunny days to cloudy days, from winter to summer. The machine must also be operating at a constant speed. It cannot be ramping up, or coasting down, as many VFD controlled motors are preprogrammed to do.

A simple vibration meter can be obtained for as low as $1000. This is not to be confused with vibration analyzers, which would cost in excess of $10.000! Analyzers are also used to trend vibration, but they go much farther by giving you a frequency spectrum plot to not only compare a vibration reading, but to identify a particular frequency that could be a cause of the vibration. Obviously, special vibration analyzing training is required, so many companies will find this cost prohibitive. In these cases, subcontracting the service can frequently be justified.

Vibration trending will not only give you an historical footprint of the condition of your machine, but it can be used to predict when the machine will most likely fail! If you find the overall vibration levels have increased from say .20 in/sec to .30 in/sec over the course of one year, it doesn't take much extrapolating to discern that the vibration could reach alarm level(.75 in/sec) in 4 years. There are software programs designed to compare many types of data to more accurately predict when your equipment could fail.

If you know when a bearing is predicted to fail, you can prevent a bearing failure by scheduling a replacement at your convenience. Then imagine-no more bearing failures! No more late night breakdowns. Using vibration analysis in your PM program works! Invest in PM, it will save you money!

 

 

Copyright © 2015   Snyder Technical Services, LLC.  All Rights Reserved

Maintenance Minute is published each month by Snyder Technical Services, LLC and is based on the work of former Lamson National Service Manager, Bill Snyder.   Should you have any questions, or problems to discuss, please contact me.

Sincerely,