November 2, 2018
Mechanical Looseness Identification
By Chris Troutt
A common vibration signature on equipment is looseness. There are two types of looseness:
- fit between rotating components.
For this discussion, we will focus on structural and fastener looseness. Typically, it is highly directional, occurs at 1xRPM, and will look similar to this spectrum.
In this case, the vibration was confined to the vertical position and not detected in the horizontal. Additionally, the vertical 1x vibration was shared in the drive end of the motor but did not carry over to the driven machine. The Accurex report indicated structural looseness and resonance was occurring on the motor.
When looseness occurs, it is critical to pinpoint what is loose, so a closer inspection of the motor fasteners and related structure should be done.
The Falcon has a couple of special tools that make this simple. After you have taken your data, locate and press the “See” icon on the right side of the screen to view all the related spectra for that point.
Find a measurement that shows the dominant 1x. Place the Wireless Triaxial sensor back on the point of interest and press the “Live” icon/button.
The data collector will collect a live real-time measurement of that point. Add a cursor to the spectra and track the 1x vibration and then begin to move the sensor around and look for changes in amplitude of the 1x.
As an example, if you measure a significant drop in amplitude when you go from the motor foot to the base plate, you can suspect loose bolts at the motor feet. If the vibration is high on the entire base, but the floor measurement has a very low amplitude, this could indicate the base hold down bolts are loose. In addition, tightening the bolt(s) in question should reduce the vibration amplitude.
An additional tool the Falcon has is the built-in strobe light. This can be helpful when tracking down the source of looseness. Tuning the strobe light to just above or below the frequency can show movement of the bolt(s) in slow motion.
From the same screen you were using in the “live” mode you can select the shortcuts options at the lower left then press the “Stroboscope” button to turn on the Falcon’s built in strobe light.
The spectrum will still be on the screen and you can move the cursor to the 1xRPM and the strobe will match it. You can then use the strobe to look over the machine for components moving at that speed.
With the on-board diagnostics inspection tools;
- live measurement
- strobe light,
the user can make a more precise diagnosis of the problem.