Trend of four Resonance events

As a test the mill operator ran five junk rolls through the mill stand , each to breakage of the roll.  Aluminum went everywhere on the breaks, and cleanup of the mill after a break required about 30 minutes to 1 hour of downtime for the mill. This slide shows data taken one of the junk rolls going through the mill.  The operator ran the mill into resonance four times, as you can see with the trend shown above. On the fourth time into the resonance, the aluminum broke. Before breaking, the aluminum in the mill stand would vibrate up and down as the aluminum was accelerated and decelerated between the mill stands rolls. The last trend peak is wider than the others because the roll broke, and the mill was instantaneously unloaded, causing a speed up on the rolls and then a reduction in speed as the operator brought down the mill.  

Trend of four Resonance events pasted to Excel

Here we show the data copied into Excel and graphed for the trend. This is an example of how the Pathfinder software is compatible with the Microsoft Office suite of products. Here you can see each of the chatter/resonance events in detail.

Here is the trend and FFT of the resonance event as shown in PathFinder software.

Using Scenario Trend to determine frequency range for Trend.

This slide shows the “Scenario Trending” function of the PathFinder software, and this function was the key to unlocking the mystery. This is a powerful feature of the software. When a database is defined, you have the option of including frequency bands in the unit. You can then generate trends of the frequency bands. This is a normal operation that most condition monitoring people are using to perform analysis.  But what if you did not include the correct band while you were performing the data collection? With the PathFinder software, you can define a band of frequencies AFTER the data collection, and the software will generate a trend plot of the new frequency band! This function is not available on any other condition monitoring software package we have ever seen.  In this case, we were looking for a frequency band that would give the operator some warning when he was about to hit the chatter/resonance of the mill stand. This is a trial-and-error process, but after testing several frequency ranges we were able to zero in on a particular frequency range that gave us this information.

New Trend seems to precede Resonance event.

Note that the frequency range that we selected appears to give us a warning of impending chatter. The generated trend is the top display, and the bottom trend is the overall trend. AGAIN, this top trend was generated AFTER the data collection by entering in a frequency range and asking the software to go through the collected waveforms to generate the trend. The trend generation is very fast, usually taking only about 10-12 seconds. This is a very powerful feature of the PathFinder software.

New Trend accurately predicts entry into resonance 1 min before vibration amplitude increases ( 4 out of 4 times!).