| | | |

Case study

Paper Machine Press > Examples

Grooved Roll Barring Observations

The press roll rotating speeds were as follows:

Grooved Roll   320 RPM
Stone Roll       200 RPM

The frequency spectrums from the granite roll (Figure 9) and the 3rd press grooved roll (Figure 10) show the predominant vibration occurring at a frequency of 5400 CPM, both with approximately the same amplitude. Further analysis revealed side bands in the zoomed spectrum (Figure 11) separated from the main peak by 342 CPM, which equals the rotating speed of the grooved roll. The vibration at 5400 CPM stayed in the spectrum in STA mode when the analyser was triggered from the grooved roll (Figure 12), and disappeared when triggered from the granite roll (Figure 13).

The time domain data collected from the grooved roll (Figure 14) confirmed that there were 16 events for every one revolution of the grooved roll. The time signal was amplitude modulated at a rate equal to the rotating speed of the grooved roll. The STA time domain data from the grooved roll shows the amplitude modulation, and the 16-event revolution of the roll as well (Figure 15).

Diagnosis

The data indicated the grooved roll contained sixteen bars. The STA data pointed towards the grooved roll as the source of the vibration since the 16X component disappeared when the instrument was triggered from the granite roll.
The amplitude modulation observed in the time data at a rate equal to the rotating speed of the grooved roll is of interest. In this case, the correct diagnosis could have been made without the benefit of STA by simply observing the modulation, and assuming the source of the modulation was also the location of the barring condition.

The data used in this example highlights the need for high resolution spectrums when analysing press section problems. In the initial stages of examining the data, side band spacing was highly speculative because of the frequencies represented by each line in the spectrum. A subsequent inspection of the grooved roll revealed sixteen bars.

The frequency spectrums collected from the stone roll (Figure l6), and the 3rd press grooved roll (Figure 17), indicate the main vibration in both rolls is occurring at a frequency of 4680CPM. Side bands were observed in the data from both rolls with a spacing of 320 CPM. The time domain data from the grooved roll (Figure 18) clearly shows amplitude modulation at a rate equal to the rotating speed of the grooved roll, and the events occurring during one revolution of the grooved roll.

The grooved roll was diagnosed as having 15 bars.
The sidebands in the frequency spectrum indicated amplitude modulation at a rate equal to the rotating speed of the grooved roll. Without the benefit of STA data, the diagnosis was made based on the modulation rate.

The data in this example supports the need for high resolution spectrums when analysing press section problems. When compared to the first example, side band spacing is much easier to determine. A subsequent inspection of the grooved roll revealed fifteen bars.

Felt Barring Observations

The press section rotating speeds were as follows:

Grooved Roll   320 RPM
Stone Roll       200 RPM
Felt                 36 RPM

The vibration data collected from the grooved roll (Figure 19) shows a pattern similar to that found when roll barring exists. Examination of the zoomed spectrum from the grooved roll (Figure 20) reveals a main peak appears at approximately 4700 CPM, with several side peaks separated by 36 CPM.

Diagnosis

The data indicated the felt was barred.
The diagnosis is based on the fact the side peaks are separated by the rotating speed of the felt. The vibration amplitude resulting from the bars passing between the press rolls was amplitude modulated at a rate equal to the rotating speed of the felt. This could be a result of a density variation along the length of the felt, which caused the amplitude of the vibration to change as it made its way through the paper machine.

Once the felt was replaced, the vibration diminished to an acceptable level. This example also highlights the importance of high resolution spectrums. The data collector was set up to record 6400 lines within a frequency range of 0 - 12000 cpm. The resulting line spacing (1.875 cpm) allowed the analyst to clearly view the felt speed harmonics. If the normal route collection resolution of most condition monitoring programs was used (400 lines), felt speed harmonics would not have been visible. As a result, many mills are now changing their data collection strategies to include a sampling of high resolution spectrums, to minimise the need to return to the field for further data collection if a problem is detected.

Conclusions

Several conclusions are drawn from the data and analysis presented in this study:

1. The frequency of press vibration is a function of paper machine speed. If all other operating parameters remain constant, vibration frequency is directly proportional to machine speed.

2. The relationship between press vibration amplitude and paper machine speed is indeterminate.

3. It is possible to change the amplitude of press section vibration by changing the nip pressure, however, changing nip pressure will not completely eliminate press vibration.

4. The difference between sideband peaks, measured in frequency units, will equal the rotating speed of a barred press roll.

5. Synchronous Time Averaging and high resolution data are useful tool, for isolating the source of press section vibration.

6. The vibration generated by felt barring is comprised of frequencies separated by the rotating speed of the felt.

References

1. Bearings in Papermaking Machines. Application Handbook, Publication 4200E, Denmark (1991)
2. Geschmay Wet Felts Vibration Seminar notes, Wagner systems
3. Hoyland, R.W, "Reducing press section vibration problems", Paper Trade Journal, pp51 - 54 (April 1986)
4. Huston, E.J, "Paper machine press section vibration", Vibrations, 10:2, pp3 - 6 (1994)
5. Pedersen, T.A, "An on-line system for Paper Machine Condition Monitoring", Pulp and Paper Canada, 93:4, pp45 - 52 (1992).
6. Perrault, J. "More about press section vibration analysis", Pulp and Paper Canada, 87:2, pp31 - 39 (1987)
7. Perrault, J. "Practical aspects of troubleshooting wet end barring", TAPPI seminar notes, pp359 - 367 (1987)
8. Vinicki, J. "Vibration analysis in the press section", TAPPI Journal, pp91 - 95, (Nov 1987)
9. Vinicki, J. "Analysis of felt induced vibration", TAPPI Journal, pp131 - 134 (Feb 1989)

Although care has been taken to assure the accuracy of the data compiled in this study, the apt Group does not assume any liability for error or omissions.

Top of page  |  Back to Case Studies