HD Technologies: Press Roll Bearing Damage Detection

1 Introduction

This case study describes online shock pulse and vibration measurements taken from a press roll bearing in the paper machine K25 at Vrancart S.A. in Romania, one of the most notable producers of corrugated cardboard, paperboard, and tissue paper in the country. The total of finished pulp and paper/paperboard products are approx. 80.000 tons/year.

The paper mill is currently investing in upgrades of the K25 paper machine, aiming to increase its working speed. An important part of achieving this is having a reliable system for online condition monitoring in place.

At the moment, the online SPM system Intellinova monitors 264 measuring points in the press section and five drying sections in this paper machine.

The subject of this case study is the drive end bearing on the lower roll on the drive side of Press №2. This is a large and very expensive bearing working under high load, and continuous monitoring is thus essential.

2 Conclusion and summary

The online system installed on this part of the paper machine consists of eight Intellinova Standard units and one Intellinova Compact. The pre-warning time for the bearing problems described in this case study was about six weeks.

From the beginning of the measurements on the press roll, starting on July 1st, 2016, until September 17th, 2017, there were visible frequencies in the SPM HD Spectrum matching the BPFO bearing symptom. The amplitude, however, was low: HDm/HDc = 1 / -10 dB.

From September 17, 2017, a small but stable increase in the shock pulse levels (HDm/HDc = 8 / -12 dB) was noticed.

On October 16, 2017, there was a second, more rapid increase and levels raised to HDm/HDc = 27/- 11 dB. At the same time, in addition to the BPFO symptom, frequencies matching the BPFIM bearing symptom also appeared in the SPM HD Spectrum.

On October 30, 2017, the shock pulse levels reached HDm/HDc = 45/-11 dB, while the vibration levels remained low.

On November 2nd, 2017, the paper machine was stopped for investigation, and the bearing was replaced due to a visible crack on the inner race.

During the specified time, vibration levels did not rise at all, and the vibration spectrum did not show any signs of bearing damage. As can be seen in Fig. 22, the RMS levels did not show much, but with HD ENV quite good results were achieved. When comparing readings with the different measuring technologies, it can be seen that SPM HD and HD ENV Filter 4 showed very similar results.

The cause of this bearing failure was most probably the extra high load on the press.

On the bearing outer race, there were visible traces of rust and small spots which could be the source of the BPFO symptom before the inner race crack. The bearing was under warranty, and the client called the bearing manufacturer for revision and investigation of the cause of the failure.

Thanks to the long pre-warning time and planned bearing replacement, the customer saved at least 10.000 Euro.

The bearing number is 23280.

3. Application description

In the paper machine, the wet fiber web passes between large press rolls loaded under high pressure in order to squeeze out as much water as possible.

Figure 1. Paper machine press rolls.

Figure 1 shows a principle view of the paper machine press section. The paper goes through two consecutive presses and continues to the drying section. The speed varies from 80 to 110 RPM.

4 System setup

4.1 Measuring equipment

Online system:                 Intellinova Compact

Vibration sensor:              DuoTech

RPM sensor:                    Proximity switch

4.2 Measuring techniques

The measuring techniques used are the SPM HD shock pulse tecknology, EVAM vibration, and HD ENV, Filters 3 and 4.

4.3 Condmaster setup

Settings used in Condmaster Ruby 2018.2.1:

Measuring technique SPM HD:

• Measuring time: Same as FFT measurement
• Short/long time memory: Time signal and FFT
• Upper frequency: 100 Orders
• Lines in spectrum: 3200
• Symptom Enhancement Factor (SEF): 3
• Max RPM: 200
• Min RPM: 50

Measuring technique EVAM:

• Short/long time memory: Time signal and FFT/Full Spectrum
• Time signal unit: ACC
• Spectrum unit: VEL
• Order tracking: Yes
• Upper frequency: 80 Orders
• Lower frequency: 2 Hz
• Lines in spectrum: 3200

Measuring technique HD ENV, Filter 3 (500 – 10 000 Hz) and Filter 4 (5000 – 40 000 Hz):

• Short/long time memory: Time signal and FFT
• Upper frequency: 100 Orders
• Lines in spectrum: 3200
• Symptom Enhancement Factor (SEF): 3
• Max RPM: 200
• Min RPM: 50

5 Case description

Measuring point Lower Press Roll Drive Side – PU2-VI – DE

5.1 SPM HD measurement results

Figure 2. SPM HD trend graph HDm/HDc, from August 2016 to November 2017

Figure 5. SPM HD Spectrum after inner race crack – Press №2, lower roll bearing DS, showing BPFO and BPFIM symptoms.

5.2 HD ENV measurement results

Figure 12. HD ENV – Filter 4 spectrum before inner race crack – Press №2, Lower roll bearing DS with BPFIM symptom.

Figure 13. HD ENV – Filter 3 spectrum after inner race crack – Press №2, Lower roll bearing DS, BPFIM symptom.

Figure 14. HD ENV – Filter 4 spectrum after inner race crack – Press №2, Lower roll bearing DS with BPFIM symptom.

Figure 15. HD ENV – Filter 3 Time signal and circular plot before inner race crack.

Figure 16. HD ENV – Filter 4 Time signal and circular plot before inner race crack.

Figure 18. HD ENV – Filter 4 Time signal and circular plot after inner race crack.

5.3 Colored Spectrum Overview comparison, SPM HD and HD ENV

5.4 Vibration velocity measurement results

1 Appendix

Below are pictures of the bearing after replacement.

2 Reference

Dobromir Dobrev, Managing Director, SPM Instrument Bulgaria spm.d_dobrev@mbox.contact.bg

ddobrev1967@gmail.com ddobrev1967@icloud.com spm.office@mbox.contact.bg Mobile phone +359 888 623 631