PAPER MACHINE FORMING ROLL ( Bearing Defect ) The forming roll shown below is positioned in the wet end of the paper m/c. It runs between 150 rpm - 200 rpm depending on the type of paper being made. In this case the machine was running at 816 meters per minute, this equated to a speed of 181 rpm on the roll. The roll has two large supporting bearings and an internal bearing where the inner race is fixed. Monthly vibration readings were taken on the front and back bearings. Upon analysis of the readings it was noticed a set of harmonics were found to be developing. The spectrum below shows the defect harmonics starting from 8.91 orders. This pointed towards a bearing defect, all the bearing defect frequencies were overlaid and a match was found with the inner race of the internal bearing skf 22334. This confirmed a defect on the inner race of the 22334 brg.

PS76 - Wire Forming Roll (1435mm)

Frm/Roll -DSA Forming Roll Drive Side Axial

Label: INNER RACE DEFECT ON SKF 22334CC

Route Spectrum 29-JAN-00 14:52:03

OVRALL= 2.10 V-DG PK = .0915 LOAD = 100.0 MPM = 816. RPM = 181.

0 10 20 30 40 50 60

0

0.01

0.02

0.03

0.04

0.05

0.06

Frequency in Order

PK

Acc

eler

atio

n in

G-s

8.81

17.6

2

26.4

3

35.2

4

44.0

5

52.8

6

Ordr: Freq: Spec:

8.810 1593.7 .04402

>SKF 22334CC M=BPFI : 8.81

M M M M M M

On tracking the bearing fault over the coming weeks it was noticed that the bearing was deteriorating rapidly. After discussions with production and maintenance it was decided to take advantage of the next wire change and replace the roll within a planned shut. Wire changes occur every 3 months to ensure paper quality is maintained. This action would incur no downtime because it was a planned outage. The multiple spectrum plot below shows the bearing defect deteriorating over time.

The next plot below shows a trend of the overall value. The bearing was rapidly deteriorating The monitoring frequency was increased to once a day so the fault could be monitored closely until the planned shut arrived.

PK

Acc

eler

atio

n in

G-s

Frequency in Order

PS76 - Wire Forming Roll (1435mm)Frm/Roll -TSA Forming Roll Tender Side Axial

0 10 20 30 40 50 60

0

0.02

0.04

0.06

0.08

0.10Max Amp .11

28-AUG-9921-SEP-99

15-NOV-9906-JAN-00

12-JAN-0013-JAN-00

14-JAN-0014-JAN-00

17-JAN-0019-JAN-00

22-JAN-0024-JAN-00

27-JAN-0028-JAN-00

29-JAN-0004-FEB-00

15-FEB-00

Bearing detected

Bearing Changed

PS76 - Wire Forming Roll (1435mm)Frm/Roll -TSA Forming Roll Tender Side Axial

Trend Display of OVERALL VALUE

-- Baseline -- Value: .475 Date: 02-JUL-98

240 300 360 420 480 540 600

0

1

2

3

4

5

6

Days: 31-JUL-98 To 15-FEB-00

RM

S V

elo

city

in m

m/S

ec

ALERT FAULT

BEARING CHANGED

The roll was replaced for the spare roll in the planned shut. The roll was stripped and the inner bearing was inspected for damage. As predicted the inner race was badly spalled ( see below ). The bearing would not of lasted much longer. Failure of this bearing would have incurred heavy production losses and expensive damage to the 30 ton forming roll. The bearing was sent away for analysis to find the root cause of the damage.

Estimated Cost Savings

Actual Costs ( Action Taken ) Costs ( No Action Taken ) Parts : New Bearings Skf 239/710 35% of ERV ( Estimated replacement Value Skf 230/500 0.35 x £ 150000 ( Cost of New Roll ) Skf 22334 = £ 52500 = £ 22000 New wire needed if unplanned breakdown Labour : 6 men , 10 hours @ £ 30/ hour occurred = £ 24000 ( New Wire ) To remove and replace roll = £ 1800 Labour : 6 men, 12 hours @ £45 /hour = £ 3240 Production Losses: None, job planned in with routine wire change Production losses: 12 hours downtime @ £ 3600 / hour = £ 43200 Total Cost = £ 23800 Total Cost = £ 122940 £ 23800 - £ 122940

Estimated Avoided Cost = £ 99140