MG705: Management Models for the 21st Century Workforce
feng shui estrellas voladoras xuan kong china analisis
CASE 3
motorbus company
Descripción: These are the slides from the third eCommerce lecture on Ocado case study at the Business School - University of Hertfordshire.
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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 Wire Formin g Roll (1435mm) (1435mm) Frm/Roll -DSA Forming Roll Drive Side Axial
Frequency in Order Label: INNER RACE DEFECT DEFECT ON SKF 22334CC 22334CC
40
50
60
Ordr: 8.810 Freq: 1593.7 Spec: .04402
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.
PS76 - Wire Forming Rol l (1435mm) Frm/Roll -TSA Forming Roll Tender Side Axial 0.10
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.
PS76 - Wire Forming Roll (1435mm) Frm/Roll -TSA Forming Roll Tender Side Axial
6
BEARING CHANGED
5
c e S / m m n i y t i c o l e V S M R
Trend Display of OVERALL VALUE
-- Baseline -Value: .475 Date: 02-JUL-98
4
3
2
1 FAULT ALERT 0 240
300
360
420
480
Days: 31-JUL-98 To 15-FEB-00
540
600
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
Actu al Costs ( Acti on Taken )
Cos ts ( No Act io n Tak en )
Parts : New Bearings Skf 239/710 Value Skf 230/500 Skf 22334 = £ 22000
35% of ERV ( Estimated replacement 0.35 x £ 150000 ( Cost of New Roll ) = £ 52500 New wire needed if unplanned br eakdown occurred = £ 24000 ( New Wire )
Labour : 6 men , 10 hours @ £ 30/ hour To remove and replace roll = £ 1800
Labour : 6 men, 12 hours @ £45 /hour = £ 3240
Production Losses: None, job planned in with routine wire change
