1

Advanced Condition Monitoring Techniques Applied in Mining.

By Peter Watson, Vibration Engineer, U.K. Coal Mining Ltd. Abstract

Historically third party specialists have always provided condition monitoring services to U.K.Coal. In 1999 the management at U.K.Coal decided to bring the condition monitoring function “In House”. Many different Software and Hardware packages were researched. Emerson Process Management were invited into a working partnership with U.K. Coal. We were particularly impressed by the powerful analysis features available in their Machinery Health Manager Software, allowing the oil and vibration programmes to run from a single platform. Emerson’s were also able to offer hardware solutions by the means a C.S.I. data collector that would meet the legislative requirements required to take the instrument underground into a hazardous environment. A Used Oil Analysis Laboratory was set up at the company Head Quarters in Doncaster along with individual R.C.M. departments at each mine. Each mine collecting and managing the used oil samples before forwarding them to the lab, as well as running a vibration monitoring programme. In this paper I aim to show some of the success achieved by the R.C.M. programme operated by U.K.Coal. Diagnosing Machinery Faults using Vibration Analysis Vibration analysis is a non-invasive test, which tells us a machines condition whilst the machinery is under load. We use this data to help diagnose machinery faults. Each machine defect generates a specific vibration characteristic, which is determined by the machines geometry and operating speed. A single vibration measurement can provide information about multiple components, including:

• Imbalance • Misalignment • General Looseness or Wear • Bearing Defects • Gear Defects

In the first section of this paper I aim to provide case studies of how the Vibration Monitoring Programme has successfully highlighted various types of defects, allowing corrective actions to be taken in planned maintenance periods.

2

Imbalance Fault The first case study covers an Imbalance fault detected at Wistow Mine on their Main South Intake conveyor. At the time the fault was detected the conveyor was providing coal clearance for two single entry faces and four developments. Figure 1 shows a waterfall plot of vibration data collected from the input shaft of the gearbox in a radial plane. The waterfall plot is an analytical feature within the software that allows the annalist to analyse the data, also allowing the data to be trended. The highlighted synchronous peak at 24.9Hz (one order of rotation) indicates vibration at the frequency of the input shaft, at an amplitude of 11.54mm/s. A considerable increase can be seen in the shaft frequency vibration compared to the data collected on the 26th of April. Figure 1.

A work instruction was raised, requesting that the input shaft assembly be inspected, paying particular interest to the coupling security. On inspection three of the six motor to resilient plate bolts were found to have come adrift, and the resilient plate was found to be broken and cracked. See figure 2. Figure 2.

RM

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Frequency in Hz

SIT - DRIVE 1DRIVE1 -G1H Shaft 01 Inboard Vertical

0 20 40 60 80 100 120 140

0

3

6

9

12Max Amp 11.5

10:58:4126-Apr-01

12:22:5411-May-01

11:45:5214-May-01

RPM= 1470. 12:22:54 11-May-01

Freq: Ordr: Sp 2: Dfrq:

24.90 1.016 11.54 .00000

CCrraacckk

11: May 01 12:22 RPM1470 Freq. 24.90 Ordr: 1.016 Spec: 11.64

3

The work order was raised on a Friday, the inspection and repairs were carried out over the weekend which was a planned non production period, with the conveyor being available to run on the Monday morning, with no delay to production. Figure one shows the vibration at shaft frequency returned to a acceptable level after the corrective works had been carried out. Misalignment Shaft misalignment is another problem that can be detected using Vibration Analysis, which if left un-corrected can lead to seal failure, which then leads to dirt and water ingress, which then leads to oil contamination leading to bearing failure, that’s if the bearing hasn’t already failed due to the stresses induced by the misalignment. Vibration analysis can detect parallel offset misalignment, angular misalignment, more often than not both are experienced. My next case study covers a misalignment fault detected on the North East Booster Fan at Maltby Colliery. The online vibration monitoring system detected an high level of low frequency vibration when the fan was re started after an annual maintenance inspection. Because of this detailed vibration data was collected aiming to determine the nature and severity of the excessive low frequency vibration. Figure 3 shows a single vibration spectra collected in a radial plane from the fan bearing. The highlighted synchronous peak at Two Times Shaft Frequency indicating offset misalignment.

Angular

Both

Offset

4

Figure 3.

Laser alignment equipment was used to check the shaft alignment condition, with measurements being taken from the fan assembly and inputted into the alignment computer. The alignment computer then makes a calculation as to the alignment condition once alignment measurements have been taken. See figure 4 Figure 4. The alignment condition was found to outside of an acceptable tolerance. The laser was used to re-align the shafts to with in an acceptable tolerance band. See figure 5. Figure 5

NEBF - NE BOOSTER FANNE BOOSTER-F1H FAN DE

Route Spectrum 19-Jul-04 10:47:42

OVERALL= 6.11 V-DG RMS = 6.07 LOAD = 100.0 RPM = 1493. (24.88 Hz)

0 50 100 150 200 250 300 3500

1

2

3

4

5

6

7

8

Frequency in Hz

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Freq: Ordr: Spec:

49.92 2.006 6.016

Freq. 49.92 Ordr: 2.006 Spec: 6.019

5

Further vibration data was collected to access the level of improvement after the corrective actions had been completed. Figure 6 shows a waterfall plot of vibration data taken from the fan bearing. The data collected 15th of June 01 shows acceptable levels of vibration at two times shaft frequency, with an increase at this frequency being recorded after the maintenance works had been carried out. A return to acceptable levels of vibration was recorded after the shafts were realigned, data 21st July 04.

6

Figure 6.

The software allows various parameters to be trended, with a trend of the 2 times shaft frequency parameter, indicating a return to acceptable levels of vibration. See figure 7. Figure 7.

NEBF - NE BOOSTER FANNE BOOSTER-F1H FAN DE

Trend Display of 2xTS

-- Baseline -- Value: .397 Date: 19-Sep-01

0 20 40 60 80 1001

2

3

4

5

6

7

Days: 04-May-04 To 05-Aug-04

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Date: Time: Ampl:

19-Jul-04 10:47:48 6.028

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Frequency in Hz

NEBF - NE BOOSTER FANNE BOOSTER-F1H FAN DE

0 20 40 60 80 100 120 140

0

1

2

3

4

5

6Max Amp 5.23

10:35:0115-Jun-04

10:47:4219-Jul-04

08:18:5221-Jul-04

RPM= 1493. 10:47:42 19-Jul-04

Freq: Ordr: Sp 2: Dfrq:

50.31 2.022 5.997 .00000

7

SKF state that 34% of bearings fail prematurely due to abuse in service. It is important that any misalignment is corrected as soon as possible, preventing any secondary damage from occurring.

Rolling Element Bearings.

Probably the most detected fault using vibration analysis techniques are faults with-in Rolling Element Bearings. We are able to accurately predict four defects with in a bearing. See figure 8.

The Four Bearing Defect Frequencies

Ball Spin Frequency

Bearing Cage Frequency

Ball Pass Frequency Inner Race

Ball Pass Frequency Outer Race

(BPFO)

8

My third case study covers a bearing fault detected at Gascoigne Wood Mine on their Anderson Strathclyde Conveyor using vibration and oil analysis techniques.

Gascoigne Wood Mine was the coal handling plant for the Selby Coal Field. The mine was designed to process the output of five deep mines via two conveyor systems. At the time of the bearing fault only three mines were in production, Wistow, Stillingfleet and Riccall producing five million tonnes per annum. The Selby Coalfield ceased production in November 2004. The A.S.L. Conveyor is 12.2 Km long, with a capacity of 3500 tonnes per hour and with a lift of 800m, achieving over 98% availability. Figure 9 shows a plan of the Selby Coal Field.

9

A bearing defect was detected at our oil laboratory whilst carrying out routine oil analysis on a drive deflection drum. (see fig.10) Figure 10 shows the oil sample report from the Conveyor Drum in question, with large ferrous particles being present in the oil between three hundred and eight hundred microns. Figure 10.

At this time routine vibration data was not being collected due to access restrictions. As a result of the concerns highlighted by the oil analysis programme, remote accelerometers were fitted and vibration data was collected to determine the severity and nature of any defect. See figure 11.

MR I.DIXON, GASCOIGNE WOOD MINE.

Readings appear stable; some large ferrous particles were found, indicating much heavier than normal wear. Also there are a few very large non-magnetic particles, could be from a bronze cage. Check vibration for bearing activity. We would advise change and/or inspection at the next opportunity.

10

Figure 11 shows a single Vibration Spectra and Time Domain Waveform taken using C.S.I. Peakvue technology from the right hand bearing of the snub drum. The Spectra indicating a bearing defect. Figure 11. No bearing specifications were available as the bearings were non-standard, specifically designed for the application. Although bearing specifications were not available it was apparent the bearing was in the final stages of failure. The severity of any defect using Peakvue Technology is judged by analysing the Peak-to-Peak amplitude in the time domain waveform. With force being proportional to speed a conservative alarm for a bearing operating at this frequency would be 1g Peak to Peak. Rule of thumb calculations were used, aiming to identify the defective component with in the bearing. Ball Pass Freq. Inner Race = No Rolling Elements*Rotational Freq.*0.6 12.5 = ? * 1.77 *0.6 After transposing the formula I calculated the predicted number of rolling elements to be 11.77. If that number is rounded up to 12 the Fundamental Fault Frequency rises by only 0.2Hz to 12.7Hz Ball Pass Freq. Inner Race = No Rolling Elements*Rotational Freq.*0.6 = 12 * 1.77 *0.6 Ball Pass Freq. Inner Race = 12.7Hz A spare drum was available, this was inspected and a component change was planned. The change out of the drum ran for three twelve-hour shifts over a planned non-production period. On investigation the inner raceway of the bearing was defective as predicted.

ROUTE WAVEFORM 31-Oct-03 08:30:33 (PkVue- HP 500 Hz) PK = .9137 PK(+) = 5.13 PK(-) = .2505 CRESTF= 7.95

0 3 6 9 12 15-1

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1

2

3

4

56

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ASL - SNUB DRUMROLLER 5 -R2P SNUB DRUM NORTH BEARING

ROUTE SPECTRUM 31-Oct-03 08:30:33 (PkVue- HP 500 Hz) OVERALL= .4592 A-DG PK = .4568 LOAD = 100.0 RPM = 106. RPS = 1.77

0 50 100 150 200 250 300 350 4000

0.04

0.08

0.12

0.16

0.20

0.24

Frequency in Hz

PK A

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Freq: Ordr: Spec:

12.50 7.069 .167

Fault frequency @12.5Hz

11

Figure 12. shows the inner raceway of the bearing

Figure 13 shows the drum shaft and bearing parts.

12

Figure 14 shows the bearing cage and rolling elements.

Figure 15 shows an Overall Value Trend of the vibration measurements taken, up to a point where the drum was changed. Figure 15.

ASL - SNUB DRUMROLLER 5 -R1P SNUB DRUM SOUTH BEARING

Trend Display of Overall Value

-- Baseline -- Value: .216 Date: 28-Oct-03

0 2 4 6 8 10 12 140.12

0.18

0.24

0.30

0.36

0.42

Days: 31-Oct-03 To 13-Nov-03

PK A

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Last reading before drum was changed

13

Conclusion Had the fault not been detected and the bearing in question subsequently failed in service Riccall Mine would have lost two days production, Wistow and Stillingfleet Mines would deliver onto the standby conveyor running at reduced capacity. Due to the design of the drum amounts oil debris collected were inconsistent. The fault would have been confirmed earlier had vibration data been collected, reducing the risk of an unplanned conveyor stoppage. With SKF quoting that 16% of bearings fail prematurely due to poor fitting, 36% due to inadequate lubrication and 14% failing prematurely due to contamination. I feel that it is important that bearings are monitored to predict these problems, so corrective actions can be taken, reducing the risk of bearing failure. Poor Gearbox Build Highlighted using Vibration Monitoring Techniques.

The gearbox in question had been over hauled at our workshop facility. The gearbox was then sent to one of our suppliers for testing on their test rig. The unit in question was a Meco 400 Horse Power 28:1 gearbox to be fitted to an in line chain conveyor, carrying coal for one coal face and four tunnel drivages at Stillingfleet Mine. Figure 8 shows a single vibration spectrum taken from the input shaft of the gearbox. The first highlighted peak of 499Hz indicates the gear mesh activity between the first and second gear. Gear mesh activity is a natural characteristic of gears in mesh, but the excessive side band activity evident indicates excessive clearance between the gear flanks. By measuring the sideband peaks we can determine which of the two meshing gears are a cause for concern. Figure 8.

STIL - S400T 28:1 GEARBOXS/FLEET -G1H Shaft 01 Inboard Horizontal

Route Spectrum 15-Jul-03 09:46:18

OVERALL= .3927 A-DG PK = .3919 LOAD = 100.0 RPM = 1498. RPS = 24.96

0 500 1000 1500 2000

0

0.03

0.06

0.09

0.12

Frequency in Hz

PK A

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Freq: Ordr: Spec:

499.18 20.00 .08772

>JOY S400T F=Grmesh(1>2)

F F F F

Sideband activity

Gear Mesh Frequency @ 499Hz

14

Meco ST400 28:1 Gearbox

Figure 9 shows a plan of the gearbox, with gear mesh calculations. Gear Mesh Frequency = Shaft Frequency * Number of Gear Teeth = 24.95Hz * 20 = 499Hz Figure 10 shows the single vibration spectra, concentrating around the gear mesh peak to measure the sideband activity in order to identify the problem and give a positive recommendation. Figure 10.

Gear Mesh Frequency @ 499Hz

STIL - S400T 28:1 GEARBOXS/FLEET -G1H Shaft 01 Inboard Horizontal

Route Spectrum 15-Jul-03 09:46:18

OVERALL= .3927 A-DG PK = .1598 LOAD = 100.0 RPM = 1498. RPS = 24.96

400 440 480 520 560 600 640

0

0.03

0.06

0.09

0.12

Frequency in Hz

PK A

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in G

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Freq: Ordr: Spec: Dfrq:

508.43 20.37 .02696 9.250

Sidebands measured at 9.25Hz

15

Sidebands indicate the rotational frequency of the offending gear. Frequency of Shaft/Gear 2 = Gear Mesh Frequency / Teeth on Gear 2 = 499 / 54 = 9.24Hz The sideband activity indicates the second gear to be causing the excessive gear mesh activity. The backlash on this gearbox is set by shimming the second shaft along, thus adjusting the depth of mesh between the gears. Because of this recommendations were made to check the backlash and adjust if required. On investigation the backlash was found to be out of tolerance and was reset. Figure 11 shows a vibration waterfall plot taken from the input shaft of the gearbox. The data in blue dated 24th July 03 showing a positive effect on the gearbox vibration after the backlash was reset. Figure 11.

RM

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Frequency in Hz

STIL - S400T 28:1 GEARBOXS/FLEET -G1H Shaft 01 Inboard Horizontal

0 500 1000 1500 2000

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07Max Amp .0603

13:24:4124-Jul-03

09:46:1815-Jul-03

Conclusion. Had the excessive backlash not been detected and reset premature wear would have been inevitable, reducing the service life of the gearbox. The gearbox was to be fitted in an extremely awkward location once it had been transported to site two miles underground, hence making the quality of the build paramount.

16

Testing of Equipment at the Original Equipment Manufacturer.

As part of our in house quality assurance procedures items of critical plant are vibration tested at the Original Equipment Manufacture prior to being despatched. When you consider the work involved in transporting the items of plant often weighing up to 15 tonnes down the mine shaft.

Then transporting the machinery long distances often in excess of 5 miles to the coalface and development areas of the mine. It is extremely important that the equipment leaves the O.E.M. in perfect working order. Ineffective Component Inspection Procedure, Highlighted using Emerson’s PeakVue™ Technology. The unit in question was a cutting head gearbox that had been overhauled at our own workshop facility. On an initial test run concerns were raised over an abnormal noise from the unit. Standard vibration and PeakVue ™ measurements were taken along the gearbox, aiming to identify any potential faults, with concerns being raised around the third shaft. Figure 12 shows a plan of the Cutting Head Gearbox.

G1

G3

G4

G5

G6

G7

G8

G9

G10

G11

G12

M1 M2

Faulty Gear

17

Figure 13 shows a single PeakVue Vibration Spectrum taken from shaft 3 of the gearbox. Emerson’s PeakVue Technology works by filtering out background noise, looking at the high frequency activity associated with metal to metal impacting. The 1 order peak highlighted at 6.9Hz indicates an impact every revolution of the third shaft. Figure13

When the Time Domain data is analysed the true extent of the problem becomes apparent. A severe impact can be seen every revolution of the third shaft. Figure 14. When we referred to the standard vibration measurement, no activity of any significance was recorded. The time waveform showed no signs of the once per revolution impact.

DTB - Boom Gear BoxBGB -G5P Shaft 03 Inboard Horz Peakvue

Route Spectrum 09-Jan-01 13:30:21 (PkVue-HP 1000 Hz)

OVERALL= 1.55 A-DG RMS = 1.47 LOAD = 100.0 RPM = 415. (6.91 Hz)

0 40 80 120 160 200 240 280 320

0

0.1

0.2

0.3

0.4

0.5

0.6

Frequency in Hz

RM

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Freq: Ordr: Spec:

6.914 1.000 .494

Freq: 6. 9Hz Order: 1.00 Spec: .494

DTB - Boom Gear BoxBGB -G5P Shaft 03 Inboard Horz Peakvue

Route Waveform 09-Jan-01 13:30:21 (PkVue-HP 1000 Hz)

RMS = 2.14 LOAD = 100.0 RPM = 431. (7.19 Hz)

PK(+) = 14.25 CRESTF= 6.65 DCoff = -1.32

0 0.5 1.0 1.5 2.0 2.5 3.0

0

3

6

9

12

15

Revolution Number

Acc

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18

Figure15 PeakVue™ Technology has proved extremely effective and reliable, helping us detect many low frequency bearing problems and high frequency gear defects. Because of the PeakVue™ data, recommendations were made to strip down and inspect the gearbox, with the suspected fault being a damaged tooth on the third shaft assembly. On inspection a crack was found at the root of the gear tooth as predicted. See figure 16. Figure16.

Route Waveform 09-Jan-01 13:30:33 RMS = .1546 PK(+/-) = .5971/.5595 CRESTF= 3.86

0 1 2 3 4 5

-0.8-0.6-0.4-0.20.00.20.40.60.8

Revolution Number

Acc

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DTB - Boom Gear BoxBGB -G5V Shaft 03 Inboard Vertical

Route Spectrum 09-Jan-01 13:30:33 OVERALL= .9308 V-DG RMS = .2367 LOAD = 100.0 RPM = 431. (7.19 Hz)

0 300 600 900 1200 1500

0

0.03

0.06

0.09

0.12

Frequency in Hz

RM

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19

This road heading machine is transported modular to the development area of the mine and then assembled. Had the gearbox been fitted it would have failed in a catastrophic manner, causing excessive secondary damage to the gearbox as well as a delay to the development well in excess of 24 hours. Figure17.

20

Ineffective Component Inspection Procedure: Ranging Arm Gearbox. My 2nd case study in this section again covers an ineffective component inspection on a Ranging Arm gearbox. Figure 18 shows a typical Retreat coal face.

With all the equipment being transported modular via a network of roadways before being assembled at the coal face. Figure 19.

Shearer

Powered Roof Supports

AFC

BSL

Gate Conveyor

21

The gearbox in question drives from a motor via speed reduction and transmission gears, then out through a epicyclic section to which the cutting disk is mounted. See Figure 20. Various vibration measurements were taken along the gearbox to assess its condition. Figure 20.

Figure 21 shows a single PeakVue™ Vibration Spectrum taken from the epicyclic section of the gearbox, with excessive Gear mesh and sideband activity being present. Figure 21.

EL60 - EL600-EL32A L/H RANGING ARMEL32A RANG-10P Shaft 07 Inboard Horz Peakvue

Route Spectrum 09-Nov-04 11:51:46 (PkVue-HP 1000 Hz)

OVERALL= 1.80 A-DG PK = 1.80 LOAD = 100.0 RPM = 552. (9.20 Hz)

0 200 400 600 800 1000

0

0.1

0.2

0.3

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0.6

0.7

Frequency in Hz

PK A

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Typical Ranging Arm Gearbox.

Gear Mesh and Sideband Activity

22

Using the waterfall plot feature, the data was compared with the information collected from the Shearer’s other ranging arm gearbox. See figure 22. A significant difference in characteristic and amplitude can be seen. Figure 22.

I calculated the frequency of the planet carrier with in the epicyclic to be 2.9Hz. Reduction Calculation = 1 . 1-RO RO = (Static Ring/Sun)+1 = (59 / 28) +1 = 3.1 Output Freq.(Planet Carrier)= Input Freq./ RO = 8.98Hz / 3.1 Output Freq.(Planet Carrier)=2.9Hz

Using the software to manipulate the data the sidebands measured 2.9Hz. See figure 23 Sidebands indicate excessive clearance between the gear flanks. In this case the sidebands match the rotational frequency of the planet carrier, which supports the planet gears. In this instance the Epicyclic section wasn’t new, but had been inspected and passed fit for use. Figure 23.

PK A

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Frequency in Hz

EL60-EL600-EL32A L/H RANGING ARM EL32A RANGEL60-EL600-EL32A R/H RANGING ARM EL32A (15-Nov-04)

0 100 200 300 400 500

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35Max Amp .34

EL32A

EL32A RANG

L/Hand Ranging Arm

R/Hand Ranging Arm

23

Because the gearbox had always run in the same direction I carried out some tests running the gearbox in the opposite direction, effectively driving on a new gear flank. See figure 24. As anticipated the gear mesh and sideband activity were virtually non-existent. Figure 24. To prove the activity recorded wasn’t a characteristic of running direction, further vibration tests were carried out on the Shearer’s other ranging arm. See figure 25. With the same low levels of activity being recorded in both directions.

Figure 25.

EL60 - EL600-EL32A L/H RANGING ARMEL32A RANG-10P Shaft 07 Inboard Horz Peakvue

Route Spectrum 09-Nov-04 11:51:46 (PkVue-HP 1000 Hz)

OVERALL= 1.27 A-DG RMS = .5974 LOAD = 100.0 RPM = 539. (8.99 Hz)

155 160 165 170 175 180 185

0

0.1

0.2

0.3

0.4

0.5

Frequency in Hz

RM

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Freq: Ordr: Spec: Dfrq:

172.27 19.16 .149 2.963

Sidebands at Rotational Freq. of Planet Carrier 2.96Hz

Gear Meshing Activity of Sun/Planets 169.31Hz

Freq: 172.27 Ordr: 19.16 Spec: .149 Dfrq: 2.963

Right Hand Ranging Arm Direction Comparison

24

In my opinion the gearbox would not reach its intended design life if ran with the excessive gear mesh activity present. Because of this recommendations were made for the gearbox to be re handed before being put into service, without any new components being required.

Changing out a ranging arm underground requires a considerable amount of hard work. If the gearbox failed in service many production shifts would be lost.

Figure 26

The old unit would have to be removed, with the new one was being transported to site and fitted.

25

Figure 27 shows a coal face supply gate with excessive floor heave, making the transportation of equipment to site difficult. Making an effective quality assurance procedure essential.

BEARING FAULT DETECTION ON A CONVEYOR DRIVE MOTOR USING VIBRATION ANALYSIS TECHNIQUES.

The R.C.M. Department at Rossington Colliery detected a bearing fault on the N.D.E. of the above-mentioned Motor. After further investigation and analysis the Site Engineer was advised that the motor’s N.D.E. bearing was in the final stages of failure and that the motor be removed from service at the first available opportunity. 68’s No3 Conveyor at the time was supporting coal clearance for one production coalface and four tunnel drivages. Figure 12 shows a Peakvue frequency based vibration spectra and a time domain waveform collected from the non-drive end of the motor in question. The frequency of the fault is showing at two times ball spin frequency. The severity of the fault being judged by analysing the Peak to Peak Value in the time waveform. The average values recorded were in excess of 30g’s Peak to Peak, an alarm level for this type of fault at this operating frequency being 6g’s Peak to Peak.

26

Figure 28.

Route Waveform 06-Jul-04 11:45:09 (PkVue-HP 1000 Hz) RMS = 15.83 PK(+) = 58.51 CRESTF= 3.42 DCoff = 0.0

0 1 2 3 4 5

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10

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30

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68s3 - Drive 2Drive2 -M1P Motor Outboard Horz Peakvue

Route Spectrum 06-Jul-04 11:45:09 (PkVue-HP 1000 Hz) OVERALL= 7.09 A-DG RMS = 7.05 LOAD = 100.0 RPM = 1496. (24.93 H

0 200 400 600 800 1000

0 0.51.01.52.02.53.03.54.0

Frequency in Hz

RM

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Freq: Ordr: Spec:

132.77 5.326 3.403

>SKF N317 R=BSF -OB

R R R R R R R R R R R R R R R

Figure 29 shows a Waterfall Plot of Vibration data collected from the motor. The data in purple showing the faulty bearing and the data in blue with a new motor fitted. Figure 29.

RM

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Frequency in Hz

68s3 - Drive 2Drive2 -M1P Motor Outboard Horz Peakvue

0 200 400 600 800 1000

0

0.5

1.0

1.5

2.0

2.5

3.0Max Amp 3.00

09:02:3614-Jul-04

11:45:0906-Jul-04

27

On investigation severe Brinelling on both inner and outer raceways was found. The following photographs show the Brinelling on the raceways at equal intervals to the rolling elements. Figure 30 shows Brinelling evident on the outer race of the bearing. Figure 31 shows Brinelling evident on the inner race of the bearing.

28

Cost Benefit Analysis. Production Cost Calculations.

1. Anticipated lost production time. 240 Mins 2. Rossington Face Cycle Time 42 Mins/Strip 3. Tonnes per Strip 614 Tonnes 4. Cost per Tonne £26.64

Figures calculated assuming no delays. 240Mins/42Mins per Strip 5.72 Strips 614 Tonnes * 5.72 Strips 3512 Tonnes 3512Tonnes * £26.64 £93,559.68 Cost avoidance of potential Dangerous Occurrence ! Anticipated lost production time. 4 Hours £93,559.68 (Carry out on-site investigation, pull back the motor after disengaging transmission) Anticipated Repair Costs had Motor Failed £8126 in a catastrophic manner, less the quoted repair. Total £101685.68 Conclusion. This bearing fault had shown no temperature increase, which is usually a good indication of a bearing in failure mode. On researching this I have found that this type of bearing fault does not generate any temperature increase until the bearing collapses. Had a bearing of this type failed in service a risk of creating an ignition could have occurred. In an underground environment this failure had the potential to cause a fire, putting many lives at risk. Eighty per cent of underground fires are related to bearing failures, making a good R.C.M. programme essential. This paper has demonstrated how we can predict many different types of fault, all of which required significant corrective actions to be taken. What is of great benefit is to be able to detect something, which if left uncorrected has the potential to cause a fault, which if diagnosed early enough requires no more than a lick of grease or a drop of oil to prevent any fault developing. The last case study covers the overhaul of a 90kW auxiliary fan at the O.E.M. The fan had passed the O.E.M.s own quality assurance procedure before being sent out to Rossington Colliery. The R.c.m. team at Rossington tested the fan as part of our own quality assurance procedure. The fan motor failed the test due to excessive high frequency vibration, with the suspected fault being a lack of lubrication at the drive end bearing. The fan was sent back to the O.E.M. and Vibration data was collected from the Drive End Bearing of the motor, with High Frequency Broad band Energy seen, see figure 32.

29

Fig.32.

16.2 - 90Kw FAN-150090150090 -M2H Motor Inboard Horizontal

Route Spectrum 17-Feb-04 10:40:23

OVERALL= 1.47 V-DG RMS = 1.83 LOAD = 100.0 RPM = 2978. (49.63 Hz)

0 1000 2000 3000 4000

0

0.04

0.08

0.12

0.16

0.20

0.24

Frequency in Hz

RM

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High Frequency Broadband Energy usually indicates a lack of lubrication. The drive end bearing was greased, with small amounts being applied over a period along with further vibration measurements being taken. Eventually the Broad Band Energy reduced. The waterfall plot shows a considerable improvement, with no permanent damage being recorded. See figure 33. Figure 33.

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16.2 - 90Kw FAN-150090150090 -M2H Motor Inboard Horizontal (17-Feb-04)

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High Frequency Broadband Energy Indicating a Lack of Lubrication

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Auxiliary fans are used to ventilate the development areas of the mine (see fig.34), this often involves transporting the fan in excess of 5 miles to site. Because of the danger posed by a bearing failing on a fan it is essential that the fans bearing condition is checked at commissioning then monitored as part of a pro active Condition Monitoring Programme. Figure 34.

Equipment Change-out Summary 2005 So far 2005 has been a good year for the Condition Monitoring programme operated by U.K. Coal, with approximately three hundred and thirty critical plant systems being monitored within the R.C.M. programme on a two weekly schedule. Throughout the year a over of 236000 vibration measurements will be taken with over 33000 oil samples being collected and analysed across the seven deep mine sites. The table below shows a summary of plant items changed so far in 2005.

R.C.M. Technology. Planned Change. Unplanned Change

Vibration Monitoring 94 16 Oil Analysis 25 10 Both Technologies 33 11 Total Plant Items Changed 152 37 Many of the planned equipment changes were investigated with defective components found as predicted. Of the thirty seven unplanned changes over fifty per cent of the failures were reported as being a cause for concern, but for various reasons were not investigated or the equipment examination was rescheduled due to production demands.

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Income Lost per Minute of Lost Production

Daw Mill £519 Harworth £262 Kellingley £468 Maltby £274 Rossington £274 Thoresby £310 Welbeck £246

When you consider the cost of lost production to us at U.K.Coal you will can understand why we place great emphasis on operating an effective condition monitoring policy. Condition Monitoring Statement. Planned equipment changes do not interrupt production and early equipment change out reduces the consequential cost of repair. It is my opinion that if planned equipment change recommendations are ignored the item of plant in question often makes the decision for you at a later date. Cen-tech Ltd Cen-tech Ltd is a wholly owned subsidiary of U.K.Coal Mining Ltd. We are using Cen-tech as a vehicle to sell our Condition Monitoring expertise to third parties. We are able to offer a wide range of Condition Monitoring services, including Vibration and Oil Analysis, Laser Alignment and Thermographic Surveys.