Lubrication issues

Rolling Element skidding

Pulverized Fuel Mill

Laurence-Scott985 RPM 522KW

Driving a bowl mill

Continuous operation

12 Across the site

Details

Drive End Bearing - NU322

Greased weekly with 8 ‘shots’

Audible screech from bearing on various motors

Cavity shows grease exiting grease relief, some more than others

Hay stacks around 4000 Hz

RM

S A

ccel

erat

ion

in G

-s

Frequency in Hz

VBLR - Mill 5CMILL5C -M2X Motor DE Vertical (ACC)

0 2000 4000 6000 8000

Max Amp .27

Plot Scale

0

0.14

14:18:4722-Apr-10

10:55:1125-May-10

15:51:3125-Aug-10

Autocorrelation

Autocorrelation indicates random noise

VBLR - Mill 5CMILL5C -M2X Motor DE Vertical (ACC)

Route ACorr(Wf) 25-May-10 10:55:11

RMS = .0352 LOAD = 100.0 RPM = 975. (16.24 Hz)

PK(+) = .7861 PK(-) = .9181 CRESTF= 26.11

3.0 3.3 3.6 3.9 4.2

-1.0

-0.5

0

0.5

1.0

Rev olution Number

Co

rre

lati

on F

ac

tor

Overall acceleration trend is erratic

VBLR - Mill 5CMILL5C -M2X Motor DE Vertical (ACC)

Trend Display of Ov erall Value

-- Baseline -- Value: .460 Date: 09-Feb-10

0 50 100 150 200

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

Days: 09-Feb-10 To 25-Aug-10

RM

S A

cce

lera

tio

n i

n G

-s

ALERT FAULT

Date: Time: Ampl:

25-May-10 10:55:10 2.025

PeakVue spectrum shows no significant changes60 Orders (990 Hz)1600 LOR1kHz HP

RM

S A

cce

lera

tio

n i

n G

-s

Frequency in Hz

VBLR - Mill 5CMILL5C -M2P Motor DE Horiz Peakv ue

0 200 400 600 800 1000

Max Amp .20

Plot Scale

0

0.10

14:18:1722-Apr-10

10:54:3825-May-10

15:51:0625-Aug-10

PeakVue waveforms show no significant impacting events, but a slight increase in amplitudes.

VBLR - Mill 5CMILL5C -M2P Motor DE Horiz Peakvue

Revolution Number

Ac

cel

era

tion

in

G-s

0 2 4 6 8 10 12 14

6.40 .0

22-Apr-10 14:18

7.55 .0

25-May-10 10:54

3.53 .0

25-Aug-10 15:51

Overall PeakVue trend shows no increase in stress wave activity. Downward trend could indicate that the reduction in grease quantity could be heading in the right direction.

VBLR - Mill 5CMILL5C -M2P Motor DE Horiz Peakvue

Trend Display of Ov erall Value

-- Baseline -- Value: 1.714 Date: 09-Feb-10

0 50 100 150 200

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

Days: 09-Feb-10 To 25-Aug-10

RM

S A

cce

lera

tio

n i

n G

-s

WARNING

ALERT

FAULT

Date: Time: Ampl:

22-Apr-10 14:18:16 .910

Primary Air Fans

Laurence-Scott2130kW1485 RPM

Four in continuous operation

Similar noise from Drive End bearing

NU330

Greased weekly on a ‘shot’ basis

Temperature spike coincides with the weekly lubrication program. In some cases up to 90 Degrees C.

RMS

Acce

lera

tion

in G

-s

Frequency in Hz

VBLR - Primary Air Fan 5APAF5A -M2X Motor DE Vertical (ACC)

0 2000 4000 6000 8000 10000

0

2.8

Max Amp 2.72

13:12:2509-Feb-10

10:48:3809-Mar-10

14:10:5901-Apr-10

12:09:0525-May-10

09:21:1323-Jun-10

14:33:2220-Jul-10

16:04:5925-Aug-10

Broadband non synchronous energy

PeakVue shows fault frequency’s

RM

S A

ccel

erat

ion

in G

-s

Frequency in Hz

VBLR - Primary Air Fan 5APAF5A -M2P Motor DE Horiz Peakvue

0 400 800 1200 1600

0

1

2

3

45

Max Amp 4.25

15:41:4401-Apr-10

09:15:0223-Jun-10

14:21:5920-Jul-10

16:04:0825-Aug-10

Autocorrelation shows a BPFO

VBLR - Primary Air Fan 5APAF5A -M2P Motor DE Horiz Peakvue

Route ACorr(Wf) 20-Jul-10 14:21:59 (PkVue-HP 2000 Hz)

RMS = .1208 LOAD = 80.0 RPM = 1480. (24.67 Hz)

PK(+) = .9579 PK(-) = .2318 CRESTF= 7.93

0 1 2 3 4 5 6

-1.0

-0.5

0

0.5

1.0

Revolution Number

Co

rre

lati

on F

ac

tor

Rev : Ampl:

2.439 .539

>SKF NU330 F=BPFO

F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F

PA Fan 6A

VBLR - Primary Air Fan 6APAF6A -M2X Motor DE Vertical (ACC)

Route Spectrum 24-Sep-10 09:37:12

OVERALL= 5.14 A-DG RMS = 5.15 LOAD = 100.0 RPM = 1493. (24.89 Hz)

0 2000 4000 6000 8000 10000

0

0.3

0.6

0.9

1.2

1.5

1.8

Frequency in Hz

RM

S A

cce

lera

tio

n i

n G

-s

Autocorrelation shows FTF and BPFO

VBLR - Primary Air Fan 6APAF6A -M2P Motor DE Horiz Peakv ue

Route Spectrum 24-Sep-10 09:36:49 (PkVue-HP 2000 Hz)

OVERALL= 3.13 A-DG RMS = 2.46 LOAD = 100.0 RPM = 1493. (24.88 Hz)

0 80 160 240 320 400 480

0

0.3

0.6

0.9

1.2

1.5

Frequency in Hz

RM

S A

cce

lera

tio

n i

n G

-s

Freq: Ordr: Spec:

10.00 .402 1.102

>SKF NU330 D=FTF

D D D D D D D D D D

VBLR - Primary Air Fan 6APAF6A -M2X Motor DE Vertical (ACC)

Route ACorr(Wf) 24-Sep-10 09:37:12

RMS = .0901 LOAD = 100.0 RPM = 1480. (24.67 Hz)

PK(+) = .7620 PK(-) = .6932 CRESTF= 8.46

0 1 2 3 4 5 6 7 8

-1.0

-0.5

0

0.5

1.0

Rev olution Number

Co

rre

lati

on F

ac

tor

Rev : Ampl:

2.440 -.460

>SKF NU330 D=FTF

D D D D

Other Symptoms

•During lubrication, little or no grease will exit the grease relief

Why? As grease is worked by the rolling elements oil is squeezed out of the matrix, causing the grease to harden in service. This can block the grease relief and grease can no longer be flushed through the bearing. When lubricated the fresh grease will take the path of least resistance, on older motors this is usually the inboard motor bearing seal. This results in the grease entering the windings or armature.

•Using a strobe can detect irregular movement of the rolling element

•However the noise is an obvious method to detect skidding. Skidding sounds like a high pitched screech that goes away with a pump of grease but usually comes back shortly after.

Adding grease can increase the overall trend

VBLR - Mill 5DMILL5D -M2P Motor DE Horiz Peakv

Strip Chart of Overall

0 30 60 90 120 150 180

1

2

3

4

5

6

7

8

Time in Seconds

RM

S A

ccel

erat

ion

in G

-s

Time: Ampl:

.00000 2.439

VBLR - Mill 5DMILL5D -M2P Motor DE Horiz Peakvue

Route Spectrum 22-Jun-10 16:53:26 (PkVue-HP 1000 Hz)

OVERALL= 1.04 A-DG RMS = 1.04 LOAD = 100.0 RPM = 990. (16.50 Hz)

0 200 400 600 800 1000

0

0.1

0.2

0.3

0.4

0.5

0.6

Frequency in Hz

RMS A

ccele

ration

in G

-s

Freq: Ordr: Spec:

93.75 5.682 .408

>SKF NU330E F=BPFO

F F F F F F F F F F

RMS A

ccele

ration

in G

-s

Frequency in Hz

VBLR-Mill 6A MILL6AVBLR-Mill 6F MILL6F (09-Feb-10)

0 2000 4000 6000 8000

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Max Amp .14

MILL6A

MILL6F

Spectrum will show haystacks PeakVue can show BPFO (not always)

Bearing skiddingCauses

• Over lubrication

If a grease cavity is full, the rollers can pull in (churn) extra grease causing over lubrication

• Blocked grease relief (causes over lubrication)

• Grease too thick for the application• Light radial loading i.e. Minimum load

requirements have not been met; gearbox is taking all of the load; magnetic centering of the motor has unloaded the bearing.

Minimum load requirement

NU 322 ECJ

Dynamic load rating 468 kN (47 tonne)

Minimum load rating 3.36 kN (340 kg’s)

Rotor weight 17% – 33% of total weight

Total weight=5080 kg

Rotor weight = 864 kg’s – 1524 kg’s

At the most each bearing is supporting 762 kg’s without taking into consideration magnetic centering, and weight supported by the gearbox.

Action by the ClientThe charge of grease has been reduced significantly. This has resulted in less over temperature alarms

However vibration data does not suggest a significant reduction in skidding.

Why no more action?Lack of conclusive evidence. Lack of understanding of vibration analysis, no acoustic data, no grease analysis performed.

No recommendation for specific action and fear of inducing further damage by changing current practice i.e. overheating a bearing by flushing out the cavity with fresh grease.

SolutionsMost desirable• Convert to oil lubricated

bearings• Purge old hard grease from

the cavity• Reduce the amount of

grease• Machine down the shaft and

install the appropriate bearing

• Replace the cylindrical roller with a deep groove roller

Least desirable• Utilise an out of round

raceway• Use two preloaded hollow

rollers

Not recommended• Misaligning the driver to

driven component

Other possibilities:

The noise and non synchronous broadband energy could be from a rub e.g. A bearing seal. This would also cause a temperature increase.

There could be metal to metal contact occurring. Why? If the grease has thickened in service metal to metal contact could be occurring due to the increased base oil separation and lack of fluid film thickness.

What effect does skidding have on longevity of the bearing?

Actions:Utilise Acoustic monitoringInspect the bearingTake a grease sampleClear the grease path/grease reliefAlter the lubrication interval – Reduce the lubrication frequency, increase the chargeChange the lubrication method – Use the appropriate technologyChange grease

What is missing?

More data:

•Acoustic•Temperature•A structured approach to problem solving•Evidence:- Strobe the rolling elements, inner and outer race inspection

Useful Web Resources

Emerson CSi Technical Notes

http://www2.emersonprocess.com/en-US/brands/csitechnologies/productsupport/Pages/TechnicalNotes.aspx

Svenska Kullagerfabriken (SKF) calculators

http://www.skf.com/skf/productcatalogue/jsp/calculation/calculationIndex.jsp?&maincatalogue=1&lang=en

References:

Drayton M, case studies viewed 28th September 2010 at http://www.lubrication.com.au/cs_bearing_skidding.htm

Goodman M, 2006, Using PdM technologies to determine, optimize lube condition, viewed 1 October 2010 at http://www.reliableplant.com/Read/23990/pdm-technologies-optimize-lube

Granger M, 2006, Using Sound Analysis to Monitor Lubrication Condition in Greased Roller Element Bearings, Doctor Know application paper, Computational Systems incorporated

Hall J, 2006, Acoustic/Ultrasonic Lubrication, viewed 16th April 2010 at www.reliabilityweb.com/art07/hall_lube_doc.pdf

Honeycutt J, et al, How To Design An Electric Motor Re-greasing Program, Tennessee Valley Authority, cited Johnson W, Electrical Power Research Institute

Jacobyansky B, et al, 2009, Changing Greasing Habits with Predictive Maintenance, Guardian Industries

Bearings Reference Centre, viewed 1 October 2010 at http://www.bearings.machinedesign.com/guiEdits/Content/BDE_6_4/bdemech6_30.aspx