Part 3 - Condition Monitoring

At the beginning of the project there was a need to identify the rolls with loose or failed bolts. A non-intrusive testing method was desired. The test process developed: Use vibration data measured at the end of the roll to detect faulty bearings. (This had been used in an aborted program). Monitor for changes in the natural frequency of the shaft-roll assembly to detect changes in the bolted joint stiffness, i.e., an indicator of loose or failed bolting. Develop a rotor model to calculate the natural frequencies, mode shapes, rotor deflection and bearing loading. Perform free-free and installed experimental modal testing of a shaftroll assembly Use bump testing to determine if this test could be used to identify defective shaft-roll bolted joints. 35

At the beginning of the project there was a need to identify the rolls with loose or failed bolts. A non-intrusive testing method was desired. The test process developed: Measure roll run out using a contact slider block or shaft rider instrumented with a low frequency accelerometer. Establish run out limits to indicate when to pull a roll.

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Although not considered the preferred method, access to the bearing housings was limited so a long stinger was used at the end of the rolls. (This method had been used previously in a now aborted program.)

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The data from the end of the roll could be used to identify the stage of bearing failure Ref. TA Vibration Chart. ! " # %

" # %

$ $&

&

$ '

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Roll End Brg

Outer race damage. Spalling and fatigue failure evident. Roller impressions occurred during pressing the bearing off the shaft. Most load carried by the outer set of rollers.

Roll End Brg Vibration data indicated outer race bearing flaw frequencies. DRol - J12 Drawrolls J12 DRolls-R19 Drawroll 19_OB Axial

PK Velocity in In/Sec

0.25

ROUTE SPECTRUM 24-Oct-01 10:36:45 (SST-Corrected) OVERALL= .2838 V-DG PK = .2821 LOAD = 100.0 RPM = 90. RPS = 1.50

0.20 0.15 0.10 0.05 0 0

2000

4000 Frequency in CPM

6000

8000

Acceleration in G-s

0.8

ROUTE WAVEFORM 24-Oct-01 10:36:45 RMS = .1472 PK(+) = .6766 PK(-) = .6234 CRESTF= 4.60

0.4 0 -0.4 -0.8 0

1

2

3 4 Time in Seconds

5

6

7

Roll End Brg

One large flaw was found in the outer race. The load zone track is clearly visible. The shape of the flaw indicated either corrosion or impact damage as the initiator. Since evidence of corrosion was not present, impact damage during installation was the most likely initiator of the flaw.

Load Zone Track

Roll End Brg, SKF 222348 CC Spherical Roller

Typical bearing failure indication in the data - Outer Race Defects with modulation by run speed (sidebands). (Vibration levels are low)

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Step One

Roll-Shaft Natural Frequency & Mode Shape Test Process

Develop Rotor Models Calculate Free-Free and Installed In Gearbox Natural Frequencies (Critical Speeds) and Mode Shapes.

Step Two Conduct Modal Testing Free-Free Modal Test of Suspended Shaft-Roll Curve Fit Data to Find Natural Frequencies and Mode Shapes Compare to Rotor Models Installed Shaft-Roll Modal Test Curve Fit Data to Find Natural Frequencies and Mode Shapes Compare to Rotor Models & Correct Models If Required

Step Three Bump Test of Installed Shaft-Roll Assembly To Identify Defective Rotors Compare Peak Hold or Triggered Spectrum To Modal Data & Model Use This Test Method To Test all Suspect Rolls if It Proved Successful Follow-up With Modal Testing On As Needed Basis

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Step One Develop Rotor Models • Calculate Free-Free and Installed Natural • Frequencies (Critical Speeds) and Mode Shapes.

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Step Two Free-Free Impact Modal Test of Shaft & Roll. - The assembly is supported by Nylon Slings - An instrumented hammer is used to impact the assembly - An Accelerometer is used to measure the response at each point along the shaft as indicated by the dots.

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Free-Free Impact Modal Test of Shaft & Roll. - The assembly is supported by Nylon Slings - An instrumented hammer is used to impact the assembly in the horizontal direction. - An Accelerometer is used to measure the response at each point along the shaft as indicated by the dots.

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Free-Free Impact Modal Test of Shaft & Roll. - The assembly is supported by Nylon Slings - An instrumented hammer is used to impact the assembly in the horizontal direction. - An Accelerometer is used to measure the response at each point along the shaft as indicated by the dots.

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Free-Free Impact Modal Test of Shaft & Roll. - The assembly is supported by Nylon Slings - An instrumented hammer is used to impact the assembly in the horizontal direction. - An Accelerometer is used to measure the response at each point along the shaft as indicated by the dots.

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