Part 4 modalbump tseting 02 2004

Free-Free Impact Modal Test of Shaft & Roll Results # 1:188.30 Hz 3 4 5 7 89 89 10 11 10 11 89 10 11 12 12 12 13 13 13 14 15 15 15 16 16 16 17 17 17 X Z Y Modal Analysis test results of Feed Roll & Shaft Most bending is indicated in the shaft as predicted by the rotor model Some movement is indicated at the bolted joint Point is on the shaft flange and point is on the roll 49 Figure 2: Rotor model, third mode 10,862 CPM Bending occurring in the shaft but not in the roll, which is primarily a very stiff hollow cylinder The bolted joint was modeled as solid The FRF of the Driving Point shows the 1st natural frequency of the shaft-roll at 187 Hz ~ 11,220 cpm The rotor model calculated to 181 Hz ~ 10,860 cpm or 96.8% Figure 3: Frequency response function (FRF) of the Driving Point, Bottom Plot Coherence of the measurement is shown in the top plot The data becomes noisy above 500Hz because the instrumented hammer tip was not hard enough to input adequate energy into the rotor to excite the structure in this frequency region However, this does not present a problem because the primary mode of interest is 188 Hz The mode at about 500 Hz is the first circular mode of the roll 50 Step Two Shaft & Roll Installed Impact Modal Test - The shaft is installed in the gearbox and supported by the bearings - An instrumented hammer is used to impact the end of the roll - An Accelerometer is used to measure the response at points along the roll as indicated by the red dots Note that the response will be affected by any looseness in the bearing assembles This may cause non-linearity in the response and reduce coherence Typically this would not be considered a good test setup, however; the test should be useful in identifying potential problems such as loose bolts, traverse shaft crack, and looseness in the bearing assembly Page 51 Installed Shaft & Roll Impact Modal Test - The assembly is tested while installed in the gearbox and supported by the bearings - A medium sledge instrumented hammer is used to impact the roll - An Accelerometer is used to measure the response at each points along the roll 52 Installed Shaft & Roll Impact Modal Test - The assembly is tested while installed in the gearbox and supported by the bearings - A medium sledge instrumented hammer is used to impact the roll - An Accelerometer is used to measure the response at each points along the roll 53 The rotor model predicted the shaft-roll first flexure mode with the shaft supported by bearings (Brg Stiffness Estimated) at 10,208 cpm ~ 170 Hz 54 The measured FRF showed a fairly narrow range of resonance for the 1st flexure mode In the FRF plotted, the resonance measured 204.38 Hz ~ 12,263 CPM ! 55 Results from one machine with 23 shaft-rolls All of the rotors “rang” except the #2 Disassembly of the #2 roll showed loose bolts The rolls natural frequency were in the 200 Hz range with exception of roll 21 Draw Roll-Shaft Natural Freq in Hz 350.00 300.00 N atu ral F req H z 250.00 200.00 Series1 150.00 100.00 50.00 0.00 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Draw Roll # 56 Although the individual roll response had similar natural frequencies, the response in g/lbf showed some variation Roll Re s pons e M easure d By Im pact M odal Tes t A m p litu d e R esp o n se @ N atu ral F req g /lb f 1.40E-03 1.20E-03 1.00E-03 8.00E-04 g/LBF 6.00E-04 4.00E-04 2.00E-04 0.00E+00 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Roll # 57 Plotting the roll response in lbf/mil provides a measurement of the dynamic stiffness Generally the rolls were in a range of 5,000 to 10,000 lbf/mil with exception of roll 21 which had much higher stiffness and natural frequency The reason for roll 21’s response was not determined Shaft-Rolls Lbf/M il (Dynam ic Stiffne s s) 30000 C o m p lian ce L b f/M il 25000 20000 Series1 15000 10000 5000 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Roll # 58 The FRF from Roll #2 did not show a natural frequency Typically, modal analysis requires a linear structure but in this case we are looking for a nonlinear structure with poor resonance qualities Inspection showed a loose bolted joint 59 Step Three Bump Test of Installed Shaft-Roll Assembly To Identify Defective Rotors Compare impact data from triggered spectrum & time waveform to modal data (FRF) tests for location of roll natural frequencies Monitor natural frequencies during operation for shifting (A shift lower would indicate a change in the stiffness of some components in the system such as broken bolts, shaft traverse crack, bearing assembly looseness.) Follow-up with modal testing on as needed basis Page 60 Step Three Bump Test of Installed Shaft-Roll Assembly To Identify Defective Rotors Bump testing did not prove to be useful in detecting shafts with loose or broken bolts After several tests, it was discontinued Page 61 " # $ % % ' & ( ) ) * 62 + 63 Example of time waveform and spectrum from a roll The FFT shows 12.46 mils P-P run out The time waveform shows much less amplitude P-P due to roll off of the accelerometer The FFT is multiplied by a curve to compensate for the roll off and yields the correct amplitude 64 This roll measured 37.6 mils runout Note the time waveform clearly shows asymmetrical stiffness indicating a loose joint Broken bolts were found 65 Rolls: Vibration Condition T able 11/16/01 Update: Feedroll and Drawroll Condition Frame J1 J2 J2 J2 J2 J2 J6 J6 J7 J7 J7 J7 J7 J7 J7 J7 J7 J7 J7 J7 J7 J8 J8 J8 J8 J8 J8 J8 J9 J9 J9 J9 J13 J14 J15 J15 J15 J15 J17 J17 J17 J17 J17 J18 J18 J18 Roll ID WO # Status DR 13 2E+06 Monitor DR Monitor DR Monitor DR Monitor DR 12 Monitor DR 15 2E+06 Monitor DR 18 Monitor DR 20 603301 Repair FR Monitor FR Monitor DR 603302 Repair DR Monitor DR Monitor DR Monitor DR Monitor DR Monitor DR 12 603863 Repair DR 13 603864 Repair DR 16 603865 Repair DR 17 Monitor DR 19 2E+06 Repair DR 2E+06 Monitor DR Monitor DR Monitor DR 2E+06 Repair DR Monitor DR 11 Monitor DR 20 603303 Repair FR (DS 2) Monitor DR Monitor DR Monitor DR 10 Monitor DR 13 Monitor DR 1-20 FR 603305 Repair FR6 603306 Repair DR 19 2E+06 Monitor DR 20 2E+06 Repair FR 603308 Repair FR 603309 Repair DR Monitor DR Monitor DR 14 Monitor FR Monitor DR Monitor DR 22 Monitor Last Read Bearings Last Re ad Ra dia l Runout Last Read Stiffness W orked 10/25/2001 10/8/2001 10/8/2001 10/8/2001 10/8/2001 10/8/2001 10/10/2001 10/10/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 10/23/2001 10/23/2001 10/23/2001 10/23/2001 10/23/2001 10/23/2001 10/23/2001 10/18/2001 10/8/2001 10/8/2001 10/8/2001 10/8/2001 10/8/2001 10/23/2001 10/23/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 11/15/2001 10/12/2001 10/12/2001 10/12/2001 10/12/2001 10/12/2001 10/12/2001 10/12/2001 20 Mils 19 Mils 13 Mils 11 Mils 42 21 16 20 17 25 32 32 Mils Mils Mils Mils Mils Mils Mils Mils 11/16/2001 11/16/2001 11/16/2001 11/16/2001 11/16/2001 14 Mils 12 Mils 10/24/2001 10/24/2001 10/24/2001 10/25/2001 10/2/2001 17 Mils 19 Mils 38 Mils 16 Mils 10 Mils 13 Mils 9/27/2001 9/27/2001 8/30/2001 8/30/2001 OK 10 Mil to 30 Mil Monitor More Frequently > 30 Mils Schedule Maintenance for inspection of bolts 9/27/2001 11/16/2001 11/16/2001 11/16/2001 11/16/2001 11/16/2001 11/16/2001 11/16/2001 11/16/2001 9/26/2001 9/26/2001 9/26/2001 10/9/2001 8/6/2001 Roll run out tolerance measured at the end of the roll: 30 Mils RO = W ork Requested 66 Detection Process: Modal testing was successful in identifying shaft-roll rotors with lower stiffness, i.e., did not ring when impacted as likely candidate of loose bolting, failed bolting, or shaft with a developing crack The roll rider data was useful in identifying rolls with loose bolting Limits were established as follows: 15 > 30 Mill PP Schedule inspection of the bolts Vibration data A Collected using the long stinger in the end of the roll cover plate was successful in detecting defective bearings B Data from permanent accelerometers installed on the bearing housings were not as useful in detecting bearing defects as data collected on the end of the rolls Physical inspection of bolting, shaft and roll mating faces, condition of tapped holes, bearing fits, etc 67 Correction Process: The roll and shaft mating surface finish, flatness, hole angularity and depth of full thread tolerances were enforced by inspection at the repair shops The bolt length was reduced ½” to 6” Thread lubricant was changed to Loc-Tite Graphite which has a very low K factor Bearing heating procedures were modified to use a temperature controlled heater for all bearing installations 68 Conclusions Use of Modal testing to detect loose rolls was effective But, testing had to be scheduled when a line was down We were not aware that this test method had been used previously The roll rider block with accelerometer is a modification of a well know test method using a wood stick also called a beaver tail (sold by IRD) After some modification of the initial block design and data collection methods, the test proved successful in identifying rolls with excessive run out Vendor shop visits were very helpful to improve understanding of the repair processes and identify problem areas Modification of the repair processes, tightening of tolerances, initiation of inspections of repaired Shafts & Rolls with documentation were successful in improving the quality of Shaft & Roll repairs performed by repair shops 69 Conclusions Modification of Bearing and Roll maintenance installation practices proved successful in reducing the number of improperly installed rollshaft assemblies 70 Results The Roll-Shaft reliability improvement project was initiated in the Fall of 2001 Bolting Failures in 2003 reduced 74% compared to 2002 Roll Shafts With Bolt Failures 45 40 35 Cause of large number of failures in 1997-1998 were not identified 30 25 No data available before 1997 20 15 10 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 71 Results Bearing Failures in 2003 reduced 79% compared to 2002 Lowest number of failures documented over 10 years Roll Shaft Bearing Failures 60 50 Bearing Failures 40 30 20 10 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Bearing Failures 72 73