International Journal of Modern Engineering Research (IJMER)             Vol.2, Issue.6, Nov-Dec. 2...
International Journal of Modern Engineering Research (IJMER)              Vol.2, Issue.6, Nov-Dec. ...
International Journal of Modern Engineering Research (IJMER)              Vol.2, Issue.6, Nov-Dec. ...
International Journal of Modern Engineering Research (IJMER)              Vol.2, Issue.6, Nov-Dec. ...
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Bearing Life Improvement of Centrifugal Blowers by Vibration Analysis


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Bearing Life Improvement of Centrifugal Blowers by Vibration Analysis

  1. 1. International Journal of Modern Engineering Research (IJMER) Vol.2, Issue.6, Nov-Dec. 2012 pp-4026-4029 ISSN: 2249-6645Bearing Life Improvement of Centrifugal Blowers by Vibration Analysis B. A. Kardile, Associate Member, IEI,Abstract: This study work is proposed to carry out II. BLOWER STRUCTURAL ANALYSISvibration analysis of heavy duty centrifugal Blowers & Machine vibration has several categories ofbearing failure analysis. The life of bearing can be causes that we have discovered after so many repairs, butimproved by carrying corrective actions on blower & it is useful now to review them to gain more confidence inmodifying its accessories like Plumber block to prevent the diagnosis. The actual structure of blower shown in Figbearing failure. The proposed work is planned in following 1.phases Preparation of measuring instrument for data The Major categories of diagnoses are –collection (PRUFTECK VIBROEXPERT METER) • Design defectsCollection of data from various locations on blower • Manufacturing defectssurfaces in different directions. Data analysis is done on • Operational stressesthe basis of spectral plot, amplitude against frequencies • Maintenance actionswith the help of prufteck vibroexpert meter. In comparison • Agingof vibration spectral with experimental actions are carried Design defects are mostly structural related without under the vibration severity standard, the chart results active resonances built-in because of improper sizing andof rectification will be compared with spectral plot & proportioning of the parts statically, the structure seemscorrective action. The results will be compared with initial good, but it remains dynamically weak. This is notcondition & condition monitoring schedule is prepared for discovered until the machine is energized and brought upavoiding premature failure of equipment. to the required speed. This is more common than it shouldStandard schedule for maintaining basic condition of be, but the designers are not well equipped to predict orvariables of equipment like as CBM /TBM will be planned test for natural frequencies. In addition, the owners’to avoid premature failure of the bearing. foundation or base has a significant effect on natural frequencies, which the designer has little control over.Index Terms: Blower Vibration Data Collection, Hence, resonances are best detected during startup testingSpectral plot analysis, analysis of bearing structure, and corrected on-site with strategic stiffeners added.Corrective actions on equipment,, Comparison of results Manufacturing defects are built-in during the casting,& Standardize the method machining, heat-treating, and assembly processes. They are latent defects that may show up in the first 24-hours of I. INTRODUCTION running, or they may not be obvious during the run-inThe Report Contents period, appearing years later. The machine does not1] Blower readings with Vibro-meter survive to a normal life expectancy as vibration may or2] Blower problem Diagnosis may not be present.3] Bearing & Plumber block analysis An example is residual stresses in a shaft that4] Bearing failure analysis gradually distorts the shaft over a period of years.5] Bearing with Wavy leaf spring analysis Manufacturing defects are difficult to control, impossibleScope: This Report contains fault diagnosis with the to predict, and elusive to fix. The best strategy to deal withanalysis and recommendations for corrective actions. both design defects and manufacturing defects is to insistThese all are supported by spectrum plots for each point of on start up vibration testing with limits of acceptability inthe equipment identified as being deviated. A color coding accordance.system is employed, as per ISO standard which make it Here in Table1 we have tabulated velocity &easy to understand the criticality of the fault and how shock pulse readings on plumber block at drive end & nonquickly it needs to be investigated & rectified. drive end in axial, horizontal & vertical direction atMeasurement: An overall vibration reading of threshold .The Colour coding is used to classify vibrationdisplacement & velocity are measured in micron & severity as per ISO 10816, as good, satisfactory,mm/sec respectively, A RMS values are used to determine unsatisfactory & unacceptable from green to red markgeneral mechanical and electrical fault within rotating indicates alarming zone. This experiment conducted onmachinery. 110 Kw capacity blowers with Prufteck VibroexpertEquipment Used: PRUFTECHNIK VIBXPERT DUAL Meter.CHANNEL ANALYZER Table1.Velocity & shock pulse reading with alarm code Fig-1.Structure of Centrifugal Blower 4026 | Page
  2. 2. International Journal of Modern Engineering Research (IJMER) Vol.2, Issue.6, Nov-Dec. 2012 pp-4026-4029 ISSN: 2249-6645 The analysis of the data indicates that the • Bearing replacementexcessive operational stresses on blower are developed due • Identifying other bad parts and replacing themto material buildup or erosion, which changes the balance • Mass balancingcondition, or thermal expansion that changes component • Alignmentalignment. Both of these cause high dynamic loads at the • Lubrication is just greasing noisy bearings tobearings which lead to accelerated wear out. These defects Quiet them, but changing the lubrication scheduleare easily detected with periodic vibration measurements Extent their livesand there are well established methods to correct them on • Structural stiffening to raise natural Our maintenance actions, or interactions, are the most • Mass loading and stiffening reduces anycommon cause of blower failure. It is well known in the Measured vibrationrepair business that a blower machine never goes back If blower has lower motion, it may increase local stressestogether the same way. Some of this is due to rough at the bearings resulting in faster bearing wear. This is tohandling, but some is simply the fact that field repair is be used only as a last resort when nothing else works andless controlled than the original factory build. The field measured motion must be lowered.environment is darker, dirtier, and less precise tooling isavailable to control fits and alignments. The repair is The Fig-2 gives the velocity (mm/sec) trend of 110kwusually rushed by management. It is surprisingly difficult blower from Dec-2007 to June-2012 with alarming zoneto install a bearing into aluminium housing in the field andnot get it crooked. The first question to ask in vibration Vibration Monitoring Trend- ABS Line : Top Coat Booth Exhaust Bloweranalysis is “What recent maintenance activity has occurred Vibration Trendon this machine?” other maintenance activities that affect MM/sec Bearings & Plummer block changed in 20 December Shut-down 18on blower vibration are- 16 14 Replace• Excessive localized heating, like welding on a shaft 12 10 7.8 8 7.6 7.6 Warning 8 6.5• Too high belt tension 6 4.5 3.2 3.4 3.5 3.8 3.1 Good 4 2• Shaft, or bearing, misalignment 0 ar n p 07 08 09 10 n 03 ec 06 n ep ec Ja se Ju Ju M D 20 20 20 20 D v S ov -1 3 o 1 -2 -4 2 3 4 N -Q N -Q -Q -Q -Q Q• Substandard replacement parts Q -Q - - 11 11 11 12 12 12 12 11 M ce 20 20 20 20 B 20 20 20 20 n le el xc E• Coupling, or other component, binding Fig-2.Vibration monitoring trend for exhaust blower• Lack of lubrication 110 Kw capacities• Loose hardware• Replacing hardware with different weights that Finally, a few blowers are still generating Affects on balance excessive vibration, the cause has not been discovered nor• Re-assembling hardware in different orientations corrected, and they have not shaken themselves apart yet. (also affect on balance ) Some blowers are just rough characters and it is neither• Hammering on a bearing necessary nor desirable to retrain them. As long as the• Unclean, or burred, precision machine surfaces vibration amplitude remains stable, it is safe to continue to Aging effects are only be detected with long term operate at elevated levels, thus avoiding repair cost andvibration monitoring. The two dominant aging effects are downtime. Regular vibration monitoring has allowedresidual stress relaxation and softening of structural joints. machines to operate longer into the wear out cycle withoutThe residual stresses left behind in machine components fear of failure.are always relieve themselves over time. This process isaccelerated at higher temperature of shaft, being long and IV. FFT SPECTRUMslender component, are particularly vulnerable to bowing. The prufteck vibroexpert meter is the simplest,The symptoms are an increase in 1x RPM balance and least expensive, is an overall meter. It provides notcondition and beating up of the bearings. Bearing only frequency information, but also overall amplitudes forreplacements do not restore the original smooth running the analysis of data. It is useful for trending or comparisoncondition, and mass balancing is unsuccessful, until the measurements on similar machines, but for diagnosingshaft is replaced. problems on machines, it is best left turned off. The other All joints soften over time, and joints are the two major vibration instruments are tuneable filters andweak links in any structure. These are the prominent FFT (Fast Fourier Transform) analyzers. Analyzer is asymptom of lowering of the natural frequencies of the misnomer because analysis is a human function. Anmachine. This has usually first detected with high electronic “analyzer” does not analyze. It only measuresvibration when the lowest natural frequency drops down and display electrical signals. The electrical signals frominto the operating speed range of the machine. accelerometers and velocity transducers are very small AC voltages, typically millivolts. Hence, the tuneable filters III. BALANCING & ALIGNING METHOD and FFT instruments are nothing more than fancy AC This is well known that blower vibration related voltmeters with a frequency display axis. Any of these twoproblems are corrected in place. The corrective methods major vibration measuring instruments, from anyare well experienced undergoing the trouble shooting of manufacturer, can be used effectively to diagnose machinethe blower problem in depth. These are listed here to close vibrations. No specific instrument or manufacturer has athis discussion. unique connection to a higher intelligence. As it’s FFT• Disassembly, visual inspection, cleaning, and re- spectrum is shown in Fig-3 assembly fix some elusive problems without knowing 4027 | Page
  3. 3. International Journal of Modern Engineering Research (IJMER) Vol.2, Issue.6, Nov-Dec. 2012 pp-4026-4029 ISSN: 2249-6645 4] Bearing life in Revolutions L= (C/W) ^ (10/3) X 10^6 C= Basic Load Carrying Capacity C= W (L/100) L= 60 X N X LH, Where LH in Hours W= Equivalent Dynamic Load L= Life in Revolutions 5] Heat calculation Fig- 3.FFT Spectrum for blower vibration a) Heat generated due to friction Qg= µ.W.V Watt However, some are an order of magnitude or two µ= Coefficient of frictionmore complicated to use by design. The instrument in use W= Load on bearing in N=P x Ais the least significant factor in diagnosis. The instrument V= Speed of journal in RPMoperator and the methods employed are the most b) Heat dissipated.significant. Qd= C.A (Tb-Ta) in Watt The fundamental method of using a vibration C= Heat dissipation coefficientinstrument is to conduct a survey of the entire blower A= Projected area of bearing in m2system; driver, driven, and any intermediary machines Tb= Temperature of bearing surface °Csuch as gearboxes & pulleys of belt drive. Ta= Temperature of surrounding air °C Tb-Ta=1/2(To-Ta) c) Heat conveyed by the oil Qt=M.S.T in Watt M= Mass of oil S= Specific heat of oil 1840-2100 J/kg°c T=Temperature difference between outlet & inlet 6] Grease quantity inside bearing Gg= 0.005 X D X B Fig- 4.Frequency verses time graph for exhaust Gg=Gram of grease Blower 110 Kw capacity D=Bearing dia in mm B= Bearing width The spectrum shown in Fig-4 implies that the 7] Coefficient of friction for bearing is expressed asdisplacement varies with outer race wear in Axial, vertical, µ=Ǿ [ZN/P, d /c, l/dhorizontal direction as rotor moves under centrifugal µ=33/10^8[ZN/P][d/c]+kforces. Which lifts the shaft from impeller side causes µ= Coefficient of frictionreducing amplitude the displacement for non drive end to Ǿ=Functional relationshipdrive end. Z=Absolute viscosity of lubricant in kg/m-s The velocity of vibration depends upon the shaft N=Speed of journal in RPMspeed, type of bearing, type of drive supporting distance of P=Bearing pressure=load/areathe shaft within the bearing & cantilever of the shaft along d=Diameter of journalwith the pulley end. The bearing condition can be detected l=Length of bearingby vibrating parameters trend and the life of bearing can be c=Diameteral clearanceincreased by taking corrective action to prevent extreme k=Factor of correction for end leakagecondition of the equipment. The bearing & shaft assembly ZN/P=Bearing characteristic number, dimensionlessis shown in Fig-5 number, helps to predict bearing performance called Bearing modulus V. BEARING FAILURE ANALYSIS The dampening of the bearing inside the plumber block can be absorbed by providing Wavy leaf spring of adequate stiffness which can prevent the transmission of vibrating wave from inner race to outer race through roller by sharing the load as shown in Fig-6. Which minimize theFig- 5. Bearing assembly & Bearing load of exhaust shock impulse influence directly on bearing & plumber Blower block cause the life improvement for certain hour. A step change in amplitude is symptomatic of an 4. MATHS & EQUATIONS unstable bearing. Examination of the bearings and their1] Ball Pass Frequency for the outer race supports is in order as soon as practical. A drop in =No of Roller x Shaft Speed x 0.4 frequency is bad news. It indicates structural softening2] Ball Pass Frequency for the inner race such as cracks or joint loosening. Slow changes in =No of rollers x Shaft Speed x 0.6 amplitude from cold to hot running conditions are related3] Ball pass frequency train race to alignment of the shafts. = Shaft Speed X 0.3 4028 | Page
  4. 4. International Journal of Modern Engineering Research (IJMER) Vol.2, Issue.6, Nov-Dec. 2012 pp-4026-4029 ISSN: 2249-6645 6] Total hours of working 7] Lubrication standard & frequency 8] Condition of bearing & lubricant after removalFig- 6.Bearing with Roller condition & wavy leaf spring VI. CONCLUSION The vibration analysis of the heavy duty centrifugal A fourth judgement criterion is operational blower gives the results ascondition. The load level has a dramatic effect on vibration The bearing life the rotating parts depends uponlevels, especially electrical machines such as generators. It 1] The bearing characteristic number, ZN/Pis usually assumed in analysis that the machine has no 2] Running condition-Temperature & RPM underoperational problem. Which the machine runs The taper roller bearings are used for heavy duty 3] Bearing load condition as static & dynamic loadcentrifugal blower mounted with on sleeve with lock nut & Carrying capacitywasher inside plumber block. Taper roller bearings are 4] Clearance between roller & outer racedesigned for carrying radial load. This bearing are 5] Heat dissipation capacity of the plumber block &specified with 5 digit number as 32224 K C3,32226 K C3 Other accessories,K suffix is attached for taper roller bearing only & C3 is 6] Lubrication frequency & standard of lubricantattached for bearing clearance, as bearing clearance varies Generally the vibration parameters as displacement &from C1 to C5 for high temperature & high RPM. Material velocity are depends upon the bearing wear of outer raceused for taper roller bearing are babbit metal, branze, cast because of roller hits on surface of the race at highiron & silver. temperature Bearing clearance is provided for the purpose ofadjust thermal expansion, deflection of rollers & provide VII. ACKNOWLEDGEMENTfilm thickness in lubrication. This clearance is kept 90 to The author would like to thanks the Institution of120 µm before mounting & expected to reduce by Engineers (India) for permission to publish the paper. The30 % in assembly, if it increases than this the bearing is to author gratefully thanks to Bajaj Auto Ltd, Pune to providebe replaced. platform for the experiment & Dr.D.Y.Patil College of Engineering, Pune for inspiring the subject choosen. REFERENCES [1] Analysis Guide for Machine Designers, journals of white paper,Fig-7.Assembly of taper roller bearing on shaft sleeve 2008. With lock nut [2] Analytical Diagnostic Approach & Innovative Impeller Design The bearing manufacturers are SKF, NTP, FAG By Bruno Schiavello & Gian Carlo cicatalli,& KEYDON. The duplicity in the bearing are easily 2006.identified by its finishing standard & clearance value. The [3] Vibration Transmission through Rolling Element-clearance is measured with filler gauge & dial gauge, if by T.C Lim &measured closer to the bearing assembly with dial gauge. R.Sing 1990, 139(2)Bearing assembly with shaft sleeve & lock nut is shown in [4] Rolling Bearing Analysis by T.A.Harris, NewFig-7 York: John wiley, The taper roller bearings for heavy duty blowers 1966.are fitted by heating the oil upto120°C with induction coil [5] Study of Vibration Characteristic of Bearing, byor flame. Lubrication life of this bearing is depend on load, O. Gustafson,RPM, bearing ID/OD, Width,& bearing mounting method SKF Report, AL62 L005, expressed in equation 6. [6] Standards for Vibration Monitoring & AnalysisThese sliding contact bearing should have following by J.Michael,properties Robichaud, P.Eng.2005. 1] Compressive & fatigue strength [7] Maedel, Jr, P. Vibration Standards and Test 2] Confirmability Codes, Shock and 3] Embeddability Vibration Handbook 5th Edition (Cyril Harris, 4] Bondability editor), McGraw Hill Publishing Co. 5] Corrosion resistance (2001) 6] Higher thermal conductivity & lower expansionThe bearing failure analysis requires following information BIOGRAPHIESas Mr.Balasaheb a Kardile AMIE (Mech, ST-438760-6), ME 1] Date of mounting & type of bearing (Design), Engineer, Bajaj Auto Ltd, Pune, A 2/3 wheeler 2] Load type, temperature & RPM Mfg Group. 3] M/c & bearing surrounding 4] M/c precision/accuracy 5] Frequency of failure 4029 | Page