1、04FTM11Gear Lubrication as aReliability Partnerby: M. Holloway, NCH CorporationTECHNICAL PAPERAmerican Gear Manufacturers AssociationGear Lubrication as a Reliability PartnerMichael Holloway, NCH CorporationThe statements and opinions contained herein are those of the author and should not be constr
2、ued as anofficial action or opinion of the American Gear Manufacturers Association.AbstractPerformance lubrication is quickly becoming a component of preventive, predictive, proactive and reliabilitybased maintenance programs. Using the best gear lubricant coupled with system condition, monitoring a
3、ndanalysis actually reduces overall operating expenses dramatically. Various techniques such as systemconditioning, oil and equipment analysis along with product selection and management are valuable tools,which convert many maintenance departments into reliability centers. These concepts and others
4、 arediscussedinthisinformative,handsondiscussionwhichwillreviewbestmaintenancepractices fromvariouscompanies and review how to implement similar programs.Copyright 2004American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314October, 2004ISBN: 1-55589-834-31G
5、ear Lubrication as a Reliability PartnerMichael Holloway, NCH CorporationIntroductionGearboxes are applied in many mechanicalsystems. They may only be a few in coolingtowers or dozens on conveyor lines orhundreds in mixing facilities. For many com-panies, it can be difficult to accurately identifyth
6、e factors and conditions that contribute togearbox failures. The majority of the directand indirect costs associated with equipmentreliabilityareespeciallydifficulttounderstand.Some engineering and maintenance teamsuse software to help track equipment repaircostswiththegoalofimplementingrootcauseana
7、lysis and corrective action plans, whilemany others engage in reactive maintenancepractices and do not track these costsbecause it would be too difficult.In order to increase overall reliability, manycompanies follow a four-step approach to im-prove plant reliability in general and gear-boxes reliab
8、ility specifically:1) Identify the Failure Sources2) Measure the Financial Impacts3) Analyze Options to Increased Reliability4) Control the Failure Sources1. Identify Failure SourcesAGMA identifies the following gear failuremodes:D Wear: uniform wear associated to met-al-to-metal or metal-to-contami
9、nantcontact.D Surfacefatigue: identifiedbyhighwearmetalconcentrationandtheformationofcavities.D Plasticflow:surfacedeformationduetohigh-contact stresses combine with therolling and sliding action.D Breakage: partial or whole gear toothfracture caused by sporadic or continu-ous overloading.These fail
10、ures are typically associated withovertaxing the component or system,improper maintenance practices or incorrectapplication.In the book Root Cause Failure Analysis byKeith Mobly, several problems associatedwith gearbox failures and the causes for eachproblem are discussed (table 1). The lack oflubri
11、cation and excessive torsional loadingare identified as the most common causes offailure. Excessivetorsionalloadingistypicallytheresult of poor maintenance practices, mis-use or improper application. Lack of properlubrication is directly related to gear oilperformance and proper oil change intervals
12、.Performance gear oil can improve gearboxreliability dramatically and in some case actu-ally reduce the energy demands of the motor.Various failure sources as they relate to gearoil performance have been identified, theyare:Leaking Seals - Seals leak because they be-comebrittleandcrackwithage,acidsf
13、romox-idizedoilattackthem,metalshavingsandrustparticlescauseabrasivewearandfoambuild-up increases pressure and causes them torupture. Someplastisizers usedin sealmate-rial will actually dissolve in synthetic gear oils.Synthetic gear oils are known by many main-tenance technicians as the weeping oils
14、 be-cause they would leak or “weep” from thegearboxes.Gear oil leaks result in poor or no lubrication,entry of abrasives and contaminants, the po-tential for safety and environmental problemsand oil loss.Dry Start Wear - 80 to 85% of gear wear oc-curs during start-up. Most gear oils drain offduring
15、shut down and leave gears unprotec-ted. Dry starts lead to mechanical wear andcold welding, flash rusting and corrosion. Drystarts increase heat and friction on unpro-tectedgears. Increased heat and frictionleadtowearandoilbreakdown. Metalparticlesareexcellent nucleationsites for internalcontami-nan
16、ts such as sludge.2Table 1The ProblemThe CauseGearFailuresVariationsinTorsionalPowerInsufficientPowerOutputOverheatedBearingsShortBearingLifeOverloadonDriverHighVibrationHighNoiseLevelsMotorTripsLack of Proper Lubrication X X X X X X XExcessive Torsional Loading X X X X X X XBent Shaft X X X XBroken
17、 or Loose Bolts or Screws X XDamaged Motor X X XElliptical Gears X X X XExceeds Motors Brake Hp Rating X XExcessive or Too Little Backlash X XForeign Object in Gearbox X X X XGear Set Not Suitable for Application X X X XGears Mounted Backward on Shaft X X XIncorrect Center-to-Center Distance X XInco
18、rrect Direction or Rotation X X XMisalignment of Gears X X X X X XOverload X X X X XProcess Induced Misalignment X X X XUnstable Foundation X X X XWater or Chemicals in Gearbox XWorn Bearings X XWorn Coupling XOxidation - the chemical breakdown of oil inthe presence of heat and oxygen. Oil oxida-tio
19、n results in sludge and varnish. Also acidsthat promote corrosion, pitting and seal failu-re. Oxidation will thicken oil, which causesequipment to work harder and depending onthe gear design, provide inadequate oil flowand film formation.Foaming - naturally occurs when air mixeswith oil during opera
20、tion. Foam causes highoperating temperatures, excessive gear wearfrom poor lubrication, increased internal pres-sure, which can blowout seals and gasketsand out of vents.Water Contamination - all gearboxes containacertainamountofwater. Asoilheatsupthencools down, condensation forms. Water canquickly
21、 emulsify with oil, which promotesfoaming and non-lubricated hot spots. Waterwill accelerate oil to breakdown and oxidizefaster leading to deposit build-up. Increasedrust and corrosion from water will lead to pit-tingofgearsandbearings,abrasivewearfromrust particles will continue to damage thegears
22、and bearings.32. Measure the Financial ImpactsIt is a common fact amongst experiencedmaintenance managers and even plant man-gers that 20% or less of equipment failuresrepresent 80% of the maintenance cost in amanufacturing facility. This means that weonly have to perform root cause failure analy-si
23、s on 20% or less of our failure events to re-duce or eliminate 80% of our facilities lossesprovided the failures are accurately identifiedand repair or replace costs are understood.The20% arethe“SignificantFew”. Inordertodetermine the significant few you must per-form a few simple steps:1) Totalallo
24、fthefailureeventsintheanaly-sis to create a global total loss. Arrangeaccordingtofailureevents,failuremode,frequency and impact on manufacturingand maintenance as it relates to down-time, parts replacement and labor costs.2) Make a spreadsheet and sort the totalcolumnindescendingorder(i.e.,highestto
25、 lowest).3) Multiply the total loss column by 80% or.80. This will give you the “SignificantFew” loss figure that you will need todetermine what the ”Significant Few”failures are in your facility.4) Gotothetopofthetotallosscolumnandbegin adding the top events.5) Whenthesumoftheselossesisequaltoorgre
26、aterthanthe“SignificantFew”lossfigurethanthoseeventsareyour“Signif-icant Few” failure events.3. Analyze Options for IncreasedReliabilityBy identifying the potential sources of failure,correctiveactionisthenextstep. Gear oilcanhelp increase reliability provided that perfor-mance gear oil is used. The
27、 following gear oilperformance ingredients are found in the bestgear oils and are used for all industrial andconstruction applications calling for singleweight gear oil for protection against lubrica-tion related failure sources: leaking seals, drystarts, water contamination, oxidation, andfoaming.P
28、erformance IngredientsThe gear oil should contain all of the followingingredients in order to be considered for in-creased reliability:Premium Grade Base Oil: Group IIA or IIImineralbaseorPAOsyntheticbase. Helpsprevent oxidation, viscosity shearing, andcarbonization.Adhesive/Cohesive Polymers, Tacki
29、nessAgents: Prevents mechanical wear, stressfractures, and dry starts.SealConditionersandLeakInhibitors: Pre-vents seals from hardening, shrinking, andrupturing.Friction Reducers and Anti-Wear Addi-tives: Prevents heat welding on “hot spot”contact points to reduce friction and loweroperating tempera
30、tures.EP Additives and Shock Load Reducers:Prevents metal-to-metal contact underheavy loads, low speeds, high torque, andhigh stress conditions; cushions impactand reduces drive train chatter to prolonggear and bearing and bearing life.Oxidation Inhibitors: Prevents oil break-down in the presence of
31、 agitation, heat, ormoisture; reduces formation of corrosiveacids, resins, and oxidation sludge that at-tacks seals and causes wear on bearings.Rust and Corrosion Inhibitors: Maintains afull protective barrier on gear and bearingteeth, gear and bearing faces, and entiredrive train to prevent corrosi
32、ve pitting, rustflaking, and metal deterioration.Anti-Foam Agents: Prevents foaming dur-ing agitation and heat to reduce pressurelevels on seals and vents.Demulsifiers: Displaces water, moisture,and condensate to reduce chemical wearand extend equipment life.Detergents and Dispersants: Keeps solidco
33、ntaminants in suspension to preventformation of harmful deposits.Pour Point Depressants (for automotivegrades): Prevents thickening to allow theoil to flow freely in cold temperatures.Having the aforementioned performance in-gredients is a good start. Increased reliabilityin gear oil also requires e
34、xceptional perfor-mance when tested in accordance to certainASTM test procedures. Table 2 summarizesthe appropriate tests and provides a reliabilitydefinition as well.4Table 2. Tests for Characterizing Gear OilsProperty Test Method DescriptionReliability Value Test Results and What TheyMeanViscosity
35、ASTM D2983Brookfield Vis-cosityMeasures low temperature viscosity of automotivefluid lubricants using the Brookfield viscometer.scoASTM D2270 Viscosity IndexMeasures variation in viscosity due to changes intemperature. The higher the number, the better.ASTM D3233Falex LoadTestMeasures extreme pressu
36、re properties (in pounds)ofafluidlubricantusingthefalexpinmethod. Greateramount equals greater extreme pressure character-istics.ASTM D2783 Film StrengthUses4-ballmethodtodetermineload-carryingprop-ertiesoflubricatingfluid. Thehighernumberthebet-ter.ExtremePressure andAnti-WearASTM D2783 Weld PointM
37、easures the lowest applied load in kilograms atwhich the rotating ball welds to the three stationaryballs. The higher the number the better extremepressure characteristics.ASTM D2783Load Wear In-dexAn index of the ability of a lubricant to minimize wearat applied loads. The higher the better.ASTM D2
38、782Timken Meth-odLine contact, similar to roller bearing, the higher thenumber the greater load carrying capabilities.ASTM D4172Four-ball(wear scar)Measures the relative wear preventive properties oflubricating fluids in sliding contact, using the 4-ballmethod. The lower the number the more protecti
39、onthe oil provides.Corrosion ASTM D130Copper Corro-sion1Aisthebestrating,mostare1B,measuresabilitytoprotect yellow metals.OxidationResistanceASTM D2070ThermalStability TestMeasures thermal stability ofoil. Pass is good. Alsomeasures viscosity increase and insolubles recor-ded. The lower percent the
40、better.FoamingTendencyASTM D892 Foam TestMeasures the amount of foam produced at specifiedtemperatures and different air blowing intervals. Nofoam is best.Residue ASTM D189ConradsonCarbon Resi-dueMeasures the residue formed by evaporation andthermal degradation of the oil. The less percentageof carb
41、on residue the better.FluidityFTM 3456 Channel PointWhenagearpassesthroughthegearoil,theoilflowsin behindit fillingin thechannel leftby thegear. Thismethodrecordsthetemperatureatwhichthegearoilwill no longer flow back into the channel.ASTM D97 Pour PointThe lowest temperature at which movement of th
42、efluid is observed is recorded as the pour point. Thelower the pour point, the better utility the fluid has forcertain applications at low temperature.Safety andPrecautionsASTM D92 Flash PointMeasures the lowest temperature at which applica-tion of a test flame causes the vapors above the sur-faceof
43、theliquidtoignite. Thehighertemperaturethebetter (safer).rec onsASTM D92 Fire PointMeasures the lowest temperature at which the flamecausestheoiltoigniteandburnforatleast5second-s. The higher temperature the better (safer).54. Control the FailureTo implement a purchasing specification forimproved re
44、liability requires a procurementspecificationtobeputinplace. Oncetheprob-lemsareidentifiedandperformancelevelses-tablished, thebasic steps for specifying aper-formance gear oil procurement process aresimple:1) Identify the problem(s) that lead to fail-ure leaking seals, varnish formation,bearing wea
45、r, water contamination, etc.2) Identify the standards that address thatproblem(s) ASTM and Industry stan-dard values3) Select the best product according to thestandard(s)4) Try in selected areas and compareagainst what is being used.ConclusionBy following the basic steps of the procure-ment process,
46、 increased cost savings can berealized. It is important that the engineering,maintenance and even purchasing depart-ments become familiar with not only the prob-lems but also the ASTM and industry stan-dards. Gear lubrication can increaseequipmentreliability,whichwillequatetoover-all savings. By pre
47、ssuring vendors to delivermore inthe way of valueand performance, in-creased plant reliability and decreased costare almost guaranteed. An example of twoseparate performance procurement specifi-cations follows.STANDARDREQUIREMENTSFORHEAVYDUTYSINGLEWEIGHTISO68,150,220,320,460,680 GEAR OILPERFORMANCE
48、COMPONENTSD Premium Grade Base OilD Adhesive/Cohesive Polymers, Tackiness AgentsD Seal Conditioners and Leak InhibitorsD Friction Reducers and Anti-Wear AdditivesD EP Additives and Shock Load ReducersD Oxidation InhibitorsD Rust and Corrosion InhibitorsD Anti-Foam AgentsD DemulsifiersD Detergents an
49、d DispersantsD Pour Point DepressantsPERFORMANCE RESULTS FOR ISO 68, 150, 220, 320, 460, 680 GEAR OILSD ASTMD2983BrookfieldViscosityTest: ISO68:72.6cSt. at40_Cand9.5cSt. at100_C,ISO150: 154 cSt. at 40_C and 16.8 cSt. at 100_C, ISO 220: 220 cSt. at 40_C and 20.9 cSt. at100_C,ISO320:291cSt. at40_Cand24.5cSt. at100_C,ISO460:468cSt. at40_Cand30.6cSt. at 100_C, ISO 680: 745 cSt. at 40_C and 55.2 cSt. at 100_CD ASTM D2270 Viscosity Index: 95D ASTM D2783 Weld Point: 250 kgD ASTM D2783 Load Wear Index: 50D ASTM D2782 Timken Method: 55lbs.D ASTM D4172 Four-Ball (
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