Lubricant Application: Grease Volumes And Frequencies

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Best PracticesMike Johnson / Contributing EditorLubricant application:Grease volumes and frequenciesDeveloping a consistent and systematic replenishment approach can go along way toward ensuring the quality of your relubrication practices.In previous articles we’ve addressed lubricant selection forall types of components. This month we’ll address greasetype lubricant application methods for common grease lubricated components.Unlike oil application, applying grease to componentsholds a bit of mystery and intrigue. Unfortunately, the mystery part often produces great inconsistency and poor qualityon the plant floor.Most oil reservoirs provide machine operators with aportal through which the operator can determine that theright quantity of oil is in place. Whether the machine’s oiltanks are square-, round- or trapezoid-shaped, the machinedesigner is expected to provide a simple, easy way to judgeoil volume and, hence, oil application effectiveness.This option doesn’t translate well for grease lubricatedmachine sumps. Given that grease doesn’t flow so well insidethe machine sump, a grease sump viewport would quicklybecome obscured by grease.In addition, since there are no transparent materials withthe strength of steel from which bearing housings could beKey Concepts: Calculating the volume and frequency of lubricant can be determined by using two simpleapproaches. Automatic lubrication systems are now beingincorporated in modern grease applicationmethods for geared machines. Proposed grease application volumes are basedon gear size, speed, lubricant type and lubricantapplication method.20 APRIL 2009constructed, we have to settle with carefully planning the replenishment volumes and then verifying the effectiveness ofthe practice with readily available measurement tools.SUPPLY VOLUME:PLAIN AND ELEMENT BEARINGSFollowing selection of the best fit grease lubricant, the nextstep toward creating precise, reliability-centered lubricationpractices is to apply the right volume of lubricant at the bestor at least a healthy interval. (Note, you can find archives ofBest Practice articles addressing selection of appropriate viscometric range and additive structure for bearings and gearsin the Members Only area of the STLE Web site, www.stle.org)Grease lubricated applications are nearly always expectedto be continuous loss systems. As such, a planned, consistent, systematic replenishment practice is necessary to protect both the grease in the machine components and thecomponents themselves. This article presents grease application and frequency for plain and element bearings.Plain bearing grease application. There isn’t muchprinted literature providing practical advice for quantity andfrequency of application for plain journal bearings withoutdelving into the original design parameters and operatingstates. Given that the original design considerations greatlyinfluence the viscosity and supply rates, this is understandable. Following the OEM’s advice should be fully consideredbefore proceeding with a model that doesn’t include all of thedesigner considerations.Grease replacement volume for plain bearings is influenced by several key factors that influence the replenishmentrequirement (flow rate) for a plain bearing, including lubricant product type (oil, grease), grade (ISO viscosity, NLGIgrade), sealing integrity, shaft and element size and surfacefinish, shaft speed, dynamic loading characteristics, eccentricity, radial clearance, cooling methods, etc.Each factor should be accounted for in the design processfor a plain bearing application.TRIBOLOGY & LUBRICATION TECHNOLOGYWWW.STLE.ORG

Grease lubricated applications are nearly always expected tobe continuous loss systems.The practitioner may choose to verify OEM recommendations if the complete set of machine design parameters isavailable. Experience suggests that the full set of details isdifficult to locate once the machine is operating in a production environment. A complete treatment of this topic can befound in The Tribology Data Handbook1 by Michael Khonsari.At a minimum, the OEM’s advice should be fully consideredbefore proceeding with a model that doesn’t include all of thedesigner considerations.Assuming the proper product has been selected for theoperating state, proper quantity and frequency of lubricationcan be estimated using a couple of simple formulas.Following are two options that are dependable and easyto-use for frequency and volume calculation.Option 1—Michael Neale Method. This approach provides the volume in grams per hour. Figures 1 and 2 maybe used to calculate the grease replacement volume. The information required is generally easy to obtain. Requirementsinclude bearing dimensions, shaft speed and diametricalclearance. Standardized diametrical clearances for a varietyof bearing qualities are provided, both by the supplier and inengineering handbooks.This approach does not take into account an operatingfrequency or the operating environment. Heat, moisture,Figure 1 Option A for Grease Relubrication Replacement VolumePer Hour2Qg k g * C d * π * d * bQg Grease volume per hourWherek g Rotation Speed Factor (Figure 2)C d Diametrical Clearanceπ 3.14d Shaft Diameterb Bearing WidthFigure 2 Shaft Speed Parameter for Formula in Figure 1.Shaft speed rev/minWWW.STLE.ORGkgUp to 100101 - 2500.10.2251 - 500501 - 10000.41sealing effectiveness, component mechanical fitness and corrosiveness of the process all influence lubricant coverage andeffectiveness. Some instances require the lubricant to serveas a flushing media to reject process chemical and contaminants. In these instances, a factor to increase relubricationfrequency should be incorporated to provide the feed volume at shorter intervals.Option 2—Trabon Lubriquip Method. This approachalso assigns lubricant quantity at a projected oil film thickness (1/1000th-inch) and during a given period. This method has been used successfully for many years beginning inthe early days of automatic system design and use3.The approach recommends the application of the lubricant (oil or grease) at the rate of 2/1000th film thickness pereight hours for manual lubrication and 1/1000th film thickness per four hours for automatic feed. With this approachthe interval is set, or at least proposed, and the volume iscalculated based on component surface area.Figure 3(a) Graco/Trabon Formula for ReplenishmentLubricant Volume RequiredV A x T x SfWhere,A Equivalent AreaT Film ThicknessSf Service Factor Severity1.0 Nominal1.3 - 3.0 for Shockloading1.3 - 3.0 for Extreme Heat1.0 - 0.5 for High Speed1.3 - 8.0 for Dirt and Water.75 - .25 for Process ContaminationSurface area calculations differ per type of component.Following are calculations that would be used for grease lubricated journal bearings.Figure 3(b) The Graco/Trabon Plain Bearing Dimension FormulaPlain BearingsA π *D *LWhere,π 3.14D Shaft DiameterL Bearing LengthTRIBOLOGY & LUBRICATION TECHNOLOGYAPRIL 2009 21

As shown in Figure 4, these two options applied to a tailpulley bearing on a drag conveyor, with bearing dimensionof four-inch diameter and eight-inch length, provides similarresults for volume during an eight-hour shift. It is difficultto say that one is wrong. Either method both should provideadequate coverage, assuming a quality lubricant is matchedto the production demands.The recommended grease volume works best when uniformly distributed during the course of the final time cycleor to the extent that program management can allow. If thecalculated quantity was 6 grams per hour, then 1 gram pereach 10 minutes would be better than 6 grams at 60 minutes.This is part and parcel in the system engineering thoughtprocess for automatic system design. It is more difficult formanual lubrication practices. As a rule, grease lubricatedjournal bearings should be automatically lubricated anyway.ELEMENT BEARING GREASE LUBRICATIONBearing manufacturers have provided a significant amountof detailed advice and simple methods for estimating lubricant type, volume and frequency to match machine operating components and conditions. The object with elementbearing lubrication is to place, and then replace, the greasein the housing that is enough to feed oil continuously to theelement race but not enough to crowd the elements, whichcreates churning and heat and degrades the lubricant.BEARING NET CAPACITYAND INITIAL FILL VOLUMESWhen an element bearing is first placed into service, the initial fill material generally fills the vacant space around theelements and between the races. This material may be a corrosion inhibitor or it may be lubricating grease. The initialfill volume can be based on the bearing net capacity as longas there is sufficient space at the sides of the element to al-low the excess grease to vacate the element path when themachine is put into service.In addition to the grease introduced into the elementspaces, enough grease should be placed into the housing tobring the grease level up to the lip of the bottom race of thebearing. When the excess from the initial fill is pushed awayfrom the elements it accumulates on the grease shelf at therace and becomes a reservoir to continuously serve oil backto the raceway without crowding the elements.The bearing net capacity is calculated as follows:4V ((Pi/4) * W * (OD2 - ID2) * 10-9 - G/7800)*106,whereV Volume in cubic centimetersOD Bearing outer diameter, mmID Bore diameter, mmW Bearing width, mmG Bearing weight, kg (21.5)REPLENISHMENT REQUIREMENTS FORLOW PLV ELEMENT BEARINGSA replacement volume for low to medium pitch line velocity (PLV 300,000 for ball and cylindrical roller, 100,000for spherical and thrust roller) element bearings is somewhateasier to estimate. Initial fills for very low PLVs can rangefrom 33% to 80%, assuming accurate bearing selection. Theinitial fill amount can be a higher percentage of the originalvolume as the PLV declines and vice versa.As with plain bearings, one should consider both feedvolume and frequency. The formula shown in Figure 5 canprovide grams or ounces for three different interval types depending on whether the bearing dimension is given in millimeters or inches.Figure 4 Comparing the Different Approaches Shows Similar End Result from Fairly Different Standards of Measure.Option 1: M. Nea le methodQ(oz - hour) Kg * Cd * π * D * BKgCdπDBQgOption 2 : T ra bo n methodV(cu" / 4 hrs) A * T * Sf Speed Factor .005" 0.1 .005 3.14 Shaft Diameter Bearing Width 3.14 4 8 oz. / hour .50AT D*L*п .002 100.48 .002DLSf 3.14 Shaft Diameter Bearing Length 3 (heat) 3.14 4 8 3πVConv. to oz.Qg22 APRIL 2009 oz. / shift (8 hrs) .41VTRIBOLOGY & LUBRICATION TECHNOLOGY3 in. / 4 hours3(1.805 in. /oz.) .60288 0.33 oz. / shift (8 hrs) 0.67WWW.STLE.ORG

Figure 5 The Element Bearing Replenishment Volume FormulaGq - Annually D * B * .0912 (.004 for mm)Gq - Monthly D * B * .0684 (.003 for mm)Gq - Weekly D * B * .0546 (.002 for mm)Figure 6 Grease Lifecycle Value Calculation—Useful for Determing Relubrication IntervalsF10 Real F1 * F2 * F5 * F6 * F10Where,WhereGq Ounces (cubic centimeters)D Bearing Outer Diameter, inches (mm)B Bearing Width, inches (mm)Where actual bearing dimensions are not known, a closeproximity to the actual suggested value could be estimatedby using housing dimensions and factoring again by onethird{(D * B * .114)*.33}. This provides only a close approximation. For critical applications the actual bearing makeand model should be determined.FF10 Adjusted Frequency, Hrs Calculated Nominal Grease Lifecycle (P; T; Kf*n*dm)and,PTKfdmnF1F2F5F6 FE9 Load FactorFE9 Temperature FactorFactor for Bearing TypeBearing Pitch Line, mmBearing Speed, RPMOp. Environmental PolutionOp. Load Dynamics/VibrationOp. Outer Ring RotationOp. Mounting Type and CentrifugalEnergyREPLENISHMENT FOR HIGH PLV ELEMENT BEARINGSA replacement volume for high velocity (PLV 330,000 forradial ball type; for spherical roller and thrust type) element bearings requires a careful approach due to shearingand heat produced by overfilling. Bearings of any type operating at high speeds benefit from more frequent applicationof very low doses, emulating with grease the type of continuous replenishment that occurs when the element is oillubricated.For instance, the volume calculated for the short interval,Gq-Weekly, would ideally be uniformly distributed into thenumber of working hours for the time period and appliedaccordingly. This statement brings into question the periodicity of the relubrication event.REPLENISHMENT FREQUENCY FORELEMENT BEARINGSA relubrication interval is based on theoretical reduced service life (F10 Real) in hours, which is based on known greasedegradation performance under test conditions (FAG testerFE9, SKF tester R0F). The FE9 test is more severe than theR0F, incorporating high axial and radial loading vs. pure axial load.Grease lifecycles can be predicted empirically. Much likea bearing L10 lifecycle value that indicates an operating interval for which 10% of a given bearing population wouldfail under identical operating conditions, the grease F10 valueprojects an operating interval for grease lifecycles and, consequently, relubrication intervals. It is predicated on workconducted by the German Society of Tribology (GfT, worksheet 3), and has been adopted as a viable method to projectfrequencies.5WWW.STLE.ORGLubrication interval selections through this method require a very clear understanding of the exact machine operating conditions, bearing details and certainly grease F10values.When F10 values for specific products are not available,a modified approach can provide the reliability practitionerwith a well-educated starting point. This empirically derivedapproach assumes nominal operating conditions for bearingsoperating at low PLV values ( 300K for ball and roller typeelements, 140K for spherical and thrust type elements), asfollows:Figure 7 Generic Grease Replenishment Formulatf K *[(614 * 10n* d)-4*d]Where,tf Time in hours for replacementK Product of environmental correction factorsN Shaft speedD Bearing bore in millimetersTRIBOLOGY & LUBRICATION TECHNOLOGYAPRIL 2009 23

Figure 8 Bearing Relubrication Frequency Correction Factors.LUBRICANT APPLICATIONBearing Relubrication Frequency Correction FactorsConditionAverage Operating RangeBearing Bore (b), mm3.44Shaft Speed (n), rpm12001 Svc Factor (Ft)TemperatureHousi ng bel ow 15 0 F15 0 to 1 75 F17 5 to 2 00 FContaminationHeavy, abrasive dustMoistureHumidity between 80 and 90%Occasional condensationOccasional water on housingAbove 0.410 .70 .40 .210 .70.40.11Less than 0.2 ips velocity, peak0 . 2 t o 0 .4 i p s0.50.1Humidity mostly below 80%Vibration10.4Light, non-abrasive dustLi ght, a b rasi ve dust4 Svc Factor (Fv)3.44120010.1Heavy, non-abrasive dust3 Svc Factor (Fm)Value0.2Above 200 F2 Svc Factor (Fc)FactorThere are various methods that maybe selected to add the required quantity to the designated component.The high volume and short frequency applications benefit most fromsome form of automatic lubricationsupply. Semiautomatic (single pointautomatic lubricator), as shown inFigure 9.10 .6Figure 9 Single Point Lubricators(Courtesy of Trico Corp.)0 .3Most machine grease replacementis still conducted by manual greaseHorizontal bore centerline1gun. This method is labor-intensive45 degr ee b ore ce nter l i ne0.5and leaves opportunity for the proVertical centerline0.3cess of lubrication to compromise1Bearing Design6 Svc Factor (Fd)the effectiveness of the lubricant seBall Bearings10lected but at the same time providesCylindrical and needle roller bearings5a means through which the mainteTapered and spherical roller bearings1nance department can gather usefulCalculated PM cycle (hr) . 36machine condition information viaCalculated PM cycle (day) . 1.4977the skilled lubrication technicianCalculated PM cycle (mo.) . 0.050on a timely basis. Without machineinspections and feedback from a lubrication technician, manual lubrication is prone to degrading machine productivity and reliThe correction factors (see Figure 8) allow the engineer toability.adjust frequencies based on machine operating and environFigure 10 shows a fully automatic multipoint automaticmental considerations. The six provided conditions reflectlubricationsystem, typical for use where there are multiplepractical issues that degrade bearing life and grease perforpoints located in close proximity. Properly designed andmance.installed, these lubricant applicators provide exceptionallyFigure 8 includes the correction factors for a 3.44-inchgood value in terms of the long-term cost per lubricationbore spherical roller bearing operating at 1,200 rpm (PLVpoint and in terms of the reliability potential that this type of 160,800) in direct exposure to rain and in a dusty enviautomation can provide.ronment such as on an unpaved building easement near aroadway and exposed to the weather. The calculated interGEARSval amounts to 36 hours between relubrication events. Forthis short of an interval, an automatic application method isThe American Gear Manufacturers Association (AGMA)strongly recommended.Technical Bulletins ANSI AGMA 9005 E02 provides backBearing OEM Lubrication Guideline publications proground and detailed knowledge for product selection, prodvide alternate quantitative approaches that are also valid anduct performance and volumetric application recommenda6,7,8could be considered as a strong reference starting point.tions for open gear applications.95 Svc Factor (Fp)24 APRIL 2009Position1TRIBOLOGY & LUBRICATION TECHNOLOGYWWW.STLE.ORG

Greaseapplicationvolumes are proposedbased on gear size, speed,lubricant type and lubricant application method.AGMA members haveworked closely togetherto offer their best collective advice to machineowners to optimize lubricant feed frequency andvolumes. Similarly to thatof bearings, the principalis based on a replenishment of a small quantityof lubricant across themachine contact surfacesfor a given amount ofFigure 10 A Multipoint Progrestime. The faster the masive Grease Lubrication Systemchine surfaces come in(Courtesy of Lincoln Corp.)contact with one another(based on gear pitch line velocity), the greater the quantityof lubricant. Also, the larger the gear surface, the greater therequired quantity of lubricant.Modern grease application methods for geared machinesinvariably incorporate the use of automatic lubrication systems, as shown in Figure 11.Without machine inspectionsand feedback from alubrication technician,manual lubrication is proneto degrading machineproductivity and reliability.COUPLINGSCouplings require visual observation during the relubrication process. Proper methods required removing the housingand the old material, examining and replacing the components and hand-packing the components before restoring thehousing. Once the housing is in place, grease may be provided to fill the housing until grease is produced at both sides.Excellent advice is available from most coupling manufacturers, including product selection, viscosity, product volume and application methods per type of coupling. Again,AGMA provides very specific detail on coupling lubricationthrough Technical Bulletin ANSI/AGMA 9001 B97. Thisbulletin may be found at the web reference.10,11 Figure 12depicts a typical grease spray configuration for grease lubricated gears.Figure 11 AGMA Recommended Guidelines for Open Gear Volume and Frequencies.AGMA Guideline - Lubricant Application Volume, ml/Operating .37.98.5Face Width of Pinion, in :More frequent application of small quantities is preferred. If a diluent is used to thin the lubricant, the intervals between application cycles must be long1.enoughMoretofrequentof small quantities is preferred. If a diluent is used to thin theallow theapplicationdiluent to evaporate2.lubricantIf the lubricantis appliedbetweento the drivinggear, thenthe applicationspraycycle durationsshouldlast through4 to 8 full revolutions of the driving gear.the intervalsapplicationcyclesmust beandlongenoughto allow thediluentto evaporate3. If the lubricant is applied to the driven gear, then the application and spray cycle durations should last through 1 to 2 full revolutions of the driven gear.2. If thelubricant is applied to the driving gear then the application and spray cycle durations should4. Routine visual inspections of the pressure flanks of the gear sets should be conducted to assure lubricant coverage is adequate for the operating conditions.lastthroughto 8volumesfull revolutionsof the drivingSpraypatters4andshould be confirmedat the gear.time of all inspections.3. If thelubricant is applied to the driven gear then the application and spray cycle durations shouldWlastW Wthrough. S T L E . O R1Gto 2 full revolutions of the drivenTgear.RIBOLOGY & LUBRICATION TECHNOLOGY4. Routine visual inspections of the pressure flanks of the gear sets should be conducted to assureAPRIL 2009 25

CHAINSReferencesAlthough it is best to lubricate chains with oil, grease is stilloften used for extended lubrication intervals. Helpful chainrelubrication information may be found in the AmericanChain Association document: Identification, Installation,Lubrication and Maintenance of Power Transmission RollerChains in ANSI B29.1 and ANSI B29.3 and Fundamentals ofChain Lubrication.12,131. Khonsari, M. The Tribology Data Handbook, Chapter 61, CRC Press.2. Neale, M. Tribology Handbook, 2nd Edition, p.A7.5.3. Lubriquip Technical Bulletin #20115. http://www.lubriquip.com/pdf/20115.pdf.4. LubCon GMBH, Bearing Lubrication CalculationWorksheet, FAG Bearings, German Society of Tribology and others.5. LubCon USA, LubCon GMBH, Bearing Lubrication Calculation Worksheet.6. FAG Roller Bearing Lubrication GuidelineWL81115E. d/1/15/40/37/FAG RollingBearing Lubrication WL81115E.pdf.Figure 12 Typical Configuration for Grease Application for OpenGears. (Courtesy of Lincoln Corp.)7. Web Reference X.X - Timken Bearing Co. g/pdf/general/form640.pdf.SUMMARY8. Web Reference X.X - SKF Bearing Co. http://mapro.skf.com.Common machine components such as bearings and gearscannot survive without timely and sufficient relubrication.Grease provides an efficiency opportunity that doesn’t exist with oil lubricated sumps, and accordingly is a commonchoice by machine designers.Without the benefit of thoughtful, purposeful practices,grease relubrication methods have the potential to negativelyimpact component life and machine health. Common methods for plain and element bearings can be used by the lubrication and reliability engineer to greatly enhance the usefulness of grease products.Automatic lubrication methods should be consideredwhenever multiple points operate in very close proximityand whenever calculated frequencies are at, or less than,seven days.9. American Gear Manufacturers Association. Standard 9005-EO2.10. American Gear Manufacturers Association. Technical Bulletin ANSI/AGMA 9001 B97.11. Falk Corp. Installation and Maintenance of Double and Single Engagement Gear Couplings Technical Bulletin 458-110. cations.asp.12. Web reference X.X http://www.americanchainassn.org/ACAPubs.htm.13. Wright, J.L., “Fundamentals of Chain Lubrication,” Machinery Lubrication Magazine. http://www.machinerylubrication.com/article detail.asp?articleid 316&relatedbookgroup Lubrication.Mike Johnson, CLS, CMRP, MLT, is the principalconsultant for Advanced Machine Reliability Resources, in Franklin, Tenn. You can reach him atmike.johnson@precisionlubrication.com.26 APRIL 2009TRIBOLOGY & LUBRICATION TECHNOLOGYWWW.STLE.ORG

Option 2—Trabon Lubriquip Method. This approach also assigns lubricant quantity at a projected oil film thick-ness (1/1000th-inch) and during a given period. This meth-od has been used successfully for many years beginning in the early days of automatic system design and us

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