Guide to Electric Motor Bearing Lubrication

1 Guide to Electric MotorBearing LubricationElectric Motor photo courtesy of Baldor Electric Company2003767_electricmotormanual 3/19/02 10:26 AM Page 1 Choosing the Right Electric MotorGreaseImportant grease Characteristics for ElectricMotor BearingsThe following criteria may be used as typical indicators of agood Electric Motor grease :nViscosity:Oil viscosity should be appropriate for theload and speed of the application at operating tempera-ture. This will help to insure maximum protection andcomponent life. The typical mineral oil viscosity in anelectric Motor grease is in the range of 500 to 600 SUSat 100 F.

2 Your Electric Motor builder may provide a spe-cific :A grease s consistency is one of itsmost visible characteristics. A grease s consistency orfirmness is stated in terms of its NLGI (NationalLubricating grease Institute) grade, which ranges from000 to 6. The consistency of a grease should beappropriate to the application, as it affects pumpabilityand ability to reach the areas to be lubricated. A NLGI 2grade grease is the most commonly used in electricmotor applications. nOxidation Resistance: Electric Motor greasesshould have outstanding resistance to oxidation. Thisextends the life of bearings running at high speeds andhigh temperatures.

3 ASTM D 3336 High TemperatureGrease-Life test results give a good indication whenoperating under extreme conditions. Choose a greasewith a high ASTM D 3336 oxidation :Unless a Motor is mounted so there is athrust load on the bearings, it is generally advisable touse a grease without extreme pressure (EP) additives can shorten the life of the grease andshould not be recommended where they are notneeded. On the other hand, bearings designed tohandle heavy thrust loads may require a grease with anEP Point:The dropping point gives an indica-tion of the temperature at which the grease will melt orthe oil will separate from the thickener.

4 Due to the hightemperatures that can be reached in an Electric motorbearing, a grease with a high dropping point is frequent-ly desirable. Lithium-complex greases and polyurea-thickened greases both have dropping points of approx-imately 500 F or Guide to Electric MotorBearing LubricationThe proper Lubrication of Electric Motor bearings is essentialto maintaining them in peak operating condition and,ultimately, in reducing unnecessary downtime. This bulletin,for ExxonMobil customers, is intended to serve as apractical Guide to the proper Lubrication of Electric motorbearings utilizing grease as a lubricant.

5 It can help you toapply ExxonMobil's years of Lubrication experience with thatof Bearing and Motor manufacturers from around the worldto provide you with a Guide to the proper Lubrication ofelectric Motor LubricationGrease is frequently used as an Electric Motor bearinglubricant because of its simplicity of application and uniquecharacteristics. The primary functions of an Electric motorbearing grease are to:nReduce friction and prevent wearnProtect bearings against corrosionnAct as a seal to prevent entry of contaminantsGrease is a semi-solid lubricant composed of a base oil, athickener and additives.

6 These components are combined incomplex chemical reactions under controlled temperaturesand pressures. The base oil used in greases may be mineralor synthetic. Mineral oils are adequate for most electricmotor Bearing applications. However, synthetic base oilsmay be required for extreme temperature applications orwhere longer regreasing intervals are desired. The thickenerprimarily serves as a carrier for the oil and prevents it fromleaking out of the application. Some common thickenersinclude metallic soaps that can be composed of calcium,lithium, sodium, aluminum or barium and complex metallicsoaps such as lithium-complex.

7 A thickener increasinglyemployed in Electric Motor Bearing Lubrication is EMutilizes a polyurea thickener. As with manylubricating oils, additives are frequently used to impart spe-cial properties to the grease . Commonly used additivesinclude, corrosion inhibitors, anti-wear or extreme pressureagents, oxidation and corrosion inhibitors, pour pointdepressants, lubricity agents, and dyes or pigments. 12003767_electricmotormanual 3/19/02 10:26 AM Page 2nShear stability:ASTM D 217 Cone Penetration ofLubricating grease test measures the consistency of thegrease after it has been worked 100,000 strokes.

8 Anelectric Motor Bearing grease should soften no morethan 1 to NLGI grades in this test. An Electric motorbearing grease that softens more than that may leak outof the Bearing with compatibilityWith some exceptions, greases with different types ofthickeners should be considered incompatible with eachother. We recommend running grease compatibility tests ifmixing different greases is unavoidable. Generally, incom-patible greases will soften or become fluid. This can result inlack of Lubrication and can lead to premature Bearing , stiffening may occur and can also lead to a lack oflubrication.

9 Always purge as much of the old grease as pos-sible, and then regrease more frequently to purge all the oldgrease out of the grease to Electric MotorBearingsRe-greasing IntervalsElectric motors utilizing double shielded or double sealedbearings, which are typically of the lubricated-for-life design,usually do not require regreasing. On the other hand, allothers, those being open or single shielded or sealedbearings, should be re-lubricated periodically to replacegrease that has deteriorated, leaked away, or becomecontaminated. Generally, operating conditions will dictatethe relubrication interval greases deteriorate at some rate, even under moderateoperating conditions.

10 The principal causes are oxidation,excessive oil bleeding, and mechanical working. At hightemperatures, oil evaporation may also be a factor. Oxidationeventually increases the oil viscosity and hardens the oil bleeding is desirable, but too much reduces theability of the grease to maintain an effective Lubrication working, or shearing, may change greaseproperties such as consistency, making the grease lesssuited to the application. Excessive oil evaporation mayharden the grease . Deterioration often ends in hard, dry,deposits that can neither lubricate bearings nor protect themagainst and other factors that influence relubricationfrequency include: temperature, continuity of service,quantity of grease in housing, size and speed of Bearing ,vibration, exposure to contaminants, effectiveness of seals,and the grease 's suitability for the particular High grease temperatures increase the oxidation rate,doubling it for every 18 F (10 C) rise above 120 F(49 C).