ROLLING BEARING LUBRICATION - Mounting …

1 ROLLING BEARING LUBRICATIONFAG Kugelfischer Georg Sch fer AGIndustrial Bearings and ServicesRolling BEARING LubricationPubl. No. WL 81 115/4 EAFAG Kugelfischer Georg Sch fer AGIndustrial Bearings and ServicesPostfach 1260D-97419 SchweinfurtGeorg-Sch fer-Stra e 30D-97419 SchweinfurtTel. +49 9721 91-2349 Fax+49 9721 91-4327E-mail: of Contents1 Lubricant in ROLLING Bearings.. of the Lubricant in ROLLING Bearings .. The Different Lubricating Conditions in ROLLING Bearings .. Lubricating Film with Oil LUBRICATION .. Influence of the Lubricating Film and Cleanlinesson the Attainable BEARING Life .. Lubricating Film with Grease LUBRICATION .. Lubricant Layers with Dry LUBRICATION .. Calculation of the Frictional Moment .. Operating Temperature .. 182 LUBRICATION System.

2 Grease LUBRICATION .. Oil LUBRICATION .. Dry LUBRICATION .. Selection of LUBRICATION System .. Examples of the Different LUBRICATION Systems .. Central LUBRICATION System .. Oil Circulation System .. Oil Mist LUBRICATION System .. Oil-Air LUBRICATION System .. Oil and Grease Spray LUBRICATION .. 243 Lubricant Selection.. Selection of Suitable Greases .. Grease Stressing by Load and Speed .. Running Properties .. Special Operating Conditions and EnvironmentalInfluences .. Selection of Suitable Oils .. Recommended Oil Viscosity .. Oil Selection According to Operating Conditions .. Oil Selection According to Oil Properties .. Selection of Dry Lubricants .. Quickly Biodegradable Lubricants.

3 334 Lubricant Supply.. Grease Supply .. Lubricating Equipment .. Initial Grease Charge and Grease Renewal .. Grease Service Life .. LUBRICATION Intervals .. Relubrication, Relubrication Intervals .. Examples of Grease LUBRICATION .. Oil Supply .. Lubricating Equipment .. Oil Sump LUBRICATION .. Circulating LUBRICATION with Average and Above Average Oil Volumes .. Throwaway LUBRICATION .. Examples of Oil LUBRICATION .. Dry Lubricant Application .. 52 FAG25 Damage Due to Imperfect LUBRICATION .. Contaminants in the Lubricant .. Solid Foreign Particles .. How to Reduce the Concentration of Foreign Particles .. Oil Filters .. Liquid Contaminants .. Cleaning Contaminated ROLLING Bearings.

4 Prevention and Diagnosis of Incipient BEARING Damage by Monitoring .. 566 Glossary of Terms.. 57 Lubricant in ROLLING BearingsFunctions of the Lubricant in ROLLING Bearings1 Lubricant in ROLLING Functions of the Lubricant in ROLLING BearingsThe LUBRICATION of ROLLING bearings similar to that of sliding bearings main-ly serves one purpose: to avoid or at leastreduce metal-to-metal contact betweenthe ROLLING and sliding contact surfaces, to reduce friction and wear in , adhering to the surfaces of theparts in ROLLING contact, is fed between thecontact areas. The oil film separates thecontact surfaces preventing metal-to-met-al contact ( physical LUBRICATION ).In addition to ROLLING , sliding occurs inthe contact areas of the ROLLING amount of sliding is, however, muchless than in sliding bearings.

5 This slidingis caused by elastic deformation of thebearing components and by the curvedform of the functional pure sliding contact conditions,existing for instance between ROLLING ele-ments and cage or between roller facesand lip surfaces, the contact pressure, as arule, is far lower than under ROLLING con-tact conditions. Sliding motions in roll-ing bearings play only a minor role. Evenunder unfavourable LUBRICATION condi-tions energy losses due to friction, andwear are very low. Therefore, it is possibleto lubricate ROLLING bearings with greasesof different consistency and oils of differ-ent viscosity. This means that wide speedand load ranges do not create any , the contact surfaces arenot completely separated by the lubricantfilm. Even in these cases, low-wear opera-tion is possible, if the locally high temper-ature triggers chemical reactions betweenthe additives in the lubricant and the sur-faces of the ROLLING elements or rings.

6 Theresulting tribochemical reaction layershave a lubricating effect ( chemical lubri-cation ).The lubricating effect is enhanced notonly by such reactions of the additivesbut also by dry lubricants added to the oilor grease, and even by the grease special cases, it is possible to lubricaterolling bearings with dry or solid lubri-cants functions of ROLLING bearinglubricants are: protection against corro-sion, heat dissipation from the BEARING (oil LUBRICATION ), discharge of wear parti-cles and contaminants from the BEARING (oil circulation LUBRICATION ; the oil is fil-tered), enhancing the sealing effect of thebearing seals (grease collar, oil-air lubrica-tion). The Different Lubricating Condi-tions in ROLLING Bearings Friction and wear behaviour and theattainable life of a ROLLING BEARING dependon the lubricating condition.

7 The follow-ing lubricating conditions exist in a roll-ing BEARING : Full fluid film LUBRICATION : The surfac-es of the components in relative mo-tion are completely or nearly com-pletely separated by a lubricant film(fig. 1a).This is a condition of almost purefluid friction. For continuous opera-tion this type of LUBRICATION , which isalso referred to as fluid LUBRICATION ,should always be aimed at. Mixed LUBRICATION : Where the lubri-cant film gets too thin, local metal-to-metal contact occurs, resulting inmixed friction (fig. 1b). Boundary LUBRICATION : If the lubricantcontains suitable additives, reactionsbetween the additives and the metalsurfaces are triggered at the high pres-sures and temperatures in the contactareas. The resulting reaction productshave a lubricating effect and form athin boundary layer (fig.)

8 1c).Full fluid film LUBRICATION , mixed lu-brication and boundary LUBRICATION occurboth with grease LUBRICATION and with oillubrication. The lubricating conditionwith grease LUBRICATION depends mainlyon the viscosity of the base oil. Also, thegrease thickener has a lubricating effect. Dry LUBRICATION : Solid lubricants ( and molybdenum disul-phide), applied as a thin layer on thefunctional surfaces, can prevent metal-to-metal contact. Such a layer can,however, be maintained over a longperiod only at moderate speeds andlow contact pressure. Solid lubricants,added to oils or greases, also improvethe lubricating efficiency in cases ofmetal-to-metal : The different lubricating conditions3 FAGa) Full fluid film lubricationThe surfaces are completely separatedby a load carrying oil filmb) Mixed lubricationBoth the load carrying oil film andthe boundary layer play a major rolec) Boundary lubricationThe lubricating effect mainly depends on thelubricating properties of the boundary layerBoundary layerLubricant layerLubricant in ROLLING BearingsFunctions of the Lubricant in ROLLING Lubricating Film with Oil Lubri-cationMain criterion for the analysis of thelubricating condition is the lubricatingfilm thickness between the load transmit-ting ROLLING and sliding contact lubricant film between the rollingcontact surfaces can be described bymeans of the theory of elastohydrody-namic (EHD) LUBRICATION .

9 The lubrica-tion under sliding contact conditionswhich exist, between the roller facesand lips of tapered roller bearings, is ade-quately described by the hydrodynamiclubrication theory as the contact pressurein the sliding contact areas is lower thanin the ROLLING contact minimum lubricant film thick-ness hminfor EHD LUBRICATION is calculat-ed using the equations for point contactand line contact shown in fig. 2. Theequation for point contact takes into ac-count the fact that the oil escapes fromthe gap on the sides. The equation showsthe great influence of the ROLLING velocity , the dynamic viscosity 0and the pres-sure-viscosity coefficient on hmin. Theload Q has little influence because theviscosity rises with increasing loads and FAG42: Elastohydrodynamic lubricant film. Lubricant film thicknesses for point contact and line contactEHD-pressuredistributionHertzian pressure distributionLubricant inletLubricant outletRollerdeformationLubricant filmRacewaydeformationp0according to Hertz2baccordingto Hertzhminr2r1v1v2 QPoint contact according to Hamrock and Dowsonhmin= W (1 e k) Rr[m]Line contact according to Dowsonhmin= W' Rr[m]withU = 0 v/(E' Rr)G = E'W = Q/(E' Rr2) for point contactW' = Q/(E' Rr L)

10 For line contactwherehmin[m]minimum lubricant film thickness in the area of ROLLING contactUspeed parameterGmaterial parameterWload parameter for point contactW'load parameter for line contactee = , base of natural logarithmskk = a/b, ratio of the semiaxes of the contact areas [m2/N] pressure-viscosity coefficient 0[Pa s]dynamic viscosityv[m/s]v = (v1+ v2)/2, mean ROLLING velocityv1= ROLLING element velocityv2= velocity at inner ring or outer ring contactE'[N/m2]E' = E/[1 (1/m)2], effective modulus of elasticityE = modulus of elasticity = 1011[N/m2] for steel1/m = Poisson s ratio = for steelRr[m]reduced curvature radiusRr= r1 r2/(r1+ r2) at inner ring contactRr= r1 r2/(r1 r2) at outer ring contactr1= ROLLING element radius [m]r2= radius of the inner and outer ring raceways [m]Q[N] ROLLING element loadL[m]gap length or effective roller lengthLubricant in ROLLING BearingsFunctions of the Lubricant in ROLLING Bearingsthe contact surfaces are enlarged due toelastic calculation results can be used tocheck whether a sufficiently strong lubri-cant film is formed under the given con-ditions.