Bearing lubricationH1

nullBearing LubricationBearing LubricationnullFilm Thickness FormulaThe load dependent variable (W) has a weak exponent (-0.073). The important variables are velocity (u), nominal viscosity (m0) and pressure viscosity coefficient (a) with larger exponents Lambda definitionLambda definitionLambda Ratio: With Rq, a measure of the surface roughness. Kappa definitionKappa definitionTo simplify the EHL theory, the term Kappa was introduced:  =  / 1  = ^1.3  = operating viscosity of the lubricant, mm2/s 1= required viscosity depending on the bearing mean diameter and rotational speed, mm2/s, to yield  equal 1. nullRequired viscosity diagramViscosity vs. TemperatureViscosity vs. TemperatureBearing Lubrication Bearing Lubrication Rolling bearing lubricants primary functions: To create a separating film between the rolling elements and the raceways. To minimize friction and wear between the retainer and other components; To minimize friction and wear in sliding contacts between the rolling elements and the raceways.What is the Purpose of Lubrication?Bearing Lubrication What is the Purpose of Lubrication?Bearing Lubrication What is the Purpose of Lubrication?Secondary functions are: To protect the highly finished surfaces from corrosion; To help seal against foreign matter (done with grease pack); To provide a heat transfer medium. Both oil and greases are used for rolling bearings.null Bearing Lubrication Base oil types, additional: Mineral paraffinic standard, economical 1 naphthenic improved properties 2 Synthetic PAO higher viscosity index 3 polyglycol excellent VI, rubber comp. 3 ester low T., high VI, biodegr. 10 silicone VI, low and high T. 100 PFPE very high T., chem. stab. 500 Natural rapeseed food comp., biodegradable 3 type subtype reason pricev 1.1, 1/14 Bearing Lubrication Oil (vs. Grease) Bearing Lubrication Oil (vs. Grease) Advantages 1. Better Heat Dispersement 2. Higher Speed Capability 3. Can be Circulated 4. Can be Cleaned Disadvantages 1. Possibility of Leakage 2. Does not Seal 3. Can be Displaced by WaternullBearing LubricationAdditive package: Extreme pressure (EP) – High Loads Anti wear(AW) – boundary lubrication Anti oxidation Anti foaming null Thickener types, additional: Metal soap Lithium standard, effective. Calcium water resistance. Aluminum thermal stability. complexes sometimes increased performance. Non-soap polyurea high or wide temp. clay no drop point, wide temp. silicon no drop point, wide temp. PTFE thermal stability, high temp.Type Subtype Reason v 1.1, 1/18Bearing Lubricationnull Importance of base oil viscosity: operating viscosity speed of rotation loadLubricant film thickness in the bearing depends on:Base oil viscosity is the main tool to adjust lubricant film thicknessv 1.1, 2/10Bearing Lubricationnull 1. Select consistency:NLGI 2 grade: for normal bearing applications for large bearings, NLGI 3 grade: for small ball bearings for vibrating installations, at high ambient temperatures, for vertical shaft applications NLGI 1 grade: at low ambient temperatures, for oscillating applications, when pumpability is a problemChoose:v 1.1, 3/6Bearing LubricationBearing Lubrication GreaseBearing Lubrication Grease Advantages 1. Easy to apply 2. Helps to seal 3. Wide range of applications 4. Better control of leakage Disadvantages 1. Poor heat dissipation 2. Collects and retains contaminants 3. Structural change possibility (i.e. - work hardening) 4. Possible compatibility problems if greases are mixednull Grease or oil? Grease: Oil: + simple installation + additional cooling + additional bearing protection + filtering and quality (against dirt, moisture) control possible80% of all bearings are grease lubricatedBearing LubricationBearing Lubrication Grease SelectionBearing Lubrication Grease SelectionConsistency Thickener Viscosity of base oil Speed limit Bleed rate Noise characteristics Moisture resistancenull Grease selection process:1 Select consistency 2 Check EP / solid lubricant requirements 3 Select additional grease properties 4 Select base oil viscosityAdvised selection process, simplified approachv 1.1, 3/5Bearing LubricationnullCalculation of Actual Grease Life La: Difference between grease life & relubrication interval Corr. Fact’s: Temp., load, vibration & shocks,moisture, dust, air-flow through, vertical shaft, OR rotation GPF: Specific performance factors based op. temperature & speed null Grease selection without knowledge :Further knowledge or advise needed, when: operating temperature above 100 °C or below 50 °C bearing speed very high or very low bearing subjected to heavy loads or shock loads special grease properties required (extra water or corrosion resistance, low torque, low noise, compatibility with other media, etc.)v 1.1, 3/4Bearing LubricationnullBearing Lubrication Grease FillFill the Bearing Completely Work grease in around cage pockets & rolling elements Fill the housing only 1/3 full Incompatibility of GreasesIncompatibility of GreasesA lithium grease . . . . . . Which is mixed with a sodium grease . . . . . Gives a softer grease than the two in isolation. The grease leaks out and, moreover, has a lower maximum operating temperature.Greases with the same thickener and a similar base oil can be mixed.If two greases which are not compatible are mixed, the consistency usually becomes softer.Mixing of greases with incompatible thickeners usually results in softer consistency sometimes results in higher consistency