>> P.52
LubricationPurpose of lubricationThe main purpose of bearing lubrication is to reduce friction and wear and to prevent heat generation and seizure. The lubricant and the lubricating method have a big inuence on the operating performance of the bearing, and it is therefore necessary to select them suitably for the operating conditions.The effects of lubrication are as follows.1 Reduction of friction and wearAt the contact surfaces between the race rings, rolling elements and cage of the bearing, lubrication prevents metal-to-metal contact, and reduces friction and wear due to sliding and rolling, in the latter of which micro-slips occur by differential slip, skew, spin, or elastic deformation.2 Elimination of frictional heatThe lubricant removes the heat generated by friction or transferred from outside, and prevents overheating of the bearing. Circulating lubrication is generally used for this purpose.3 Influence on bearing lifeThe bearing life is extended if the rolling contact sur-faces between the race rings and rolling elements are Methods of lubricationGrease lubrication and oil lubrication are generally used for rolling bearings. In special cases, solid lubri-cants are also used.In general, grease lubrication requires the simplest sealing structure. It is therefore economical and widely used. Also, once lled with grease, the bearing can be used for a long period without replenishing the grease. However, compared with oil, its heat removal properties and cooling capacity are inferior, since grease has high flow resistance, which causes high churning heat.Oil has greater fluidity and superior heat removal properties. It is therefore suitable for high-speed operations. In addition, it is simple to lter out dust and dirt from oil. Thus it can prevent the generation of noise and vibration and increase bearing life. Another advantage of oil lubrication is that it offers the possibility for selecting the appropriate method for particular operating conditions from among various available lubrication methods. However, measures to prevent oil leakage are required. As a guideline for selection, Table 34 compares grease and oil lubrica-tion.For the lubricants used for IKO Spherical Bushings, see page K8.Table 34 Comparison between grease lubrication separated by an oil lm of adequate thickness, and is and oil lubricationshortened if the oil lm is inadequate due to low oil viscosity, etc.4 Rust preventionThe lubricant prevents rust formation on the inside and outside surfaces of the bearing.5 Dust preventionGrease lubrication is particularly effective for dust pre-vention. Oil circulating or jet lubrication is effective in washing foreign particles away from the area around the bearing.ItemGrease lubrication(1)Oil lubricationSealing structure, Housing structureSimpleSlightly complicatedTemperatureHigh temperature not allowedHigh temperature allowed (Cooling effect by circulation)Rotational speedLow and medium speedsHigh speed allowedLoadLow and medium loadsHigh load allowedMaintenanceEasyElaborate(Pay special attention to oil leaks. )Lubricant replacementSlightly complicatedSimpleLubrication performanceGoodVery goodDust filtrationDifficultSimpleEntry of dust and dirtEasy measures for protectionDust and dirt can be removed by filtering in circulating lubrication. Note(1)This represents bearing grease for general use.A49
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