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  • LUBRICATION

  • Purposes of Lubrication
    The main purposes of lubrication are to reduce friction and wear inside the bearings that may cause premature failure. The effects of lubrication may be briefly explained as follows:

    (1) Reduction of Friction and Wear
    Direct metallic contact between the bearing rings,rolling elements and cage, which are the basic components of a bearing, is prevented by an oil film which reduces the friction and wear in the contact areas.
    (2) Extension of Fatigue Life
    The rolling fatigue life of bearings depends greatly upon the viscosity and film thickness between the
    rolling contact surfaces. A heavy film thickness prolongs the fatigue life, but it is shortened if the viscosity of the oil is too low so the film thickness is insufficient.
    (3) Dissipation of Frictional Heat and Cooling
    Circulation lubrication may be used to carry away frictional heat or heat transferred from the outside to prevent the bearing from overheating and the oil from deteriorating.
    (4) Others
    Adequate lubrication also helps to prevent foreign material from entering the bearings and guards against corrosion or rusting.
              


    Lubricating Methods
    The various lubricating methods are first divided into either grease or oil lubrication. Satisfactory bearing performance can be achieved by adopting the lubricating method which is most suitable  for the particular application and operating condition.
    In general, oil offers superior lubrication; however, grease lubrication allows a simpler structure around the bearings. A comparison of grease and oil lubrication is given in Table 3.

                          


                            

    Item

    Grease Lubrication

    Oil Lubrication

    Housing Structure and

    Sealing Method

     

    Speed

     

    Cooling Effect

     

    Fluidity

     

    Full Lubricant

    Replacement

     

    Removal of Foreign

    Matter

     

     

    External Contamination due to Leakage

    Simple



    Limiting
     speed is 65% to

    80% of that with oil lubrication.

    Poor

     

    Poor

     

    Sometimes difficult

     

     

     

    Removal of particles from grese 

     

    is impossible.

     

     

    Surroundings seldom 

    contaminated by leakage.

    May be complex, Careful 

    maintenance required.

     

    Higher limiting speed.

    Heat transter is possible using 

    forced oil circulation.

    Good

     

     

    Easy


    Easy

     

     

     

     

     

     

    Often leaks without proper 

    countermeasures. Not suitable if external 

    contamination must be avoided.


      Table 3  Comparison of Grease and Oil Lubrication

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