• Grease Lubrication

  • (1) Grease Quantity

    The quantity of grease to be packed in a housing depends on the housing design and free space, grease characteristics, and ambient temperature. For example, the bearings for the main shafts of machine tools, where the accuracy may be impaired by a small temperanture rise, require only a small amount of grease. The quantity of grease for ordinary bearings is determined  as follows.

    Sufficient grease must be packed inside the bearing including the cage guide face.The available space inside the housing to be packed with grease depends on the speed as follows:

    1/2 to 2/3 of the space    When the speed is less than 50% of the limiting speed.

    1/3 to 1/2 of the space     When the speed is more than 50% of the limiting speed.

    (2)Replacement of Grease
    Grease, once packed, usually need not be replenished for a long time; however, for severe  operating conditions, grease should be frequently replenished or replaced. In such cases, the bearing housing should be designed to facilitate grease replenishment and replacement.
    When replenishment intervals are short, provide replenishment and discharge ports at  appropriate positions so deteriorated grease is replaced by fresh grease. For example, the housing space on the grease supply side can be divided into several sections with partitions. The grease on the partitioned side gradually passes through the bearings and old grease forced from the bearing is discharged through a grease valve . If a grease valve is not used, the space on the discharge side is made larger than the partitioned side so it can retain the old grease, which is removed periodically by removing the cover.

    (3)Replenishing Interval
    Even if high-quality grease is used, there is deterioration of its properties with time; therefore,periodic replenishment is required.

    If the bearing temperature exceeds 70 , the replenishment time interval must be reduced by half for every 15 temperature rise of the bearings.

    In case of ball bearings especially, the replenishing time interval can be extended depending on  used grease type. If the temperature of the bearings is less than 70℃, the usage of lithium soap-mineral oil grease or lithium soap-synthetic oil grease is appropriate.

    (4)Grease Life of Totally Enclosed Ball Bearings
    When grease is packed into single-row deep groove ball bearings, the grease life may be estimated using Equation (1) or (2)

    General purpose grease (1)

    Wide-range grease (2)

    where    t : Average grease life, (h)
                  n : Speed (rpm)
         Nmax : Limiting speed with grease lubrication(rpm)        
                 T : Operating temperature

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