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Miniature & Small ball bearings -18. Lubricants

Lubricant selection has a strong impact on ball bearing performance. Bearing performance such as life, torque, rotation stability, and noise depend on lubricants even if the bearings use the same material and components.
Either grease or oil is filled inside the bearings. They are rarely changed once filled. Generally, grease is the standard in enclosure type bearings because the life of grease is longer than that of oils.

Grease is composed of thickener and oil (base oil). Fiber bonding and oil separation of thickener plays an important role in grease. Fiber bonding keeps the oils in, and the oils are released gradually by oil separation. If only oils were filled, they would tend to leak out. Since grease thickener is a solid, it is able to stay inside. The slow release of base oils due to oil separation makes longer lubrication life possible. When extreme low torque or limited torque fluctuation is required in specific applications, oils perform better than grease. While oils spread out well, grease does not because it is solid. This grease characteristic causes resistance against rotation. If a lubricant which is composed of only oil is used, it is necessary to focus on life,. Other components of grease are additives. Oxidation-resistant agents, lube agents (improving boundary lubrication), extreme pressure agents (preventing from seizure by burning), and rust-resistant agents are the some of the additives, and they can make a performance difference in various types of grease.


Lubricant fill amount

The standard lubricant fill amount for small and miniature size bearings is 30 %. Grease fill amount varies in each application, and is specified as follows.

Fill amount symbols Fill amount Fill amount symbols Fill amount
X 5 ~ 10% No code (standard) 25 ~ 35%
L 10 ~ 15% H 40 ~ 50%
T 15 ~ 20% J 50 ~ 60%

Notes

Chemical attack

Plastics are now used more frequently for assemblies using ball bearings due to the trends toward smaller and lighter devices. Unfavorable combinations of grease and plastics could result in a chemical reaction that degrades and cracks components.
When selecting grease and oil, application conditions and environment need to be reviewed.
Please refer to 17. Combination with plastic parts for details.


Conductivity

Conductive grease is one of the choices for specific applications where the environment is conductive. Conductive capability depends on the application condition (RPM, Load, and so on).
Please note that the grease life and conductivity life are not equal.

Name Lithium soup grease Urea grease Fluornated grease Conductive grease Oil
Thickener Lithium soup Urea PTFE carbon -
Base Oil Major Component Ester Synthetic hydrocarbon Ester Fluorinated Fluorinated + Ester Synthetic hydrocarbon Fluorinated Ester Synthetic hydrocarbon
Noise
(△)

(△)
× ×
Torque ◎◎ ×
High temperature ◎◎ ◎◎ ◎◎ ◎◎ ◎◎
Low temperature
(△)
◎◎
(○)
High Speed
plastic degradation × × × - - - ×
conductivity - - - - - - - - - -
low dust × × - - - - - - - × ×
price × × × ×
code LY121 LY72 LY551 LY706 LY500 LY586 LY699 LY655 LY727 LY746 LO1 LY650
Characteristic general low torque heat resistance, high speed heat resistance heat resistance heat resistance heat resistance heat resistance conductivity heat resistance, conductivity low torque plastic resistance
base oil viscocity mm2/S@40℃ representing value 24 16 48 100 190 85 85 210 148 208 12 32
cone penetration representing value 250 275 235 263 280 280 280 290 235 327 - -
application temperature range* -50

+150
-50

+130
-40

+200
-40

+180
-50

+260
-65

+260
-50

+220
-50

+200
-40

+125
-50

+225
-57

+177
-40

+130

* These ranges are based on the information given by each grease manufacturer. Please note that they are not the specific temperature ranges for bearing application.

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