Selecting a bearing

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.

Thickener		Lithium soup			Urea		PTFE
Name		Lithium soup grease			Urea grease		Fluornated grease
Base Oil	Major Component	Ester			Synthetic hydrocarbon	Ester	Fluorinated
Noise		◎	◎	◎	◎	△	△	◯ (△)	◯ (△)
Torque		◎	◎	◯	◯	△	△	◎	◎◎
High temperature		◯	△	◎	◎	◎	◎◎	◎◎	◎◎
Low temperature		◯	◎	◯	◯ (△)	△	△	◎	◎◎
High Speed		◯	△	◯	◎	◎	△	△	△
plastic degradation		×	×	×	◎	×	△	-	-
conductivity		-	-	-	-	-	-	-	-
low dust		×	×	×	◯	-	-	-	-
price		◎	◎	◯	◎	◯	×	×	×
code		LY121	LY72	LY552	LY551	LY532	LY500	LY586	LY699
Characteristic		general	low torque	wide range	heat resistance, high speed	heat resistance, high speed	heat resistance	heat resistance	heat resistance
base oil viscocity mm³/S@40℃	representing value	26	15	55	48	100	190	85	210
cone penetration	representing value	250	275	240	225	255	280	280	280
application temperature range^*		-50~ +150	-50~ +150	-40~ +130	-40~ +200	-40~ +180	-50~ +260	-50~ +220	-40~ +200

Thickener		PTFE	carbon			-
Name		Fluornated grease	Conductive grease			Oil
Base Oil	Major Component	Fluorinated + Ester	Synthetic hydrocarbon		Fluorinated	Ester	Synthetic hydrocarbon
Noise		△	×	×	×	◎	◎
Torque		△	△	△	×	◎	◎
High temperature		◎◎	◎	◯	◎◎	△	△
Low temperature		△ (◯)	◯	◯	◯	◎	◎
High Speed		△	△	△	△	△	△
plastic degradation		◎	◎	-	-	×	◎
conductivity		-	◎	◎◎	◎	-	-
low dust		-	-	-	-	×	×
price		△	△	△	×	△	◯
code		LY655	LY727	LY722	LY707	LO1	LY650
Characteristic		heat resistance	conductivity	conductivity	conductivity, heat resistance	low torque	plastic resistance
base oil viscocity mm³/S@40℃	representing value	85	148	20	420	12	32
cone penetration	representing value	280	235	263	230	-	-
application temperature range^*		-50~ +200	-40~ +125	-40~ +125	-30~ +250	-50~ +120	-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.