Lubricating

Lubricant v.s Grease
Lubricant:Under high-speed and high-temperature conditions, lubricant can be used when grease is not applicable. Through the circulation of lubricants, a large amount of heat can be released.
Viscosity is an important characteristic of lubricant.Viscosity affects the fluidity of the lubricant and the thickness of the oil film formed between the friction surfaces. The viscosity of the lubricant when the bearing is operating is generally 12-15 cst. The higher the speed, the lower the viscosity should be selected, and the heavier the load, the higher the viscosity should be selected. ommonly used lubricants include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, cylinder oil, etc.
When applying lubricant to bearings, the most important thing is to select a suitable lubricant according to the using conditions. If the viscosity is too low, the oil film will break easily, which will cause abnormal wearing and burnout of the bearing. If the viscosity is too high, there will be increased torque, power loss, and abnormal rise in temperature. Generally, the higher the load, the higher the viscosity of the lubricant. Comparably, higher rotation speed requires lower viscosity.

Working temperature of the bearing ( °C )	dn value	ISO viscosity level of the lubricant (VG)(VG)		Applicable bearing
		Normal load	Heavy load or shock load
-30 ~ 0	Range of permissible rotation speed	22  32	46	All
0 ~ 60	Below 15000	46  68	100	All
	15000 ~ 80000	32  46	68	All
	80000 ~ 150000	22  32	32	Excluding thrust ball bearing
	150000 ~500000	10	22  32	Single row radial roller bearing Cylindrical roller bearing
60 ~ 100	Below 15000	150	220	All
	15000 ~ 80000	100	150	All
	80000 ~ 150000	68	100  150	Excluding thrust ball bearing
	150000 ~500000	32  46	68	Single row radial roller bearing Cylindrical roller bearing
100 ~ 150	Range of permissible rotation speed	320		All
0 ~ 60	Range of permissible rotation speed	46 68		Automatic spherical roller bearing
60 ~ 100	Range of permissible rotation speed	150

※ dn value = Bearing center distance (mm) x rotation speed (rpm).
※This table is a lubricant selection guide based on JIS K 2001 industrial lubricant viscosity classification.
※Information shown in this table is a lubricant selection guide for mist lubricant or circulation lubricant..

​
Grease:A lubricant composed of base oil, thickening agent, and additives.
A grease that is suitable for the using conditions of the bearing shall be selected before use. The performance of the grease varies due to differences in trademarks. Please pay attention when selecting.
Commonly used bearing greases include calcium grease, sodium grease, calcium-sodium grease, lithium grease, aluminum grease, and molybdenum disulfide grease. The amount of grease applied to bearings is preferably 1/2 to 1/3 of the internal space of the bearing, which should be reduced to 1/3 at high speed. Excessive grease tends to increase the bearing temperature during operation.

Advantages of Selecting of Grease:
・Convenient – During manufacturing, bearings are pre-sealed with grease and do not require maintenance.
・Low cost - Reduces the number of mechanical parts and installation procedures when using sealed bearings.
・Grease is easier to handle compared to lubricants.
・The grease itself also has a sealing effect to prevent foreign matter from entering the internal space of the bearing.

When the bearings bought is of open type or with single-sided covers, you may need to apply the grease in most cases.
The amount of grease applied at this stage should not be too much, excessive grease will result in moment increase, power loss, and temperature rise due to stirring heat. The best-recommended amount of grease to apply is:
・When the rotation speed is less than 50% of the permissible rotation speed, the amount of grease applied shall be 1/2 to 2/3 of the internal space of the bearing.
・When the rotation speed exceeds 50% of the permissible rotation speed, the amount of grease applied shall be 1/3 to 1/2 of the internal space of the bearing.
​

Using conditions	Grease	Lubricant
Temperature	Cannot be used in high temperature environment	Can be used in high temperature environment (circulating cooling)
Speed	Low speed to moderate speed	Can be used in high speed
Load	Below moderate load	Applicable to high load
Structure and maintenance of bearing housing	Simple	Complicated, need to pay attention to oil leakage
Concentrated apply of lubricant	Possible	Easy
Filter foreign matter	Impossible	Possible (circulating filtration)
Rotation impedance	High	Low (must maintain an appropriate amount of lubricant)