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Why should FAG bearings be lubricated

Writer: Eric Bearing Limited

FAG bearing lubrication mainly plays a role in two main points. The first point is to separate the contact surface of the bearing (eliminate wear and reduce friction); the second point is to protect the bearing (to avoid bearing corrosion and avoid impurities affecting the use of the bearing).

2. How to choose bearing lubricant

(1) Selection of FAG bearing lubricant

a. Solid lubricants: mainly suitable for FAG deep groove ball bearings, temperature> 200℃.

b. Grease: Suitable for all types of FAG bearings, selected according to bearing speed and grease type, except for thrust spherical roller bearings. It is characterized by low friction and low noise.

c. Lubricant (large dose): suitable for all FAG bearings. The viscosity of the lubricating oil determines its noise reduction effect, and the heat dissipation effect is good. The cyclic movement of the lubricating oil and the lubrication between the oil and the steel can discharge the friction particles from the motion system, but the vortex formed by a large amount of lubricating oil will cause friction , Resulting in energy loss.

d. Lubricating oil (small dose): suitable for all FAG bearings. The viscosity of lubricating oil determines its noise reduction effect, and the dosage and viscosity of lubricating oil determine the magnitude of friction.

(2) Selection of bearing lubricant

The following points should be considered when selecting lubricants for FAG bearings:

a. Working environment;

b. Requirements for operation, noise, friction and temperature;

c. Safety requirements, for friction, fatigue, corrosion and damage caused by foreign objects (water, sand, etc.) infiltrated from the outside world in previous accidents;

d. Installation and maintenance costs;

e. 70%-80% of the bearings are lubricated with grease.

3. FAG bearing lubrication principle

FAG bearing lubrication principle basis: elastohydrodynamic theory.    FAG NUP309-E-XL-M1 bearings online , pls click here : 

Question: Will the oil film be destroyed by load pressure ?

The thickness of the oil film depends on the viscosity of the base oil. The higher the viscosity, the thicker the oil film.

Note: The yield strength of FAG bearing steel is 1750MPa; the pressure that the oil film can withstand is 1000~5000MPa.

4. Grease lubrication

(1) Characteristics of grease lubrication

a. Simple operation.

b. Good sealing effect, long service life, no maintenance, simple lubrication equipment.

c. Applicable speed range: n*dm <500.000 [mm/min] (n=speed[1/min], n*=maximum speed; dm=average bearing diameter (D+d)/2 [mm]).

d. There is no need to replace lubricants under low load conditions (speed, temperature, load).

e. The friction torque is small.

(2) Replacement features of grease lubrication

a. Under high load conditions (speed, temperature, load), the lubricant must be replaced regularly.

b. When changing the grease, prepare a grease change valve and a waste grease collector.

c. The principles of elastohydrodynamics theory also apply to grease lubrication (oil is fixed in the oil soap skeleton).

(3) Selection characteristics of grease

a. Temperature: Table of grease temperature characteristics.

b. Speed: FAG bearing rated working speed.

The maximum speed of FAG bearings depends on the viscosity of the grease. According to the definition of viscosity, the viscosity of the grease affects the relative flow of the grease, so the viscosity is high and the speed is low.

c. Viscosity: the viscosity of the base oil of the grease.

For FAG rolling bearing grease, the viscosity of the base oil at 40°C is usually between 15 and 500 mm/s. If the viscosity of the grease base oil is higher than 1000mm2/s at 40°C, its oiling rate will be very low and the bearing cannot be sufficiently lubricated. If the calculated viscosity at 40°C is much higher than 1000mm2/s because of the low speed, it is best to use a grease with a viscosity of 1000mm2/s or less and good oiling characteristics, or use oil lubrication.

d. Consistency; degree of dilution (soft and hard).

In applications with vibration, the grease will be repeatedly crushed, because under the action of the vibration, the grease will be continuously thrown back into the bearing. In this case, using a thicker grease will definitely help. But hardness itself does not mean that it can provide sufficient lubrication. Therefore, grease with better mechanical stability should be used.