Lubrication has an important impact on the fatigue life, friction, wear, temperature rise, vibration, etc. of rolling bearings. Without normal lubrication, the bearing cannot work. Analysis of the causes of bearing damage shows that about 40% of bearing damage is related to poor lubrication. Therefore, good lubrication of bearings is an effective measure to reduce bearing friction and wear. In addition, bearing lubrication also has multiple functions such as heat dissipation, rust prevention, sealing, and impact mitigation. The function of bearing lubrication can be briefly explained as follows:

(1) A layer of oil film is formed between the two rolling surfaces or sliding surfaces that are in contact with each other to separate the two surfaces and reduce the friction and wear of the contact surfaces.

(2) When oil lubrication is used, especially when circulating oil lubrication, oil mist lubrication and oil spray lubrication are used, the lubricating oil can take away most of the frictional heat inside the bearing and play an effective role in heat dissipation.

(3) When grease lubrication is used, it can prevent foreign matter such as external dust from entering the bearing and play a sealing role.

(4) Lubricants have the effect of preventing metal corrosion.

(5) Extend the fatigue life of the bearing.

    Bearing lubrication methods are roughly divided into two types: grease lubrication and oil lubrication. In order to give full play to the function of the bearing, it is important to adopt a lubrication method according to the usage reduction and usage purpose.

(1) Grease lubrication

Grease is a lubricant composed of base oil, thickener and additives. When choosing, you should choose the lubricating oil that is very suitable for the service conditions of the bearing. Due to the different trademarks, there will be great differences in performance, so you must pay attention when choosing. Commonly used greases for bearings include calcium-based grease, sodium-based grease, calcium-sodium-based grease, lithium-based grease, aluminum-based grease, and molybdenum disulfide grease. The amount of grease filled in the bearing is suitable to fill 1/2-1/3 of the internal space of the bearing. It should be reduced to 1/3 at high speed. Too much grease raises the temperature.

When selecting grease according to the working temperature, the main indicators should be the dropping point, oxidation stability and low temperature performance. The dropping point can generally be used to evaluate the high temperature performance, and the actual working temperature of the bearing should be 10-20°C lower than the dropping point. The operating temperature of synthetic grease should be 20-30°C lower than the dropping point. When selecting grease according to the bearing load, grease with a small needle penetration should be selected for heavy loads. When working under high pressure, in addition to small penetration, it also needs to have high oil film strength and extreme pressure performance. When selecting grease according to environmental conditions, calcium-based grease is not easily soluble in water and is suitable for dry and less-moisture environments.

(2) Oil lubrication

Under the condition of high speed and high temperature, oil lubrication can be used when grease lubrication is no longer suitable. Through the circulation of lubricating oil, a lot of heat can be taken away.

Viscosity is an important characteristic of lubricating oil. The size of viscosity directly affects the fluidity of lubricating oil and the thickness of the oil film formed between friction surfaces. The viscosity of lubricating oil at the working temperature of the bearing is generally 12-15cst. The higher the rotation speed, the lower the viscosity should be selected, and the heavier the load should be, the higher viscosity should be selected. Commonly used lubricating oils include mechanical oil, high-speed mechanical oil, steam turbine oil, compressor oil, transformer oil, cylinder oil, etc.

Oil lubrication methods include:

①Oil bath lubrication

Oil bath lubrication is the most common lubrication method, suitable for low and medium speed bearings. Part of the bearing is immersed in the oil tank, and the lubricating oil is carried by the rotating bearing parts, and then flows back to the oil tank. The oil level should be slightly lower than the minimum rolling body center.

② Drip oil lubrication

Oil drop lubrication is suitable for bearing parts that require a quantitative supply of lubricating oil. The amount of oil drop is generally one drop every 3-8 seconds. Too much oil will cause the temperature of the bearing to increase.

③circulating oil lubrication

The filtered oil is delivered to the bearing parts by an oil pump, and the lubricating oil after passing through the bearing is filtered and cooled before use. Because the circulating oil can take away a certain amount of heat to cool down the bearing, this method is suitable for bearing components with high speed.

④Spray lubrication

Dry compressed air is mixed with lubricating oil through a sprayer to form oil mist, which is sprayed into the bearing. The air flow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the lubrication of high-speed, high-temperature bearing components.

⑤ Spray lubrication

Use an oil pump to inject high-pressure oil into the bearing through the nozzle, and the oil injected into the bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at high speed, the rolling elements and the cage also make the surrounding air flow at a relatively high rotation speed. It is difficult to send the lubricating oil to the bearing with the general lubrication method. At this time, the lubricating oil must be sprayed by high-pressure injection In the bearing, the location of the nozzle should be placed between the inner ring and the center of the cage.

    Under some special conditions of use, adding a small amount of solid lubricant to the grease, such as adding 3~5% of No. 1 molybdenum disulfide can reduce wear and improve the ability to resist pressure and heat. For high temperature, high pressure, high vacuum, corrosion resistance , anti-radiation, and extremely low temperature and other special conditions, adding solid lubricants to engineering plastics or powder metallurgy materials can be made into bearing parts with self-lubricating properties, such as bonding solid lubricants to raceways, On the cage and rolling elements, a lubricating film is formed, which has a certain effect on reducing friction and wear.

    (1) Grease replenishment interval

Due to mechanical action, aging and increased pollution, the lubricating base filled in the bearing arrangement will gradually lose its lubricating properties. Therefore, the lubrication rank needs to be continuously supplemented and updated. The interval for relubrication varies depending on the shape, size, and rotational speed of the bearing, and the approximate interval for relubrication depends on the operating time. In addition, when the bearing temperature exceeds 70°C, the replenishment interval of the grease should be reduced by half for every 15°C rise in the bearing temperature. Double-sided sealed bearings have been filled with grease during manufacture. "HRB" uses standard grease in these products. The total operating temperature range and other properties are suitable for the specified occasions, and the amount of grease filled is also corresponding to the size of the bearing. The service life of the grease generally exceeds the service life of the bearing, except for special occasions, there is no need to replenish the grease.

(2) Lubricating oil replacement cycle

The replacement cycle of lubricating oil is different depending on the conditions of use and the amount of oil. Generally, when the operating temperature is below 50°C and the environment with less dust is used, it should be replaced once a year. When the oil temperature reaches 100°C, it should be replaced every 3 Replace every month or less.

    Bearing vibration is very sensitive to bearing damage, such as peeling, indentation, rust, cracks, wear, etc., will be reflected in the bearing vibration measurement, so the vibration can be measured by using a special bearing vibration measuring device (frequency analyzer, etc.) The size of the abnormality cannot be inferred from the frequency. The measured value differs depending on the service conditions of the bearing or the installation position of the sensor, etc., so it is necessary to analyze and compare the measured value of each machine in advance to determine the judgment standard.

The temperature of the bearing can generally be inferred from the temperature outside the bearing chamber. It is more appropriate if the temperature of the outer ring of the bearing can be directly measured through the oil hole.

Usually, the temperature of the bearing starts to rise slowly with the operation of the bearing, and reaches a steady state after 1-2 hours. The normal temperature of the bearing varies with the heat capacity, heat dissipation, speed and load of the machine. If the lubrication and installation are not suitable, the temperature of the bearing will rise sharply and abnormally high temperature will appear. At this time, the operation must be stopped and necessary preventive measures must be taken.

The thermal sensor can be used to monitor the working temperature of the bearing at any time, and when the temperature exceeds the specified value, it can automatically alarm or stop to prevent the combustion shaft accident.

High temperature often indicates that the bearing has been in an abnormal condition. High temperatures are also detrimental to bearing lubricants. Sometimes bearing overheating can be attributed to the lubricant of the bearing. If the bearing is continuously rotated at a temperature exceeding 125°C for a long time, the life of the bearing will be reduced. Causes of high temperature bearings include: insufficient lubrication or excessive lubrication, lubricant. Contains impurities, excessive load, bearing damage, insufficient clearance, high friction caused by oil seal, etc.

Therefore, it is necessary to continuously monitor the bearing temperature, whether it is measuring the bearing itself or other important parts. If the operating conditions are constant, any temperature change may indicate that a malfunction has occurred.

Regular measurement of bearing temperature can be done with the help of thermometers, such as skf digital thermometer, which can accurately measure bearing temperature and display it in ℃ or Fahrenheit.

Important bearings mean that when they are damaged, the equipment will be shut down, so it is best to install a temperature detector on such bearings.