Under normal circumstances, compressor parts cannot "peacefully coexist" with the bearing under high-speed and high-temperature conditions. Oil lubrication can only be used when grease lubrication is not 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 the viscosity directly affects the fluidity of the lubricating oil and the thickness of the oil film formed between the friction surfaces. The viscosity of the lubricating oil at the working temperature of the bearing is generally 12-15cst. The higher the speed, the lower the viscosity, the heavier the load, the higher the viscosity. Commonly used lubricants include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, and cylinder oil.
Oil lubrication methods include:
The temperature of the bearing can generally be inferred from the temperature of the outer surface of the bearing. It is more appropriate if the oil hole can be used to directly measure the temperature of the outer ring of the bearing. Generally, the temperature of the bearing slowly rises as it starts to run, 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 parts are proper, the bearing temperature will rise sharply and abnormally high temperature will occur. At this time, the operation must be stopped and necessary precautions must be taken.
Because the temperature is affected by lubrication, speed, load, and environment, the use of thermal sensors can monitor the working temperature of the bearing at any time, and automatically alarm the user or stop the combustion shaft accident when the temperature exceeds the specified value.
Lubrication has an important influence on the fatigue life and 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 the bearing is an effective measure to reduce bearing friction and wear. In addition, the lubrication of the bearing also has multiple functions such as heat dissipation, rust prevention, sealing, and impact mitigation.
The function of bearing lubrication can be briefly described as follows: 1. An oil film is formed between the two rolling surfaces or sliding surfaces that are in contact with each other to separate the two surfaces, reducing the friction and wear of the contact surfaces; 2. When using oil lubrication, especially When using circulating oil lubrication, oil mist lubrication and oil spray lubrication, the lubricating oil can take away most of the friction heat inside the bearing and play an effective heat dissipation effect; 3. When grease lubrication is used, it can prevent foreign objects such as external dust from entering Bearings play a sealing role; 4. Lubricants have the effect of preventing metal corrosion; 5. Extend the fatigue life of the bearing.
Bearing vibration is very sensitive to bearing damage. For example, peeling, indentation, rust, cracks, wear, etc. will be reflected in the bearing vibration measurement. Therefore, the vibration can be measured by using a special bearing vibration measuring device. The specific circumstances of the exception cannot be inferred. The measured value is different due to the use condition of the bearing or the installation position of the sensor, so it is necessary to analyze and compare the measured value of each machine in advance to determine the judgment standard.
The rolling sound of the bearing uses a sound meter to check the size and sound quality of the rolling sound of the bearing in operation. Even if the bearing is slightly damaged such as peeling, it will emit abnormal and irregular sounds, which can be distinguished by the sound meter.
a. Spray lubrication, dry compressed air is mixed with lubricating oil through a sprayer to form an oil mist. In the spray bearing, the airflow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the lubrication of high-speed and high-temperature bearing components.
b. Circulating oil lubrication uses an oil pump to deliver the filtered oil to the bearing parts, and the lubricating oil after passing through the bearing is filtered and cooled for use. Because circulating oil can take away a certain amount of heat and cool the bearing, this method is suitable for bearing parts with higher speeds.
c. Jet lubrication oil pump injects 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 a high speed, the rolling elements and the cage also make the surrounding air form an air flow at a relatively high rotation speed. It is difficult to send the lubricating oil to the bearing by the general lubrication method. At this time, the lubricating oil must be sprayed by high-pressure injection. In the bearing, the position of the nozzle should be placed between the inner ring and the center of the cage.
d. Oil bath lubricating oil bath lubrication is the most common lubrication method, suitable for the lubrication of low and medium speed bearings. Part of the bearing is immersed in the groove, and the lubricating oil is picked up by the rotating bearing parts and then flows back to the oil surface of the oil groove. It should be slightly lower than the center of the lowest rolling element.
e. Dripping oil lubrication Dripping oil lubrication is suitable for bearing parts that require a quantitative supply of lubricating oil. The amount of oil dripping is generally one drop every 3-8 seconds. Too much oil will cause the bearing temperature to increase.
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 use adjustment and the purpose of use. Grease is a lubricant composed of base oil, thickener and additives. When choosing, you should choose a grease that is very suitable for the bearing conditions. Due to 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 appropriate to fill 1/2-1/3 of the inner space of the bearing. Should be reduced to 1/3 at high speed. Too much grease increases the temperature.
When selecting grease according to working temperature, the main indicators should be dropping point, oxidation stability and low temperature performance. The dropping point can generally be used to evaluate high temperature performance. The actual working temperature of the bearing should be 10-20℃ lower than the dropping point. The use temperature of synthetic grease should be 20-30℃ lower than the dropping point. When selecting the grease according to the bearing load, the grease with a small penetration degree should be selected for heavy loads. In addition to low penetration when working under high pressure, it also has higher oil film strength and extreme pressure performance. When selecting grease based on environmental conditions, calcium-based grease is not easily soluble in water and is suitable for dry and low-water environments.