Bearing operation check and fault handling
The inspection items in operation include the rolling sound, vibration, temperature, and lubrication status of the bearing. The details are as follows:
1.Rolling sound of the bearing
The sounder is used to check the size and sound quality of the rolling sound of the running bearing. Even if the bearing is slightly peeled off, abnormal sounds and irregular sounds are emitted, which can be distinguished by the sounder.
2. Bearing vibration
Bearing vibration is very sensitive to bearing damage. For example, peeling, indentation, rust, crack, wear, etc. are reflected in the bearing vibration measurement. Therefore, vibration can be measured by using a special bearing vibration measuring device (frequency analyzer, etc.). The size of the abnormality can be inferred by frequency analysis. The measured values vary depending on the conditions of use of the bearing or the mounting position of the sensor. Therefore, it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard.
3. Bearing temperature
The temperature of the bearing is generally estimated by the temperature outside the bearing. If the oil hole can directly measure the temperature of the bearing outer ring, it is more suitable. Usually, the temperature of the bearing rises slowly as the operation starts, 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 suitable, the bearing temperature will rise sharply and abnormal temperature will occur. At this time, it is necessary to stop the operation and take necessary precautions.
4.1 The role of bearing lubrication
Lubrication has an important influence on the fatigue life of rolling bearings and friction, wear, temperature rise, vibration, etc. Without normal lubrication, the bearings cannot work. Analysis of the cause of bearing damage indicates that about 40% of bearing damage is associated with poor lubrication. Therefore, good lubrication of the bearings is an effective measure to reduce bearing friction and wear. In addition, the lubrication of the bearing also has various functions such as heat dissipation, rust prevention, sealing, and shock mitigation. The role of bearing lubrication can be briefly explained as follows:
a. Forming an oil film between the two rolling surfaces or sliding surfaces that contact each other to separate the two surfaces, reducing friction and wear on the contact surface.
b. When using oil lubrication, especially when using circulating oil lubrication, oil mist lubrication and fuel injection lubrication, the lubricating oil can take away most of the friction heat inside the bearing and effectively dissipate heat.
c. When grease lubrication is used, foreign matter such as dust can be prevented from entering the bearing and sealing.
d. Lubricants have the effect of preventing metal corrosion.
e. Extend the fatigue life of the bearing.
4.2 Comparison of grease lubrication and oil lubrication
The lubrication method of the bearing is 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 use a lubrication method depending on the conditions of use and the purpose of use.
4.3 Grease lubrication: Grease is a lubricant composed of base oil, thickener and additives. When selecting, you should choose a grease that is very suitable for the conditions of use 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 greases, sodium-based greases, calcium-sodium-based greases, lithium-based greases, aluminum-based greases, and molybdenum disulfide greases. The amount of grease filled in the bearing is preferably 1/2-1/3 of the internal space of the bearing. It should be reduced to 1/3 at high speed. Excessive grease causes the temperature to rise.
4.4 Selection of grease: 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 lower than the dropping point of 10-20 °C. . Synthetic grease should be used at a temperature below the drop point of 20-30 °C. When selecting the grease according to the bearing load, the grease with a small penetration should be selected for the heavy load. When working under high pressure, in addition to the small penetration, it also has higher 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 drying and low moisture environments.
4.5 Oil lubrication: Under high-speed and high-temperature conditions, oil lubrication can be used when grease lubrication is not suitable. A large amount of heat can be taken away by the circulation of the lubricating oil. Viscosity is an important characteristic of lubricating oil. 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 12-15 cst. The higher the speed, the lower the viscosity, and the heavier the load, the higher the viscosity. Commonly used lubricating oils include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, cylinder oil, and the like.
Oil lubrication methods include:
a. Oil bath lubrication: Oil bath lubrication is the most common lubrication method, suitable for lubrication of low and medium speed bearings. Part of the bearing is immersed in the oil groove. The lubricating oil is taken up by the rotating bearing parts and then flows back to the oil tank. The surface should be slightly below the center of the lowest rolling element.
b. Drip oil lubrication: Drip oil lubrication is suitable for bearing parts that need to supply lubricating oil quantitatively. The amount of oil dripping is generally one drop every 3-8 seconds. Excessive oil quantity will cause the bearing temperature to increase.
c. Circulating oil lubrication: The oil pump is used to transport the filtered oil to the bearing components, and the lubricating oil after passing through the bearings is filtered and cooled for use. Since the circulating oil can take a certain amount of heat to cool the bearing, this method is suitable for bearing parts with higher rotational speed.
d. Spray lubrication: The dry compressed air is mixed with the lubricating oil through a sprayer to form an oil mist. In the jet 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.
e. Injection lubrication: The high-pressure oil is injected into the bearing through the nozzle by the oil pump, 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 form a gas flow at the relatively high rotation speed of the surrounding air. 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 the high-pressure injection method. In the bearing, the position of the nozzle should be placed between the inner ring and the center of the cage.