The equipment is inspected regularly, the operation check and the bearings that have been removed during the replacement of the peripheral parts are inspected to determine whether it can be reused or used. Carefully investigate and record the removed bearings and appearance. In order to clarify and investigate the remaining amount of lubricant, the bearings should be cleaned well after sampling. Next, check the condition of the raceway surface, the rolling surface and the mating surface, and the wear state of the cage, etc., for damage and abnormality.
To determine whether the bearing can be used again, it is necessary to consider the degree of bearing damage, mechanical properties, importance, operating conditions, inspection cycle, etc. If the bearing is found to be damaged or abnormal, find out the cause and make a countermeasure. In addition, the inspection results, if there are the following defects, the bearing can no longer be used, need to replace the new bearing.
a. Cracks and fragments appear in any of the inner and outer rings, rolling elements, and cages.
b. Any one of the inner and outer rings and the rolling elements are peeled off.
c. The raceway surface, ribs, and rolling elements are significantly khocked.
d. The cage is worn out or the rivets are loose.
e. The raceway surface, rolling elements are rusted and flawed.
f. There are significant indentations and marks on the rolling surface and rolling elements.
g. Creep on the inner diameter of the inner ring or the outer diameter of the outer ring.
h. Superheated and discolored.
i. Grease seal bearing seals and dust caps are severely damaged.
(1), in-service inspection and troubleshooting
The inspection items in operation include the rolling sound, vibration, temperature, and lubrication status of the bearing. The details are as follows:
First, the 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.
Second, the vibration of the bearing
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 frequency can not be inferred from the specific circumstances of the abnormality. The measured value differs depending on the conditions of use of the bearing or the position at which the sensor is mounted. Therefore, it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard.
Third, the temperature of the bearing
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.
Fourth, lubrication
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 mitigation of impact. The effect 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.
2. Comparison of grease lubrication and oil lubrication
Lubrication methods for bearings are broadly classified into 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 purpose of use reduction and use.
3, grease lubrication
Grease is a lubricant composed of a base oil, a thickener and an additive. When choosing, you should choose a grease that is very suitable for the conditions of use of the bearing. Because of 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 raises the temperature.
4, the choice of grease
When selecting the 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. 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 a 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.
Five, 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, and cylinder oil.
Oil lubrication methods include:
a. Oil bath lubrication
Oil bath lubrication is the most common lubrication method. It is suitable for the lubrication of low and medium speed bearings. Part of the bearing is immersed in the groove. The lubricating oil is taken up by the rotating bearing parts and then flows back to the oil groove. The oil level should be slightly lower than the minimum. The center of the rolling element.
b. drip 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 filtered oil is delivered to the bearing components by an oil pump, filtered through the lubricating oil after the bearings, and then cooled and used. Since the circulating oil can take a certain amount of heat to cool the bearing, this method is suitable for bearing parts with a 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 injection bearing, the air flow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for lubrication of high speed and 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 a high speed, the rolling elements and the cage also form a gas flow at a relatively high rotational speed, and it is difficult to send the lubricating oil to the bearing by a general lubrication method. At this time, the lubricating oil must be sprayed by a 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.