Problems related to greasing and heating of motor bearings
Case: A manufacturer in Northeast China overhauled a 200kW motor and supplied lubricating grease in the first and middle of January. The motor adopts double deep groove ball bearing structure. The lubricating grease originally used for rolling bearings was No. 2 grease of a large brand. At that time, about 15g of lubricating grease was added. After lubricating, the vibration of the motor bearing increases gradually, and the temperature of the motor bearing increases gradually. After nearly 2 hours, the temperature and vibration of the motor bearing still keep rising. Among them, the temperature of motor bearing rises from about 25 ℃ to about 39 ℃. After 3.0 hours of continuous operation, the temperature of motor bearing gradually decreased, and the vibration of motor bearing decreased significantly. The motor status gradually recovered. Check the historical fault records and find that similar problems have occurred in the past.
Case study: The whole accident was related to the lubrication supply at that time, so the key to the inspection was the lubrication supply.
First of all, the description of the accident did not mention the replacement of lubricating grease brand and manufacturer. In the process of grease replacement, if the grease is mixed, it may lead to the mutual reaction between the lubricating greases, thus seriously affecting the lubricating performance. Also, this kind of situation is not reversible without treatment. The problem will disappear automatically after several hours, so the problem of oil mixing can be largely eliminated. Second, the amount of grease added: the rolling bearing used by this motor is 15g grease added on site. Do not exceed the amount of grease supplied. Therefore, the consideration of adding too much grease is excluded. Third, grease adding method: check that the grease adding method is normal at that time. According to the problem of motor bearing vibration and temperature automatic recovery, pollution and other related problems can also be eliminated. At that time, the operation sequence was to take the grease, inject it into the greasing equipment, and complete the greasing. The whole process seems scientific and reasonable.
However, the time for motor lubrication is in the first and middle of January, and the motor is located in northern China. It is speculated that the same temperature treatment was not done before adding grease. It is confirmed that the lubricating grease has not been treated at the same temperature in advance, and it is directly replenished for lubrication. Also, this kind of addition method has been used for a long time. It is recommended to conduct appropriate isothermal treatment in advance for future supply lubrication. The same temperature treatment mentioned above means that the temperature difference between the new grease and the old grease must be reduced before the motor bearing is lubricated. The common practice is to put the grease that needs to be lubricated immediately in the room for a period of time before adding it. At this moment, the consistency of lubricating grease decreases with the rise of temperature and increases with the drop of temperature. The lubricating grease inside the motor bearing has the same temperature as the motor bearing. The grease standing in the environment is the same as the ambient temperature
The ambient temperature in winter in Northeast China is often low, so the oil consistency is high. After adding the cold grease into the hot grease, the consistency of the two is different, so the grease will be stirred during the operation of the rolling bearing, and the cold grease will be relatively caked and cannot be mixed. As a result, the rolling bearing temperature rises and the vibration increases. However, as the running time increases, the lubricating grease is completed at the same temperature. If the surface of bearing raceway and rolling body is not damaged at this time, the fault phenomenon will be eliminated by itself.