Analysis of installation and maintenance of vertical roller mill grinding roller bearings

Analysis of installation and maintenance of vertical roller mill grinding roller bearings

The vertical roller mill has the advantages of high grinding efficiency, low power consumption and high automation. It has been widely used in cement production. The grinding roller is the main grinding component of the vertical roller mill. The roller shaft supports the roller body through the double row spherical roller bearing and the cylindrical bearing roller bearing. The shaft end is equipped with a grinding roller bracket, and the grinding roller rotates around the roller shaft during operation. The normal operation of the grinding roller is the premise to ensure the operation of the vertical roller mill, and the grinding roller bearing is an important part of the grinding roller work.

1 Roller bearing assembly clearance

The assembly level of the roller bearing is one of the important factors affecting its service life. The failure of the roller bearing due to improper assembly is numerous.

In the working state, the vertical temperature of the vertical roller mill is extremely high, while the outer ring of the grinding roller bearing is in a rotating state, and the inner ring is in a stationary state. When the bearing is in working condition, the inner ring temperature rises greatly during operation, and the thermal expansion is large, so that the bearing clearance is reduced. At the same time, due to the action of the load, elastic deformation occurs at the contact between the rolling element and the raceway, so that the bearing clearance is increased. Whether the bearing working clearance is larger or smaller than the installation clearance depends on the combined effect of these two factors. If the installation is unreasonable during assembly, the clearance is too tight or too loose will cause the bearing to fail.

If the roller bearing is too loosely assembled, the inner ring of the bearing will not be in close contact with the roller shaft, which will create a gap, which will cause relative movement between the bearing inner ring and the grinding roller shaft during operation, resulting in the bearing inner ring and the grinding roller shaft. Wear and, in severe cases, bite, resulting in premature bearing failure. Moreover, after the wear roller shaft is worn, it is easy to cause eccentricity, which makes the bearing replacement procedure more complicated. When the roller bearing is over-tightened, the installation clearance is too small, and an oil film cannot be formed between the inner wall of the bearing and the roller shaft, thereby increasing the friction coefficient between the two, resulting in a sharp rise in the operating temperature, which also causes the bearing to fail prematurely. Or scrapped. Another intuitive phenomenon caused by over-tightening is that it cannot be removed from the grinding roller shaft when the bearing is replaced next time. It can only be separated by cutting means, causing the bearing to be directly scrapped.

In order to avoid the economic loss caused by improper installation of the bearing, it is recommended to use the method of grinding the spacer on site. This method can ensure the accuracy of the installation clearance and achieve the ideal working clearance. In the specific operation process, it is necessary to measure the size of the shaft, the inner diameter of the bearing seat, and the relevant dimensions of the bearing in the field, so as to calculate the thickness of the spacer to be removed to achieve a good installation clearance. In addition, the installation should be carried out in strict accordance with the operating instructions, the assembly personnel's operating experience is also an important factor to ensure the quality of the installation.

2 lubrication effect of the roller bearing

UM56. 4 The vertical lubrication roller bearing lubrication method is oil pool lubrication. Because the grinding roller has a certain inclination angle under working condition, the grinding roller bearing can be immersed in the oil pool for good lubrication. However, in actual production, the temperature in the vertical roller mill is high, and the effects of medium and high pressure and heavy load are difficult to ensure the lubrication effect of the oil pool. The dust concentration in the vertical roller mill is extremely high, and its harsh production environment is undoubtedly worse for the lubrication effect of the bearing. A large number of examples show that most of the damage of bearings in the later stages of use is caused by improper lubrication. Therefore, choosing the right lubricant and adopting the correct lubrication method is essential for the service life of the roller bearing. In addition, regular replacement of the oil in the oil pool, routine maintenance and testing, is also an important condition to ensure its service life.

For the harsh working environment of the vertical roller mill bearing, our company selects the circulating oil lubrication system for the lubrication method of the UM56. 4 vertical roller mill in the grinding roller bearing (as shown in Figure 3). On the one hand, the use of the circulating oil circuit can take away a large amount of thermal energy generated during the working process of the bearing, and cool and cool the bearing; on the other hand, some impurities in the lubricating oil can be taken away during the circulation to purify the oil. The role.

The standard for oil change depends on the quality of the oil. Generally, the vertical roller mill should replace the bearing oil when it is running for 3 000 h. After replacing the new lubricant, it is required to check the quality of the oil every two months to see if there is any impurity and whether the oil is contaminated. The grinding roller oil level is checked once a month. When the oil level is too low, a new lubricating oil should be added in time.

3 sealing effect of the roller bearing

The sealing effect of the roller bearing also has a great influence on the service life of the bearing. The special working condition of the grinding roller bearing determines the high sealing requirement. When the sealing effect is reduced, the tiny particles will enter the bearing interior, which will reduce the lubrication performance. In severe cases, indentation will be formed on the raceway surface, causing pitting, The raceway surface peeling off, the cage disintegration and other serious consequences, which in turn caused the bearing to disintegrate quickly. Therefore, it is important to choose high-performance parts with good sealing results.

The measuring method of the roller bearing seal uses a pressure detecting method. When the bearing is installed, the bearing end cap is tightened, and the air pressure roller is used to perform the pressure test on the roller bearing chamber. The test pressure is generally selected to be 0.05 MPa. After the lapse of 0.5 h, the allowable pressure is reduced to 0. 025 MPa, meeting the above requirements, the bearing sealing effect is good.

The vertical roller mill grinding roller bearing has high temperature, dust and working environment in the working process. In order to ensure the effective service life of the roller bearing and prevent the damage caused by dust and high temperature, the accuracy of the bearing installation clearance should be ensured, the lubricating agent with high lubricating performance should be selected, and the replacement should be checked regularly to do the routine maintenance work. In addition, the high sealing of the bearings should be ensured to ensure the normal service life of the bearings.

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