For more than 30 years of reform and opening up, China’s economy has maintained rapid growth, the construction of a large number of railways, highways and other transportation facilities, as well as the large-scale urbanization process, the rapid development of the real estate industry, has promoted the long-term prosperity of China’s cement industry. According to statistics, since 1985, China’s cement output has been ranked first in the world, and it is the fastest developing country in the cement industry in the world. As a basic industry, cement industry plays an important role in national economic construction.
Vertical mill is the core equipment of modern cement production line grinding system, which has the advantages of low energy consumption, high grinding efficiency, strong drying ability, simple system flow and large production capacity. The roller is the key grinding part of vertical mill, and it is the core part. And the roller bearing is the key part of the roller, is the heart of the roller. Therefore, whether the roller bearing is correctly selected and correctly assembled will directly affect the operating performance of the vertical mill, affect the service life of the roller bearing, and even affect the production efficiency of the entire cement production line.
Timken’s bearings have been used in the cement industry for decades, and we have accumulated a wealth of application experience. Below we will affect the application performance of vertical grinding roller bearing several main aspects are elaborated in detail.
How to correctly optimize the bearing installation clearance
In the modern cement production line raw mill and cement mill roller, the mainstream design in the market is conical roller design.
In this design, most vertical mill manufacturers use a combination configuration of double-row tapered roller bearings (or two single-row tapered roller bearings mounted in pairs) and cylindrical roller bearings. Among them, the tapered roller bearing is used as the fixed end to withstand the axial working thrust and radial working pressure from the roller sleeve; As a floating end, cylindrical roller bearings only bear radial working pressure and do not bear any axial working thrust. When the roller is working normally, the axial working thrust often causes the force of two rows of double-row tapered roller bearings to be uneven. Because the indoor temperature of the vertical grinding chamber is very high, and the outer ring of the grinding roller bearing rotates during work, and the inner ring is stationary, therefore, the working temperature of the bearing outer ring is often higher than that of the inner ring, resulting in the thermal expansion of the outer ring is larger than the expansion of the inner ring, so the working clearance of the tapered roller bearing is often larger than the installation clearance, which aggravates the load unevenness of the double-row roller of the tapered bearing. Even the full axial load is borne by one row of rollers, and the other row of rollers does not bear any load.
In order to make the double row roller of tapered roller bearing bear a reasonable load when working, it is necessary to adjust its installation clearance correctly, and it is usually necessary to pre-tighten installation. The preload of the bearing should be appropriate, too much preload will produce too large starting torque and working torque, causing excessive temperature rise, leading to premature fatigue damage, and even bearing burns; The lack of preload will lead to the bearing working clearance is too large, the single row roller is loaded, and the position of the bearing roller that is not loaded is easy to distort and skew, and it will produce friction and collision with the bearing cage during rotation. This phenomenon is particularly obvious under the impact load, which is easy to cause damage to the cage and lead to bearing failure and shutdown. At the same time, under the action of impact load, the working clearance is too large, which may cause damage to the bearing seal.
On the other hand, in many roller applications, it is difficult to achieve better installation clearance through tapered roller bearings with preset clearance. The reason for this situation is that bearings, shafts and bearing housings have a certain range of machining errors. The existence of this manufacturing tolerance range leads to a large range of clearance reduction caused by bearing interference fit, that is, the possible installation clearance range is very wide, and it is even likely that the final installation clearance falls outside the ideal installation clearance range of the bearing.
How to improve bearing lubrication
Choosing the right amount of lubricant and taking the right lubrication method is crucial to the successful operation of any bearing, because bearing lubricants have three main functions: to separate contact surfaces and reduce friction; Heat dissipation; Prevent corrosion.
In the application of vertical grinding rolls, the application environment of high temperature, impact, heavy load and low speed makes it difficult to form a good lubrication condition of bearings, and the bad dust environment and impact aggravate the lubrication condition. The practical application results show that most of the roller bearing damage is the result of improper bearing lubrication. In view of the harsh application conditions of vertical grinding roller bearings, in the choice of lubrication system design, the use of circulating oil lubrication system is relatively effective, on the one hand, circulating oil can effectively take away most of the heat generated during bearing work and external thermal radiation, on the other hand, it can also take away the small impurities existing in the bearing by circulating oil, and purify the bearing working environment.
In the selection of lubricating oil model, it is necessary to select the appropriate viscosity of lubricating oil according to the working temperature of the roller and the size of the specific working load. When the bearing is working, the lubricating oil with higher viscosity can form a lubricating film thick enough to extend the application life of the bearing. For the above roller application case, we use three different viscosity lubricating oil (ISO VG 150, ISO VG 220, ISO VG320) for analysis, by comparing their analysis life, can illustrate the important impact of lubricating oil viscosity on the working life of the bearing. By using higher viscosity lubricating oil to improve the bearing life, the effect is still very obvious. In the application of large working loads, the use of relatively high viscosity lubricants is particularly important to improve bearing performance.
How do I select Sealing components
The seal also has a great influence on the working life of the grinding bearing. It must prevent the lubricant from leaking out of the bearing, and at the same time must prevent external pollutants from entering the bearing. In the fine particle working environment, a large number of small hard particles are easy to enter the interior of the vertical grinding roller bearing, deteriorate the working environment of the bearing, reduce the lubrication effect, and even form indentation on the raceway surface, causing pitting and even raceway surface spalling, reducing the working life of the bearing. Therefore, the selection of sealing parts with high accessibility is crucial to improve the working life of bearings.
In addition, the design of multiple seals and a certain pressure difference between the inside and outside the roller can effectively prevent external pollutants from entering the inside of the bearing.
Sum up
The above from the impact of several factors on the application performance of vertical grinding roller bearings are described. It is hoped that through such analysis, the majority of vertical mill designers and users can be helped to better choose and use bearings, reduce downtime, extend the service life of bearings, and improve production efficiency.
Post time: Nov-01-2024