Vertical mill is the core equipment of the modern cement production line grinding system. It has the advantages of low energy consumption, high grinding efficiency, strong drying ability, simple system flow and large production capacity. Among them, the grinding roller is the essential part of the vertical grinding, which is the core part; and the grinding roller bearing is the key part of the grinding roller, which is the heart of the grinding roller. Therefore, whether the grinding roller bearing is correctly selected and correctly assembled will directly affect the running performance of the vertical grinding mill, affect the service life of the grinding roller bearing, and even affect the production efficiency of the entire cement production line.
Bearings manufactured by Timken have decades of application history in the cement industry.
At the same time, we have accumulated a wealth of application experience. Below we will elaborate on several major aspects that affect the application performance of vertical grinding roller bearings.
1. How to properly optimize the bearing installation clearance
In the raw material grinding and cement grinding grinding rolls of modern cement production lines, the current mainstream design on the market is the tapered roller design. In this design, most vertical mill manufacturers use a combination of double row tapered roller bearings (or two single row tapered roller bearings installed in pairs) and cylindrical roller bearings. Among them, the tapered roller bearing acts as a fixed end and receives the axial working thrust and radial working pressure from the roller sleeve; the cylindrical roller bearing acts as a floating end and only bears the radial working pressure and does not bear any axial working thrust. When the grinding roller is working normally, the axial working thrust tends to make the two rows of rollers of the double row tapered roller bearing have uneven force. Because the indoor temperature of the vertical grinding chamber is very high, and the outer ring of the grinding roller bearing rotates during operation, the inner ring is stationary. Therefore, the working temperature of the outer ring of the bearing tends to be higher than the inner ring temperature of the bearing, resulting in the amount of thermal expansion of the outer ring being larger than that of the inner ring. Large, so the working clearance of the tapered roller bearing is often larger than the installation clearance, which exacerbates the load non-uniformity of the double-row roller of the tapered bearing, and even the entire axial load is received by one row of rollers, and the other column is rolled. The child does not bear any load.
In order to make the double row roller of the tapered roller bearing bear a reasonable load during operation, it is necessary to adjust the installation clearance correctly, and it is usually necessary to pre-tighten the installation. The pre-tightening amount of the bearing should be suitable. If the pre-tightening amount is too large, excessive starting torque and working torque will be generated, causing excessive temperature rise, resulting in premature fatigue damage and even bearing burn; and insufficient pre-tightening will result in The working clearance of the bearing is too large, and the single row of rollers is loaded. The position of the bearing roller that is not loaded is easy to be skewed and skewed. During the rotation process, friction and collision will occur with the bearing cage. Under the impact load, this phenomenon Especially obvious, it is easy to cause damage to the cage and cause bearing failure to stop. At the same time, under the action of the impact load, the excessive working clearance will also cause the roller sleeve to move back and forth in a large amount, which may cause damage to the bearing seal.
On the other hand, in many roll applications, it is difficult to achieve better installation clearance by pre-set tapered roller bearings. The reason for this is that the bearings, shafts and housings have a certain range of machining tolerances. The existence of such a manufacturing tolerance range results in a large range of clearance reduction due to bearing interference fit, which means that the range of possible installation clearances is very wide, and it is even possible that the final installation clearance falls on the bearing. The ideal installation clearance range.
To illustrate the problem, let's take a practical example. In a certain type of vertical mill, two single-row tapered roller bearings are used for face-to-face installation. Due to the cooperation of the shaft and the inner hole of the bearing, the influence of the tight fit of the bearing housing and the outer diameter of the bearing, if a predetermined spacer is used, the axial clearance reduction due to the tight fit will cause axial clearance of the bearing after installation. The difference between the upper and lower limits of the range is 0.3 mm.
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