Application and failure countermeasures of bearings for multi-roll mills (4)
Lubrication of imported bearings: Due to the integral structure of the Sendzimir mill stand, the space between the rollers is limited, the installation space of the supporting bearing is very narrow, and the heat dissipation Zhang Yan, etc.: Application of multi-roll mill bearings and failure countermeasures 35 is a very Big problem. The support bearing can be lubricated and cooled by means of roll fluid, or a separate lubrication system can be adopted. Lubricants are mostly emulsions (40 o [u003d viscosity about 1.1 n萐2/s), because the back-up roller bearings need to be lubricated with an atomized oil system; and emulsions have strong cooling capacity and low viscosity If the surface quality requirements of the rolled parts are high, it is necessary to use relatively pure low-viscosity mineral oil (viscosity at 40 oC about 8 ~ l2 nm2/s) as a lubricant. When the rolling speed is less than 5 m/s, low-viscosity mineral oil can be used as a common lubricant for roller and backup roller bearings, but the lubrication of GMN rolling bearings generally requires medium-viscosity oil, and the use of low-viscosity mineral oil will inevitably affect the fatigue life of the bearing. Therefore, in practical applications, the pressure can be increased (up to 0.6), the flow of rolling oil (up to 4000 L/min) can be increased, and the heat removal method can be used to compensate. At higher speeds and heavy loads, it is more effective to use a separate lubrication system for oil mist lubrication of the back-up roller bearings, which can ensure the best service life of the back-up bearings. The minimum viscosity of lubricating oil is 150 nm2/s, and it contains extreme pressure additives. O1 0.03 m3/s enters the groove of the support roller mandrel. A condensing nozzle can be installed in the lubrication hole of the bearing inner ring to condense the oil from the compound to lubricate the backup roller and raceway, as shown in Figure 4. AA section of oil washer Figure 4 Lubrication system of back-up roll bearings 4 Common failure modes and countermeasures of back-up bearings Peeling occurred under the action. In addition, if the accuracy of the bearing decreases and the rolled sheet is unqualified, it means that the bearing fails; there are some more serious phenomena, such as severe spalling of the BARDEN bearing, poor lubrication and other factors that cause the bearing's outer ring to fracture. Early fatigue failure of multi-roll mill back-up roll bearings undergoes elastic deformation of the outer ring under load, and the load distribution of the raceway changes. The maximum load is much higher than that of ordinary bearings. In addition, the rolling force of the multi-roll mill is very large, resulting in the raceway. Early fatigue peeling occurs. For the 20-high Sendzimir mill, the supporting bearings on both sides receive a particularly large rolling force, and are more prone to fatigue spalling than other supporting bearings. In addition, if there are installation errors, poor lubrication, insufficient cooling, and impurities entering the inside of the bearing, early fatigue failure may occur. Measures to effectively improve the service life of the backup roller bearing: (1) Improve the cleanliness of the bearing steel, reduce the oxygen content, and use vacuum degassed steel. (2) The roller element line adopts a logarithmic curve profile, which can maintain the best stress distribution on the contact surface, and the influence of wear on the edge profile is small; the roller element line arc slope trimming convexity will decrease with wear. (3) Improve the processing quality of the bearing surface to improve the lubrication condition. (4) Select the appropriate bearing clearance. Practical application shows that it is more advantageous to take a smaller clearance value. (5) The bearing is equipped with seals, such as cylindrical roller bearings with ribs, and the ribs act as seals to prevent foreign matter from entering the bearing raceway. (6) Improve the design of the outer diameter of the back-up roller bearing, so that the outer diameter has a certain degree of convexity to prevent stress concentration on the outer ring surface edge, improve the contact state, and also improve the surface quality of the rolled parts.