Application and failure countermeasures of bearings in multi-roll mills (4)
Lubrication of imported bearings: Due to the overall structure of the Sendzimir mill stand, the space between the rolls is limited, the installation space of the support bearing is very narrow, the heat dissipation Zhang Yan, etc.: The application and failure countermeasures of multi-roll mill bearings 35 is a big problem. question. Support bearings can be lubricated and cooled by means of roll fluid, or a separate lubrication system can be used. Emulsion is mostly used as lubricant (viscosity is about 1.1 n cc2/s at 40 o [u003d], because the backup roller bearing needs to be lubricated by atomized oil system; while emulsion has strong cooling capacity and low viscosity , If the surface quality of the rolled piece is high, it is necessary to use a relatively pure low-viscosity mineral oil (viscosity of about 8 ~ l2 nm2/s at 40 oC) as a lubricant. When the rolling speed is below 5 m/s, low-viscosity mineral oil can be used as a common lubricant for roll and backup roll 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 bearing fatigue life. Therefore, in practical applications, it can be compensated by increasing the pressure (up to 0.6), increasing the flow of rolling oil (up to 4000 L/min), and strengthening heat removal. At higher speeds and heavy loads, it is more effective to use a separate lubrication system for oil mist lubrication of the backup roller bearings, which can ensure the best service life of the backup bearings. The minimum viscosity of the lubricating oil is 150 nm2/s, and contains extreme pressure additives, and the oil mist is 0.0. O1 0.03 m3/s enters the groove of the mandrel of the backup roll. A condensing nozzle can be installed in the lubrication hole of the inner ring of the bearing to condense the oil from the compound to lubricate the backup roller and raceway, as shown in Figure 4. AA section oil washerFig. 4 Lubrication system of back-up roller bearing 4 Common failure modes and countermeasures of back-up bearings peeling that occurs under the action. In addition, if the accuracy of the bearing decreases, resulting in the unqualified rolled sheet, it means that the bearing fails; there are some more serious phenomena, such as severe peeling of the BARDEN bearing, bearing burns caused by poor lubrication and other factors that cause the outer ring of the bearing to break. Early fatigue failure The outer ring of the multi-roll mill back-up roller bearing elastically deforms under the 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 race Early fatigue spalling occurs. For a twenty-high Sendzimir mill, the rolling forces on both sides of the back-up bearings are particularly high, and they are more prone to fatigue spalling than other back-up 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 backup roller bearings: (1) Improve the cleanliness of bearing steel, reduce oxygen content, and use vacuum degassed steel. (2) The roller element line adopts a logarithmic curve profile, which can keep the best stress distribution on the contact surface, and the impact of wear on the edge profile is small; the roller element line arc slope trimming convexity will decrease with wear. (3) Improve the machining quality of the bearing surface to improve the lubrication condition. (4) Select the appropriate bearing clearance. Practical applications show that it is more beneficial to take a smaller clearance value. (5) The bearing is equipped with a seal, such as a cylindrical roller bearing with a rib, and the rib acts as a seal to prevent foreign matter from entering the bearing raceway. (6) Improve the design of the outer diameter of the backup roller bearing, so that the outer diameter has a certain convexity to prevent stress concentration on the edge of the outer ring surface, improve the contact state, and also improve the surface quality of the rolled piece.