Application and failure countermeasures of bearings in multi-roll mills (5)
Burns caused by poor lubrication Use roll fluid as NSK bearing lubricant, which has fast heat dissipation capacity, but its low viscosity affects the fatigue life of bearings. For cylindrical roller bearings with ribs or double row tapered roller bearings that can withstand axial force, the friction between the roller end face and the inner ring ribs is large, and it is easy to cause burns in the case of poor lubrication. In addition, for cylindrical roller bearings without ribs, a bronze or plastic flat washer is installed on the saddle of the rolling mill to bear the axial force, and the outer ring of the bearing is pressed against the flat washer, which has high friction and unsatisfactory lubrication. Hot cracks are prone to occur on the end face. Under unfavorable rolling mill lubrication conditions, the design and application of the bearing should try to improve the lubrication state of the bearing. The lubrication system and the type of lubricant must be selected efficiently. For example, tapered roller bearings must be lubricated with a separate oil mist lubrication system; when lubricating cylindrical roller bearings with low-viscosity mineral oil, the flow of lubricant must be increased, and appropriate cooling facilities should be used in the lubrication system to increase the oil flow rate. viscosity, higher flow rates are required under heavy loads or high rolling speeds. Two detachable retaining rings can be used for the inner ring to form a gap seal with the outer ring raceway to prevent external dirt from entering the bearing and causing pollution. The cleanliness of the oil also has a decisive influence on the service life of the EZO bearing, so the circulation and filtration of the oil is a very important issue in the lubrication system. When the bearing adopts a separate lubrication system, it is necessary to prevent the external debris emulsion from entering the bearing and causing pollution, which affects the service life of the bearing. The outer ring breaks during operation due to poor lubrication and cooling. The surface of the outer diameter of the bearing is burned, and a crack source appears, which leads to cracking or because the bearing bears too much axial force, the end face of the bearing rubs against the adjacent washer during operation, resulting in cracks in the outer ring and fracture of the outer ring. The outer ring of the support bearing must ensure sufficient strength, and the wall thickness of the outer ring must be increased as much as possible, but at the same time, the rated load of the bearing must be guaranteed. From the design point of view of the bearing. Under the condition of low speed and heavy load, the full complement roller structure is adopted to make the center distance between the rollers as small as possible to reduce the bending moment. In terms of material selection, the actual application shows that it is best to use carburized steel in heavy-duty work, with a thick carburized layer on the outer diameter, high surface hardness, good core toughness, and high tensile strength; or The ring and outer ring are hardened by bainite to ensure better fracture resistance of the bearing ring. Improper adjustment and maintenance of the roll system The multi-roll mill has a large rolling load and high rotational speed. During the rolling process, the outer ring of the bearing, which is used as a backup roll, is worn, resulting in concavity in the axis of the work roll, and the rolled sheet will be defective. This needs to be compensated by adjusting the mandrel of the backup roll and increasing the deflection. The bearing that becomes the convex part is subject to the largest force and is easily overloaded, resulting in increased internal wear of the bearing. Therefore, the adjustment amount should be controlled as small as possible, and the roll shape should be well trimmed. The bearing of the backup roller is different due to the different installation locations and tolerances. It will inevitably cause uneven force. After a period of use, the bearings should be replaced, and the bearings on the heavy-load spindle should be regularly moved to the lighter-load spindle to make full use of them and prolong the bearing life. On the same mandrel, the supporting DODGE bearing in the middle of the roll bears a larger load than the supporting bearing at the end of the roll, and the wear of the middle bearing is larger than that of other bearings, and the position of the bearing on the same mandrel should also be regularly exchanged. As a non-rotating ring, the inner ring bears a fixed load. In order to prolong the service life, the position of the load zone should be changed regularly. After rolling the thin steel strip for a period of time, if the outer diameter surface of the backup roller bearing is damaged, including indentation, wear and surface peeling, it is necessary to change the roller and regrind the removed bearing. After regrinding the outer diameter. It is necessary to re-measure, mark the point with the largest thickness, and then assemble with the corresponding roller and inner ring, and regroup according to the new section thickness. The appropriate interval for exchanging bearings, turning the inner ring, and regrinding the outer diameter of the outer ring depends on the operating conditions. Conclusion Due to the low service life of the multi-roll mill back-up roller bearings, the bearing design must take measures to improve the bearing capacity of the bearing to achieve a higher service life; at the same time, avoid installation errors, poor lubrication and cooling, impurities and other factors The reasonable adjustment of the roller system also plays a great role in extending the service life of the bearing.