slewing bearingDiscussion on the cause of damage

Influence of 1. safety factor. At present, most manufacturers choose to calculate the slewing bearing according to the external load. According to the existing data, the contact stress of the slewing support of the small-tonnage crane is less than that of the large-tonnage crane, and the actual safety factor is higher. But the larger the crane tonnage. The lower the manufacturing precision,slewing bearing/The larger the diameter, the lower the safety factor, which is also the root cause of the large tonnage crane slewing ring/more easily damaged than the small tonnage crane slewing ring. At present, it is generally believed that the line contact stress of cranes above 40 t slewing bearing should not exceed 2.0±102 kN/cm. The safety factor shall not be less than 1.10.

Second, the influence of the stiffness of the turntable structure. The slewing bearing is an important part to transmit various loads between the turntable and the chassis. The rigidity itself is not large, mainly depends on the chassis and the structural rigidity of the turntable supporting it. In theory, the ideal structure of the turntable is a high-rigidity cylinder, so that the load on the turntable can be evenly distributed, but due to the height of the whole machine. This is impossible. The results of the finite element analysis of the turntable show that the base plate connected by the slewing bearing has a large deformation, resulting in a concentrated load acting on a few rollers. The deformation is more serious when the eccentric load is large, which increases the pressure of a single roller. In particular, the deformation of the turntable structure greatly reduces the contact length. It will change the contact conditions between the roller and the raceway, resulting in a substantial increase in contact stress. At present, the widely used calculation methods of static bearing capacity and contact stress are based on the premise that the effective contact length of the roller and the uniformity of the rotary bearing force are 80% of the roller length. Obviously, this is another reason why the slewing bearing is easily damaged. Because this premise does not conform to the actual situation.

Third, the effect of heat treatment state. The machining quality of the slewing bearing itself is greatly affected by the axial clearance, manufacturing accuracy and heat treatment state. The factor that is easily overlooked here is the influence of the heat treatment state. Obviously, in order to prevent cracks and depressions on the raceway surface, the raceway surface is required to have not only sufficient hardness, but also sufficient core hardness and hardened layer depth.

Countermeasures:(1) Through finite element analysis, appropriately increase the thickness of the connecting part of the turntable and the slewing bearing. Improve the structural rigidity of the turntable. (2) In the design of large-diameter slewing bearings, the number of rollers and the safety factor should be appropriately increased to improve the contact conditions between the rollers and the raceway. (3) Improve the manufacturing accuracy and heat treatment process of the slewing bearing. It can reduce the medium frequency quenching speed, strive for greater quenching depth and surface hardness, and prevent quenching cracks on the raceway surface.