| dc.description.abstract | Slewing bearings are mostly the bearings with a diameter more than one meter. Because of their ability to bear high loads under low speeds, they are often combined with gears to serve as a driving mechanism. Among them, the four-point contact bearing can bear axial force, radial force and tilting moment at the same time, and can transmit a small starting torque due to ball design. Most of them are used in rotation mechanisms such as wind turbines, excavators, crane turrets or military turrets, etc.
One of the most easily damaged parts of the slewing bearing is the rolling element, so most of the research focus on the acting force of rollers or balls. However, in order to reduce the weight of large slewing gear bearings, the wall thickness of the bearing ring is often reduced. Although the weight can be reduced, it also increases the risk of damage to the ring structure. Therefore, this paper analyzes the impact of the bearing loads on the wall thickness under static and dynamic loads. On the other hand, in addition to the general working loads, the pre-load of the screws will also affect the deformation of the bearing, which is considered in the analysis.
The objective of this paper is to analyze the slewing gear bearing of a vehicle with a turret. The structure is composed of an inner ring, an outer ring, 178balls, a turret and a vehicle body. 36 screws are used for connection between the bearing ring and the turret and the vehicle respectively.
In the static load analysis, MSC.Marc is used to analyze the structural strength of the bearing. In the element modeling, the ball is replaced by a spring element, the stiffness curve is calculated by KISSsoft according to ISO/TS16281. The screw is replaced by a beam element. This modeling can greatly reduce the analysis time without affecting the analysis results for the bearing structure. In general, either the load contact analysis model or the Finite Element Method_(FEM) is based on the static load analysis. However, the effect of the dynamic load on the slewing bearing cannot be ignored. Therefore, in addition to the static load analysis, MSC.CoSim combined with MSC.Adams_(dynamic analysis) and MSC.Marc_(FEM) to simulate the dynamic force on the balls and the bearing structure in accordance with the real situation.
Slewing bearing under dynamic loading is divided into two types of conditions: impact loading on the bearing in the case of flat and sloping field, and transport vibrations in the case of flat field. MSC.CoSim is used to analyze the slewing bearing under these conditions to confirm whether the ball load can be within the safe range, the structural strength of the bearing ring can bear dynamic impact, and the load variation of the bolts in locked state.
On the other hand, the interface plate connected with the slewing bearing has a certain degree of flatness error. The bearing ring will be deformed when the screws locked. Therefore, it must be able to ensure that the rings, balls and raceways of the bearing under the worst tolerance condition, can meet the strength requirements, and the deformation of the raceway will not cause uneven running of the bearing.
In the static analysis results, the bearing preload of the screws will cause the deformation of bearing ring and also more load on the balls which are close to the screws. When the bearing is under working loads, the radial force and the eccentric weight cause the shared load of the individual ball increase from ball 1 to ball 89. The thin-wall stress and screw load are greatly affected by the screw preload, less by the working loads. The bearing clearance will lead to a smaller distribution interval. When the flatness of the interface plate is the maximum value of the specification, 0.4 mm, the maximum bearing load is about 5400 N, which is within a safety range. In this case, the starting torque is increased to 900 N-m, the value is about twice to the normal interface.
In terms of dynamic analysis results of the bearing under the impact load, the shared load of the individual ball increases from the 1st ball to the 89th ball, because the impact direction is toward the 1st roller and the center of gravity of the bearing is near to the 89th roller. The time point of the maximum ball load value will be consistent with the time point of the maximum value of the impact in case of flat field. And in case of the slope condition, the maximum ball load value occurs after the time point of the maximum impact value, due to an increased load caused by the tilting moment after the impact. The bearing loads due to transportation vibration are more evenly distributed on the balls with the contact pair I than contact pair II, because the tilting moment will make the maximum value at the 89th ball. The maximum ball load occurring at the time point will be the same as the time point for the maximum vibration amplitude. From the point of view of the stress value corresponding to the load. The condition will not cause the balls and bearing ring walls damage. The effect of the screws on the bearing can also be seen from the results, the bearing will be deformed mainly due to the screws preload. As consequence the stress on the balls and the thin wall of the bearing rings near the screws is enlarged. | en_US |