Finite Element Analysis And Research On Design Defects Of Broken Tooth In Rotary Support Of Large Portal Crane

Portal cranes(hereinafter referred to as " portal crane ")are typical rotary cranes that are widely used in ports,shipyards and other places,and are mainly used to complete cargo handling,loading and unloading operations.The slewing bearing is a key structure that connects the swinging and non-rotating parts of the portal crane,and its importance is self-evident.After investigation and research,it was found that large portal crane slewing bearings of various ports in China had a common tooth breakage phenomenon before the design life,and the broken tooth rate was as high as 30%,resulting in failure of the slewing ring,and the maintenance cost and economic loss were huge.The main parameters of this type of portal crane are: 40~60t rated capacity,38~45m maximum amplitude,and 40 m or more lifting height.In this type of portal crane,the phenomenon of similarity failure occurs in large quantities,which can be excluded due to the factors of the bad working conditions of the equipment.The cause of failure should be found in terms of design,manufacture,and installation.Through the analysis of the design process,it was found that during the design of the portal crane,the load on the slewing bearing was converted into equivalent axial load and equivalent overturning moment,and the slewing bearing was selected based on the bearing capacity curve.This design does not calculate the relative displacement between the slewing ring gear teeth.This displacement will cause the axis of the gears to be non-parallel,affecting the meshing relationship between the gear teeth,and causing the large ring gear teeth to be broken.When installing a slewing drive mechanism,the manufacturing enterprise guarantees the meshing relationship between the pinion gear and the ring gear under the no-load condition,and under the load-carrying condition,the pinion gear generates a relative displacement,resulting in poor meshing between the gear teeth,which is also a cause of broken teeth.This article takes the MQ4038 type portal crane as the research object,analyzes and studies the reasons of the failure of the slewing bearing large ring gear.This type of door has a high cylinder structure and uses a three-row roller slewing ring.By establishing the finite element model of the turntable structure,slewing ring and cylindrical structure assembly,the relative displacement relationship between the pinion gear and the ring gear and the stress properties of the teeth of the ring gear are analyzed.Under the load-carrying conditions,the relative displacement of the pinion gear and the ring gear caused an angle between the axis of the two gears,causing pinching of the gear teeth at the meshing of the ring gear.Long-term compression would accelerate tooth fatigue and result in gear teeth fracture.Dynamic data acquisition instrument and resistance strain gauge were used to test and analyze the pinion and ring gear displacement and cylinder structure stress.The test results were consistent with the finite element analysis results.In order to reduce the relative displacement between gear teeth,two improvements are proposed.First,the finite element design exploration module is used to improve the stiffness of the cylinder structure.After the improvement,the good meshing relationship between the gear teeth is ensured;under load conditions,the displacement of the upper and lower end faces of the pinion gear tooth is compared with the standard clearance value,and the meshing relationship between the pinion gear and the ring gear is quantified to achieve the correct assembly of the pinion gear.The main research results of this paper are as follows:(1)After slewing bearing selection of large-scale door machine,it is proposed that the finite element modeling calculation of the relative displacement between the pinion gear and the ring gear should be carried out to determine the meshing relationship of the gears under the load-carrying conditions.(2)According to the finite element analysis of the results of relative displacement between gears,a design method for checking the stiffness of cylindrical structures is proposed to achieve good meshing of gear teeth.(3)When the slewing drive pinion is installed,it is proposed that the meshing relationship between the pinion and the ring gear should be determined quantitatively according to the displacement value under the load-carrying condition,and a reasonable installation is performed.