# Failure Analysis of Gantry Crane Slewing Bearing Based on Gear Position Accuracy Error
## 1 Introduction  
With the continuous advancement of global integration and the rapid development of international trade, port transportation has increased dramatically. In large ports, shipyards, and other places of handling operations, gantry cranes are widely used. Large bearing gantries are particularly common due to their advantages of fewer components, novel structure, and a small tail diameter of the rotary part. At present, as the main power component of large portal cranes' slewing bearing, its large gear ring gear has a high probability of teeth breaking as a consequence of tooth root crack, which seriously affects the service life of portal cranes and reduces port transportation efficiency. Therefore, analyzing the causes of broken teeth of gantry crane slewing ring gears is important. The rotary movement of gantry cranes mainly relies on the rotary mechanism. The mechanism contains two parts: The slewing drive and the slewing support device. The driving force of the gantry crane's slewing action is mainly provided by the slewing drive [1,2]. The slewing support device is used to connect the slewing and non-slewing parts of the gantry crane, providing support and restraint to ensure the neutrality of the two parts [3, 4, 5, 6]. The slewing support device is used to connect the slewing and non-slewing parts of the gantry crane, providing support and restraint to ensure the alignment of the two parts. In this study, through the research on gantry cranes in Caofeidian, Lianyungang, Rizhao, and other large Chinese ports, it is found that the gantry crane's slewing ring gearteeth generally have tooth root cracks and broken teeth, and the average rate of broken teeth of each port gantry crane's slewing bearing is more than 30%. Regarding the broken teeth of the slewing bearing, [PERSON] [7] established a gear tooth calculation model for the slewing mechanism when braking and stopping. The dynamic response characteristics of gears were analyzed according to different slewing speeds. It follows that tooth surface pitting and tooth breakage are basically caused by large impacts. [PERSON] [8] analyzed the causes of the broken slewing gear of a port gate machine and pointed out that the load condition of the slewing gear and driving pinion are influenced by the side clearance of gear teeth. The corresponding broken gear repair plan was put forward as a consequence. [PERSON] [9] analyzed the factors that caused the broken gears of gantry cranes' slewing bearing such as tooth side clearance, gear tooth lubrication, and crane operation normality. [PERSON] and [PERSON] [10] focused on the GQI-5 crane that has been in overload operation for a long time. The two gear teeth of its slewing bearing were determined to have broken from the root of the teeth, and a repair process combining welding and implantation of gear teeth was proposed. Existing research on the broken teeth of gantry cranes' slewing ring mainly focuses on impact, crane operation specifications, and other factors that lead to breaking. There is no research on the position accuracy error of the large gear ring and pinion of gantry cranes after lifting. However, this position accuracy error, which further leads to tooth breakage, will have a significant influence on the analysis of slewing ring dynamics. In this paper, a new fault analysis method based on the gear position accuracy error is proposed. Firstly, through the finite element analysis method, the displacement and force nature of the pinion and the large gear ring before and after the assembly of the slewing bearing model and slewing structure are studied, and the cause of a large gear ring broken tooth fault is initially proposed. Secondly, the dynamic data acquisition instrument is used to conduct displacement tests on the driving pinion and the large gear ring of the slewing bearing, and the test results are compared with the finite element calculation results to verify the reasonableness of the results.