# Failure Analysis of Gantry Crane Slewing Bearing Based on Gear Position Accuracy Error
## 4 Discussion and Conclusions
### Conclusions  
Slewing bearing of large gantry cranes is one of the important components. The broken teeth failure of the slewing bearing's large gear rings is a common phenomenon in China's ports' large gantry cranes but also the development of the gantry cranes has been a problem for many years, which seriously reduces a port's production efficiency, causing huge economic losses. Therefore, it is important to analyze the causes of the universal broken teeth phenomenon of large gantry cranes. In this paper, the MQ4038-type gantry crane was used as the research object to analyze the causes of broken teeth. Through the analysis of the design process, it was found that after the selection of the slewing bearing, the relative displacement generated between the gear teeth during operation is usually not calculated. However, the relative displacement has an impact on the parallelism of the pinion and large gear ring axes, resulting in poor gear meshing and causing broken teeth. Figure 22: Gear axis non-parallel diagram. 1. Combined with the large gantry crane slewing bearing universal broken teeth failure, we analyzed the selection of the slewing bearing and slewing mechanism installation process problems. The bearing capacity and fatigue life of the slewing bearing and the gear force were checked, as was the installation quality of the slewing mechanism, and the results met the requirements. The analysis pointed out that when the gantry crane was designed and installed, the relative displacement between the teeth of the slewing bearing was not calculated during operation, which had a large impact on the meshing relationship between the pinion and the large gear ring. 2. In view of the problems in design and installation, a model of the gantry crane turntable structure, slewing bearing, and cylinder structure was established to analyze the relative displacement of the pinion and large gear ring and the stress of the large gear ring teeth after the assembly of these three parts. It was found that without the influence of adverse factors such as overload and impact, the pinion gear and the large gear ring still produced inconsistent displacement, leading to an angle of 0.48\({}^{\circ}\) between the two axes. Meanwhile, the stress in the upper tooth root upon the engagement of the large gear ring increased by 23%, which was five times the value of the lower tooth root stress. The result shows that the gear meshing situation is not ideal, and the upper part of the gear teeth of the large gear ring is subjected to abnormal extrusion and stress concentrations. That is an important reason behind the fatigue fracture of gear teeth. 3. In order to verify the poor meshing situation between the return gear teeth and the reasonableness of the finite element analysis results, this paper used a dynamic data acquisition instrument and a dynamic resistance strain gauge to analyze the approximate displacements of the pinion and large gear ring and the structural stress of the cylinder, respectively. The difference between the test results and the FEA results is small. The stress analysis results show that even if the design and installation process meet the requirements of use, the pinion and large gear ring will still produce inconsistent displacements, causing fatigue tooth breakage problems. Conceptualization, [PERSON], Y.W., W.L. and C.X. ; methodology, [PERSON], Y.W. and W.L. ; software, J.X., Y.W. and C.X; validation, [PERSON], Y.W., W.L. and C.X. ; formal analysis, [PERSON] and C.X. ; investigation, [PERSON] and Y.W. ; resources, [PERSON], Y.W., W.L. and C.X. ; data curation, J.X. and C.X; writing--original draft preparation, [PERSON], Y.W. and C.X; writing--review and editing, [PERSON], Y.W., W.L. and C.X. ; visualization, [PERSON] and W.L. ; supervision, [PERSON], Y.W., W.L. and C.X. ; project administration, [PERSON], Y.W., W.L. and C.X. ; funding acquisition, [PERSON], Y.W., W.L. and C.X. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable.