# Failure Analysis of Gantry Crane Slewing Bearing Based on Gear Position Accuracy Error
## 2 Slewing Bearing Mechanical Analysis and Test
### Gear Meshing Characteristics after Assembly
#### 2.3.2 Definition of Contact Parameters and Boundary Conditions  
According to the actual operation of the MQ4038 gantry crane, the contact part is first defined. The contact form still chooses \"surface-face\" contact, and the pinion and the large ring gear contact mode are set the same as before. Considering the roller contact, because the roller is convex, the contact surface selects three rows of roller surfaces, the target surface selects each roller seat surface, the setting of the contact parameters is basically the same as 2.2, and the rest of the components are set to the bound contact form and finally complete the definition of the contact pair. The axial load \(\mathrm{F_{a}}\), the radial load \(\mathrm{F_{r}}\), and the overturning moment \(\mathrm{M}\) of the slewing bearing are calculated when the rated load (40 t) of the test gantry crane is lifted and located at the maximum amplitude (38 m). 1. Axial load calculation  
Considering the additional dynamic load under inertia when the gantry crane lifts the rated load of 40 t, the dynamic load during lifting \(Q_{m}\) is taken. The dynamic load is analyzed by the product of the dynamic load coefficient \(\varphi_{2}\) and the lifting load \(Q\):  
\[Q_{m}=\varphi_{2}\cdot Q \tag{1}\]  
\[\varphi_{2}=\varphi 2_{min} \tag{2}\]  
where \(\varphi_{2 min}\) is the minimum value of the hoisting dynamic load factor, \(\beta_{2}\) is the factor set by the hoisting status level, and \(v\) is the steady hoisting speed (m/s). The values of the coefficients \(\varphi_{2 min}\) and \(\varphi_{2 min}\) are shown in Table 1 and are divided into four levels. Figure 8: Assembly body meshing results. The whole level of the gantry crane is A7, which belongs to the more frequent heavy load use type considering that its lifting state level is HC4. \(v\) takes the lifting mechanism speed at a rated load of 35 m/min, so according to Formulas (1) and (2), the lifting load \(Q_{m}\) can be obtained:  
\[Q_{m}=55.2\ \text{t} \tag{3}\]  
Since the gantry crane slewing structure self-weight \(F_{G}=321.94\ \text{t}\) (refer to MQ4038 type swing part self-weight load), the magnitude of the axial load on the slewing bearing can be obtained:  
\[F_{a}=Q_{m}+F_{G}=3.70\ \times\ 10^{6}\ \text{N} \tag{4}\]  
2. Radial Load Calculation  
In the calculation of the radial load of the slewing bearing, the main consideration is the horizontal load generated by wind-induced cargo deflection, through the lifting weight and cargo deflection angle \(\alpha\) calculated according to Formula (5). \[T=Q\cdot\tan\alpha \tag{5}\]  
where \(T\) is the horizontal load from cargo deflection, \(Q\) is the lifting load, and \(\alpha\) is the deflection angle. Since the gear is mainly affected by the horizontal force in the direction of the boom when it is engaged, the deflection angle of the goods in the plane of the boom variation is considered. The deflection angle \(\alpha\) is determined to be \(10^{\circ}\) according to the parameters of the gantry crane, and the deflection horizontal load is calculated via Formula (5). Therefore, the radial load on the slewing bearing \(F_{\text{r}}\) can be calculated:  
\[F_{\text{r}}=\text{T} \tag{6}\]  
3. Calculation of overturning moment  
Under the consideration of wind action, the total load of the slewing bearing is shown in Table 2.  
According to the magnitude of each load calculated in Table 2, the slewing bearing structure was loaded into the assembly model. Axial load was added on the roller seat surface on the inner ring of the slewing ring. The radial load was added on the roller seat surface in the slewing bearing, and the load direction was the same as the direction of the cargo. The overturning moment was added to the roller seat surface on the inner ring of the slewing ring. Considering the driving force effect of the pinion on the slewing bearing, the rated torque of 3.5 \(\times\) 10\({}^{7}\) N-mm is added to the pinion.