## 5 Strength Check of the Conductive Center Pole  
In order to assemble the conductive module, it is necessary to expand the hollow inside the center pole, which causes the pipe wall at the threaded part to be thinned. The cross-section of the threaded connection is shown in Figure 20.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Scoring Item and Weight**} & \multicolumn{3}{c}{**Design Scheme**} & \multirow{2}{*}{**Schematic Diagram**} \\ \cline{2-2} \cline{4-5}  & **Scheme A** & & **Scheme B** & **Scheme C** & \\ \hline Structural design & & & & \\ (0.1309) & 0.4931 & 0.3342 & 0.1727 & **Scheme A** \\ Installation and assembly & & & & \\ (0.2032) & 0.2413 & 0.1235 & 0.6352 & \\ Material properties & & & & \\ (0.0343) & 0.3333 & 0.3333 & 0.3333 & \\ Independence & & & & \\ (0.2051) & 0.1572 & 0.3193 & 0.5235 & \\ Functionality & & & & \\ (0.3231) & 0.1616 & 0.3025 & 0.5359 & \\ Manufacturing & & & & \\ (0.1034) & 0.4025 & 0.3291 & 0.2684 & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comprehensive evaluation of the optimized conductive center pole.  
Figure 20: The cross-section of the threaded connection.  
Therefore, it is necessary to check the strength of the threaded connection structure of the center pole after processing and thinning to ensure that the center pole can complete the lifting of the core remover.  
During the operation of the core remover, it is always in a vertical working state. After the core is completed, the center pole needs to vertically lift the core with a weight of about 350 kg. The threaded connection strength when the central pole is subjected to an axial load, and the tensile strength of the structure at the weakest part of the central pole need to be identified and resolved [44].  
The connection of the center pole adopts an M30 standard thread, the pitch P is 2 mm, and the minor diameter d\({}_{1}\) of the thread is 27.835 mm. The center pole is made of 304 stainless steel, its yield strength \(R_{\rm{EL}}\) is 310 MPa, and its tensile strength \(R_{\rm{m}}\) is 620 MPa. In the case of a static load, the safety factor \(S_{\rm{S}}\) of the bolt connection is taken as 4. To ensure the reliability of the threaded connection, it is required that the residual pre-tightening force of 1.3 times the working load is retained when the center pole is tensioned.  
\[\sigma=\frac{1.3(1.3F_{0}+F_{0})}{\frac{\pi}{4}d_{1}^{2}}=17.1\;\text{MPa} \tag{7}\]  
The allowable strength is:  
\[[\sigma]=\frac{R_{\rm{EL}}}{S_{\rm{s}}}=77.5\;\text{MPa} \tag{8}\]  
The strength check value is far less than the allowable strength, and the strength of the threaded connection meets the needs of use.  
The tensile strength of the thinned part of the center pole must be checked. The cross-sectional area of the threaded connection of the center pole is \(A_{\rm{s}}\), and the area of the hollow is \(A_{\rm{d}}\).  
\[A_{\rm{s}}=\pi d_{1}^{2}-A_{\rm{d}}=215.9\;\text{mm}^{2} \tag{9}\]  
\[\sigma=\frac{1.3F_{0}+F_{0}}{A_{s}}=37.29\;\text{MPa} \tag{10}\]  
Taking the safety factor \(S_{\rm{s}}\) as 4, the allowable tensile stress is \([\sigma_{\rm{s}}]\).  
\[[\sigma_{\rm{s}}]=\frac{R_{\rm{m}}}{S_{\rm{s}}}=155\;\text{MPa} \tag{11}\]  
The tensile strength value is much smaller than the allowable tensile strength, which meets the operation requirements of the center pole pulling and lifting.