# Sand Removal Mechanism of a High-Speed Roller Bit with Helical Sealing
## 5 Discussion  
First, the rotation direction and the sealing mechanism of helical sealing are determined with sealing theory. According to the literature on helical sealing and the optimized helical structure parameters with better pumping performance, the helical sealing structure is preliminarily determined \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Numerical Simulation Results**} & \multicolumn{2}{c}{**Test Results**} \\ \hline \multirow{3}{*}{**Structural Parameters**} & \multicolumn{2}{c}{\begin{tabular}{c} **The Averaged** \\ **Pressure Change** \\ **Rate (Mpa/mm)** \\ \end{tabular} } & \begin{tabular}{c} **Maximum Retention** \\ **Time of Debris** \\ **Particles (s)** \\ \end{tabular} & \begin{tabular}{c} **Optimization** \\ **Results** \\ \end{tabular} & \begin{tabular}{c} **Weight** \\ **Difference** \\ **(g)** \\ \end{tabular} & \
\begin{tabular}{c} **Test** \\ **Results** \\ \end{tabular} \\ \hline \multirow{3}{*}{Pitch (mm)} & 1.6 & \(-\)0.201 & 0.0546 & & 7.5 & \multirow{3}{*}{2} \\  & 2.0 & \(-\)0.22533 & 0.0498 & & 6.25 & \\  & 2.4 & \(-\)0.26567 & 0.0448 & & 8.75 & \\ \hline \multirow{3}{*}{Sealing gap (mm)} & 0.5 & \(-\)0.22533 & 0.0209 & & 6.25 & \multirow{3}{*}{0.5} \\  & 0.8 & \(-\)0.06567 & 0.0688 & & 13.75 & \\ \cline{1-1}  & 1.1 & 0.003 & 0.0827 & & 15 & \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Inclination of \\ helical surface (\({}^{\circ}\)) \\ \end{tabular} } & 23 & \(-\)0.25133 & 0.0345 & & 6.25 & \multirow{3}{*}{23} \\  & 27 & \(-\)0.21633 & 0.0328 & & 26.25 & \\ \cline{1-1}  & 30 & \(-\)0.23767 & 0.0563 & & 12.5 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Optimization results of structural parameters. by combining the size of the roller bit with the specific working conditions. This structure is then selected as the original model with which to lay the foundation for subsequent simulation. This paper conducts simulations and experiments to verify the feasibility of helical sealing and then to optimize the structural parameters. For the feasibility analyses, a three-dimensional model of a flow channel is established on the basis of the original model. Moreover, a discrete phase model is established with the boundary conditions set up. Results show that the velocity direction from the top to bottom of the sealing end can achieve good sand removal performance. The pressure field is distributed from high to low. Additionally, it is found that the variation rate of pressure can abruptly change at each variation level of the screw, and the pressure can rapidly decrease, promoting the removal of sand. Meanwhile, the helical structure parameters play an important role in the performance of sand removal. The remaining amount of rock debris decreases and the sand removal performance increases with a decreasing migration time of rock debris. According to the simulation study, the sealing mechanism is revealed to verify the feasibility of helical sealing, and the main factors affecting the sand removal performance are investigated, while criteria for judging the sand removal performance (i.e., a downward direction of movement, low-pressure change rate, and short migration time of rock debris) are obtained. Through experimental study, the sealing effects with and without helical sealing are compared. Because variations in the pressure field and velocity field cannot be experimentally studied, the sealing performance is evaluated by observing the water leakage of the sealing chamber, as shown in Figures 12 and 13. Additionally, the difference in weight of the roller at rest and rotation is measured (16.25 g versus 7.5 g); it is found that the roller at rest has no sand removal effect and the roller with high speed has a good sand removal effect. It is feasible to apply the helical sealing to the high-speed roller bit. The feasibility of helical sealing is verified according to the simulation and experiment.