## 3 Results
### Impact of the Surface Roughness  
Notably, the coating made steel nozzles like ceramic ones in terms of surface processing speed. Its disadvantage is rapid wear after about 100 h of continuous operation depending  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \(d\), mm & \(t\), time & \(m_{a}\), kg/s & \(m_{p}\), kg/s & \multicolumn{2}{c}{\(c_{2}\), m/s} \\ \cline{4-5}  & & & \multicolumn{2}{c}{**FlowVision**} & **ANSYS** \\ \hline
7 & 5.2 & 0.020 & 0.023 & 237 & 244 \\
8 & 4.1 & 0.029 & 0.030 & 261 & 288 \\
10 & 4.3 & 0.044 & 0.047 & 250 & 276 \\
12 & 4.8 & 0.055 & 0.068 & 266 & 291 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Parameters of the cylindrical nozzle from steel C40 with a length of 44 mm and pressure ratio \(\beta\) = 0.51.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(d\), mm & \(t\), time & \(m_{a}\), kg/s & \(m_{p}\), kg/s & \multicolumn{2}{c}{\(c_{2}\), m/s} \\ \cline{4-5}  & & & \multicolumn{2}{c}{**FlowVision**} & **ANSYS** \\ \hline
7 & 5.2 & 0.025 & 0.023 & 476 & 466 \\
8 & 4.1 & 0.034 & 0.030 & 482 & 472 \\
10 & 4.3 & 0.052 & 0.047 & 490 & 485 \\
12 & 4.8 & 0.073 & 0.068 & 500 & 494 \\ \hline \hline \end{tabular} \(d\)—nozzle diameter, mm; \(t\)—processing time, min; \(m_{a}\), \(m_{p}\)—mass flow rates of air and particles, kg/s.  
\end{table}
Table 3: Parameters of the cylindrical nozzle from ceramics with a length of 22 mm and pressure ratio \(\beta\) = 0.51.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(d\), mm & \(t\), time & \(m_{a}\), kg/s & \(m_{p}\), kg/s & \multicolumn{2}{c}{\(c_{2}\), m/s} \\ \cline{4-5}  & & & \multicolumn{2}{c}{**FlowVision**} & **ANSYS** \\ \hline
7 & 8.2 & 0.024 & 0.023 & 366 & 395 \\
8 & 5.8 & 0.031 & 0.030 & 384 & 399 \\
10 & 5.8 & 0.049 & 0.047 & 394 & 402 \\
12 & 7.4 & 0.070 & 0.068 & 412 & 422 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Parameters of the cylindrical nozzle from steel C40 with a length of 22 mm and pressure ratio \(\beta\) = 0.51.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(d\), mm & \(t\), time & \(m_{a}\), kg/s & \(m_{p}\), kg/s & \multicolumn{2}{c}{\(c_{2}\), m/s} \\ \cline{4-5}  & & & \multicolumn{2}{c}{**FlowVision**} & **ANSYS** \\ \hline
7 & 5.2 & 0.025 & 0.023 & 476 & 466 \\
8 & 4.1 & 0.034 & 0.030 & 482 & 472 \\
10 & 4.3 & 0.052 & 0.047 & 490 & 485 \\
12 & 4.8 & 0.073 & 0.068 & 500 & 494 \\ \hline \hline \end{tabular} \(d\)—nozzle diameter, mm; \(t\)—processing time, min; \(m_{a}\), \(m_{p}\)—mass flow rates of air and particles, kg/s.  
\end{table}
Table 3: Parameters of the cylindrical nozzle from ceramics with a length of 22 mm and pressure ratio \(\beta\) = 0.51.  
on coating thickness. The impact of the inner surface roughness of the nozzle UDC32-459 with a critical diameter of 6 mm was also analyzed. The results are summarized in Table 7.  
It can be seen from the table that when wall roughness was 3.2 \(\upmu\)m, a reduction in the jet force of 14% occurred for the nozzle UDC32-450 with a critical diameter of 6 mm.  
The results of the experimental studies of the cylindrical nozzle are presented in Table 8, and the impact of air consumption on the output mass flow rate in Figure 8.  
Table 8 and Figure 8 summarize the results of the experimental studies of the material surface with an initial roughness of 50 \(\upmu\)m, which was processed with abrasive grains from 0.2 to 0.5 mm and with an initial roughness of 35 \(\upmu\)m processed with abrasive grains from 0.1 to 0.2 \(\upmu\)m. The roughness of the inner surface of the nozzle was measured using a professional profilometer PCE-RT 2300.  
As a result, it is apparent that the roughness of the nozzle surface affected its characteristics; namely, roughness reduced the velocity of the air-abrasive mixture by up to 10% in comparison with that in a smooth hydraulic nozzle.