# Impact Performance of Helmholtz Self-Excited Oscillation Waterjets Used for Underground Mining
## 2 Research Method
### Experimental Setup  
In order to better understand the impact performance of HSEOW nozzles, a test system of water jet erosion was established, as shown in Figure 2. Water stored in the tank was pressurized by a plunger pump with a maximum flow rate 120 L/min and a maximum operating pressure 60 MPa. A control panel was deployed to regulate pressure through frequency conversion and an accumulator was used to keep the pressure steady. Water went through a series of pipes, ejected from the nozzle at the end of the connecting rod and finally impacted on the target plate. The specimen was fixed at the bottom of the tank and the standoff distance \(S\) was defined as the distance from the specimen surface to the nozzle exit wad adjusted from 10 mm to 90 mm. The data acquisition system was Quantum X and the pressure transducer for the test was BD DMK331P. The test data of the flowmeter and pressure transducer was transmitted to the computer through the acquisition card.  
Before the test, the protective films on the surface of the aluminum blocks were teared off. A specimen was placed in the tank on the loading platform and fixed by a stop screw. The vertical distance from the nozzle outlet center to the aluminum block was measured, and the coordinates on the operation panel were calibrated. During the test, the standoff distance was adjusted by accurately  
\begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline
**Material** & **Chinese Industry Standard** & **Al** & **Si** & **Cu** & **Mg** & **Zn** & **Mn** & **Ti** & **V** & **Fe** \\ \hline Aluminum & 1060A & 99.6 & 0.25 & 0.05 & 0.03 & 0.05 & 0.03 & 0.03 & 0.05 & 0.35 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Chemical compositions of specimen (%).  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & **Chinese Industry Standard** & **Density \(\rho\) (\(\times\)10\({}^{3}\) kg/m\({}^{3}\))** & **Elasticity Modulus \(E\) (GPa)** & **Tensile Strength \(\sigma_{b}\)** & **Yield Strength \(\sigma_{0.2}\)** & **Vickers Hardness \(H\
u\)** (GPa)** \\ \hline Aluminum & 1060A & 2.70 & 70 & 105 & 50 & 24 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Physical properties of specimen.  
Figure 2: Schematic diagram of experimental apparatus.  
reading the number of coordinates on the control panel and controlling the vertical coordinates of the nozzle through the vertical sliding rail motor. The inverter and high-pressure pump power supply were firstly opened. Then the water tank valve and the pipeline pump kept running until the gas in the pipeline was completely discharged. The nozzle was located 500 mm underwater and the pressure was set to the specified value. The above process was repeated after the nozzle and aluminum block were replaced, thus the erosion of various nozzles was accomplished under different operating conditions.  
The erosion intensity was evaluated by the mass loss of specimen, \(\Delta m\), which was defined as the weight of subtracting after and before the test. The mass loss was weighed by an electronic balance with resolution to 0.1 mg. Each erosion test under the same conditions was repeated three times and then the mass loss was averaged in order to reduce the impact of casual factors, thus making the results more reliable. The mass loss changing with time was shown in Figure 3. At the initial stage of erosion, mass loss increased linearly with the increase of erosion time. When the erosion time was higher than 150 s, the mass loss changed little. At this time, increasing the erosion time will only increase the energy consumption. In present study, 180 s was chosen as the erosion time of all tests.