OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 6 No. 3 2024 pores in the melted material are mainly spherical 3 or irregularly shaped 4 (Figure 3). On the plasma torch of the developed design, gas pressure less than 2 bar increased the risk of formation of this phenomenon. Increasing the pressure above 2.5-3.0 bar and setting the gap between the nozzle and the electrode not less than 1.0-1.5 mm practically canceled the risk of failure of the plasma torch as a result of double arc formation or short circuit in the discharge chamber. The second type of catastrophic failure of plasma torches of this design is melting of channels in the swirl ring (Figure 4). In this case, during operation, due to the fairly close location of the junction of the swirl ring and nozzle to the discharge zone (Figure 4, b), its partial fusion may occur. During operation, the distortion of the elements in this area gradually accumulates under the action of the starting arc to such an extent that the gas supply holes are partially blocked, which causes the temperature of the nozzle and electrode to rise sharply. Then, as in the previous case, it suddenly melts, boils and plugs the nozzle hole. At the same time, on the surface of both the electrode and the nozzle there are signs of erosion and oxidation during operation. This phenomenon occurs partly for design reasons, and partly due to insufficient clearance between the electrode and the nozzle during assembly. It is possible to reduce the risk of this process by adjusting this clearance at a level of 1.0–1.5 mm. During plasma cutting, ignition of the starting arc between the electrode and the nozzle forms the initial plasma flow into the cutting zone, after which it is switched to the working arc and cutting in the normal mode. If the starting arc is not switched off in time during operation, it is possible to increase the intensity of wear of working elements of the plasma torch and formation of deposits on the electrode surface (Figure 5). According to the data of scanning electron microscopy, the composition of deposits (5, 6 in Figure 5) Fig. 4. The structure of plasma torch elements after a catastrophic failure of the nozzle and electrode due to clogging of the gas supply channels in the swirl ring: a, b – macrostructure of the electrode and nozzle, c–e – microstructure of individual sections of the electrode; f–h – microstructure of nozzle sections
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