OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 6 No. 3 2024 Introduction Plasma cutting of various metals and alloys has advantages for industrial applications related to high productivity, cutting quality and the ability to cut hot-rolled plates [1–3]. The plasma cutting is an effective method for obtaining workpieces from steels [4], aluminum [5], copper [6], titanium [7] alloys. When cutting, it is possible both to form a clear cut at an angle of 90 degrees to the surface of the sheet, and to form the necessary cutting edges for further welding of structures [8]. Mainly, equipment operating on direct polarity current [9, 10], which has limitations for cutting hot-rolled plates, is used for plasma cutting. The use of plasma cutting technology with reverse polarity current makes it possible to increase the productivity of the process [11–14], especially in the production of large capacity workpieces. Actually in the literature there is quite a small amount of data on cutting of non-ferrous metal and alloy sheets with a thickness of about 30–100 mm [15–18]. At the same time, plasma cutting of thick plates has difficulties associated with high values of plasma arc current and its intensive impact on the working elements of the plasma torch. In addition to studies aimed at establishing the influence of cutting process parameters on the surface quality and structural-phase changes in the impact of the plasma jet on the material [12, 16], it is necessary to carry out work in the field of changing the state of the plasma torch during cutting. This is especially relevant from the point of view of economic efficiency of plasma cutting with reverse polarity current, since it is characterized by a lower degree of wear of plasma torch elements during operation [11]. Plasma cutting with reverse polarity current, despite the long operating time, is a promising method for obtaining workpieces from thick plates in industry. Plasma cutting with reverse polarity current is the most relevant for obtaining workpieces from thick sheet metal. This is due to the lower current values at the same thickness of the cut plates in comparison with cutting with direct polarity current. The systems with a hollow anode used for cutting with reverse polarity current allow obtaining lower current density on its surface in comparison with thermochemical cathodes for cutting with direct polarity current, which also contributes to the increase of plasma torch life. For these reasons, plasma cutting with reverse polarity current for thick plates is more relevant both in terms of process efficiency and from the point of view of equipment reliability and durability. In this direction, the development of modern design solutions and the development of domestic plasma cutting equipment with a number of advantages in comparison with existing analogues are currently required. At present time, within the framework of the joint project of ISPMS SB RAS and “ITS-Siberia” modern equipment for plasma cutting of thick rolled non-ferrous metals and alloys of large thicknesses with a reverse polarity current is being developed. The purpose of this work is to identify the main regularities of the process of failure of working elements of plasma torches of the developed design depending on various factors in the cutting process. Materials and methods The studies were carried out at the manufacturing area of “ITS–Siberia” and on experimental equipment at ISPMS SB RAS. Cutting was carried out on a plasma torch with reverse polarity, developed in the course of a joint scientific and technical project. The scheme of the plasma cutting process is shown in Figure 1, a. The plates 1 were cut by a plasma jet 2 formed in the environment of a protective and plasma-forming gas 3 due to the burning of the starting arc 4 at the start of the process and the working arc 5 during cutting. The supply of protective and plasma-forming gas 6 to the cutting zone is performed at fixed pressure from the compressor. Nozzle 7 is fixed by a nut 8 and serves to form a dense jet of gas and plasma 9 formed by swirl ring 10 and arcing. Additionally, the plasma torch of the developed design provides for the introduction of water 11 into the cutting zone through the hole in the working electrode 14. This allows increasing the quality of the cut and reducing the wear of the nozzle and electrode [19, 20]. Protection against overheating of the nozzle and electrode is also provided by a constant flow of water 12 through channels in the body 13. Water supply in the plasma torch is arranged in such a way that the flow 13 first washes the nozzle, then the electrode, and then is carried partially to the exit of the plasma torch and into the inner cavity of the nozzle and then by the flow 11 into the working zone. Current is supplied to the electrode through a copper
RkJQdWJsaXNoZXIy MTk0ODM1