OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 6 4 includes impurities that were part of the water, copper and oxygen. There is also a significant amount of oxygen on the nozzle surface. Nozzle and electrode wear accelerates in comparison with wear in normal mode, but in this case, the consumables withstood up to 150 starts when cutting hot-rolled products. Separately, we can emphasize the influence of nozzle and electrode manufacturing accuracy on the wear of working elements. When operating in normal mode without a significant excess of wear intensity of the working elements of the plasma torch, deviation from the nominal position of the nozzle hole causes its uneven wear (Figure 6). In the case presented in Figure 6, when manufacturing the nozzle, the misalignment of the nozzle outlet and conical nozzle cavity of the order of 0.4-0.5 mm was allowed. This caused the initial deviation of the arc and plasma column during cutting from the vertical orientation and more significant wear at an angle to the vertical axis, which with the time of operation increased and led to even more significant changes in the shape of the nozzle. The irregularity of electrode wear is also evident. Timely starting arcing off, control and observance of the gap between the nozzle and electrode, gas pressure in the system and water supply lead to a small risk of catastrophic wear of consumables and formation of deposits on the electrode surface. However, uneven wear leads to deviation of the plasma jet from its nominal position and, as a consequence, to insufficient cut quality after 100–150 starts. For this reason, the alignment of the hole at the outlet and in the conical part in the nozzle of the plasma torch should be at a high enough level to ensure the accuracy of the cut during operation of the plasma torch. Cutting of specimens in the standard mode is characterized by the minimum intensity of wear of consumable elements, which is shown in Figure 2, l, k. Increasing the gas (air) pressure in the system from 2.0–2.5 to 3.0–3.5 bar increases the service life of consumable elements of the plasma torch by more than two times and reduces the risk of double arcing during operation. Increasing the pressure in the discharge Fig. 5. The structure of the plasma torch elements after the gradual failure of the nozzle and electrode during constant operation of the starting arc: 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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