Characterization of opportunity for upgrading of the system based on arc plasma torch for thermal spaying of ceramic materials, by means of use of fuel vortex intensifier. Part I: Thermodynamic modeling of the system efficiency parameters

One of the main trends in the field of improving the modern technologies of thermal spraying, including plasma one, for functional ceramic coatings formation is the reducing the energy consumption of the process. In this regard, one of the important directions for improving these technologies is the development of their new versions, using the principle of adding inexpensive fuel-oxidizer mixtures based on hydrocarbons with air. This type of plasma-fuel type of spraying will be promising for application at the present time, first of all, in order to obtain refractory functional coatings. For this purpose, we investigated the opportunity for upgrading an industrial unit/system for plasma spraying of ceramic powder materials with arc plasma torch of 25–40 kW power by the use of experimental variant of a fuel gas-vortex intensifier. The thermodynamic assessment of possible parameters of the generated mixed flow after the torch with this fuel intensifier was carried out to estimate the applicability of this system to optimize the spraying of oxide and carbide coatings (based on the examples of Al2O3, Cr3C2 and other powders). The analysis of possible parameters of the produced flow after the torch with intensifier was performed for the cases of main C–H–O–N–Ar–Me (Me = Al, Cr) systems and additional C–H–O–Al-system to assess the potential of this system to modify the technology of oxide and carbide ceramic coatings formation. New regimes, which were analyzed in our research as the simulants of Al2O3 spraying, surpass on calculated energy efficiency characteristics (by 10–20 %) one of the new prospective spraying methods with (СO2+СH4)-plasma, as well as the conventional method of powder heating during the spraying with N2-plasma. The case of our proposed fuel assisted process (FA-APS) with liquefied petroleum gas (LPG) fuel for the heating of ceramic powders (especially, Al2O3) demonstrates the advantage of the process (in particular, on the energy efficiencies and energy consumption) in a comparison with the conventional regimes of APS of the powders (in N2 plasma of the standard torch). For the variants of the FA-APS with Al2O3 and Cr3C2 feedstock powders it was established to be potentially possible to obtain (at the moderate values of total electric energy consumption for the torch and auxiliary equipment, – near 1.8 and 1.0 kWh/(kg of product)) such high level of the process productivity on the final product as approximately 17 and 28 kg/h, respectively; at the values of required power of the torch:  28.2 and  22.3 kW.

Formation of highly concentrated heterogeneous flows during plasma deposition of powder materials

Most industrial installations for plasma spraying of powder materials are equipped by nozzles with local (radial) powder input into the thermal plasma jet generated by the plasma torch. Such a local input of the sprayed material significantly perturbs the flow of the plasma jet, and causes dispersion of temperature and velocity of the particles of the sprayed powder materials. This work presents study of high-temperature heterogeneous flows generated by the electric arc plasma torch PNK - 50 with an annular (circular) input unit of powder materials with their gas-dynamic focusing developed at ITAM SB RAS. The performed experiments proved that the annular injection of a powder material guarantees the stable formation of a highly concentrated flow of thermal plasma with particles of sprayed powder materials. The comparative analysis clearly showed the advantages of annular powder input unit with its gas-dynamic focusing. In contrast to local point injection, axisymmetric annular injection practically does not disturb the jet of thermal plasma and, thus, significantly increases the efficiency of interphase exchange.

Experimental investigation into the anode erosion phenomenon in a DC non-transferred arc plasma torch

Anode erosion phenomenon in a DC non-transferred arc plasma torch was experimentally investigated. Anode weight loss and anode erosion position with changes in plasma current, gas-flow rate and anode length were studied. The results show that all these influences could be explained by plasma power. Anode erosion position was closely related to the structure of anode nozzle and the working conditions of plasma torch. The influence of anode arc root position and the energy flow through it on anode erosion was also analyzed. Moreover, the mechanism of anode erosion and its influence on plasma jet were studied. The results can serve as a reference for revealing the mechanism of plasma discharge, for the optimization design of arc plasma torch, and for high-quality plasma generation.