Investigation of Upgraded Technology for Plasma Spraying of Bronze Powder Using the Combined Process with Hydrocarbon Additions

Abstract

The object of the research is thermal spray process for the formation of metal coating from bronze powder in plasma-fuel variant, using direct current (DC) electric arc plasma torch, on steel samples. The aim of the work was to investigate and develop the technology for plasma-fuel spraying of functional coatings (for wear-resistant and antimicrobial applications) on machine-building and medical purpose pieces with increased process capacity and moderate energy consumptions in a comparison with conventional thermal spray technologies with use of inert and oxygen-free gas media. During the study, using experimental and thermodynamic estimation methods, the thermal and chemical parameters of the process under the spraying conditions at ambient pressure were characterized, which made it possible to determine the area of preferred regimes of the developed technology. On the modernized testing unit for plasma spraying of metal powders with power of up to 40 kW, operating using a controlled combination of three types of gases – technical nitrogen and propane-butane (LPG) with compressed air, the measurement and optimization of the operating and constructive/assembling parameters of the system for aluminum bronze coating spraying were established. In this case, the experiments were carried out using the designed fuel intensifier, which is joined with the PP-25 arc plasma torch, as well as additional technological equipment (protective shroud). For samples of the resulting coatings with a thickness of 100 to 450 m from the bronze material, testing of phase composition and some parameters of the resulting coatings on steel products was carried out. Operating capacity of the proposed process reaches 7–15 kg/h for bronze powder when using a moderate power of the torch – up to 35–40 kW and a limited flow rate of hydrocarbon gas (for example, LPG of the SPBT grade) – 0.1–0.35 kg/h. Analysis of the energy efficiency parameters of the developed technology, as well as its calculated technical characteristics, in a comparison with plasma and combined equipment of a similar purpose, showed that it has an advantage in terms of target indicators, in particular, in terms of energy consumption and total energy efficiency of the spraying unit, not less than 20–30 %. This makes it to proceed later to the stage of application of this technology into production based on a new process for the metal coating formation, in particular with antimicrobial properties, with improved energy efficiency of the process.