Demianov A. Physical and metallurgical processes in plasma-arc spraying of coatings with fusible wire-anode.

Scientific bases of the process of plasma-arc sputtering with a moving wire-anode in the form of: a set of physical and mathematical models of heat and mass transfer processes in the electric arc zone and turbulent plasma jet, basic and magnetohydrodynamic (MHD) equations in the turbulent limit approximation; regularities of melting and spraying of moving metal wire-anode; regularities of formation of structure and physical and mechanical properties of coverings depending on conditions of technology and structure of a wire anode. Based on the study of physical and metallurgical features of the process of plasma-arc sputtering of coatings with fusible metal wire-anode, it is proposed to laminarize the plasma jet by compressing it with external high-velocity air flow from 16 to 40 m3/h, which increases the electric field strength. Reliable protection of molten metal droplets from oxidation. It is established that the current-voltage characteristic of the arc column during plasma-arc spraying with fusible metal wire-anode is increasing and significantly depends on the consumption of plasma-forming gas, and in the current range I = 160…260 A the growth rate U increases with increasing I. melt on the anode wire is the failure of metal droplets with a diameter of 500…700 μm and their subsequent crushing to diameters of 40…150 μm in the plasma jet. Recommendations for the choice of optimized technological modes are developed, which allow to obtain metal coatings up to 5 mm thick and more with reduced porosity (1-2%) and adhesion strength to the base of about 40-50 MPa at a material utilization factor of up to 72% by plasma-arc wire spraying. -anode with a diameter of 1.0-1.6 mm, melting at currents of 160…260 A, using as plasma-forming gas argon or air-gas mixture with a flow rate of 1.0-1.5 m3/h. By studying the temperature of formation of liquid metal droplets and the rate of their transfer to the treated surface during plasma-arc spraying of coatings with fusible metal wire-anode, recommendations for the design of equipment and modes of its operation are created. Comparison of the results of calculations performed on the created physical and mathematical models with the results of physical experiments, showed that the accuracy of calculations is not worse than 5-10%. This result is acceptable and indicates the adequacy of the simulation. As a result of wear resistance tests it is confirmed that the technology of plasma-arc spraying with a moving wire-anode and the flow of associated shielding gas provides a high level of wear resistance of the applied coatings under sliding friction, in particular can exceed the wear resistance of the base up to 3-4 times. Industrial implementation (at Zibo KNC Petroleum Equipment Co., Ltd, PRC) of plasma-arc spraying with metal wire-anode in technologies of repair, restoration and increase of resource of threaded sections of pump-compressor pipes and contact surfaces of steel power supplies is performed. It is established that the coatings applied according to the developed technologies ensure the tightness of threaded joints, prevent the ingress of aggressive corrosive environment, increase the number of cycles "screwing - unscrewing" during lowering and lifting operations up to 50 cycles.