Coating thickness of the restored contact of electrical equipment and the method of its determination
Authors:   The National University of Life and Environmental Sciences of Ukraine, Korobsky V. , Sobol S. ,   The National University of Life and Environmental Sciences of Ukraine, Lapshin S. ,   The National University of Life and Environmental Sciences of Ukraine
Published: April 2021

The regularities of the formation of the main variants of coatings obtained by gas-plasma spraying with subsequent liquid-phase sintering, depending on the conditions of wetting the powder particles with the melt and the porosity of the sprayed layer, have been established. The analysis of methods for controlling the thickness of thermal gas coatings, which indicates the advantages and disadvantages of three methods of measuring the thickness: magnetic, electromagnetic (eddy currents) and metallographic. The research of the dependence of the thermal power of the plasma jet (directly affects the thickness of the sprayed coating) on the thermal equivalent of the electric power of the arc was carried out; dependence is characterized by an effective efficiency. As a result of the research, the thickness of the sprayed coatings of the contacts and the tolerances for their processing were calculated depending on the height of the contact piece. Coating thickness is the shortest distance between the coating surface at a given point and the base metal surface. As a technological characteristic, the thickness affects such an important performance property as the strength of the bond with the base metal. Increasing the thickness of the coating above the optimum leads not only to a deterioration in quality (decrease in bond strength), but also to economic costs. The coating was applied to a given area due to the linear movement of the spray device in combination with either the transverse displacement of the spray device or contact piece. With a single linear movement of the spray device, the sprayed material forms a uniform coating layer, the cross-section of which is described by the Gaussian curve. The requirements for the thickness of the sprayed layer are indicated in the technological documentation, based on the uniformity of the distribution of the coating thickness on the contact surface. The required thickness of the sprayed coating was determined based on the thickness of the working layer, the tolerance for subsequent processing and the tolerance for the dimensions of the contact piece and the thickness of the sprayed layer. The thickness of the sprayed coating on the contacts, in which the lost dimensions are restored, provided for a tolerance for their following processing: turning and grinding. As a result, the thicknesses of the sprayed coatings of the contacts and the tolerances for their machining were calculated depending on the height of the contact piece (the number of switching cycles of the sprayed contact pieces). In thermal spraying of coatings, the build-up of parts occurs at a relatively high rate, that is, approximately 10 - 20 times faster than electrolytic deposition of steel and approximately 100 - 200 times faster than electrolytic chromium plating.