SU1394258A1 - Method of applying contact coating onto the contact-part of vacuum high-voltage ferreed switch - Google Patents

Abstract

The invention relates to electrical engineering and is intended for switching high-voltage low-voltage electrical circuits. The aim of the invention is to increase the wear resistance of the contact coating by improving the quality of the surface by degassing it and reducing porosity. The method includes plasma powder coating of a tungsten contact coating on the contact details of the contact and polishing the surface of the coating. Polishing is carried out by bombarding the surface of the coating with accelerated tungsten ions followed by deposition of the surface layer of tungsten from a vacuum arc discharge plasma. about S (L with so 4 th ate 00

Description

The invention relates to electrical engineering, in particular, to a technology for manufacturing an erosion resistant tungsten contact coating for sealed magnetically controlled contacts (reed switches) intended for switching high-voltage low-voltage electrical circuits, and can be used in mass production of reed switches.

The purpose of the invention is to increase the wear resistance of the contact coating by improving the surface quality by degassing it and reducing the porosity.

The method is carried out as follows.

Pre-cleaned (degreased) contact parts of the high-voltage contact are placed in a special cassette, the design of which provides selective shielding of the surface of the parts. The cassette is installed in a sputtering device equipped with a plasma feeder with a powder feeder. P plasma torch serves plasma-forming gas (for example, argon) and ignites the arc discharge. A fine tungsten powder is fed into the plasma torch through the feeder; The particles of the foam melt, are entrained by the plasma jet and are deposited on the contacting surface of the contact parts. After coating with a thickness of 25-30 microns, the cartridge with the parts is removed from the sputtering device. After cleaning the parts (for example, using ultrasonic washing and annealing in hydrogen), they are re-installed on an insulated holder of a vacuum device equipped with an arc evaporator with a tungsten cathode. When a vacuum of 10–10 Pa is reached in the evaporator, an arc discharge is initiated in pairs of cathode material, and a negative potential is applied to the cassette with contact details, which accelerates the tungsten ions extracted from the discharge plasma to an energy exceeding the threshold sputtering energy tungsten (effective sputtering occurs at potentials KB, where K is from 1 to 2), the ion treatment of the coating is carried out for a time-period from fractions to several minutes depending on the discharge current, the magnitude of the accelerating potential,

evaporator and cassettes. Then, without interrupting the process, the accelerating potential is reduced to a value at which condensation prevails over spraying, and a relatively thin surface layer of the coating is deposited. The optimum thickness of this layer is 5-6 µm, at which complete healing of the pores and the formation of a sufficiently smooth surface are achieved. After that, turn off the power to the evaporator, depressurize the device and remove the cartridge. The contact details processed in this way arrive at the welding of reed switches,

The proposed method combines the capabilities of the technology of plasma powder spraying of metallic coatings and the technology of surface treatment with metal ions from a vacuum arc discharge plasma. As is known, tungsten is a brittle material with a high temperature of cold brittleness. Dense textured tungsten coatings are similar in their properties to monolithic material and are therefore also prone to brittle fracture. In the case of using such vacuum-sprayed coatings in high-voltage contacts in the contact gap, crumbled particles poorly bonded to the surface can form, which reduce the electrical strength of the gap, contribute to the localization of high-voltage discharges during the switching process, causing an increase in electrical erosion of the coating. Plasma powder spraying is the most productive process of spraying refractory coatings and, importantly, during plasma spraying, the coating is formed from individual melted or in a liquid-plastic state not interacting with each other, having a high velocity, and, as a rule, represents It is a layered scaly structure. A coating with such a structure is more resistant to mechanical failure under the action of shock loads that occur in the process of switching the reed switch.

These deficiencies of plasma-coated powder coating (high degree of surface roughness, the presence of through pores and gas

impurities adsorbed in the pores are eliminated in the proposed method by treating the formed coating with tungsten ions from a vacuum arc discharge plasma. The vacuum arc discharge burning in the vapors of the material of one of the electrodes (usually the cathode) generates intense fluxes of metallic plasma, the degree of ionization of which in the case of tungsten is as high as 80%. At the same time, the energy of ions extracted from the discharge plasma can be regulated over a wide range by applying a negative potential to the workpiece. During the bombardment of the coating with accelerated ions, not sputtering of asperities on the surface occurs, but also intense heating (mainly near surface layers), which stimulates the removal of adsorbed gases from the coating. During the subsequent deposition of low-energy ions from the vacuum arc-discharge plasma, the pores overgrow and a dense textured surface layer is formed. The resulting rather smooth and dense tungsten layer with high adhesion to the main plasma-deposited coating provides a significant increase in the resistance of the coating to electrical erosion, as well as the electrical strength of the contact gap. In this case, the surface layer is also resistant to brittle fracture due to the fact that plastic deformation of the lower groove of the mononapilated layer reduces the level of mechanical stresses arising in it under the action of shock loads during the switching process.

Example. The studies were carried out on a commercially available vacuum contact of the type ЖА-5214, intended for switching high-voltage low-current electrical circuits with voltage up to 5000 V. The application of the main coating (thickness, 25 microns) on the contact parts was carried out using a plasma Coating A-440.43, in which BCG-H brand tungsten powder was sprayed in a stream of nitrogen-argon plasma; coating deposition rate 10 µm / min. Then the coated parts went through ultrasonic

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freon and hydrogen annealing at temperature. The ion treatment and deposition of the top layer of the coating were carried out using a stationary end plasma accelerator on the URM unit. 3.279.048. The evaporated cathode of the accelerator is made of extruded tungsten. The process was carried out in a vacuum 5 x 10 mm Hg. The discharge current was 130 A. The ion bombardment was carried out when applying to a cassette with 600 processed parts of a potential of -1300 V for 2 minutes, while the ion current density on the cassette was 30 mA / cm. Then, the arc discharge was not interrupted, the potential on the cassette was reduced to -40 V and the surface layer of the coating was deposited with a thickness of 5 µm at a speed of 0.25 µm / min. After cooling in vacuum, the parts thus processed were transferred to the welding of reed switches. After being rejected, the reed switch was electrically tested for a short period of time under high voltage, and then put on resource tests in the U switching mode (3–1СРв ;; IK 2 f to 50 Hz, the load was active. 15 reed switches were tested before operating time 6-10 with one failure;

5 hours of operation 3.18- 1 O operations. The minimum operating time of reed switches with a coating made using the existing technology of the enterprise manufacturer was 10 operations.

Thus, the proposed method allows to significantly increase the minimum operating time of high-voltage contacts. At the same time, a slight increase in production costs due to the introduction of an additional operation of vacuum-arc processing of the contact coating into the technological process pays off by increasing the service life of the contacts.

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Claims (1)

Invention Formula The method of applying a contact coating on a contact part of a vacuum high-voltage magnetically controlled contact, including plasma powder deposition of a tungsten layer, ultrasonic removal, hydrogen annealing and polishing the surface of the specified plasma-deposited vol. framed layer distinguished-by accelerated bombardment so that, in order to increase tungsten ions from vacuum plasma the wear resistance of the contact coating of the arc discharge; then, the acceleration is reduced by increasing the quality of the surface potential of the rifling potential to by degassing it and reducing which condensation prevails over porosity, polishing the surface with spraying and precipitating on it a second pneumonic tungsten layer plasma-tungsten tungsten layer.