SU1292955A1 - Method of electro-erosion coating - Google Patents

Abstract

The invention relates to the field of electroerosive coating of current-conducting particles in a fluidized working medium, making low-frequency oscillations, and allows the coating to be applied to powder materials. To do this, the coated particles are treated, mixed with the coating particles. The ratio of particle diameters satisfies the inequality (df: yed) / Td5d: where d is the particle diameter; T is the melting point; S is the electrical resistivity of the material of the particles (index A refers to the particles to be coated, B refers to the particles of the coating material). 1 tab. ND SO y;

Description

The invention relates to electrophysical treatment methods, in particular to electro-erosion coating.

The purpose of the invention is to provide a coating for powders.

The use of a mixture of particles from different materials (provided they are mixed) makes it possible to carry out an electric-spark treatment of the entire surface of each powder particle, without having to fix and specify a deterministic trajectory of particle motion.

During the EDM processing of a mixture of powders, discharges arise between particles of the same and unlike materials. The effectiveness of the coating process depends on the fraction of payloads, i.e. bits between particles of opposite materials. The occurrence of contacts, and therefore the appearance of discharges between particles in a mixture, is probabilistic in nature. According to the theory of probability, the proportion of contacts between unlike particles in a mixture can be estimated as 2pAPS, and of like particles - as the value (where n ,;; (NB and n are the number and proportion of powder particles to be coated in the mixture; N and n are the number and proportion of particles of the coating material in the mixture.) At the same time, mixtures with the ratio 1 have the largest share of unlike contacts and share of the plasma bits. The permissible ratios of the number of powder particles to be coated and the particles of the coating material are from 1/3 to 3. If the ratio is less than 1/3 or more 3, d The number of useful bits (process efficiency) is significantly reduced.

The relative movement of particles with the formation and breaking of contacts (suspended state), necessary to ensure the occurrence of a spark discharge between them, is reported by imposing vibration on the mixture of powders with an amplitude of at least 0.8 mm. At a smaller vibration excitation amplitude, vibroplate of powder particles occurs, which causes destabilization of the process (welding of the particles between themselves and the generator operation in the short-circuit mode).

Vibration excitation also provides the mixing of a mixture of particles necessary for coating them over the entire surface.

During the EDM treatment, an arbitrarily picked up particle in the mixture with respect to particles of a material of a different name can be either a cathode or an anode; therefore, there is a transfer of material both in the desired direction (onto the coated powder particles) and in the opposite direction (on particles of coverage). However, experiments have shown that after some processing time

a solid coating is formed only on the coated powder particles when the following condition is met: the ratio of the diameters of the particles of the coating material to the coated powder particles (dg / dft) is less than the square root of the ratio of the products of the melting temperature and electrical resistance of the materials to be coated and the coating

dY

/ T. 5l VL) Spent EDM processing mixtures of powders of various materials and sizes of powders (used powders of narrow fractional composition). The treatment was carried out on an installation with an electromechanical vibrator and a pulse generator with thyristor control. Powders of the coating material and the material to be coated were loaded into a container mounted on the vibrating plate of the installation, which was simultaneously the current-carrying element - the cathode (container capacity 200 ml, loading of the powder material 0.6-0.7 container volume). The other current-carrying element, the anode (in the form of a rod), was fixed on a fixed bracket and immersed in powder to a depth of 2/3 of the container loading height. The anode was made from an applied coating material (copper, iron, titanium) or tungsten. The latter has a low ability to electrospark transfer.

Processing was conducted under the following modes: container oscillation frequency 25-35 Hz; bit rate 30-50 Hz; the discharge start voltage is 100-150 V. As a result of treatment for 5-15 minutes, a continuous uniform coating was formed on the powder particles to be coated. The efficiency of the process was evaluated by increasing the mass of the powder per unit of its initial mass (specific weight gain, mg / g). The data are given in the table.

The proposed method allows the coating to be applied to powders of electrically conductive materials that can be used in the production of composite materials by powder metallurgy methods.

Claims (1)

Invention Formula The method of electroerosive coating of a fluidized working medium in a container with low-frequency oscillations, with an electric potential applied between the container body and the current-conducting electrode, characterized in that, in order to coat the powder particles, the process is carried out in a mixture of coated powder particles and particles of coating material. moreover, the ratio of the diameters of the particles of the coating material and the particles to be coated is chosen to be less than square root. Characteristics of the powders and coatings being treated The product is the melting point and electrical resistivity of the material to be coated and the coating.