RU2088007C1 - Electric brush manufacturing process - Google Patents

Abstract

FIELD: electrical engineering; materials for electrical machine brushes; electromechanical engineering and transport. SUBSTANCE: carbon filler of material is prepared by crushing carbon blanks containing in their composition soot, coke and/or artificial graphite, element graphite, and coke of high-temperature coal tar pitch. EFFECT: improved strength and mechanical endurance of electric brush material due to more homogeneous structure and low size of voids. 4 cl, 2 tbl

Description

 The invention relates to the field of electrical engineering of the material for brushes of electric machines and can be used both in electrical engineering and in vehicles.

 The prior art method for the manufacture of carbon brushes from carbon material, including the preparation of a filler from carbon black and elemental graphite, mixing the filler with a binder, which serves as coal tar pitch in the form of powder, subsequent pressing and firing [1, 2] The carbon components are mixed in a vibration mill without heating with simultaneous grinding. Annealed the resulting workpiece in coke backfill. Thus obtained electrobrushes have low wear resistance at variable and increased sliding speeds and, as a result, have a limited service life. In addition, this method leads to the fact that after the exhaustion of the service life of the electric brush enter the waste.

 The objective of the present invention is to improve the quality and operational characteristics of electric brushes, as well as reducing production costs.

 The solution to this problem is provided by the fact that the carbon filler is prepared from carbon blanks containing soot, coke and / or artificial graphite, elemental graphite and high-temperature coal tar coke.

 The solution to the problem is also ensured by the fact that as such carbon blanks, the used life of the electric brush or blanks (lumpy waste) of the antifriction carbon material is used (hereinafter referred to as the exhausted resource of the electric brush or blanks (lumpy waste) of the antifriction carbon material, we will call carbon blanks).

 The method is implemented as follows.

Carbon blanks containing these components are crushed, and then crushed in a vibratory mill to obtain particles with a particle size of not more than 90 microns. The crushed filler powder is mixed at room temperature with high-temperature coal tar powder (softening temperature 135-150 ^° C.). After mixing, the resulting mixture is loaded into a mold lined with refractory electrical insulation material, installed on a hot pressing press and joint pressing and firing (SPO) are carried out at a pressure of 300-400 kgm / cm ² and a temperature of 900-1100 ^o C with electric current passing through the mixture for 1.5-2.0 hours. The resulting preform is cooled in the mold to about 300 ^o C with a decrease in pressure, then extruded and cooled to room temperature.

 The preparation of filler powder from carbon blanks improves the strength and wear resistance of the resulting electrobrushes. This is explained by the fact that the material obtained has a matrix structure, where the filler grains are interconnected by bridges of a coked high-temperature coal tar pitch pitch formed during heating to high temperatures during combined pressing and firing. The use of carbon billets with a finished formed material structure in the preparation of the powder of the filler provides low abrasion and high strength of the electric brushes obtained from the material using such a filler.

 When combined pressing and firing, simultaneous pyrolysis of the sorbed low molecular weight and high molecular weight fractions of the binder occurs. The preparation of filler powder from carbon preforms increases the concentration of bonds on the filler-binder interface, which strengthens the material of the electric brushes due to the homogeneity of the structure, which is close to isotropic.

 The manufacture of the material of the electric brushes based on the filler powder obtained from carbon blanks, due to the uniform structure of the filler, to avoid stress concentrations in the STR that cause a decrease in the strength of the electric brushes.

 It is known that the wear rate of electric brushes largely depends on the coefficient of friction, the value of which is determined by the type and amount of dry lubricant (solids with a mucous structure) introduced into the carbon charge. Of the known lubricants (elemental graphite, boron nitride, talc, molybdenum disulfide, etc.), only elemental graphite can be used in the composition of the material of the electric brushes, as it has high conductive properties, which provides the necessary switching properties of the electric brushes. In this regard, as carbon blanks for the preparation of filler powder, only blanks of those carbon materials that have elemental graphite in their composition can be used. Such carbon materials also include used-up electric brushes.

 This ensures a reduction in production costs, as it eliminates the need for special manufacturing of carbon blanks through the use of scrap scrap brushes. On the other hand, billets or wastes of commercially available antifriction carbon materials containing elemental graphite (grades AO-600, AO-1500, AG-600, AG-1500, MG-1) are suitable for use.

 The solution to this problem is also ensured by the fact that in the manufacture of electric brushes pressing and firing are carried out by the STR method. Using this method, passing an electric current through the charge promotes the formation of the texture of the electric brush due to microelectric arcs arising between the grains of the filler and piercing the binder film at a local temperature increase. In this case, intense melting of the high-temperature coal tar pitch occurs, and its high-molecular fractions are adsorbed on the surface of the filler particles. This ensures the formation of a uniform microstructure of the material with a small pore size and increases the yield of high density material.

 The proposed method is illustrated by examples of obtaining material for electric brushes according to the described technology, which contain compositions with equal ratios of components to represent a variety of compositions.

 With the total content in the material of the electric brush powder of the crushed carbon billet in the range of 85-90 wt. a decrease in the amount of high molecular weight coal tar pitch (less than 10 wt.) leads to a decrease in the strength and wear resistance of electric brushes, and its content is more than 15 wt. to increase the stress concentration in the material and the appearance of cracks. In the future, this leads to the destruction of electrobrushes during operation.

 The results and compositions are given in table. 1 and 2.

 Example 1

The filler was prepared from carbon blanks, which were used as a spent brush EG-84. They were crushed to a particle size of ≅ 90 μm. Grade G high molecular weight coal tar pitch (TU 14-6-84-7) with a particle size of not more than 0.5 mm and powdered ground carbon batch were dosed into the mixing machine. Then, without stopping the machine, elemental graphite grade GE-4 (GOST 7478-75) was dosed and further mixed for 60 minutes. The finished mixture was loaded into a mold lined with refractory electrical insulation material, mounted on a hot-pressing press, and an open-loop press was carried out at a pressure of 400 kgf / cm ² and a temperature of 1000 ^o C with passing through an electric charge of 6-9 V for 1.5 h The resulting preform in the mold was cooled to 300 ^° C. while maintaining pressure, then pressed out and cooled to room temperature.

 Example 2

The filler was prepared from carbon blanks, which were used as blanks from antifriction carbon-graphite material brand AG-1500 (TU 48-20-4-87). They were crushed to a particle size of ≅ 90 μm. Grade G high-grain coal tar pitch (TU 14-6-84-7) with a particle size of not more than 0.5 mm and powder of the crushed carbon billet were dosed into the mixing machine. Then, without stopping the machine, elemental graphite grade GE-4 (GOST 7478-75) was dosed and further mixed for 60 minutes. The finished charge was loaded into the mold, as in example 1, and the STR was carried out at a pressure of 350 kgf / cm ² and a temperature of 1100 ^o C with passing through the charge an electric current of 6-9 V for 2.0 hours. The resulting billet in the press -form was cooled to 300 ^o C while maintaining pressure, then extruded and cooled to room temperature.

 The optimal transition resistance, ensuring the normal operation of the electric brushes, are values in the range of 3.0-5.0 microns.m. As can be seen from the tables, a deviation from the optimal composition of the compositions (NN 4 and 5) leads to a deviation of the transition resistance from the optimum, an increase in the wear rate, and a decrease in strength and yield.

Claims (4)

 1. A method of manufacturing electric brushes, including the preparation of a carbon filler and a mixture based on it, the formation of billets from the mixture and subsequent firing of the billets, characterized in that the carbon filler is prepared by grinding carbon billets made on the basis of soot, calcined coke and / or artificial graphite, elemental graphite and coal tar high temperature graphite.  2. The method according to claim 1, characterized in that the carbon billets use spent electrobrushes or billets of antifriction carbon-graphite material.  3. The method according to PP.1 and 2, characterized in that the resulting mixture is subjected to joint pressing and firing with the passage of electric current through it.  4. The method according to PP.1 to 3, characterized in that the mixture is prepared in the following ratio of components, wt. Powder ground carbon blank 85 90
High-temperature coal tar pitch 10 15 °

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