RU2708291C1 - Method of producing graphite-based material for sliding electric contacts and material - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to electrical engineering, in particular to materials for sliding electric contacts used on electric transport. Method of making material for sliding electric contacts involves the following stages: (A) producing a mixture based on graphite, coke and a coke-forming binder, where the content of graphite is not less than 15 % of the weight of the mixture; (B) forming, from a mixture, a workpiece; (C) annealing the workpiece, which provides formation of residual coke from the binder, to produce a porous workpiece with open porosity; (D) gas-phase thermogradient saturation of workpiece from stage (C) with pyrolytic carbon in reaction chamber by means of pulsed supply of hydrocarbon gas and its decomposition with formation of pyrolytic carbon on surface of open pores in moving zone of pyrolysis and its further pumping. Moving pyrolysis zone is created by maintaining the temperature of one of the walls of said billet in the range of decomposition temperatures of said hydrocarbon gas and increasing the temperature of the opposite wall of the workpiece from the ambient temperature at the beginning of the gas-phase thermogradient saturation process to the decomposition temperatures of said hydrocarbon gas at the end of the gas-phase thermogradient saturation process at rate of 1.0–10.0 °C/hour. Invention makes it possible to produce material for sliding electric contacts with improved operational characteristics: hardness on outer surface of not less than 36 HS, hardness at depth equal to half of thickness of material, measured by layer-by-layer method, at least 30 HS, specific electric resistance, 4–17 mcOhm⋅m, volume loss in electric arc, (2.3 kA, 0.5 s) 3–49 mmand density of 1.33–1.8 g/cm.EFFECT: disclosed is a method of making graphite-based material for sliding electrical contacts and material.11 cl, 1 ex, 1 tbl

Description

FIELD OF TECHNOLOGY.

The invention relates to the field of electrical engineering, in particular, to materials for sliding electrical contacts used in electric vehicles.

BACKGROUND OF THE INVENTION

As materials for sliding electrical contacts, materials based on natural or artificial graphite are used.

These materials are obtained in several stages - at the first stage, the composition of the mixture is selected from particles of graphite, a carbon-containing binder and other carbon-containing materials. Sometimes, also, particles of metals or chemical compounds of metals are introduced into the mixture.

Then, after mixing the components of the mixture with obtaining a given composition, get the workpiece.

The function of the workpiece is to create the skeleton of the future material.

The billet is obtained by processing the pressure of a mixed mixture, for example, pressing, extrusion, rolling in rolls, etc., and subsequent firing for its carbonization.

The preform obtained in this way has a porous structure, and then this porous structure is densified.

Compaction of the preform can be achieved in two ways, the first of which is liquid-phase impregnation of the preform with hydrocarbons followed by carbonization, the second is the deposition of pyrolytic carbon by chemical infiltration from the gas phase in the porous volume of the preform.

The patent RU 2441854 discloses a technology for producing material for the manufacture of contact current collector devices using a liquid phase seal. The known method involves mixing particles of graphite, coke, a binder and forming a green billet from the resulting mixture, then firing the obtained billet under conditions that provide a sintered billet with porosity having no more than 10% closed pores, impregnating the billet under pressure with the same binder and subsequent firing for carbonization of the binder.

The material obtained in accordance with this method contains the following components, in mass. %:

Graphite 30-70 Coke 20-60 Coke residue rest.

This known invention allows impregnation to the entire depth of the material so that the mechanical properties and wear resistance of the material do not change with its depth.

The disadvantages of the known technical solutions include the fact that the method requires firing for carbonization after impregnation to decompose carbon and converting it into coke residue. The weight gain of the material decreases, in order to obtain acceptable properties, it is necessary to carry out the impregnation and firing operations several times, which increases the cost of obtaining the material.

If we also consider that the implementation of this technology emits a lot of harmful hydrocarbons, then we can also talk about the deterioration of the environmental situation at the place of production of this material.

Much more attractive, from the point of view of implementing acceptable environmental conditions for the process of obtaining the material, is to obtain material using the deposition of pyrolytic carbon by chemical infiltration from the gas phase

Such a technical solution is disclosed in patent RU 2150444.

The method of obtaining material for electrical contacts involves mixing particles of graphite and a binder, forming a preform from the finished mixture and firing it, where natural graphite particles are used in the mixing process, forming the preform by pressing, firing to form through porosity - at 800-1100 ° С, and after firing, pyrocarbon is saturated.

Also described is a compressed composite material containing in mass. %: particles of natural graphite - 10-90, coke residue - 5-20 and pyrolytic carbon - 6-70, while the material is characterized by the texture of graphite throughout the volume in a plane perpendicular to the direction of pressing.

A current-collecting contact product made in accordance with this patent, which is made of a material containing in wt. %: particles of natural graphite 10-90, coke residue 5-20, pyrolytic carbon 5-70 and characterized by a density of -1.5-2.2 g / cm ³ and has a wear rate of not more than 0.1-0.14 mm per 1000 km run of the current collector.

The disadvantages of the technical solution include the fact that by this method it is possible to carry out the deposition of pyrolytic carbon only near the surface. Sealing of the internal parts of the preform will be prevented by clogging of its surface pores, as a result of which the wear rate of the material is realized only to a depth of 8 mm, while the wear rate during operation increases, and after wear is 8 mm, it increases significantly and reaches catastrophic values. In addition, the known material does not have sufficient arc resistance.

These shortcomings create a big technical problem in the operation of collector elements.

SUMMARY OF THE INVENTION

The technical problem inherent in the known technical solution is eliminated in accordance with the following.

A method for manufacturing a material for sliding electrical contacts is proposed, which includes the following steps:

(A) obtaining a mixture based on graphite, coke and a binder, where the graphite content is at least 15% by weight of the mixture;

(B) the formation of the billet from the charge;

(B) firing the preform to obtain a porous preform with open porosity;

(D) gas-phase thermogradient saturation of the preform from step (B) with pyrolytic carbon in the reaction chamber by pulsed supply of hydrocarbon gas and its decomposition to form pyrolytic carbon on the surface of open pores in the moving pyrolysis zone, where the moving pyrolysis zone is created by maintaining the temperature of one of the walls of the aforementioned the workpiece in the temperature range of the decomposition of the aforementioned hydrocarbon gas and increase the temperature of the opposite wall of the workpiece from the ambient temperature in n Chal gas phase process thermogradient saturation before decomposition temperature of said hydrocarbon gas saturation at the end of the gas-phase process at a rate thermogradient 1,0-10,0 ° C / hour. In private embodiments of the invention, gas-phase thermogradient saturation of the preform in step (D) is carried out at a pulse frequency of 3-20 cpm, a pressure of hydrocarbon gas in the reaction chamber of not more than 1 atm and a saturation duration of from 50 to 300 hours.

In private embodiments of the invention, the mixture in step (A) is obtained by mixing particles of natural graphite with a particle size of at least 0.2 mm, coke and a binder with a particle size of not more than 0.4 mm for 1-3 hours.

Natural graphite is used as graphite in stage (A).

In the best embodiments of the invention at stage (A), the mixture is obtained in the following ratio of components, mass. %:

Graphite 15.0-80.0 Coke 3.0-40.0 Binder rest

To the mixture at the stage (A) can be additionally introduced carbon fibers in an amount up to 15.0 mass. %

In the mixture at the stage (A), a pore former in an amount of up to 20.0 masses can be added. %

The formation of the workpiece in stage (B) can be carried out to a density of from 1.0 to 1.5 g / cm ³ by pressing.

Pressing in this case, as a rule, is carried out in a blank matrix at a temperature not exceeding 80 ° C and a pressure not exceeding 1000 kg / cm ² .

Firing at stage (B) is carried out until an open porosity of at least 90% of the total porosity is obtained.

The firing in stage (B) is carried out at 1000-1100 ° C in an inert medium with a heating rate of not more than 100 ° C / hour.

After gas-phase pyrolytic saturation of the workpiece at the stage (D) carry out mechanical processing.

DETAILED DESCRIPTION OF THE INVENTION

The main idea of the present invention is to carry out a method of manufacturing a material for sliding electrical contacts in such a way as to achieve its high wear resistance and electrical conductivity by gas-phase pyrolytic sealing by combined thermogradient and pulsed methods of gas-phase saturation.

For this, a number of preliminary operations are carried out: (A) obtaining a mixture based on graphite, coke and a binder, where the graphite content is at least 15% of the mass of the mixture and (B) forming a billet from the mixture and (C) firing the billet to obtain a porous billet with open porosity.

Next comes stage (D) - gas-phase thermogradient saturation of the preform from stage (B) with pyrolytic carbon in the reaction chamber by pulsed supply of hydrocarbon gas and its decomposition with the formation of pyrolytic carbon on the surface of open pores in the moving pyrolysis zone.

The movement of the pyrolysis zone is created by maintaining the temperature of one of the walls of the billet in the range of decomposition temperatures of the said hydrocarbon gas and increasing the temperature of the opposite wall of the preform from the ambient temperature at the beginning of the gas-phase thermogradient saturation to the decomposition temperatures of the said hydrocarbon gas at the end of the gas-phase thermogradient saturation at a speed of 1 , 0-10.0 ° C / hour.

Such a gas-phase thermogradient saturation provides the most complete filling of open pores throughout the volume of the workpiece with the exception, essentially, the effect of "bottleneck". The decomposition of gaseous hydrocarbon in the material occurs only in the space between the hot wall and the moving zone of thermal decomposition (pyrolysis). In this case, in the pores, the entrance to which is closer to the opposite wall in comparison with the “bottom” of the pore, filling with pyrolytic carbon will begin from the “bottom” of the pore. Thus, as the hydrocarbon decomposition zone advances toward the entrance to the pore (“bottleneck”), the pore will be filled with pyrolytic carbon. The entrance to the pore (“bottleneck”) will be filled with pyrolytic carbon last after filling the entire pore with pyrolytic carbon, because the hydrocarbon decomposition zone will reach the entrance to the pore after passing through the entire pore. Therefore, at least half of the open pores will be completely filled with pyrolytic carbon. In known technical solutions, as a rule, the pores are filled by one quarter.

It is also significant that hydrocarbon gas enters the reactor by pulses, i.e. alternating gas supply and its subsequent pumping. Compared to pyrolysis carried out in a stationary process at constant pressure, with a pulsed gas supply, the pyrolysis rate increases. This is due to the fact that in a stationary process, as the pyrolysis occurs, the concentration of hydrocarbon gas at the pore walls decreases, and the concentration of hydrogen increases. Accordingly, the pyrolysis process slows down, and the removal of hydrogen occurs due to natural diffusion.

In a pulsed mode, a hydrocarbon gas without hydrogen is constantly supplied to the pyrolysis zone, and gas with hydrogen is removed artificially during pumping. This leads to the fact that the pyrolysis rate in the pulsed mode is constantly maintained at the initial one, i.e. the maximum level characteristic of the initial stage of pyrolysis in a stationary mode.

The pulse mode is as follows. The gas supply device consists of inlet and outlet valves. The inlet valve delivers gas to the displacement at a predetermined frequency. The exhaust valve exits gas from the working volume to the gas pumping system. Both valves operate at the same frequency in antiphase (when one valve is open, the other is closed and vice versa).

The parameters for the supply of gas pulses are selected each time from the operating conditions of the reactors in which the gas-phase thermogradient saturation is carried out. Optimal for carrying out the process in some embodiments of the invention is a pulse frequency of 3-20 pulses / min, although the process can go at other frequencies.

The pressure of the hydrocarbon gas in the reaction chamber at stage (D) can also be maintained in a wide range, however, the capabilities of the installation in which the claimed method was carried out make it possible to maintain a pressure in the reaction chamber of not more than 1 atm, while a saturation duration of 50 to 300 is realized hours.

These parameters are determined, to a greater extent, by the capabilities of reactors for conducting gas-phase saturation than the properties obtained with these parameters.

When conducting preliminary operations (stages A, B and C), it is essential to obtain a mixture at stage (A) containing graphite, coke and a binder, while the graphite content, as follows from the formula, should be at least 15% of the mass, and the coke and binder content can vary widely. This graphite content is selected based on the fact that at these values the required level of electrical resistance and self-lubricating properties, as well as high arc resistance, are achieved. The specific ranges of binder and coke content from the point of view of achieving these properties are not significant, since during firing in stage (B), residual coke is formed from the binder.

As a binder, any pitch can be used - coal or oil, tar, bakelite varnish, etc.

However, for some embodiments of the invention, the composition of the charge is essential. The most optimal composition of the mixture contains these components in the following ratio, mass. %: graphite 15.0-80.0, coke 3.0-40.0 and a binder - the rest. Such a composition of the charge allows to obtain not only an arc-resistant material with the required level of electrical resistance and self-lubricating properties, but also with improved strength, which is affected by the residual coke formed during the firing process.

In private embodiments of the invention, the mixture in step (A) is obtained by mixing particles of natural graphite with a particle size of at least 0.2 mm - when using particles of a smaller size, in some cases, the electrical resistance of the material can increase.

The particle size of the coke and the binder, it is desirable that were not more than 0.4 mm With this size, the spread of hardness over the volume of the material can be reduced.

The mixing time is selected taking into account many conditions - the mass of the mixed components, the size of their particles and the achievement of complete uniformity of the mixture.

The best view for the charge is natural graphite. This is due to a higher level of properties, which were discussed above than, for example, for artificial graphite, as well as the fact that graphite particles have a scaly shape. This form allows you to provide thermal and electrical conductivity in the necessary directions.

To the mixture at the stage (A) can be additionally introduced carbon fibers in an amount up to 15.0 mass. % Fibers serve as a reinforcing element and can increase the strength of the material. If you enter the fiber in an amount of more than 15 mass. %, all material properties, including strength, may decrease.

In the mixture at the stage (A), a pore former in an amount of up to 20.0 masses can be additionally introduced. %, which will facilitate the formation of through pores and increase their share, accelerating the process of pyrolytic saturation. As a blowing agent, for example, wood flour can be used.

The formation of the workpiece in stage (B) can be carried out to a density of from 1.0 to 1.5 g / cm ³ by pressing. These densities are optimal for the implementation of the pyrolytic gas-phase compaction process, although the process can go beyond these limits.

Pressing in this case, as a rule, is carried out in a blank matrix at a temperature not exceeding 80 ° C and a pressure not exceeding 1000 kg / cm ² . A competent specialist should understand that the workpiece can be obtained by other methods of pressure treatment, for example, extrusion, etc.

Firing at stage (B) is carried out until an open porosity of at least 90% of the total porosity is obtained. These data are estimated and obtained by calculation, for example, when measuring gas permeability.

Such data on open porosity were obtained after firing at stage (B) at 1000-1100 ° C in an inert medium with a heating rate of not more than 100 ° C / hour. The specialist should be clear that the firing conditions can be changed to obtain the same declared technical result. For example, the firing temperature can be reduced, but its duration can be increased, or, conversely, the firing temperature can be increased, but its duration can be reduced, etc.

After gas-phase pyrolytic saturation of the preform at stage (D), it is possible to carry out mechanical processing to bring the material to the required geometric dimensions ..

Thus obtained material for sliding electrical contacts, which contains graphite, pyrolytic carbon and coke with a graphite content of at least 15 mass. %, has a hardness on the outer surface of at least 55 HS, hardness at a depth equal to half the thickness of the material, measured by the layered method, at least 40 HS.

In particular embodiments, as discussed above, the material may contain components in the following ratio, mass. %:

Graphite 15.0-60.0 Coke 1,5-35,0 Pyrolytic carbon 10.0-60.0 Coke residue rest

An example implementation of the invention.

A mixture was prepared from particles of natural graphite with a particle size of 200 microns according to GOST 5420-74, a binder (coal tar pitch grade B according to GOST 1038-75) with a particle size of up to 400 microns, wood flour and electrode coke according to GOST 3213-91 with a size particles up to 400 microns.

The composition of the mixture are shown in table 1.

All components were mixed in a closed rotating drum for 2 hours at a rotation speed of 60 rpm.

Then, by pressing in a blank steel matrix at a temperature of 60 ° C, a preform was formed with a force of 900 kg / cm ² , after which firing was performed at 1000-1100 ° C for 0.5-1.5 hours. Heating to the firing temperature was carried out at a rate of 50 ° C / h. Porous preforms were obtained in which the number of open pores was at least 90% of the number of all pores.

Then, gas-phase thermogradient saturation of the blank with open pores was carried out. For this, the preform was placed in a reactor. After placing the billet in the reactor, a vacuum was created in it (pressure 10 ^-3 mm Hg), then one of its walls was heated to a temperature of 1180 ± 10 ° C, heat from the reactor was transferred to the adjacent wall of the billet and the wall was heated to the same temperature. The temperature of the opposite wall of the reactor and the adjacent opposite wall of the workpiece at the beginning of the process corresponded to the ambient temperature.

After heating and creating a vacuum, a pulsed methane gas supply system was switched on to the reactor with a frequency of 10 cpm. The gas flow rate was selected in such a way as to provide a maximum pressure in the reactor of 0.5 atm.

After methane was fed into the reactor, heating of the opposite wall began at a rate of 8 ° C / h. Heating at this rate to a temperature of 1180 ± 10 ° C was carried out for 130 hours. Then the process was stopped and the workpiece was cooled with the furnace. After cooling to a temperature of not more than 150 ° C, a sample of the material was removed from the furnace.

As follows from the presented data, the invention allows to obtain material for sliding electrical contacts with improved performance characteristics: hardness on the outer surface of at least 36 HS, hardness at a depth equal to half the thickness of the material, measured by the layered method, at least 30 HS, Electrical resistivity, 4-17 μOhm⋅m, volume loss in an electric arc, (2.3 kA, 0.5 s) 3-49 mm ³ and density 1.33-1.8 g / cm ³ .

¹ Artificial graphite

Claims (17)

1. A method of manufacturing a material for sliding electrical contacts, characterized in that it includes the following steps: (A) obtaining a mixture based on graphite, coke and a coke-forming binder, where the graphite content is at least 15% by weight of the mixture; (B) the formation of the billet from the charge; (B) firing the preform to form residual coke from the binder to form a porous preform with open porosity; (D) gas-phase thermogradient saturation of the preform from step (B) with pyrolytic carbon in the reaction chamber by pulsed supply of hydrocarbon gas, its decomposition with the formation of pyrolytic carbon on the surface of open pores in the moving pyrolysis zone and its subsequent pumping out, where the moving pyrolysis zone is created by maintaining the temperature one of the walls of the said preform in the temperature range of decomposition of the aforementioned hydrocarbon gas and the temperature increase of the opposite wall of the preform from the temperature tours environment early in the process of gas-phase thermogradient saturation before decomposition temperature of said hydrocarbon gas saturation at the end of the gas-phase process at a rate thermogradient 1,0-10,0 ° C / hour. 2. The method according to p. 1, characterized in that the gas-phase thermogradient saturation of the preform at stage (D) is carried out at a pulse frequency of 3-20 cpm, a pressure of hydrocarbon gas in the reaction chamber of not more than 1 atm and a saturation duration of from 50 to 300 hours . 3. The method according to p. 1, characterized in that the mixture in stage (A) is obtained by mixing particles of natural graphite with a particle size of at least 0.2 mm, coke and a binder with a particle size of not more than 0.4 mm for 1 -3 hours. 4. The method according to p. 1, characterized in that natural graphite is used as graphite in stage (A). 5. The method according to p. 3, characterized in that at stage (A) the mixture is obtained in the following ratio of components, mass. %: Graphite 15.0-80.0 Coke 3.0-40.0 Binder Rest 6. The method according to p. 1, characterized in that the mixture at the stage (A) is additionally introduced carbon fibers in an amount of up to 15 mass. % 7. The method according to p. 1, characterized in that the mixture at the stage (A) is additionally introduced with a pore former in an amount of up to 20 mass. % 8. The method according to p. 1, characterized in that the formation of the workpiece in stage (B) is carried out to a density of from 1.0 to 1.5 g / cm ³ by pressing. 9. The method according to p. 7, characterized in that the pressing is carried out in a blank matrix at a temperature not exceeding 80 ° C and a pressure not exceeding 1000 kg / cm ² . 10. The method according to p. 1, characterized in that the firing at the stage (B) is carried out until an open porosity of at least 90% of the total porosity is obtained. 11. The method according to p. 9, characterized in that the firing in stage (B) is carried out at 1000-1100 ° C in an inert medium with a heating rate of not more than 100 ° C / hour. 12. The method according to p. 1, characterized in that after gas-phase pyrolytic saturation of the workpiece at the stage (D) carry out mechanical processing.