RU2523156C1 - Charge for production of material for high-current contacts and method of its production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed composition contains the following substances, in wt %: copper particles - 20-85, titanium hydride particles - 1-10, graphite particles making the rest. To make material billet, this charge is sintered by feeding electric current pulses there through, current density making 200-500 A/mm², with simultaneous single-axis reduction.

EFFECT: high-density material, required resistivity, reliable wetability of graphite particles by copper.

6 cl, 1 tbl

Description

The field of technology.

The invention relates to the production of electrical contact graphite-copper materials for high current electrical contacts by powder metallurgy methods, in particular to a charge and a method for producing material for these contacts from it.

The prior art.

Carbon-copper and copper-carbon materials are widely used in high-current (in the sense of high current density) sliding electrical contacts, such as a collector-brush assembly, a collector assembly of electrified vehicles, and hoisting-and-transport devices.

The main disadvantage of these materials is the lack of physico-chemical interaction between copper and carbon. Copper does not form carbides. The wetting angle of graphite with liquid copper is 140 ° at a temperature of 1100 ° C, i.e. copper does not wet or penetrate carbon.

It is known that alloying copper with metals of the IV-VI group of the periodic table reduces the contact angle of carbon wetting with copper to 40-0 °.

So, the addition of 1% wt. Cr reduces the contact angle to 40 °, and the addition of 10% Cr to copper reduces the contact angle to 20 ° at a temperature of 1200 ° C. The addition of 5% Ti to copper reduces the contact angle of graphite at 1200 ° С to almost 0 °, so that copper spontaneously spreads over graphite.

This approach to obtaining copper-graphite materials for electrical contacts is used in patent RU 2088682C1.

In accordance with one aspect of the invention according to patent RU 2088682, a mixture for producing a material may contain the following components, wt.%:

Graphite particles 10-60 At least one carbide metal of IV VI groups of the Periodic system 25-40 At least one metal selected from the group containing titanium, zirconium, hafnium and chromium 3,50-5,00 Copper Rest

A method of obtaining material from this charge involves mixing graphite particles clad with carbide of at least one metal of groups IV-VI of the periodic system with powders of copper or its alloys and powders of titanium, zirconium, hafnium and chromium, molding from a finished mixture of material by uniaxial pressing with a load of 5-25 MPa and sintering of the material in vacuum at a temperature of 1100 to 1600 ° C or in an atmosphere of protective gas (nitrogen or argon) at a temperature of 1350-1660 ° C.

However, it is rather difficult to prepare an alloy of the Cu-Ti-C system because of the high oxygen affinity for titanium. This leads to the departure of almost all titanium to slag during melting in an atmosphere of air. Titanium oxidation problems also exist in melting in vacuum furnaces. Typically, a ligature is first prepared in a vacuum furnace, which is then alloyed with molten copper in a vacuum furnace. The impregnation of carbon with a Cu-Ti melt should also be carried out in the absence of oxygen.

In the production of copper-graphite or graphite-copper material by powder metallurgy methods, the same problems remain. Sintering of a powder of a Cu-Ti alloy with graphite should also be carried out in a protective atmosphere or in vacuum in the absence of oxygen. Sintering of copper is usually carried out at temperatures of 800-900 ° C, when copper does not melt. In the solid state, titanium may not have time to diffuse in a sufficient amount to the boundaries with carbon to form carbides.

If you make a mixture of powders of copper, titanium and carbon, then sintering such a mixture is also necessary in the absence of oxygen.

Disclosure of the invention.

The objective of the invention is to develop a simple method for the manufacture of graphite-copper material, in which copper reliably moistens graphite and is not collected in globules and does not sweat from graphite during melting.

The problem is solved by the mixture for the manufacture of material for high-current electrical contacts, which contains particles of copper, graphite and titanium hydride in the following ratio of components, wt.%:

Copper 20-85 Titanium hydride 1-10 Graphite rest

In private embodiments of the charge, the particle size of graphite is 40-80 microns, and the particle size of copper and hydride does not exceed 100 microns.

The problem is also solved by a method of manufacturing a material for high-current electrical contacts, in accordance with which particles of graphite, titanium hydride and copper are mixed in a predetermined ratio to obtain the above mixture, the material is prepared from the mixture by sintering the material by passing electric current pulses with a density of 200-500 A / mm ² with simultaneous uniaxial compression of the material.

In other embodiments of the invention, uniaxial compression during sintering is carried out under a pressure of 150-600 MPa.

In this case, uniaxial compression during sintering is possible with electrodes supplying current pulses.

The essence of the proposed technical solution is as follows.

The mixture is made in the form of a mixture of powders of natural graphite, titanium hydride and copper. The content of the components is selected from the following considerations.

The content of titanium hydride in the mixture should be from 1 to 10% wt. It is calculated depending on the amount of copper so that titanium hydride provides reliable wettability of copper, which is ensured by the declared redistribution of its content. When going beyond the claimed limits of the content of titanium hydride in the charge, when the content is less than 1%, reliable copper wetting with graphite is not provided, when the content is more than 10%, the electrical resistivity of the material increases

The claimed content of copper in the charge together with the declared content of titanium hydride provide the necessary electrical resistivity and self-lubricating properties of the material. When going beyond the declared limits of the content in the copper mixture, the following occurs: when the copper content is lower than 20%, the electrical resistivity increases, when the copper content exceeds 85%, the self-lubricating properties of the material decrease.

For some embodiments of the invention, the sizes of flakes of natural graphite and powders of copper and titanium hydride are regulated.

The size of flakes of natural graphite is from 40 to 80 microns. The particle sizes of copper and titanium hydride should not exceed 100 microns. With this limitation of the size of the powder provides the necessary density during sintering and pressing.

The method of obtaining the material is carried out in accordance with the following.

A mixture of graphite particles with titanium hydride and copper is prepared.

To create reliable contact between titanium hydride and graphite, particles of graphite and titanium hydride are first mixed, and then copper powder is added and the final mixture is prepared.

Such a mixture can be sintered by the electric pulse method with simultaneous uniaxial compression in an air atmosphere.

Titanium hydride begins to decompose at a temperature of 400 ° C. At temperatures of 800-1200 ° C, which usually develop during sintering by passing electric current pulses with a density of 200-500 A / mm ² with simultaneous uniaxial compression under a pressure of 150-400 MPa, titanium hydride decomposes almost completely.

The released hydrogen creates a reducing atmosphere for a short period, reducing copper oxides and preventing titanium from oxidizing. If titanium does not oxidize, then it forms carbides on the surface of graphite, significantly improving the interaction of copper with carbon, while copper reliably moistens graphite.

When going beyond the claimed intervals of the current density, at a value of less than 200 A / mm ^2, copper may not melt and spread over graphite, and at a value of more than 500 A / mm ² , the electrodes may melt or burn out.

The invention can be illustrated by the following specific example. The material was made according to the following technology:

1. In a predetermined ratio, graphite with a particle size of 40-80 μm and TiH ₂ with a particle size of 50 to 100 μm was mixed in a drunk barrel mixer at a speed of 30 rpm for an hour.

2. Copper particles with a size of 50 to 100 μm were added to this mixture. The resulting mixture was mixed in a drunk barrel mixer at a speed of 30 rpm for an hour to obtain a charge.

3. The resulting mixture was placed in a matrix of insulating material. The matrix was a tube with not sealed ends.

4. Then, sintering was carried out using movable water-cooled copper electrodes with a diameter of 12-0.05 mm, simultaneously acting as punches. Between the electrodes and the molded billet, 0.1 mm thick tungsten plates were placed. Punched electrodes were pressed against the ends of the formed workpiece with a pressure of 150-400 MPa. An electric current with a density of 200-500 A / mm ^{2 was} passed between the electrodes for 2 s.

As a result, samples of material were obtained with dimensions: 5–8 mm high, 12 mm in diameter, from which samples were made by machining to measure density, electrical resistance, and Brinell hardness.

As our experience shows, the compressive strength of a composite material obtained from a mixture of powders of Cu-C-TiH _{2 by} electropulse sintering is 200 MPa, which is approximately 2-3 times higher than the compressive strength of a composite material obtained from a mixture of powders of Cu- C-Ti electropulse sintering, and 4-5 times higher than the tensile strength of similarly obtained material from a mixture of Cu-C.

Table 1 shows the compositions of the charge of the material and the parameters for producing this material, as well as the properties of these compositions.

As follows from the presented data, the invention allows to obtain a material manufactured by a simplified technology without the use of vacuum or protective atmospheres, the porosity of which is 1-5%, in which copper reliably moistens graphite particles, its electrical resistivity is from 0.2 to 0, 6 μOhm.m, and the strength properties of the material make it possible to use it for the production of high-current electrical contact products.

Composition number The composition of the charge, wt.% Particle size, microns The parameters of the method of obtaining the material Properties of the resulting material Hydride tee
that
on Me
q Graphite Guide
reed tita
on Copper Gras
fit Raft
current spec
NII, A / mm ² Uniaxial pressure
Mr. formova
research and sintering Raft
the value of the material, g / cm ³ Udel
electronic
riches
some copro
tivle
μm Coefficient of friction for copper Limit
news on soot
tie, MPa one. 1,5 twenty rest 50-100 50-100 40-80 200 200 2.62 1,2 0.15 120 2. four 40 80-100 80-100 40-80 400 300 3.25 0.3 0.22 180 3. 1,0 thirty 50-100 50-100 40-80 300 250 2.86 0.4 0.18 160 four. 10 85 60-100 60-100 40-80 500 400 7.19 0.09 0.33 250

Claims (6)

1. The mixture for the manufacture of material for high current electrical contacts, characterized in that it contains particles of copper, graphite and titanium hydride in the following ratio of components, wt.%:
copper 20-85 titanium hydride 1-10 graphite rest 2. The mixture according to claim 1, characterized in that the particle size of graphite is 40-80 microns. 3. The mixture according to claim 1, characterized in that the particle size of copper and titanium hydride does not exceed 100 microns. 4. A method of manufacturing a material for high-current electrical contacts, comprising mixing particles of graphite, titanium hydride and copper in a predetermined ratio to obtain a charge according to claim 1 and obtaining a billet of material from the mixture by sintering by transmitting electric current pulses with a density of 200-500 A / mm ² s simultaneous uniaxial compression. 5. The method according to claim 4, in which uniaxial compression during sintering is carried out under a pressure of 150-400 MPa. 6. The method according to claim 4, in which uniaxial compression during sintering is carried out by electrodes supplying current pulses.