RU2769344C1 - Material for arc-quenching and breaking electrical contacts based on copper and method of its production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy, particularly, to production of graphite-copper electrocontact materials which can be used for production of working layer of high-precision bilayer electric contacts. To produce material for arc-quenching and breaking electric contacts, initial mixture is prepared, obtained charge is subjected to pressure, sintered and cooled. Initial charge contains, wt.%: 1.0–2.0 of activated carbon with particle size less than 1.0 mcm and specific surface area of 1,000 m²/g, 1.5–2.0 of Fe-Cu nanopowder of pseudoalloy with particle size of not more than 0.1 mcm, the rest is copper powder PMS-1, is subjected to two-stage pressure treatment by rolling and sintering in hydrogen atmosphere with isothermal holding and subsequent cooling in the same atmosphere together with the furnace at each stage.

EFFECT: invention enables to obtain material with low electrical resistance, high hardness and plasticity, high electrical erosion resistance.

2 cl, 1 tbl

Description

The invention relates to the field of powder metallurgy, in particular to the production of graphite-copper electrical contact materials that can be used to manufacture the working layer of high-current bilayer electrical contacts.

The creation of electrical materials is associated with the difficulties of combining such properties in them as high electrical conductivity and strength, refractoriness, and corrosion resistance. At the same time, the materials of discontinuous contacts must be heat- and electrically conductive, erosion-resistant when exposed to an electric arc, and not be welded during operation. Obtaining materials with such almost mutually exclusive properties without the use of precious metals is a very difficult task. In this regard, the development of new materials for high-current contactors is an urgent problem of modern materials science.

Known powder material based on copper for serial discontinuous electrical contacts MG-3 (Libenson G.A. Production of sintered products. M. Metallurgy, 1982. 256 s), having a composition, wt. %: graphite - 3, copper - 97.

The disadvantages of this material are: low hardness 20-25 HB, high electroerosive wear (mass loss over 55 g/million cycles).

Also known is a method of manufacturing a material for arcing and discontinuous electrical contacts and material (RF patent No. 2522584, IPC H01H 1/025, H01H 1/027, H01H 1/04, C22C 30/02, op. 20.07.2014). The method includes mixing graphite particles clad with niobium carbide or chromium carbide with powders of copper or its alloys in the following ratio, wt. %: graphite particles 5-20, chromium carbide or niobium carbide 5-20, copper or copper-based alloy - the rest, and the ratio of the graphite content to the content of the said carbide is 0.9-1.1, molding from the resulting mixture of the workpiece by pressing under pressure to a density of at least 70% of the theoretical density and subsequent sintering of the workpiece by passing electric current pulses with a density of 100-300 A/mm ² with simultaneous uniaxial compression of the material. At the same time, the method is characterized in that the molding of the workpiece is carried out under a pressure of 100 to 200 MPa at room temperature, uniaxial compression during sintering is carried out under a pressure of 50-200 MPa by electrodes supplying current pulses. The material obtained by this method has a porosity not exceeding 5%.

The disadvantages of the known material are: low erosion resistance of the material; high complexity and multi-stage manufacturing; high electrical resistance of the contact material.

The closest in technical essence and the achieved result to the proposed solution is a mixture for the manufacture of material for high-current electrical contacts and a method for manufacturing the material (RF patent No. 2523156, IPC C22C 1/05 (2006.01), B22F 3/14 (2006.01), H01H 1/ 027 (2006.01), C22C 9/00 (2006.01, op. 20.07.2014).

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, wt. %: copper - 20-85, titanium hydride - 1-10, graphite - the rest. In this case, the particle size of graphite is 40-80 μm, and the particle size of copper and titanium hydride does not exceed 100 μm.

A method for manufacturing a material for high-current electrical contacts, including mixing particles of graphite, titanium hydride and copper in a given ratio to obtain a charge according to claim 1 and obtaining a material blank from the charge by sintering by passing electric current pulses with a density of 200-500A/mm2 with simultaneous uniaxial compression. At the same time, uniaxial compression during sintering is carried out under a pressure of 150-400 MPa by electrodes supplying current pulses.

The disadvantages of this method of manufacture and composition of the material are: low erosion resistance of the material; high complexity of its manufacture; injury risk of the necessary equipment; high electrical resistance of the contact material.

The proposed method is designed to obtain a powder composite material for the working layer of bilayer discontinuous high-current contacts.

The technical result of the invention is to obtain an electrocontact copper-based powder material with low electrical resistance, increased hardness and ductility, and high electrical erosion resistance.

The specified technical result is achieved by the fact that the proposed material for arcing and discontinuous electrical contacts based on copper contains wt. %: 1.0-2.0 activated carbon powder with a particle size of less than 1.0 μm (specific surface area - 1000 m ² /g), 1.5-2.0 Fe-Cu pseudoalloy nanopowder particle size not more than 0.1 microns, the rest - copper powder PMS - 1.

The specified technical result is achieved by the fact that in the method for manufacturing a material for arcing and breaking electrical contacts based on copper, including preparation of the initial charge, processing of the resulting mixture by pressure, sintering and cooling, according to the invention, the initial charge containing wt. %: 1.0-2.0 activated carbon with a particle size of less than 1 μm (specific surface - 1000 m ² /g), 1.5-2.0 Fe-Cu pseudoalloy nanopowder, particle size not more than 0.1 μm, the rest - copper powder PMS-1, is subjected to two-stage pressure treatment by rolling and sintering in a hydrogen atmosphere with isothermal holding and subsequent cooling in the same atmosphere together with the furnace at each stage, while at the initial stage rolling is carried out at a pressure of 300-350 MPa to a relative density 0.35-0.40, then heated to a temperature of 720-750°C and held for 30-40 minutes, and at the final stage rolling is carried out in rolls with box-type calibers to a relative density of 0.95-0.97, heated to a temperature of 900-950°C and maintained for 55-65 minutes.

The indicated signs characterizing the composition of the electrocontact powder material: the composition of the initial charge, dispersion and mass ratios of the incoming components are necessary to achieve the specified technical result, i.e. to obtain electrocontact powder material with low electrical resistance, increased hardness and high electrical erosion resistance.

The essence of these characteristics is as follows: - activated carbon powder with a specific surface area of 1000 m ² /g, particle size less than 1.0 μm, in the amount of 1.0-2.0 wt. % provides a double effect: it acts as an arc-extinguishing element and strengthens the matrix. The amount of activated carbon powder less than 1.0% reduces the erosion resistance of the composition, and the use of this powder more than 2.0%, in the absence of positive effects, significantly reduces the density of the electrical contact material, increases the electrical resistivity, reduces its plasticity and hardness. The particle size of activated carbon powder less than 1.0 μm allows at a concentration of 1.0-2.0 wt. % to ensure its distribution in any microvolume of the material and, therefore, to ensure that the arc arrow hits the activated carbon, extinguishing it;

- Fe-Cu pseudoalloy nanopowder in the amount of 1.5-2.0% was used as a precursor - sequentially precipitated Fe-Cu hydroxide, which was mixed with copper powder and reduced during sintering of the electrocontact material. As a result, Fe-Cu pseudo-alloy nanopowder is a nano-sized (no more than 0.1 μm) reinforcing matrix element that increases the hardness of the electrocontact material. The concentration of the pseudoalloy is important: when the Fe-Cu nanopowder concentration of the pseudoalloy is less than 1.5%, the hardness of the electrocontact material drops by more than 30%, and the presence of a pseudoalloy of more than 2.0% leads to a significant increase in the electrical resistance of the electrocontact material.

These features characterizing the method of manufacturing a material for arcing and discontinuous electrical contacts based on copper, characterizing the type, the force of the initial pressure treatment by rolling the initial charge, as well as the conditions for the primary sintering of the compacted material, the final pressure treatment for compacting the material by rolling in rolls with box calibers type and re-sintering are necessary to achieve the specified technical result, ie. to obtain an electrical contact material with increased electrical conductivity and high erosion resistance, improved mechanical characteristics.

The essence of the proposed method is as follows:

- processing of the initial powder mixture by rolling at a pressure of 300-350 MPa ensures the formation of an electrocontact powder material with a relative density of 0.35-0.40, which allows the reduction of oxides on the surface of copper powder particles and the addition of Fe-Cu hydroxide to a metal pseudo-alloy during the primary sintering process ;

- rolling at a pressure of less than 300 MPa does not guarantee sufficient mechanical strength of the molding when handling it before sintering, and rolling with a force of more than 350 MPa does not provide the specified parameters for the relative molding density;

- heating at the initial stage to a temperature of 720-750°C in a hydrogen atmosphere and holding for 30-40 min ensures the reduction of copper oxides and Fe-Cu hydroxide to a pseudo-alloy, the mechanical strength of the compact for further processing. Heating below 720°C does not guarantee sufficient mechanical properties of the electrocontact material, and heating above 750°C significantly complicates the compaction process during secondary rolling;

- rolling in rolls with box-type calibers provides non-destructive processing of the compact and leads to the production of electrocontact material with a relative density of 0.95-0.97. Compaction of the compact in rolls with a smooth barrel leads to its brittle fracture, and processing in a closed deformation zone created by four drive rolls greatly complicates and increases the cost of the process (RF patent No. 2529605).

- heating at the final stage to a temperature of 900-950°C and keeping the workpiece for 55-65 minutes in a hydrogen atmosphere, followed by cooling in the same atmosphere together with the furnace, results in a material with desired mechanical properties, high electrical conductivity and erosion resistance. Heating below 900°C and holding time less than 55 min does not provide compaction of the workpiece, and heating above 950°C and at

holding for more than 65 min is impractical because the characteristics of the material do not differ from those obtained at 900°C. An example of a specific implementation.

Experimental verification of the proposed electrocontact powder material based on copper and the method of its production was carried out in laboratory conditions at the Institute of Metallurgy of the Ural Branch of the Russian Academy of Sciences using the following technology:

Activated carbon powder grade VNIITU SB RAS with particle size < 1 μm and specific surface area - 1000 m2/g in the amount of 1.0-2.0 wt. %, nanopowder (≤0.1 μm) Fe-Cu pseudo-alloy in the amount of 1.5-2.0 wt. %, the rest copper powder MPS-1 with a size of <70 μm was mixed in a vibro-aeration mixer for 3 min, then the resulting mixture was placed in the feed hopper of the laboratory rolling mill MLS-82 IMET Ural Branch of the Russian Academy of Sciences and rolled at a pressure of 300-350 MPa to a relative density 0.35 -0.40. The strip thus obtained was placed in a chamber electric furnace with a hydrogen atmosphere and heated at a rate of 5 deg/min to a temperature of 720–750°C, then it was isothermally held at this temperature for 15–20 min and cooled in the same atmosphere together with the furnace. The resulting billet of electrocontact powder material was rolled in rolls with box calibers to a relative density of 0.95-0.97 and re-heated in the same furnace with a hydrogen atmosphere, but at a temperature of 900-950°C with an isothermal 55-65 min, followed by cooling together with oven. The results of the exposure experiment are shown in the table.

As can be seen from the table, samples No. 1, 2, 3 are made within the claimed processing modes and, as a result, meet all the requirements for the proposed material (electrical, mechanical and erosion).

When performing 4 samples during the first rolling, the pressure was below the lower limit and, as a result, the mechanical strength of the sample is so low that it collapsed at the outlet of the mill.

Samples 5 and 6 also do not meet the specified requirements for the material due to the fact that the amount of activated carbon does not meet the specified parameters. In sample 5, the coal is less than required, as a result of which the arc, falling into copper, burns longer, which increases erosive wear. Sample 6 contains more coal than required, which leads to a deterioration in compaction during compaction, a decrease in the density of the material and its mechanical and electrical properties.

Samples 7 and 8 have deviations in the concentration of the Fe-Cu pseudo-alloy nanopowder, which led to a discrepancy in the quality of the electrical contact material. The content of Fe-Cu pseudo-alloy below the norm (sample 7), despite the good density of the material, sharply lowered its mechanical properties due to insufficient nanodispersed hardening. The Fe-Cu content of the pseudo-alloy is higher than the norm (sample 8), did not allow sufficient compaction of the material and increased its resistivity by a third.

Samples 9-12 have deviations from the heat treatment parameters. Insufficient and exceeding primary sintering temperatures led to the fact that in the first case, the sample was destroyed during re-rolling, and in the second case, it did not allow the material to be sufficiently compacted due to high deformation resistance.

The lower temperature during the secondary heat treatment sharply reduced the plastic properties of the material and limited the formation of contacts from it. The increased heat treatment temperature led to thermal softening of the material and its deformation in the furnace under its own weight.

Claims (3)

1. The material for arcing and discontinuous electrical contacts based on copper contains, wt. %: activated carbon powder with particle size less than 1.0 µm and a specific surface area of 1000 m ² /g 1.0-2.0 Fe-Cu pseudoalloy nanopowder with a particle size of not more than 0.1 microns 1.5-2.0 copper powder PMS-1 rest 2. A method of manufacturing a material for arcing and discontinuous electrical contacts based on copper, including preparing the initial mixture, processing the resulting charge by pressure, sintering and cooling, according to the invention, the initial charge containing, wt. %: 1.0-2.0 activated carbon with a particle size of less than 1.0 μm and a specific surface of 1000 m ² /g, 1.5-2.0 Fe-Cu pseudoalloy nanopowder with a particle size of not more than 0.1 μm, the rest - copper powder PMS-1, is subjected to two-stage pressure treatment by rolling and sintering in a hydrogen atmosphere with isothermal holding and subsequent cooling in the same atmosphere together with the furnace at each stage, while at the initial stage rolling is carried out at a pressure of 300-350 MPa up to relative density of 0.35-0.40, then heated to a temperature of 720-750°C and held for 30-40 minutes, and at the final stage, rolling is carried out in rolls with box-type calibers to a relative density of 0.95-0.97 , heated to a temperature of 900-950°C and maintained for 55-65 minutes.