RU2380781C1 - Material for electric contacts and method for manufacturing of electric contacts - Google Patents

Abstract

FIELD: electric engineering.

SUBSTANCE: invention may be used in electromechanical relays, for alarm, interlocking and blocking devices (AIB devices) at railway transport, which require high reliability and long lasting operation of contacts, namely more than million of closing and opening cycles of electric contacts. Material has graphite base arranged with porosity of not more than 20 vol. %, and metal additions distributed in volume of base, discretely and unevenly, concentration of additives is maximum in surface layers and reduces down to zero deep into base. Initially contact stock is made of graphite, by method of dimensional processing, then using one of physical or chemical methods of metal depositing, metal additives are added to base, and afterwards, in case solid layer forms on surface intended for contact with response contact, method of dimensional processing is used to remove this layer.

EFFECT: development of material for electric contacts, which is not disposed to welding of contacts in process of the whole period of contacts operation and having stable parametres of transition resistance in period of contacts running-in with simultaneous increase of contacts operational resource.

2 cl, 1 tbl, 3 ex

Description

The invention relates to electrical engineering, mainly to materials used for the manufacture of electrical contacts of low-voltage equipment. They can be used in electromechanical relays, for signaling, centralization and blocking devices (signaling devices) in railway transport, which require high reliability and a long service life, more than a million cycles of closing and opening of electrical contacts. A distinctive feature of the operating conditions of low-voltage equipment is the presence of shock loads and large switching currents when the contacts are closed.

The materials from which electrical contacts are made must have a set of properties. So, the contact surfaces of the material that come into contact with the response contacts should have high oxidation and electrical erosion resistance in the state of contact closure and opening, a slight tendency to weld with response contacts, good thermal conductivity and electrical conductivity with high stability of the transition resistance in the closed state of the contacts.

These tough and contradictory requirements can only be satisfied by creating composite materials. So, high electrical and electrical discharge properties are achieved by creating composite materials based on graphite with the addition of copper, nickel, cobalt, aluminum, silver in various proportions. (Powder metallurgy. Materials, technology, properties, applications: Handbook / Ed. I.M. Fedorchenko. - Kiev: Naukova Dumka, 1985, p. 422).

Known material for the manufacture of electrical contacts, containing 3-10 wt.% Graphite and silver the rest (P. RF No. 2110100, publ. 1998).

Also known material for electrical contacts, adopted for the prototype, containing 38-44 wt.% The rest of the graphite (TU 16-538.158-72.4).

A disadvantage of the known materials is a high tendency to weld, especially during the running-in period of the contacts, when the contact spot has not yet formed. During this period, the readings of the transition resistance are also unstable.

The task of the invention is to increase the service life of electrical contacts.

The technical result achieved in the process of solving the problem lies in eliminating the welding of contacts, ensuring the stability of the readings of the transition resistance during the running-in period of the contacts.

The specified technical result is achieved by the claimed material for the manufacture of contacts containing a graphite base and metal additives, while the graphic base is made with a porosity of not more than 20 vol.%, And metal additives are distributed in the volume of the graphite base discretely and unevenly in concentration from the maximum in the surface layers decreasing to zero deep into the basics.

Using the claimed invention, the technical problem of obtaining a material that is not inclined to weld contacts during the entire period of operation of the contacts, having stable readings of the transition resistance during the running-in period of the contacts with a simultaneous increase in the service life of the contacts, is solved.

For the manufacture of the inventive material, a method is proposed, the prior art of which is known from a method in which contact materials are made by sintering. Contacts are made from sintered billets of the required sizes and shapes (p. 191-192. G. A. Libenson. Production of powder products. - M.: Metallurgy. 1980.-240).

The disadvantage of this method lies in the complexity of technological methods of sintering and the inability to obtain a material with a discrete and uneven distribution of concentration from the surface into the depths of the base.

This disadvantage is eliminated by the claimed method, which consists in the preliminary manufacture of the contact blank by dimensional processing from graphite. Then, using one of the physical or chemical methods of metal deposition, metal additives are introduced into the base, and then, in the case of the formation of a continuous (non-discrete) layer on the surface intended for contacting with the return contact, this layer is removed by the dimensional processing method.

New, not found in the analysis of scientific, technical and patent literature, in the claimed invention is that the material for electrical contacts, containing graphite as a base, before the addition of metallic additives of silver and / or another metal, and / or their composition has a porosity not more than 20 vol.%. Metal additives distributed in the volume of the base discretely and unevenly have a maximum concentration in the surface layers and decrease from the surface deep into the base to zero. And in the method for producing it initially from graphite having a porosity of not more than 20 vol.%, A contact blank is made by the method of dimensional processing. Then, using one of the physical or chemical methods of metal deposition, metal additives are introduced into the base. In the case of the formation of a continuous layer on the surface intended for contacting with the reciprocal contact, a continuous layer is removed by the method of dimensional processing.

The proposed material for electrical contacts and the method of its manufacture have an inventive step, since for a specialist neither the material nor the method of its manufacture explicitly follow from the prior art. A detailed study of the wear mechanisms during contact failure according to available publications (see Myshkin N.K. et al. Electrical Contacts. Intellect Publishing House) and the studies conducted by the authors made it possible to formulate requirements for the properties of the base material and its surface. Thus, the presence of porosity in the surface layer and the base of a material consisting of graphite does not contribute to the formation of volumes of molten metal at the contact points of contact when it is closed and opened, i.e. welding of contacts during the entire period of operation of the contacts does not occur. The authors found that in composite materials based on graphite, the maximum concentration of metals and their compounds in the surface layer is necessary only in the initial period of running in of contacts, this is about a tenth of the entire period of work of contacts. The pores present in the base material allows the metal additive to be introduced discretely and unevenly in concentration from the maximum on the surface and decreasing to zero deep into the base.

The presence of a high content of metal additives in the surface layer contributes to the rapid formation of an optimal contact spot, and the presence of porosity does not contribute to the accumulation of wear products, which include the formed oxides of the introduced metals, and the formation of a non-conductive layer leading to a violation of the conductivity of the contacts.

It was established that the optimal porosity for a graphite base should be within no more than 20% of the volume. If, when metallic additives are added to the substrate, a continuous layer forms on the surface intended for contact with the return contact, it should be removed. The presence of a continuous layer on the surface leads to the welding of contacts and a sharp increase in the transition contact resistance.

In addition, the inventive material for electrical contacts based on graphite and the method of its manufacture provides an additional result, which consists in reducing the cost of manufacturing an electrical contact due to a significant reduction in the content of expensive metal in case of its use.

For the practical implementation of the inventive material for electrical contacts and the method of its manufacture, MPG-6 structural graphite was used as the base material, having a volume porosity of less than 18%, silver and copper and their alloy composition containing 30 wt.% As metal additives , silver - the rest is copper. The introduction of metal additives into the base was carried out by the ion-plasma method. Dimensional processing was carried out by turning and milling, removing a continuous layer from the contact surface by grinding. The presence of a continuous surface layer on the surface was monitored using an instrumental microscope.

The material (prototype) for electrical contacts based on graphite containing 40 wt.% Silver, the rest is carbon, is currently used in production. They took finished products.

EXAMPLE 1. Of the synthetic graphite of the brand, for example, MPG-6, having a porosity of 18%, contacts similar to the prototype were made, silver was introduced into the base by the ion-plasma method, the contact surface was not further processed, because there was no continuous layer on the surface, contact parts were mounted on contact springs, installed in a relay of the NMSh1 type and tested. The test results are presented in the table.

EXAMPLE 2. Analogously to example 1, the contacts were prepared, copper was added to the base, the contact surface was ground

EXAMPLE 3. Analogously to example 1, contacts were prepared, a silver-nickel metal composition was added to the base, and the contact surface was not ground.

Their tables show that the proposed material for electrical contacts and the method of manufacturing electrical contacts can almost halve the transitional electrical resistance in the initial period of running-in of contacts, more than 2 times increase the service life of contacts, eliminate weldability of contacts throughout the entire life of the contacts, which will provide a significant effect.

Claims (2)

1. A material for electrical contacts containing graphite and metal additives, characterized in that the graphite base is made with a porosity of not more than 20 vol.%, And metal additives are distributed in the base volume discretely and unevenly in concentration, from the maximum in the surface layers and decreases to scratch deep into the basics. 2. A method of manufacturing electrical contacts based on graphite and metal additives, which consists in obtaining blanks by dimensional processing, characterized in that one of the physical or chemical methods of deposition of metals is based on metal additives, and in the case of the formation of a continuous layer on the surface intended for contacting with the reciprocal contact, the method of dimensional processing removes this layer.