RU2229752C1 - Laminated electric contact - Google Patents

Abstract

FIELD: low-voltage switching devices. SUBSTANCE: laminated electric contact has silver-containing effective layer and copper or copper alloy auxiliary layer; open surface of auxiliary layer is embossed in the form of semi-spheres. Embossed semi-sphere diameter ranges between 0.5 and 1.0 mm. There are three such embossed semi-spheres. Introduction of embossed semi-spheres makes it possible to attain high current density at contacting points and complete fusion of semi-sphere material. EFFECT: enhanced reliability of contact welding to contact holder. 1 cl, 3 dwg, 2 ex

Description

Layered electrical contact refers to the technique of creating electrical contacts for low-voltage switching equipment.

Known layered electrical contact with the working layer of a material based on silver and a technological layer of copper or its alloys [1]. The technological layer in the contact serves to ensure a solid connection of contacts with contact holders of switching devices by spot welding or soldering.

The patent does not indicate the presence of a relief on the technological layer, but from the description it follows that the contacts are cut out of the rolled strip and have a flat surface of the technological layer. Since the technological layer is made of copper or its alloys, this makes it difficult to weld the contacts to the contact holders, since with a large contact surface of the parts to be welded, a large current is required, which destroys the silver-containing working layer. At low currents, the strength of the connection of parts is not ensured.

Contacts with a flat technological layer can be soldered by laying pieces of solder cut from foil between the soldered parts. However, the described contact contains layers based on silver and copper, which in contact with each other melt at a temperature of 779 ° C [2], forming a eutectic melt and destroying the contact. This speeds up and increases the cost of the brazing technology, which is already more laborious compared to welding, since it requires the use of special medium-melting, usually silver-containing solders (for example, PSr40 according to GOST 19738) and fluxes.

Thus, the disadvantage of the known layered contact is its unsuitability for fastening to the contact holders of switching devices by spot welding.

Closest to the proposed invention is a contact made of a bimetallic tape, the working layer of which is made of a composition of silver with base metal oxides, and a relief is applied to the technological layer in the form of longitudinal protrusions [3].

The relief on the technological layer reduces the contact surface of the contact with the contact holder. Accordingly, with a constant current in the welding pulse, the density of the current passing through the protrusions increases, and the melting of the materials of the technological layer and the contact holder can be achieved at a current value that is much lower than the current required to weld the contact holder to a flat (without relief) surface technological layer.

However, this solution is effective only for technological layers of silver or alloys based on it. For contacts with the technological layer of copper or its alloys, which are much worse connected by welding with contact holders made of base metal due to the higher melting temperature and high content of oxides in the welding zone, this solution is not enough. When the values of the weld current, when the silver-containing material of the working layer is not yet destroyed, the strength of the welded joint is not high enough.

Thus, the disadvantage of layered contact with a relief technological layer in the form of longitudinal protrusions is the low strength of the connection with the contact holder by the spot welding method if the material of the technological layer is made of copper or its alloys.

When creating the invention, the task was to increase the strength of welding of the contact holder and layered electrical contact with the technological layer of copper or its alloys.

Obtaining this technical effect is achieved by the fact that in a layered electrical contact with a silver-containing working layer and a technological layer of copper or a copper alloy, the open surface of the technological layer is made with a relief in the form of protrusions in the form of hemispheres. Moreover, the diameter of the hemispheres of the protrusions of the relief is in the range (0.5-1.0) mm, and the number of protrusions of the relief is at least three.

The limitation of the size of the protrusions is caused, on the one hand (minimum diameter), by the need to prevent the occurrence of an electric discharge between the flat part of the technological layer and the contact holder, and on the other hand (maximum diameter), by the need to ensure complete melting of the material in the protrusion for reliable connection of the technological layer and the contact holder.

The use of hemispherical protrusions allows to achieve a high current density at the points of contact and melting of the material of the protrusions, up to the limiting values of the current in the welding pulse, at which the destruction of the silver-containing working layer is possible.

The number of protrusions - at least three - is due to the stability of the contact when it is installed on the contact holder before welding.

The method is illustrated by drawings.

Figure 1 - layered electrical contact with longitudinal relief projections on the open surface of the technological layer (prototype).

Figure 2 - layered electrical contact with hemispherical embossed protrusions on the open surface of the technological layer.

In Fig. 1, a layered electrical contact consists of a working layer 1 and a technological layer 2 having longitudinal, rounded protrusions 3 over the entire length of the contact.

In Fig.2, a layered electrical contact consists of a working layer 1 and a technological layer 2 having hemispherical protrusions 3 in the amount of 3 (Fig.2a) and 5 (Fig.2b) pieces.

In these figures: h is the height of the protruding relief element; b is the width of the longitudinal protrusion; D is the diameter of the hemispherical protrusion.

It is clear that even the presence of two longitudinal protrusions (the minimum amount to ensure contact stability) in FIG. 1 leads to a larger contact area between the contact technological layer and the contact holder than in the case of hemispherical protrusions in FIG. 2. Therefore, the use of hemispherical protrusions allows to achieve a higher current density at the points of contact and the complete melting of the material of the protrusions, which will ensure reliable welding of the contact to the contact holder.

Layered electrical contact is made as follows.

A silver-metal oxide fine mixture is obtained by coprecipitation or a mixture of silver and nickel powders is obtained by mechanical mixing. Copper powders and copper mixtures with other elements (e.g. nickel) are prepared.

From the manufactured powders and powder mixtures, a layered preform is pressed with a working layer of a silver-metal oxide composition and a technological layer of copper or its composition with other elements. The specific pressing pressure (2-5) t / cm ² . Then the laminated preform is sintered and rolled into a strip with a thickness of 0.5 to 2 mm, which is the usual thickness of the contacts. Then, cylindrical blanks of contacts with a diameter of (3-6) mm or rectangular blanks ranging in size from 3x3 to 12x12 mm are cut out of the strip. After that, the contact blanks are calibrated in closed matrices. The punch, pressing on the contact blank from the technological layer, has recesses corresponding to the inverse relief that must be applied to the contact.

The dimensions of the hemispherical protrusions formed by this method on the technological contact layer are controlled in an instrumental microscope and metallographically on a cross section of thin sections.

As specific examples of the manufacture of a layered electrical contact with a hemispherical relief on the technological layer, rectangular contacts with dimensions of 3.5 × 3.5 mm and a thickness of 1.2 mm are presented.

Example 1

Working layer: silver - 12.5 wt.% Cadmium oxide.

The technological layer is copper - 10 wt.% Nickel.

5 hemispherical protrusions with a diameter of 0.8 ± 0.1 mm (protrusion height 0.4 mm).

Example 2

The working layer is silver - 8.0 wt.% Tin oxide.

The technological layer is copper - 10 wt.% Nickel.

3 hemispherical protrusions with a diameter of 1.0 ± 0.1 mm (protrusion height 0.5 mm).

To assess the strength of the welded joint on the basis of NPO Blagovest (Istra), ten contact options were tested, including two versions of layered electrical contact (with two and three longitudinal relief projections on the open surface of the technological layer), taken as a prototype . As examples of contacts according to the claimed invention, contacts were tested with a silver-containing working layer (silver - cadmium oxide, silver - tin oxide and silver-nickel) and a technological layer of copper or a copper alloy with nickel. At the technological layer, the open surface was made with a relief in the form of three or five hemispherical protrusions having different diameters (from 0.35 to 1.2 mm).

The strength of the joint was evaluated according to the shear force in the installation for tensile testing 1231 U10 at the boundary of the welded joint of the contact with the contact holder plate made of brass L63 with a thickness of 0.5 mm. The welding of contacts to contact holders was carried out on a spot welding machine of the MT-7.01 type with a current strength in the welding pulse of 4.5 kA and a duration of the welding pulse of 50 ms.

The test results showed that the shear force at the boundary of the welded joint of the contact with the contact holder plate for the prototype with three longitudinal strips is 110 N, and with two - 150 N.

The shear force at the boundary of the welded joint of the contact with the contact holder plate for the claimed invention, but with a hemispherical protrusion diameter of less than 0.5 mm and more than 1.0 mm, respectively, is 80 and 170 N.

The shear force at the boundary of the welded joint of the contact with the contact holder plate for the claimed invention with a diameter of hemispherical protrusions from 0.5 mm to 1.0 mm and the number of these protrusions: 3 or more is in the range 290-460 N.

Thus, the tests confirmed that the strength of the welded joint at the claimed contact is significantly higher than that of the prototype. In addition, it was shown that the claimed diameter range of hemispherical protrusions (0.5 mm-1.0 mm) plays a significant role for the strength of the welded joint. The number of protrusions (3 or 5) affects only the convenience of the welding process.

Literature

1. RF patent No. 2033653 C1, 04/20/1995.

2. Hansen M., Anderko K. The structure of double alloys. Handbook, t. 1, p. 31-34.

3. RF patent No. 2069023 C1, 11/10/1996.

Claims (1)

Laminated electrical contact with a silver-containing working layer and a technological layer of copper or a copper alloy with a base metal, the open surface of which is made with a relief in the form of protrusions, characterized in that the protrusions of the relief have the shape of hemispheres, the diameter of which is in the range 0.5 ÷ 1 , 0 mm, and the number of relief ledges is at least three.

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