SU1734128A1 - Method of manufacture of contact parts of hermetically sealed reed relays - Google Patents

Abstract

Use: in electrical engineering. The essence of the invention is that after punching and applying a contact coating, before the operation of the contact coating, test parts are selected from the batch, the contact coating is applied to them, subjected to tests in a sealed reed switch, during which the DC current is switched to the maximum permissible of this type of reed switch, then the radius of the erosion holes is measured on the anodic contact part, the contact coating is applied to the remaining contact details, and the recrystallization annealing is performed in t 0.5-1.0 hours at T (0.3-0.4) T ™, where TPL is the melting point of the contact coating material in degrees Kelwig, and the thickness of the contact coating layer is selected from the ratio dc r + di, where dc - coating thickness; g is the maximum unit radius of the erosion hole on the test anodic contact part, di is the thickness of the interdiffusion layer of the coating materials and the contact part. 2 tab. (/ WITH

Description

ihO 100

The invention relates to electrical engineering and can be used in the technology of magnetically controlled contacts (MC).

In order to ensure low and stable resistance, the contacting surfaces of contact parts (CD) M K are coated with noble metals and alloys based on them.

There is a known method of making CDs, in which an alloy (diffusive gold) is formed on the contacting surface of the CD by thermally annealing a previously applied gold coating.

Due to the intense interdiffusion of gold and the components of permallo, from which KD, iron and nickel are made, the stability of resistance of MK is reduced. To eliminate the instability of resistance, one more layer of gold has to be applied after heat treatment, which is extremely non-technological.

There is a known method of making CD, in which the development of erosion in the plane of the contact coating is artificially stimulated to increase the erosion resistance. This is achieved by applying a non-continuous layer of a material with a low work function (for example, an alkali metal) to the surface of the contact coating. In this case, due to a decrease in the work function in certain areas, a pulsed discharge is initiated, under the influence of which the coating is destroyed and the next discharge is initiated in a different place. Thus, the development of erosion in the plane of the coating is ensured and the working life of the devices is increased.

However, due to the high chemical activity, alkali and alkaline earth metals are prone to the formation of oxide films, the presence of which leads to an increase in MK resistance.

The closest to the present invention is a method for manufacturing a CD of a commercially available MCA-27101 by punching a CD body from a wire and electrolytically depositing a gold-nickel radium coating.

The erosion resistance of the coating is achieved by choosing the optimal percentage of nickel at the level of 5-16 wt.% And is provided in this case by reducing the mass transfer during the switching process.

Under actual conditions of mass production, stable reproduction of the nickel concentration in the gold – nickel – radium electrochemical coating is difficult, therefore, the EDM resistance of the coating decreases with concentration fluctuations. Increasing the thickness of the coating increases the erosion resistance, but increases the material consumption of the coating, which is unacceptable due to the high resistance and scarcity of gold, as well as an increase in the coating time.

The aim of the invention is to increase the erosion resistance of the coating with optimum material consumption.

The goal is achieved by the fact that in the method of manufacturing contact parts for reed switches, including stamping the wire and applying a contact coating, before the operation of applying a contact coating from the batch, test contact details are selected, they are applied to the contact coating, subjected to testing in a sealed reed switch in the process of which the DC current is switched to the maximum permissible value for this type of reed switch, after which the radius of the single erosion holes produced as a result of the surface test is measured and a layer of contact coating on the anodic contact, then a layer of contact coating is applied to the remaining contact details and a recrystallization annealing procedure is applied for 0.5–1.0 h at a temperature (0.3–0, 4) Tpl

0 where Tm is the melting point of the material of the contact coating in degrees Kelvin, and the thickness of the layer of application of the contact coating is chosen from the ratio:

 + di, where dc is the coating thickness;

5 g - the maximum radius of a single erosion hole on the test anode CD; di is the thickness of the zone of mutual diffusion of coating materials and CD.

The essence of the invention is as follows.

0 When switching MK electrical circuits, coatings are destroyed by the action of plasmaless pulse discharges and electric arc discharges. In all cases, a positive electrode is subjected to preferential destruction, on which, under the action of torch jets (with pulsed discharge) or anodic arc spots (with arc discharge), local heating and evaporation occur.

0 contact material, leading to the appearance of round-shaped erosion holes.

When the thickness of the coating is greater than the radius of the erosion hole on the anode CD, the erosion resistance increases. Still

5, a greater effect is achieved in this case during the heat treatment of the CD after coating in the mode: the treatment time is 0.5-1.0 h; treatment temperature (0.3-0.4) Tm, where Tp is the melting point of the coating material. When choosing the thickness of the coating, it is necessary to take into account the intermediate layer formed by the mutual diffusion of the elements of the coating material and the CD material, which intensively flows with increasing temperature.

The increase in erosion resistance is explained as follows. In the case when the thickness of the coating is less than the radius of the erosion hole in the places of thermal impact on the anode, at the interface the temperature becomes higher than the melting temperature of the coating and the CD material. As a result, there is an intense diffusion saturation of the coating with the use of the material of the CD and, as a result, a decrease in the thermal conductivity of the coating.

Temperature in the zone of thermal impact of pulse and arc discharges

T (r, t)

0)

can be estimated from the analytical model of a point heat source of finite duration using the formula:

p ™ er d) 21gTg erp}

where T (rd) is the current temperature on an isothermal surface of radius r;

RTI is the power of thermal radiation; A - heat conductivity;

g is the radius of the isothermal surface;

erf (

- error function;

4 Vat

and - thermal diffusivity.

An analysis of this dependence shows that a decrease in thermal conductivity leads to an increase in temperature and, consequently, to an even greater increase in the melt zone and further destruction of the coating. In places of saturation of the coating with elements of KD material with iron and nickel, localization of the discharge will occur, stimulating the transition to volumetric erosion of the coating. and refusal MK. In this case, erosion resistance is increased due to additional recrystallization annealing at a temperature of (0.3-0.4) TPl, where Tpl is the melting point of the coating material. In the recrystallization process, the density of point (vacancies) and linear (dislocations) defectors first decreases, new grains with a perfect structure are formed and grow. This stage of primary recrystallization occurs at a temperature starting with T 0.3 Tpl. With a further increase in temperature, the newly formed perfect grains of the coating grow and the grain boundaries sprout, resulting in a decrease in the area of grain boundaries. This stage of secondary recrystallization occurs at a temperature of about T 0.4 Tpl. A decrease in the concentration of structural defects and a decrease in the area of the boundaries leads to an increase in the thermal conductivity of the material, as a result of which, as can be seen from formula (1), the radius of the melt zone and, accordingly, the radius of the erosion hole decreases, and consequently, the coating erosion becomes less. At the same time, there is a process of diffusion of iron and nickel into the coating, which reduces its thermal conductivity. With an increase in the annealing temperature, the diffusion process intensifies and at a temperature of more than 0.4 Tpl the thermal conductivity of the coating begins to decrease.

The lower limit of the annealing time is determined by the minimum required time for the processes to pass.

ten

15

20

25

thirty

recrystallization in the coating and 0.5 hours. An increase in the annealing time deepens the recrystallization process and, accordingly, improves the thermal conductivity of the coating. However, it is impractical to heat treat the coating for more than 1.0 h, as the productivity of the process decreases and the thickness of the diffusion zone also increases. In this case, the diffusion of CD elements into the coating, filling it, forms a diffusion zone with low thermal conductivity. Therefore, the thickness of the coating should be defined as

dc r + di, (2)

where dc is the coating thickness;

g - the radius of the erosion hole;

dj is the thickness of the diffusion zone.

The thickness of the diffusion zone is determined by the expression

di 2VDF, (3)

where D is the diffusion coefficient;

t is the annealing time.

Wherein

D D0 -expC -), (4)

where Do is the frequency factor;

Q is the activation energy of diffusion; K-constant of Boltzmann; T is the temperature in degrees Kelvin. From (3) and (4) we get

di 2VD0t-exp (). (five)

CT scan;

PRI me R 1. The tests were carried out on the basis of commercially available reed switches MKA-27101. Gold alloyed on a stamped permalloyed QD wire by electrolytic deposition.

- nickel - radium.

Electrolyte composition: potassium dicyanourate pure 2.7 - 3.1 g / l; potassium pyrutrivodnogo phosphate of chd 50 - 80 g / l; rhodi salt complex solution 1.0 - 1.5 g / l; nickel pyrophosphate solution 0.7 - 1.2 g / l.

Deposition was carried out in the mode: density 1.4 - 1.6 A / dm2, electrolyte temperature 27

-35 ° C, deposition time 10-12 minutes to obtain a coating thickness of 1.2-1.3 µm and 19-20 minutes to obtain a coating thickness of 2.4-2.6 µm. The result is a coating of the following composition: Nickel 1.5 - 6%; rhodium 0.2 - 1%; the rest is gold

Tests conducted in two stages. At the first stage, four batches of MK were tested.

60 pcs in each batch. The coating thickness in the first and second batch was 1.1-1.2 µm, and in the third and fourth batch, 2.4-2.6 µm.

MK tested in two modes. The first and third installments are in mode I (UK 60B, IK 25 mA). The second and fourth mode II (UK 60B, 1k 60mA).

In mode I, the maximum radius of the erosive well was 1.3 µm, and in mode II, 2.0 µm.

As a criterion for the erosion resistance of a coating when testing gold-nickel-radium MKs, the percentage of failed reed switches in a batch with an operating time of 5 million hits was taken. This is due to the fact that the working resource of the MC in both switching modes is the same.

The failures in the first and second batch x were 10–12%, and in the third and fourth batch x -1.1– 1.2%.

At the second stage, MK was tested with a coating thickness of 2.4-2.6 µm under various conditions of annealing. Lot size - 60 devices.

The test results are shown in table 1.

An analysis of the test results shows that at the first stage of testing, positive results were obtained in the third and fourth batches. In this case, formula (2) is fulfilled.

The results of the tests at the second stage show that the annealing mode of 0.3–0.4 Tm for 0.5–1.0 h makes it possible to further reduce the percentage of failures (batches 3–7, Table 1). The radius of the erosion holes and the thickness of the coating were measured by electron microscopic studies, and the thickness of the diffusion zone was calculated using formula (5). In the calculation, it was considered that the mechanism of grain-grained diffusion of iron and nickel into gold was dominant, while the frequency factor D0 and the activation energy Q were taken equal to:

-5 2-1-32 -1

D0 2.7-10cm with D0 3-10cm with

(Fe - Au) (NI - Au)

Q (Fe - Au) 20.1 kcal Q (Ni - Au) 27 kcal

PRI mme R 2. Tests were carried out on the basis of commercially available reed switches МКА-50201. A layer of molybdenum was deposited on the stamped out of permalloy CD wire by the method of vacuum-laser deposition. Sputtering mode, arc discharge current of a plasma accelerator 130 A; focusing 0.5 A; accelerating voltage on a cassette with CD 20-30 V; spraying time 20 min.

Devices were tested in two modes: first-30 V; K 2 A; second-UK 30 V, 1K- 1 A.

As a criterion of electroerosion resistance of coatings when testing MK in these modes, the operating time before the first failure of MK in a batch is selected. The choice of this criterion is due to the fact that in these test modes, the working life of the MC differs 10-100 times and therefore it is impossible to use the criterion as a percentage of failures (as in Example 1).

An empirical formula was used to determine the thickness of the diffusion zone.

, 8-10t-exP (-). (6)

The test results are shown in Table. 2

Analysis of the test results given in table. 2 shows that an increase in erosion resistance, on average by an order of magnitude, is observed on devices subjected to heat treatment (batches 4, 5, 7, 9-11) in the indicated modes. Batches 1 and 2 were not heat treated. In batch 3, the annealing temperature was insufficient. In batch 8, the expression (2) is not observed. In batches 12 and 13, the annealing time is overestimated, which leads to an increase in the diffusion zone. In this case, there is a reduction in the operating time to the 1st failure with an increase in the annealing time, which unnecessarily reduces the productivity of the process and is unacceptable. In addition, molybdenum alloys are formed in the diffusion layer with elements of the CD material, in particular, the ResMo2 intermetallic compound is formed, which has a heat conductivity of 6-10 times worse than molybdenum.

Thus, the use of the proposed method makes it possible to realize the technology of manufacturing CD with the minimum required thickness of the coating and the optimal processing mode to achieve a high erosion resistance of the coating.

Claims (1)

Invention Formula A method of manufacturing reed contact parts, including punching wire and applying a contact coating, characterized in that, in order to increase the electrical erosion resistance with optimum material consumption of the coating, test contact parts are selected from the lot before the contact coating operation, they are subjected to tests in a sealed reed switch, during which the direct current is switched by the maximum permissible value for this type of reed switch, after which the erosion radius is measured The wells formed as a result of testing on the surface of the contact coating layer on the anodic contact part, then applying the contact coating to the remaining contact details and introducing the recrystallization annealing operation for 0.5-1.0 h at a temperature ( 0.3 - 0.4) Tm, where Mp is the melting temperature of the contact coating material in degrees 0 Kelvin, wherein the thickness of the layer of contact coating is chosen from the ratio dc r + di, where dc is the coating thickness; g - the maximum radius of a single erosion hole on the test anode contact details; di is the thickness of the interdiffusion zone of the coating materials and contact details. Table 1 table 2