RU2665689C1 - Method of manufacture of reed switch with nitrogen contact sites - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and can be used in the electronics industry for manufacturing sealed magnetically controlled contacts (reed switches). Ion-plasma treatment is carried out under conditions of action on the contact part of the reed switch of the magnetic and electric fields that cause a periodic closing-opening of the contact parts with a frequency of 200–1,000 Hz, leakage and rupture of an electric current through a reed switch under the influence of a voltage of 100–250 V AC 10–250 mA applied to its contact parts with a frequency of polarity reversal of 50 Hz during 0.25–60 minutes. Thus, the process of nitriding the surface of the contact-parts of the reed is realized due to electric erosion and transfer to the cathode of the anode material in the medium of nitrogen plasma.

EFFECT: technical result is the improvement of the quality and service life due to the localization of nitrided contact pads in the area of physical contact when the contact-parts of the reed contact are closed.

1 cl, 6 dwg

Description

The invention relates to electrical engineering and can be used in the electronics industry in the manufacture of sealed magnetically controlled contacts (reed switches).

The technical result is the reduction in the cost of the reed switch by replacing the complex and expensive special high-frequency high-voltage equipment used for the manufacture of reed switches, with a simpler and cheaper mass-produced low-frequency low-voltage equipment, as well as improving the quality and resource of work, due to the localization of nitrided contact pads in areas of physical contact when contact parts are closed.

The proposed method of manufacturing a reed switch allows using cheaper equipment to form wear-resistant contact pads of iron and nickel nitrides in the surface region of the reed contact parts directly where physical contact of parts and erosion of the contact surface occur during electrical current switching, which increases the erosion resistance of contact surfaces and , as a result, the operating time of reed switches to failure.

The known method used in the manufacture of serial reed switch MKA-14103 with a glass cylinder length of 14 mm, described in [1], which includes the following operations.

Permalloy wire is subjected to purification from preservative lubricant as a result of degreasing in a bath with hot trichlorethylene and subsequent ultrasonic (UZV) cleaning, after which it is fed to a reed contact element stamping machine. After degreasing in a bath with perchlorethylene, sorting and packing into a technological container, the contact parts are subjected to ultrasonic (UZV) washing in a bath with deionized water and, after drying, annealed in a furnace in a hydrogen atmosphere with the formation of specified magnetic parameters.

The technological process of applying galvanic coatings to contact parts includes 17 transitions between various operations, including environmentally hazardous ones: degreasing, decapitation in an acid solution, pregilding, gilding, ruthenization. After ultrasonic washing and drying in a centrifuge, the contact parts are welded into a glass cylinder filled with nitrogen.

Brewed reed switches after annealing a glass bottle and magnetostrictive training arrive at the chemical polishing of the leads with subsequent tinning and control of electrical parameters.

Significant disadvantages of this method are: high consumption and loss of precious materials, long manufacturing time, complexity and high cost of equipment, high energy costs, the difficulty of deposition of the alloy, a given chemical and phase composition and a given structure, the difficulty of obtaining thin non-porous or thick films with low internal stresses and with high adhesion to the material of the contact part.

The closest method of manufacturing a reed switch is the technological process described in the patent [RU 2393570, IPC Н01Н 1/66, Н01Н 11/04, publ. 06/27/2010, bull. No. 18] [2].

A known method of manufacturing a reed switch with nitrided contact parts includes: cleaning permalloy wire, stamping of contact parts, degreasing and washing, magnetic annealing, welding of the reed switch, ion-plasma treatment of contact parts with spark discharges, coating of leads and control of electrical parameters.

The disadvantage of this method is the high cost of the equipment used, the insufficient hardness of the contact surfaces and, as a consequence, the high cost and insufficiently high erosion resistance of the reed switches.

The objective of the invention is to improve the manufacturing method of the reed switch by replacing the ion-plasma nitriding regime with a new process that allows you to replace expensive, high-frequency high-voltage equipment with cheaper mass-produced low-frequency low-voltage equipment, to form wear-resistant contact pads of iron and nickel nitrides in the surface region contact surfaces of the reed switch, directly where, when switching electric current, It means physical contact of parts and erosion of the contact surface, which lowers the cost and increases the erosion resistance of the contact surfaces and, as a result, the operating time of the reed switches for failure.

The problem is solved by the fact that a method for manufacturing a reed switch with nitrided contact pads is proposed, including cleaning permalloy wire, stamping contact parts, degreasing and washing, magnetic annealing, welding the reed switch with nitrogen injection and annealing the reed switch, coating the terminals, ion-plasma processing of the reed switch and control electrical parameters, characterized in that the ion-plasma treatment is carried out under the influence on the contact details of the reed switch of alternating magnetic and electric fields, causing periodic closing-opening of contact parts with a frequency of 200-1000 Hz, flow-breaking of an electric current through a reed switch under the action of a voltage of 100-250 V applied to its contact parts, an alternating current of 10-250 mA with a frequency of polarity reversal of 50 Hz for 0, 25-60 minutes

The proposed mode of ion-plasma processing (IPO) leads, when the contact parts are brought closer together, to a spark breakdown of the contact gap and to microexplosions of the materials of the contact parts, and when they open (rupture of the current), to the microexplosion of the molten bridge that occurs when the current contraction region is melted between contact details of a reed switch, ionization of an intercontact medium (nitrogen), mass transfer of a substance formed during microexplosions, in the plasma, vapor, and liquid phases from one contact part (anode) to another (cathode) in a nitrogen pl azma and, as a result, to electrospark alloying with nitrogen (nitriding) the surface of the contact parts of the reed switch.

Thus, in the proposed method of manufacturing a reed switch with nitrided contact pads, the process of nitriding the surface of the contact parts of the reed switch is carried out due to electrical erosion and transfer to the cathode of the anode material in a nitrogen plasma environment.

The inventive electrical parameters of the IPO mode are necessary conditions for electrospark alloying with nitrogen of the contact surfaces of the reed switch. The choice of values of the IPO mode of the contact parts depends on the composition and pressure of the working gas, on the size of the contact gap and the breakdown voltage.

An alternating voltage of 100-250 V supplied to the contacts of the reed switch with a frequency of polarity reversal of 50 Hz and a current of 10-200 mA, switched with a frequency of 200-1000 Hz, provides the formation of nitrided contact pads on the surface of the contact parts of the reed switch for a rational time period of 0.25 -60 min and does not require any complex equipment, just a regular AC voltage lator, a standard coil and generator are enough (Fig. 1).

At voltages less than 100 V, when a spark breakdown occurs at a distance comparable to the mean free path of electrons, ionization of the contact gap does not occur, there are no ions and nitrogen atoms in it and, therefore, nitriding of contact surfaces does not occur.

The upper limit of the applied voltage is limited by the breakdown voltage of the reed switch, in the most common types of reed switches it does not exceed 280-300 V.

The lower limit of 10 mA switched AC is limited by the allowable IPO time. The smaller the current, the longer the nitriding process takes.

With an increase in current, the processing time decreases, but the temperature of the contact parts increases, and at currents of more than 250 mA the glass softens at the junction with the contact parts, and the reed switch is depressurized.

The upper limit of the switching frequency, on the one hand, should not exceed the resonant frequency of the reed switch, and on the other hand, it must provide physical contact of parts during a short circuit. Therefore, in accordance with these requirements, its value does not exceed 1000 Hz.

With a decrease in switching frequency, the IPO time increases. At switching frequencies less than 200 Hz, the duration of the nitriding process significantly increases and exceeds 60 minutes.

Therefore, the definition of a rational IPO mode is always a search for a compromise between the set values of the IPO mode parameters.

The criterion for choosing the electrical parameters of the processing mode is to ensure a stably low in the value of the reed switch resistance after IPO and switching DC circuits (switching tests - KI) with an operating time of at least 10 ⁶ operations without failure.

The combination of distinctive features, which consists in creating conditions for electrical erosion of the surface of the reed contacts and transfer of the anode material to the cathode in a nitrogen plasma environment, leads to the formation of nitrided contact pads and to achieve a new technical result.

The method is as follows.

Contact details of a commercially available reed switch, for example, MKA-14103, made of Dilaton 52 iron-nickel alloy and not having Au-Ru contact coatings, after magnetic annealing are welded into a glass container in a nitrogen atmosphere. After annealing and coating the terminals, the reed switch is installed in the control coil of the IPO installation, a simplified diagram of which is shown in FIG. one

FIG. 1. A simplified diagram of the experimental setup for IPO and KI of reed switches: PS - source of switched current (AC at IPO, constant at KI), R - resistor, C - stray capacitance, V - reed switch, L-control coil, G - generator.

Reed switch V, located in a standard control coil L (number of turns 5000, resistance 870 Ohms), is connected to an alternating current source during an IPO, and to a direct current source PS through a resistance R during a RI. A sinusoidal voltage is supplied to the coil from the generator G with an IP with a frequency of 400 Hz, and with KI, a square wave of voltage pulses of 2 ms duration and a frequency of 50 Hz is supplied. The closing of the contacts of the reed switches during IPO and KI occurs under the action of a magnetomotive force of 1.5 Fcp.

The structure and elemental composition of the surface of the samples were studied by scanning electron microscopy (SEM) and X-ray spectral microanalysis (PCMA).

Measurements of electrical resistance (R), breakdown voltage (U), magneto-driving response forces (Fcp) and release (Fot), as well as switching tests (CI) of reed switches were carried out using specialized equipment and according to the methods used in [1].

With IPO, an alternating voltage of 220 V - 50 Hz was applied to the contacts of the reed switches, and the switched current (I) reached 95 mA. The processing time is 20 minutes.

The obtained SEM images and the PCMA spectrum of the reed contact surface area after its IPR in the I = 95 mA mode, at ν = 400 Hz (Figs. 2–4) showed that, as a result of IPO, two contact pads (KPs) were formed on the contact surface with an area of 79446.297 and 20943.146 μm (Fig. 2), on the surface of which microcraters with a diameter of 2.4-3.6 μm are randomly located (Fig. 3.) The nitrogen concentration in the near-surface layer of the CP was 8.1 at . % (Fig. 4).

FIG. 2. SEM - image of the surface area of the contact part of the reed switch, made according to the claimed method, with two nitrided contact pads with an area of 79446.297 and 20943.146 microns.

FIG. 3. The surface area of the contact pad shown in FIG. 2 with an area of 79446.297 microns.

FIG. 4. PCMA — spectrum of the surface area of the contact pad shown in FIG. 3

Measurements of R and U were performed before and after IPO.

The initial values (up to IPO) of the electrophysical parameters of the reed switch were: R = 0.15 - 0.2 Ohm (at a rate of R ≤ 0.1 Ohm for serial devices MKA-14103), U = 285 V.

The measurements of the resistance and breakdown voltage of this reed switch showed that the values of these parameters as a result of the IPO tend to decrease to R = 0.08 Ohm (R corresponds to the norm) and to U = 265 V (U decreased by AU = 20 V) .

The amount of nitrogen N in the near-surface layer of the KP and the thickness of the nitrided layer (t) can be estimated by the formulas:

N = (pShN _A n) / A (1);

N = St / a ³ , (2);

t = (pa ³ hN _A n) / A (3),

where ρ, A, h is the density, atomic weight of iron, h = 0.5 μm is the depth of the x-ray signal output from iron, calculated by the Monte Carlo method using the INCA X-MAX 20 energy dispersive microanalyzer software;

- постоянная решетки сплава внедрения,a = 3.8

- the lattice constant of the alloy introduction,

N _A is the Avogadro number;

S, n — experimental data obtained as a result of SEM and PCMA studies;

S is the area of the contact pad;

n is the relative concentration of nitrogen in the near-surface layer averaged over the depth of the output of the X-ray PCMA signal.

The calculations carried out according to formulas (1) and (3) taking into account the results of SEM and PCMA studies of the contact surface showed that with IPR of reed switches processed according to the 220 V mode - 95 mA-50 Hz with a switching frequency of 400 Hz, on the contact surface, in their overlap zone is formed, for example, by a KP with an area of 79446.297 μm ² , with a nitrided layer thickness of approximately 149 nm, which contains 2.57 × 10 ¹⁴ nitrogen atoms.

Therefore, the spark breakdown that occurs when the contacts come together and the mass transfer of a part of the material of the contacts from one contact to another, a periodic change in the direction of transfer create the necessary conditions for the ionization and atomization of molecular nitrogen and the formation of nitrided contact pads on the surface of the contact parts of the reed switch.

When the contacts open, nitriding of the contact surface continues.

The process of opening contacts consists of three stages, differing from one another by the mechanism of current conduction.

The first opening stage starts from the moment the contacts move. There is still no separation of the electrodes, but already there is a removal of deformation in the contact zone, a decrease in the solid conductive surface, an increase in the current density in the region of current contraction and an increase in the temperature of the contact elements up to a value equal to the melting temperature. Then the second stage of contact opening begins, at which the current conductivity is carried out by a liquid metal bridge formed from a drop of molten metal between the contact parts when they are expanded. When the temperature at the most heated point of the bridge becomes equal to the boiling point of the metal, it explodes and the third stage begins. At this stage, the ionization of the interelectrode medium occurs, it becomes conductive and an electric spark or arc is ignited between the contacts, with its subsequent extinction when the contacts of the reed switch are opened.

These processes and the mass transfer of a part of the material of the contact material from one contact to another, as well as during the convergence of the contacts, create the necessary conditions for the ionization and atomization of molecular nitrogen and the formation of nitrided contact pads on the surface of the contact details of the reed switch.

Thus, reed switches are made according to the proposed method.

After ion-plasma treatment, the reed switches are automatically unloaded and transferred along the route to the next technological operation.

Comparative tests of reed switches made according to the claimed method and prototype [2] were carried out with DC switching to active load.

The reed switches CI after IPO were idling (without current load, CI mode No. 3) and in the process of switching a constant electric current with an active load (CI mode No. 4, 5) at the installation, a simplified diagram of which is shown in Fig. 1.

In modes No. 4, 5 a constant voltage of 24 and 100 V was applied to the contacts of the reed switches and a current of 400 and 100 mA was switched, respectively. In all three KI modes, the switching frequency corresponded to 50 Hz. The total uptime of the reed switches made by the claimed method in modes No. 3, 4 and 5 amounted to more than 10 ⁶ operations and exceeded by about 20% the operating time of the reed switches made according to the prototype [2].

Reed switches are considered to have passed the tests, in which the processes of erosion and mass transfer did not lead to non-opening of the contacts or to their welding and resistance, which did not exceed the norm of 0.1 Ohm.

The dynamics of mass transfer, surface erosion processes that occur during current switching are discussed in [3, 4] from the standpoint of the ecton model.

At the breakdown stage, when the contacts come closer, a current of field-emission and field-emission emissions (AEE and ATEE) flows in the reed switch. Then, due to reaching the threshold current density j≈10 ⁸ A / cm ² on the points, spark discharge stage starts. In it, due to the large field enhancement (E≈10 ⁸ V / cm) on the cathode microscopic inhomogeneities occur explosive electron emission (SEE). Electrical explosions of the cathode metal occur. Several states of matter are formed: solid, liquid, gaseous, and plasma. Drops of liquid metal fly apart at a speed of v _M ≈10 ⁴ cm / s. The cathode plasma torch moves toward the anode at a speed of V _i ≈10 ⁶ cm / s [3, 4]. The VEE current flows in the form of portions - ectons (electron packet), which in the cathode torch have zero work function and are injected from it by the field in the direction of the anode. The speed of electrons v _e leaving the cathode torch is approximately 10 ⁸ cm / s, i.e. v _e »V _i [3, 4].

Thus, an SEE occurs at the spark stage and an electron current flows between the cathode plasma and the anode in the form of a portion (pack) of electrons - an ecton. The ecton formation time t _e ≈10 ⁸ s. It is limited by the cooling process of the cathode crater due to heat removal, the release of molten metal and a decrease in current density. The number of electrons in the ecton is Ne≈10 ¹⁰ -10 ¹² [3, 4].

With the formation of a spark, the temperature in the zone of the breakdown channel reaches 10,000 ° C. The localization of the energy of the cathode ecton (spark discharge) in the microvolume of the surface of the anode leads to its explosion as a result of which several states of matter are formed: solid, liquid, gaseous, plasma and a crater at the site of the explosion. The anode crater is larger than the cathode crater, since the electrons from the anode torch return to the anode, heating it additionally, and the anode ions, compensating for the space charge of the electron electron beam electron beam, increase the current of this beam, which leads to even more heating of the anode. As a result of such heating of the anode, with the same materials of the electrodes, there occurs a polar portion mass transfer from the anode to the cathode. Anode plasma torch, vapors and drops of anode material move towards the cathode torch, vapors and drops of cathode material. As a result, one or several protrusions are formed on the cathode surface, consisting of a huge number of approximately the same geometric dimensions and shape of saucer-shaped disks (Fig. 5a), and on the anode the same number of small craters (Fig. 5b) located on the inner surface depressions, from the material of which are mainly formed, as a result of polar mass transfer, protrusions on the cathode.

FIG. 5. AFM - top view: a - anode crater, b - cathode disk. DC switching mode: 24 V - 400 mA - 50 Hz.

After closing the contacts, a force arises that can lead to their rebound. This force is due to the elasticity of the contact springs and the high vapor pressure and plasma of the metal as a result of microexplosions in places of contact zones.

When the current is opened due to surface roughness, the contact diverges at the same time. Through separate spots all current in a chain will flow. Therefore, the region of contraction of the current is melted and a molten metal bridge is formed, which, exploding in the region of constriction forms an ecton, which leads to erosion of the contact surface by the same mechanism as when they are closed [4].

The explosion of metal bridges formed in the process of bounce of contacts can also initiate SEE with the formation of an ecton.

Thus, the main role of the bridge in opening contacts in the formation of an ecton at the time of the explosion of the isthmus. Acton, subsequently, hitting the anode and forming a microcrater on it, starts the erosion process of mass transfer of the anode material to the cathode [3, 4].

At the stages of impact of an ecton on the anode surface, the following processes can occur: melting of the surface layer material, heating of the samples due to thermal conductivity, the formation of a gas-flame cloud, the formation and propagation of shock waves, crater formation in the surface layers of the anode, and the removal of contaminants from the surface; redistribution of elements in the recrystallized zone, phase formation under conditions of high-speed crystallization, an increase in the density of vacancies and dislocations.

The combination of these processes determines the surface condition of the anode crater and cathode disks after electronic processing of the anode.

Information sources

1. Karabanov S.M., Meisels P.M., Schoff V.N. // Magnetically controlled contacts (reed switches) and products based on them. Dolgoprudny: Intellect Publishing House, 2011. - 408 p.

2. RF patent No. 2393570. A method of manufacturing a reed switch with nitrided contact parts / Karabanov S.M., Meisels P.M., Arushanov K.A., Zeltser I.A., Provotorov B.C., publ. 06/27/2010 Bul. Number 18.

3. Zeltser I.A., Karpov A.S., Moos E.N., Rybin N.B., Tolstoguzov A.B. Surface Erosion of Low-Current Reed Switches. // Coatings. 2017.7, no. 6: 75.

4. Month G.A. Acton - avalanche of electrons from a metal // UFN. 1995.Vol. 165. No. 6. C 601.

Claims (1)

A method of manufacturing a reed switch with nitrided contact pads, including cleaning permalloy wire, stamping contact parts, degreasing and washing, magnetic annealing, welding the reed switch with a nitrogen blow and annealing the reed switch, coating leads, ion-plasma processing of the reed switch and control of electrical parameters, characterized in that ion-plasma processing is carried out under the influence of alternating magnetic and electric fields on the reed contact parts, causing periodic contact-detail opening-opening with a frequency of 200-1000 Hz, leakage-gap electric current through the reed switch by the action applied to its contact pieces 100-250 volt AC 10-250 mA with frequency of 50 Hz polarity during 0,25-60 m.

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