RU2812459C1 - Device for making thermocouples - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: device is equipped with an optical binocular microscope, a nozzle for supplying process gas and a digital magnifying video camera connected to a monitor. The laser radiation source, which ensures the formation of a liquid metal junction between the wire electrodes of the manufactured thermocouples, is installed on a base with the ability to move along three coordinates and is combined with a microscope and a video camera. Two axisymmetric two-channel holders with clamping devices for the mentioned wire electrodes are coaxially placed on two supports. The holder on the first support is equipped with a device for rotation around its longitudinal axis, for example, in the form of a self-braking worm gear. The holder on the other support is configured to move along the longitudinal axis and is equipped with a force accumulating element, for example, in the form of springs, and on its outer side the holder together with the support forms a sliding bearing.

EFFECT: production of high quality solders while simplifying the process.

3 cl, 7 dwg

Description

The invention relates to the field of thermometry and can be used for the manufacture of thermocouples.

A device for manufacturing thermocouples is known, disclosed in a method for manufacturing a hot junction of a thermocouple from refractory materials (SU 1224610 A, IPC G01 K7/02, 04/15/1986). According to this technical solution, pre-twisted thermoelectrodes with a pre-coated thermoplastic metal are installed in a heat-removing clamp at a distance of at least two turns from the end of the twist, and the protruding twisted ends of the thermoelectrode wire are welded using fusion welding.

The disadvantage of this device is, in particular, that the junction of wire electrodes coated with a layer of ductile metal made with it contradicts the basic requirements for thermocouple junctions (Gerashchenko O.V., Fedorov V.G. Thermal and temperature measurements: Reference manual. Kiev, Naukova Dumka, 1965, p. 95), namely: the zone of heterogeneity formed in the junction should be minimal, while due to the introduction of additional coating metal into the junction, the structural heterogeneity of the junction increases. In addition, the introduction of additional metal into the junction area can provoke a decrease in the chemical resistance of the junction compared to the chemical resistance of wire electrode materials. In addition, the strength of the junction may decrease due to the coating material provoking intercrystalline erosion in the materials of the wire electrodes, as well as the formation of intermetallic compounds in the junction zone. Intermetallic compounds are brittle compounds and, as a rule, are centers of stress concentration, crack formation and further destruction of the material. Reflow welding of wire electrodes will result in the formation of metal oxides, which will increase the heterogeneity and resistance of the junction. The metal coating of the wire electrodes can serve as additional solder, which when welding the ends of the wire electrodes will lead to an increase in the size of the junction (king) and soldering of the wire electrodes to the heat-sinking clamp, which increases the percentage of defects. Increasing the size of the junction leads to a decrease in the accuracy of the thermocouple and an increase in its inertia. The device does not provide the production of thermocouples in the form of a single technological cycle; it is necessary to use additional technological operations, for example, applying layers of ductile metal to the surface of the electrodes, which requires additional equipment and a significant investment of working time. The technological process for manufacturing a thermocouple using this device is complex, labor-intensive, expensive and difficult to reproduce.

A device for the manufacture of microthermocouples (RU 2681859 C2, MPK V23K 11/04, G01K 7/02, 03/13/2019) is known, including a hopper with graphite powder, a clamping device with jaws on the tip, an optical binocular microscope, a clamp for twisting wires.

The disadvantage of such a device for making thermocouples is the large size of the thermocouple ball (junction) relative to the diameter of the wire, which is a negative factor, since the size of the junction affects the inertness of the thermocouple - the larger the diameter of the junction, the higher the inertness. During the melting of the twist according to the mentioned patent, graphite particles are welded to the junction, and metal oxides and carbides are also formed in the ball itself, since in fact the melting of the metals of the wire electrodes occurs in a gaseous environment (between the graphite particles there is air, carbon dioxide resulting from the evaporation of solid carbon and etc.). To remove graphite particles and oxides, etching of the junction in acids is required. Chemical etching is a labor-intensive and harmful technological operation. But subsequent chemical treatment of the ball does not fully remove the by-products of the chemical interaction of the molten metal with graphite and gases. Due to the above reasons, when welding wire electrodes, the junction contains a large number of by-products, which contradicts the basic requirements for thermocouple junctions (Gerashchenko O.V., Fedorov V.G. Thermal and temperature measurements: A reference guide. Kiev, Naukova Dumka, 1965, p.95). The technological process for manufacturing a thermocouple according to this patent is complex, requires a lot of time, highly qualified personnel, additional materials and equipment.

The closest technical solution is a device for the manufacture of microthermocouples (RU 2660323 C1, IPC G01K 7/02, H01L 35/34, B23K 11/04, B23K 11/26, 07/05/2018) with a wire diameter of 200 μm or less end-to-end, including frame, optical binocular microscope, digital video camera connected to the monitor, two opposite clamps for wire electrodes and a nozzle for supplying process gas to the welding site, an electronic unit for reproducing the welding pulse.

The disadvantage of this device is that for butt welding of thin, micron-sized wires, preliminary precise processing of the ends of the wires is required, since the quality of welding depends on the quality of the fit of the wires being butt welded. The technological operation of bringing the ends of two thin wires together with an error of several micrometers along two coordinates to the welding point is labor-intensive and time-consuming, requiring highly qualified personnel. The compression force of the ends of the wires also depends on the level of qualification of the personnel. The device does not ensure the production of thermocouples in the form of a single technological cycle; it is necessary to use additional technological operations, namely, preliminary precise processing of the ends of thin wires is necessary to obtain a cut plane perpendicular to the axis of the wires. The use of this device requires additional equipment, significant investment of working time and highly qualified personnel. In addition, butt welding with large wire diameters is difficult and does not always make it possible to obtain identical junctions in a batch of thermocouples. The listed factors do not allow us to ensure repeatability of the technological process and, accordingly, the same quality of thermocouples. It should be noted that the device makes it possible to obtain a welding junction only when butt welding, which does not make it possible to produce more popular and common thermocouples with parallel arrangement of wires.

The technical result of the proposed invention is:

- ensuring high quality of junctions in the manufacture of thermocouples;

- simplification of the technological process of manufacturing thermocouples and reducing qualification requirements for operating personnel;

- increasing the productivity of thermocouples manufacturing;

- reducing the cost of manufacturing thermocouples.

The specified technical result is achieved by what is proposed:

1. A device for manufacturing thermocouples, containing a base on which two oppositely located clamping devices for wire electrodes are installed, above which an optical binocular microscope is placed, a nozzle for supplying process gas, a digital magnifying video camera connected to a monitor, characterized in that a a laser radiation source with the ability to move along three coordinates, combined with a microscope and a video camera, while on the base two axisymmetric two-channel holders with clamping devices are coaxially placed at a given distance on two supports, and the holder installed on the first support is equipped with a device for rotation around its longitudinal axis , and the holder, placed on another support, is configured to move along the longitudinal axis and is equipped with an element for accumulating forces and along its outer side forms a sliding bearing together with the said support.

2. The device according to claim 1, characterized in that a self-braking worm gear is used as a rotation device.

3. The device according to claim 1, characterized in that a spring is used as an element for accumulating tensile force and returning to its original position.

Figure 1, Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6 show drawings illustrating the presented technical solution, and Figure 7 shows a photo of samples of the resulting thermocouples, where:

- Fig.1 – schematically shows the main view of the device with two wire electrodes 11, 12 passed through the hollow channels of axisymmetric holders 8, 9 and clamps 10 fixed against axial movement relative to the channels of the holders 8, 9;

- Fig.2 – schematically shows view B of the device;

- Fig.3 – cross-section E-E of a plain bearing is schematically shown;

- Fig.4 – schematically shows the twisting of 17 wire electrodes in the laser welding zone between holders 8, 9 and the occurrence of a breaking force in the twisting 17;

- Fig.5 – schematically shows the supply of process gas to the twisting area 17, the supply of a laser pulse to twisting 17 and the formation of a primary liquid junction 18 of liquid metal in the contact spot;

- Fig.6 – schematically shows the division under the action of the breaking force of the compressed spring 16 of the primary liquid junction into two secondary liquid junctions 19, 20 with the subsequent formation of spherical beads on the twisted electrodes.

- Fig.7 – shows the appearance of thermocouple samples, and a match head is attached to demonstrate the small size of thermocouples.

The proposed device contains a laser radiation source 1 which is mounted on a base 2 with the ability to move along three mutually perpendicular coordinates, as shown in Fig.1. The laser radiation source 1 is combined with a binocular microscope and a video camera 3, to which a monitor 4 is connected, a device for supplying process gas 5 to the laser welding zone of wire electrodes 11, 12. On the base 2 there are two supports 6 and 7, on which two axisymmetric two-channel holder 8 and 9 with clamps 10 for wire electrodes 11 and 12. The two-channel holder 8 mounted on the support 7 is equipped with a device for rotating the holder 8 around its longitudinal axis without longitudinal movement, for example, a self-braking worm gear, which includes a gear 13, a worm 14 and flywheel 15, as shown in FIG. 2. The holder 8 is rigidly coaxially fixed to the gear wheel 13 and can rotate together with the gear wheel 13. When the flywheel 15 rotates, the torque is transmitted to the worm 14 and, further, to the gear wheel 13 together with the holder 8, as a result of which the gear wheel 13 together with the holder 8 and the clamp 10 are driven into rotation. Another holder 9, placed on the support 6, is equipped with a device for longitudinal movement without axial rotation, for example, on its outer side it is made with a support 6 in the form of a quadrangular sliding bearing, as shown in Fig.3. Thus, the holder 9 together with the clamp 10 can move along its longitudinal axis without axial rotation. Between the support 6 and the holder 9 with the clamp 10 there is a compression spring 16. When the flywheel 15 rotates, the gear wheel 13 and, accordingly, the holder 8 rotates by the required number of revolutions. In this case, in the area between the holders 8 and 9, the wire electrodes 11 and 12 are twisted, as shown in Fig. 4. When twisting wire electrodes 11 and 12, a tightening force appears between holders 8 and 9, since wire electrodes 11 and 12 are rigidly fixed by clamps 10 and cannot move in the channels of holders 8 and 9. Under the influence of this force, holder 9 moves in the direction of twisting wire electrodes 11, 12 and spring compression 16.

Twisting of wire electrodes 11, 12 by holders 8, 9 occurs by rotation of one holder 8 around its longitudinal axis and reciprocating movement of the other holder 9.

The proposed device for making thermocouples works as follows. A laser installation model LAT-S-300 is used as a source of laser radiation 1. The laser radiation source 1 is combined with a binocular microscope and a video camera 3, to which a monitor 4 is connected, a device for supplying process gas 5 to the laser welding zone of wire electrodes 11, 12. Wire electrodes 11, 12 are made of chromel and alumel wire (GOST 1790- 2016 Interstate standard. Wire made of chromel, alumel, copel and constantan alloys for thermoelectrodes of thermoelectric converters) with a diameter of 0.2 mm. First, the wire is passed through axisymmetric two-channel holders 8 and 9. Next, the wire electrodes 11 and 12 are fixed from axial movement relative to the holders 8 and 9 by means of clamps 10. When the flywheel 15 rotates, the gear wheel 13 and, accordingly, the holder 8 rotates by the required number of revolutions. In this case, in the area between the holders 8 and 9, 17 twisted wire electrodes 11 and 12 are obtained, as shown in Fig. 4. When twisting the wire electrodes 11 and 12, a tightening force appears between the holders 8 and 9. Under the influence of this force, the holder 9 moves towards the twist 17 and the spring 16 is compressed. Next, process gas was supplied into the gap between the holders 8 and 9 for the twist 17. The gas mixture TU 2114-002-45905715-2015 argon (99% Ar) + hydrogen (1% _H2 ) was used as a process gas. After this, with a time delay of several seconds, a laser pulse was applied to the twist 17, as a result of which a contact patch was formed, followed by the formation of a primary liquid junction 18 from the molten metals of the wire electrodes 11 and 12, as shown in Fig. 5. Under the action of the tensile force of the spring 16 in the center of the primary liquid junction 18, a division occurs into two secondary liquid junctions 19 and 20 and the wire electrodes 11, 12 fixed in the holders 8, 9 are moved apart by several millimeters in opposite directions, as shown in Fig. 6. In this case, the spring 16 straightens and returns the holder 9 to its original position. Under the action of surface tension forces, two secondary liquid junctions 19 and 20 acquire a spherical shape, then they cool and solidify. The process of forming the primary liquid junction 18 and, subsequently, the secondary liquid junctions 19 and 20, as well as their subsequent cooling, occurs in an inert gas environment, which reduces the formation of oxide films, and this increases the homogeneity of the junction.

A gas mixture consisting of 99% argon (Ar) and 1% hydrogen ( _H2 ) was used as a process gas. The addition of hydrogen contained in the gas mixture makes it possible to almost completely restore the metal oxides formed as a result of the melting of wire electrodes and thereby improve the quality of the junction.

As a result of dividing the primary junction 18 into two parts, the secondary junctions 19, 20 of the resulting two thermocouples have a low mass and size, which increases the sensitivity of thermocouples and reduces their inertia.

The final operation is to loosen the clamps 10 and remove the completed two thermocouples from the holders 8 and 9.

Thus, the technological process using the proposed device has good repeatability, which is proven by the manufacture of a large number of thermocouples. In addition, the technological process using the proposed device does not require expensive technological equipment and has high productivity, since two thermocouples are manufactured in one technological cycle. The device for making thermocouples ensures good quality of junctions, since the process takes place in an inert reducing environment without the use of foreign metals and substances. The device is universal for a wide range of used wire electrode diameters. Also, the cost of thermocouples produced using this device is reduced by almost half, since consumables and resources (inert gas, water, electricity, preparatory and final time, etc.) are spent on the production of not one, but two thermocouples at the same time.

Claims (3)

1. A device for manufacturing thermocouples, containing a base on which two oppositely located clamping devices for wire electrodes are installed, above which an optical binocular microscope is placed, a nozzle for supplying process gas, a digital magnifying video camera connected to a monitor, characterized in that a a laser radiation source with the ability to move along three coordinates, combined with a microscope and a video camera, while on the base two axisymmetric two-channel holders with clamping devices are coaxially placed at a given distance on two supports, and the holder installed on the first support is equipped with a device for rotation around its longitudinal axis , the holder, placed on another support, is configured to move along the longitudinal axis and is equipped with an element for accumulating tensile force and returning to its original position, and along its outer side forms a sliding bearing together with the said support. 2. The device according to claim 1, characterized in that a self-braking worm gear is used as a rotation device. 3. The device according to claim 1, characterized in that a spring is used as an element for accumulating tensile force and returning to its original position.