JP2009025294A - Thermocouple and its temperature measuring contact formation method - Google Patents

Abstract

A thermocouple in which two thermocouple wires are melt-bonded and a thermocouple in which the melted portion is not enlarged in a dumpling shape and a method for manufacturing the same are provided.
A thermocouple temperature measuring unit is a method in which a portion where two thermocouple wires are in contact with each other is fused and integrated in a solder-free manner, and the size of the melted portion is equal to the thickness of the wire. It is characterized by being less than double.
[Selection] Figure 4

Description

The present invention relates to a thermocouple having a temperature measuring part formed by melting and joining two thermocouple wires, and a method for forming a temperature measuring contact.

The thermocouple has a temperature measuring section in which two thermocouple wires constituting the thermocouple are melt-bonded. As shown in FIG. 12, the temperature measuring section is enlarged in a dumped form. On the other hand, in order to make the sensitivity sensitive, it is said that it is better to reduce the diameter of the wire and reduce the volume of the temperature measuring part, but there is a limit to increase the sensitivity because of the enlargement of the melting part. there were.
In addition, forming a small temperature measuring part having a diameter of 100 microns or less conventionally requires soldering. Due to the influence of the solder, the measurement at a high temperature is performed by the melting temperature of the solder. It was supposed to be up to.

In view of such a situation, the present invention aims to provide a thermocouple in which a molten part is not enlarged in a dumpling form and a manufacturing method thereof, and a solder-free micro-temperature measuring part.

In the thermocouple of the invention 1, in the temperature measuring unit, the portions where the two thermocouple wires are in contact with each other are melted and integrated, and the size (diameter) of the melted portion is 2 of the wire thickness. It is characterized by being less than double.

Invention 2 is the thermocouple of Invention 1, characterized in that the wire diameter of the thermocouple wire is 100 μm or less.
A third aspect of the present invention is the thermocouple of the first or second aspect, wherein the temperature measuring unit is solder-free.

Invention 4 is a method for forming a temperature measuring contact of a thermocouple according to any one of Inventions 1 to 3, wherein the K shown in the following (Equation 1) is 0.2 or more in fusion joining of two thermocouple wires. As described above, it is characterized by performing pulsed high-voltage microdischarge in an inert gas.
(Formula 1)
The invention 5 is the thermocouple temperature measuring contact forming method of the invention 4, wherein the K shown in the (Equation 1) is 1.5 or more, and the high voltage micro discharge is performed only once for two thermocouples. It is characterized by performing fusion bonding of strands.
The invention 6 is the thermocouple temperature measuring contact forming method of the invention 4, wherein the K shown in the (Equation 1) is 0.3 or more, and the high voltage micro discharge and the cooling by non-discharge are repeated many times. It is characterized by melting and joining two thermocouple wires.

By suppressing the enlargement of the temperature measuring section and reducing the diameter of the thermocouple wire, measurement sensitivity and responsiveness are improved, providing an extremely sensitive thermocouple that could not be expected in the past. I was able to.
In addition, since a solder-free temperature measuring unit has been achieved, it has become possible to measure high temperatures without being affected by solder.

Invention 4 improves the energy controllability for forming the temperature measuring contact and suppresses the enlargement of the melted part, compared with the conventional welding method, and the size of the temperature measuring part is reduced. It was possible to make it less than twice the thickness.
Moreover, solder-free was realized by melting and integrating the strands.

In the following examples, a method for forming a temperature measuring contact of a K thermocouple (+ leg: chromel alloy,-leg: alumel alloy) is described. Applying this method, there are examples in which a high melting point tungsten wire and metal particles other than gold and nickel are bonded to each other, such as platinum thermocouples such as R thermocouples and B thermocouples, WRe5: 26 type, etc. The melting point of the ultra-high temperature thermocouple material is lower than the melting point of tungsten at 3422 ° C. Therefore, if it is an ultra-thin thermocouple with a wire diameter of several tens of μm, it can also be used to form temperature measuring contacts for these thermocouples it can. (For details, see [No.01-26] Proceedings of the 9th meeting of the Japan Society of Mechanical Engineers, Mechanical Materials and Materials Processing Technology [2001-11.08,09, Okinawa], p.89-90, Unexplored Science and Technology Association 14th. Abstracts of the 1st Intelligent Materials / Systems Symposium Asia Workshop “2005-03.09,10, Tokyo”, p.78-79, Proceedings of the 2002 Fall Meeting of the Powder Engineering Society [2002-11.14,15, Chiba], p.144-145)
In these public information and examples, the strands are moved by hand and crossed while observing the tip portions of the two strands with a microscope as a pre-stage of temperature measuring contact formation. With such a method, it is difficult to cross the tip portions of the two wires with high accuracy, and in the first embodiment, the tip portions of the two thermocouple wires are crossed so as to protrude slightly. The protruding part remains even after the temperature measuring contact is formed, which hinders temperature measurement with high accuracy and high sensitivity. Therefore, it is necessary to cross so that the tip of the thermocouple wire does not jump out. Therefore, if a mechanism for feeding out the thermocouple wire wound in a reel shape along the guide is provided, the tips can be crossed only by feeding the strand.
The energy at this time was set so that K shown in the following (Expression 1) was 0.3 or more.
(Formula 1)
In the case where the strands are melted by only one high voltage micro discharge, K is set to 1.5 to 3.0, more preferably 2.5 or less. In this case, if K in (Expression 1) is 1.4 or less, a part of the temperature measuring contact is melted but is not completely melted and integrated.
Further, if K is excessive, energy is excessively supplied, and it is considered that melting of the strands and enlargement of the temperature measuring contact may occur.
In the case where the high-voltage micro discharge and the non-discharge cooling are repeatedly performed, the energy during one discharge is K in (Expression 1), more preferably 0.2 or more. It is preferably 3 or more and 1.0 or less, more preferably 0.8 or less.
If it is less than 0.2, the wires are not sufficiently melted and cannot be used stably as a temperature measuring contact.
Further, it is considered that if the discharge exceeding 1.0 is repeated, melting of the strands and enlargement of the temperature measuring contact may occur.

Embodiments of the present invention will be described with reference to the accompanying drawings. In this example, an example of producing an alumel alloy-chromel alloy (K) thermocouple using ultrafine thermocouple wires having wire diameters of 13 μm, 25 μm, and 50 μm is shown. Note that the K thermocouple is a material that has a large difference in the melting point of the two strands and is difficult to join because it is easily oxidized at a high temperature. 1 and 2 show schematic views of a method for forming a temperature measuring portion of a thermocouple according to the present invention. FIG. 1 is a method of standing a thermocouple wire vertically, and FIG. 2 is a method of laying a thermocouple wire horizontally. In any case, in order to facilitate the handling, the base wire (1) which is considerably thicker and the same quality as the above-mentioned wire is used and an extra fine thermocouple wire is added. In the method of FIG. 1, a pair of base lines (1) having a diameter of 0.2 mm are fixed to a metal substrate (5) serving as a ground electrode standing vertically, and the metal substrate is fixed to a work table (12). At this time, the base line (1) and the metal substrate are set to the same potential.

Also, an extremely fine alumel alloy wire (2) and a chromel alloy wire (3) are soldered to each base line (1). The tips of the ultrafine alloy wires are fixed so that they protrude from the metal substrate by 0.5 mm or more and cross and contact each other. The metal needle is arranged vertically so that the tip of the metal needle (6) serving as the application electrode comes to a position about 1 mm or less directly above the intersection (4). The voltage application side of the pulse type high voltage power source (7) was connected to the metal needle, and the ground potential (8) side was connected to the metal substrate. While flowing an inert gas (9) from above the metal needle, a high voltage is applied to the metal needle to cause discharge between the metal needle and the intersection.
In addition, the time t in the formula (1) is an application time when a current is applied in the pulse method.

In the method of FIG. 2, a pair of base wires (1) having a diameter of 0.2 mm, to which ultrafine thermocouple wires are soldered, are fixed to a metal substrate (5) serving as a ground electrode, and the upper surface of the work table (12) of the apparatus. Put on. The metal needle is vertically arranged so that the tip of the metal needle (6) serving as the application electrode is positioned at a position of about 0.1 mm directly above the intersection (4), and an inert gas is formed from above the metal needle as in FIG. While flowing (9), a high voltage is applied to the metal needle to cause discharge between the metal needle and the intersection. The metal needle was tungsten having a tip radius of 2 μm, a tip angle of 5 °, and an axial diameter of 0.66 mm. The applied voltage was 2 kV to 10 kV and applied for 0.5-1 second. Note that a power source having a Cockcroft-Walton circuit whose voltage is restored at a high speed when a discharge occurs is used, and a current of about 1 mA is actually flowing in pulses during the discharge for one second. The inert gas was allowed to flow from 5 seconds before the start of discharge to 5 seconds after the end of discharge.

FIG. 3 shows a state during discharge when a thermocouple wire having a wire diameter of 25 μm is used upright as shown in FIG. As the inert gas, a mixed gas of helium-10% hydrogen was flowed at a rate of 1 liter per minute, and the whole including the base line was maintained in a state of being enveloped by the mixed gas, and the periphery of the discharge flame was shielded from the atmosphere. The surrounding pressure was maintained at normal pressure (the same applies hereinafter). The distance between the metal needle and the thermocouple element crossing was 400 μm, the applied voltage was 5 kV, the rated current was 1 mA, and the discharge time was 0.5 seconds. Each photo in the figure was taken at 1/30 second intervals, and there are two images on one screen because the same thing is taken simultaneously from different directions. The discharge occurs while wrapping the two strands, and after about 0.1 seconds from the start of the discharge, the strands become incandescent (photo at the right end of the upper stage in the figure). Further, about 0.4 seconds after the start of discharge, the two strands were fused and integrated. At this time, the tip of the strand was bent because of high temperature (second photo from the left in the fourth row in the figure). FIG. 4 is an SEM photograph showing the appearance of the thermocouple after the end of discharge. The white circle part in the center of the photograph is melt-bonded, and the size is about 1.5 times the wire diameter. The wire in front of the photo is the chromel alloy leg (wire), and the back is the alumel alloy leg (wire). Since the alumel alloy has a melting point lower than that of the chromel alloy, it is considered that the alumel alloy is completely melted and gathered at the intersection or partly blown off by discharge. Only the chromel alloy was bent.

FIG. 5 shows one frame of a moving image in which a state during discharge when a thermocouple strand having a strand diameter of 50 μm is vertically set is photographed. Nitrogen is flowed as an inert gas at a rate of 1 liter per minute, the periphery of the discharge flame is shielded from the atmosphere, and the discharge is generated so as to wrap the thermocouple wire. The operation of separating the metal needle from the thermocouple element by 600 μm, setting the applied voltage to 5 kV, applying the voltage for 1 second, and resting for 0.5 seconds (non-discharge and cooling with the shielding gas) was repeated 26 times. When the number of repetitions of discharge-pause was 10 times or more, the rate of heat dissipation with respect to heat input was reduced, and the upper part of the alumel alloy wire near the metal needle was accumulated and became incandescent.
In addition, one time K in (Formula 1) was 0.4.

FIG. 6 shows the appearance of the intersection after the end of discharge. The region indicated by the solid circles is the portion where the thermocouple wires at the intersection are joined. Rather than the wires being integrated, a large number of minute joints are generated at the contact portion. The melted part that becomes the temperature measuring part is very small and has a small heat capacity. Therefore, it is considered that the temperature can be measured with high responsiveness and high sensitivity.
A region indicated by a dot-and-dash line is a portion where the alumel alloy wire is melted into a spherical shape by high-voltage discharge and has a diameter of 70 μm (1.4 times the strand diameter). In this experiment, the tips of the two thermocouple wires intersect each other in a slightly protruding shape, but by minimizing the protrusion and optimizing the discharge conditions, the wire diameter is 25 μm. It is possible to form a temperature measuring part in which the intersecting part is completely melted and to form a temperature measuring contact having a minute volume equivalent to the spherical part indicated by a one-dot chain line.

FIG. 7 shows an example of the result of component analysis of the temperature measuring contact portion of the produced ultrafine thermocouple using an energy dispersive X-ray fluorescence analyzer (hereinafter abbreviated as EDX). The presence of Ni, Cr and Mn, which are components of the alumel alloy as the leg and the chromel alloy as the leg, was clearly shown. Table 1 shows the results of displaying the composition of the wire and the temperature measuring contact portion measured by EDX in weight%, and the upper part shows the minimum value and the lower part shows the maximum value, respectively.

Since EDX is originally intended for qualitative analysis of a minute region and accurate quantitative analysis is difficult, the maximum and minimum values of each measurement result vary greatly, and there are some that differ by about an order of magnitude. FIG. 8 is an SEM photograph of the entire cross section polished after embedding the temperature measuring unit shown in FIG. 4 with resin. The large round part shown in the lower left of the photo is bubbles left in the resin. A portion surrounded by a white circle is a cross section of the temperature measuring unit. Cross sections other than the temperature measuring section are a chromel alloy wire and an alumel alloy wire. FIG. 9 shows an enlarged image of the cross section of the temperature measuring section. A thin film is present on the surface of the cross section after polishing. Table 2 shows the results of measuring the surface of the thermocouple temperature measuring section of FIG. 4, the cross section thereof shown in FIG. 9 and the surface of a commercially available K thermocouple temperature measuring section having a wire diameter of 0.5 mm by EDX.

* Indicates the result of the surface of the temperature measuring unit in FIG. 4, ** indicates the result of the cross section of the temperature measuring unit shown in FIG.
There are few Ni components of the surface of the temperature measuring part made as a trial compared with the inside. On the other hand, each component of Al, Cr, Si, and Mn is largely detected on the surface side. The thin film in FIG. 9 is a deposited layer due to rapid heating / cooling phenomenon of high voltage discharge. It cannot be said that the components detected in the cross section of the temperature measuring section are different in composition from the commercially available thermocouple wires having a wire diameter of 0.5 mm, except that each component of Pb and Sn exists.

Table 3 shows the results of measuring the temperature while raising the temperature stepwise by placing the prototype thermocouple and a commercially available thermocouple in the same thermostat (SIBATA, STO-300).

The difference from a commercially available thermocouple was less than 1 degree until the set temperature of the thermostat was about 250 ° C. Table 4 shows thermocouple prototypes, commercial products with a diameter of 50 μm, and commercial products with a diameter of 0.5 mm arranged in a heating furnace (KDF, Model 1700), and the set temperature is set to 150 ° C. to 650 ° C. at intervals of 50 ° C. The results of temperature measurement while increasing in steps are shown. Up to 450 ° C, the output temperature difference between each thermocouple was about 2-3 ° C. Above that, only the 50 μm diameter commercial product tends to have a lower output temperature. At 650 ° C., there is a difference of 8 ° C. from the other two thermocouples.

* Indicates the result of the surface of the temperature measuring unit in FIG. 4, and *** indicates the result of the surface of a commercial product.
In addition, in the method of forming the temperature measuring contact of the ultrafine thermocouple, the thermocouple fixing method, the distance between the metal needle and the thermocouple, the applied voltage, the application time, the inert gas species, etc. are limited to the values shown here. Not.

FIG. 10 is a schematic explanatory diagram of the apparatus. This apparatus is a pulse-type high-voltage bonding apparatus that enables thermocouple wires having a diameter of 20 μm or more to be melt-bonded to form a temperature measuring contact of a thermocouple while observing and recording a microscopic image. This apparatus includes an electric stage (10) for moving a metal substrate (5) attached to a workbench (12) to a predetermined position, a pulse-type high voltage power source (7), a metal needle (6), an inert gas A supply part (13) and a microscope (11) for observing the joining of the thermocouple are the main components.

The outline of the apparatus of the present invention will be described below with reference to FIG. Since the wire diameter of the target thermocouple is 20 μm or more, the resolution and repeat position accuracy of the electric stage are preferably about 1 μm or less. The pulse-type high-voltage power supply is a Cockcroft-Walton type that can instantaneously boost the voltage from the low-voltage region to the high-voltage region and has a small current value. The microscope is used to observe the region to be processed and to set the initial position of the metal needle and object. It can observe from low magnification to high magnification, and an entity that uses a long focus objective lens to secure a working space. A microscope was used. The inert gas is used to shield the target portion from the atmosphere, to generate a stable discharge flame, and to suppress the generation of oxides generated at the melt joint. In the present invention, a helium mixed gas containing nitrogen gas or hydrogen is used as the inert gas, but other inert gases can also be used.

Comparative Example 1

FIG. 11 is a comparative example using a strand having a wire diameter of 25 μm, and is an SEM photograph of a melted portion obtained by repeating a discharge-pause cycle of applying a voltage for 0.5 seconds and resting for 0.5 seconds. is there. The spherical part in the center of the photograph is melt-joined, and its size is more than five times the wire diameter measured on the photograph, and the part that becomes the temperature measuring contact is enlarged. In this comparative example, the rated current is the same as the result shown in FIG. 4, but the junction is enlarged because the discharge operation was applied several times instead of once.

Comparative Example 2

FIG. 12 shows a tip portion of a thermocouple having a wire diameter of 0.3 mm that is generally used. The temperature measuring part is almost spherical, and its diameter is about 1.5 mm, which is about 5 times the wire diameter.

Table 5 summarizes the above examples and comparative examples, and clarifies that the formula 1 is correct. In addition, (circle) and x of the evaluation column were judged visually from the SEM photograph.

The thermocouple according to the present invention can measure at high speed and high sensitivity, which was impossible in the past, and the thermocouple having such characteristics is considered useful in the following fields. Electronic components: Surface temperature measurement of microprocessors and other integrated circuit components for feedback control. Microtus field: Making full use of microfabrication technology, pumps, valves, flow paths, etc. are produced on the chip, analyzing biomolecules at high speed, diagnosis with trace blood, measuring drug effects, synthesis and analysis of chemical substances, Technology to perform on-chip environmental monitoring is being researched. Of the operations on the chip, it can be used for temperature measurement and control. General household: Built-in electronic thermometer, cooking thermometer and cooking utensils. Other plant temperature measurement and heat research in general: direct temperature measurement and confirmation of temperature simulation.

Of the thermocouple temperature measuring contact formation method shown in Example 1, the schematic diagram of the method of standing the thermocouple strand vertically Of the thermocouple temperature measuring contact formation method shown in Example 1, the schematic diagram of the method to lay the thermocouple wire horizontally Continuous photograph showing high-voltage discharge state in Example 1 SEM photograph showing the appearance of an ultrafine thermocouple with a diameter of 25 μm made according to Example 1. Photograph showing high-voltage discharge state in Example 1 A photograph showing the appearance of an ultrafine thermocouple having a diameter of 50 μm made according to Example 1. Qualitative analysis result by EDX of the thermocouple thermometer shown in Fig. 6 SEM photograph showing a cross section of the thermocouple of FIG. 4 made according to Example 1. Enlarged SEM photograph of the cross section of the temperature measuring section in FIG. Schematic schematic diagram of the apparatus shown in Example 2 SEM photograph showing the appearance of the ultrafine thermocouple obtained in Comparative Example 1 Photograph showing the appearance of a commercially available wire diameter 0.3 mm thermocouple

Explanation of symbols

(1) One pair of base lines (2) Extra fine thermocouple element (3) Extra fine thermocouple element (4) Intersection of thermocouple element (5) Metal substrate (6) Metal needle (7) Power source (8) Ground potential (9) Inert gas (10) Motorized stage (11) Optical microscope (12) Worktable (13) Inert gas supplier (14) Gas supply source (15) Image display / recording

Claims (6)

A thermocouple having a temperature measuring unit formed by melting and joining two thermocouple wires, wherein the temperature measuring unit is integrated by melting the portion where the two thermocouple wires are in contact with each other. A thermocouple characterized in that the size (diameter) of the melted portion is less than twice the wire thickness. The thermocouple according to claim 1, wherein a wire diameter of the thermocouple wire is 100 μm or less.   The thermocouple according to claim 1 or 2, wherein the temperature measuring unit is solder-free. The thermocouple temperature measuring contact forming method according to any one of claims 1 to 3, wherein two thermocouple wires are melt-bonded and K shown in the following (Equation 1) is 0.2 or more. A method for forming a temperature measuring contact of a thermocouple, characterized in that it is performed by pulsed high-voltage microdischarge in an inert gas.
(Formula 1)
5. The thermocouple temperature measuring contact forming method according to claim 4, wherein the K shown in (Equation 1) is 1.5 or more, and the high voltage micro discharge is performed only once for two thermocouple elements. A method for forming a temperature measuring contact of a thermocouple, characterized by performing fusion bonding of wires. 5. The thermocouple temperature measuring contact forming method according to claim 4, wherein K shown in (Equation 1) is set to 0.3 or more, and the high voltage micro discharge and the non-discharge cooling are repeated in a large number. A thermocouple temperature measuring contact forming method, characterized by melting and joining thermocouple wires of a book.