JP2008241267A - Thermocouple and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermocouple excellent in insulation reliability, position accuracy, etc. <P>SOLUTION: The thermocouple 10 is provided with a fused part 3 formed by fusing two different types of metal wires 11 and 12 to each other. The fused part 3 and the different types of metal wires 11 and 12 are coated with a DLC (Diamond-Like Carbon) layer 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermocouple and a method for manufacturing the thermocouple, and more specifically to a thermocouple capable of accurately measuring a temperature at a narrow portion and a method for manufacturing the thermocouple.

Knowing the temperature distribution of the heat medium flowing in the heat dissipation device and the molten metal in the metal manufacturing device with high accuracy is very important in the development of the heat dissipation device and the metal manufacturing device. For example, accurate grasp of the temperature distribution of cooling water in a heat radiating device for semiconductor modules for automobiles, the distribution of molten steel temperature just before solidification in a continuous casting facility for steel, etc. is very useful for the development of these devices. However, current thermocouples do not fully meet such requirements. For example, thin-film thermocouples have been proposed (Patent Documents 1 and 2) that cover a joint between dissimilar metal films formed on an insulating substrate with a protective film (Patent Documents 1 and 2). It is difficult to accurately perform temperature (position accuracy, temperature accuracy). In order to overcome such a problem, a metal wire that forms a thermocouple has been proposed in which the tip of the metal wire is covered with an insulating film (Non-Patent Document 1). According to such a thermocouple, it is possible to measure the temperature of a narrow portion with high positional accuracy.
JP-A-6-104494 JP 7-218348 A http://www.anbesmt.co.jp/tcindex.html

  However, in the thermocouple with an insulating film attached to the above metal wire, etc., an insulating coat is formed on the metal wire by applying a heat resistant resin dissolved in a solvent, so that pits etc. are likely to occur after drying and solidification. Insulation reliability is not high, and for this reason, it is necessary to form a thick insulating film by repeated coating. A thick insulating film depends on the material of the insulating film, but usually it takes a long time to stabilize the temperature due to its thick film thickness, or it can be used repeatedly from high temperature to room temperature during measurement. This causes a problem of being easily peeled off from the metal wire. For this reason, development of a thermocouple having high insulation reliability and excellent positional accuracy is desired.

  An object of the present invention is to provide a thermocouple having high insulation reliability and excellent positional accuracy.

  The thermocouple of the present invention is a thermocouple having a fusion part formed by fusing two different metal wires. This thermocouple is characterized in that the fused portion and the dissimilar metal wire are covered with a DLC (Diamond Like Carbon) layer.

DLC is composed of a diamond structure (sp ³ bond), a graphite structure (sp ² bond), and an amorphous structure, and partially includes bonds with hydrogen. The structure does not have a fixed crystal structure. Since the electric insulation tends to be determined by the portion having the highest electric resistance in the series arrangement of the crystal parts, the electric resistance of the DLC is close to the high electric resistance of the diamond structure. Further, regarding mechanical properties such as flexibility, since it includes a graphite structure, it is more elastic and has less friction than ordinary insulators.

  In general, it is not easy to form a coating film on a linear body having a diameter of a millimeter unit or less by a gas phase process. For this reason, it is usually unthinkable to form an insulating film directly on a bare thermocouple or thermocouple body by a vapor phase process. However, as a result of thinking that a vapor phase process may be effective for forming a thin insulating layer with high insulation reliability, the present invention has been achieved. To complete the present invention, there is a big factor that came up with a DLC layer as an insulating layer, but it was also due to the fact that the insulating layer that directly covers the thermocouple wire could be formed by a gas phase process. is there.

  As a result, according to the above configuration, the thermocouple body can be covered with a layer having high electrical insulation, smoothness, slidability, and hardly peeling. Since the DLC layer is formed by a gas phase process at a relatively low temperature, a dense insulating layer with few cracks and pits (pores) can be formed, and an insulating layer with high insulation reliability can be obtained. Here, the vapor phase process refers to a so-called dry process in which the material constituting the insulating layer is attached to the fused portion or the like through any one of atomic, molecular, and ionic states.

  The thickness of the DLC layer can be 2 μm or less. Thereby, peeling from the metal wire etc. of a thermocouple main-body part can be prevented much more reliably. According to this configuration, since the fused portion and the metal wire in the vicinity thereof are covered with the thin insulating layer, the temperature of the narrow portion can be accurately measured in a short time. Since the internal stress of the DLC layer is relatively large, if the thickness exceeds 2 μm, peeling from the metal wire is likely to occur under severe conditions, and the surrounding heat is transmitted through the insulating layer to the fused portion. It takes time to reach. The thickness of the DLC layer is preferably 1.5 μm or less, more preferably 1.3 μm or less, from the viewpoints of inhibiting the above-described peeling and shortening the heat conduction time. Moreover, the effect which raises peeling tolerance can also be anticipated by providing a DLC layer so that the circumference | surroundings of a line may be enclosed.

  The main body of the thermocouple can be of type K or type T. Thereby, for example, it is possible to cover all the operating environment temperatures of automobiles on the earth, and to accurately grasp the temperature distribution of the heat medium in the heat radiating device of the automobile. Of course, it can be used in a usable temperature range for applications other than automobiles. The K and T types represent the types of JIS C1602-1995 thermocouples. The K type is mainly made of plus leg (metal wire) = nickel and chromium alloy (chromel) and minus leg = nickel. The temperature range of use is −200 to 1000 ° C., and the overheat use limit temperature is 1200 ° C. The T type is an alloy (constantan) mainly composed of plus leg = copper, minus leg = copper and nickel, the use temperature range is −200 to 300 ° C., and the overheat use limit temperature is 350 ° C.

  The thermocouple manufacturing method of the present invention includes a step of fusing two dissimilar metal wires to form a fused portion, and a step of forming a DLC layer on the surface of the fused portion and the dissimilar metal wire by a vapor phase process. It is characterized by providing.

  According to this configuration, the fused portion and the metal wire in the vicinity thereof (thermocouple main body) can be covered with a dense and thin DLC layer, and the temperature of the high-temperature fluid can be measured after the DLC layer is formed. After performing, even if it cools to room temperature, it can suppress that the said DLC layer cracks and peels with a thermal stress. In this case, the thickness of the DLC layer is preferably 5 μm or less from the viewpoint of ensuring insulation. When the thickness of the DLC layer exceeds 5 μm, peeling from the metal wire is likely to occur, and it takes time for the surrounding heat to travel through the insulating layer and reach the fused portion. The thickness of the DLC layer is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 1.3 μm or less, from the viewpoints of inhibiting the peeling and shortening the heat conduction time during temperature measurement.

  As described above, the gas phase process refers to a so-called dry process in which the material constituting the edge layer is attached to the fused portion or the like through each of atomic, molecular, and ionic states. There is a wet process such as painting with a solvent as a process to be positively excluded. Specific vapor phase processes include thermal CVD (Chemical Vapor Deposition), plasma CVD, PVD (Physical Vapor Deposition) (evaporation, ion plating, sputtering), plasma ion implantation (Plasma Source Ion Implantation) ) Method. By these methods, a dense insulating layer can be formed, and an insulating layer with high insulation reliability can be obtained.

  In the DLC layer forming step, a state in which the surface of the narrow portion where the two metal lines including the fused portion intersect is exposed to the atmosphere for forming the DLC layer is predetermined with respect to the time of the DLC layer forming step. It can be done while taking the time ratio. As a result, it is possible to reliably form the DLC layer having a predetermined thickness even in a place where it is difficult to form the DLC layer. Opposite exposure means that when the atmosphere comes from a predetermined direction, it means to take an attitude toward the source, and when a static atmosphere is formed without flying in a predetermined direction. It means to take a posture toward the center of the atmosphere and expose it. The above posture can be realized by rotating the thermocouple main body. Further, the predetermined time ratio with respect to the time of the DLC layer forming step refers to a time ratio with respect to a time during which the DLC layer is in a state where it can be formed at any location of the thermocouple body.

  In the DLC layer forming step, a DLC source gas can be ionized and a bias voltage can be applied to the main body of the thermocouple or its support member. This makes it possible to efficiently form the DLC layer despite the shape of the linear body of the thermocouple that is difficult to form a film directly in the gas phase process.

  Further, in the above DLC layer forming step, the DLC layer may be covered without being actively heated. Thereby, it is possible to form a DLC layer that is hardly peeled off and excellent in electrical insulation. Here, not actively heating does not mean active heating by heaters, lamps, energization, etc., but it does not even cool the temperature rise (natural heating) due to heat generated in the film formation process. It means that it is a (left) method.

  According to the thermocouple and the manufacturing method thereof of the present invention, temperature measurement with high insulation reliability and high positional accuracy is possible.

(Embodiment 1)
FIG. 1 is a diagram showing a thermocouple 10 according to Embodiment 1 of the present invention, and FIG. 2 is an enlarged cross-sectional view of a tip portion thereof. In FIG. 1, the main body of the thermocouple 10 is a K type, a chromel wire of an alloy mainly comprising nickel and chrome constituting the plus leg 11, and an alumel wire comprising an alloy mainly comprising nickel constituting the minus leg 12. And a fused portion 3 formed by fusing them. The DLC layer 5 covers the fusion part 3, the plus leg 11 and the minus leg 12. In particular, as shown in FIG. 2, the surface of the narrow portion N where the fused portion 3 intersects the plus leg 11 and the minus leg 12 is completely covered. If the vicinity of the fusion part including the fusion part 3 is not completely covered with the DLC layer 5, an electromotive force that accurately corresponds to the temperature of the fluid does not occur, such as when measuring the temperature of an electrically conductive fluid. This is because accurate temperature measurement cannot be performed.

As described above, DLC has a long bond because the carbon-carbon bond form is composed of a diamond structure (sp ³ bond), a graphite structure (sp ² bond), and an amorphous bond, and partially includes a bond with hydrogen. It is a structure that does not have a fixed crystal structure in order of distance. The specific resistance of the DLC layer 5 shown in FIGS. 1 and 2 is (10 ⁺⁶ to 10 ⁺⁸ ) Ωcm or more. The surface roughness of the DLC layer is about 80 to 100 mm, is excellent in smoothness, and is dense. Further, the coefficient of friction is as low as 0.1 to 0.25, and the slidability is also excellent. Hardness is as hard as HV1000-4000.

  The thickness of the DLC layer 5 is preferably 5 μm or less, but is preferably 2 μm or less from the viewpoint of time response. More preferably, it is 1.5 μm or less, and further 1.3 μm or less. The DLC film 5 is highly flexible, and can be deformed following the deformation of the metal wires constituting the plus leg 11 and the minus leg 12 by reducing the thickness as described above.

  As a result, since the fused portion and the metal wire in the vicinity thereof are covered with the thin insulating layer, the temperature of the narrow portion can be measured accurately in a short time. When the thickness of the DLC layer exceeds 2 μm, peeling from the metal wire is likely to occur under severe conditions, and it takes time for ambient heat to travel through the insulating layer and reach the fused portion. The thickness of the DLC layer is preferably 1.5 μm or less, more preferably 1.3 μm or less, from the viewpoints of inhibiting the above-described peeling and shortening the heat conduction time.

(Embodiment 2)
FIG. 3 is a diagram illustrating the principle of a thermocouple manufacturing method according to Embodiment 2 of the present invention. Using the apparatus shown in FIG. 3, DLC layers are formed on the thermocouple main body portions 3, 11 and 12 by high-frequency plasma CVD. Methane (CH ₄ ) was used as the source gas, and glow discharge was generated between the opposing anode electrode and cathode electrode by applying high-frequency power, and the methane was decomposed and supported by a rotating rod-shaped support member 19. A DLC layer is formed on the thermocouple bodies 3, 11, 12. The film forming temperature is less than 200 ° C., and the hydrogen content can be set to 30 to 40 atm%. In addition, about a thermocouple main-body part, a commercially available or homemade thermocouple can be used.

  The temperature (deposition temperature) of the thermocouple main body when forming the DLC layer is ½ of the superheat limit temperature corresponding to the type of the thermocouple main body from the viewpoint of preventing alloy formation at the dissimilar metal interface. For example, the K type superheat use limit temperature is 1200 ° C., and the T type superheat use limit temperature is 350 ° C., so that it is preferably 600 ° C. or less or 175 ° C. or less, respectively. In order to further increase the temperature accuracy, it is desirable that the temperature (film formation temperature) of the thermocouple main body when forming the DLC layer be room temperature.

  According to the method of the above gas phase process, a DLC layer having good surface roughness and excellent smoothness can be obtained. In addition, since the thermocouple bodies 3, 11, and 12 are rotated, a DLC layer can also be formed on the surface of the narrow portion N. Furthermore, a uniform layer can be formed by repeatedly turning on and off the high frequency power to be applied in a short cycle.

(Embodiment 3)
FIG. 4 is a diagram illustrating the principle of the thermocouple manufacturing method according to the third embodiment of the present invention. In the present embodiment, the DLC layer is formed on the thermocouple main body by ionization vapor deposition. In this ionization deposition method, benzene (C ₆ H ₆ ), which is a raw material gas, is decomposed and ionized using thermoelectrons generated from a tungsten (W) filament, and the support member 19 and / or the thermocouple bodies 11, 12, 3. The DLC layer is formed on the thermocouple bodies 3, 11, 12 by a bias voltage applied to the thermocouple body 3. According to the method shown in FIG. 4, the film formation temperature can be less than 200 ° C., the hydrogen content can be about 15 atm%, and the hardness can be increased. Since the hardness can be controlled by the amount of hydrogen in this way, it can be used properly according to the application.

  According to the above method, since a bias voltage is applied to the thermocouple bodies 11, 12, and 3, ions intensively fly and accumulate toward the thermocouple bodies 11, 12, and 3. For this reason, although it is a linear body, a DLC layer can be efficiently formed in the thermocouple main bodies 11, 12, and 3. This is particularly effective for completely covering the narrow portion N with the DLC layer. The support member 19 and the thermocouple bodies 11, 12, and 3 need to be rotated while a bias voltage is applied, and a rotation mechanism and a voltage transmission mechanism for that purpose are required. However, a conventional rotation drive device (not shown) It can implement | achieve using the mechanism 20 containing.

(Embodiment 4)
FIG. 5 is a diagram illustrating the principle of a thermocouple manufacturing method according to Embodiment 4 of the present invention. In this embodiment, the DLC layer is formed by an arc ion plating method. In this method, a solid graphite raw material is used as a cathode, a vacuum vessel (trigger) is used as an anode, and an arc discharge is generated in a vacuum by applying a DC voltage therebetween. A plasma of carbon element is generated by this arc discharge, and a negative bias voltage is applied to the support member 19 and / or the thermocouple bodies 11, 12, and 3 more than the evaporation source, and the carbon ions in the plasma are converted into thermocouples. The film is accelerated toward the main bodies 11, 12, and 3 to form a film. According to this method, a hard DLC layer of about HV3000 that does not contain hydrogen can be formed.

  Also in the above method, since the bias voltage is applied to the thermocouple bodies 11, 12, and 3, ions intensively fly toward the thermocouple bodies 11, 12, and 3 and accumulate. For this reason, although it is a linear body, a DLC layer can be efficiently formed in the thermocouple main bodies 11, 12, and 3. This is particularly effective for completely covering the narrow portion N with the DLC layer. The support member 19 and the thermocouple bodies 11, 12, and 3 need to rotate while being applied with a bias voltage. A rotation mechanism and a voltage transmission mechanism are required for the rotation, but the mechanism 20 including a rotation drive device (not shown) is included. Can be realized. In addition to the above method, the DLC layer can also be formed by applying an ion implantation technique (PSII: Plasma Source Ion Implantation) using pulsed plasma.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the thermocouple and the manufacturing method thereof of the present invention, the temperature distribution in the electrically conductive fluid is excellent in time responsiveness, and enables highly accurate temperature measurement with respect to position and temperature.

It is a figure of the thermocouple in Embodiment 1 of this invention. It is an expanded sectional view of the front-end | tip part of the thermocouple of FIG. It is a figure which shows the principle of the DLC layer formation method in Embodiment 2 of this invention. It is a figure which shows the principle of the DLC layer formation method in Embodiment 3 of this invention. It is a figure which shows the principle of the DLC layer formation method in Embodiment 4 of this invention.

Explanation of symbols

  3 fusion part, 5 DLC layer, 10 thermocouple, 11, 12 metal wire (plus leg, minus leg), 19 support member, 20 voltage application bearing mechanism, N narrow part.

Claims (7)

A thermocouple having a fusion part formed by fusing two different metal wires,
The thermocouple, wherein the fusion bonded portion and the dissimilar metal wire are covered with a DLC (Diamond Like Carbon) layer.   The thermocouple according to claim 1, wherein the DLC layer has a thickness of 2 μm or less.   The thermocouple according to claim 1 or 2, characterized in that the thermocouple is of type K or type T. A step of fusing two dissimilar metal wires to form a fused portion;
And a step of forming a DLC layer by a vapor phase process on the surface of the fused portion and the two different metal wires.   In the DLC layer forming step, the state in which the surface of the narrow portion where the two metal lines including the fused portion intersect is exposed to the atmosphere for forming the DLC layer with respect to the time of the DLC layer forming step. The method of manufacturing a thermocouple according to claim 4, wherein the method is performed while taking a predetermined time ratio.   The thermocouple manufacturing method according to claim 4 or 5, wherein, in the DLC layer forming step, a source gas of DLC is ionized and a bias voltage is applied to the main body of the thermocouple or a support member thereof. Method. The method for manufacturing a thermocouple according to any one of claims 4 to 6, wherein in the DLC layer forming step, the DLC layer is coated without being actively heated.

Images