JP4853269B2 - Sheath thermocouple and manufacturing method thereof - Google Patents

Description

  The present invention relates to a sheathed thermocouple and a manufacturing method thereof, and more particularly, a manufacturing method of a sheathed thermocouple suitable for temperature measurement of a high-temperature / high-speed fluid such as a gas turbine, a steam turbine, and a petrochemical plant, and the manufacturing thereof. Sheathed thermocouples.

  The thermocouple uses two types of strands, and when there is a temperature difference between these connections (hot junctions), a thermoelectromotive force is generated in the closed circuit, and the Zepeck effect is used, in which current flows through the circuit. The temperature is then measured. In the sheath thermocouple, a thermocouple wire is placed in a metal sheath and filled and sealed with an inorganic insulator such as magnesium oxide (MgO) and integrated. A conventional sheathed thermocouple has two thermocouple strands whose tips are connected to each other in parallel with the folded shape at the connection, and is inserted from the base end of the rod-shaped metal sheath. In addition to being positioned at the portion, the distal end side is protruded into the fluid to be measured by supporting the sheath proximal end side in a cantilever shape, and the temperature is measured at the sheath distal end portion where the hot junction is located (for example, (See Patent Documents 1 and 2.)

  As a method for forming the tip portion of such a sheathed thermocouple, welding is performed when sealing the tip opening 110a of the metal sheath 110 containing the thermocouple 202, as shown in the sheath thermocouple 101 of FIG. There has been proposed a method in which a rod is melted and melted by an arc electrode to form a tip sealing portion 104 and a lid is applied so that an insulator does not jump out (see, for example, Patent Document 3). However, in this method, since it is necessary to use the same material as the metal sheath for the welding rod, it is necessary to check the material of the welding rod and the metal sheath every time, and whenever the material of the metal sheath changes. In addition, it is necessary to change the material of the welding rod, and there is a problem that the stock of welding rods of different materials increases, making it difficult to reduce the cost, thereby increasing the product price. Further, since it is necessary to accurately align the welding rod and the metal sheath when welding, it is difficult to automate the manufacture of the sheath thermocouple including such a welding process. Furthermore, the dedicated welding rods actually used are slightly different from the composition of the metal sheath, which causes the deterioration of durability such as oxidation resistance due to the different components.

  Further, as shown in the sheath thermocouple 201 of FIG. 13 (b), a sealing member 240 is fitted into the distal end opening of the metal sheath 210 containing the thermocouple 202, and fixed to the opening edge 210a by welding. Although a method for forming the sealing portion 204 is also performed, it is necessary to prepare a sealing member 240 that matches the inner diameter of the metal sheath separately in this method, which causes an increase in cost such as an increase in the number of parts and man-hours. . In addition, if a space is formed between the inner wall of the sheath and the embedded surface of the inorganic insulator in the distal end sealing portion, the temperature measurement accuracy is adversely affected. In such a method using the sealing member 240, the sealing member 240 itself There is a possibility that a space is likely to be generated due to the accuracy and thermal expansion / contraction of the sealing member 240, and there is a concern that the accuracy may be reduced.

JP-A-8-82557 JP 2001-165780 A Japanese Examined Patent Publication No.59-37771

  Therefore, in view of the above-mentioned situation, the present invention is to solve the problem by reducing the man-hours and improving the production speed, reducing the cost, and being suitable for automation, excellent in durability and measurement accuracy. Another object of the present invention is to provide a method for manufacturing a sheathed thermocouple and a sheathed thermocouple manufactured thereby.

  In order to solve the above problems, the present invention accommodates at least a pair of thermocouple wires and an inorganic insulator filling the gap between the thermocouple wires and the metal sheath inside the metal sheath, and hermetically seals the distal end side. In the sheath thermocouple thus formed, as a hermetic seal on the metal sheath tip side, a tip end portion made of the metal sheath material is melted by melting a sheath tip portion extending a predetermined length from the embedded surface of the inorganic insulator A sheathed thermocouple characterized by forming a portion was constructed. Here, the “predetermined length” is a length set in order to form a tip sealing portion having a target capacity, and is set as appropriate based on dimensions such as the thickness and diameter of the metal sheath.

  Here, it is preferable to melt the sheath distal end portion in a cylindrical shape, after the distal end is reduced in diameter, or after being crimped into a predetermined shape.

  In addition, it is preferable that the sheath distal end portion is formed in a substantially hemispherical shape by being melted substantially uniformly over the entire circumference from the distal end edge while keeping the tubular shape or reducing the diameter of the distal end.

  The present invention also includes a sheath thermocouple in which at least a pair of thermocouple wires and an inorganic insulator that fills the gap between the thermocouple wires and the metal sheath are housed inside the metal sheath and the tip side is hermetically sealed. In the manufacturing method, the hermetic sealing at the distal end side of the metal sheath sets the embedded surface of the inorganic insulator at a predetermined depth from the distal end edge of the metal sheath, thereby extending a predetermined length from the embedded surface. A sheath thermocouple manufacturing method is also provided, wherein the sheath tip portion is melted to form a tip sealing portion made of the metal sheath material.

  Also here, it is preferable to melt the sheath distal end portion in a cylindrical shape, after the distal end is reduced in diameter, or after being crimped into a predetermined shape.

  In addition, it is preferable that the sheath distal end portion is formed in a substantially hemispherical shape by being melted substantially uniformly from the distal end edge over the entire circumference after the distal end portion remains in a cylindrical shape or the diameter of the distal end is reduced.

  More specifically, a long metal sheath containing at least a pair of thermocouple wires and an inorganic insulator that fills a gap between the thermocouple wires and the metal sheath is cut to a predetermined length, and the cut metal sheath is cut. The inorganic insulator is removed from one end of the substrate, the pair of thermocouple wires is projected, the protruding thermocouple wires are connected to form a hot junction, the inorganic insulator is backfilled, and the inorganic insulator After setting the embedded surface at a position at a predetermined depth from the metal sheath front edge and after crimping the sheath tip portion extending a predetermined length from the embedded surface as it is or after reducing the diameter of the tip, or after crimping to a predetermined shape It is preferable that the tip sealing portion is formed by melting. Here, “long” means, for example, about 10 m, and a length that can be efficiently divided into a plurality of lengths is set, but the dimensions are not particularly limited.

  Further, the method of forming the hot junction is such that the inorganic insulator is removed from a jig provided with an outer peripheral surface fitted into one end of the metal sheath and a notch portion having a substantially V-shaped longitudinal section at the tip end surface. The inorganic insulator attached to the inner wall of the end portion of the metal sheath is scraped off at the outer peripheral surface of the jig, and at the same time, a pair of thermocouple wires forming a hot junction are substantially V-shaped in the notch portion. It is preferable that the thermocouple element ends are connected by bending them so that they stand against each other.

  In addition, a long metal sheath containing at least a pair of thermocouple wires and an inorganic insulator that fills a gap between the thermocouple wires and the metal sheath is cut into a predetermined length, and one end of the cut metal sheath is cut The inorganic insulator is removed from the side, a pair of thermocouple wires are protruded, the sheath tip portion is melted, and the protruding thermocouple wires are embedded in the tip sealing portion made of the metal sheath material. Preferably, for example, the sheath tip portion is crimped into a predetermined shape so as to sandwich the protruding thermocouple wire, and then melted.

  Further, in the method of melting after crimping the sheath distal end portion into a predetermined shape, the length along the sheath longitudinal direction of the caulking portion caulking the sheath distal end portion into a predetermined shape is 1 to 3 times the outer diameter of the sheath. It is preferable that the cross-sectional shape of the caulking portion caulking the sheath distal end portion into a predetermined shape is symmetrical with respect to the sheath axis, and in particular, the caulking portion is in at least three directions from the sheath axis. It is preferable that it is comprised from the crimping piece extended.

  The sheath tip portion is preferably melted by welding.

  According to the present invention as described above, since it is not necessary to use a welding rod, the material confirmation work of the welding rod and the sheath is not required, man-hours can be reduced, the production speed can be improved, and a stock of welding rods of different materials is held. Therefore, it is possible to reduce the cost, and it is not necessary to accurately position and weld the welding rod and the metal sheath, so that it is suitable for automating the manufacturing process. Moreover, the problem that the different components of the welding rod lower the oxidation resistance is solved, and a sheath thermocouple excellent in durability and measurement accuracy can be provided at low cost.

  In addition, the sheath distal end portion can be reliably secured by an appropriate method according to the sheath diameter, thickness, etc., by melting the sheath distal end portion in a cylindrical shape, after reducing the diameter of the distal end, or after crimping to a predetermined shape. And it can be made to melt | dissolve so that it may become a substantially semicircle.

  In addition, a long metal sheath containing a thermocouple wire and an inorganic insulator is cut to a predetermined length, the inorganic insulator is removed from one end of the cut metal sheath, and a pair of thermocouple wires is attached. Projecting, connecting the protruding thermocouple wires to form a hot junction, backfilling the inorganic insulator, setting the embedded surface of the inorganic insulator at a predetermined depth from the metal sheath tip edge, and extending Since the sheath tip portion that is being taken out is melted, it is excellent in response to mass production, and production efficiency can be improved.

  In addition, as a method of forming a hot junction, a jig provided with an outer peripheral surface fitted into one end of the metal sheath and a notch portion having a substantially V-shaped longitudinal section at the tip end surface is formed by removing the inorganic insulating material from the empty surface. The inorganic insulator attached to the inner wall of the end portion of the metal sheath is scraped off at the outer peripheral surface of the jig, and at the same time, a pair of thermocouple wires forming a hot junction are formed on the substantially V-shaped surface of the notch. Since the ends of the thermocouple strands are connected by bending them so as to guide each other, deposits can be removed and hot junctions can be formed at the same time, stably without increasing the number of man-hours. It can be sealed with high airtightness.

  In addition, a long metal sheath containing a thermocouple wire and an inorganic insulator is cut to a predetermined length, the inorganic insulator is removed from one end of the cut metal sheath, and a pair of thermocouple wires is attached. By projecting, melting the sheath tip portion, and embedding the projecting thermocouple wire in the tip sealing portion made of the metal sheath material, a contact-type sheath thermocouple with quick response can be obtained at low cost. Can be provided.

  In addition, by setting the length of the caulking portion along the longitudinal direction of the sheath to 1 to 3 times the outer diameter of the metal sheath, the size of the caulking piece is optimal for melting, and the sheath after being melted It becomes easy to seal with high airtightness by making the thermocouple tip shape good.

  Furthermore, by making the cross-sectional shape of the caulking portion symmetrical with respect to the sheath axis, it is easy to form the sheath tip shape after melting into a substantially hemispherical shape without uneven thickness. Become.

  In addition, since the caulking portion is composed of caulking pieces extending in at least three directions from the sheath axis, the strength of the caulking portion is improved, and the occurrence of defective products due to bending of the caulking pieces can be reduced.

  Further, the sheath tip portion can be easily and reliably hermetically sealed by melting by welding.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an explanatory view showing a sheath thermocouple according to the present invention. FIGS. 1 to 5 are a first embodiment, FIG. 6 is a second embodiment, FIGS. 7 to 11 are a third embodiment, and FIG. In the drawings, reference numeral 1 denotes a sheath thermocouple, 2 denotes a thermocouple, 3 denotes an inorganic insulator, 4 denotes a tip sealing portion, and 10 denotes a metal sheath.

  As shown in FIG. 1, the sheath thermocouple 1 includes a thermocouple 2 including a pair of thermocouple wires 21 and 21 inside the metal sheath 10, and an inorganic insulator that fills a gap between the thermocouple 2 and the metal sheath 10. 3 and the tip side is hermetically sealed, and the one end side that is hermetically sealed is the tip side that protrudes into the fluid to be measured when measuring the temperature. In particular, as shown in FIG. 3, the present invention melts the sheath tip portion 11 extended from the embedded surface 31 of the inorganic insulator 3 by a predetermined length L as an airtight seal on the tip side of the metal sheath 10, It is characterized by forming a tip sealing portion 4 made of a metal sheath material.

  Except for the tip sealing portion 4, the same material as the conventional sheathed thermocouple can be used for the materials such as the metal sheath 10, the thermocouple 2, and the inorganic insulator 3 and the structure of each part. As the metal sheath 10, austenitic stainless steel (SUS304, SUS316, etc.), nickel chrome heat-resistant alloy (Inconel), or the like can be used, and magnesium oxide (MgO) or the like is used as the inorganic insulator 3 filled in the sheath. However, it is not limited to these. Further, the thermocouple element 21 constituting the thermocouple 2 can be made of, for example, a nickel-chromium alloy for the plus element and a nickel alloy for the minus element, but is not particularly limited. In this example, only one pair of thermocouple wires 21 and 21 is accommodated, but a plurality of pairs may be inserted as a matter of course. Further, although the thermocouple is connected to the lead wire 6 via the compensating lead wire in the connecting portion 5 on the proximal end side of the sheath thermocouple 1, it is not limited to such a structure, and for example, a sleeve-like protection Various conventional connection structures such as a flameproof explosion-proof type supported by a tube and connected to a measuring instrument with a compensating lead wire extending from the terminal box, and those with a detachable connector without using a terminal box can be adopted. .

  First, based on FIGS. 1-5, 1st Embodiment of this invention is described.

  The sheath thermocouple 1 of the present embodiment is a non-contact type sheath thermocouple, and as shown in FIG. 3, the embedded surface 31 of the inorganic insulator is used as an airtight seal on the tip side of the metal sheath 10 as shown in FIG. 10a is set to a position of a predetermined depth L, so that the sheath distal end portion 11 extended from the embedded surface 31 of the inorganic insulator by a predetermined length is melted substantially uniformly over the entire circumference from the distal end edge 10a in a cylindrical shape. By doing so, a substantially hemispherical tip sealing portion 4 is formed.

  The steps until the sheath tip portion 11 is configured are as shown in FIG. That is, first, the long metal sheath 10 containing the pair of thermocouple wires 21 and 21 and the inorganic insulator 3 filling the gap between the thermocouple wires 21 and the metal sheath 10 is cut to a predetermined length (S101). Then, the inorganic insulator is removed from one end side of the cut metal sheath 10 and a pair of thermocouple wires 21 and 21 set to a predetermined length are projected (S102), and the thermocouple wires 21 and 21 are The hot junction 22 is formed by connecting at the tip (S103). Here, the hot contact 22 is formed in the same manner as in the third embodiment described later by simultaneously scraping off the inorganic insulator 3 attached to the sheath inner wall 25 using the jig 9 as shown in FIG. The pair of thermocouple strands 21 and 21 may be bent so as to lean against each other, and the tip portions of the thermocouple strands may be connected to each other.

  Then, after refilling the inorganic insulator 3 and burying the hot junction 22 (S104), the inorganic insulator 3 is removed so that the buried surface 31 is positioned at a predetermined depth L from the distal end edge of the metal sheath. (S105). Here, in order to remove the inorganic insulator, an end mill, a drill, or the like is preferably used, and it is more preferable to carry out while removing the shavings generated at this time by suction or air blowing. Thereby, it is possible to prevent the inorganic insulator from being included when the sheath tip portion 11 is melted.

  As another method for forming the sheath distal end portion 11, as shown in FIG. 4, the metal sheath 10 is cut to a predetermined length (S301), and a pair of hot contacts 22 are previously formed on the metal sheath 10. It is of course possible to adopt a method in which the hot junction 22 is buried with the inorganic insulator 3 and set to a predetermined depth L after the thermocouple element 21 is inserted (S302).

  Next, in the step of melting the sheath distal end portion 11 to form the distal end sealing portion 4, as shown in S 201 to 203 in FIG. 3, the sheath distal end portion 11 is melted substantially uniformly over the entire circumference from the distal end edge 10 a. Thus, the substantially hemispherical tip sealing portion 4 is formed (S204). Although it does not restrict | limit especially as a melting method, Since welding can be carried out easily and reliably, welding is used. Specifically, the sheath distal end portion 11 is melted by arc welding or TIG welding without using a welding rod. By melting the sheath tip portion 11 in this way, it becomes easy to produce a sheath thermocouple having almost no excess bubbles at the sheath thermocouple tip and having high airtightness. Since it is not necessary to accurately position and weld, it is suitable for automating the manufacturing process. When melting, suction from the other end of a metal sheath (not shown) with a vacuum pump or the like to keep the inside of the sheath in a reduced pressure state ensures airtight sealing without any air remaining inside. Is preferable.

  The sheath thermocouple manufactured in this way has a substantially hemispherical tip shape that is not biased in thickness, and the thermal expansion of the bubbles occurs when the bubbles are bitten or when the bubbles melt the sheath thermocouple tip. As a result, surface irregularities and distortions are hardly generated, the airtightness is high, and the cost can be reduced. In addition, since it is a non-contact type, it is highly durable and can withstand long-time use.

  In the above example, the sheath distal end portion 11 is melted in a cylindrical shape. However, as shown in FIG. 5, the distal end is reduced in diameter and melted substantially uniformly from the distal end edge 10a over the entire circumference. Is also a preferred embodiment. According to this, even when the diameter of the metal sheath 10 is large, welding can be performed smoothly.

  Next, a second embodiment of the present invention will be described based on FIG.

  In the present embodiment, a contact-type sheath thermocouple is configured. As shown in FIG. 6, a pair of thermocouple wires 21 and 21 are accommodated, and an inorganic insulator 3 is placed between these thermocouple wires. The filled long metal sheath 10 is cut to a predetermined length (S401), the inorganic insulator 3 is removed from one end side of the cut metal sheath 10, and the thermocouple strand 21 set to a predetermined length, 21 is protruded, and the embedded surface 31 of the inorganic insulator 3 is set to a predetermined depth L (S402). Then, the sheath tip portion 11 protruding from the embedded surface 31 is melted, and the thermocouple wires 21 and 21 protruding similarly are embedded in the tip sealing portion 4 made of the metal sheath material (S403). ).

  The sheath thermocouple manufactured in this way has a substantially hemispherical tip shape with no bias in thickness, has almost no excess air bubbles, has high airtightness, and is low in cost. Become. Moreover, since it is a contact type, the response at the time of temperature measurement is quick. Others are the same as those in the first embodiment, and a description thereof will be omitted.

  Next, a third embodiment of the present invention will be described with reference to FIGS.

  The sheath thermocouple 1 according to the present embodiment is of a non-contact type, and after the sheath tip portion 11 extended by a predetermined length L is caulked into a predetermined shape to form a caulking portion 13, the caulking portion 13 is melted to form the tip sealing portion 4 made of the metal sheath material. In the present invention, “caulking” is performed in the same manner as the conventional caulking method using a jig or mold having various shapes (not shown) in order to obtain the desired caulking portion 13 shape. Although not limited, in order to obtain a desired caulking shape, it is preferable to gradually form the desired caulking portion 13 shape through several steps of load application because the load on the metal sheath 10 is dispersed. .

  Specifically, as shown in FIG. 8, a long metal sheath 10 containing a pair of thermocouple wires 21 and 21 and filled with an inorganic insulator 3 between the thermocouple wires has a predetermined length. (S501), the inorganic insulator 3 at one end of the cut metal sheath 10 is removed, and a pair of thermocouple wires 21 and 21 set to a predetermined length are protruded (S502). The strands 21 and 21 are connected to form a hot junction (S503). Then, the buried surface 31 in which the inorganic insulator 3 is backfilled and the hot junction 22 is buried is set to a predetermined depth L (S504), and then the sheath distal end portion 11 extending from the buried surface 31 by a predetermined length is determined in advance. The shape is caulked (S505), and the caulking portion 13 is melted to form the tip sealing portion 4 (S506).

  More specifically, when forming the hot junction 22, as shown in FIG. 9, an outer peripheral surface 9b fitted into one end of the metal sheath 10 and a notch 9a having a substantially V-shaped longitudinal section at the distal end surface thereof. Is inserted into the void from which the inorganic insulator 3 is removed ((a) in the figure), and the inorganic insulator 3 attached to the inner wall 25 at the end of the metal sheath 10 is inserted into the outer peripheral surface of the jig 9. At the same time as scraping off at 9b, the pair of thermocouple wires 21 forming the hot junction 22 are guided to the substantially V-shaped surface of the notch 9a and bent so as to lean against each other ((b) in the figure). The ends of the thermocouple strands are connected ((c) in the figure).

  As the shape of the jig 9, it is more preferable that the notch has a conical shape, and it is more preferable to insert such a jig 9 while rotating the jig 9 into a space where the inorganic insulator 3 is removed. Needless to say, the step of forming the hot junction 22 and the step of scraping off the inorganic insulator 3 attached to the inner wall 25 at the end of the metal sheath 10 may be provided separately. As a method for removing the inorganic insulator 3, other than the above method, for example, a method of removing by an ultrasonic wave may be employed.

  As in the first embodiment, as another method of constructing the sheath distal end portion 11, as shown in FIG. 10, the metal sheath 10 is cut to a predetermined length (S601), and the metal sheath 10 is preheated. After inserting the pair of thermocouple wires 21 forming the contact 22 (S602), the hot contact 22 is buried with the inorganic insulator 3 and set to a predetermined depth L (S603, S604). Is also possible.

  For example, as shown in FIGS. 11 (a) to 11 (e), the cross-sectional shape of the caulking portion 13 is symmetrical with respect to the sheath axis 23, so that the sheath tip shape after melting is the meat. It is preferable because it is easy to form a substantially hemispherical shape with no uneven thickness. Further, by forming the caulking portion 13 from the caulking piece 12 extending in at least three directions from the sheath axis 23, the strength of the caulking portion can be improved, and the occurrence of defective products due to bending of the caulking piece can be reduced. Since it can do, it is more preferable. For example, the caulking portion shown in FIGS. 11 (b) and 11 (d) is formed of caulking pieces 12 that are symmetrical with respect to the sheath axis 23 and extend in three directions, as shown in FIG. 11 (c). The caulking portion shown is symmetrical with respect to the sheath axis 23 and is composed of caulking pieces 12 extending in four directions. Further, by setting the length A of the caulking portion 13 along the sheath longitudinal direction to 1 to 3 times the sheath outer diameter B, the size of the caulking piece 12 is optimal for melting, and is high. It becomes easy to seal with airtightness.

  As in the first embodiment, the caulking portion 13 is melted by welding, in particular, by welding the metal sheath 10 while reducing the pressure inside the metal sheath 10 by sucking the other end 24 of the metal sheath using, for example, a vacuum pump. preferable. By forming the caulking portion 13 in this way and melting it, welding can be performed smoothly even if the metal sheath has a large diameter, and the tip sealing portion 4 is substantially hemispherical with no uneven thickness. Can be. Others are basically the same as those in the first embodiment, and the same structure is denoted by the same reference numeral and the description thereof is omitted.

  Next, based on FIG. 12, 4th Embodiment of this invention is described.

  The sheath thermocouple 1 of the present embodiment is a contact type thermocouple in a case where a caulking portion is formed and melted as in the third embodiment. As shown in FIG. 12, a pair of thermocouples is used. A long metal sheath 10 containing the pair of strands 21 and 21 and filled with the inorganic insulator 3 between these thermocouple wires is cut to a predetermined length, and inorganic insulation is provided from one end of the cut metal sheath 10. The object 3 is removed, the thermocouple wires 21 and 21 set to a predetermined length are projected to set the embedded surface 31 to a predetermined depth L, and each thermocouple wire 21 is cut to an appropriate length (S701), after crimping the sheath tip portion 11 into a predetermined shape so as to sandwich the thermocouple wires 21 and 21 (S702), the tip 13 made of a metal sheath material is melted by melting the crimp portion 13 Thermocouple strands 21 and 21 are embedded in stopper 4 Those were.

  In this case, since it is necessary to crimp the pair of thermocouple wires 21 so as to be sandwiched in the crimping piece 12, the shape of the crimping portion 13 is as shown in FIGS. 11 (a), 11 (c) and 11 (e). In addition, it is preferable that the shape is constituted by the caulking pieces 12 that are symmetrical with respect to the sheath axis 23 and extend in an even number direction.

  The embodiments of the present invention have been described above, but the present invention is not limited to these examples. For example, when the metal sheath has a small diameter (for example, an outer diameter of 0.25 to 1.6 mm), Since the space volume in the sheath is small, there is no particular problem as a sheath thermocouple having a space in the interior without burying the hot junction 22 with the inorganic insulator 3, and the scope not departing from the gist of the present invention. Of course, it can be implemented in various forms.

A 3.2 mm, 2.3 mm, and 1.6 mm Inconel sheath type K thermocouple with the tip sealed and welded using a welding rod for Inconel defined by JIS standards by the conventional manufacturing method shown in FIG. As a result of conducting tests at 1150 ° C., 1100 ° C., 1050 ° C. and other accelerated test temperatures and measuring the time-dependent change in EMF, the estimated inconel endurance time while the EMF value was within the range of class II The sheath was damaged in a shorter time. The consideration will be described below.

  FIG. 14 shows an observation result of the cross-section of the damaged part by an optical microscope, and Table 1 below shows a comparison result of quantitative analysis of SEM / EDX elements in the vicinity of the welded part of the damaged product. From this FIG. 14 and Table 1, the following is considered. The sheath base material portion in the vicinity of the tip sealing portion of the damaged product is covered with an oxide whose main component is dense chromium oxide (location B), but the base material (location C) remains. . Although grain boundary oxides of the constituent elements Cr, Fe, and Ni are precipitated at the crystal grain boundaries of the base material, the grain boundary oxidation does not reach to the extent that it penetrates the base material. On the other hand, the sheath tip sealing portion is not completely oxidized and a part of the metal structure remains. A characteristic of the residual structure is that a large amount of oxide is precipitated at the grain boundaries. Further, as can be seen from Table 1, the component of the residual structure is different from the original Inconel sheath base material, and is probably a component that has disappeared due to oxidation from the component of the tip welded portion (welding rod component) immediately after welding.

  Next, the Inconel sheath type in which the tip is sealed and welded using a welding rod for Inconel defined by JIS standards in the same way as the damaged product, in order to investigate the cause of oxidative wear in the range of about 1 mm length near the tip of the damaged product A K thermocouple (Comparative Example 1) and an Inconel sheath type K thermocouple (Example 1) in which the sheath tip part is melted and sealed without using a welding rod by the method of the first embodiment of the present invention. A comparative observation was conducted. 15A shows the result of observation by the scanning electron microscope of the cross section near the tip sealing portion of Comparative Example 1, and FIG. 15B shows the result of scanning electron microscope observation of the cross section near the tip sealing portion of Example 1. FIG. A result is shown and Table 2 has shown the SEM / EDX element quantitative analysis comparison result of the welding part vicinity of the comparative example 1 and Example 1. FIG. The difference between the two in the scanning electron micrograph of FIG. 15 is clear. In Example 1, the base material and the tip sealing portion were naturally uniform, but in Comparative Example 1 sealed with a welding rod, welding was performed. There are signs of heterogeneity at the interface. From the analysis results of Table 2, Comparative Example 1 contains Mn and Nb that are not originally included in the sheath base material, and other elements are slightly different from the base material.

  From the above-mentioned damaged products, the observation results of Comparative Example 1 and Example 1, the following is assumed. First, the welding rod for Inconel is inferior in oxidation resistance to Inconel itself. In addition, the sheath base material forms a dense chromium oxide film on the surface, and the oxide film functions to suppress uniform oxidation from a certain level of the surface. From the characteristics of the welded rod, the grain size of the crystal structure after welding is larger than that of the base material, and easily oxidizable additive elements such as Mn and Nb are precipitated at the grain boundaries, resulting in a uniform surface from the surface. It can be considered that grain boundary oxidation occurred in addition to oxidation. Therefore, it is considered that the oxidation durability was inferior to that of the base material. From this, it can be seen that the present invention in which the base material itself is melted without using a welding rod and the tip is sealed has excellent oxidation resistance.

Explanatory drawing which shows the sheath thermocouple which concerns on 1st Embodiment of this invention. Explanatory drawing which shows the process until it comprises a sheath front-end | tip site | part. Explanatory drawing which shows the process of fuse | melting a sheath front-end | tip part and comprising a front-end | tip sealing part. Explanatory drawing which shows the other method of forming a sheath front-end | tip part. Explanatory drawing which shows the modification which shrinks | reduces a sheath front-end | tip part and fuse | melts. Explanatory drawing which shows the manufacture procedure of the sheath thermocouple which concerns on 2nd Embodiment of this invention. The perspective view which shows the typical shape of the crimping | crimped part in the manufacturing process of the sheath thermocouple which concerns on 3rd Embodiment of this invention. Explanatory drawing which similarly shows the manufacture procedure of the sheathed thermocouple which concerns on 3rd Embodiment. (A)-(c) is explanatory drawing which shows the method of forming the hot junction of a thermocouple. Explanatory drawing which shows the other method of forming a sheath front-end | tip part. (A)-(e) is explanatory drawing which shows the modification of a caulking part shape, respectively. Explanatory drawing which shows the manufacture procedure of the sheath thermocouple which concerns on 4th Embodiment of this invention. (A), (b) is explanatory drawing which shows the conventional sheathed thermocouple. An optical micrograph of a cross-section of a damaged part. (A) is a scanning electron micrograph of the cross section near the tip sealing portion of Comparative Example 1, and (b) is a scanning electron micrograph of the cross section near the tip sealing portion of Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sheath thermocouple 2 Thermocouple 3 Inorganic insulator 4 Tip sealing part 5 Connection part 6 Lead wire 9 Jig 9a Notch 9b Outer peripheral surface 10 Metal sheath 10a Tip edge 11 Sheath tip part 12 Caulking piece 13 Caulking part 21 Thermocouple Wire 22 Warm contact 23 Axle 24 Other end 25 Inner wall 31 Embedded surface

Claims (6)

In a sheath thermocouple, in which at least a pair of thermocouple wires and an inorganic insulator that fills the gap between the thermocouple wires and the metal sheath are accommodated inside the metal sheath, and the tip side is hermetically sealed, the tip of the metal sheath As a hermetic seal on the side, the sheath tip part extended a predetermined length from the embedded surface of the inorganic insulator remains in a cylindrical shape or the tip is reduced in diameter, and then substantially uniformly from the tip edge to the entire circumference. A sheathed thermocouple characterized by melting and thereby forming a substantially hemispherical tip sealing portion made of the metal sheath material. In the method of manufacturing a sheath thermocouple, in which at least a pair of thermocouple wires and an inorganic insulator that fills the gap between the thermocouple wires and the metal sheath are housed inside the metal sheath, and the tip side is hermetically sealed,
Upon hermetic sealing of the metal sheath tip side, the embedded surface of the inorganic insulator is set at a position at a predetermined depth from the metal sheath tip edge,
Thereby, after the sheath tip portion extending a predetermined length from the embedded surface remains in a cylindrical shape or the tip is reduced in diameter, it is melted substantially uniformly over the entire circumference from the tip edge,
Thus, a substantially thermospherical tip sealing portion made of the metal sheath material is formed. A long metal sheath containing at least a pair of thermocouple wires and an inorganic insulator that fills the gap between the thermocouple wires and the metal sheath is cut to a predetermined length, and from one end side of the cut metal sheath Remove the inorganic insulator, protrude the pair of thermocouple wires, connect the protruding thermocouple wires to form a hot junction, backfill the inorganic insulator, and replace the embedded surface of the inorganic insulator with metal set from the sheath tip edge position of a predetermined depth, the tip seal of the substantially hemispherical shape by melting after the sheath distal end portion that extends a predetermined length from said buried surface, which has a reduced diameter as it or tip The method for manufacturing a sheathed thermocouple according to claim 2, wherein the stop portion is formed. The method for forming the hot junction is to remove the inorganic insulator from a jig provided with an outer peripheral surface fitted into one end of the metal sheath and a notch portion having a substantially V-shaped longitudinal section at the tip end surface. The inorganic insulator attached to the inner wall of the end portion of the metal sheath is scraped off at the outer peripheral surface of the jig, and at the same time, a pair of thermocouple wires forming a hot junction are guided to the substantially V-shaped surface of the notch portion. 4. The method for manufacturing a sheathed thermocouple according to claim 3, wherein the thermocouple element ends are bent so as to lean against each other. A long metal sheath containing at least a pair of thermocouple wires and an inorganic insulator that fills the gap between the thermocouple wires and the metal sheath is cut to a predetermined length, and from one end side of the cut metal sheath The inorganic insulator is removed, a pair of thermocouple wires are protruded, the sheath tip portion is melted, and the protruding thermocouple wires are embedded in a tip sealing portion made of the metal sheath material. A method for manufacturing a sheathed thermocouple according to claim 2 . The method of manufacturing a sheath thermocouple according to claim 2 or 3 , wherein the sheath tip portion is melted by welding.