JP2008107115A - Sheathed thermocouple and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheathed thermocouple hardly generating disconnection of a thermocouple element, having an elongated lifetime, and its manufacturing method. <P>SOLUTION: This sheathed thermocouple 1 has a constitution wherein a pair of thermocouple elements 3, 3 and an insulating material 4 are provided inside a cylindrical metal sheath 2 having a closed tip, and each of the pair of thermocouple elements 3, 3 is formed spirally. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sheathed thermocouple used for measuring the temperature in a furnace, for example, in a heating furnace, and a manufacturing method thereof.

  As the above-described sheath thermocouple, a pair of thermocouple wires 102 and 102 are formed by interposing a powdered inorganic insulating material 101 made of magnesia, alumina, or the like in a metal sheath 100 as shown in FIGS. What was accommodated is known (see, for example, Patent Document 1).

Such a sheathed thermocouple is a bare wire because the thermocouple wire 102 is isolated from the atmosphere by the metal sheath 100 when used in a harsh environment such as a corrosive atmosphere such as a heating furnace or an oxidizing atmosphere. Compared to the steel material, there is an advantage that it has a long life, and since the insulating material 101 is provided, the metal sheath 100 and the thermocouple wire 102 are not easily in contact with each other, and the steel material that is the outer shell of the heating furnace that is the installation object There is also an advantage that it is not necessary to consider the insulation between the metal materials.
JP 2006-138647 A

  However, since the conventional thermocouple wire 102 is linear, there is a problem that the thermocouple wire 102 is easily broken in the following cases.

  One of the cases is when the sheath thermocouple is repeatedly heated and cooled repeatedly. That is, when the sheath thermocouple is heated rapidly, a state in which the sheath is hot and the thermocouple strand is still cold is transiently generated, and the thermocouple strand is subjected to stress that is pulled in the axial direction due to thermal expansion of the sheath. work. Conversely, when it is rapidly cooled, the sheath is transiently cooled first and compressive stress is applied. Due to cycle fatigue associated with the repeated generation of tensile and compressive stresses, the thermocouple wire may break. At this time, if the thermocouple wire has scratches or uneven dimensional dimensions, or if the sheath thermocouple has a bent portion with a small bending radius, the thermocouple wire is more likely to break. The reason is that when the former thermocouple wire has scratches or dimensional irregularities, the stress concentrates on the scratches or small diameter portions. Further, when the latter sheath thermocouple has a bending portion with a small bending radius, stress concentration occurs on the thermocouple wire in the bending portion due to repeated rapid heating and cooling as described above.

  The other is a case where a bending force is repeatedly applied to the sheath thermocouple. For example, when the sheath thermocouple is installed in the movable part, the sheath may be bent repeatedly due to the sheath thermocouple being bent along with the movement of the movable part.

  The present invention has been made in order to solve the above-described problems of the prior art, and is suitable for a sheathed thermocouple and a sheathed thermocouple that can prevent the disconnection of the thermocouple wire and prolong the service life. An object is to provide a manufacturing method.

  In the sheath thermocouple of the present invention, a pair of thermocouple wires and an insulating material are provided inside a cylindrical metal sheath whose tip is closed, and each of the pair of thermocouple wires is formed in a spiral shape. (Claim 1).

  A method for manufacturing a sheathed thermocouple according to the present invention is a method for manufacturing a sheathed thermocouple according to claim 1, wherein a pair of thermocouples is formed on a surface of an insulator made of an inorganic insulating material and having a substantially cylindrical shape. A step of winding each of the strands in the opposite direction; and the insulator around which the pair of thermocouple strands are wound is inserted into a sheath metal tube, and an insulating material is interposed between the sheath metal tube and the insulator A step of filling the sheath metal tube, a step of drawing the sheath metal tube, reducing the diameter of the sheath metal tube, stretching a pair of thermocouple wires, and crushing the insulator It is characterized by including.

  In the case of the sheath thermocouple according to the present invention, the pair of thermocouple wires provided inside the cylindrical metal sheath whose tip is closed are spiral and act like a coil spring. Even if heating and cooling are suddenly repeatedly applied or bending force is repeatedly applied to the sheath thermocouple, it is difficult for the thermocouple element to break, thereby extending the life of the sheath thermocouple. obtain.

  In the case of the sheath thermocouple manufacturing method of the present invention, each of the pair of thermocouple wires is wound around an insulator made of an inorganic insulating material in the opposite direction, and the powdered inorganic insulating material is used as the sheath metal tube and the above insulator. A pair of spiral thermocouple wires with a desired dimension of the axial length (L) of one turn can be easily produced by extending each thermocouple wire by drawing after that. can do. Further, since the insulator is pulverized and powdered by drawing, the bendability of the sheath thermocouple is not lost.

  The sheath thermocouple according to the present invention will be specifically described below. FIG. 1 is a cross-sectional view showing a sheath thermocouple according to an embodiment of the present invention.

  This sheath thermocouple 1 is provided inside a cylindrical metal sheath 2 whose tip is closed, a pair of thermocouple wires 3 and 3 provided inside the metal sheath 2, and the metal sheath 2. The insulating material 4, the cylindrical sleeve 5 fixed to the opening side of the metal sheath 2, the sealing material 6 provided inside the sleeve 5, and the thermocouple wires 3 and 3 inside the sleeve 5, respectively. Compensation conductors 7 and 7 connected to each other.

  The metal sheath 2 is made of, for example, stainless steel such as SUS304 or SUS316, or a material such as Inconel 600. The outer diameter of the sheath 2 is 4.8 mmφ, and the thickness of the sheath 2 is 0.72 mm. The material of the sheath 2 is not limited to the stainless steel or Inconel 600, but may be other materials. Further, the outer diameter and thickness of the sheath 2 are not limited to the above dimensions.

  Each thermocouple wire 3 is formed in a spiral shape, and a temperature measuring contact 3a connected to each other is provided on the tip side thereof. That is, the shape of each thermocouple wire 3 is a spiral shape in which the distance from the axis is substantially constant and the axial length (L) of one turn is the same except for the temperature measuring contact 3a. Yes. Compensation lead wires 7 are connected to the base end side (opposite the tip) of each thermocouple wire 3. An insulating coating 8 is provided on the outer side of each compensation lead wire 7 so that they are insulated from each other. As the material of the thermocouple wire 3, for example, chromel is used on the plus side and alumel is used on the minus side. The diameter of the strand 3 is set to 0.76 mm, for example. The material and diameter of the strand 3 are not limited to those described above, and other materials and diameters can be used.

  The axial length (L) of one turn in the spiral thermocouple element 3 is, for example, 5 mm. However, the length (L) of one turn in the axial direction may be other dimensions, may be different over the entire length, and may be different in each thermocouple wire 3.

  The insulating material 4 is for preventing the thermocouple wire 3 and the sheath 2 from coming into contact with each other, and is a powder made of an inorganic material such as magnesia, for example.

The sheath thermocouple according to the present embodiment having such a configuration is manufactured as follows, for example.
As an example, a sheath thermocouple in which the outer diameter of the sheath 2 is 4.8 mmφ and the one-turn axial length (L) of the spiral thermocouple element 3 is 5 mm will be described. As shown in FIG. 2 (a), for example, an inorganic insulating material made of magnesia is used as a raw material, and a cylindrical insulator 10 having an outer diameter of about 3 mmφ is used, and the tip is joined to the surface of the insulator 10 to measure the temperature. A thermocouple wire 3a 3a is wound in a spiral shape with an axial length (L ′) of one turn shorter than an axial length (L) of one turn of 5 mm. At this time, the temperature measuring contact 3a is positioned at the end of the insulator 10, and each thermocouple element 3 is wound in the opposite direction.

  Next, as shown in FIG. 2 (b), a sheath 2 metal tube 2 'having an outer diameter of 6 mmφ and a shorter length than the sheath 2 is used, and the insulator 10 is inserted into the metal tube 2'. To do. At this time, it is preferable to make the axial center of the insulator 10 and the axial center of the metal tube 2 ′ coincide. Subsequently, the powdered inorganic insulating material 4 is filled into the metal tube 2 ′. The metal tube 2 'is open at both ends.

  Next, as shown in FIG. 2C, the metal tube 2 ′ in this state is reduced in diameter and length by drawing using a die 11. As the die 11, a hole die or a roller die is used. By this drawing process, a rod-shaped body having a spiral thermocouple element 3 and an insulating material 4 having a one-turn axial length (L) of 5 mm in a sheath 2 having an outer diameter of 4.8 mmφ. Is produced. In the drawing process, the insulator 10 is pulverized and powdered to become a part of the insulating material 4.

  Subsequently, although not shown in the figure, for the sheath 2 in which both ends are open, a process for sealing the opening on the temperature measuring contact 3a side and a process on the other end side of the sheath 2 (that is, the cylindrical sleeve 5 and the sealing material 6). Then, the sheathing thermocouple 1 shown in FIG. 1 is manufactured.

  Note that the timing of joining the temperature measuring contact 3a may be performed after the drawing process and in the process of sealing the temperature measurement contact 3a side opening of the sheath 2. Further, by setting the position of the temperature measuring contact 3a when the thermocouple wire 3 is spirally wound around the surface of the insulator 10 to a position other than the end, for example, the temperature measuring contact in the middle of the length of the insulator 10 By positioning 3a, it is also possible to produce a sheathed thermocouple 1 having a temperature measuring contact 3a at a desired position in the axial direction.

  In the case of the sheathed thermocouple according to this embodiment having this configuration, since the thermocouple element 3 formed in a spiral shape is used, disconnection hardly occurs in the thermocouple element. This will be described in detail below.

  The spiral thermocouple element 3 works like a coil spring. Therefore, even if rapid heating / cooling is repeatedly applied, the tensile / compressive force received by the thermocouple wire 3 is small, so that even if the thermocouple wire 3 has scratches or uneven dimensional dimensions, disconnection hardly occurs. Further, when the sheath thermocouple has a bent portion having a small bending radius, a certain amount of stress concentration occurs in the thermocouple wire 3 of the bent portion, but the thermocouple wire 3 is also spiral in the bent portion. Yes, if the axial length (L) of one turn of the spiral wire is set to a sufficiently short length of about 5 mm as described above with respect to the length of the bent portion, stress is concentrated in one place. The thermocouple wire 3 is not easily broken due to dispersion and rapid heating / cooling repetition. Further, even when a bending force is repeatedly applied to the sheath thermocouple, the thermocouple wire 3 is not easily broken because the stress of the thermocouple wire in the bent portion is also dispersed.

  In the above-described embodiment, the thermocouple element 3 is applied to the K thermocouple shown in JIS1602 using chromel on the plus side and alumel on the minus side. The invention can be similarly applied to other types of thermocouples such as R thermocouples and N thermocouples.

  Moreover, although the example which used magnesia is given as the inorganic insulator 10 and the powdered inorganic insulating material 4 in the above-described embodiment, the present invention is not limited thereto, and other inorganic insulating materials such as alumina and silica are used. Further, different inorganic insulators may be used for the inorganic insulator 10 and the inorganic insulator 4.

It is sectional drawing which shows the sheath thermocouple which concerns on one Embodiment of this invention. It is explanatory drawing of the manufacturing method of the sheath thermocouple of FIG. It is sectional drawing which shows the conventional sheathed thermocouple. It is sectional drawing by the IV-IV line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sheath thermocouple 2 Metal sheath 3 Thermocouple strand 4 Powdered inorganic insulating material 2 'Metal tube for sheaths 10 Insulator 11 Dice

Claims (2)

  A sheath in which a pair of thermocouple wires and an insulating material are provided inside a cylindrical metal sheath whose tip is closed, and each of the pair of thermocouple wires is formed in a spiral shape thermocouple. A method for manufacturing a sheathed thermocouple according to claim 1, comprising:
A step of winding each of a pair of thermocouple wires in opposite directions around the surface of an insulator made of an inorganic insulating material, which is substantially cylindrical,
Inserting the insulator around which the pair of thermocouple strands are wound into a sheath metal tube and filling a powder for an insulating material between the sheath metal tube and the insulator;
A step of drawing the sheath metal tube to reduce the diameter of the sheath metal tube, extending a pair of thermocouple strands, and crushing the insulator. Manufacturing method.

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