JPS6361606B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sheathed thermocouple and a method for manufacturing the same, and more specifically, it can be effectively used in an oxidizing or reducing atmosphere in a temperature range of 350 to 1000°C,
Moreover, the present invention relates to a thermocouple and a method for manufacturing the same that enable stable temperature measurement over a long period of time without breaking the thermocouple wire even under conditions accompanied by vibrations. Conventional sheathed thermocouples, such as thermocouples using wires made of chromel/alumel or chromel/constantan, can effectively measure temperatures up to about 1000°C in an oxidizing atmosphere, but on the other hand, they cannot be used in a reducing atmosphere, especially hydrogen. Under conditions including hydrogen, the chromel wire is rapidly selectively oxidized by the action of hydrogen diffusing into the sheath wall, which not only makes the thermoelectromotive force value unstable, but also leads to wire breakage in some cases. It has its drawbacks. On the other hand, iron/constantan and copper/constantan are known as thermocouple wires that can be used in a reducing atmosphere, but both iron and copper wires have poor oxidation resistance, and in the case of iron wires, temperatures around 770°C It has a magnetic transformation point, which is usually 0.02~ in the case of copper wire.
Contains 0.06% oxygen by weight, which makes the 350
Hydrogen embrittlement is significant in a reducing atmosphere of ℃ or higher, especially in conditions containing hydrogen, which not only makes the thermoelectromotive force value unstable, but also has the disadvantage of easily breaking the wire in a short time under usage conditions accompanied by vibration. The operating temperature is
It is also determined by the JIS standard, and the value is 750 for iron wire when the sheath outer diameter is 6.4 mm.
℃, and in the case of copper wire, it is limited to 350℃ or less.
Putting all the above together, a conventional sheathed thermocouple will reach a temperature of 350°C.
As mentioned above, measuring temperature over a long period of time under both oxidizing and reducing atmospheres at high temperatures of 750 to 1000° C. has its own problems. The present invention was developed to solve the above-mentioned conventional drawbacks and problems. A hot junction is formed using a certain oxygen-free copper (hereinafter copper with an oxygen content of approximately 0.005% by weight or less is referred to as oxygen-free copper) in a vacuum or an inert gas atmosphere such as argon or helium. The sheath is placed separately from the sheath tip sealing part, and the sheath is evacuated or filled with an inert gas such as argon or helium to airtightly seal the open end of the sheath. This is a sheath type thermocouple that can be used in both reducing and reducing atmospheres. Hereinafter, a specific example of the thermocouple of the present invention will be explained based on the drawings. In FIG. At the same time, make the inside a vacuum or fill it with an inert gas such as argon or helium, and the other end (right end in the figure)
The opening is sealed with a sealant 7 made of epoxy resin or the like to prevent oxidizing gas such as air from entering the sheath. 2 is an inorganic insulator made of MgO, etc., which is filled in the metal sheath 1 to prevent the thermocouple wires 3 and 4 from coming into contact with each other and with the metal sheath 1; Abbreviation for content
It is made of oxygen-free copper limited to 0.005% by weight or less, preferably 0.0004 to 0.0009% by weight, and is separated from the welded sealing part 6 by constantan or other conventionally known thermocouple wire 4 to form a hot junction 5. The thermocouple of the present invention is constructed as described above. Further, it is desirable that such a sheathed thermocouple of the present invention be manufactured by the following manufacturing method. In other words, the oxygen content in the thermocouple copper wire 3 is approximately 0.005.
Oxygen-free copper with a content of not more than 0.0004 to 0.0009% by weight is used, and this copper wire 3 and other thermocouple wires 4, such as constantan, are inserted into the sheath 1, and an inorganic insulator such as MgO is used. 2, the inorganic insulator 2 in the tip of the sheath is removed to create a space in which a hot junction 5 can be formed between the two strands 3 and 4. The hot junction 5 can be formed in a vacuum or with argon, The test shall be conducted in an inert gas atmosphere such as helium. Next, after filling the space at the tip of the sheath 1 with the inorganic insulator 2 again, the tip was closed with a welded sealing part 6 using an appropriate means, and this welding sealing part 6 was separated from the hot junction 5. After that, the remaining air inside the sheath 1 is removed or replaced with an inert gas such as argon or helium, and the open end of the sheath 1 is sealed with a sealing material 7 to ensure airtightness. It is the one that obtains the pair. The atmosphere during the formation of the hot junction 5 is a vacuum or an inert gas atmosphere, and the residual air inside the sheath 1 is removed or replaced with an inert gas before sealing the open end with the sealing material 7. In one example, the inside of a container with a predetermined capacity is evacuated or filled with an inert gas such as argon or helium, and the hot junction 5 is formed and sheathed with the sealing material 7 in this container. 1. The open end shall be sealed. Furthermore, the present invention is not limited to the above-mentioned sheath type thermocouple; for example, the thermocouple copper wire 3 made of the above-mentioned oxygen-free copper and another thermocouple wire 4 such as constantan can be combined with an insulator. It goes without saying that the present invention is also applicable to a protective tube that is internally sealed at one end and manufactured in the same manner as the manufacturing method described above. In the thermocouple of the present invention constructed and manufactured as described above, the thermocouple copper wire 3 has an oxygen content of 0.005% by weight or less, more preferably 0.0004 to 0.0009% by weight.
By using so-called oxygen-free copper, the hydrogen embrittlement resistance of the copper wire 3 can be dramatically improved, and therefore a stable thermoelectromotive force value can be maintained even in a reducing atmosphere, especially under conditions containing hydrogen. Not only that, but also a thermocouple copper wire having excellent mechanical strength such as repeated bending strength can be obtained.In addition, by using this thermocouple copper wire 3 and other thermocouple wire 4 such as constantan Since the hot junction 5 is formed in a vacuum or in an inert gas atmosphere such as argon or helium, oxygen absorption from the atmosphere is eliminated when the hot junction 5 is formed, thereby preventing hydrogen embrittlement of the hot junction 5. We were able to.
In addition, this hot junction 5 is connected to the welded sealing part 6 at the end of the sheath 1.
Because it is placed separately from the sheath, the sheath material can be changed to stainless steel,
Even when the sheath 1 is made of a heat-resistant alloy such as Inconel, there is no need to consider problems such as the integrity of the bond between the heat-resistant alloy and the thermocouple wire. By filling with an inert gas such as argon or helium, it is possible to prevent the thermocouple copper wire 3 and the hot junction 5 from oxidizing under high-temperature usage conditions, and it can be used for a long time even in an oxidizing atmosphere. This allows stable temperature measurement over time. Below, various experimental results regarding the thermocouple according to the present invention will be described. First of all, Table 1 below shows comparative experimental values of the repeated bending strength of copper strands.
After being held in a hydrogen atmosphere at temperatures of 1 hour and 950°C, the repeated bending strength at room temperature was compared.

[Table] As is clear from Table 1, conventional thermocouple copper wires suffer from significant hydrogen embrittlement and cannot withstand even one bending, leading to wire breakage. The wire can be repeatedly bent at least three times even under the most severe conditions of 950°C, and a copper wire with an oxygen content of 0.0006% by weight can be bent repeatedly as many as nine times. It has been confirmed that this copper wire has extremely superior hydrogen embrittlement resistance compared to conventional products, and thermocouples using this copper wire can be used in reducing atmospheres containing hydrogen at temperatures above 350°C and up to at least 950°C. Moreover, it is possible to measure temperature stably over a long period of time without disconnection even under conditions accompanied by vibration. Next, the sheath type thermocouple of the present invention has a sheath 1 having an outer diameter of 6.4 mm, and a copper wire 3 made of oxygen-free copper with an oxygen content of 0.005% by weight and a constantan wire 4 having a diameter of 1.1 mm. is placed in a circular electric furnace,
Furnace temperature 750℃, 850℃, 950℃ under oxidizing atmosphere
The temperature was maintained at a constant temperature, and an experiment was conducted to examine the change in thermoelectromotive force value at each temperature. The results are shown in FIG. Note that these temperatures cannot be measured with conventional copper/constantan thermocouples. Curve A in the graph in the figure represents the results at 750°C, curve B at 85°C, and curve C at 950°C.As is clear from this graph, the sheathed thermocouple of the present invention has an initial temperature of The thermoelectromotive force change after 500 hours relative to the electromotive force value is +0.7℃ at 750℃ and +0.7℃ at 850℃ in temperature terms.
It was confirmed that the thermoelectromotive force value was extremely small, such as +1.2°C at 1.0°C and 950°C, and showed a stable thermoelectromotive force value for a long time up to a high temperature range of about 1000°C. In this way, the thermocouple of the present invention achieves its original purpose.
It enables stable temperature measurement over long periods of time in both oxidizing and reducing atmospheres at high temperatures of 350 to 1000°C, and can be used without any problems, especially in hydrogen-containing atmospheres and under operating conditions with vibrations. It is possible to do so.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a sheath type thermocouple showing an example of the present invention, and FIG. 2 is a graph showing changes over time in the thermoelectromotive force value at a predetermined temperature of the thermocouple of the present invention. 1: Metal sheath, 2: Inorganic insulator, 3: Thermocouple copper wire, 4: Thermocouple wire, 5: Hot junction, 6: Weld sealing part, 7: Sealing material.

Claims (1)

[Scope of Claims] 1. A sheath type thermocouple which is used in both oxidizing and reducing atmospheres at 350 to 1000°C and is made by housing a pair of thermocouple wires in a metal sheath via an inorganic insulator. The oxygen content in one thermocouple wire is approximately 0.005.
Oxygen-free copper with a weight percentage of less than A sheath type thermocouple filled with 2 Oxygen content as oxygen-free copper is approximately 0.0004 ~
The sheathed thermocouple according to claim 1, which utilizes 0.0009% by weight of copper. 3. A method for manufacturing a sheath type thermocouple, which comprises a pair of thermocouple wires used in both oxidizing and reducing atmospheres at 350 to 1000°C and housed in a metal sheath via an inorganic insulator. Using oxygen-free copper with an oxygen content of approximately 0.005% by weight or less for the thermocouple wire, a hot junction is formed in a vacuum or an inert gas atmosphere such as argon or helium, and then separated from the hot junction. A method for producing a sheathed thermocouple, in which the tip of the sheath is sealed, the remaining air inside the sheath is removed, or after removal, the air is filled with an inert gas such as argon or helium, and the open end of the sheath is hermetically sealed.