JPS5984126A - Sheath thermocouple - Google Patents

Abstract

PURPOSE:To obtain a sheath thermocouple whose fixing operation is comparatively easy and having good sealability by providing a thermocouple in a protecting tube consisting of a sealing alloy through an insultor, and forming the sheath thermocouple. CONSTITUTION:A chormel-alumel thermocouple is inserted into a protecting tube consisting of a sealing alloy e.g. 50wt% Ni-Fe to fill an insulator e.g. magnesia type ceramics. The diameter of the protecting tube is decreased to a desired value by surface decrease working, and further the protecting tube is cut down to the desired length. Respective wires of the thermocouple are connected at the another cut end, where the protecting tube is sealed airtightly to form a pre-oxide film on the surface of the protecting tube in a moist hydrogen furnace.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an improvement in a temperature detection system and a method for manufacturing the same.

[Technical background of the invention and its problems]

Conventionally, when fixing the heat pair to a glass thread for temperature detection, the thermocouple was fixed to the glass system using low melting point glass. This method has the effect of relatively easily fixing the thermocouple to the glass system, but on the other hand, the sealing property, that is, the airtightness between the thermocouple and the glass system, is not sufficient, and improvements have been desired.

In particular, improvements have been desired for sealing in vacuum systems where airtightness is required. However, improving sealing properties generally results in inferior fixing workability, and it has been relatively difficult to achieve both properties.

[Purpose of the invention]

An object of the present invention is to provide a temperature detection system in which (0) the fixing operation is relatively easy when fixing a thermocouple to a glass system, and (2) the sealing performance is good.

[Summary of the invention]

To achieve the above object, the present invention provides a sheathed thermocouple in which a thermocouple is provided in a sealing alloy protective tube through an insulator, and a method for manufacturing the same.

In the present invention, it is not necessary to fix each wire of a thermocouple as in the conventional case, and it is only necessary to fix one protective tube, making the fixing work relatively easy.

Furthermore, the sealing alloy has good wettability with glass, which also contributes to ease of fixing work. A sealing alloy with optimal wettability may be selected as appropriate depending on the glass to be fixed.

Next, we will discuss sealing properties.

In the present invention, since a sealing alloy is used for the protection tube, it is easy to approximate the coefficient of thermal expansion to that of glass, and it is possible to prevent deterioration of sealing properties due to temperature changes. Among the sealing alloys, it is preferable to select a sealing alloy whose thermal expansion coefficient is similar to that of the glass to be fixed within the operating temperature range.1 For example, 45.4 to 50 in the temperature range of 30 to 400 degrees Celsius. By selecting a nickel-cobalt-iron alloy as the sealing alloy for glass having a coefficient of thermal expansion of .8 (XIO-'/''C), a bond with excellent sealing properties can be obtained.

In addition, the current temperature range of 30 to 330°C is 45 to 65 (XIO
By selecting a 42 wt % nickel-iron alloy as the sealing alloy for glass having a thermal expansion coefficient of -7°C, a bond with excellent sealing properties can be obtained.

In addition, 94-104 (XIO
By selecting a 5Qwt% nickel-iron alloy as the sealing alloy for glass having a thermal expansion coefficient of 1/°C), a bond with excellent sealing properties can be obtained.

In addition, 95 to 102 (XIO
By selecting a nickel-chromium-iron alloy as the sealing alloy for glass having a thermal expansion coefficient of -77'C), a bond with excellent sealing properties can be obtained.

In addition, 110 to i 19 (
By selecting a chromium-titanium-iron alloy as a sealing alloy for glass having a coefficient of thermal expansion of 100° C. (XI O-7/° C.), a bond with excellent sealing properties can be obtained.

Also, 105 to 114 (X
By selecting a chromium-iron alloy as the sealing alloy for glass having a coefficient of thermal expansion of 10° C.), a bond with excellent sealing properties can be obtained.

As described above, the sealing alloy provides excellent sealing performance by selecting the optimum alloy based on both the wettability and thermal expansion coefficient of the glass to be fixed.

Next, the manufacturing method will be described.

In the present invention, a thermocouple is inserted into a sealed alloy protection tube, the tube is filled with an insulator, the area of the protection tube is reduced to a desired diameter, and the protection tube is cut to a desired length.

Then, connect the thermocouples at one end of this cut,
The protective tube at the edge of the blade is hermetically sealed and a preliminary oxidation film is formed on the surface of the protective tube in a wet hydrogen furnace.

This method is an industrially advantageous method with less waste in producing the sheathed thermocouple of the present invention. Thermocasople of the required length can be obtained by cutting a single long seed-41 mokatsuburu into the desired length, so there is no need to create a production process for each length, and industrial production is possible. The cost is advantageous. When a protective tube is sealed to a glass-based material, an oxide of the sealing alloy, which has better wettability than the sealing alloy and has a coefficient of thermal expansion similar to that of glass, is formed as a bonding layer. However, in the case of a chromium-based sealing metal, its oxide is extremely brittle and reduces the sealing performance. As a result of research into the production method of chromium oxide, we discovered the following.

It has been found that a dense and uniform oxide film can be produced by pretreating a chromium-based sealing metal with an acid in a reducing atmosphere. By performing preliminary oxidation in a reducing atmosphere, the sealing properties of chromium-based sealing alloys can also be significantly improved.

As a reducing atmosphere, a wet hydrogen atmosphere is industrially inexpensive and easy to use.

[Embodiments of the invention]

Example 1 An embodiment of the sheathed thermocouple of the present invention will be described.

An alumel-chromel thermocouple is wrapped in magnesia ceramic, and the magnesia ceramic is placed in a 50 wt% nickel-iron alloy R1i tube. Using this sheathed thermocouple, we sealed it to a soda-lime glass vacuum chamber, but it was easy to work with, and the sealing properties were not so good, so we were able to obtain a vacuum that was reliable during the day.

Example 2 An example of the method for manufacturing a sheathed thermocouple of the present invention will be described.

18th% chromium-Q, 4wt% iron alloy pipe is filled with one thermocouple wire Almeru-Chromel, filled with magnesia and drawn to a diameter of 0.6 mm. Next, this pipe was cut into a length of 4 m, an alumel wire and a thin chromel wire were connected at one end of the cut, and the insulated pipe was hermetically sealed by welding. Next, this image storage tube was heated to a furnace temperature of 900°C to 1200"C1 hydrogen dew point of 0 to 40°C for 1 hour.
A wet hydrogen treatment was performed for 0 to 90 minutes to form an oxide film on the surface.

When this sheathed thermocouple was sealed to a soda-lime glass vacuum tube, a highly reliable vacuum was obtained.

[Effects of the Invention] The present invention provides a sheathed thermocouple in which a thermocouple is placed in a sealing alloy storage tube through an insulator, and a method for manufacturing the same, so that the fixing work is relatively easy and the sealing process is easy. A temperature sensing thread with good properties can be provided.

Claims (1)

[Claims] 1. A sheathed thermocouple comprising a thermocouple, an insulator containing the thermocouple, and a sealing alloy protection tube containing the thermocouple and the insulator. 2. The sheathed thermocouple according to claim 1, wherein the sealing alloy is a nickel-cobalt-iron alloy. 3. The sheathed thermocouple according to claim 1, wherein the sealing alloy is a nickel-iron alloy. 4. The sheathed thermocouple according to claim 1, wherein the sealing alloy is a nickel-chromium-iron alloy. 5. The sheathed thermocouple according to claim 1, wherein the sealing alloy is a chromium-titanium-iron alloy. 6. The sheathed thermocouple according to claim 1, wherein the sealing alloy is a chromium-iron alloy. 7. Insert a thermocouple into a sealed alloy protective tube, fill it with an insulator, reduce the area of the protective tube to a desired diameter, cut the protective tube to a desired length, and then cut the protective tube to a desired length. Manufacturing method 8 of a sheathed thermocouple, in which thermocouples are connected at their ends, a protective tube at one end is hermetically sealed, and a preliminary oxide film is formed on the surface of the protective tube in a reducing atmosphere. 8. The method for manufacturing a sheathed thermocouple according to claim 7, wherein is a wet hydrogen atmosphere.