JP2001183240A - Thermocouple - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermocouple effectively used for measuring a temperature of the copper molten bath and having the superior thermal impact resistance and the protection against corrosion of copper molten bath. SOLUTION: This thermocouple has a MgO layer 4 superior in the corrosion resistance to copper molten bath, on a surface of a protecting tube 1, and an oxide layer 10 mainly composed of SiO2-Al2O3 and a reaction layer 9 composed of MgO-SiO2-Al2O3 are mounted between the protecting tube 1 and the MgO layer 4 for absorbing the difference in thermal expansion between both layers. The MgO layer 4 exercises the corrosion resistance to the copper molten bath, and the silicon nitride ceramic as a base material of the protecting tube exercises the thermal shock resistance. This thermocouple achieves high durability and long life.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocouple particularly suitable for measuring the temperature of a molten metal such as a molten copper.

[0002]

2. Description of the Related Art In general, a thermocouple measures the temperature and heat of an object by using a thermoelectromotive force generated in a temperature detector such as two kinds of alloys. The sheath-type thermocouple accommodates the element wire of the temperature detector in a protective tube, and surrounds the MgO, A
It has a structure filled with an inorganic insulator such as l ₂ O ₃ ,
The purpose is to protect the wires of the temperature detector and to reduce the temperature measurement response time.

A protective tube for continuous temperature measurement of molten steel disclosed in Japanese Patent Application Laid-Open No. 61-246636 has a bulk density of 2.6.
It consists of an outer tube made of reactive sintered silicon nitride of greater than g / cm ³ and an inner tube made of dense ceramics. Further, a thermocouple disclosed in Japanese Patent Application Laid-Open No. 9-89683 is a protection pipe made of heat-resistant and heat-shockable ceramics, and a type extending longitudinally from one end to the other end in the protection pipe. , A thin film forming a temperature sensing portion formed at the tip of the protection pipe, and Si ₃ N ₄ and Ti inserted into the protection pipe.
It is composed of an insulator made of a composite material made of N.

[0004]

With conventional thermocouples, however, in order to measure the temperature of oxygen-free molten copper at about 1300 ° C., a relatively high melting point and stable Pt-
A Rh wire was used, which was fixed to a paper pipe, but the temperature measurement was performed once or twice. Therefore, the thermocouple must be replaced with a new one each time the temperature of the oxygen-free molten copper or the like is measured, and there has been a problem that it takes time and cost to replace and transport the thermocouple.

A thermocouple in which the thermocouple is protected by a ceramic protection tube is made of a MgO when the protection tube is made of MgO.
Since gO has low thermal shock resistance, it is damaged by thermal shock during immersion in the molten metal. Further, when the protection tube of the thermocouple is made of SiO ₂ , there is a problem that SiO ₂ is damaged by being corroded by the molten copper.

When measuring the temperature of a substance using a thermocouple, among various kinds of metal melts, oxygen-free copper melts include:
If impurities are mixed in the molten copper, the electric resistance changes and the quality of the molten copper deteriorates.
It must be made of a material that does not cause mixing or reaction of the material constituting the thermocouple into the molten metal due to the melting of the protective tube.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. A protective tube is manufactured using a silicon nitride ceramic having excellent thermal shock resistance as a base material, and the protective tube is provided outside the protective tube. An object of the present invention is to provide a thermocouple having a thermal shock resistance and a corrosion resistance to molten copper by forming a structure in which an MgO layer having excellent corrosion resistance to molten copper is arranged.

According to the present invention, there is provided a ceramic protective tube having a temperature measuring section for measuring the temperature of a molten metal, the ceramic protective tube having one end formed at a closed end, and a pair of different compositions which are included in the protective tube and whose ends are joined. A temperature detector comprising a wire of the above, a filler filled in a gap between the wire and the wire in the protection tube, a sealing member for sealing an open end of the other end of the protection tube, and a sealing member for the protection tube. A thermocouple comprising an outer MgO layer.

The protective tube is made of silicon nitride, sialon,
It is formed from any material selected from silicon carbide and a composite thereof.

The protection tube includes a first protection tube provided with the temperature measuring section, and a second protection tube fixed outside a region of the first protection tube excluding the temperature measurement section. I have.

[0011] Between the protective tube and the MgO layer, M
An intermediate layer having a graded composition in which the component ratio of gO, SiO ₂ and Al ₂ O ₃ changes stepwise or continuously is interposed. Further, the intermediate layer includes an oxide layer made of SiO ₂ —Al ₂ O ₃ disposed on the side of the protection tube and the Mg layer.
O layer and a reaction layer and made of MgO-SiO ₂ -Al ₂ O ₃ which is formed by performing a MgO sprayed to the oxide layer to form a. Further, the reaction layer of the intermediate layer has a structure in which the MgO is present in the SiO ₂ —Al ₂ O ₃ in an inclined manner from the outside to the inside by the thermal spraying of the MgO.

Further, the oxide layer is made of Si in terms of oxide.
O ₂ contains 30 wt% or more and Al ₂ O ₃ contains 20 wt% or more. The MgO layer has a thickness of 50 to 400 μm.
m, the reaction layer is 5 to 50 μm, and the oxide layer is 2 μm.
It is formed with a thickness of 0 μm or less. Further, the alloy wire constituting the temperature detector is a W-5Re alloy wire and a W-5Re alloy wire.
-26Re alloy strand. Further, the filler is made of ceramics.

This thermocouple is preferably applied to measuring the temperature of the copper melt, wherein the metal melt is a copper melt.

Since the thermocouple is constructed as described above, the MgO layer prevents corrosion by the molten metal of the protective tube, particularly, the molten copper, and also forms the base material of the protective tube such as silicon nitride. The ceramic exhibits thermal shock resistance against thermal shock when the temperature measuring part is immersed in the molten copper, thereby preventing damage to the protective tube. Further, since an intermediate layer made of a graded material is interposed between the protective tube and the MgO layer, the difference in thermal expansion between the ceramics and MgO is reduced by the intermediate layer, and the sprayed film of the MgO layer on the intermediate layer is formed. Has a laminated structure in which no chemical bond is formed between the particles, so that the relaxation is further improved, and M
The sprayed film of the gO layer does not peel off, and the life of the protective tube is extended.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a thermocouple according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a thermocouple according to the present invention, and FIG. 2 is a sectional view showing a detailed structure of a protection tube of the thermocouple of FIG.

The thermocouple includes a ceramic protection tube 1 provided with a temperature measuring section 13 for measuring the temperature of a molten metal such as a copper molten metal at a closed end 11, and is enclosed in a protective tube 1. Temperature sensing element 6 composed of a pair of wires 7, 8 having different compositions joined together as indicated by reference numeral 12, and ceramic filler 5 filled in the gap between wires 7 and 8 in protective tube 1. ,
A sealing member (not shown) for sealing the open end of the protection tube 1;
And the MgO layer 4 disposed outside the protection tube 1. The protection tube 1 is formed of any ceramic material selected from silicon nitride, sialon, silicon carbide, and a composite thereof. The protective tube 1 is composed of a first protective tube 2 having a temperature measuring section 13 and a second protective tube 3 fixed outside the region of the first protective tube 2 excluding the temperature measuring section 13. In some cases, in particular, the second protective tube 3 may be configured in a laminated structure to increase the degree of heat insulation. An open end is formed at the end of the first protective tube 2 opposite to the temperature measuring unit 13, and the temperature detector 6 is disposed in the first protective tube 2 through the open end, and a ceramic filler is provided. 5
Is filled, the open end of the first protection tube 2 is sealed with a sealing member such as a dense glass.

In this thermocouple, as shown in FIG. 2, between the protective tube 1 and the MgO layer 4, MgO, SiO ₂ and A
An intermediate layer (9, 10) having a gradient composition in which the component ratio of l ₂ O ₃ changes stepwise or continuously is interposed. The intermediate layer (9, 10) is made of S disposed on the protection tube 1 side.
Reaction composed of an oxide layer 10 of iO ₂ —Al ₂ O ₃ and MgO—SiO ₂ —Al ₂ O ₃ formed by spraying MgO on oxide layer 10 to form MgO layer 4 And a layer 9. Therefore, in this thermocouple, the oxide layer 10, the reaction layer 9, and the MgO layer 4 are formed on the outermost surface from the surface of the protection tube 1. As shown in FIG. 2, the oxide layer 10, the reaction layer 9 and the MgO layer 4 change stepwise on the surface of the protective tube 1 as shown in FIG. And the MgO layer 4 may be configured to have a continuously graded composition.

The reaction layer 9 as the intermediate layer has a structure in which MgO is present in the SiO ₂ —Al ₂ O ₃ in an inclined manner from the outside to the inside by spraying of MgO. The oxide layer 1
0 is 30% by weight or more of SiO _{2 in} terms of oxide;
l ₂ O ₃ is contained in an amount of 20 wt% or more. In this thermocouple, the MgO layer 4 has a thickness of 50 to 400 μm, and the reaction layer 9 has a thickness of 5 to 5 μm.
0 μm, and the oxide layer 10 is formed with a thickness of 20 μm or less. The filler 5 is made of a silicon nitride-based ceramic or the like.

The alloy wire constituting the temperature detector 6 disposed in the first protective tube 2 is composed of a W-5Re alloy wire 7 and a W-26Re alloy wire 8, and the filler 5 The first protection tube 2 is disposed so as to be insulated from each other and to prevent a short circuit. The temperature detector 6 has, for example, a wire diameter of the element wires 7 and 8 of 0.25 mm and a length of 3 mm.
It is 00 mm, and is joined by welding or the like at a temperature measuring section, that is, a joining section 12. The joint 12 between the wires 7 and 8 is in close contact with the inner surface of the distal end 11 of the first protective tube 2 to form the temperature detector 6.

This thermocouple has the above configuration,
It can be manufactured as follows. First, protection tube 1
Is a material obtained by adding a predetermined amount of a sintering aid (eg, SiO ₂ , Al ₂ O ₃ ) to silicon nitride as a main component, mixing and kneading the mixture, and then using an extruder to form a shape of the protective tube 1. Then, the formed body was degreased at a predetermined temperature and in a predetermined atmosphere, and fired to produce a silicon nitride-based ceramic protection tube 1 as a base material. Here, the protection tube 1
The first protective tube 2 is formed into a molded body having a shape in which the second protective tube 3 is disposed in a region other than the end portion of the first protective tube 2.

Next, the surface of the protective tube 1 was irradiated with a plasma flame to form an oxide layer 10 made of SiO ₂ —Al ₂ O ₃ . Next, a film of the MgO layer 4 was formed on the surface of the oxide layer 10 formed on the surface of the first protection tube 2 by plasma spraying. Next, the protective tube 1 on which the MgO layer 4 is formed with the oxide layer 10 interposed therebetween is subjected to a heat treatment in an Ar atmosphere, whereby the SiO ₂ —Al ₂ O ₃ oxide layer 10
The interface layer with the O layer 4 is converted into a reaction layer 9 composed of MgO—SiO ₂ —Al ₂ O ₃ , and the protective layer provided with the coating layer composed of the MgO layer 4, the reaction layer 9 and the oxide layer 10 of the present invention. Tube 1
Was prepared.

After the aluminum phosphate solution containing the silicon nitride powder is filled in the first protective tube 2 of the protective tube 1 manufactured by the above process, the wire diameter is 0.25 mm and the length is 300 mm.
The temperature detector 6 composed of the W-5Re alloy wire 7 and the W-26Re alloy wire 8 which were welded at the joint portion 12 of the tip 11 in mm was inserted. Next, the end of the protective tube 2 on the side opposite to the temperature measuring section was sealed with a sealing member made of dense glass, thereby producing a thermocouple according to the present invention.

In order to compare the thermocouple of the present invention with another thermocouple, a protective tube (not shown) was made of silicon nitride ceramics as a comparative thermocouple, and the same filler 5 and temperature detector 6 were used. Was produced as a first comparative thermocouple.
A protection tube (not shown) was made of MgO as another thermocouple for comparison, and the same filler 5 and temperature detector 6 were formed.
A thermocouple of a second comparative product was manufactured.

Therefore, a test for repeatedly measuring the temperature of the oxygen-free copper melt at 1300 ° C. was performed using the product of the present invention, the first comparative product, and the second comparative product. The results were as follows: The product of the present invention had 500 temperature measurements until breakage. The first comparative product made of a protective tube made of a silicon nitride ceramic had a temperature measurement number of times up to breakage of 50 times, indicating that the protective tube was in a molten state. The second comparative product manufactured with the MgO protective tube had five temperature measurements until breakage, in which the protective tube was damaged by thermal shock.

The following was found from the temperature measurement test of the molten copper using these thermocouples. The protection tube made of MgO was damaged by thermal shock during repeated immersion in molten copper because of its low thermal shock resistance. In addition, silicon nitride ceramic protective tubes are subject to corrosion of silicon nitride by the molten copper, and the protective tubes gradually decrease in wall thickness.
A hole was made in the protection tube, and the molten copper penetrated into the inside of the protection tube through the hole, breaking the wires and leading to damage. On the other hand, in the product of the present invention, the outer MgO layer 4 prevents the corrosion of the silicon nitride protective tube base by the molten copper, and the silicon nitride of the protective tube base has a thermal shock resistance against thermal shock during immersion. It is thought that it prevented damage by sex. In particular, the difference in thermal expansion between MgO and silicon nitride is due to the fact that the reaction layer 9 and the oxide layer 10 are interposed in the middle, and the thermal expansion of MgO
The sprayed film of the gO layer 4 is relaxed by having a laminar structure in which there is no chemical bond between particles, that is, a laminated structure, whereby the film of the MgO layer 4 does not peel off, and the life of the protection tube 1 is extended. ing.

[0026]

Since the thermocouple according to the present invention is constructed as described above, the MgO layer constituting the surface of the protective tube prevents corrosion of the ceramic protective tube base from the molten copper,
The thermal shock is secured by the silicon nitride ceramics of the base material of the protective tube, and the difference in thermal expansion between the outer layer of MgO and the silicon nitride of the base material is reduced by the intermediate layer, that is, the reaction layer and the oxide layer. It will be extremely durable. The intermediate layer is a gradient material composed of a reaction layer and an oxide layer, and can satisfactorily reduce the difference in thermal expansion between MgO and silicon nitride. Therefore, this thermocouple is preferable for measuring the temperature of a molten metal, particularly, a molten copper, and has characteristics of thermal shock resistance and molten copper corrosion resistance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a thermocouple according to the present invention.

FIG. 2 is a cross-sectional view showing a detailed structure of a protection tube of the thermocouple of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Protective tube 2 1st protective tube 3 2nd protective tube 4 MgO layer 5 Filler 6 Temperature detector 7 W-5Re wire 8 W-26Re wire 9 Reaction layer 10 Oxide layer 11 Closed end part 12 Joint part 13 Temperature measurement Department

Claims (10)

[Claims] 1. A ceramic protective tube provided with a temperature measuring section for measuring the temperature of a molten metal, the ceramic protective tube having one end formed at a closed end, and a pair of elements having different compositions contained in the protective tube and having ends joined thereto. A temperature detector composed of a wire, a filler filled in a gap between the wire and the wire in the protection tube, a sealing member sealing an open end at the other end of the protection tube, and a sealing member outside the protection tube. A thermocouple consisting of an MgO layer disposed. 2. The thermocouple according to claim 1, wherein the protection tube is formed of any material selected from silicon nitride, sialon, silicon carbide, and a composite thereof. 3. The protection tube according to claim 1, further comprising a first temperature measuring section.
2. The thermocouple according to claim 1, comprising a protection tube and a second protection tube fixed outside a region of the first protection tube excluding the temperature measuring section. 4. Between the protective tube and the MgO layer,
_{2. The} thermocouple according to claim 1, wherein an intermediate layer having a graded composition in which the component ratio of MgO, SiO ₂ and Al ₂ O ₃ changes stepwise or continuously is interposed. 5. An intermediate layer comprising: an oxide layer made of SiO ₂ —Al ₂ O ₃ disposed on the side of the protection tube;
To form the O layer consists by being composed of said oxide layer reaction layer made of MgO-SiO ₂ is formed by performing a thermal spraying of MgO -Al ₂ O ₃ with respect to claim 4
The thermocouple described in. 6. The reaction layer of the intermediate layer, wherein the MgO
MgO is converted to the SiO ₂ —Al ₂ O ₃
6. The thermocouple according to claim 5, wherein the thermocouple has a structure that is inclined from the outside to the inside. 7. The oxide layer is made of SiO _{2 in} terms of oxide.
6. The thermocouple according to claim 5, comprising 30 wt% or more of Al ₂ O _{3 and} 20 wt% or more of Al ₂ O ₃ . 8. The thermocouple according to claim 5, wherein the MgO layer has a thickness of 50 to 400 μm, the reaction layer has a thickness of 5 to 50 μm, and the oxide layer has a thickness of 20 μm or less. 9. The alloy wire constituting the temperature detector comprises a W-5Re alloy wire and a W-26Re alloy wire, and the filler is made of ceramics. 2. The thermocouple according to 1. 10. The thermocouple according to claim 1, wherein the molten metal is a molten copper and can be applied to measure the temperature of the molten copper.