JPH1183639A - Thermocouple for measuring temperature of molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life thermocouple for measuring the temperature of metal wherein temperature-measurement responsiveness and temperature- measurement precision are improved while repeated use is allowed. SOLUTION: The thermocouple is comprised of a first protective pipe 1 of cermet whose parent-phase is silicon nitride, SIALON, or Mo, a coat 4 allocated on the outside surface of the first protective pipe 1, a pair of temperature detecting alloy element wires 6 and 7 of different composition allocated in the first protective pipe 1, none-conductive filling member 3 filled in the first protective pipe 1, a sealing member 8 which seals up an open end part 15 of the first protective pipe 1, and a second protective pipe 2 which is, of cermet whose base is Mo, attached on the outside periphery of the first protective pipe 1 through a heat-shield layer 5. The coat 4 comprises Mo-ZrN, Mo-ZrB2 , or Mo-ZrO2 which is hard to react with iron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocouple for measuring the temperature of a molten metal having a protective tube for measuring the temperature of a molten metal such as iron.

[0002]

2. Description of the Related Art Conventionally, a thermocouple for measuring the temperature of a cast iron melt at about 1500 ° C. has a relatively high melting point as a material and is made of Pt-Rh, which is stable in the atmosphere, as a strand.
A structure in which an element wire is fixed to a pipe made of alumina silica fiber is used. Such thermocouples have been discarded after measuring the temperature of molten cast iron about once or twice, and it is now impossible to measure the temperature accurately, and the thermocouple is repeatedly used many times. Instead, thermocouples themselves have become extremely expensive.

[0003] A sheath-type thermocouple using W-Re as a strand is used as a protective tube for a metal sheath-type component used at a high temperature, and is known to be made of a metal such as stainless steel (SUS). Have been. Some SUS sheathed thermocouples are used in an atmosphere of 1000 ° C or higher.
In that case, it is made of a special heat-resistant alloy such as Inconel. Alternatively, a thermocouple having a structure in which a protective tube is made of cermet and Pt-Rh is used as a wire inside the protective tube is also known.

Japanese Patent Application Laid-Open No. Hei 6-160200 discloses a sheath-type thermocouple with an airtight terminal. The thermocouple does not cause a measurement error even if a temperature gradient occurs at the terminal due to a transient temperature change or the like. A thermocouple wire composed of a dissimilar metal wire of an alumel wire and a chromel wire is connected to a stainless steel sheath. The sheath is housed together with the inorganic insulating material while being insulated from each other, and the base end side of the sheath is hermetically sealed by an airtight terminal portion. An insulating sleeve is inserted into the inside of two copearl through pipes attached to the ceramic end plate of the hermetic terminal, and each thermocouple wire is drawn out without passing through the inside thereof and directly contacting the through pipe. Have been.

[0005]

[Problems to be solved by the invention] However. Pt-
The Rh thermocouple cannot be used in an inert gas atmosphere, and its usable temperature in the atmosphere is 1500 ° C. as a limit temperature.
Further, the W-Re thermocouple can be used in the atmosphere and in an inert gas atmosphere.
00 ° C is the limit temperature, and the usable temperature in an inert gas atmosphere is 2300 ° C. Furthermore, Pt-
Regarding the PR thermocouple using the Rh strand, the thermoelectromotive force of the PR thermocouple is about 1/15 of that of the CA thermocouple and about 1/7 of that of the W-Re thermocouple. There is a problem that the accuracy of temperature measurement is inferior and the response is poor. Therefore, at the site, in order to measure the temperature of the molten metal in the blast furnace, the operator is forced to stay at the measurement place for about 8 seconds until the temperature stabilizes near the blast furnace.

[0006] Further, the conventional thermocouple has a problem that when measuring the temperature of the molten metal, the molten iron easily adheres and the response is poor. The cast iron of the molten metal adheres to the Pt-Rh strand and the protection tube of the thermocouple, and the process for removing the cast iron becomes complicated. In addition, the current product has a temperature measurement that has a life of about two times. There is a problem that the replacement work is also troublesome. Also,
The W-Re wire in the thermocouple is easily oxidized in the atmosphere and cannot be used for measuring the temperature of the molten cast iron.
In addition, there is a problem that the molten iron easily adheres to the outer protective tube.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, improve the response and improve the durability, and measure the heat of the molten metal by a thermocouple. To minimize the heat capacity of the tip in order to concentrate on the tip of the hot spot in a short time, and to minimize the escape of heat to the rear and side surfaces of the first protection tube of the thermocouple, First
To minimize the escape of heat to the rear and side of the protection tube, to reduce the heat passage area and to construct a heat shield structure to provide sufficient durability,
An object of the present invention is to provide a thermocouple for measuring the temperature of a molten metal made of a material having high heat resistance and hardly reacting with iron.

According to the present invention, there is provided a first protective tube made of cermet having silicon nitride, sialon or Mo as a mother phase, one end of which is closed and the other end of which is open, and a thermal expansion coefficient arranged on an outer surface of the first protective tube. A pair of temperature-sensing alloy wires of different composition, which are arranged in the first protective tube and are joined at the tip end thereof, the heat-resistant coating having a small size and hardly reacting with iron, and the first protective tube A non-conductive filling member filled with the alloy wire buried therein, and a dense heat-resistant glass sealing the open end of the first protective tube with the alloy wire extended. And a second protective tube made of a cermet based on Mo and attached to the outer periphery of the first protective tube via a heat shield layer.

The film is made of Mo-ZrN, Mo-ZrB ₂ , Mo-Zr, which has a small coefficient of thermal expansion and does not easily react with iron
It is composed of a thermal spray coating made of any one of O ₂ or a composite.

The alloy wire is a tungsten-rhenium alloy wire.

Further, the filling member is a reaction sintered silicon nitride to which Ti is added.

The filling member is a heat-resistant glass containing Fe ₂ O ₃ and SiO ₂ .

[0013] The first protective tube is formed to have an outer diameter of 5 mm or less.

The heat shield layer interposed between the first protection tube and the second protection tube is made of a heat shield air layer or ceramic fiber for preventing heat from flowing out from a side surface of the first protection tube. Have been.

An end of the first protection tube and the second protection tube opposite to the temperature measurement region is in a state in which a gap between the first protection tube and the second protection tube is sealed. And is fixed to a metal support pipe by a collet chuck.

This ceramic thermocouple for measuring the temperature of molten metal is
As described above, a heat-resistant material such as silicon nitride in which the diameter of the first protective tube is made as small as possible is used, and the surface of the first protective tube is formed by spraying a metal such as iron and a coating which is hardly wetted. An outer cylinder, also made of heat-resistant material, that is, a second protective tube is provided around the protective tube to prevent damage and prevent heat from escaping from the side of the protective tube. An air layer or a heat shield layer made of ceramic fiber is provided on the first protection tube, and the ends of the first protection tube and the second protection tube are open. When immersed in a molten metal, the air layer is closed and both protection tubes are closed. The molten metal does not intrude between the wires, the heat shielding effect can be exhibited, the wire diameter of the alloy wire is made as small as possible, and heat is prevented from escaping through the wire.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a thermocouple for measuring molten metal temperature according to the present invention will be described below with reference to the drawings. FIG.
2 is a sectional view showing an embodiment of the thermocouple for measuring molten metal temperature, and FIG. 2 is an enlarged sectional view of a first protective tube of the thermocouple for measuring molten metal temperature in FIG.

This thermocouple for measuring the temperature of the molten metal is covered with the second protective tube 2 as a protective tube outside the temperature measuring region via the heat shield layer 5 as a protective tube outside the temperature measuring region. This is an improvement in loss. This thermocouple for measuring molten metal temperature is
Mainly, the first protective tube 1, one end of which is closed and the other end of which is open, the heat-resistant coating 4, which is disposed on the outer surface of the first protective tube 1 and has a small coefficient of thermal expansion and does not easily react with iron. A pair of temperature sensing alloy wires 6 of different compositions constituting the temperature measuring unit 9 arranged in the
7, an open end of the first protection tube 1 with the filler members 3 filled with the alloy wires 6, 7 buried inside the first protection tube 1 and the alloy wires 6, 7 extended. And a second protective tube 2 attached to the outer periphery of the first protective tube 1 with a heat shield layer 5 interposed therebetween.

The first protective tube 1 is made of silicon nitride (Si)
₃ N _4), sialon (SiAlON), cermet (Mo-ZrO ₂ to Mo mother phase), optionally is manufactured by ceramic selected of silicon carbide (SiC). The first protective tube 1 is formed with a size having an outer diameter of 5 mm or less, for example, an outer diameter of 3.5 mm.
The second protection tube 2 is made of a cermet (Mo) based on Mo.
-ZrO ₂ ). The coating 4 sprayed on the outer peripheral surface of the first protective tube 1 has a small coefficient of thermal expansion and does not easily react with iron such as Mo—ZrN, Mo—ZrB ₂ , and Mo—Zr.
It is composed of any one or a composite of O ₂ . The first protective tube 1 is provided on the outer peripheral surface of the second protective tube 2.
Like Mo, Mo has a small coefficient of thermal expansion and does not easily react with iron.
It can be sprayed a coating consisting -ZrN and / or Mo-ZrB _2. In addition, the sealing member 8 includes the first protective tube 1.
Is made of dense heat-resistant glass whose end is sealed.

A pair of alloy wires having different compositions arranged in the first protective tube 1 are tungsten-rhenium alloy wires, and are composed of W-5Re wires 6 and W-26Re wires 7. It is configured. W-5Re strand 6 and W-26
The Re wires 7 are arranged so as to extend apart from each other in the first protection tube 1. The distal ends of the W-5Re strand 6 and the W-26Re strand 7 are connected to each other to form a temperature measuring section 9. The other ends of the W-5Re strand 6 and the W-26Re strand 7 are terminals 12, 13 extending from the end of the first protective tube 1.
Is connected to The terminals 12 and 13 are Kovar tubes 24 extending from the sealing member 8 at the end of the first protection tube 1.
Is connected to the lead wire 25 (compensation lead wire).

The heat shield layer 5 formed in the gap between the first protective tube 1 and the second protective tube 2 is made of a layer containing a large amount of air or a ceramic fiber such as a silicon carbide fiber. It is configured to prevent heat from flowing out of the side surface of the tube 1. The first protective tube 1 is supported by a support ring 17 made of silicon nitride and disposed in the second protective tube 2 at a distance from the thermal barrier layer 5. The heat shield layer 5 has a function of preventing heat from flowing out of the outer peripheral surface of the first protective tube 1 to the outside.
The heat capacity of the first protection tube 1 can be made as small as possible. A collet chuck 22 having a tapered surface with a slit 23 is provided at an end of the first protection tube 1 and the second protection tube 2.
Thus, it is fixed to a metal pipe 18 which is a support rod made of stainless steel. In FIG. 1, the metal pipe 18 has a double structure, a collet chuck 22 having a tapered surface on the outer surface is fixed to the inner metal pipe 18, and a tapered surface on the inner surface is fixed to the outer metal pipe 18. The collet chuck 20 is fixed. A fixing nut 26 is screwed into a screw 27 formed at the end of the metal pipe 18 via a leaf spring 19. Also, if the nut 21 screwed into the screw 27 of the inner metal pipe 18 is tightened against the spring force of the leaf spring 19, the slit 23 of the collet chuck 22 is elastically tightened by the collet chuck 20 and contracted. And the first by the collet chuck 22.
The protection tube 1 will be tightened.

The first protective tube 1 is filled with a non-conductive filling member 3 and is filled with an inert gas such as Ar or N ₂ , which is oxidized and corroded by the W-Re wires 6 and 7. It has a function to prevent disconnection. The filling member 3 is made of a porous silicon nitride ceramic (reaction sintered silicon nitride ceramic) to which Ti is added, or Si ₃ N ₄ , SiO ₂ , Fe ₂
It is made of heat resistant glass containing O ₃ and Cr ₂ O ₃ .

The tip 14 of the first protective tube 1 is
The protective tube 2 is disposed so as to slightly protrude from the open end 10. When the thermocouple is immersed in the molten metal, the open end 10 is sealed with the molten metal itself, and the air existing between the first protection tube 1 and the second protection tube 2 is sealed.
Intrusion of the molten metal between the first protection tube 1 and the second protection tube 2 is prevented. The temperature measurement area of the distal end portion 14 of the first protective tube 1 has a double structure including the first protective tube 1 and the second protective tube 2 disposed outside the first protective tube 1. The first protection tube 1 has a heat passage area as small as possible.
The transfer of heat to the rear end 15 can be reduced.

Further, the second protective tube 2 made of cermet is excellent in heat resistance and erosion resistance, and gently breaks even if cracks occur due to thermal shock due to the presence of the heat shielding layer 5. For example, it does not lead to catastrophic destruction like a conventional shell made of ceramics. The first protective tube 1 enclosed in the second protective tube 2 is made of a ceramic containing silicon nitride or the like as a main component, and when exposed to a molten metal such as iron, silicon nitride reacts with iron and melts. Although the heat loss is severe and the thermal shock resistance is inferior to that of the cermet, the first protective tube 1 does not directly contact the molten iron, so that the heat transfer coefficient can be reduced, and therefore the first protective tube 1 can be reduced. 1 is prevented from being damaged by thermal shock.

This thermocouple for measuring the temperature of the molten metal can reduce the total heat capacity of the first protective tube 1 and the coating 4.
Even if the tip of the temperature measurement area is configured in a double structure, the response of temperature measurement does not decrease. The sealing member 8 provided at the rear end of the first protection tube 1 is made of a dense heat-resistant glass member. A filling member 3 is provided inside the first protection tube 1.
When an inert gas such as N ₂ or Ar is filled during the production by filling the first protective tube 1, the sealing member 8 is fitted to the end of the first protective tube 1 to form a sealed state.

The filling member 3 filled in the first protective tube 1 has a porous structure made of a material such as a Si ₃ N ₄ reactive sintered ceramic and has a small thermal conductivity. Have been. For example, the filling member 3 can be configured to have a low thermal conductivity by forming a structure having many voids. Therefore, this thermocouple for measuring the temperature of molten metal is
The heat capacity of the temperature measuring area where the first protective tube 1 placed in the molten metal of iron or the like is located can be made small, and the conduction of heat from the temperature measuring area to the rear area can be prevented.

Embodiment A pair of W-Re wires 6, 7 are
W-5Re and W-26Re having different compositions
, Each having a wire diameter of 0.2 mm, a length of 200 mm, and a connecting portion 16 whose distal ends are welded to each other. The W-Re wires 6 and 7 were deposited with heat-resistant glass raw material powder mainly composed of Si ₃ N ₄ powder. The outer diameter of the first protection tube 1 is 3.
A silicon nitride having a length of 5 mm, a length of 120 to 150 mm, a closed front end 14 and an open rear end 15 was used. On the outer surface of the first protective tube 1, a coating 4 made of Mo—ZrN, Mo—ZrB ₂
Has been sprayed. W-Re with the above raw material powder
The wires 6 and 7 were inserted from the open rear end 15 of the first protection tube 1 and arranged in the first protection tube 1. Further, an inert gas such as Ar or N ₂ is injected into the first protective tube 1,
The rear end 15 of the protective tube 1 was sealed with a sealing member 8 made of heat-resistant dense glass.

The second protective tube 2 is made of Zr based on Mo.
10 mm outer diameter and 7 inner diameter by cermet made of O ₂
mm. On the outer peripheral surface of the second protective tube 2,
A coating of a composite material based on Mo with ZrN and / or ZrB ₂ dispersed therein is formed by thermal spraying. The first protective tube 1 is inserted into the inside of the second protective tube 2 sprayed with the coating.
Was inserted. At this time, the first protective tube 1 is
Are inserted so as to slightly protrude from the open end 10 of the second protection tube 2. A support ring 17 is disposed between the first protection tube 1 and the second protection tube 2 so as to form an air chamber 11 between the first protection tube 1 and the second protection tube 2. , A heat shield layer 5 in which a heat shield material is filled in the air chamber 11 is formed. The ends of the first protection tube 1 and the second protection tube 2 are fixed to a stainless steel support pipe 18 by a collet chuck 22.

When the temperature of the cast iron melt was measured at about 1450 ° C. using the thermocouple for measuring the temperature of the molten metal (product of the present invention) configured as described above, the raw material powder constituting the filling member 3 was calcined. It took about 4 seconds to stabilize,
The temperature measurement of the molten cast iron was repeated 500 cycles. After repeating the temperature measurement of the molten cast iron for 500 cycles,
Although cracks were found in the second protective tube 2, there was no problem in the temperature measurement performance of the molten cast iron.
Although the temperature of the molten cast iron was measured 000 times or more, there was no change in the electromotive force of the thermocouple for measuring the temperature of the molten metal, and the temperature could be measured stably.

In addition to the temperature measurement of the molten cast iron, continuous measurement of the temperature of the other molten metal at about 1500 ° C. was performed using the thermocouple for measuring the temperature of the molten metal. At this time, no abnormality such as a change in the electromotive force of the thermocouple for measuring molten metal temperature could be confirmed. That is, it was found that the thermocouple for measuring the temperature of the molten metal has good heat resistance and erosion resistance.

In order to compare this thermocouple for measuring the temperature of the molten metal (the product of the present invention) with another thermocouple, as a comparative example, a W was prepared by mounting the above raw material powder in a protective tube made of cermet having an outer diameter of 13 mm. A thermocouple (comparative product) having a structure in which -Re wires were inserted was produced. Responsiveness of comparison product, adhesion of molten iron,
And the durability was evaluated. Due to the large outer diameter, the response was poor and could not be made within 5 seconds. From this, it has been found that the outer diameter of the first protective tube 1 is preferably formed to 5 mm or less in order to improve the response.

[0032]

As described above, in the thermocouple for measuring molten metal temperature according to the present invention, the first protective tube made of silicon nitride is protected by the second protective tube made of a composite material such as cermet based on Mo. Therefore, the heat resistance and erosion resistance can be improved, and even when used repeatedly, the temperature of molten metal such as molten iron can be measured with high accuracy and speed, and its life can be improved.
By forming the outer diameter of the first protective tube as small as possible, the heat capacity can be reduced, and the temperature measurement responsiveness can be improved. By forming a coating made of a Mo-based material in which ZrB ₂ and / or ZrN dispersed with a small coefficient of thermal expansion and hard to react with iron on the surfaces of the first protection tube and the second protection tube, the molten cast iron is formed. Prevention of adhesion and improved temperature measurement performance. Further, the temperature of the temperature measurement area is limited by the filling member made of porous ceramic in the first protection tube, and it is difficult for heat to escape backward through the first protection tube, so that the heat capacity of the temperature measurement area is reduced. Temperature response of the thermocouple can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a thermocouple for measuring molten metal temperature.

FIG. 2 is an enlarged sectional view of a first protection tube of the thermocouple for measuring molten metal temperature in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st protective tube 2 2nd protective tube 3 Filling member 4 Coating 5 Heat shield layer 6,7 Tungsten-rhenium alloy strand 8 Sealing member 9 Temperature measuring part 10 Open end part 12,13 Terminal 14 Tip part 15 Rear End 16 Joint 17 Support ring 18 Metal pipe 20, 22 Collet chuck

Claims (8)

[Claims] 1. A first protection tube made of silicon nitride, sialon, or a cermet having a parent phase of Mo, one end of which is closed and the other end of which is open, and having a small thermal expansion coefficient disposed on an outer surface of the first protection tube. A pair of temperature-sensing alloy wires of different compositions, which are arranged in the first protective tube and are joined at the tip, and are resistant to reacting with iron;
A non-conductive filling member filled with the alloy wire buried inside the first protection tube, and sealing an open end of the first protection tube with the alloy wire extended; A thermoelectric element for measuring temperature of molten metal, comprising: a sealing member made of dense heat-resistant glass; and a second protection tube made of Mo-based cermet attached to the outer periphery of the first protection tube via a heat shield layer. versus. Wherein said coating has a thermal expansion coefficient smaller and iron react with hard _{Mo-ZrN, Mo-ZrB 2} , Mo-Z
_2. The thermocouple for measuring the temperature of a molten metal according to claim 1, wherein the thermocouple is formed of a thermal spray coating made of any one of rO ₂ or a composite. 3. The thermocouple according to claim 1, wherein the alloy wire is a tungsten-rhenium alloy wire. 4. The thermocouple according to claim 1, wherein the filling member is made of reactive sintered silicon nitride to which Ti is added. 5. The filling member is made of Fe ₂ O ₃ or SiO _2.
The thermocouple for measuring the temperature of a molten metal according to claim 1, wherein the thermocouple is a heat-resistant glass containing: 6. The thermocouple according to claim 1, wherein the first protective tube has an outer diameter of 5 mm or less. 7. The heat shield layer interposed between the first protection tube and the second protection tube may be a heat shield air layer or ceramic fiber for preventing heat from flowing out from a side surface of the first protection tube. 2. The thermocouple for measuring molten metal temperature according to claim 1, wherein the thermocouple comprises: 8. An end of the first protection tube and the second protection tube on a side opposite to a temperature measurement area, the first protection tube and the second protection tube being connected to the second protection tube.
2. The thermocouple for molten metal temperature measurement according to claim 1, wherein the thermocouple is fixed to a metal support pipe by a collet chuck in a state in which a gap between the protective tube and the protective tube is sealed.