JPH11201831A - Metal fusion temperature measuring thermocouple - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal temperature measuring thermocouple of a long lifetime in which a protection pipe is constituted as a multiple structure of a multilayer an a plurality of repetition uses are possible. SOLUTION: This thermocoupler comprises a protection pipe 1 of which one end is closed and the other end is opened; a filler material 8 composed of a heat-resistant porous ceramic filled in the protection pipe 1; and a pair of W-Re wires 6, 7 of a different composition disposed in the filler material 8. The protection pipe 1 has a cermet layer 2 in which Mo is a parent phase; and a multiple laminated structure in which layers 3 of at least a species or more out of C, MgO, CaO, Al2 O3 m and ZrO2 are alternately laminated. A cermet layer 2 forms at least an outermost core layer, and is composed of a species or a composite substance out of Mo-ZrN, Mo-ZrB2 , Mo-ZrO2 and Mo-ZrC in which a thermal expansion coefficient is small and 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 molten steel at about 1700 ° C. has a relatively high melting point as a material and is made of Pt-Rh, which is stable in the air, 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 the molten steel about 1 to 2 times or so, and it is impossible to measure the temperature accurately. At present, thermocouples are 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. Thermal shock resistance of the cermet protective tube is 1.5 times stronger the Si ₃ N ₄ protective tube, also the thermocouple the Si ₃ N ₄ protective tube 17
When the protective tube is directly immersed in molten iron at a temperature higher than 00 ° C., the protective tube is cracked in a relatively short time, which leads to breakage.
Further, the Pt-Rh thermocouple cannot be used in an inert gas atmosphere, and its usable temperature in the atmosphere is 1500 ° C. as a limit temperature. In addition, the W-Re thermocouple can be used in the atmosphere and in an inert gas atmosphere. The usable temperature in the atmosphere is 400 ° C., which is the limit temperature. The limit temperature is 2300 ° C.
Furthermore, for a PR thermocouple using a Pt-Rh strand,
The thermoelectromotive force of the R thermocouple is about 1/15 of that of the CA thermocouple and about 1/7 of that of the W-Re thermocouple, so the accuracy of temperature measurement is inferior to those thermocouples and the response is poor. It has a problem of poor performance. 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 In order to solve the above-mentioned problems, the object of the present invention is to improve the responsiveness and improve the durability, use a tungsten-rhenium wire as a strand, and use an iron as a protective tube. It has a laminated structure consisting of a cermet layer that is molybdenum-based (Mo), a material that is unlikely to react with iron, and a layer that has a high resistance to iron. The protective tube has sufficient thermal shock resistance, and is used many times. It is an object of the present invention to provide a thermocouple for measuring the temperature of a molten metal, which enables the above.

According to the present invention, a protective tube closed at one end and open at the other end, a filler filled in the protective tube, and a temperature measuring unit disposed on the filler and connected at a distal end portion are provided. In a thermocouple for measuring temperature of a molten metal comprising a pair of alloy wires for temperature detection having different compositions, the protective tube includes a cermet layer having Mo as a mother phase, and C, MgO, CaO, and Al.
It has a multi-layer structure in which at least one or more layers of ₂ O ₃ and ZrO ₂ are alternately laminated, the filler is made of heat-resistant porous ceramics, and the opening of the protective tube is a dense heat-resistant member. The present invention relates to a thermocouple for measuring the temperature of a molten metal, which is sealed with glass.

The cermet layer of the protective tube has a low thermal expansion coefficient and does not easily react with iron.
It is composed of any one of ZrB ₂ , Mo-ZrO ₂ , and Mo-ZrC or a composite thereof. The molybdenum-based (Mo) cermet has a high melting point of 2000 ° C. or higher, has excellent thermal shock resistance, and can withstand the thermal shock temperature due to the temperature of the molten iron during steelmaking.

[0010] The laminated structure of the protective tube is made of carbon (C) or magnesia (Mg) having a large resistance to iron.
O), calcium (CaO) etc.
Even if cracks and cracks occur in the outermost shell layer due to thermal shock, the cracks and the like do not spread to the inner layer at a stretch, but are deflected at those parts due to the presence of C, MgO, CaO, etc. This increases the energy required for breaking, increases the strength of the protection tube, prolongs the life of the protection tube, improves the durability, and enables the thermocouple to be used repeatedly.

The temperature sensing alloy wire is made of tungsten-
Rhenium wire, and the tungsten-rhenium wire is 23
Since it has a melting point of 00 ° C. or higher, it is possible to increase the burning resistance temperature by maintaining a sealed state, and to withstand the temperature of molten iron during steelmaking.

Since the heat-resistant porous ceramic of the filler is a reaction sintered silicon nitride to which Ti is added,
No sintering shrinkage occurs, no gap is generated between the inner surface of the protective tube and the W-Re element wire, and the durability can be improved.

The heat-resistant porous ceramic of the filler is a mixture of an inorganic substance converted from an organosilicon polymer containing Si ₃ N ₄ powder and a heat-resistant ceramic powder.

Further, the mixture constituting the heat-resistant porous ceramic contains at least one of carbon and BN. Since carbon and BN have a better combination with oxygen than a tungsten-rhenium wire, Oxygen contained in the mixture is not oxidized with the tungsten-rhenium wire but oxidized with carbon or BN to form a gas, which remains in the heat-resistant porous ceramic in the gaseous state and oxidizes the tungsten-rhenium wire. Can be prevented and durability can be improved.

[0015] The heat-resistant porous ceramic of the filler contains Zr, O, Al, and P.

This ceramic thermocouple for measuring the temperature of molten metal is
As described above, the protective tube is constructed in a laminated structure, so that cracks caused by thermal shock do not spread to the inside at a stretch, and are deflected at the boundary layer such as carbon, resulting in a large fracture energy. The life of the protection tube is improved by configuring the structure to be hardly damaged.

[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.
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 tip portion of the thermocouple for measuring molten metal temperature in FIG.

In this thermocouple for measuring molten metal temperature, the protective tube 1 in the temperature measuring region is formed in a laminated structure, and in the laminated structure of the protective tube 1, the cermet layer 2 whose main phase is Mo is the outermost shell. Layers, then C, MgO, CaO, Al ₂ O
₃ and ZrO ₂ , at least one or more layers 3 are arranged, and these laminated states are repeated to form a cermet layer 2.
And other layers 3 to 20 to 50 layers.
That is, the protection tube 1 is composed of a cermet layer 2 having Mo as a mother phase.
With the, C, MgO, CaO, a layered structure Al ₂ O _3, at least one or more layers 3 of ZrO ₂ was repeated alternately.

This thermocouple mainly comprises a cermet layer 2
Protective tube 1 having an alternate laminated structure of
It is composed of a filler material 8 filled in the protective tube 1 and a pair of temperature sensing alloy wires 6 and 7 of different compositions arranged in the filler material 8 in the protective tube 1. The filler 8 is made of heat-resistant porous ceramic, and the opening of the protective tube 1 is sealed with a sealing member 10 made of a dense heat-resistant member and glass. The protective tube 1 has a structure in which an end constituting the temperature measurement area 4 is closed and the other end is open, and a sealing tube 5 made of a stainless steel pipe is attached to the open end.

The cermet layer 2 of the protective tube 1 forms at least the outermost layer, and 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 of O ₂ and Mo-ZrC or a composite thereof.

The alloy wires 6 and 7 for temperature detection are tungsten-rhenium wires, and one of the wires 6 has a composition of W-5R.
e, and the composition of the other strand 7 is W-26Re.
The W-5Re strand 6 and the W-26Re strand 7 are arranged so as to extend apart while being buried in the filler 8 in the protection tube 1. W-5Re strand 6 and W-26Re strand 7
Are connected to each other at a temperature measuring area 4 at the tip end thereof to form a temperature measuring section 9. W-5Re strand 6 and W
The other end of the −26Re strand 7 extends from the sealing member 10 at the end of the protection tube 1, and is fixed to the fixing ceramic cement 11 filled in the sealing tube 5 fixed to the end of the protection tube 1. In the terminal, for example, a terminal 12 extending from an end of the protection tube 1 via a lead wire (compensation conductor) in a Kovar tube,
13, respectively. The sealing tube 5 constitutes a support ring.

The heat-resistant porous ceramic of the filler 8 is T
i-added reaction sintered silicon nitride or Si ₃ N
It is composed of a mixture of an inorganic substance converted from an organosilicon polymer containing _four powders and a heat-resistant ceramic powder. When the filler 8 comprises a mixture of an inorganic substance and a heat-resistant ceramic powder, at least one of carbon and BN is contained in the mixture.
Contains seeds. The heat-resistant porous ceramic of the filler 8 contains Zr, O, Al, and P. The filler 8 filled in the protective tube 1 is made of Si ₃
It has a porous structure made of a material such as N ₄ reaction sintered ceramics, and has a small thermal conductivity. For example, the filler 8 can be configured to have a low thermal conductivity by being configured to have a structure having many voids.
Therefore, this thermocouple for measuring the temperature of the molten metal can reduce the heat capacity of the temperature measuring area 4 where the protective tube 1 to be put into the molten metal of iron or the like is located, and the heat from the temperature measuring area 4 to the area behind is provided. Can be blocked.

The protective tube 1 having a laminated structure is excellent in heat resistance and erosion resistance. Moreover, since the protective tube 1 has a multi-layer structure, even if a crack occurs in the outermost shell layer due to thermal shock, the inner layer is gradually broken. Therefore, there is no catastrophic destruction such as the case of a conventional ceramic shell. In addition, since the outermost shell layer of the protective tube 1 is the cermet layer 2 having Mo as a mother phase, the molten iron does not adhere to the protective tube 1 and can be used repeatedly. Further, an inert gas such as N ₂ or Ar can be sealed in the inside of the protective tube 1 when manufacturing it by filling the filler 8, and in this state, a sealing member 10 is provided at the end of the protective tube 1. Fit to form a closed state.

Example 1 First, Mo-Zr, a cermet having Mo as a mother phase, was prepared by a doctor blade method for producing a green tape.
O ₂ , Mo-ZrN, Mo-ZrB ₂ and Mo-ZrC
Was made into a sheet about 100 microns thick. Then,
On one side of these sheets, C (carbon), MgO
(Magnesia) or CaO (calcia) powder was sprayed and sprayed. These sheets are wound around a stainless steel rod so that one end is closed, and then placed in a rubber mold to be compacted by the CIP method, and an integrated molded body is produced. Here, when the load is released after the pressurization by the CIP, the compact is slightly spread by the spring back, and the stainless steel bar is pulled out from the compact. Then,
After the molded body was degreased, it was fired in a hydrogen atmosphere to produce a protective tube 1 having a multilayer structure having one end closed and one end open. On the other hand, a pair of W-Re5 strands 6 and W-Re26 strands 7 each having a wire diameter of 0.2 mm and a length of 200 mm and having different compositions are joined by welding at one end to form a temperature measuring section 9. did.

Next, after filling the organic silicon polymer (PCS) solution containing Si ₃ N ₄ powder into the protective tube 1, the W-Re wires 6, 7 having one end bonded thereto are connected to the protective tube 1. The protective tube 1 was inserted until it almost touched the closed end of the protective tube 1. Further, a dense glass (B ₂ O)
_(3- ZnO). At this time, after the inert gas such as Ar or N ₂ is injected into the protection tube 1, the protection tube 1 can be sealed with the sealing member 10. Further, a support pipe made of stainless steel, that is, a sealing pipe 5 was fixed to an end of the protection pipe 1 using a collet chuck or the like, thereby producing a thermocouple as shown in FIG.

Example 2 In this thermocouple manufacturing process, a filler 8 is placed in the protective tube 1.
Prior to filling with carbon, carbon and B
N is added 5% each, and the filler 8 is changed to the W-Re strand 6,
A composition was prepared to prevent oxidation of No. 7, and a thermocouple was prepared by the same manufacturing process as above. That is, when carbon and BN are added to the filler 8, even if oxygen is contained in the filler 8, the oxygen is combined with carbon and BN, and oxidation of the W-Re wires 6, 7 is prevented. The durability of the W-Re strands 6, 7 can be improved.

Example 3 In the thermocouple manufacturing process, a paste made of zirconia, aluminum phosphate and aluminum hydroxide was used as the filler 8 to fill the protective tube 1 in the same manner as described above. A thermocouple was produced by a manufacturing process. The paste is solidified by a dehydration reaction and becomes a heat-resistant material.

Therefore, the temperature of the molten steel at about 1750 ° C. was measured using the thermocouples prepared in Examples 1, 2 and 3. These thermocouples took about 10 seconds to stabilize. The temperature of the molten steel at about 1750 ° C. was measured at least 500 times using these thermocouples (specifically, the life was 521 times). It was confirmed that the temperature measurement of the molten metal can be sufficiently performed. Observation of these thermocouples after repeated temperature measurements of the molten metal revealed that
Although a crack had occurred, it was growing in a state deflected at the carbon layer, but the crack had stopped in the inner laminated layer, and it was confirmed that there was no crack propagation inside. Was.

For the purpose of comparison, a protective tube made of a monolithic material was formed from a single layer instead of a laminated structure, and a comparative thermocouple composed of the protective tube was fabricated. At this time, the protective tube of the comparative product, was prepared by cermet Mo-ZrO _2. Using a comparative thermocouple, the same as above, about 175
When the temperature of the steel melt at 0 ° C was measured,
Repeated temperature measurement of more than 10 times (specifically, 12 times was the life), cracks were generated by thermal shock, further cracks propagated inside the protective tube, that is, the filler, and the metal melt was measured. The temperature has become impossible.

[0030]

As described above, the thermocouple for measuring the temperature of molten metal according to the present invention comprises a cermet layer having a protective tube of Mo as a mother phase and C, MgO, CaO, Al ₂ O ₃ and ZrO ₂ . Since it has a multi-layered structure in which at least one or more layers are alternately laminated, there is no adhesion of iron, cracks in the protective tube do not propagate to the inside, and measurement of the molten metal is repeated 500 times or more. The temperature can be measured accurately and quickly, the durability can be improved, and a long-life thermocouple can be provided. The protection tube is made of ZrN, which has a small coefficient of thermal expansion and does not easily react with iron.
Since it is made of a material based on Mo in which ZrB ₂ , ZrO ₂ , and ZrC are dispersed, adhesion of molten iron can be prevented, and temperature measurement performance can be improved. In addition, the temperature of the thermocouple temperature measurement area is limited by the porous ceramic filler inside the protective tube, making it difficult for heat to escape backward through the protective tube and reducing the heat capacity of the temperature measurement area. The temperature measurement responsiveness 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 distal end portion of the thermocouple for measuring molten metal temperature in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Protective tube 2 Cermet layer 3 Other layers 4 Temperature measuring area 5 Sealing tube 6, 7 W-Re strand 8 Filler 9 Temperature measuring unit 10 Sealing member 11 Ceramic cement 12, 13 Terminal

Claims (7)

[Claims] 1. A protective tube closed at one end and open at the other end, a filler filled in the protective tube, and a different composition constituting a temperature measuring unit disposed on the filler and joined at a tip end. In the thermocouple for measuring the temperature of molten metal comprising a pair of alloy wires for temperature detection, the protective tube has a cermet layer whose main phase is Mo, C, MgO, CaO, Al ₂ O ₃ , Z
It has a multi-layer structure in which at least one or more layers of rO ₂ are alternately laminated, the filler is made of heat-resistant porous ceramics, and the opening of the protective tube is sealed with a dense heat-resistant member and glass. A thermocouple for measuring temperature of molten metal. 2. The cermet layer of the protective tube forms at least an outermost layer, and has a small thermal expansion coefficient and does not easily react with iron such as Mo—ZrN, Mo—ZrB ₂ , and Mo—Zr.
O _2, Mo-ZrC any one or thermocouple molten metal temperature measurement according to claim 1, characterized in that consisting of composites of. 3. The alloy wire for temperature detection according to claim 1, wherein the wire is a tungsten-rhenium wire.
The thermocouple for measuring the temperature of molten metal described in 1. 4. The temperature measuring method for molten metal according to claim 1, wherein the heat-resistant porous ceramic of the filler is a reaction sintered silicon nitride to which Ti is added. For thermocouple. 5. The heat-resistant porous ceramic of claim 1, wherein the heat-resistant porous ceramic is a mixture of an inorganic substance converted from an organosilicon polymer containing Si ₃ N ₄ powder and a heat-resistant ceramic powder. The thermocouple for measuring the temperature of a molten metal according to any one of the preceding claims. 6. The thermocouple according to claim 5, wherein at least one of carbon and BN is contained in the mixture. 7. The temperature measuring method according to claim 1, wherein the heat-resistant porous ceramic of the filler contains Zr, O, Al, and P. thermocouple.