JP3731501B2 - Thermocouple for molten metal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a molten metal thermocouple excellent in durability and responsiveness suitable for measuring a temperature of a molten metal.
[0002]
[Prior art]
Conventionally, as a thermocouple used to measure the temperature of molten metal, an alumina insulating tube with a metal wire of a Pt-Rh (platinum-rhodium) thermocouple inserted is used as alumina Al ₂ O ₃ or silicon nitride Si ₃ N _4. The thing of the structure inserted in the protective tube which consists of is known. However, the protective tube made of alumina has a drawback that it cannot withstand a sudden change in temperature, that is, thermal shock. On the other hand, the protective tube made of silicon nitride can withstand thermal shock, but the Si component of the protective tube reacts with the Pt component of the metal strand at a high temperature to form a compound having a melting point of about 800 ° C. There is a problem that it is easy to do and lacks durability. Further, temperature measurement at a temperature of 1500 ° C. or higher using a Pt—Rh thermocouple is not suitable for use because the melting point of the metal strand itself is close to the measurement temperature.
[0003]
[Problems to be solved by the invention]
In view of the above-described problems, an object of the present invention is to provide a thermocouple for molten metal that is capable of measuring a temperature in a high temperature range and is excellent in durability and responsiveness.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the configuration of the present invention is configured such that a second internal protective tube made of a stainless steel tube is connected to a proximal end portion of a ceramic first internal protective tube whose tip is closed, A pair of metal strands whose tips form measurement contacts are inserted into the inner protective tube, and a gap between the first and second inner protective tubes and the metal strand is filled with a filler made of a heat-resistant ceramic, The tip of the first inner protective tube projects from the outer sleeve covering the first inner protective tube, both ends of the outer sleeve are fixed to the first and second inner protective tubes by fixing members, and the inner sleeve and the inner protection are protected. An air layer is provided between the pipe and the tube.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the first inner protective tube is closed at the tip, and is molded from ceramic powder and fired. The second inner protective tube is made of a stainless steel tube and is connected to the proximal end of the first inner protective tube.
[0006]
The outer sleeve has a multi-layer structure in which a layer composed mainly of silicon nitride Si ₃ N ₄ and a layer composed mainly of silicon nitride Si ₃ N ₄ and doped with boron nitride BN are stacked concentrically or spirally. In the outermost layer, a layer containing silicon nitride Si ₃ N ₄ as a main component and boron nitride BN is disposed. Specifically, the outer sleeve has a thick layer with silicon nitride Si ₃ N ₄ as the main component and 40 vol.% Boron nitride BN added on the outside, and a thin layer with silicon nitride Si ₃ N ₄ as the main component on the inside. The arranged sheets are stacked concentrically or spirally to form a multiple stacked structure, and the multiple stacked structure is sintered.
[0007]
The fixing member that fixes the inner protective tube to the outer sleeve is made of ceramic fiber or inorganic glass.
[0008]
【Example】
1 is a side view showing a schematic configuration of a molten metal thermocouple according to the present invention, FIG. 2 is an enlarged side sectional view showing a base end portion of the molten metal thermocouple, and FIG. 3 is a molten metal thermocouple. It is a side cross section which expands and shows the front-end | tip part. The first inner protective tube 3 that accommodates the metal wires 1, 1 a of the thermocouple protrudes from the outer sleeve 5 at the distal end, and the base end of the outer sleeve 5 is joined by the stainless steel tube 6 and the connecting tube 7. The stainless steel pipe 6 is bent in a dogleg shape at the base end. A male connector 11 connected to the metal wires 1 and 1a is provided at the base end portion of the stainless steel pipe 6. A female connector 12 that engages with the male connector 11 is provided at the tip of the stainless steel tube 8, and the compensating conductors 13 and 13 a are connected to the female connector 12. The stainless steel pipe 6 and the stainless steel pipe 8 are joined by a connecting pipe 9.
[0009]
The pair of metal wires 1 and 1a constituting the thermocouple are made of W-Re (tungsten-rhenium) alloys having different components. The tips of the pair of metal wires 1 and 1a are joined by welding to form a measurement contact 2 for measuring temperature, that is, a temperature detector. The base ends of the metal wires 1 and 1a form a reference contact, and are connected to the potentiometer through the male connector 11, the female connector 12, and the compensating lead wires 13 and 13a. The temperature indicator 10 displays the temperature based on a potentiometer.
[0010]
As shown in FIGS. 2 and 3, the pair of metal wires 1, 1 a is connected to the first inner protective tube 3 and the second inner protective tube 4 whose tips are closed, and the tip portion where the measurement contact 2 is closed. It is inserted and held so that it is located in The first inner protective tube 3 is formed from a silicon nitride-based ceramic powder by an extrusion molding machine and fired in a nitrogen gas atmosphere at a pressure of 50 atm and a temperature of 1850 ° C. for 4 hours. Therefore, the first inner protective tube 3 can withstand a rapid change in temperature, that is, has excellent heat resistance and impact resistance. The second inner protective tube 4 is made of stainless steel.
[0011]
Between the metal strands 1 and 1a and the first inner protective tube 3 and the second inner protective tube 4, a filler 14 made of a heat-resistant ceramic powder, specifically, silicon nitride powder is filled. The filler 14 may be added with aluminum phosphate or magnesia in addition to silicon nitride.
[0012]
The base end of the second inner protective tube 4 is a sealing portion 15 and is sealed with glass so as to hold the metal strands 1 and 1a. Both ends of the outer sleeve 5 are formed between the first inner protective tube 3 and the outer sleeve 5 and between the second inner protective tube 4 and the outer sleeve 5 so that an air layer 17 is formed between the first inner protective tube 3 and the outer sleeve 5. The protective tube 3 is fixed by a fixing member 16. The material of the fixing member 16 is made of silicon carbide SiC or alumina Al ₂ O ₃ ceramic fiber, or inorganic glass such as zirconia ZrO ₂ , alumina Al ₂ O ₃ , or silica SiO ₂ . The tip of the first inner protective tube 3 protrudes from the outer sleeve 5 by, for example, about 20 mm.
[0013]
The external sleeve 5 is produced, for example, by winding a sheet into a cylindrical shape and firing it. First, a sheet A having a thickness of about 100 μm is produced from a powder obtained by adding a small amount of a sintering aid to silicon nitride as a main component or a basic component, using a doctor blade apparatus. Further, 10-40 vol.% Boron nitride BN as a hot water repellent component with respect to the molten metal is added to silicon nitride as a main component, and a sheet B having a thickness of about 100 μm is used by using a doctor blade device as described above. Is made. At that time, four sheets having different boron nitride BN addition ratios, for example, a sheet B1 prepared by adding 10 vol.% Boron nitride BN to silicon nitride, and 20 vol.% Boron nitride BN to silicon nitride are added. Sheet B2 was prepared by adding 30 vol.% Boron nitride BN to silicon nitride, and sheet B3 was prepared by adding 40 vol.% Boron nitride BN to silicon nitride. And The addition ratio of boron nitride BN in each of the sheets B1 to B4 is not limited to the above-described numerical values, and any addition ratio may be used.
[0014]
Sheets B1 to B4 were combined and laminated to produce two types of cylinders 5a and 5b. Specifically, the cylindrical body 5a is formed by laminating about 10 layers of sheets A and B1 alternately or irregularly (randomly) concentrically or spirally, and then the sheet A and the sheet B2 on the outside of the cylinder 5a. Similarly, about 10 layers are laminated, then about 10 layers are laminated on the outside of the sheet A and B3 as before, and further about 10 layers are laminated on the outside of the sheet A and B4 as before. In addition, the sheet B4 was laminated on the outermost layer, and as shown in FIG.
[0015]
The cylindrical body 5b was obtained by changing the thickness of the above-mentioned sheet A by 20 μm from 80 μm to 300 μm, and by changing the thickness of the above-mentioned sheet B4 having 40% by volume of boron nitride BN by 20 μm from 80 to 300 μm. B5 is prepared, and when the sheets A and B5 are alternately stacked concentrically or spirally, the sheet A is used from the thicker to the thinner as it goes from the inside to the outside, and conversely, the sheet B5 is the outside from the inside From the thin to the thick, the sheet B5 is arranged on the outermost layer, and as shown in FIG. 6, the combined thickness of the sheet A and the sheet B5 is 200 to 300 μm. Sheet A and sheet B5 having different thicknesses were selected and formed.
[0016]
The two types of cylinders 5a and 5b were subjected to secondary molding by CIP (cold isostatic pressure), and each molded body was fired in a nitrogen atmosphere at a temperature of 1850 ° C. for 4 hours to produce an external sleeve 5. Since the outer sleeve 5 has an improved inner layer adhesion and strength, the outer sleeve 5 can withstand sudden changes in temperature, that is, heat resistance and impact resistance. Excellent and repellent to molten metal.
[0017]
Since the first inner protective tube 3 is made of silicon nitride, it has excellent heat resistance and impact resistance, and is nitrided between the metal strands 1 and 1a and the first and second inner protective tubes 3 and 4. By filling the filler 14 of heat-resistant ceramic powder made of silicon, aluminum phosphate or magnesia, oxidation of the metal wire made of W-Re alloy can be prevented, and temperature measurement in a higher temperature range becomes possible.
[0018]
When measuring the temperature of the molten metal using the thermocouple for molten metal according to the present invention, most of the outer sleeve 5 is immersed in the molten metal. The silicon nitride ceramic constituting the outer sleeve 5 has excellent heat resistance and low heat transfer, the air layer 17 exists between the outer sleeve 5 and the inner sleeve 3, and the ceramic fiber constituting the fixing member 16 is Since heat resistance is excellent and heat conductivity is small, and the tip portion of the first inner protective tube 3 protruding from the outer sleeve 5 is small, the heat capacity of the portion immersed in the molten metal of the molten metal thermocouple is small, Responsiveness to temperature measurement of the molten metal is improved.
[0019]
FIG. 7 shows the result of a temperature measurement test performed on the molten metal at a temperature of 1450 ° C. using the molten metal thermocouple according to the present invention. In the conventional thermocouple, the time required for the temperature measurement value to settle to a predetermined value is 10 seconds, whereas in the thermocouple for molten metal according to the present invention, the improvement in responsiveness was confirmed to 8 seconds.
[0020]
Moreover, when the durability test which repeatedly immerses in the molten metal of temperature 1450 degreeC was done, the frequency | count of temperature measurement until a metal strand reaches a disconnection is as showing in FIG. In the conventional thermocouple, the temperature of the temperature measurement was about 100 times, and the metal wire was broken. On the other hand, the molten metal thermocouple according to the present invention can measure the temperature repeatedly about 400 times. The durability was almost 4 times that of the pair. Moreover, in the thermocouple for molten metal according to the present invention, no damage to the outer sleeve 5 is observed even after 400 times of temperature measurement, no slag adheres to the surface of the outer sleeve 5, and the water repellency to the molten metal. Was found to be high.
[0021]
In addition, the results of examining the relationship between the bonding strength of the sheet A containing silicon nitride as the main component and the sheet B obtained by adding boron nitride BN to silicon nitride and the amount of boron nitride BN added to the sheet B are shown in Fig. As shown in FIG. It was confirmed that when the amount of boron nitride BN added to silicon nitride (including the sintering aid) exceeds 40 vol.%, The bonding strength is extremely reduced. Further, when the outer sleeve 5 made of a sheet B made of silicon nitride and boron nitride BN added to the outermost layer is immersed in the molten metal, the amount of boron nitride BN added with respect to the contact angle between the surface of the sheet B and the molten metal The result of investigating the relationship is shown in FIG. It was confirmed that when the amount of boron nitride BN added was 10 vol.% Or less, the contact angle was extremely reduced, and the repellency to the molten metal was lowered. From this result, it was found that the addition ratio of boron nitride BN added to silicon nitride which is the main component in sheet B is most preferably 10 to 40 vol.
[0022]
【The invention's effect】
In the present invention, as described above, a second internal protective tube made of a stainless steel pipe is connected to the proximal end portion of the first ceramic internal protective tube whose tip is closed, and the distal end is connected to the first internal protective tube. Is inserted into the gap between the first and second inner protective tubes and the metal strand, and a filler made of a heat-resistant ceramic is inserted into the first inner protective tube. The front end of the first inner protective tube protrudes from the outer sleeve that covers the outer sleeve, both ends of the outer sleeve are fixed to the first and second inner protective tubes by fixing members, and air is interposed between the outer sleeve and the inner protective tube. The silicon nitride ceramic that constitutes the outer sleeve is excellent in heat resistance and has low heat conductivity, that there is an air layer between the outer sleeve and the inner sleeve, and that constitutes the fixing member. Ceramic fiber has excellent heat resistance The first end of the first inner protective tube protrudes from the outer sleeve when the molten metal thermocouple is immersed in the molten metal because of the low performance and the end portion of the first inner protective tube protruding from the outer sleeve is small. The amount of heat transfer to the part or in the reverse direction is small, the heat capacity of the part of the metal melt thermocouple immersed in the metal melt is small, and the responsiveness to the temperature measurement of the metal melt is improved.
[0023]
Since silicon nitride is used for the internal protective tube, it has excellent heat resistance and thermal shock resistance, and since the outer sleeve outer layer is made of silicon nitride added with boron nitride, it also has excellent heat resistance and thermal shock resistance. Further, when the outer sleeve is immersed in the molten metal, it exhibits a water repellency with respect to the molten metal and the number of repeated temperature measurements can be increased.
[0024]
By using a W-Re alloy for the metal element and filling a filler such as silicon nitride between the metal element and the inner protective tube, oxidation of the metal element is prevented and the thermocouple is heated in the high temperature range. Temperature measurement is possible.
[Brief description of the drawings]
FIG. 1 is a side view of a molten metal thermocouple according to the present invention.
FIG. 2 is an enlarged side cross-sectional view showing a base end portion of the molten metal thermocouple.
FIG. 3 is an enlarged side cross-sectional view of a tip portion of the molten metal thermocouple.
FIG. 4 is a side view showing a schematic configuration of a connector for connecting a metal element wire and a compensating conductor in the molten metal thermocouple.
FIG. 5 is a plan sectional view of an outer sleeve in the molten metal thermocouple.
FIG. 6 is a plan sectional view of another example of an external sleeve in the molten metal thermocouple.
FIG. 7 is a diagram showing temperature measurement responsiveness between the molten metal thermocouple and the conventional thermocouple.
FIG. 8 is a diagram showing temperature measurement durability of the molten metal thermocouple and the conventional thermocouple.
FIG. 9 is a diagram showing the relationship between the amount of boron nitride added to silicon nitride and the bonding strength of the sheet on which the outer sleeve of the molten metal thermocouple is laminated.
FIG. 10 is a diagram showing the relationship between the amount of boron nitride added to silicon nitride and the contact angle with respect to the molten metal in the outermost layer sheet on which the outer sleeve of the molten metal thermocouple is laminated.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 1a: Metal wire 2: Measuring contact 3: 1st internal protection pipe 4: 2nd internal protection pipe 5: External sleeve 6: Stainless steel pipe 7: Connection pipe 8: Stainless steel pipe 9: Connection pipe 10: Temperature Indicator 11: Male connector 12: Female connector 13, 13a: Compensation conductor 14: Filler 15: Sealing part 16: Fixing member 17: Air layer

Claims (7)

A second internal protective tube made of a stainless steel tube is connected to the base end of the first internal protective tube made of ceramic whose tip is closed, and a pair of tips whose measurement contacts are connected to the first internal protective tube A metal strand is inserted, a filler made of a heat-resistant ceramic powder is filled in the gap between the first and second inner protective tubes and the metal strand, and the first is started from the outer sleeve covering the first inner protective tube. The end of the inner protective tube protrudes, both ends of the outer sleeve are fixed to the first and second inner protective tubes by fixing members, and an air layer is provided between the outer sleeve and the inner protective tube. A thermocouple for molten metal. The outer sleeve is formed by inclining a layer mainly composed of silicon nitride Si ₃ N ₄ and a layer composed mainly of silicon nitride Si ₃ N ₄ while changing the addition amount of boron nitride BN of 10 to 40 vol.%. However, it has a multi-layered structure in which concentric layers or spiral layers are alternately stacked, and layers in which silicon nitride Si ₃ N ₄ is a main component and boron nitride BN is added are arranged on the outermost layer. Thermocouple for molten metal. The outer sleeve has a thick layer containing silicon nitride Si ₃ N ₄ as a main component and 40 vol.% Boron nitride BN added outside, and a thin layer mainly containing silicon nitride Si ₃ N ₄ arranged inside. 2. The molten metal thermocouple according to claim 1, which has a multilayer structure in which the two layers having a thickness of 200 to 300 μm are stacked concentrically or spirally. The thermocouple for molten metal according to claim 1, wherein the inner protective tube is made of a material mainly composed of silicon nitride Si ₃ N ₄ . 2. The fixing member according to claim 1, wherein the fixing member is made of one of silicon carbide SiC or alumina Al ₂ O ₃ ceramic fiber and zirconia ZrO ₂ , alumina Al ₂ O ₃ or silica SiO ₂ inorganic glass. Thermocouple for molten metal. _{2. The} thermocouple for molten metal according to claim 1, wherein the filler is made of silicon nitride Si ₃ N ₄ , magnesium oxide MgO, or aluminum phosphate Al ₃ (PO ₄ ) ₂ . The thermocouple for molten metal according to claim 1, wherein the metal strand is made of a W-Re (tungsten-rhenium) alloy.

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