JP2013015488A - Thermo couple - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermo couple which can measure a temperature accurately and continuously in a high temperature region.SOLUTION: The thermo couple includes a first metal wire 1, a second metal wire 2 formed of a material different from that of the first metal wire 1, and a conductive ceramics 3 for connecting the first metal wire 1 and the second metal wire 2 and functioning as a hot junction.

Description

  The present invention relates to a thermocouple, and more particularly, to a thermocouple including a hot junction portion electrically connected to a first metal wire and a second metal wire.

  Thermocouples are widely used as the most reliable method for temperature measurement in a high temperature range. Standards have also been established for thermocouples. A thermocouple is a sensor that measures a temperature difference. When two different kinds of metals are joined, a voltage corresponding to different temperatures at the two joining points is generated due to the difference in thermoelectric power between them, and a current flows in a certain direction. A thermocouple is a temperature sensor that utilizes a phenomenon (Seebeck effect) in which a thermoelectromotive force is generated by a temperature difference between two contact points of different metals.

  The generated thermoelectromotive force varies for each metal to be joined. Each metal to be joined has different stability, magnitude of electromotive force, linear characteristics of electromotive force, and the like. For this reason, the type of thermocouple, the wire diameter, etc. are determined by various standards (IEC: International Electrotechnical Commission, JIS: Japanese Industrial Standard, ANSI: American National Standards Institute, etc.). The metal to be used is appropriately selected in consideration of the cost of the material because the measurement range, the measurement accuracy, and the like differ for each metal to be joined.

  Noble metal thermocouples are used for high temperature measurements such as the melting temperature of metals. In the precious metal thermocouple, the stability of the material itself is good, but since the thermoelectromotive force is low, the precious metal thermocouple is not suitable for measurement from low temperature to middle high temperature. In addition, since noble metal materials are extremely expensive when all the wirings are used, noble metals are used only for the temperature sensing part (the hot junction). An alloy wire composed of a relatively inexpensive metal having a thermoelectric power similar to that of a noble metal is used for the wiring portion at about 250 ° C. or lower. This alloy wire is called “compensation lead”. If there is a temperature difference at the connection point between the temperature sensing part and the compensation conductor, the temperature difference becomes an error factor.

  As the temperature measuring portion (hot junction) of the thermocouple, a grounding type (earth type) or a non-grounding type (non-earth type) is used according to the temperature measurement request. The grounding type is used to measure the temperature in contact with the measurement object, and the non-grounding type is used to measure the temperature without contacting the measurement object.

  In the case of high temperature measurement, a “protection tube” is used to protect a thin thermocouple. This protective tube is generally made of metal (copper, stainless steel, cantal, inconel, titanium, hastelloy, platinum in special cases), non-metal (hard glass, high-purity alumina, quartz, zirconia, silicon nitride, Teflon (registered) Trademark)). When measuring the temperature of molten metal, for example, a quartz protective tube is used for one measurement with a measurement time of about 10 seconds, and refractory (alumina graphite, etc.) is protected for continuous measurement with a measurement time of several hours or more. A tube is used.

  The metal protective tube also has a role of reducing temperature measurement errors by performing stable temperature measurement with less noise by shielding electrical noise from the external environment during temperature measurement. Therefore, it is preferable that the thermocouple wire inside the thermocouple and the metal protective tube are electrically insulated. For this purpose, a structure in which the inside of a metal protective tube is filled with magnesium oxide, silica powder or the like is called a “sheath thermocouple”. Sheath thermocouples have a large circulation volume and are widely used with standardized thickness, shape, protective tube material, and the like.

  When the molten metal (and slag) temperature is measured for a long time by the thermocouple described above, there are the following problems with respect to the durability of the hot junction.

  First, there are the following problems in the case of a hot junction open type thermocouple configured with the hot junction exposed from the protective tube and the tips of two kinds of metals being opened. For example, as disclosed in JP-A-10-281886 (Patent Document 1), when the temperature of a molten metal having conductivity is measured using a thermocouple, even when the hot junction is an open type, Temperature measurement is theoretically possible because a thermocouple is formed through the molten metal to be measured.

  However, this method cannot be applied to temperature measurement of non-conductive melts such as slag. Furthermore, in a refining furnace environment where molten metal and molten slag coexist like a converter, the slag suspended in the molten metal easily solidifies and adheres to the exposed portion of the metal body of the thermocouple. There is also a possibility that the thermocouple is not formed by being coated.

  Also, in the refining furnace such as a converter, the molten metal being smelted flows violently, so even if the melting point of the metal body of the thermocouple is higher than the molten metal, the metal body precedes the surrounding refractory. It is often melted and a mortar-shaped space is often formed. And the molten metal which penetrate | invaded into this space often leads to the situation where the function of a thermocouple is impaired by solidification shrinkage.

  Furthermore, Japanese Patent Laid-Open No. 10-281886 discloses a case where tungsten having a high melting point is used as a metal body. However, tungsten cannot be used in a furnace having an oxidizing atmosphere such as a converter because it is rapidly oxidized and worn.

  Further, since the temperature of the refractory around the metal body of the thermocouple is generally several tens of degrees lower than the temperature of the molten metal, the measured temperature in this method may be lower than the temperature of the molten metal. Therefore, accurate temperature measurement of the molten metal is difficult.

  As one method for solving these problems, two metal bodies are fed into the molten metal at an appropriate speed, and the contact surface between the molten metal and the metal body is constantly updated, and at the same time the temperature measuring position is changed from the surface of the refractory. A method of keeping a certain distance can be considered.

  However, in this case, the size of the device for feeding the metal body becomes large, and it is difficult to secure an installation space close to the existing molten metal container. In addition, the wear cost of the metal body (mostly noble metal) increases. Moreover, since the seal between the metal body continuously inserted and the surrounding fixed refractory is not perfect, leakage of the molten metal from the container is inevitable. Because of these problems, this method is not practically used.

  Next, in the case of a hot junction junction type thermocouple in which hot junctions are joined, there are the following problems. When the temperature of the molten metal is directly measured by immersing the hot junction bonded thermocouple in the molten metal, if the hot contact portion is exposed, the hot contact portion is immediately melted by the molten metal, and measurement cannot be performed. Therefore, the hot junction needs to be protected by a protective tube.

  A quartz tube is often used as a protective tube for a single measurement. In the case of continuous measurement, a metal protective tube is often used like a sheath type thermocouple. Even if the thermocouple is protected by the metal protective tube, the metal protective tube melts and disappears almost simultaneously with the immersion in the molten metal, so that the function as the thermocouple disappears instantaneously. As a method for solving this problem, there are mainly the following two methods for protecting the hot junction from the molten metal during continuous temperature measurement.

  First, there is a method of protecting the hot junction with a refractory protection tube. In this method, by further surrounding the sheath type thermocouple with a protective tube made of refractory, the durability against molten metal (and slag) is greatly increased, so that continuous temperature measurement is possible.

  However, in this case, the temperature of the molten metal (and slag) is measured through a protective tube made of a refractory having a large heat capacity. For this reason, the temperature measurement value is lower than when the temperature is measured by immersing the thermocouple directly in the molten metal, and the measurement temperature does not sufficiently follow the change with time of the temperature of the molten metal (and slag). In order to reduce these problems as much as possible, a refractory having a relatively high thermal conductivity and a high durability against molten metal (and slag) is selected as the material of the protective tube. And it is necessary to make the thickness of the refractory as thin as possible while considering the balance with the lifetime. Alumina graphite refractories are a typical example.

  There are the following two methods for immersing such a refractory protective tube in the molten metal. One method is to suspend the protective tube of the refractory and insert the protective tube from above the molten metal. However, at the time of molten metal refining, a slag layer exists on the surface of the molten metal. Particularly in the case of steel refining, since the slag is an active oxidizing slag, the portion where the refractory protective tube comes into contact with the slag is quickly worn out. This has the disadvantage that the upper limit of the continuous temperature measurement time is determined.

  Another method is to install a refractory protective tube so as to penetrate the inner wall (furnace wall) of the molten metal holding furnace. In this case, since the refractory protective tube is held by the refractory constituting the furnace wall, the heat is always removed by the furnace wall. For this reason, in order to accurately measure the temperature of the molten metal with a thermocouple protected by a refractory protective tube, according to experience, the temperature of the portion protruding from the furnace refractory wall to the inside of the molten metal by at least about 150 to 200 mm It is necessary to measure.

  When the refractory protection tube is designed in consideration of the conditions such as the measurement position, responsiveness, and melting resistance, the outer diameter of the refractory protection tube is 100 mm or more and the protrusion length in the furnace is 200 mm or more. As a result, the overall heat capacity (product of volume and specific heat) is generally 100 times greater than the heat capacity of a sheathed thermocouple having a diameter of 1 to 10 mm.

  This refractory protection tube is gradually melted by molten metal or slag during temperature measurement, and its lifetime is at most several hours to several tens of hours. Since the life of a smelting furnace is usually several months or more, as a result, the probe as a thermocouple protected by a refractory protection tube needs to be frequently replaced. For this reason, the probe must be designed so that it can be inserted and replaced from the outside in the furnace body, and it must be designed with sufficient consideration for workability and sealing performance with the refractory surrounding the probe (prevention of molten metal leakage). Must not.

  However, it is considered unfavorable to provide a hole having a diameter of 100 mm for inserting a probe in such a high-temperature smelting furnace because of the possibility of a molten metal leakage accident, so such a method is adopted in an actual furnace. There are few things.

  Secondly, there is a method of protecting the hot junction by measuring the internal temperature of the furnace wall refractory. In other words, as a suboptimal measure, there is a method to give up accurate measurement of the molten metal temperature and to continuously measure the temperature inside the furnace wall by installing a hot junction junction type sheathed thermocouple at a certain position inside the furnace wall. is there. For example, Japanese Patent Laid-Open No. 2009-41842 (Patent Document 2) discloses an example of such a method. By using this method, it is possible to prevent the sheath thermocouple from being worn by the molten metal (and slag). Moreover, the life of the thermocouple is about the same as that of the furnace wall refractory, which is satisfactory.

Japanese Patent Laid-Open No. 10-281886 JP 2009-41842 A

  However, in the method described in the above Japanese Patent Application Laid-Open No. 2009-41842, the temperature measured by the thermocouple indicates the temperature inside the furnace wall, and thus is much lower than the actual temperature of the molten metal. Therefore, it is almost impossible to accurately estimate the temperature of the molten metal from the measured temperature. For example, in the above-mentioned Japanese Patent Application Laid-Open No. 2009-41842, the measured temperature is about 1200 ° C. at maximum, and it is impossible to estimate and calculate an accurate molten metal temperature (generally 1500 ° C. or more in the case of molten steel) from this value. It can be said that. Therefore, it is impossible to accurately measure the temperature of the molten metal by this method. Therefore, the conventional method cannot measure the temperature accurately and continuously in a high temperature range such as the temperature of the molten metal.

  Further, the hot junction junction type thermocouple has a problem of deterioration of thermoelectromotive force. That is, while being exposed to a high temperature for a long time, the components diffuse to each other through the junction of the two kinds of metal bodies, and the thermoelectromotive force inherent in the thermoelectromotive force (the heat obtained by calibration in advance). There is a problem that it gradually deviates from the electromotive force. This is an essential problem when a hot junction type thermocouple is used at a high temperature for a long time. As a result, there is a problem that a temperature measurement error occurs.

  This invention is made | formed in view of the said subject, The objective is to provide the thermocouple which can measure temperature correctly and continuously in a high temperature range.

  The thermocouple of the present invention electrically connects a first metal wire, a second metal wire made of a material different from the first metal wire, and the first metal wire and the second metal wire. And a conductive ceramic functioning as a hot contact portion.

  According to the thermocouple of the present invention, since the conductive ceramics electrically connects the first metal wire and the second metal wire and functions as a hot contact portion, the conductive material that functions as a hot contact portion on the measurement object. The temperature of the object to be measured can be accurately measured by contacting the ceramic. Moreover, since the conductive ceramic which functions as a hot junction part is hard to melt, it can be continuously measured in a high temperature range. Therefore, the temperature can be measured accurately and continuously in the high temperature range.

  In the above thermocouple, the first metal wire and the second metal wire are preferably held by the conductive ceramics in a non-contact state. Thereby, it can prevent that a component spread | diffuses mutually because a 1st metal wire and a 2nd metal wire contact. For this reason, deterioration of the thermoelectromotive force can be prevented. Therefore, it is possible to prevent the occurrence of temperature measurement errors.

In the above thermocouple, preferably, the material of the conductive ceramic includes ZrB ₂ . Thereby, corrosion resistance with respect to a molten metal can be made high.

  In the above thermocouple, preferably, the material of the conductive ceramic contains SiC. Thereby, corrosion resistance can be made high with respect to oxidizing slag.

In the above thermocouple, preferably, the material of the conductive ceramic has ZrB _{2 in a range} of 60% by mass to 95% by mass and SiC in a range of 5% by mass to 40% by mass. Thereby, corrosion resistance can be effectively made high with respect to oxidizing slag.

  In the above thermocouple, preferably, the material of the conductive ceramic contains an antioxidant. Thereby, corrosion resistance can be further improved with respect to oxidizing slag.

In the above thermocouple, preferably, the antioxidant contains B ₄ C. Thereby, corrosion resistance can be effectively improved with respect to oxidizing slag.

  In the above thermocouple, the conductive ceramic preferably has a hole provided on the surface. The first metal wire and the second metal wire are held by the conductive ceramics while being inserted into the hole. Thereby, the 1st metal wire and the 2nd metal wire can be firmly held to conductive ceramics. For this reason, it can suppress that a 1st metal wire and a 2nd metal wire are isolate | separated from electroconductive ceramics. Therefore, it can measure stably and continuously.

  As described above, according to the thermocouple of the present invention, the temperature can be measured accurately and continuously in the high temperature range.

It is a schematic perspective view of the thermocouple in Embodiment 1 of this invention. It is a schematic perspective view of the electroconductive ceramic in Embodiment 1 of this invention. It is a figure which shows the relationship between the volume specific resistance value of the electrically conductive ceramic in Embodiment 1 of this invention, and a SiC compounding rate. It is a figure which shows the erosion rate of the comparative example 1 and this invention example 1. FIG. It is a figure which shows the relationship between the erosion rate of the electrically conductive ceramics in Embodiment 1 of this invention, and a SiC compounding rate. It is a figure which shows the relationship between the erosion rate of this invention example 1 and this invention example 2, and a SiC compounding rate. It is a figure which shows the relationship between the heat conductivity of the electrically conductive ceramic in Embodiment 1 of this invention, and a SiC compounding rate. It is a figure which shows the relationship between the temperature measurement value by this invention example 3, and the temperature measurement value by the comparative example 2. FIG. It is a schematic sectional drawing of the ladle in Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
First, the configuration of the thermocouple according to the first embodiment of the present invention will be described.

  Referring to FIGS. 1 and 2, thermocouple 10 of the present embodiment mainly has sheath wire 100 and conductive ceramics 3 functioning as a hot junction part. The sheath wire 100 includes a first metal wire 1 and a second metal wire 2 made of a material different from that of the first metal wire 1. The conductive ceramic 3 is configured to electrically connect the first metal wire 1 and the second metal wire 2 to function as a hot junction part.

The conductive ceramic 3 of the present embodiment has a volume resistivity of 1 × 10 ⁻² Ω · cm or less, a thermal conductivity of 50 W / m · K or more, and a relative density (bulk density / theoretical density) of 95%. The above ceramics are applied.

The first metal wire 1 and the second metal wire 2 of the sheath wire 100 are held by the conductive ceramics 3 in a non-contact state. The material of the conductive ceramic 3 contains ZrB ₂ (zirconium diboride). The volume resistivity value of ZrB ₂ is, for example, 1.74 × 10 ⁻⁵ Ω · cm (room temperature). The thermal conductivity of ZrB ₂ is, for example, 58.8 W / m · K (room temperature), 64.4 W / m · K (1027 ° C.), and 134 W / m · K (2027 ° C.).

  Further, the material of the conductive ceramic 3 may include SiC (silicon carbide). As the first metal wire 1, for example, a Pt (platinum) wire is used, and as the second metal wire 2, for example, a Pt—Rh (rhodium) wire is used.

  The thermocouple 10 is configured to come into contact with a measurement object such as a molten metal (and slag) on the one end 3a side of the conductive ceramic 3. The conductive ceramic 3 constitutes a hot contact part as a whole. The sheath wire 100 having the first metal wire 1 and the second metal wire 2 is connected to the other end 3 b side of the conductive ceramic 3. The first metal wire 1 and the second metal wire 2 are configured not to contact the molten metal (and slag) directly. Therefore, the first metal wire 1 and the second metal wire 2 are not worn by the molten metal (and slag).

The temperature of the conductive ceramic 3 follows the temperature change of the molten metal (or slag) without delay so that the temperature of the conductive ceramic 3 becomes substantially the same as the temperature of the molten metal (and slag) to be measured. In order to change (responsiveness), it is preferable to design the heat capacity of the conductive ceramic 3 as small as possible. For example, in the case of a 250T (capacity 250 t) ladle, the conductive ceramics 3 is 8 mm in diameter × 10-50 mm in length, 0.5-2.5 cm ³ in volume, and designed to have a mass of 3-15 g. Is preferred.

  Furthermore, it is preferable that the periphery of the conductive ceramic 3 is covered with a refractory having high heat insulation (for example, MgO; magnesium oxide) except for the contact surface with the molten metal (and slag). Thereby, the heat transfer loss to the surrounding refractories can be prevented. According to the above, the structure is such that the temperature of the small conductive ceramics of only a few dozen grams is always substantially the same as the temperature of the molten metal (and slag) and sufficiently follows the temperature change of the molten metal (and slag). Can do.

  Moreover, it is preferable to connect so that the electrical resistance value of a connection part may become the minimum as for the connection method of the conductive ceramic 3 and the 1st metal wire 1 and the 2nd metal wire 2. FIG. Therefore, it is preferable that the conductive ceramic 3 and the first metal wire 1 and the second metal wire 2 are connected with, for example, a platinum paste as an example.

  Further, the components in the conductive ceramic 3 are diffused into the first metal wire 1 and the second metal wire 2, and no change occurs in the electromotive force of the first metal wire 1 and the first metal wire 2. In order to confirm, a thermocouple 10 is produced using the conductive ceramics 3 and held at a high temperature of 1600 ° C. for 24 hours. In the Pt which is the material of the first metal wire 1 and the second metal wire 2 The amount of B (boron) diffused into was analyzed. As a result, B was not detected in Pt. Therefore, in the thermocouple 10 of the present embodiment, it has been confirmed that the deterioration of the thermoelectromotive force with time, which is generally found in the hot junction junction type thermocouple, does not occur.

Subsequently, an example of the structure of the thermocouple of the present embodiment will be described more specifically.
The conductive ceramic 3 is formed in a cylindrical shape having a diameter of 8 mm and a length of 30 mm, for example. The conductive ceramic 3 has a hole 30 provided on the surface. The hole 30 has a first small hole 31, a second small hole 32, and a large hole 33. The large hole 33 is formed so as to extend from the other end 3b toward the one end 3a. The large hole 33 is formed with, for example, an inner diameter of 3 mm and a length of 10 mm. The first small hole 31 and the second small hole 32 are formed so as to extend from the tip of the large hole 33 toward the one end 3a. The first small hole 31 and the second small hole 32 are each formed with an inner diameter of 1 mm and a length of 10 mm, for example.

  The distal end portion of the sheath wire 100 is inserted into the hole 30. As the sheath wire 100, for example, a JIS Standard TypeR thermocouple having an outer diameter of 2 mm is used. As the strands, a Pt line is used for the first metal line 1 and a 13% Rh-Pt line is used for the second metal line 2.

  The first metal wire 1 and the second metal wire 2 are held by the conductive ceramics 3 while being inserted into the holes 30. The first metal wire 1 is inserted into the first small hole 31 in a state where the first metal wire 1 and the second metal wire 2 at the tip of the sheath wire 100 are exposed, and the second metal The line 2 is inserted into the second small hole 32. The first metal wire 1 and the second metal wire 2 at the distal end portion of the sheath wire 100 are each exposed 5 mm. The first metal wire 1 and the second metal wire 2 are fixed by platinum pastes 4 and 5 filled in the first small hole 31 and the second small hole 32, respectively. A portion of the distal end portion of the sheath wire 100 where the first metal wire 1 and the second metal wire 2 are not exposed is held in the large hole 33. A gap between the sheath wire 100 and the large hole 33 is filled with heat-insulating refractory powder 6. The sheath wire 100 is fixed with the adhesive 7 at the other end 3 b of the conductive ceramic 3.

Next, the material of the conductive ceramic 3 of the present embodiment will be described in more detail.
The present inventors have focused on conductive ceramics as a connection material that functions as a hot junction. With reference to Table 1, the result of having compared the characteristic of various ceramics is shown.

  Each evaluation item evaluates the following characteristics required for the connection material. FeO (iron oxide) resistance indicates resistance to erosion by oxidizing slag. The thermal conductivity indicates that the temperature difference from the molten metal or molten slag can be minimized. The conductivity indicates whether or not the first metal wire 1 and the second metal wire 2 can be used as a connecting material. The Pt reactivity indicates that Pt is not reduced by coexisting with Pt that is widely used as a material for thermocouple wires. Overall indicates the overall rating. For the symbols of the evaluation items, 項目 indicates very good, ◯ indicates good, Δ indicates normal, and x indicates bad.

As shown in Table 1, the present inventors have found that ZrB ₂ is superior to other ceramics as a connecting material for thermocouple hot junctions in the presence of oxidizing slag. ZrB ₂ has heat resistance unique to ceramics, corrosion resistance against molten metal and slag, and conductivity equivalent to pure iron (induction heating is possible).

With reference to Table 2, the composition of ZrB ₂ of the present embodiment is shown. The balance other than those shown in Table 2 is Zr (zirconium).

Further, as shown in Table 1, the present inventors have found that there is room for improvement in the corrosion resistance to oxidizing slag for ZrB ₂ ceramics. That is, the present inventors have found that ZrB ₂ ceramics are sufficiently resistant to wear due to reducing slag, but not sufficiently resistant to oxidizing slag. That is, the present inventors have found that a sufficiently long life cannot be obtained because the wear of ZrB ₂ proceeds by gradually oxidizing B, which is a constituent element of ZrB ₂ , at a high temperature. It was.

Accordingly, the present inventors have found that when the conductive ceramic 3 is fired by adding SiC to the raw material ZrB ₂ , the corrosion resistance is improved with respect to the oxidizing slag. As a result of various studies by the present inventors, when the compounding ratio of SiC was changed and the performance was compared and verified, if SiC was added in an amount of 5% by mass or more and 40% by mass or less, it would be practical for oxidizing slag. It was confirmed to have sufficient resistance.

That is, the present inventors have confirmed that when the compounding ratio of SiC is 5% by mass or more, it has sufficient resistance against the oxidizing slag. Referring to FIG. 3, the volume resistivity value does not exceed 1 × 10 ⁻² Ω · cm when the SiC content is 60% by mass, but the volume resistivity is 70% by mass when the SiC content is 70% by mass. Since it exceeded 1 × 10 ⁻² Ω · cm, it was confirmed that the requirements for the conductive ceramic 3 were not satisfied.

With reference to Table 3, an example of the blending ratio of ZrB ₂ and SiC of the conductive ceramic 3 of the present embodiment will be shown.

As described above, when the conductive ceramic 3 has ZrB ₂ of 60% by mass or more and 95% by mass or less and SiC has 5% by mass or more and 40% by mass or less, practically sufficient resistance to the oxidizing slag. The present inventors have found that the requirements of the volume resistivity of the conductive ceramic 3 are satisfied.

Subsequently, the corrosion resistance of the conductive ceramic 3 in which SiC is mixed with ZrB ₂ of the present embodiment will be described in more detail.

As Inventive Example 1, a ZrB ₂ -20 mass% SiC sintered product was prepared. And according to old JIS standard R2214 "slag erosion test method by the refractory brick crucible method", the erosion test by slag was done. The test temperature was 1550 ° C. and the test time was 10 hours. As the test slag, an oxidizing slag obtained by adding 20% by mass of FeO to a synthetic slag having a CaO / SiO ₂ ratio of 1.5 was used. As shown in Formula (1), the ratio of the decrease in the sample thickness after the test was used as an index for evaluating durability as the erosion rate. Here, S0 (mm) is the sample thickness before the test, and S1 (mm) is the sample thickness after the test.

Erosion rate (%) = 100 × (S0−S1) / S0 (1)
MgO-20% C brick generally used in steelmaking was prepared as Comparative Example 1 for comparison with refractories. Comparative Example 1 was also subjected to an erosion test under the same conditions as Example 1 of the present invention. As a result, referring to FIG. 4, the erosion rates of Comparative Example 1 and Invention Example 1 were substantially the same. As a result, Invention Example 1 showed corrosion resistance comparable to that of Comparative Example 1. As a result, the conductive ceramics 3 in which SiC is blended with ZrB ₂ of the present embodiment can exhibit the same corrosion resistance as the MgO—C refractories widely used in steelmaking refining vessels. confirmed.

Moreover, the change of the erosion rate was examined by changing the SiC compounding rate of the conductive ceramic 3.
Referring to FIG. 5, improvement in corrosion resistance was observed in the range of 1 to 40% by mass of SiC. In particular, the improvement in corrosion resistance was observed when the SiC content was in the range of 5 to 40% by mass.

Furthermore, the present inventors added a small amount of an antioxidant for the purpose of improving the corrosion resistance of the SiC-containing ZrB ₂ conductive ceramics against the oxidizing slag (FeO-containing slag). In steel refractories, corrosion resistance to oxidizing slag can be improved by dispersing and blending 0.1 to 5% by mass of a minute (particle size of about 0.3 to 5 μm) antioxidant in the refractory. As the antioxidant, metal powder, boron compound, nitride, carbon, carbide or the like is used. Specifically, as the antioxidant, Al (aluminum), Si (silicon), Si ₃ N ₄ (silicon nitride) B ₄ C (boron carbide), BN (boron nitride), MoC (molybdenum carbide) or the like is used. It is done. The antioxidant is preferably added to the SiC ratio of about 5%. The blending ratio of the antioxidant is preferably 0.5% by mass or more and 5.0% by mass or less.

The reason why the corrosion resistance can be improved is that, for example, when Al (aluminum) is added as an antioxidant, the oxide formed by oxidation of the antioxidant and SiO ₂ formed by oxidation of SiC is combined and strong. It is conceivable that the B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ glass film is formed and the oxidation resistance is improved.

Referring to FIG. 6, the present inventors confirmed the corrosion resistance when ZrB ₂ —SiC conductive ceramic was blended with B ₄ C having a SiC ratio of 5% as Invention Example 2. In the present invention example 2, the corrosion resistance was improved in a wide range of the SiC content. The blending ratio of B ₄ C is preferably 0.5% by mass or more and 5.0% by mass or less.

Moreover, as a result of measuring the volume resistivity value at room temperature (23 ° C.) for the conductive ceramic 3 of the present embodiment, as shown in Table 4 and FIG. 3, the volume resistivity value is 2.51 × 10 ⁻⁵ to It was 8.09 × 10 ⁻⁵ Ω · cm. Thereby, in the conductive ceramics 3 of this Embodiment, it was confirmed that the volume specific resistance value equivalent to a metal can be obtained.

  Furthermore, as a result of measuring the thermal conductivity at room temperature in the conductive ceramic 3 of the present embodiment, the thermal conductivity is 65.3 to 107.6 W / m · K as shown in Table 5 and FIG. It was. It was confirmed that a thermal conductivity equal to or higher than that of iron having a thermal conductivity of 80 W / m · K can be obtained. Therefore, it was confirmed that the conductive ceramic 3 of the present embodiment sufficiently functions as a hot junction part of a thermocouple because it has the same conductivity and thermal conductivity as a metal.

Moreover, the accuracy of the temperature measurement value was examined for the conductive ceramics 3 of the present embodiment.
As Comparative Example 2, a general Type B thermocouple (element wires were 6% Rh-Pt wire and 30% Rh-Pt wire) was prepared. As Inventive Example 3, a ceramic thermocouple (ZrB ₂ -20% SiC conductive ceramic 3) was prepared.

  In a molybdenum heater atmosphere furnace, the temperature was raised in a nitrogen atmosphere at 5 ° C./min. Comparative Example 2 and Invention Example 3 were installed in the furnace at the same time, and the temperature was raised between 500 ° C. and 1650 ° C. The temperature was measured continuously, and the measured temperature values of Comparative Example 2 and Invention Example 3 were compared.

  Referring to FIG. 8, it was confirmed that the difference between the temperature measurement values of Comparative Example 2 and Invention Example 3 matched well within ± 2 ° C. over the entire temperature range. Thus, it was confirmed that Example 3 of the present invention sufficiently functions as a thermocouple because it has the same accuracy of temperature measurement values as a general Type B thermocouple.

Next, the manufacturing method of the thermocouple of this Embodiment is demonstrated.
First, the conductive ceramic 3 is prepared. For example, a large hole 33 having an inner diameter of 3 mm and a length of 10 mm is formed in the other end portion 3b of the cylindrical conductive ceramic 3 having a diameter of 8 mm and a length of 30 mm. Further, for example, a first small hole 31 and a second small hole 32 each having an inner diameter of 1 mm and a length of 10 mm are formed at the tip of the large hole 33. On the other hand, for example, a TypeR thermocouple sheath wire 100 having an outer diameter of 2 mm (wires are Pt wire and 13% Rh-Pt wire) is prepared, and the wire at the tip (first metal wire 1 and second metal wire) is prepared. 2) Each is exposed 5 mm. In addition, a platinum paste as an adhesive and a high temperature adhesive are prepared.

  The first metal wire 1 of the sheath wire 100 prepared earlier is poured with the other end portion 3b of the conductive ceramic 3 facing upward and poured into the first small hole 31 and the second small hole 32 to the extent that platinum paste does not overflow. And the 2nd metal wire 2 is inserted so that it may enter into the 1st small hole 31 and the 2nd small hole 32, respectively. After the first metal wire 1 and the second metal wire 2 are fixed with the platinum pastes 4 and 5, the gap between the large hole 33 and the sheath wire 100 is filled with heat-insulating refractory powder. Finally, the sheath wire 100 is fixed with the adhesive 7 at the other end 3 b of the conductive ceramic 3.

Then, the specific example of the manufacturing method of the conductive ceramic 3 is demonstrated.
First, the manufacturing method 1 of the conductive ceramic 3 will be described.

The average particle size, that is, the median value of particle size distribution measured by the laser diffraction / scattering method (d = 50) is 90.0% by mass of 2.1 μm of ZrB ₂ powder, and SiC powder of 10.0 μm in average particle size is 10.0 μm. After the mass% was mechanically mixed, 20 parts of an organic binder was added and heated and kneaded with a pressure kneader to prepare a uniformly dispersed compound. Thereafter, the compound was pelletized to form a molding material. This material was put into an injection molding machine, and the plasticized material was injected into a desired mold at a pressure of 50 to 100 MPa. Thereafter, after cooling and solidifying in the mold, the material was taken out to obtain a molded body. This molded body was put in an atmospheric degreasing furnace, and the organic binder was thermally decomposed. Thereafter, it was fired at 2300 ° C. in an Ar (argon) atmosphere in a graphite furnace and cooled to obtain a sintered body of conductive ceramics 3. The values obtained by measuring various physical properties of the sintered body were as follows. The bulk density was 5.37 g / cm ³ . The sintered density ratio was 96.6%. The thermal conductivity was 71.5 W / m · K. The volume resistivity value was 2.71 × 10 ⁻⁵ Ω · cm.

Further, the production method 2, will be described the case of adding B ₄ C powder as an antioxidant.

89.5% by mass of ZrB ₂ powder having an average particle size of 2.1 μm, 10.0% by mass of SiC powder having an average particle size of 0.7 μm, and 0.5% by mass of B ₄ C powder having an average particle size of 0.3 μm, After mechanical mixing, 20 parts of an organic binder was added and heated and kneaded with a pressure kneader to prepare a uniformly dispersed compound. Thereafter, the compound was pelletized to form a molding material. This material was put into an injection molding machine, and the plasticized material was injected into a desired mold at a pressure of 50 to 100 MPa. Thereafter, after cooling and solidifying in the mold, the material was taken out to obtain a molded body. This molded body was put in an atmospheric degreasing furnace, and the organic binder was thermally decomposed. Thereafter, it was fired at 2300 ° C. in an Ar atmosphere in a graphite furnace and cooled to obtain a sintered body of conductive ceramics 3. The values obtained by measuring various physical properties of the sintered body were as follows. The bulk density was 5.42 g / cm ³ . The sintered density ratio was 98.1%. The thermal conductivity was 72.1 W / m · K. The volume resistivity value was 2.84 × 10 ⁻⁵ Ω · cm.

Then, the manufacturing method 3 of the electroconductive ceramic 3 is demonstrated.
79.0% by mass of ZrB ₂ powder with an average particle size of 2.1 μm, 20.0% by mass of SiC powder with an average particle size of 0.7 μm, 1.0% by mass of B ₄ C powder with an average particle size of 0.3 μm, After mechanical mixing, 20 parts of an organic binder was added and heated and kneaded with a pressure kneader to prepare a uniformly dispersed compound. Thereafter, the compound was pelletized to form a molding material. This material was put into an injection molding machine, and the plasticized material was injected into a desired mold at a pressure of 50 to 100 MPa. Thereafter, after cooling and solidifying in the mold, the material was taken out to obtain a molded body. This molded body was put in an atmospheric degreasing furnace, and the organic binder was thermally decomposed. Thereafter, it was fired at 2300 ° C. in an Ar atmosphere in a graphite furnace and cooled to obtain a sintered body of conductive ceramics 3. The values obtained by measuring various physical properties of the sintered body were as follows. The bulk density was 4.975.42 g / cm ³ . The sintered density ratio was 98.3%. The thermal conductivity was 88.0 W / m · K. The volume resistivity value was 3.95 × 10 ⁻⁵ Ω · cm.

Moreover, the case where the compounding ratio is changed as the manufacturing method 4 is demonstrated.
ZrB ₂ powder 57.0% by mass with an average particle size of 2.1 μm, SiC powder 40.0% by mass with an average particle size 0.7 μm, B ₄ C powder 3.0% by mass with an average particle size of 0.3 μm, After mechanical mixing, 20 parts of an organic binder was added and heated and kneaded with a pressure kneader to prepare a uniformly dispersed compound. Thereafter, the compound was pelletized to form a molding material. This material was put into an injection molding machine, and the plasticized material was injected into a desired mold at a pressure of 50 to 100 MPa. Thereafter, after cooling and solidifying in the mold, the material was taken out to obtain a molded body. This molded body was put in an atmospheric degreasing furnace, and the organic binder was thermally decomposed. Thereafter, it was fired at 2300 ° C. in an Ar atmosphere in a graphite furnace and cooled to obtain a sintered body of conductive ceramics 3. The values obtained by measuring various physical properties of the sintered body were as follows. The bulk density was 4.22 g / cm ³ . The sintered density ratio was 98.7%. The thermal conductivity was 107.6 W / m · K. The volume resistivity value was 8.09 × 10 ⁻⁵ Ω · cm.

Then, the manufacturing method 5 of the electroconductive ceramic 3 is demonstrated.
94.0% by mass of ZrB ₂ powder having an average particle size of 2.1 μm, 5.0% by mass of SiC powder having an average particle size of 0.7 μm, and 1.0% by mass of B ₄ C powder having an average particle size of 0.3 μm After mechanical mixing, 20 parts of an organic binder was added and heated and kneaded with a pressure kneader to prepare a uniformly dispersed compound. Thereafter, the compound was pelletized to form a molding material. This material was put into an injection molding machine, and the plasticized material was injected into a desired mold at a pressure of 50 to 100 MPa. Then, it was taken out after cooling and solidifying in the mold, and a molded body was obtained. This molded body was put in an atmospheric degreasing furnace, and the organic binder was thermally decomposed. Thereafter, it was fired at 2300 ° C. in an Ar atmosphere in a graphite furnace and cooled to obtain a sintered body of conductive ceramics 3. The values obtained by measuring various physical properties of the sintered body were as follows. The bulk density was 5.61 g / cm ³ . The sintered density ratio was 97.8%. The thermal conductivity was 65.3 W / m · K. The volume resistivity value was 2.51 × 10 ⁻⁵ Ω · cm.

Then, the manufacturing method 6 of the electroconductive ceramic 3 is demonstrated.
20 parts of an organic binder was added to 100% by mass of ZrB ₂ powder having an average particle diameter of 2.1 μm, and the mixture was heated and kneaded with a pressure kneader to prepare a uniformly dispersed compound. Thereafter, the compound was pelletized to form a molding material. This material was put into an injection molding machine, and the plasticized material was injected into a desired mold at a pressure of 50 to 100 MPa. Thereafter, after cooling and solidifying in the mold, the material was taken out to obtain a molded body. This molded body was put in an atmospheric degreasing furnace, and the organic binder was thermally decomposed. Thereafter, it was fired at 2300 ° C. in an Ar atmosphere in a graphite furnace, and cooled to obtain a desired sintered body of conductive ceramics 3. The bulk density of the sintered body was 5.83 g / cm ³ . The sintered density ratio was 95.7%. The thermal conductivity was 58.8 W / m · K. The volume resistivity was 1.74 × 10 ⁻⁵ Ω · cm.

Similar to the above manufacturing method, ZrB ₂ and SiC components were changed to produce a sintered product.
The thermal conductivity at room temperature and the volume resistivity value of a sample having a sintered density ratio of 95% or more of the sintered product were measured and summarized in the order of the mixture ratio (mass%) of SiC of the fired product.

  Table 4 shows the relationship between the compounding ratio (mass%) of SiC and the volume resistivity (Ω · cm) at room temperature, and FIG. 3 is a graph showing the relationship.

  Table 5 shows the relationship between the compounding ratio (mass%) of SiC and the thermal conductivity (W / m · K) at room temperature, and FIG.

Next, the effect of this Embodiment is demonstrated.
According to the thermocouple of the present embodiment, since the conductive ceramics 3 electrically connects the first metal wire 1 and the second metal wire 2 and functions as a hot junction part, the hot junction is used as a measurement target. The temperature of the object to be measured can be accurately measured by contacting the conductive ceramics functioning as the part. Moreover, since the conductive ceramics 3 functioning as the hot contact portion are difficult to melt, measurement can be continuously performed in a high temperature range. Therefore, the temperature can be measured accurately and continuously in the high temperature range.

  Further, according to the thermocouple of the present embodiment, the first metal wire 1 and the second metal wire 2 are held by the conductive ceramics 3 in a non-contact state. Thereby, it can prevent that a component diffuses mutually because the 1st metal wire 1 and the 2nd metal wire 2 contact. For this reason, deterioration of the thermoelectromotive force can be prevented. Therefore, it is possible to prevent the occurrence of temperature measurement errors.

Further, according to the thermocouple of the present embodiment, the material of the conductive ceramic 3 preferably includes ZrB ₂ . Thereby, corrosion resistance with respect to a molten metal can be made high.

  Moreover, according to the thermocouple of the present embodiment, the material of the conductive ceramic 3 preferably includes SiC. Thereby, corrosion resistance can be made high with respect to oxidizing slag.

Moreover, according to the thermocouple of the present embodiment, it is preferable that the material of the conductive ceramic 3 has ZrB ₂ of 60% by mass to 95% by mass and SiC of 5% by mass to 40% by mass. Thereby, corrosion resistance can be effectively made high with respect to oxidizing slag.

  Moreover, according to the thermocouple of the present embodiment, the material of the conductive ceramic 3 preferably includes an antioxidant. Thereby, corrosion resistance can be further improved with respect to oxidizing slag.

Moreover, according to the thermocouple of the present embodiment, the antioxidant preferably contains B ₄ C. Thereby, corrosion resistance can be effectively improved with respect to oxidizing slag.

  Moreover, according to the thermocouple of the present embodiment, the conductive ceramic 3 has the holes 30 provided on the surface. The first metal wire 1 and the second metal wire 2 are held by the conductive ceramics 3 while being inserted into the holes 30. Thereby, the first metal wire 1 and the second metal wire 2 can be firmly held on the conductive ceramic 3. For this reason, it is possible to prevent the first metal wire 1 and the second metal wire 2 from being separated from the conductive ceramic 3. Therefore, it can measure stably and continuously.

(Embodiment 2)
In the second embodiment of the present invention, a case where the thermocouple of the first embodiment is applied to an actual furnace will be described.

  The thermocouple 10 of the first embodiment is embedded in the inner surface of the inner wall (furnace wall) of a molten metal, and a conductive wire having a small diameter (outer diameter of 1 to 3 mm) is connected to the thermocouple 10 to generate electromotive force. If it is guided and measured, accurate and continuous temperature measurement of the molten metal (and slag) becomes possible.

  The hot junction of the thermocouple 10 is a so-called “ground type”, and is not protected (shielded) from external electrical noise by a metal protective tube. Therefore, at the time of measuring the electromotive force, noises of various frequencies are simultaneously measured in the measured electromotive force. However, these noises can be shielded sufficiently by applying a low-pass filter built in the thermometer in advance or performing noise filter processing by frequency analysis using a fast Fourier transform (FFT) function. Therefore, it can be easily removed in real time, and does not become an obstacle during actual electromotive force measurement.

  In order to construct the thermocouple 10 in an actual furnace, a hot contact portion made of the conductive ceramics 3 is embedded in the inner surface (contact surface with the molten metal) of the furnace wall refractory, and the first connected to this is connected. The metal wire 1 and the second metal wire 2 lead the electromotive force to the outside of the furnace. Since the thermocouple 10 does not require a refractory protective tube, it does not need to protrude greatly into the molten metal from the furnace wall, and is very little damaged. Further, since the opening diameter of the furnace body necessary for the wiring of the first metal wire 1 and the second metal wire 2 is as small as several millimeters, there is a risk of leakage of molten metal outside the furnace body due to the installation of the thermocouple 10. You can think of it not.

  In addition, the conductive ceramic 3 has sufficient corrosion resistance against molten metal (and slag), and the ceramic itself will not wear out over time, but the surrounding refractory with the ceramic hot junction embedded will be refined many times. It is conceivable that it gradually melts and eventually the entire conductive ceramic 3 is exposed and dropped from the furnace wall and loses the temperature measuring function. In such a case, when it is predicted that the melting loss of the furnace body is large, the conductive ceramics 3 are disposed in advance in the furnace wall at different depths, and the refractory is gradually melted. If the thermocouples 10 are sequentially switched, temperature measurement continuity is maintained.

  Further, while the thermocouple 10 is in use, the surface of the conductive ceramic 3 is covered and insulated by solidification adhesion of the molten metal and slag, which are residues in the furnace, after the molten metal is discharged by tilting the furnace body. It is conceivable that the temperature of the conductive ceramic becomes lower than the temperature of the molten metal during the measurement. In this case, the true temperature of the molten metal cannot be measured by the thermocouple 10. In preparation for such a case, a coil is embedded in the back surface of the conductive ceramic 3 in advance, and when the coil is energized, an induced current is generated in the conductive ceramic 3 to generate heat, and the metal adhering to the conductive ceramic 3 (and It is also possible to redissolve and remove (slag) (cleaning function).

  As described above, in the thermocouple 10 of the present embodiment, the melting loss due to the molten metal (and slag) is suppressed. Further, since the metal (and slag) solidified and adhered to the surface can be easily removed, it can be used continuously for a long time, and the temperature of the molten metal (and slag) can be accurately measured.

  Then, the ladle provided with the thermocouple is demonstrated as an example at the time of applying a thermocouple to an actual furnace.

  Referring to FIG. 9, ladle 20 of the present embodiment includes thermocouple 10, iron skin 21, permanent brick 22, lining brick 23, slag line refractory 24, trunnion 25, nozzle 26, a slide gate 27, and a signal cable connector 28. In FIG. 9, a state in which the molten steel 51 and the slag 52 are stored in the ladle 20 is shown.

  The thermocouple 10 has a first thermocouple 11 and a second thermocouple 12. The first thermocouple 11 and the second thermocouple 12 are respectively provided on the inner peripheral surface of the wall portion of the ladle 20. Each of the first thermocouple 11 and the second thermocouple 12 is held on the wall so that one end 3a (see FIG. 1) is exposed from the inner peripheral surface. The 1st thermocouple 11 and the 2nd thermocouple 12 are arrange | positioned so that the one end part 3a may contact the molten steel 51 in the state in which the molten steel 51 was stored, respectively. The first thermocouple 11 is held at the upper portion of the wall portion, and the second thermocouple 12 is held at the lower portion of the wall portion.

  The ladle 20 is configured to be able to store molten steel. Permanent bricks 22 are arranged inside the iron skin 21. A lining brick 23 and a slag line refractory 24 are arranged inside the permanent brick 22. The slag line refractory 24 is disposed in contact with the upper and lower surfaces of the slag 52. That is, the slag line refractory 24 is disposed so as to contact the slag line.

  The trunnion 25 is provided so that the ladle 20 can be rotated. The nozzle 26 is provided so that the molten steel 51 can be discharged. The slide gate 27 is provided so that the molten steel 51 can be delivered to the nozzle 26 by sliding. The signal cable connector 28 is provided so as to be connectable to an instrument for deriving the electromotive force of the thermocouple to the instrument outside the furnace.

  The temperature measuring point is directly below the slag line in the ladle and on the side of the casting nozzle at the bottom of the ladle. By measuring the temperature at these two points at the same time, judgment of uniform mixing during ladle refining (presence or absence of temperature segregation in molten steel), measurement of molten steel temperature drop during casting, accumulated heat of refractory during hot pot heating, hot pot heating Can be measured.

The thermocouple of the present invention can be applied to the following application examples, for example.
Iron and steel and non-ferrous metals include coke ovens, hot blast furnaces, blast furnace furnace bodies, blast furnace tuyere, tapping, torpedo car, hot metal ladle, kneading furnace, dephosphorization furnace, converter, electric furnace, ladle, secondary smelting furnace ( LF, RH, DH), tundish for continuous casting, heating furnace, annealing furnace, etc., the thermocouple of the present invention can be applied.

  As a result of the fact that the temperature of the molten metal can be easily measured by the thermocouple of the present invention, by performing simultaneous continuous temperature measurement at a plurality of sites in the molten metal container, the molten metal container in the molten metal container being refined and transported Real-time determination of temperature segregation (non-uniformity) is possible. Furthermore, indirect estimation of component segregation (non-uniformity) is also possible. As a result, the progress determination of the refining, the end point determination, the determination as to whether the stirring and heating are necessary are ensured by the operator, and as a result, there is a great effect in improving the efficiency in the refining process, saving energy, and improving the steel quality.

  Further, as the waste melting furnace and gasification furnace, the thermocouple of the present invention can be applied to a general waste melting furnace, a nuclear waste melting furnace, and the like.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be applied particularly advantageously to a thermocouple provided with a hot junction portion electrically connected to the first metal wire and the second metal wire.

  DESCRIPTION OF SYMBOLS 1 1st metal wire, 2nd metal wire, 3 electroconductive ceramics, 4,5 platinum paste, 6 refractory powder, 7 adhesives, 10 thermocouple, 11 1st thermocouple, 12 2nd thermoelectric Pair, 20 Ladle, 21 Iron skin, 22 Permanent brick, 23 Lined brick, 24 Slag line refractory, 25 Trunnion, 26 Nozzle, 27 Slide gate, 28 Signal cable connector, 30 holes, 31 First small hole, 32 Second small hole, 33 large hole, 51 molten steel, 52 slug, 100 sheath wire.

Claims (8)

A first metal wire;
A second metal wire made of a material different from the first metal wire;
A thermocouple comprising electrically conductive ceramics that electrically connect the first metal wire and the second metal wire and function as a hot junction part.   The thermocouple according to claim 1, wherein the first metal wire and the second metal wire are held by the conductive ceramics in a non-contact state. The thermocouple according to claim 1, wherein the material of the conductive ceramic includes ZrB ₂ .   The thermocouple according to claim 3, wherein the material of the conductive ceramic includes SiC. The conductive ceramic material is:
Having ZrB ₂ in an amount of 60% by mass to 95% by mass,
The thermocouple of Claim 4 which has the said SiC 5 mass% or more and 40 mass% or less.   The thermocouple according to claim 5, wherein the material of the conductive ceramic includes an antioxidant. The thermocouple according to claim 6, wherein the antioxidant includes B ₄ C. The conductive ceramic has a hole provided on the surface,
The thermocouple according to claim 1, wherein the first metal wire and the second metal wire are held by the conductive ceramic in a state of being inserted into the hole.

Images