WO1996017230A1 - Thermometre a thermocouple et procede de fabrication de corps frittes pour ledit thermometre - Google Patents

Thermometre a thermocouple et procede de fabrication de corps frittes pour ledit thermometre Download PDF

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Publication number
WO1996017230A1
WO1996017230A1 PCT/JP1995/002411 JP9502411W WO9617230A1 WO 1996017230 A1 WO1996017230 A1 WO 1996017230A1 JP 9502411 W JP9502411 W JP 9502411W WO 9617230 A1 WO9617230 A1 WO 9617230A1
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WIPO (PCT)
Prior art keywords
thermocouple
temperature
temperature measuring
alumina
sintered body
Prior art date
Application number
PCT/JP1995/002411
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English (en)
Japanese (ja)
Inventor
Masanobu Ichinose
Masaaki Takeshita
Yukimi Ogawa
Sumihiko Kurita
Original Assignee
Kabushiki Kaisha Kouransha
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP7038966A external-priority patent/JPH08208319A/ja
Priority claimed from JP29221195A external-priority patent/JPH09113372A/ja
Application filed by Kabushiki Kaisha Kouransha filed Critical Kabushiki Kaisha Kouransha
Publication of WO1996017230A1 publication Critical patent/WO1996017230A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
    • G01K1/02—Means for indicating or recording specially adapted for thermometers
    • G01K1/026—Means for indicating or recording specially adapted for thermometers arrangements for monitoring a plurality of temperatures, e.g. by multiplexing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
    • G01K1/08—Protective devices, e.g. casings
    • G01K1/10—Protective devices, e.g. casings for preventing chemical attack
    • G01K1/105—Protective devices, e.g. casings for preventing chemical attack for siderurgical use

Definitions

  • the present invention relates to a thermocouple temperature measuring element in which a thermocouple and an insulative ceramic protection tube are integrated, a sintered body for the insulating ceramic protection tube, and a method for manufacturing the same.
  • One or more thermocouples with one or more thermocouple elements integrated into a protective tube that has two or more holes and also functions as an insulating tube The structure of the thermocouple element, the structure of the thermocouple element incorporating this element in the external protective tube, and the high temperature creep resistance in the operating temperature range of 160 ° C or lower.
  • the present invention relates to an excellent sintered ceramic protective tube and a method for producing the same. Background art
  • thermocouples of thermocouple thermometers are thermocouples that detect temperature by the difference of thermoelectromotive force and insulators that electrically insulate the wires of the thermocouple. It consists of a protective tube.
  • Thermocouples include insulated thermocouples that have been previously insulated with a teflon-based glass braid, etc., but this is generally limited to measuring temperatures in the low-temperature range of 500 ° C or lower, and measuring in the high-temperature range.
  • the temperature is controlled by passing a bare thermocouple through a two-hole magnetic insulating tube and inserting the same into the above-mentioned protective tube.
  • thermocouple materials are classified into precious metal materials using platinum rhodium and base metal materials using other metals or alloys.
  • the base metal materials are inferior in heat resistance.
  • Precious metal thermocouples are mainly used for high temperature measurement. When this noble metal thermocouple is exposed to the environment of reducing gas, metallic gas and impurities, the thermoelectromotive force decreases and the temperature error increases. For example, when a platinum wire is in contact with a refractory containing Si force at a high temperature, if C 0 gas is present, the Si force will be reduced and silicon will be absorbed by the platinum, resulting in a very brittle alloy and breaking. is there.
  • thermocouple In addition, most metals, such as copper, iron, lead, zinc, cadmium, aluminum, and tin, are made of low melting point alloys or compounds. The temperature cannot be measured due to deterioration or melting due to melting point drop or brittle crack.
  • a protection tube is used to protect the thermocouple and prevent deterioration due to the adhesion of impurities and exposure to contaminant gases.However, when measuring temperature, especially high temperature measurement is performed in a severely polluted environment. Often, contaminants also enter the small gap between the protective tube and the isolation tube, affecting the heat-sensitive part of the thermocouple and the joint of the insulating tube.
  • thermocouples are inserted into insulating tubes in a clean room with gloves so that they cannot be touched with hands.
  • this insertion work does not require much work if the strand is unused, but once used, it often causes deformation distortion and surface roughness, and this is inserted into a long hole in the insulating tube. It is an extremely difficult and tedious task to go through.
  • thermometer From the viewpoint of the performance as a thermometer, it is important to have excellent temperature responsiveness in addition to temperature accuracy.
  • a protective tube There is a protective tube, a gap, and an insulation tube between the temperature measurement target and the thermosensitive part of the thermocouple, through which heat is transferred.
  • the response speed is faster for the platform.
  • conventional thermometers have not been made very thin.
  • the outer diameter of the thinnest tube is two holes with a diameter of about 3 mm.Even if the wall thickness of the protective tube is 1 mm and the air gap is 0.5 mm, the outer diameter of the protective tube (S Is 0.6 mm.
  • One hole has an outer diameter of up to about ⁇ 1 mm. If one thermocouple wire is inserted into this hole and the other is not inserted, a thermometer with an outer diameter of ⁇ 3 mm can be made. The strength is weak, and the long-term measurement at high temperature makes the degradation of the thermocouple wire much faster than that with two wires, and the long one is difficult to manufacture and the manufacturing cost is high.
  • thermocouple in which a thermocouple, an insulator, and a protective tube have an integral structure.
  • magnesium oxide powder is mainly used for the insulator, and a heat-resistant metal such as stainless steel or Inconel is used for the sheath corresponding to the protective tube, and can be bent and stretched. Therefore, the risk of breakage is small and the airtightness is good, so there is no contamination from outside and the handling is simple. Very small size and very long size can be obtained, and the price is low.
  • the operating temperature is up to about 100,000 During the measurement, the thermocouple may be contaminated by the outer metal.
  • the temperature can be measured simply by using an oxide protective tube.
  • the protective tube has corrosion resistance and heat resistance. Materials with excellent properties such as impact resistance and leak resistance are required. That is, they are often made of high corrosion resistant non-oxide ceramics such as boron nitride and aluminum nitride, and carbon-containing refractories such as molybdenum and zirconium cermets and alumina graphite. Generates reducing gas, metal vapor, glass, etc. at high temperatures and contaminates and degrades thermocouples.
  • the oxide protective tube (mainly aluminum ceramix) is protected with a thermocouple and an insulating tube and a material excellent in the above characteristics.
  • a thermocouple and an insulating tube and a material excellent in the above characteristics Must be used as an internal protective tube between the tube. Therefore, two or more protective tube sections and an air layer between them exist between the thermocouple junction and the object to be measured, and steep response cannot be obtained.
  • the size increase due to the multi-layer structure and breakage of the protection tube due to the difference in thermal expansion between the protection tubes are likely to occur.
  • the conventional temperature measurement method generally involves inserting a thermocouple through a two-hole insulating tube into a large-diameter size protective tube and inserting it into each of the measuring points, or by using only the number of measuring points individually. This is performed using a thermometer.
  • the former there are many problems in terms of both temperature accuracy and responsiveness due to the influence of the heat flow in the air layer inside the large-diameter size protection tube. That is, when the temperature outside the protection tube changes, it takes a considerable time for the low heat conduction air layer inside the protection tube to reach a new steady state of heat flow by heat transfer. In the latter case, the overall size increases.
  • Ceramic materials are often used as materials for protective tubes for high-temperature measurement because they require high heat resistance and high corrosion resistance.
  • Typical materials include oxide ceramics such as alumina, zirconia and mullite, and non-oxide ceramics such as silicon nitride and silicon carbide.
  • oxide ceramics has the advantage that manufacturing costs are lower than non-oxide ceramics because sintering can be performed in the atmosphere with relatively low raw material costs.
  • Alumina ceramics in particular have excellent chemical stability and a high melting point of 250. Is an important material in the field where is required.
  • alumina ceramics which is superior in heat resistance and corrosion resistance, has defects inferior in high-temperature creep resistance because it is an oxide ceramic.
  • Creep is a phenomenon in which when a material is exposed to a high temperature, the material is plastically deformed by an external force at a temperature lower than the melting point of the material.
  • polycrystalline alumina ceramics is exposed to a high temperature of 1200 or more, grain boundary sliding tends to occur between alumina crystal grains.
  • this phenomenon occurs, deformation of the product, cracking and the resulting decrease in material strength and airtightness occur, making it difficult to use as a high-temperature member.
  • high temperature creep resistance at the operating temperature is required for components of high temperature measuring elements.
  • each atom constituting oxide ceramics such as alumina has a mixture of ion coupling and covalent bonds
  • non-oxide ceramics such as silicon carbide consist of covalent bonds.
  • covalent bonds have a stronger bond strength than ionic bonds. Therefore, at a high temperature of 1200 ° C. or higher, oxide ceramics having ionic bonds have a reduced bond strength between atoms and are liable to undergo plastic deformation.
  • non-oxide ceramics have a property that plastic deformation is unlikely to occur even at a high temperature of 1200 C or higher due to covalent bonds.
  • non-oxide ceramics require oxidation at a high temperature of more than 1300 ° C, high raw material costs, and a special firing furnace in a non-oxidizing atmosphere during the sintering process.
  • problems such as poor workability of the sintered body, and as a result, the product cost is high.
  • oxide ceramics that are inexpensive in product cost.
  • Aluminum oxide ceramics which have abundant raw materials among oxide ceramics and have excellent chemical stability, have low cost and high temperature characteristics if improved high temperature creep resistance is improved. Excellent material.
  • Japanese Patent Application Laid-Open No. 5-14813 discloses that the average crystal grain size of a sintered body is 99.8% by weight of alumina.
  • a description is given of an alumina ceramic and a method for producing the same, in which the sintering temperature is set to 2 or more and the sintering temperature is set to 1500 ° C. or more.
  • the grain boundary slip of the alumina crystal particles is prevented by setting the crystal grain size of the alumina sintered body to 2 m or more.
  • the sintering is performed at a high temperature of 150 ° C. or higher to increase the size of the alumina crystal grains.
  • the sintering temperature is set to a high temperature range from 150 to 170 to increase the size of the alumina ceramic crystal particles within a range where the mechanical strength does not decrease.
  • Sintering step c generally Serra mix to produce crystal particles of naturally alumina The higher sintering temperatures the grain growth, sintering costs, the higher the sintering temperature is high.
  • the operating temperature of the furnace taking the production cost into account is less than 1500 ° C, preferably less than 140 ° C.
  • thermocouple type thermometer protection tubes which are a type of thermometer used at high temperatures
  • an alumina sintered body having excellent high-temperature creep resistance at high temperatures, practically up to 160 ° C., is required.
  • alumina ceramics that can be sintered at low temperatures are inexpensive to manufacture, and have excellent high-temperature creep resistance at temperatures higher than the sintering temperature have not yet been developed.
  • the conventional temperature measuring element has no problem in the low-temperature range, but in the high-temperature range above 100 ° C, the thermocouple deteriorates mainly due to pollutants, and handling is troublesome. The cause is easy to occur. In terms of performance and size, thinner and longer ones are required.
  • thermocouple, insulator and protective tube are integrated like a sheath thermocouple, and there is a need for a high-temperature integrated temperature measuring element at a working temperature of 100 ° C or more. .
  • a sheath-ripened electric body with a ceramic sheath there is a need for a puncture element having a structure that can minimize the number of layers.
  • a compact, multi-point temperature measuring element with excellent temperature accuracy and responsiveness. Disclosure of the invention
  • the present invention has been made in view of such circumstances, and its object is to simplify handling, to have excellent temperature responsiveness, to improve the durability of a thermocouple, and to improve molten metal.
  • thermocouple 1.
  • thermocouple can be solved by the thermocouple temperature measuring element as described in 1 above, wherein a gap is provided between the thermocouple and the insulating ceramic protective tube at the temperature measuring contact section. .
  • thermocouple measurement characterized by having a multipoint temperature measurement structure in which two or more thermocouple temperature measurement elements according to 1 or 2 above are sintered and integrated at different positions of the respective stab contacts. This can be solved by a heating element.
  • thermocouple temperature measuring element characterized by having a temperature structure.
  • An insulative ceramic protection tube having three or more holes, and two or more different types of metal wires are placed in different positions on one metal wire while extending through each of the holes.
  • a multi-point thermocouple branch thermocouple that forms two or more temperature measuring junctions, and that the temperature measuring contact side of the insulating ceramic protective tube is closed. The problem can be solved by the characteristic thermocouple temperature measuring element.
  • thermocouple temperature measuring element described in 1 or 2 or 3 or 4 or 5 above has a structure including the thermocouple temperature measuring element inside and an external protective tube that cuts off from the outside by incorporating the thermocouple temperature measuring element inside. Can be solved by a thermocouple temperature measuring element.
  • thermocouple thermometer according to the item 6, wherein the material of the outer protective tube is a non-oxide ceramic, a carbon-containing refractory, a cermet, and a metal. Can be solved.
  • the above-mentioned insulating ceramic protection tube is made of an alumina sintered body containing aluminum oxide of 99.5% or more and a sintering aid as essential components, and the crystal structure of the sintered body is (1), (2), (3), (4), (5), (6) and (7), characterized by being an alumina sintered body mainly composed of a mixed structure of coarse grains having a crystal grain size of 5 m or more and fine grains of 3 m or less.
  • the problem can be solved by the thermocouple temperature element described in (1).
  • a starting material of the alumina component of the alumina sintered body composed of a substantial alumina component and a sintering aid a fine aluminum oxide powder having an average particle size of 1 m or less and a coarse aluminum oxide powder having an average particle size of 3 m or more are used.
  • the raw material is molded, and the crystal grain size is 5 m mainly based on the crystal structure after firing.
  • Figure 1 is a structural diagram of a temperature measuring element with a thermocouple and a protection tube integrated with a structure in which a temperature measuring contact is embedded in a ceramic matrix.
  • Fig. 2 is a structural diagram of a temperature measuring element in which a thermocouple and a protective tube are integrated with a structure in which a gap is provided between the temperature measuring contact and the substrate by a partition lid.
  • FIG. 4 is a structural diagram of a temperature measuring element in which a thermocouple and a protective tube are integrated with a structure in which a gap is provided by using a thermocouple.
  • Fig. 4 shows the structure of a thermometer with a thermocouple and a protection tube integrated with a structure in which a gap is provided by hollowing one end of a green body of a two-hole pipe and sealing it by pressing from the outside.
  • FIG. 4 shows the structure of a thermometer with a thermocouple and a protection tube integrated with a structure in which a gap is provided by hollowing one end of a green body of a two-hole pipe and sealing it by pressing from the outside.
  • FIG. 5 is a structural diagram of a multi-point temperature measuring element in which two or more one-point temperature measuring elements are sintered and integrated at different positions of respective temperature measuring contacts.
  • Fig. 6 shows a multipoint thermometer in which two or more thermocouples are installed in different positions of each thermocouple in an insulative ceramic protective tube with four or more even holes.
  • FIG. 3 is a structural view of a multipoint temperature measuring element incorporating a branch thermocouple connected in a different manner.
  • FIG. 8 is a structural diagram of a conventional multipoint temperature measuring method in which a plurality of thermocouples passed through an insulating tube are inserted into a protective tube.
  • FIG. 9 is a structural diagram of a temperature measuring element in which a thermocouple and a protection tube for immersing a molten metal are combined with a thermocouple and a protection tube as one body.
  • Figure 1 shows the structure of a temperature measuring element in which a thermocouple and a protection tube are integrated with a structure in which a temperature measuring contact is embedded in a ceramic matrix.
  • the two wires of the thermocouple 4 extend through the two holes, and the thermocouple junction 6 of the thermocouple is in the substrate on which one end of the two-hole insulating ceramic protective tube 1 is sealed. And is protected from external contaminants and reducing atmospheres.
  • thermocouple junction part of the thermocouple is embedded in the substrate, and there are some forces ⁇ with and without a gap between the thermocouple and the substrate.
  • FIG. 2 is a structural diagram of a temperature measuring element in which a thermocouple and a protection tube are integrated with a structure in which a gap is provided between a temperature measuring contact and a substrate by a partition lid.
  • FIG. 3 is a structural diagram of a temperature measuring element in which a thermocouple and a protection tube are integrated with a structure in which a gap is provided by using an aging and disappearing coating. This is done by previously applying a heat-dissipating material S to the temperature measuring junction of the thermocouple wire and burying it in the ceramic substrate.
  • Providing an air gap means that two holes are connected by an air gap, and the thermocouple wire passes through the connection hole without being fixed to the ceramic body. Since the position of the temperature measuring contact is shifted from the position of the distal end of the protective tube and a temperature measuring error is easily caused, it is preferable to make the temperature measuring contact as small as possible. In the case of Fig. 3, there is no worry about the displacement of the measuring junction because the measuring junction is almost immovable due to the formation of a thin L and a gap along the shape of the measuring junction.
  • the position of the temperature measuring junction must be near the tip of the protection tube from the viewpoint of temperature measurement accuracy as described above, but from the viewpoint of responsiveness, the thickness between the temperature measurement contact and the tip of the protection tube should be as thin as possible. Good to control. This is preferably about 1 to 4 mm depending on the material of the cellar and the purpose of use, and more than this is not preferable from the viewpoint of thermal shock resistance.
  • Figure 4 shows the structure of a thermometer with a thermocouple and a protective tube integrated with a structure in which a gap is provided by boring one end of a green body of a two-hole pipe and sealing it by pressing from the outside. FIG. This is excellent in responsiveness because it is relatively easy to manufacture and the thickness of the tip can be reduced.
  • FIG. 5 is a structural diagram of a multi-point temperature measuring element in which two or more single-point temperature measuring elements 13 are sintered and integrated at different positions of the respective temperature measuring contacts (6, 7, 8).
  • Fig. 6 shows two or more thermocouples 4 in an insulative ceramic protective tube 2 with four or more even holes, with the position of each temperature measuring junction (6.7.8) being changed.
  • FIG. 2 is a structural diagram of a multipoint temperature measuring element built therein.
  • Fig. 7 shows a multi-unit thermocouple with built-in branch thermocouples 5 that are connected at different positions of the temperature measuring contacts (6.7, 8) in an insulative ceramic protection tube 3 having three or more holes.
  • FIG. 3 is a structural diagram of a dot piercing element.
  • FIG. 8 is a structural diagram of a conventional multipoint temperature measuring method in which a plurality of thermocouples 4 passed through an insulation tube 14 are inserted into a protection tube 15.
  • the heat transfer from the external atmosphere 19 of the protection tube to be measured to the temperature measuring junction (6, 7.8), which is the heat-sensitive part depends on the external atmosphere.
  • Heat transfer between 19 and the outer surface of the protection tube 16, heat conduction at the pipe wall 18 of the protection tube 15, inner surface 17 of the protection tube and the air layer 10, and the air layer 10 The heat transfer between the insulation tube 14 and the heat conduction inside the insulation tube, that is, the complicated path of the so-called multi-layered tube heat transfer.
  • the response is poor and the accuracy of temperature measurement is also poor. That is, in FIG. 8, since the temperature measuring contacts 7 and 8 are affected by the air convection generated in the gap 10, the steady state of the heat flow is reached after the temperature of the puncture target (external atmosphere) changes. Before you do Takes time.
  • the heat transfer of the multipoint temperature measuring element of the present invention shown in FIGS. 5, 6, and 7 is based on the heat transfer between the external atmosphere and the outer peripheral surface of the protection tube and the pipe wall portion of the protection tube. This is a single-layer tube heat transfer that is directly transmitted to the temperature measuring junction by heat conduction at the point.
  • the responsiveness is good, and there is no air convection portion which occurs in the above-mentioned gap portion 10, so that the accuracy is good.
  • the responsiveness is further improved because the size can be reduced compared to the conventional method.
  • it is easy to handle because of its integral structure.
  • FIG. 9 is a structural diagram of a temperature measuring element in which a thermometer and a protection tube integrated with a thermocouple and a protection tube for immersion of molten gold are combined.
  • the two strands of thermocouple 4 extend through the two holes of the two-hole insulating ceramic protection tube 1, and the thermocouple junction 6 of the thermocouple has the two-hole insulating ceramic. It is completely enclosed inside protection tube 1 and is protected from external contaminants and reducing atmospheres.
  • a protective tube 20 for immersion of molten metal having erosion resistance and thermal shock resistance to molten steel is provided on the outside thereof.
  • the terminal box 21 is connected to this to form a temperature measuring element.
  • thermocouple When the above temperature measuring element is immersed in molten steel, heat transfer between the molten steel and the surface of the molten metal immersion protection tube 20, the molten metal immersion protection tube 20 and the gap 11, and a two-hole insulating ceramic Due to the heat conduction between the mix protective tubes 1, heat is transferred from the molten steel to be measured to the temperature measuring junction 6 of the thermocouple. At that time, reducing gas, glass, metal vapor, etc., which contaminate and degrade the thermocouple, are generated from the molten metal immersion protection tube.
  • thermocouple is completely sealed in the insulative ceramic protection tube, so the protection for molten metal immersion does not require an oxide ceramic protection tube.
  • the temperature measuring elements of the means 1 to 5 can be directly inserted into the inside of the tube 20 for use. Therefore, a sharp response can be obtained as compared with the conventional multilayer structure piercing method.
  • the material of the above-mentioned insulating ceramic protection tube basically any ceramic can be used as long as it does not deteriorate the thermocouple and has excellent insulation at high temperatures.
  • an oxide such as alumina or magnesium is suitable, and can be appropriately changed according to the purpose of use.
  • the creep characteristics of the sintered body of the insulating ceramic protection tube are very important.
  • the alumina sintered body most suitable as the material of the insulating ceramic protection tube particularly provided in the present invention is much superior in the high-temperature cleaving property to the conventional alumina sintered body.
  • the purity of the alumina sintered body having the heat resistance, corrosion resistance, and electrical insulation required for a thermocouple protection tube at an operating temperature of up to 160 ° C is required to be 99.5% or more.
  • the alumina sintered body of the present invention requires a sintering aid.
  • a typical example of the sintering aid is an alkaline earth metal oxide. Magnesium oxide, calcium oxide, barium oxide, and strontium oxide are used alone or in combination of two or more types of alumina sintered bodies. It is added so as to contain 0.5% by weight or less.
  • a sintering aid such as an alkaline earth metal oxide
  • crystal growth does not proceed very much at a protection tube operating temperature of about 140 ° C or lower, but the operating temperature is 1450 ° C. From around C, the grain growth proceeds and the material strength decreases.
  • a composition without the addition of a sintering aid when the operating temperature is higher than the sintering temperature, for example, when the sintering temperature is 140 ° C and the operating temperature is 160 ° C, The growth proceeds rapidly, and the value of the flexural strength after sintering of 300 MPa or more decreases to 200 MPa or less. Therefore, the addition of sintering aids such as alkaline earth metal oxides is indispensable.
  • an auxiliary agent such as an alkaline earth metal oxide is added externally to alumina so as to be 0.5% by weight or less in terms of oxide relative to the alumina raw material.
  • Addition of a sintering additive exceeding the above range is not preferable because the heat resistance and corrosion resistance are reduced because the purity of alumina itself is reduced.
  • These sintering aids can be used as long as they do not adversely affect the characteristics of the alumina sintered body.
  • magnesium oxide, calcium oxide, and sulfur oxide Alkaline earth metal oxides such as trontium and barium oxide are preferred.
  • the grain size of alumina constituting the alumina sintered body is important.
  • the sintered body mainly consists of coarse crystal grains of 5 m or more and fine crystal grains of 3 m or less.
  • An object of the present invention is to lower the production cost by lowering the sintering temperature and obtain an alumina sintered body having excellent heat resistance, corrosion resistance, and high-temperature creep resistance.
  • a low-temperature sinterable alumina sintered body is formed by molding a fine raw material powder having an average particle diameter of 1 m or less, especially 0. Sinter below ° C.
  • Such a low-temperature sinterable alumina sintered body is characterized by an extremely small alumina crystal particle diameter of 3 or less.
  • thermocouple protection tubes that require high-temperature cleaving resistance, plastic deformation at high temperatures is a fatal problem.
  • plastic deformation due to grain boundary sliding of alumina occurs at a high temperature in a low temperature range of about 1400.
  • the alumina sintered body can be heated to 140 ° C or more. It is not suitable for thermocouple protection tube because it causes remarkable plastic deformation at the operating temperature and lowers the strength.
  • low-temperature sintering at 150 ° C. or less preferably 140 ° C. or less
  • heat resistance, corrosion resistance, and high-temperature creep resistance at 160 ° C. or less In order to increase the crystallinity, it is necessary to mix two types of coarse and fine crystal grains constituting the alumina sintered body.
  • an average particle diameter of 1 m or less which is excellent in low-temperature sinterability, and preferably an average particle diameter of 3 m or less for a fine alumina raw material having an average particle diameter of 0.5 m or less.
  • the raw material is added at 2 to 20% by weight of a coarse alumina raw material having a particle size of 1 ⁇ m or more and sintered at a temperature lower than 1500 ° C., preferably at a temperature lower than 140 ° C. It is desirable that the coarse particle material used has an average particle size of 3 m or more. With raw materials having an average particle size of less than this, it is difficult to grow coarse crystal particles of 5 m or more after sintering.
  • C Fine alumina raw materials should have as small an average particle size as possible.
  • Raw materials capable of sintering to a water absorption of 0.1% or less at a temperature of less than 1500 ° C when sintered alone can be used as appropriate.
  • the average particle size of this fine raw material is approximately 1 m or less, Or less than 0.5 m.
  • the purity of both coarse and fine raw materials should be as high as 99.5% or higher, since the higher the purity, the higher the heat resistance and corrosion resistance.
  • the higher the mixing ratio of the coarse particles the better the higher the high-temperature cleaving resistance.
  • the distribution ratio of the coarse particles is too high, sintering at less than 1500 ° C, especially at 140 ° C or less, becomes difficult, and the water absorption becomes 0.5% or less. The required airtightness cannot be maintained.
  • the sintering temperature at which the water absorption rate can be reduced to 0.1% or less is required to be 150 ° C. or more, which significantly increases the production cost.
  • the mixing ratio of the coarse alumina particles to the fine alumina particles is preferably in the range of 2 to 20% by weight in order to enable sintering at less than 150 ° C. It is.
  • the blending ratio of the coarse alumina raw material is less than 2% by weight, the number of coarse alumina crystal particles in the sintered aluminum sintered body is small, and the Grain boundary sliding cannot be prevented.
  • a predetermined coarse alumina raw material is blended with the above-mentioned fine alumina raw material, and further, for example, an alumina earth metal oxide is sintered as an alumina sintering aid.
  • the normal ceramic molding process such as rubber pressing, slip casting, injection molding, extrusion method, etc.
  • the molding method described above it is formed into the desired thermocouple protection tube shape.
  • the slip casting method the end face of the protective tube can be easily sealed in a plaster-shaped shape.
  • the extrusion molding after the extrusion, it may be sealed with the extruded clay.
  • the sintering aid to be added to the alumina raw material only needs to be in the form of an oxide after sintering. Therefore, in the case of magnesium oxide, magnesium carbonate, magnesium hydroxide, or the like can be used as appropriate.
  • sintering is performed through raw processing, degreasing, and degreasing as necessary.
  • an electric furnace or a gas furnace which is usually used for sintering ceramics, can be used.
  • the heating rate is less than 300 hours and less than 150 hours.
  • thermocouple protection tube An alumina sintered body for thermocouple protection tube is obtained.
  • the heat resistance and corrosion resistance of the alumina sintered body of the present invention were evaluated by exposing a protective tube made of the alumina sintered body manufactured according to the intended application to an environment where the temperature was 140 ° C or more. This is done by checking for the occurrence of corrosion.
  • the high-temperature creep resistance was measured when an alumina sintered body with a protective tube or a shape close to the protective tube was prepared and subjected to an exposure test at 160 ° C for 5 hours. Judgment is made from the degree of self-weight deformation of the protection tube or a shape close to the protection tube.
  • insert the test resistance into the refractory protrude at least 120 mm from the end of the refractory, install the refractory in the furnace, and raise it at a rate of 100 ° C / hour or more. Raise the temperature to 160 ° C at a heating rate, hold at the same temperature for 5 hours, and cool the furnace.
  • the self-weight deformation degree means that 1 5 mm or less value, if practical problem becomes c 1 5 mm or more does not cause the plastic deformation of the product by grain boundary sliding is large, deformation of the tensile stress of the product is loaded
  • the cracked portion that is, the portion extended by the grain boundary sliding, causes fine cracks between the crystal grains, resulting in a decrease in the airtightness and strength of the protective tube.
  • the problem of difficulty in pulling out the protective tube from the refractory due to deformation arises.
  • the alumina sintered body of the present invention has heat resistance, corrosion resistance, high temperature creep resistance and low cost in a temperature range up to 160 mm. It is the most suitable sintered body for thermoelectric protection tube requiring high heat resistance.
  • the crystal grain size of the alumina sintered body of the present invention is an important factor that affects the high-temperature creep resistance.
  • the alumina sintered body in the shape of a protective tube is cut, polished, flat-polished, polished and the surface of the sintered body is mirror-finished, and subjected to thermal corrosion at a sintering temperature or lower.
  • this sample was observed with an electron microscope, if the area ratio of coarse particles of 5 m or more was 20% or more and the fine particles of 3 m or less occupied 80% or less, heat resistance, corrosion resistance, It can be used as a thermocouple protection tube with excellent high-temperature resistance.
  • the visual field of this microscopic observation should be such that at least 20 or more coarse and fine particles are present in a mixed state.
  • the maximum diameter of each particle is defined as crystal ⁇ .
  • the area occupied by each crystal is calculated using an image analyzer or assuming a circle with the largest diameter as the diameter for each particle.
  • the crystal grain size and the area occupied by the crystal are determined for five different visual fields and the average value is adopted.
  • a sample in which an R type thermoelectric element having an outer diameter of 0.4 mm, a hole diameter of ⁇ 1 mm, and a protective tube length of 50 Omm was prepared. This was used for the sintering of molten steel in a steelmaking dinner dish that is currently being carried out.
  • the integrated heating element was inserted into an external protective tube (protective tube for ALN-based molten steel) set on the side wall of the evening dish, and the temperature of the molten steel was continuously measured.
  • the temperature measurement time was set to 8 hours in a row, and the same device was repeatedly used 10 times (80 hours).
  • thermocouple was disconnected or reached 10 times (80 hours), replacing only the base where the thermowell was damaged or the damaged thermowell.
  • the multi-point temperature measuring elements of the means 3.4 and 5 a sample was prepared in the following manner.
  • CThe above three types of multi-point temperature measuring elements have different manufacturing methods.
  • a pair of thermocouples are inserted into the two-hole pipe-shaped ceramic green body, the end faces are sealed, and the green body of the single-point temperature measuring element is formed. create.
  • the raw green bodies having different lengths are immersed in water to make the surface water-absorbing, and then the temperature measuring contact is set at a predetermined position and the whole is overlaid. Finally, it is sintered and integrated.
  • thermocouple 6 two holes are formed as one set from one end face of a pipe-shaped ceramic raw element having an even number of holes of 4 or more, so that a thermocouple can be inserted. Drill the hole to the required temperature measuring contact position.
  • thermocouple is inserted and sealed at the end face to make a bundle of multi-point temperature measuring elements, which is put into a protective tube, a slurry is poured into the gap, and sintered and integrated. It is not preferable because the size increases and the manufacturing cost increases.
  • Fig. 7 two or more different types of metal wires are connected to one metal wire at different positions to form two or more temperature measuring junctions.
  • thermocouple wire Into a bundle of one-hole pipe-shaped ceramic green body cut to the required length up to the required length, apply heat-dissipative coating to the exposed portion of the thermocouple wire, put it in a protective tube, and put it in a slurry. One is poured into the gap and sintered and integrated.
  • this method has the disadvantage of increasing the size, one of the two thermocouple strands is shared by one strand, so the overall length of the strand is short, and the longer the number of temperature measuring contacts, the longer the length. The smaller the length, the more advantageous in terms of cost.
  • the samples of the multipoint temperature measuring element shown in Figs. 5, 6, and 7 were manufactured by the above method, and the comparison with the conventional method shown in Fig. 8 was attempted.
  • the test method is as follows: pre-heat the above sample to 100 ° C, quickly insert it into a semiconductor high-temperature diffusion furnace maintained at around 100 ° C, and change the temperature from the preheat temperature (100 ° C) to Estimate the response time (5 ⁇ ) by measuring the time elapsed until the temperature (1 1 26.4 ° C) equivalent to 62.3% of the temperature difference before and after the change, that is, the time constant (T) did.
  • Table 2 shows the results of the comparison.
  • the temperature measuring element diameter is 93 mm
  • Figure 8 (conventional type): Insulated tube diameter 0 3 mm, protective tube diameter 07.5 mm According to Table 2, the multipoint temperature measuring element of the present invention ( Figures 5, 6, and 7) Compared to Fig. 8), the response is faster and the difference between the temperature measuring junction 6 and the temperature measuring junctions 7, 8 is small. In particular, the case of Fig. 5 is a bundle of small-diameter one-point temperature measuring elements, and the response is extremely steep.
  • the temperature measuring element in which the thermocouple and the protective tube described in Example 1 were integrated was manufactured with an outer diameter of ⁇ 3 mm, and Was inserted into a protective tube for immersion in molten metal to obtain a sample. Pass a thermocouple through a 0.3 mm aluminum insulation tube for specific contraction, insert it into an alumina protection tube with an outer diameter of 0.6 mm and an inner diameter of 4 mm, and insert it into the same material and the same size as the above sample. The sample inserted into the protective tube for immersion in molten metal was used as a specific drawing sample.
  • the response time of the temperature measuring element of the present invention is reduced to 60 to 80% of the conventional method. Furthermore, when a thin protective tube for molten metal is used, it can be reduced to about 50%.
  • the extrusion pressure was 3 O kgf per square centimeter, and the material was extruded to a total length of about 20 Omm and cut.
  • the sintered body was sintered at the same temperature for 2 hours ( no deformation or cracks were observed in the sintered body.
  • the thermal etching treated surface of the mirror-polished surface of the obtained sintered body was observed with an electron microscope.
  • the occupied area ratio of the crystal system and the alumina crystal grain size of 3 m or less was calculated.
  • the obtained alumina sintered body having the shape of a thermoelectric protection tube has a diameter of about 3.2 mm.
  • a tube of about 16.5 mm in length is sealed at one end, and a hole of about 0.3 mm is formed in the cross section. Two were in parallel.
  • drill a hole of about 3.5 mm and a length of about 30 mm in a drill of 100 mm x 100 mm x 70 mm alumina K refractory. And protruded 120 mm from the end of the refractory surface.
  • the alumina refractory in which one end of the alumina sintered body was inserted was placed in an electric furnace. The installation was made so that the protective tube was horizontal to the hearth and at least 80 mm apart from the hearth.
  • an exposure test (creep test) was performed under the conditions of a heating rate of 200 ° C / h, a maximum temperature of 160 ° C, and a holding time of 5 h. Since the alumina test specimen protrudes 120 mm horizontally from the end of the refractory surface, it receives external stress due to its own weight.
  • the creep characteristics were evaluated by determining the amount of change (mm) in the height h (mm) of the alumina specimen from the hearth before and after the test, and evaluating the creep characteristics by its own weight deformation. The smaller the degree of deformation, the higher the high-temperature creep resistance.
  • an alumina sintered body obtained by adding 0.05% by weight of magnesium oxide to 99.9% purity alumina and sintering at 180 ° C for 1 hour at a high temperature was used.
  • Table 4 shows the mixing ratio of the coarse raw material to the fine raw material, the magnesium oxide addition ratio, and the sintering temperature.
  • Table 5 baked tracks of each composition corresponding to the numbers in Table 4, the flexural strength values before and after the test, where c indicating the occupancy of the alumina sintered grain size constituting the sintered body after sintering
  • the number 10 in the table is the alumina sintered body of the high-temperature sintering type used as a comparative sample. It is.
  • the specimen consisting of fine alumina raw material alone (specimen number 1) was creep
  • the sintered body has a small degree of bending of 15 mm or less, and even after being compared with the 180 ° C high-temperature sintering type alumina sintered body (specimen number 11). It is clear that the degree of curvature is comparable.
  • the alumina sintered body (No. 9) with a mixture of fine particles and coarse particles without adding magnesium oxide as a sintering aid was slow in maintaining the high temperature at the creep test temperature of 160.
  • Fine raw material Coarse raw material Sintering aid Sintering temperature number (% by weight) (% by weight) (% by weight) (% by weight) CC)
  • each alumina sintered body is converted into a thermoelectric protection tube (diameter 5 mm ⁇ 200 L, inner diameter 0.5 mm.2 hole) for heating steel at 150 ° C. And molded under the same sintering conditions.
  • a thermocouple protection tube made of alumina passed through a single-piece platinum wire was protruded 120 mm from the furnace wall to measure the temperature of molten steel, and the temperature was measured continuously for about 30 minutes.
  • the thermocouple protection tube made of an alumina sintered body having a composition within the range of the present invention endured continuous temperature measurement for 30 minutes, and was good in appearance without melting or corrosion.
  • the sintered couple containing the coarse grains of 30% by weight reacted violently with the molten steel and slag, and fell into a temperature-measurable state only three minutes after the start of the temperature measurement. This is considered to be due to incomplete sintering, which easily reacts with molten steel and slag, and because of its water absorption, corrosive gas penetrates into the protective tube, reacts with the single-port platinum wire, and melts the wire.
  • the composition of magnesium oxide added to the fine alumina raw material No. 2 in Table 4
  • the strand broke in 18 minutes after the start of the test.
  • the protruding part into the furnace was bent due to plastic deformation so that it was difficult to remove the specimen after the test.
  • the present invention is not limited to only the above embodiment.
  • the R thermocouple of this example can be changed to another type of thermocouple, and the external shape of the thermometer with the thermocouple and the protection tube integrated is also made to be square or elliptical, including round.
  • the tip of the element may be rounded or flat.
  • the multi-point heating element may have a plurality of temperature measuring contacts.
  • the temperature measuring element combined with the external protective tube is not limited to molten steel, but may be other molten metal or molten glass.
  • the material of the protective tube for molten metal is non-oxide, carbon-containing refractory, Any cermet or gold can be used.
  • thermocouple and the protective tube of the means 1 and 2 are integrated is narrowed down to the conventional thermocouple, the insulated tube and the protective tube assembled temperature measuring element, and the following points are excellent. ing.
  • Both protective tube and protective tube can be used.
  • Outer diameter can be reduced without the need for a protection tube, so it has excellent temperature response.
  • thermocouple contamination during assembly there is no.
  • thermocouple degradation is small and the life is extended by measuring the temperature in a polluted environment.
  • thermocouple It is easy to handle because it has an integral structure like a sheath thermocouple.
  • the difference is large especially in a contaminated environment such as molten steel temperature measurement, and the deterioration and consumption of precious metal thermocouples, which are effective with conventional assembled temperature measuring elements, are severe, and the running cost and cost are high.
  • the temperature measuring element of the present invention can measure the temperature with high accuracy for a long time, so that its practical and economical effects are extremely large.
  • the temperature measurement holes can be kept to a minimum, so that the method can be used safely. In other words, it can be said to be a sheath thermocouple for high temperature.
  • the multi-point temperature measuring element of the means 3.4, 5 does not require a large-diameter size protective tube unlike the conventional multi-point temperature measuring method in which a plurality of thermocouples passed through an insulating tube are inserted into the protective tube. Since there is no influence of the air layer and air convection with low thermal conductivity, it is excellent in temperature responsiveness and temperature measurement accuracy, and it is compact and easy to handle. It is most suitable for measuring the temperature distribution of diffusion furnaces for semiconductor manufacturing and for measuring the temperature distribution of melting furnaces, pots, tandems, etc. for steel, ferrous and non-ferrous metals. However, if it is used as a temperature measuring element of an automatic control system for these high-temperature holding devices, its practical and economical effects are extremely large.
  • the temperature measuring element in which an external protective tube such as the protective tube for molten steel of the means 6.7 described above is combined with the above-mentioned temperature measuring element is a conventional temperature measuring element comprising an external protective tube, an internal protective tube, an insulating tube and a thermocouple. Since it is not a multi-layer structure like the temperature measurement method, it has excellent temperature responsiveness and can prevent breakage due to the difference in thermal expansion between protective tubes and thermocouple deterioration due to breakage. That is, the durability of the temperature measuring device can be improved.
  • the sintered body of the temperature measuring element of the means 8 has excellent high-temperature creep characteristics. That is, the sintered body is composed of 99.5% or more of alumina ceramics and 0.5% by weight or less of an alkaline earth metal oxide as a sintering aid.
  • An alumina sintered body composed of a composite structure of coarse crystal grains having a crystal grain size of mainly 5 m or more and fine crystal grains of 3 am or less has excellent creep characteristics up to 160 ° C.
  • this alumina sintered body is obtained by adding 2 to 20% by weight of a coarse alumina raw material having an average particle size of 3 m or more to a fine alumina raw material having an average particle size of 1 m or less, and adding a sintering aid.
  • the sintering temperature is lower than 150 ° C., preferably lower than 140 ° C.
  • the sintered body is densified, and the sintered body is obtained by sintering such that the alumina crystal grain diameter is mainly composed of coarse particles of 5 or more and fine particles of 3 ⁇ m or less.
  • the alumina sintered body obtained by the present invention is excellent not only in heat resistance and corrosion resistance but also in high-temperature creep resistance, and has a low sintering temperature, so that the production cost is low and the field of application is greatly expanded. Thus, it can be applied to high temperature members such as thermocouple protection tubes. Industrial applicability
  • thermocouple temperature measuring element can be used for temperature measurement, temperature distribution measurement, and the like in a diffusion furnace for semiconductor production, steel, iron, non-ferrous metal melting pots, pots, tundishes, and the like.
  • the sintered body and the method of manufacturing the same according to the present invention can be used for manufacturing the above-described thermocouple temperature measuring element.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)

Abstract

Structures d'un thermomètre comprenant une unité monobloc constituée d'un thermocouple et d'un tube de protection, thermomètre capable de mesurer simultanément la température de points multiples, et système de thermomètre comprenant une combinaison de divers tubes de protection externes et thermomètres susmentionnés conçus pour mesurer la température d'un acier ou du verre en fusion. Un corps fritté en alumine comprenant au moins 99,5 % en poids d'un oxyde d'aluminium et un corps en plastique composite constitué de gros grains de cristal d'une grosseur ne dépassant pas 5νm et de grains de cristal fins d'une grosseur d'au plus 3 νm, est utilisé comme matériau pour le tube de protection en céramique isolante du système de thermomètre décrit ci-dessus. On prépare un mélange en ajoutant 2 à 20 % en poids d'un matériau brut constitué d'alumine grossière et un agent d'aide à la cristallisation à un matériau constitué d'alumine fine, on forme ce dernier et on le fritte à une faible température de moins de 1 500 °C, de préférence de moins de 1 400 °C. Ainsi, comme le risque de détérioration des fils du thermocouple est réduit, la durabilité est augmentée, la manipulation facilitée et la sensibilité accrue. Le système selon l'invention est particulièrement efficace pour mesurer les températures élevées dans un environnement contaminé, présente d'excellentes caractéristiques de mesure et est économique lorsqu'il est utilisé dans un four à diffusion pour la fabrication de semi-conducteurs dans laquelle une mesure multi-point est nécessaire.
PCT/JP1995/002411 1994-11-30 1995-11-27 Thermometre a thermocouple et procede de fabrication de corps frittes pour ledit thermometre WO1996017230A1 (fr)

Applications Claiming Priority (7)

Application Number Priority Date Filing Date Title
JP1592094 1994-11-30
JP6/15920 1994-11-30
JP7/38966 1995-02-03
JP7038966A JPH08208319A (ja) 1995-02-03 1995-02-03 熱電対保護管用アルミナ焼結体とその製造方法
JP7/1334 1995-02-07
JP7/292211 1995-10-13
JP29221195A JPH09113372A (ja) 1995-10-13 1995-10-13 多点測温素子

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WO1996017230A1 true WO1996017230A1 (fr) 1996-06-06

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT201600117337A1 (it) * 2016-12-13 2018-06-13 Ciarla Maria Cristina Lucia apparecchiatura per il controllo del surriscaldamento dei componenti di un motore o altre parti di un autobus, un autocarro o altro veicolo e l'azionamento di più sistemi di spegnimento localizzati, programmabile secondo le stagioni ed i cicli di lavoro
US20230101179A1 (en) * 2021-09-30 2023-03-30 Rosemount Inc. Heat flux temperature sensor probe for non-invasive process fluid temperature applications

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JPH01118731A (ja) * 1987-10-31 1989-05-11 Taiyo Yuden Co Ltd 熱電対温度センサーとその製造方法
JPH01169329A (ja) * 1987-12-24 1989-07-04 Kawasou Denki Kogyo Kk 溶融金属の連続測温装置
JPH05148013A (ja) * 1991-11-29 1993-06-15 Kyocera Corp アルミナセラミツクスおよびその製造方法

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JPH01118731A (ja) * 1987-10-31 1989-05-11 Taiyo Yuden Co Ltd 熱電対温度センサーとその製造方法
JPH01169329A (ja) * 1987-12-24 1989-07-04 Kawasou Denki Kogyo Kk 溶融金属の連続測温装置
JPH05148013A (ja) * 1991-11-29 1993-06-15 Kyocera Corp アルミナセラミツクスおよびその製造方法

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT201600117337A1 (it) * 2016-12-13 2018-06-13 Ciarla Maria Cristina Lucia apparecchiatura per il controllo del surriscaldamento dei componenti di un motore o altre parti di un autobus, un autocarro o altro veicolo e l'azionamento di più sistemi di spegnimento localizzati, programmabile secondo le stagioni ed i cicli di lavoro
US20230101179A1 (en) * 2021-09-30 2023-03-30 Rosemount Inc. Heat flux temperature sensor probe for non-invasive process fluid temperature applications

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