JPH01288738A - Thermocouple protective tube - Google Patents

Abstract

PURPOSE:To achieve a higher reliability of a thermometer, by covering the external surface of a protective tube body with an inorganic fiber layer. CONSTITUTION:A thermocouple protective tube 1 is covered with a protective tube body 1a mainly composed of non-oxide ceramics and fiber layer 1b made of ceramic fiber or the like to improve a high temperature anticorrosion against molten metal and heat impact resistance against a temperature change of the molten metal. This enables intermittent measurement of temperature of the molten metal stably for a long time, thereby achieving a higher reliability of a thermometer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermocouple protection tube for temperature measurement that protects a temperature sensor for measuring the temperature of molten metal or the like.

[Prior art] Conventionally, the method generally used to measure the temperature of molten metals such as hot metal and molten steel is to connect the tip of a platinum-rhodium thermocouple (hereinafter referred to as B thermocouple) to a quartz tube. It is a consumable thermometer that is protected by a thermometer, and if the thermocouple is immersed in hot metal or molten steel, the heat-sensitive part will melt in a very short time (10 to 20 seconds) and become unusable. The thermocouple had to be replaced after each measurement. For this reason, it is difficult to control quality, operation, etc., and temperature measurement costs are high, so there is a strong desire for a thermometer that can measure temperature continuously for a long time.
N.

Thermocouple protection tubes such as A1□0s-C and ZrO□-Mo are provided.

[Problems to be solved by the invention] However, in the case of thermometers using these protective tubes,
Continuous temperature measurement of hot metal or molten steel has extremely poor oxidation and corrosion resistance during preheating and temperature measurement during charging, and the protective tube is corroded after about 5 to 30 channels, resulting in a short life.

Moreover, when thrown into molten metal, ZrOz-Mo.

Thermocouple protection tubes using protective tubes made of Al10s-C, BN, etc. have high thermal shock resistance, so they are used without sufficient preheating, but they are weak in strength, easily oxidized, and have low corrosion resistance. There are few that can withstand temperature measurement for a sufficiently long time.

However, recently, the preferred material for such protection tubes is
That is, boride ceramics have been proposed as having excellent corrosion resistance against molten metals, sufficient strength, heat resistance, and thermal conductivity. In particular, ZrBa best satisfies the above-mentioned material conditions and can be said to be a preferable material to which the present invention is applied. However, this boride-based ceramic has lower toughness and thermal shock resistance than ordinary metals, so if it is intermittently exposed to high-temperature water such as molten metal, the temperature of the protective tube will exceed 1400℃. , the temperature will be raised and lowered 42 times to a temperature below 1200°C, which will cause minute cracks to occur inside the protective tube, causing cracking of the entire tube, resulting in a shorter service life than when measuring temperature continuously for a long period of time. There was a strong desire for a technology that could stably measure temperature for a long time even in such intermittent temperature measurement.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and it protects the temperature sensor with a protection tube body made of non-oxide ceramics such as ZrB1. This invention provides an outer surface coated with an inorganic fiber layer such as ceramic fiber that shrinks relatively easily in molten metal when the temperature is measured intermittently.6 The following description will be made with reference to the drawings.

FIG. 1 is a sectional view illustrating the basic configuration of the present invention,
The thermocouple protection tube 1 of the present invention basically consists of a protection tube body portion 1a mainly composed of non-oxide ceramics and a fibrous layer 1 made of ceramic fiber or the like coated on the outer surface of the protection tube body portion 1a.
It consists of b.

Temperature measurement devices using such thermocouple protection tubes include:
Generally, A! has a built-in thermocouple 2 inside this tube. A1□0. with built-in tOs insulating tube 3. It is constructed by incorporating a protective tube 4, and is inserted into the entire molten metal to continuously measure the temperature change of the molten metal.

The protection tube 1 consisting of the main body +a and lb will be further explained below. In the present invention, the main body 1a is made of a non-oxide ceramic sintered body, and is optimally made of ZrB1 (zirconium diboride) as a main component from the viewpoint of high-temperature corrosion resistance against molten metal.

A suitable sintered body is as follows.

The main component is boride of composition Z, with SiC and B as subcomponents.
Those containing N etc., for example ZrBa95-70 in weight%
%, SiCl ~15%, BN4~29%, etc./Physical properties Bulk specific gravity 3.0~6.0 Flexural strength 10 to 10 g/mm1 or more Thermal expansion coefficient 0.6% or less (1000℃) Specific resistance
In""0cm or more (1500℃) Thermal shock resistance (△T)
250-1000℃ Thermal shock resistance refers to the bending strength of samples that were rapidly heated to each temperature for 5 minutes in an electric furnace and then rapidly cooled in water, and indicates the processing temperature at which the strength suddenly decreased (△ T'C).

Specific resistance is the value measured at high temperature using the 4-terminal method. (Ω
cn+, 1500°C) As the non-oxide ceramic sintered body in the present invention, in addition to this ZrB1 type, TiBa type, Sialon type, etc. can also be used, but compared to ZrB2, they are less resistant to slag and molten metal at high temperatures. It is undeniable that TiBa-based materials are inferior in that they have low corrosion resistance and poor oxidation resistance.

Next, the inorganic fiber layer 1b, such as ceramic fiber, arranged on the outer surface of the protective tube body will be explained. As mentioned above, due to the non-oxide ceramic body 1a such as ZrB, when it is poured into a molten metal and the temperature repeatedly rises and falls (particularly when the temperature falls from a high temperature range, the
In the 600° C. region), minute cracks occur in the internal structure of the ceramic of the main body 1a, and if they are significant, they may lead to cracking of the entire ceramic. The cause of this is not clear, but it is thought to be due to sudden changes in the coefficient of thermal expansion, oxidation properties, Young's modulus, etc., or thermal stress. However, when measuring the temperature of hot metal or molten steel every time a blast furnace or continuous casting is performed, temperature measurement must be interrupted every 1 tap tapped and every 1 cast cast. In many cases, the protection tube breaks earlier than the amount of erosion.

In order to prevent this, the present invention provides an inorganic fiber layer 1b coated on the outer surface of the protective tube main body Ia, so that the protective tube main body 1a remains stable without breaking even if the temperature is repeatedly increased and decreased intermittently. temperature can be measured by When the protective tube covered with this fibrous layer 1b is put into the molten metal,
Also, when taken out from high temperatures (every 1 tap tapped or every 1 cast cast), this fiber layer lb acts as a thermal shock buffer and easily contracts with the molten steel, removing the adhesion coat of slag and bare metal during temperature measurement. This prevents breakage by keeping the protective tube warm without quenching it during cooling. This inorganic fiber layer 1b needs to be as heat resistant as possible from the viewpoint of protecting the protective tube body +a from thermal shock and thermal stress, so it is necessary to be an inorganic fiber, and in particular, it needs to be an inorganic fiber with a melting point of 1400°C.
It is desirable that the fibrous layer is mainly composed of ceramic fibers having the above-mentioned properties. In addition, as part of the fiber,
Of course, there is no problem even if it is blended with clay, inorganic light 14 particles, etc.

Hereinafter, a ceramic fiber layer, which is a preferred embodiment, will be specifically explained by taking as an example.

That is, the desirable ceramic fiber layer is ^1ass
A blanket or sheet-like material mainly made of ceramic fibers such as -3ins-based, silica-based, zirconia-based, or alumina-based ceramic fibers, or a cylindrical shaped object formed with an inorganic binder is suitable. A suitable ceramic fiber layer is as follows.

, composition Al*0s-3iOs is the main component, for example, A1□0.40-55%, 5iOi 60-45%.

・Physical properties Fiber specific gravity 2.5-6.5 g/c Average fiber diameter 2.0-15 μm Bulk density 0.05-0.3 g/cm" Thermal conductivity 1
．． Cal/m, h, 'C(at, 10
00°C) Specifically, the storage tube is manufactured by coating the entire outer surface of the protective tube body 1a with a ceramic fiber layer lb having the composition properties as described above to a thickness of about 5 to 50 mm, preferably 20 to 30 mm. do. If it is in the form of a blanket or sheet, tie it with wire in several places to secure it. In some cases, the coating can also be applied by spraying. Note that this coating layer 1b
Preferably the main body! Although it should be formed continuously over almost the entire outer periphery of a, it is preferable to form it over the entire outer periphery in order to protect the main body 1a and the metal fittings since the radiation caused by the molten metal is severe.

[Example] BN powder (
1μ or less purity 99% or more) is added at 10% by weight
After grinding with an ethanol solvent for 3 days using an iC ball and a bot mill and taking it out, an organic binder was added and granulation was carried out with a spray dryer. Similarly, Zr8m powder was crushed and granulated using SiC balls to obtain powder. This powder was molded using a rubber press at 2000 kg/cna'',
A "2100'l:X3hr firing in atmosphere, inner diameter 1
Protective tubes with a diameter of 5φ, an outer diameter of 25φ, and a length of 850 mmfl were manufactured. The analysis value of the sintered body is ZrB18 in weight%.
5%, BN 10%, and SiC 5%.

The outer surface of this protective tube is coated with a blanket of aluminal silica fiber (product name: Niriki Saitsuru) (bulk density: 0.128).
g/cm") to a thickness of 30 mm and fixed with a wire. The fiber analysis values were A1□h47.3%, 5iOx
It was 52.3%.

Using this protective tube, the temperature was measured in a 40 ton tundish pot. Before being immersed in molten steel at 1550°C, it was thoroughly heated to about 120°C and immersed. The temperature was measured every 18 times during each casting, and the temperature limit of the protection tube was repeatedly lowered to a total of 70 times.
The temperature could be measured normally for a period of time. When the protective tube was examined during temperature measurement, it was found that the part immersed in the molten metal had a uniform coating layer of slag of 2 to 3 mm, functioning as a protective layer to buffer thermal shock. After 70 hours, this protective tube was cut and examined, and no cracks were found on the cross section or inside surface, and the amount of corrosion on the outer surface of the ZrB1 protective tube was 2 to 3+++n.
It was about +.

On the other hand, when adiabatic temperature measurement was performed using a ZrBa protection tube whose outer surface was not coated with ceramic fiber, the temperature measured during one temperature drop was approximately 3 to 3. Even after 4 hours of temperature measurement, the protection tube was damaged and temperature measurement was no longer possible. After taking it out and examining it, we found that molten steel had entered through cracks that had formed on the outer surface of the protective tube.

When it was cut in half and the inner surface and cross section were examined, it was found that there were numerous minute cracks.

[Effects of the Invention] As described above, according to the present invention, it is possible to stably measure the temperature of molten metal intermittently over a long period of time, thereby reducing the temperature measurement cost and significantly improving the reliability of the thermometer. Its use has great industrial value, helping to save labor, improve operational and quality control accuracy, improve operational safety, improve quality, and improve productivity.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional explanatory diagram illustrating the basic structure of the present invention. In the drawing, l: thermocouple protection tube la: protection tube body lb: ceramic fiber layer 2: thermocouple 3: AIJs insulation tube 4: A1□0. protection tube

Claims (1)

[Claims] (1) A thermocouple protection tube made of non-oxide ceramics, characterized in that the outer surface of the protection tube body is coated with an inorganic fiber layer.