JPH0629789B2 - Thermocouple protection tube - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thermocouple protection tube for temperature measurement, which protects a temperature measurement sensor for measuring the temperature of hot metal and molten steel.

[Prior Art] A platinum rhodium-based thermocouple (hereinafter referred to as B thermocouple) is generally used as a method for measuring the temperature of molten metal such as molten metal such as hot metal and molten steel. It is a consumable thermometer that is protected by a thermocouple. Normally, if the thermocouple is immersed in hot metal, molten steel, etc., the heat-sensitive part will melt and become unusable within a very short time (10 to 20 seconds). It had to be finished and the thermocouple was replaced after each measurement.
For this reason, it is strongly desired to have a thermometer that can measure temperature continuously for a long time because it is difficult to control the quality and operation and the temperature measurement cost is high.Recently, Sialon, BN, A which has high corrosion resistance to molten metal
Thermocouple protection tubes such as l ₂ O ₃ -C and ZrO ₂ -Mo are available.

[Problems to be Solved by the Invention] However, in the case of a thermometer using these protective tubes,
In continuous temperature measurement with hot metal or molten steel, preheating at the time of charging and oxidation and corrosion resistance during temperature measurement are extremely poor, and the protection tube is eroded at about 5 to 30 ch, so the life is short.

When charged in molten metal, ZrO ₂ -Mo, Al ₂ O ₃ -C, BN
Since thermocouple protection tubes using such protection tubes have high thermal shock resistance, they have been used without sufficient preheating, but they are sufficiently long in terms of weak strength, easy oxidation, and low corrosion resistance. Few things can withstand the temperature measurement of time.

However, recently, a preferable material for such a protection tube, that is, excellent corrosion resistance and sufficient strength against molten metal,
Boride-based ceramics have been proposed as those having heat resistance and thermal conductivity. In particular, ZrB ₂ most satisfies the above-mentioned material conditions, and can be said to be a preferable material when the present invention is applied. However, since the boride-based ceramics generally have lower toughness than metal and poor thermal shock resistance, the temperature of the protective tube or the like is 1400 ° C or higher when the high-temperature hot water such as molten metal is intermittently repeated. Since the temperature rises and falls below 1200 ℃ repeatedly, minute cracks occur inside the protection tube, causing the entire crack, and the life is shortened compared to when measuring temperature continuously for a long time. Happened,
There has been a strong demand for a technique capable of stably measuring a temperature for a long time even in such an intermittent temperature measurement.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and has a melting point of 1400 on the entire outer circumference of a protective tube main body containing zirconium diboride (ZrB ₂ ) as a main component. The present invention provides a thermocouple protection tube used for temperature measurement of hot metal and molten steel, characterized in that it is coated with a fibrous layer having a thickness of 5 to 30 mm, which is mainly composed of ceramics fibers having a temperature of ℃ or more.

A description will be given below with reference to the drawings.

FIG. 1 is a side view for explaining the basic structure of the present invention. The thermocouple protection tube 1 of the present invention is basically a zirconium diboride.
Protective tube main body 1a containing (ZrB ₂ ) as a main component and fibrous layer 1b such as ceramic fiber coated on the outer surface thereof
It consists of

As a temperature measuring device using such a thermocouple protection tube,
Generally, in this tube, an Al ₂ O ₃ insulating tube 3 with a thermocouple 2 built-in
It is configured by incorporating an Al ₂ O ₃ protective tube 4 incorporating thereinto, and the whole is charged into a molten metal to continuously measure the temperature change of the molten metal.

In the present invention, the main body 1a is made of a non-oxide ceramic sintered body and is made of ZrB ₂ (zirconium diboride) in view of high temperature corrosion resistance to molten metal. ) Is the most suitable.

Suitable sintered bodies are as follows.

． A composition containing a boride of composition Zr as a main component and containing SiC or BN as a secondary component, for example, ZrB ₂ 95 to 70% in weight% and SiC 1 to 15
%, BN 4 to 29%, etc.-Physical properties Bulk specific gravity 3.0 to 6.0 Bending strength 10 kg / mm ² or more Thermal expansion coefficient 0.6% or less (1000 ° C) Specific resistance 10 ^-1 Ωcm or more ( 1500 ° C) Thermal shock resistance (ΔT) 250 to 1000 ° C The thermal shock resistance was measured by measuring the bending strength of a sample that was rapidly heated to various temperatures in an electric furnace for 5 minutes and rapidly cooled in water. The processing temperature of the sample is shown (ΔT ° C).

The specific resistance is a value measured at a high temperature by the 4-terminal method. (Ωc
m, 1500 ° C.) Next, the inorganic fiber layer 1b such as ceramic fibers arranged on the outer surface of the protective tube body will be described. As mentioned above, the main body 1a of non-oxide ceramics such as ZrB ₂
When it is poured into the molten metal and the temperature rises and falls repeatedly (especially when the temperature falls from a high temperature range, often 500 to 600 ℃
In the region (1), a fine crack is generated in the structure inside the ceramic of the main body 1a, and when it is remarkable, it may lead to the crack of the whole ceramic. The reason for this is not clear, but it is thought to be due to abrupt changes in thermal expansion coefficient, oxidation characteristics, Young's modulus, and thermal stress. However, when measuring the temperature of hot metal and molten steel at each blast furnace or continuous casting, the temperature measurement is interrupted at each casting of one tap for each tap, and in the case of a protective tube using boride-based ceramics. The protection tube often breaks earlier than the amount of erosion.

In the present invention, in order to prevent this, the outer surface of the protection tube body 1a is covered with the inorganic fiber layer 1b, and the protection tube body 1a is stable without being broken even if the temperature rise and fall are repeated intermittently. It can measure temperature. When the protective tube coated with the fibrous layer 1b is put into the molten metal,
When taken out from a high temperature (every tap of tap metal or every casting of cast), the fiber layer 1b becomes a thermal shock relaxation layer and easily contracts with molten steel to remove slag or metal adhesion coating during temperature measurement. It is formed and keeps the protective tube warm without cooling during cooling to prevent cracking. This inorganic fiber layer 1b needs to be as heat-resistant as possible from the viewpoint of protection against thermal shock and thermal stress of the protective tube body 1a, and therefore needs to be an inorganic fiber, and especially has a melting point of 1400 ° C or higher. A fibrous layer composed mainly of ceramic fibers is used. Of course, a part of the fibrous material may be blended with clay, inorganic lightweight particles, or the like.

The ceramic fiber layer, which is the preferred embodiment, will be specifically described below.

That is, the desired ceramic fiber layer is Al ₂ A ₃ -SiO ₂
A blanket mainly composed of a ceramic fiber such as a silica type, a silica type, a zirconia type, an alumina type or a cylindrical shape as a sheet or a molded body molded with an inorganic binder is suitable. Suitable ceramic fiber layers are as follows.

． Composition Al ₂ A ₃ -SiO ₂ mainly composed of fibers such as Al ₂ A ₃
40-55%, SiO ₂ 60-45%.

-Physical properties Fiber specific gravity 2.5-6.5 g / cm ² Average fiber diameter 2.0-15 μm Bulk density 0.05-0.3 g / cm ³ Thermal conductivity 1.0-0.4 Kcal / mh ° C (at. 1000 ° C.) Specifically, the ceramic fiber layer 1b having the above composition properties is coated on the entire outer surface of the protective tube body 1a to a thickness of 5 to 30 mm to manufacture the protective tube 1. If it is a blanket or sheet, it should be fixed at several points with wire. In some cases, the coating can be performed by spraying. Since the radiation from the molten metal is severe, the coating layer 1b needs to be formed continuously over almost the entire outer circumference of the body 1a in order to protect the body 1a and the metal fittings.

By covering the entire outer circumference of the protective tube body with a fibrous layer of ceramics fiber, the rapid heating and cooling when the protective tube is immersed in the molten metal or withdrawn from it is mitigated to avoid thermal stress cracking. The effect of being able to form a slag or a coating of adhered metal during temperature measurement and maintaining the effect of repeatedly relieving thermal shock is provided.

[Example] 10% by weight of BN powder (1μ or less and 99% or more in purity) to ZrB ₂ powder (1μ or less and 99% or more in purity) was crushed with an ethanol solvent using a pot mill with a SiC ball for 3 days and then taken out. , An organic binder was added, and the mixture was granulated with a spray dryer. Similarly, ZrB ₂ powder was pulverized and granulated using a SiC ball to obtain a powder. By rubber press using this powder
It was molded at 2000 kg / cm ² and fired in an Ar atmosphere at 2100 ° C. for 3 hours to produce protective tubes each having an inner diameter of 15φ, an outer diameter of 25φ and a length of 850 mml. The analytical value of the sintered body is ZrB ₂ 85%, BN in% by weight.
It was 10% and SiC 5%.

Alumina-silica fiber (trade name: Kaowool) bracket (bulk density 0.128 g / cm ² ) on the outer surface of this protective tube
Was coated to a thickness of 30 mm and fixed with a wire. The analytical values of the fiber were Al ₂ O ₃ 47.3% and SiO ₂ 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 sufficiently preheated at about 1200 ° C and immersed. The temperature of the protective tube was raised and lowered repeatedly every 18 times during casting, and the temperature could be normally measured for a total of 70 hours. The temperature of the protective tube during temperature measurement was checked, but the slag coating layer was 2 to 3 mm evenly in the part immersed in the molten metal.
It was confirmed that it could function as a protective layer for thermal shock relaxation. After 70 hours, the protective tube was cut and examined. As a result, no crack was found on the cross section or the inner surface, and the amount of corrosion on the outer surface of the ZrB ₂ protective tube was about 2 to 3 mm.

On the other hand, when an adiabatic temperature measurement was performed using a protection tube in which the outer surface of the ZrB ₂ protection tube was not coated with ceramics fiber, the temperature was measured adiabatically to about 3
The protective tube was damaged as soon as the temperature was measured for about 4 hours, and the temperature could not be measured. As a result of taking out and examining, the molten steel had invaded through the cracks generated on the outer surface of the protective tube. In addition, it was cut in half and the inner surface and cross section were examined, but it was found that numerous minute cracks were included.

[Advantages of the Invention] As described above, according to the present invention, the temperature of the molten metal can be intermittently measured stably for a long time, so that the temperature measurement cost is reduced and the reliability of the thermometer is significantly improved. By using this, it is useful for labor saving, stable operation by improving operation / quality control accuracy, quality improvement, productivity improvement, etc., and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional explanatory view for explaining the basic structure of the present invention. In the drawing 1: Thermocouple protection tube 1a: Protection tube body 1b: Ceramic fiber layer 2: Thermocouple 3: Al ₂ O ₃ insulation tube 4: Al ₂ O ₃ protection tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Taketsui 2-4-10-106 Midorigaoka, Takasago City, Hyogo Prefecture (56) References JP-A-57-101730 (JP, A) SAIKAI Sho 49-148982 ( JP, U) Actual opening 48-48381 (JP, U) Actual opening 55-97540 (JP, U) Actual opening 62-189629 (JP, U)

Claims (1)

[Claims] 1. A fibrous layer having a thickness of 5 to 30 mm, which is mainly composed of ceramic fibers having a melting point of 1400 ° C. or more, is coated on the entire outer circumference of a protective tube main body containing zirconium diboride as a main component. A thermocouple protective layer used for temperature measurement of hot metal and molten steel.