JPH11248541A - Thermometer for molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermometer provided with excellent durability even at the time of being used in contact with the artificial slag or refractory material of high basicity for enduring the continuous use of a long time. SOLUTION: A temperature detection element 3 composed by mounting a thermocouple 1 inside a porcelain tube 2 is provided inside a protective tube 4 composed of a calcined body containing 50-90 wt.% of magnesia and 10-50 wt.% of graphite as main components and containing 1-10 wt.% of at least one kind selected from boron nitride, boron carbide, silicon carbide, silicon and aluminum as additional components preferably. The shape of the protective tube 4 can be the one for housing and covering the entire temperature detection element or the one for covering only a part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocouple-type thermometer for measuring the temperature of molten metal such as molten steel, for example, which is equipped with a corrosion-resistant protective tube to enable continuous temperature measurement for a long time. And a thermometer for molten metal.

[0002]

2. Description of the Related Art Conventionally, thermocouples such as platinum-platinum rhodium have been used for measuring high temperatures. However, when measuring the temperature of molten metal, a protective tube having corrosion resistance to the molten metal or the like is used. Must be used to protect the thermocouple. In particular, when performing continuous casting of metal, it is necessary to continuously measure the temperature of the molten metal in a container such as a tundish. It is common to use a double-structured thermometer in which a porcelain tube is further mounted in a protective tube.

[0003] In continuous casting of molten steel, rice hulls or artificial slag is charged into a tundish for the purpose of keeping the molten steel warm and floated on the surface of the molten steel. Therefore, a protective tube of a thermometer that comes into contact with such a heat insulating material for a long time is required to have excellent corrosion resistance not only to molten steel but also to heat insulating materials such as rice hulls and artificial slag. Conventionally, therefore, for the heat insulating material such as organic matter such as rice husks carbonized, an alumina-graphite material having high corrosion resistance to molten steel or a material having a low silica content or containing no silica is protected. It has been used as a suitable material for tubes.

For artificial slag as a heat insulating material, in addition to the above-mentioned protective tube made of alumina-graphite material, a protective tube made of zirconia-graphite material having higher corrosion resistance (for example, Japanese Patent Application Laid-Open No. 62-163941), a high-strength alumina-padelite system, and a protective tube made of ceramics composed of padelite and magnesia or calcia (for example, JP-A-62-163940). In recent years, in order to protect a porcelain tube of a thermometer, a protective tube formed of a non-oxide type refractory material such as zirconium boride or a protective tube formed of a cermet type refractory material such as zirconia-molybdenum is used. It has also been suggested.

[0005]

In recent years, however, the heat insulating material has been required to play an important role in promoting the purification of steel while maintaining the temperature of molten steel. For example, artificial slag having a high basicity and mainly containing magnesia and calcia has been used. At the same time, basic refractory materials have been used as tundish lining materials and spraying materials. Therefore, the protection tube of the thermometer is required to have higher durability than the conventional one.

The present invention has been made based on the above technical problem, and has excellent durability even when used in contact with artificial slag or refractory material having a high basicity, and has a long life. It is intended to provide a thermometer that can withstand continuous use.

[0007]

SUMMARY OF THE INVENTION An object of the present invention as described above is to provide a temperature detecting element having a thermocouple mounted in a porcelain tube, comprising 50 to 90% by weight of magnesia and 10 to 50% by weight of graphite. This can be achieved by a molten metal thermometer, which is provided in a protective tube made of a fired body containing the same.

[0008] Further, the protective tube is preferably made of magnesia 50-
A fired body mainly containing 90% by weight of graphite and 10 to 50% by weight of graphite, and further containing 1 to 10% by weight of at least one selected from boron nitride, boron carbide, silicon carbide, silicon and aluminum as an additional component. If it is
Deterioration of the protective tube due to oxygen is suppressed, and a longer life can be expected.

Further, in the temperature detector for molten metal according to the present invention, the temperature detecting element is provided on the outside with a non-oxide refractory material such as zirconium boride or zirconia.
A protective sheath made of a cermet-based refractory material such as molybdenum may be provided. In this case, the protection tube may be formed as a cylindrical sleeve, and the cylindrical protection tube may be mounted on the outer peripheral surface of the protection sheath.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The protective tube used for the molten metal thermometer of the present invention is composed of 50 to 90% by weight of magnesia and 1% of graphite.
0 to 50% by weight as a main component, and the content of magnesia in the fired body is 50%.
When the amount is less than 90% by weight, excellent corrosion resistance to molten steel or slag cannot be obtained. When the amount is more than 90% by weight, sintering proceeds during use, so that cracks are easily generated. On the other hand, spalling characteristics are improved by setting the content of graphite to 10% by weight or more. However, if the content exceeds 50% by weight, corrosion resistance decreases, which is not preferable.

Further, at least one selected from the group consisting of boron nitride, boron carbide, silicon carbide, silicon and aluminum can be added to the fired body. Such an additive component has an effect of suppressing the weakening of the structure due to oxygen in the atmosphere and preventing a decrease in strength and corrosion resistance, but the effect is remarkable only when the added amount is 1% by weight or more. . However, if the added amount exceeds 10% by weight, cracks and the like tend to occur, so it is desirable to limit the amount to 10% by weight or less.

[0012] The fired body having such a special composition is
In order to show excellent corrosion resistance to highly basic slag containing a lot of calcia and magnesia, a protective tube formed of such a fired body is, for example, a bottomed shape with a closed end, and a temperature detecting element is attached to this. In this manner, the entire element can be covered to form a high-corrosion-resistant molten-metal thermometer, or a temperature detecting element having a cylindrical sleeve (unbottomed tube) open at both ends and provided with an optional protective sheath. , It is also possible to selectively enhance the corrosion resistance of only the portion that comes into contact with the slag. In this case, the protective sheath is formed of a non-oxide refractory material such as zirconium boride or a cermet refractory material such as zirconia-molybdenum.

[0013]

EXAMPLES Hereinafter, the thermometer for molten metal of the present invention will be described in more detail with reference to Examples and Comparative Examples. Unless otherwise specified, all descriptions such as compounding amounts are indicated by weight. doing.

FIG. 1 shows a cross-sectional shape of the molten metal thermometer of the present invention. The thermometer shown in FIG. 1 is a general-purpose molten metal thermometer, and a platinum-platinum rhodium thermocouple 1 is housed in a bottomed porcelain tube 2 to constitute a temperature detecting element 3. The temperature detecting element 3 is accommodated in a bottomed protective tube 4 and is sealed by a metal fitting 5 at the upper part. FIG. 2 shows a cross-sectional shape of a molten metal thermometer mainly intended to prevent erosion due to slag spreading on the surface of molten steel, and also shows a platinum-platinum rhodium thermocouple 1 and a bottomed porcelain tube 2. The temperature detecting element 3 is housed in a protective sheath 6 made of a non-oxide refractory material, and a sleeve-shaped cylindrical protective tube 7 is fixed to the outer peripheral surface of the protective sheath 6 by, for example, mortar.

In order to conduct a test on the material of the protective tube used for the molten metal thermometer, as a raw material of the fired body,
Powder magnesia (MgO), graphite (C),
Silicon carbide (SiC), boron carbide (BC), boron nitride (BN), aluminum (Al) and silicon (S
i) were uniformly mixed in accordance with the composition shown in Table 1, molded using a hydrostatic press (Cold Isostatic Press), then cut into a 50 mm × 50 mm × 200 mm rod shape, and in a reducing atmosphere at 900 to 1100 ° C. For 48 hours to produce Examples 1 to 3 and Comparative Examples 1 to 4 as respective rod-like fired body samples.

Example 1 for these rod-shaped fired body samples
-3 and Comparative Examples 1-4, the bulk specific gravity, apparent porosity (%), flexural strength (MPa), and 1000, respectively.
The coefficient of thermal expansion (%) at ℃ was measured. Further, a slag corrosion resistance test and a spalling resistance test were respectively performed according to the methods described below, and both were ◎ (good) and ○.
The results were evaluated on a three-point scale of (acceptable) and unacceptable (x), and the results are shown in Table 1.

(Slag Corrosion Resistance Test) Slag having a CaO / SiO ₂ ratio of 5 to 7 is melted in an induction furnace, and each bar-shaped fired body sample is immersed in the slag and held at a molten steel temperature of 1580 ° C. for 1 hour. The surface condition of the sample was visually observed, and the erosion amount on one side of the sample was evaluated as ◎: 0 to 2 mm;

(Sparing Resistance Test) A water-cooled spalling method was performed in which a rod-shaped fired body sample was immersed in molten steel at 1650 ° C. in an induction furnace for 5 minutes, taken out, and immersed in 5 ° C. water three times. The test was repeated, and the condition of the sample was visually observed. な い indicates that no cracks were generated, ○ indicates that a micro-crack was generated for the third time, and × was the one that generated a crack for the first and second times. evaluated.

[0019]

[Table 1]

Further, a bottomed protective tube was prepared using the same raw material composition as in the above-mentioned sample No. 1, and a molten metal thermometer of the present invention having the structure shown in FIG. 1 was assembled. When the thermometer of the present invention was used to measure the temperature of molten steel in a tundish using a slag having a CaO / SiO ₂ ratio of 6, a protective tube made of an alumina-graphite material or a zirconia-graphite material was used. It was confirmed that the service life was about three times as long as the conventional thermometer equipped with a protective tube made of the material of the system.

[0021]

As is apparent from the above description, the temperature detector for molten metal according to the present invention comprises a temperature detecting element having a thermocouple mounted in a porcelain tube, 50 to 90% by weight of magnesia and 1% of graphite.
Since it is provided in a protective tube made of a fired body containing 0 to 50% by weight as a main component, it exhibits excellent corrosion resistance to a highly basic slag containing a large amount of calcia and magnesia, and has a continuous service life. There is an effect that can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of a molten metal thermometer according to the present invention.

FIG. 2 is a cross-sectional view showing the structure of another embodiment of the molten metal thermometer of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermocouple 2 Porcelain tube 3 Temperature detection element 4 Protective tube 5 Metal fitting 6 Protective sheath 7 Cylindrical protective tube

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoichiro Mochizuki 1 Minamito, Ogakie-cho, Kariya-shi, Aichi Prefecture Toshiba Ceramics Corporation Kariya Works

Claims (4)

[Claims] 1. A temperature detecting element comprising a thermocouple mounted in a porcelain tube, comprising 50 to 90% by weight of magnesia and 10 to 5% of graphite.
A thermometer for molten metal, which is disposed in a protective tube made of a fired body containing 0% by weight as a main component. 2. The protective tube according to claim 1, wherein the protective tube is mainly composed of 50 to 90% by weight of magnesia and 10 to 50% by weight of graphite, and is at least one selected from boron nitride, boron carbide, silicon carbide, silicon and aluminum. The molten metal thermometer according to claim 1, comprising a fired body containing from 10 to 10% by weight as an additional component. 3. The temperature detecting element according to claim 1, further comprising a protective sheath formed of a non-oxide refractory material such as zirconium boride or a cermet refractory material such as zirconia-molybdenum. The thermometer for molten metal according to 1. 4. The protection tube is formed in a cylindrical sleeve,
The thermometer for molten metal according to claim 3, wherein the cylindrical protective tube is mounted on an outer peripheral surface of the protective sheath.