JPH0924457A - Method for detecting slag in nozzle and nozzle for molten metal - Google Patents

Abstract

(57) [Summary] [Purpose] An electromagnetic coil is used to detect the slag outflow start time more accurately than before. [Structure] An alternating current is applied to a molten metal passing through the molten metal nozzle 1 by a primary coil 2 and the current is detected by a secondary coil 3. Primary coil 2 and / or secondary coil 3
The flow blocker 5 is arranged at the center of the nozzle at the height position to block the inflow of the slug 4 into the center of the nozzle at the height position to decenter the nozzle wall near the inner wall of high magnetic flux density. [Effect] Since the slag flows into the vicinity of the inner wall of the nozzle having a high magnetic flux density, it is possible to accurately detect the slag outflow start time in which a small amount of slag flows.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal nozzle for mainly passing an iron-based molten metal such as low alloy steel, various stainless steels, high nickel steels, and pig iron, and slag detection in the nozzle. Regarding the method.

[0002]

2. Description of the Related Art Iron-based molten metal is manufactured by using a refining vessel such as a converter, a ladle, and a tundish. On the surface of the molten metal in these vessels, slag containing an oxide as a main component is formed. Often exists. In the process of manufacturing cast slabs from hot metal, after reactions such as decarburization and dephosphorization are performed in the converter, the steel is tapped in a ladle and undergoes secondary refining processes such as alloy addition and degassing. It is poured into a tundish and further solidified in a continuous casting mold. Various nozzles such as a tap hole of a converter, a ladle nozzle, and a dipping nozzle provided in a tundish are used to transfer molten metal between refining vessels in these steps. One of the most important points when transferring these materials is to separate the slag that causes phosphorus reconstitution and inclusions in the subsequent step as much as possible, and then discharge the molten metal with good yield.

In order to separate the slag, it is effective to accurately detect the outflow start time of the slag and to finish the discharge of the molten metal promptly. Conventionally, the start of slag outflow was visually determined by the operator, but as a technique for accurate detection, a device that applies an alternating current to the primary coil and detects the induced current by a secondary coil close to the primary coil is located near the nozzle. A method has been developed in which the secondary coil current is used to capture the change in magnetic field when slag with different electric conductivity is mixed in the molten metal in the nozzle. For example, JP-A 1-27
Japanese Patent Laid-Open No. 5-302111 describes an example in which a primary coil and a secondary coil are arranged around a nozzle, and Japanese Patent Application Laid-Open No. 5-302111 discloses an example in which a primary coil and a secondary coil are arranged with a nozzle in between. ing. As described above, by performing slag detection using electromagnetic induction, not only can metal contamination due to carry-over slag be reduced, but also the work load can be reduced, and thus it has been widely used in recent years.

[0004]

In these slag detecting methods, a high frequency current of several tens to several thousands Hz is applied to the primary coil to generate an eddy current in the molten metal in the nozzle.
However, the magnetic field distribution formed in the molten metal by the high frequency current is inevitably attenuated by the skin effect from the inner wall of the nozzle toward the center. Since a small amount of slag passes through the central portion of the nozzle at the initial stage when the slag starts to flow into the nozzle, the change in the signal received by the secondary coil is small and difficult to detect. Extremely increasing the current of the primary coil to increase the detection accuracy requires not only an expensive current amplifier but also a signal error due to heating of the coil, which requires complicated work such as special signal processing. .

An object of the present invention is to provide a technique capable of accurately and easily detecting an initial slag inflow which is usually very difficult to detect.

[0006]

According to the slag detection method of the present invention, an alternating current is applied to a molten metal passing through a molten metal nozzle by a primary coil, and the current is detected by a secondary coil. In the method, the slag inflow to the center of the nozzle at the position where the vertical cross section in the passing direction of the molten metal intersects with at least one coil is forced by specifying the angle and / or curvature of the nozzle or by a flow control structure provided in the nozzle. It is a method for detecting slag in a nozzle, which is characterized in that it is shut off temporarily. At this time, as the flow control structure, a flow blocker is arranged in the central portion of the nozzle at a position where the vertical cross section in the passing direction of the molten metal intersects with at least one coil to forcibly block the slag inflow into the central portion of the nozzle. Is simple and effective.

Further, in the molten metal nozzle of the present invention, at least one path connecting the center line of the nozzle and the inner wall is 1600 ° C.
Electrical conductivity at 500-7000 (1 / Ω cm)
A molten metal nozzle characterized by being formed of a refractory plate that is, and a molten metal nozzle having a refractory flat plate passing on the nozzle center line and connected to both inner walls, The nozzle for molten metal is characterized by having holes of 5 to 200% of the nozzle cross-sectional area at both positions sandwiched by the center line of the nozzle and the inner walls.

The most efficient slag detection method is
Applying an alternating current to the molten metal passing through the molten metal nozzle in the primary coil, in the slag detection method in the nozzle to detect the current in the secondary coil, using any of the molten metal nozzle of the present invention, In the nozzle characterized in that the refractory plate or the refractory flat plate forcibly blocks the slag inflow to the nozzle center at the position where the vertical cross section in the molten metal passage direction intersects with at least one coil. This is a slag detection method.

[0009]

The present invention will be described with reference to FIG.

FIG. 1 shows an embodiment of the present invention. The upper figure shows a side surface of a nozzle for molten metal, and the lower figure shows a cross section taken along the line AA '. An alternating current is applied to the primary coil 2 installed around the upper portion of the molten metal nozzle 1, and a change in the magnetic field is detected by the secondary coil 3 disposed below the primary coil 2. The slag 4 flows into the molten metal nozzle 1 together with the molten metal (not shown). A flow blocker 5 that divides the interior of the nozzle is provided at the center of the molten metal nozzle at a height corresponding to the positions of the coils 2 and 3. When the slag 4 passes through the coils 2 and 3, the molten metal is The nozzle 1 is forcibly controlled to pass through the eccentric position. Since the magnetic flux distribution generated by the high-frequency current is concentrated near the inner wall of the molten metal nozzle 1 by the skin effect as shown by the arrow on the left side of the figure above, the change in the eddy current that occurs when a small amount of slag passes through the center. Is extremely small, but by forcibly controlling the slag at an eccentric position where the magnetic flux density is high, the change width given to the eddy current becomes large, and even when a small amount of slag flows in, it can be detected accurately.

Although it is simple and reliable to use a flow blocker for eccentricity control of the slag, a flow control structure in which the curvature or angle of the nozzle is specified to utilize the specific gravity difference, or a special fin or the like is provided. Even if it is used, the same effect can be obtained. Regarding the arrangement of the coils, the positions of the primary coil and the secondary coil may be reversed from those shown in Fig. 1, or they may be arranged on concentric circles, or the conductive wire for the primary coil and the conductive wire for the secondary coil may be insulated and covered together. Alternatively, the coating may be processed into a coil shape and provided at the same position. Further, the accuracy improvement effect can be obtained by the same principle even in the opposite position arrangement as shown in FIG.
The primary coil and the secondary coil do not necessarily have to be a pair.

If the slag flow can always be eccentrically controlled at at least one position of the height of either the primary coil or the secondary coil, the sensitivity can be improved. It is desirable to cover the entire area to improve sensitivity. This is because the change in signal detected by the secondary coil is caused by the change in mutual inductance between the primary coil, the molten metal in the nozzle, and the three conductors of the secondary coil, so eccentricity control of the slag can be reliably performed over the entire height of the coil. This is because a large change in mutual inductance appears when it can be performed, and the slag inflow can be detected with high sensitivity.

A particularly desirable nozzle for molten metal is one in which the material of the flow blocker is a conductive material such as alumina graphite or magnesia carbon, and its electric conductivity is 1600 ° C.
At 500 to 7000 (1 / Ω cm), or a flat plate in which the flow blocker is connected to both inner walls, and a nozzle cross section of 5 to 200 at both positions sandwiched between the center line of the flat plate and the inner wall of the nozzle. The nozzle for molten metal has a hole of%. When the primary coil and the secondary coil are arranged around the nozzle, the eddy current generated in the molten metal by the magnetic field flows as shown by the arrow in the lower diagram of FIG. 1, but in order to improve the detection rate in the secondary coil. It is necessary to secure a sufficient eddy current path, and the two types of structures described above are particularly easy to construct and less likely to be damaged by molten metal flow. The electrical conductivity of the flow blocker is set to 500 (1 / Ω cm) or more at 1600 ° C. The reason for processing the iron-based molten metal is mainly from 1500 to 170.
This is because it is often carried out at about 0 ° C., and the electrical conductivity of the flow blocker is 500 (1 / Ω cm) or more, and good detection is possible, and the upper limit is the electrical conductivity of molten steel 700.
The value of 0 (1 / Ω cm) means that in the region where the electric conductivity of the molten steel exceeds, even if the electric conductivity of the flow blocker is increased, the resistance of the molten metal itself limits the eddy current passage promoting effect. This is because it becomes smaller. The reason why the hole area of the flow blocker is 5% or more of the nozzle cross-sectional area is that the hole area is necessary for good detection when the electric conductivity of the flow blocker is small, The upper limit is 200 of the nozzle cross section
The reason why the percentage is set is that the effect of promoting eddy current passage is small even if a large hole exceeding that is provided, and conversely, the strength of the flow blocker is lowered and the breakage is likely to occur.

The shape of the inner wall of the nozzle for molten metal does not necessarily have to be cylindrical, and may be rectangular or elliptical, and a plurality of flow blockers may be used.

[0015]

EXAMPLE The present invention was carried out using a 6-ton ladle. Inner diameter 1
A 90 mmφ nozzle for molten metal is provided at the bottom of a 100 mm ladle, and a 270 mm primary coil (500 Hz) is provided around the nozzle.
And the secondary coil was installed under it. Charge 6t of molten steel and 150kg of slag adjusted to basicity 1 in the pan, monitor the secondary coil voltage with a phase detection circuit while discharging to the mold, and slide nozzle when the base voltage during discharging rises. Was closed and the amount of slag flowing into the mold was measured.

The flow blocker had a thickness of 10 mm and was arranged such that both ends were in contact with the inner wall of the nozzle in a certain height range (50 mm) of the primary coil and the secondary coil. FIG. 3 shows the results of measurement by changing the electrical conductivity by changing the carbon concentration by using alumina graphite as the material of the flow blocker. The slag outflow amount could be reduced to 60 kg or less in the region where the electric conductivity was 500 (1 / Ω cm) or more. The slag outflow reduction effect was also observed when the height of the flow blocker was set only to the height of the primary coil.

In FIG. 4, the material of the flow blocker is magnesia (10 ⁻⁶ 1 / Ω cm), which has a low electric conductivity, and the area of the holes provided at the left and right ends of the flow blocker (indicated by the area of the hole on one side). ) Shows the test results with different values. 50 flow blockers
The size used was mm × 90 mm, and the part in contact with the inner wall of the nozzle was removed leaving 10 mm at the top and 10 mm at the top. It was found that the effect of reducing slag outflow was large when the area of the holes was 5% (318 mm ² ) or more of the nozzle cross-sectional area.

[0018]

According to the present invention, the slag outflow start time can be determined more accurately than the conventional slag detection method, and the quality control such as the inclusion reduction of molten metal and the prevention of rephosphorization is facilitated.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing the influence of the electrical conductivity of the flow blocker on the outflow amount of slag.

FIG. 4 is a diagram showing the influence of the area of holes provided in the flow blocker on the outflow amount of slag.

[Explanation of symbols]

 1 Molten Metal Nozzle 2 Primary Coil 3 Secondary Coil 4 Slag 5 Flow Barrier 6 Hole

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G01N 27/72 G01N 27/72 (72) Inventor Masahiro Daimon 20-1 Shintomi, Futtsu-shi Nippon Steel Technology Development Co., Ltd.

Claims (6)

[Claims] 1. A method for detecting slag in a nozzle, in which an alternating current is applied to a molten metal passing through a nozzle for molten metal by a primary coil and the current is detected by a secondary coil, in which a vertical cross section in the molten metal passage direction is at least In the nozzle characterized by forcibly blocking the slag inflow to the center of the nozzle at a position intersecting with one coil by specifying the angle and / or curvature of the nozzle or by a flow control structure provided in the nozzle. Slag detection method. 2. As the flow control structure, a flow blocker is arranged in the center of the nozzle at a position where a vertical cross section in the molten metal passage direction intersects with at least one coil, and the slag inflow into the center of the nozzle is forcibly blocked. The method for detecting slag in a nozzle according to claim 1, wherein: 3. The electrical conductivity of 500 to 700 at 1600 ° C. in at least one path connecting the center line of the nozzle and the inner wall.
A nozzle for molten metal, which is formed of a refractory plate having a diameter of 0 (1 / Ω cm). 4. A nozzle for molten metal having a flat plate made of refractory which passes on the center line of the nozzle and is connected to both inner walls, wherein the nozzle cross-sectional areas are located at both positions of the center line of the flat plate and both inner walls. A nozzle for molten metal, having a hole of 5 to 200%. 5. The method for detecting slag in a nozzle according to claim 2, wherein the molten metal nozzle according to claim 3 is used to forcibly block the inflow of slag into the central portion of the nozzle. 6. The method for detecting slag in a nozzle according to claim 2, wherein the molten metal nozzle according to claim 4 is used to forcibly block the inflow of slag into the central portion of the nozzle.