JPS63104758A - Control method for molten surface for continuous casting - Google Patents

Abstract

PURPOSE:To maintain the waving height on molten steel surface in a suitable range and to reduce the surface defect in a cast slab by controlling the waving height on the molten steel surface in a mold by making a signal of the waving height from a molten surface level meter the magnetic field control input for a static magnetic field generator. CONSTITUTION:Plural sets of the magnetic field generators 2 are arranged as facing near the molten surface level at both side faces of longitudinal direction of the mold 1, and plural eddy current type molten surface level meters 3 are arranged at the constant interval on the molten surface along the center line of longitudinal direction of the mold 1. The variation of waving height is detected by the molten surface level meter 3 and this signal is inputted to a magnetic field output controller. In accordance with this, to the magnetic field generating by the static magnetic field generator 2, the variation containing the variation caused by factor except the static magnetic field is compensated and it is controlled, so that the waving height generating near the molten surface in the mold is always maintained to constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of reducing surface flaws by controlling wave motion of the molten metal surface in a caster in continuous slab casting.

[Prior art] Waves on the surface of the mold are affected by factors such as the amount of molten steel discharged from the immersion nozzle, the flow of the molten steel discharged, the temperature of the molten steel, and the amount of Alpn blown into the immersion nozzle to prevent nonmetallic inclusions from accumulating on the nozzle. Therefore, it fluctuates and is not constant.

When the wave motion of the molten metal surface becomes excessive, a meniscus (melt powder) is formed at the interface between the molten steel and the molten steel and the molten powder is drawn into the molten steel.
When mold powder gets caught in a position close to the part where the molten steel surface contacts the mold.

The entrapped mold powder is captured by the solidified shell while floating in the molten steel, causing surface flaws.

Furthermore, when the discharge flow rate from the submerged nozzle increases, a vortex is generated near the submerged nozzle, causing suction of glossy powder. As a result, the sucked /4 powder penetrates deeply into the strand together with the discharge flow and is caught by the solidified shell, becoming powdery inclusions and defects in the steel sheet.

It is undesirable for the above-mentioned toshi tang er wave to become excessive.

However, if the surface wave motion is extremely small and the molten steel near the positive image is not renewed, the temperature of the molten steel at the surface will drop, the melting of the mold powder will be delayed, and solidification will begin at the surface. As a result, the ability of the mold powder to dissolve nonmetallic inclusions deteriorates, leading to an increase in inclusion defects.

Furthermore, when solidification begins at the surface of the hot water, a solidified shell separate from the already drawn solidified shell is formed, increasing the risk of breakout.

Therefore, various problems occur whether the surface waves are too large or too small.

In this way, the surface waves of the hot water have a great effect on the quality of the product. Therefore, as a method of controlling this, a method has been proposed in which the flow of molten steel is suppressed by a static magnetic field and the flow of the molten steel is caused by a moving magnetic field. (For example, JP-A No. 61-14035) [Problems to be solved by the invention] However, even if the surface waves are controlled in this way, the surface waves will be affected by the amount of molten steel discharged that changes during through casting as described above. , is controlled by factors such as molten steel temperature and is not constant.

Therefore, it is difficult to achieve stable hot water level waves of a constant height without considering fluctuations in these factors.

The present invention provides a control method that suppresses excessive surface waves and further maintains the minimum surface waves that are essential for reducing surface defects in slabs.

[Means and effects for solving the problem] In order to solve the above-mentioned problems, this invention suppresses the surface waves of the molten steel in the caster using a static magnetic field method, and at the same time quantifies the magnitude of the surface waves. By disposing a detector above the hot metal surface and using the output from the detector as a magnetic field control input of a static magnetic field generator to control the suppression state of the hot water surface wave, it is necessary to reduce surface defects on slabs. This is to obtain a stable and constant surface wave.

FIG. 1 is a plan sectional view of a main part near a mold in continuous slab casting, and FIG. 2 is a vertical sectional view of the main part, each of which is shown as a schematic explanatory diagram. A molten steel injection nozzle 4 installed vertically at the center of the mold 1 is immersed to below the molten metal surface 5, and molten steel R7 is discharged from the nozzle in two directions in the longitudinal direction of the mold. The molten steel injected into the mold is cooled on the inner surface of the mold, and a solidified shell d is formed downward from the meniscus.

In the present invention, a plurality of sets of magnetic field generators 2 are disposed facing each other on both longitudinal sides of the mold 1 near the hot water surface level, and are further placed above the hot water surface along the longitudinal center 11 of the mold 1. A plurality of (for example, six) vortex level gauges 3 are arranged at a constant distance.

FIG. 3 is a block diagram of the control system of the present invention, which explains the control operation. The surface wave height 8 is influenced by the fluctuation factors 9 during casting as described above, and these include various factors that cannot be fully controlled. Even if controlled, it is difficult to maintain the wave height constant during casting.

In the present invention, fluctuations in wave height are measured using a hot water level gauge, and this signal is input to the magnetic field output control device 1111C, and the magnetic field generated in the static magnetic field generator 2 is adjusted accordingly to cause fluctuations due to factors other than the static magnetic field. The height of the wave generated near the surface of the mold is controlled so that it is always maintained constant. This will be explained using specific numerical values.

Slab width 1250cm, slab width 250cm, drawing speed 2.
5ffi/11m, immersion nozzle angle, downward 15°.

Alden flow rate from the nozzle is 10)11/m1m, slab width 1100Os+, slab width 200m,
The drawing speed was 2 rn/aim, and the other conditions were the same as above.

FIG. 4 shows the relationship between the magnetic flux density and the height of the molten metal surface wave at the center 1005 mm from the short side. 700-1100
Gauge surface wave height is 7-8-.

As a result of investigating the relationship between the amount of fluctuation in the melt level and the occurrence rate of surface defects, the results shown in Figure 5 were obtained. According to this K, the appropriate surface wave height is in the range of 5 to 8 m.・The amount of discharge from the molten steel nozzle, the accumulation of non-metallic inclusions in the nozzle, the mold thickness properties, etc., and the surface wave height The temperature changes depending on the position on the hot water surface, and also changes over the course of an hour. This is captured by an eddy current water level gauge, and the current of the static magnetic field generator is changed according to the output from the hot water level gauge. By performing so-called feedback control and suppressing the height of the surface wave to an average value of 7 to 8 degrees, the amount of surface defects can be reduced to 173 or less compared to when the control method of the present invention is not implemented.

[Effects of the Invention] As described above, according to this invention, the static magnetic field in the mold is controlled to a predetermined value by the wave height signal from the hot water level gauge, so the hot water level wave height is Despite various factors, it is stably maintained within an appropriate range, and a remarkable effect is seen in reducing surface defects on slabs.

[Brief explanation of the drawing]

Figure 1 is a schematic horizontal cross-sectional view of the main part near the mold showing the arrangement of the static magnetic field generator and molten steel level gauge in an embodiment related to the present invention, and Figure 2 corresponds to the horizontal cross-section of the main part. FIG. 3 is a block diagram of the control according to the present invention, FIG. 4 is a graph showing the relationship between magnetic flux density and surface wave height according to the embodiment described above, and FIG. 2 is a graph showing the height of undulating water surface and the incidence of surface defects. DESCRIPTION OF SYMBOLS 1... Mold for continuous slab casting, 2... Static magnetic field generator, 3... Eddy current level gauge, 4... Immersion nozzle for pouring molten steel, 5... Molten metal surface, 6... Solidified shell, 7...Discharged molten steel flow. WAl Zukan': (mm)

Claims (1)

[Claims] One or more pairs of static magnetic field generators and one or more in-mold molten steel level gauges are disposed opposite to the long sides of a continuous casting mold to suppress surface vibrations on the surface of molten steel in the mold, A continuous casting hot water level control method that controls the wave height on the surface of molten steel in the mold by using the wave height signal from the hot water level gauge as the magnetic field control input of a static magnetic field generator.