JPH0555220B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) In continuous steel casting, molten steel contained in a tundish is guided into the continuous casting mold through a immersion nozzle connected to the bottom of the tundish. The flow rate of the molten steel spouted from the outlet is significantly higher than the casting speed, and if inclusions or bubbles in the molten steel penetrate deep into the crater, product defects will inevitably occur. Furthermore, when the molten steel jet has a particularly large upward flow, the mold meniscus swells up, promoting fluctuations in the molten metal level, which has a significant negative impact on the quality of the slab strand and casting operations. This invention aims to effectively improve not only the surface quality but also the internal quality of slab strands obtained by continuous casting under stable casting operations.

(Prior Art) In order to control the molten steel jet from the immersion nozzle, it has conventionally been common to modify the shape of the discharge port of the immersion nozzle or to reduce the injection speed of the molten steel. However, it has been difficult to completely prevent quality defects caused by inclusions contained in the molten steel by simply changing the shape of the discharge port of the immersion nozzle or reducing the injection speed of the molten steel. As a prior document on this point, for example, Japanese Patent Application Laid-open No. 17356/1983 describes a technique in which a static magnetic field generator is installed in a continuous casting mold to apply braking to the jet flow of molten steel from a submerged nozzle. , and Japanese Patent Application No. 1-105817 disclose a technique in which a static magnetic field is applied to the entire surface of a continuous casting mold, thereby applying damping to the jet flow of molten steel from a submerged nozzle.

(Problem to be solved by the invention) By the way, in the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 17356/1983, when braking is applied to a jet of molten steel, the direction of the jet changes as if it were hitting a wall. However, it is not possible to disperse the energy of the jet flow to create a uniform flow, and the jet flow escapes in a direction where there is no static magnetic field, making it impossible to obtain satisfactory results. In addition, the technology disclosed in Japanese Patent Application No. 1-105817 can make the jet of molten steel uniform from the immersion nozzle, and can also reduce fluctuations in the molten metal level at the meniscus, thereby improving the quality of the slab strand. However, if a static magnetic field is installed above and below the continuous casting mold and the magnetic field is strengthened so that the molten steel flow after colliding with the short side, that is, the secondary flow, becomes shallower, it is possible to give an appropriate molten steel flow at the meniscus part. As a result, dissolution of the mold powder is inhibited, surface defects are likely to occur, and there is a risk of breakout. The purpose of the present invention is to propose a new casting method and an apparatus that can be used directly to carry out the method, which makes it possible to obtain slab strands with good surface quality as well as internal quality without causing the problems described above. It is something to do.

(Means for Solving the Problems) The present invention generates a static magnetic field between a pair of upper and lower magnetic poles installed on the upper and lower sides of each back side of the opposing side walls of a continuous casting mold, thereby causing continuous casting from an immersion nozzle. In continuous casting of steel, which applies braking to the flow of molten steel supplied into the casting mold, the strength of the static magnetic field generated between one pair of magnetic poles is controlled by the strength of the static magnetic field generated between the other pair of magnetic poles. This is a continuous casting method for steel using a static magnetic field, characterized in that continuous casting is carried out with the strength of the static magnetic field weaker or stronger than that of the generated static magnetic field. Here, in this invention, it is preferable that the strength of the static magnetic field generated by the magnetic pole installed at the top is weaker than the strength of the static magnetic field generated by the magnetic pole installed at the bottom.

The present invention also provides a device comprising a pair of upper and lower magnetic fields and a pair of lower magnetic poles extending along the width direction of the side wall on each rear surface of the opposing side wall of a continuous casting mold, This is a continuous steel casting apparatus characterized by having a static magnetic field adjusting means that can arbitrarily change the strength of the static magnetic field generated between the magnetic poles of the magnetic pole.

Now, FIGS. 1a and 1b schematically show a casting apparatus according to the present invention, and number 1 in the figures indicates a pair of short side walls 1a and a long side made of copper or copper alloy (including plating), the inside of which is water-cooled. A continuous casting mold consisting of a combination of walls 1b, 2 an immersion nozzle for supplying molten steel into the continuous casting mold 1, 3a and 3b an iron core body forming a magnetic path, and 4a, 4b, 5a and 5b each iron core body. Upper and lower magnetic poles connected to 3a and 3b and extending along the width of the continuous casting mold 1, and 6 are magnetic field adjusting means for adjusting the strength of the static magnetic field generated between the magnetic poles, and this adjusting means 6 is connected to the iron core. Main body 3
a, 3b, a bracket 7 fixed to, for example, a support, a bracket 8 fixed to the core body 3, and each bracket 7,
8 and a hydraulic cylinder 10 that is fixedly held on the support and engaged with the core body.

(Function) For example, the upper magnetic pole 4a on the A side installed in the continuous casting mold 1 is set as the N pole, and the upper magnetic pole 4b on the B side is set as the S pole.
In the case of a pole, a magnetic field of A→B is generated at the upper magnetic pole, while a magnetic field of A←B is generated at the lower magnetic pole. When molten steel is supplied into such a magnetic field, the upward flow (hereinafter referred to as upward reverse flow) is caused by the upper magnetic field.
Further, the downward flow (hereinafter referred to as downward reversal flow) is decelerated by the magnetic field at the bottom. Here, the upper magnetic pole 4a,
4b, since the static magnetic field between the lower magnetic poles 5a and 5b has the same strength in the upper and lower directions, especially when the strength of the magnetic field is changed significantly to reduce the penetration depth of the downward molten steel flow, Since the flow velocity of the reverse flow decreases as the reverse flow descends, the supply of heat from the molten steel decreases, and as shown in Figure 2, the melting of the mold powder is inhibited, and this increases the sluggishness of the slab strand. Deterioration of surface quality is inevitable.

In this invention, at least one of the iron core bodies 3a and 3b is provided with a magnetic field adjusting means 6 configured as described above for adjusting the strength of the magnetic field, and by changing the distance between each magnetic pole, the mold 1 can be adjusted. Upper and/or
Alternatively, the strength of each magnetic field at the lower magnetic pole can be changed arbitrarily. Therefore, when applying large braking to the flow of molten steel, especially the downward flow, the distance between the magnetic poles at the upper magnetic pole can be increased and the strength of the magnetic field at the lower magnetic pole can be made weaker than the magnetic field near the meniscus. A suitable flow rate can be given to the molten steel, and there is no chance that the mold powder will remain unmelted. Further, in this invention, the magnetic field can be quickly set to be appropriate according to changes in the throughput amount of molten steel or the type of steel, which contributes to improved productivity. The magnetic field adjusting means 6 shown in FIG. 1 above is a hydraulic cylinder 10.
Although shown as having a structure in which the core body is rotated around the pivot pin 9 by the operation of the upper magnetic pole 4 to change the distance between the upper magnetic poles, for example, the upper magnetic pole 4
Part of the iron core in a and 4b may be replaced with a non-magnetic material (SUS304, etc.), and the strength of the magnetic field at the magnetic pole may be made smaller than that at the bottom magnetic pole.The structure can be changed in some ways. It is not limited to only.

(Example) Continuous casting was carried out under the following conditions using the apparatus according to the present invention shown in FIG. and internal quality were investigated. The results are shown in FIGS. 3 and 4. It is clear that adjusting the strength of the magnetic field depending on the operating conditions is extremely effective.

Casting conditions Casting speed: 1.7m/min, Width of slab strand: 1400mm, Thickness: 260mm Distance between upper magnetic poles: 460~520mm Distance between lower magnetic poles: 460mm Upper magnetic field strength: 2400~3200 Gauss Lower magnetic field strength: 3200 Gauss (Effect of the Invention) Thus, according to this invention, it is possible to apply accurate braking to the secondary flow after the jet of molten steel from the immersion nozzle collides with the short side, so that the inclusions caused by the flow of injected molten steel are removed from the molten steel. Getting caught deep in the pool,
Since the melting of the mold powder is not inhibited, high-quality slabs can be manufactured with high efficiency.

[Brief explanation of the drawing]

Figures 1a and b are configuration explanatory diagrams of casting equipment suitable for use in this invention, Figure 2 is a graph investigating the effect of molten steel jet on the quality of continuously cast slabs, and Figures 3 and 4 are examples of embodiments. This is a graph showing the quality of slabs obtained in . 1... Continuous casting mold, 1a... Short side wall, 1b
... Long side wall, 2 ... Immersion nozzle, 4a, 4b ...
Upper magnetic pole, 5a, 5b...lower magnetic pole, 6...magnetic field adjustment means, 7, 8...bracket, 9...pivot pin, 10...hydraulic cylinder.

Claims (1)

[Scope of Claims] 1. A static magnetic field is generated between a pair of upper and lower magnetic poles installed on the upper and lower sides of each back surface of the opposing side walls of a continuous casting mold, and this is supplied from an immersion nozzle into the continuous casting mold. In continuous casting of steel, which applies braking to the flow of molten steel, the strength of the static magnetic field generated between one pair of magnetic poles is equal to the strength of the static magnetic field generated between the other magnetic pole. A continuous casting method for steel using a static magnetic field, characterized in that continuous casting is performed at a strength weaker or stronger than the strength of the steel. 2. The method according to claim 1, wherein the continuous casting is performed by making the strength of the static magnetic field generated by the magnetic pole installed at the upper part weaker than the strength of the static magnetic field generated by the magnetic pole installed at the lower part. 3 A device equipped with a pair of upper and lower magnetic poles extending along the width direction of each side wall on the back side of the opposite side wall of a continuous casting mold, and this device is equipped with a pair of upper and lower magnetic poles extending along the width direction of the side wall, and this device 1. A continuous steel casting apparatus characterized by having a static magnetic field adjusting means that can arbitrarily change the strength of the static magnetic field generated in each of the apparatuses.