JPS589751A - Electromagnetic agitator in continuous casting for slab - Google Patents

Abstract

PURPOSE:To obtain a sound material having less skin holes in the stage of acting moving magnetic fields in the width direction of a slab by providing electromagnetic coils in the specific positions below the level of the molten metal in a mold thereby acting uniform flow near the molten metal level. CONSTITUTION:In continuous casting of slabs, coils which generate moving magnetic fields are installed in such a way that the central positions of the coils come respectively within the (0.7-1.3)XL/2 range below the level of the molten metal in the mold. Since the coil positions are specified in such way, the moving magnetic fields act in the width direction of the mold in sufficient contact therewith and form the two rotating flows symmetrical to the center of the width, thereby acting the uniform flow near the level of the molten metal. If the slab is cast under such conditions, the solidified shell is washed uniformly, and internal inclusions and hole like defects are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic stirring device for molten metal, which is used for continuous casting of molten metal, particularly for continuous casting of molten steel, for slabs in which the width to thickness of slabs is more than double, especially wide slabs. It is something. The first object of the present invention is to provide a sound material with few skin holes by applying a uniform flow near the surface of the molten metal when casting rimmed or semi-killed steel in continuous steel casting. The second purpose is to help the inclusions of the injected molten metal float up, and to reduce defects by allowing the molten metal to act on the surface of the molten metal at a uniform temperature.

In general, there have been many publications on the idea of applying electromagnetic stirring to continuous casting, but Bloom,
There are many ideas to apply it to billets. Recently, Japanese Patent Application Laid-Open No. 47-5554 proposed improving the coagulation structure by applying parallel flow in the uniaxial direction, and US Patent No. 3,656,537 proposed The purpose is to form a flowing metal flow at right angles, that is, in the width direction of the slab. Next, JP-A-47-33027
No. 1 is a system in which an electromagnetic device is installed on the upper side of the secondary cooling zone of the curved continuous casting equipment to stir and help float up inclusions. Therefore, the first purpose of performing electromagnetic stirring using these methods is
The goal is to reduce the segregation of the solidified ends and to change the solidified structure from columnar crystals to equiaxed crystals (Japanese Patent Application Laid-open No. 47
There are some methods, such as No. 33027, which try to help the floating of inclusions).

The present invention is similar to U.S. Pat. No. 3,656,537, in which a magnetic field is applied perpendicular to the direction of travel, but the purpose and implementation are different, and the ultimate goal is to form a uniform flow on the surface of the hot water. They are fundamentally different in that the purpose is to apply a washing flow to the shell at the beginning of solidification to prevent bubbles and inclusions from adhering, and to impart an excellent surface to rimmed steel and semi-killed steel in particular. .

Now, the inventors put a low melting point alloy made of blue lead-tin lead into an 18-8 stainless steel tank that is four times as tall as it is wide.
We installed a coil that generates a magnetic field that moves in the width direction, and performed electromagnetic stirring to understand the flow situation of the molten metal. As a result, it was found that when the position of the coil, that is, the position in the height direction where the coil is arranged, changes, the flow velocity of the molten metal changes drastically even at the hot water surface position and near the coil position.

The present invention is based on the inventor's prior knowledge of electromagnetic stirring and the discovery of the dependence of flow velocity on coil position described herein, and based on these findings, studies were conducted to obtain the optimal flow conditions (flow velocity, etc.) in continuous slab casting. It is what was done.

First of all, Figure 1 is a diagram of a model experimental tank made of a low melting point alloy in order to understand the relationship between the coil position and the flow situation of this molten metal, especially the flow velocity.
, mrx, a low melting point alloy E is placed in a tank corresponding to a mold, the tank has a double shell, and is heated with steam to melt the low melting point alloy. The coil is placed at the center C in the height direction of the tank, the height H is changed, and pitot tubes are placed at measurement points A and B to measure the speed.

This figure shows that when a unidirectional electromagnetic stirring flow is applied in the width direction of the slab, a large circulating flow is formed near the depth, which is basically the same as the width of the tank, and the position of the coil is It can be seen that when the position is shallower than the width dimension, significant flow interference occurs and the flow velocity decreases even at the hot water level and at the coil position.

It was thus found that the relationship between the flow velocity measured at measurement points A and B and the change in the height direction of the coil position was as shown in Fig. 2A. The inventor filed a patent application No. 48-80048.
In the issue [Electromagnetic stirring device for continuous slab casting]
submitted, and recognized the effect of forcibly forming a circulating flow within the slab surface using multiple coils, but it was found that even a single coil can produce almost good circulating flow when it matches the slab shape. This is how the scales were discovered.

In addition, the present inventor has submitted a method for continuous casting of rimmed steel and semi-killed steel in Japanese Patent Application No. 48-40642, which shows that such steel is particularly easy to produce in scales and slabs under the action of a rotating magnetic field. It was shown that even in a moving magnetic field, it is possible to manufacture something fairly good, but it cannot be said to be completely good. Now, based on the above-mentioned knowledge, it has become possible to present a complete solution.◎ Basically, the present invention involves placing a coil that generates a moving magnetic field in sufficient contact with the mold so that the moving magnetic field acts in the width direction. Assuming that the inside of the slab is L, the coil should be installed at a depth of 7 mm from the molten metal surface.

Naturally, the mounting range has a certain width, so if the mounting position is set to 7, the agitation flow will be symmetrical about the center of the width. For this reason, if the flow forms one rotating flow, it may be a little deeper, but if two rotating flows occur, the depth cannot be made too deep because of mutual interference.@The lower limit is limited to 0.7 in the present invention. The reason is clear from FIG. That is, less than 0.77 (
700%), the flow velocity will drop significantly and it will be difficult to form a uniform flow (furthermore, when measuring at point B as shown in the opening of Figure 2, a part of the flow may even form a counterflow due to vortices). This is because it is known that

Also, if the upper limit of 1.3- is exceeded, pinholes will occur,
This may remain as a flaw in the finished product.

By installing the coil at a specific position in this way, a uniform flow acts near the hot water surface. When casting under such flow conditions, the solidified shell in the area affected by this flow is washed uniformly, and there are very few inclusions or bubble defects on the inner surface. I understand.

In order to apply the above basic research to an actual machine, we decided to install an electromagnetic coil with a length of 2100 balls and a 3-phase 6-pole linearly moving magnetic field that generates a linearly moving magnetic field into a continuous casting machine that can cast up to 2200 mm wide. This type of coil is already well known. However, in order to install the coil, the coil needs to be placed sufficiently close to the slab, so it became necessary to support the slab with a structure different from the conventional guide rolls used to support the slab. . In addition, since the width of the slab generally changes, the coil mounting position can be changed accordingly and can be changed at will. In order to satisfy these conditions, the front surface of the coil is placed under a pure copper mold that is water-cooled with a non-magnetic steel skid or a water-cooled mold (cooling plate) made of non-magnetic steel. The coil body is suspended by a beam or spray zone that supports the mold vibrator, and the mounting position is moved up and down by a screw depending on the dimensions of the mold. FIG. 3 shows an example of such an embodiment, namely, 1 is a normal tundish, 2 is a tundish car, 3 is a vibrating device, 4 is a mold vibrator frame, 5 is a mold, 6 is an electromagnetic stirring lifting device such as a screw, and 7 is a tundish car. An electromagnetic stirring device, 8 is an apron frame of a guide roller shown at 10, 9 is a non-magnetic steel cooling skid, and 11 is a slab.

Therefore, the present invention has a thickness of 150 to 250 Hl x width of 150
It was installed in a curved wide slab continuous casting equipment of 0 to 2000+m. The mold length is 700111! Then, in contact with the mold, 1
8-8 stainless steel thickness 15 mm, width 45 mm, length 80 mm
A number of skids 9 are arranged at 2011 intervals.

Water is injected into this gap by a spray nozzle (not shown). The support body of the present skid 9 has a rigid support mechanism as a whole, and is not directly connected to the mold 5, and its position can be adjusted in accordance with the thickness of the mold together with the spray zone. The electromagnetic stirring device 7 is mounted on the frame 8 of the spray zone, and has a lifting device 6 such as a screw so that it can be moved over the entire length of the skid 9080ON1L.

When casting rimmed steel using the above-mentioned equipment, when the electromagnetic stirring device 7 of the present invention applies a moving magnetic field along the width of the slab and in each hand of the slab to stir the molten steel, a symmetrical flow is created as shown in Fig. 4. It is formed. The coil used in the present invention is a 3-phase, 6-pole coil, and is wired so as to generate a symmetrical flow. Note that 12 in the figure indicates the hot water level.

As a result, the agitation flows are as shown in FIG. 5, but in order to take advantage of the characteristics of these agitation flows for casting, it was necessary to devise a new method. In particular, when a unidirectional flow is formed, the problem is that the heat field becomes asymmetric with respect to the slab. FIG. 5 shows an injection scheme in which such precautions have been taken.

Figure 5 shows the injection method for Figure 4, and 1 in the figure.
2-1 is a rising portion of hot water, 13 is an injection flow, 14 is a scum, 15 is a molten metal, 16 is a nozzle, and 17 is an immersion nozzle. In FIG. 5, there were two injection flow positions, and the injection was carried out at the center of the circulation flow using a submerged nozzle. Rimmed steel was actually injected using this injection method. The equipment is as described above. Now, two types of steel with the following components were manufactured using an oxygen top-blown converter.

CSi Mn P S Al 0 (1) is aluminum killed steel, and (II) is silicon semi-killed steel. With normal injection, slipper defects occur due to alumina clusters. (U) has thin pinholes with a diameter of about 0.5 mi+ on the surface and is unusable.

Both steel types were coated with molten Y'' udder slag in a slab mold with a thickness of 200mm and a width of 1880mm using the pouring method shown in Figure 5, and cast at a casting rate of 0.18rr1/min.The obtained thin plates were inspected. However, based on the alumina clusters (known to be sulino), the number of scratches was greatly reduced and the surface condition became very good. Although there were some small pinholes in the chisel, it was found that it was sufficiently usable once it was made into a thin plate.

In this experiment, the coil was placed 1030 xyi (1
, I X1), 1220 m* (1,3X), 1
410 Tomo (1-5X 2 ) 2 It was installed under 03 conditions. There was no significant difference in the number of defects in the thin plate under the first and second conditions, but under the third condition, that is, in the case of 1.5× reciprocity, an increase in the number of defects caused by pinholes was observed at both ends and in the center of the thin plate. .

As described above, according to the present invention, surface inclusions in killed steel can be reduced, and pinholes in semi-killed steel can also be removed.

One of the effects of the present invention is that it has made it possible to manufacture rimmed steel, semi-killed steel, etc.

Although there was an idea to produce rimmed and semi-killed steel using electromagnetic stirring, it was realized that excellent materials could only be produced by the present invention when it became possible to form a uniform stirring flow near the surface of the molten metal. became.

In the present invention, the coil can be placed under the mold.

This creates a strong stirring flow.

As seen in some proposals (for example, JP-A-47-26
No. 332), it is impossible to make the mold a field for an electromagnetic coil. The reason for this is that continuous casting places a high heat load on the mold, so only materials with high thermal conductivity, such as steel, can be used. This is because most of the induced current induced to cause this is consumed in the mold. Therefore, with this method, it is not possible to form a stirring flow of 0.2 to 0.5 m/s or more, which is effective for casting rimmed and semi-killed steels and reducing inclusions. The present invention is an excellent solution to solve these electrical problems and fluid shape problems.

It should be noted that the electromagnetic coil for inducing a traveling magnetic field as used in the present invention is already well known from many documents, so a detailed explanation will be omitted.

Embodiment (1) of the present invention A coil that generates a traveling magnetic field by multiphase alternating current is installed perpendicular to the orthogonal direction of the slab, and the position of this coil from the hot water level is (with respect to the medium dimension of the slab). 0.7-1.3
) A method for arranging an electromagnetic stirring device in continuous slab casting, which is characterized by applying a strong uniform stirring flow near the melt surface by being X-' (2) Realizing the embodiment of (1) 1. Continuous slab casting equipment having an electromagnetic stirring device, characterized in that it is installed so that the coil position can be changed according to the width of the slab.

(3) The coil dimensions are the maximum medium Lm of the applicable slab.
The method of (1) using electromagnetic stirring in which the wire connection can be changed to form a moving magnetic field in an approximately symmetrical section of %L depending on the slab width for each casting, or (
2) device.

(4) The electromagnetic coil is placed at the bottom of a mold with a water-cooled pure copper cooling surface, and a water-cooled non-magnetic steel shoe is placed directly or indirectly between the slab and the coil body. The device according to (2) above, characterized in that it is installed so that the distance to the slab is as short as possible.

(An injection method characterized in that when casting is performed while applying a unidirectional circulating flow in the method of 51(1), the molten metal injection flow is placed asymmetrically on the upstream side.

[Brief explanation of the drawing]

Figure 1A, the opening is a plan view and front view of a model experimental tank made of a low melting point alloy, which the inventor manufactured in order to understand the relationship between the coil position and the flow situation of the molten metal, and Figure 2A, the opening is the 1st opening. A chart showing the relationship between the flow velocity at measurement points A and H in the figure and changes in the coil position/height direction, Fig. 3 is an explanatory diagram showing an embodiment of the present invention, and Fig. 4 shows the agitation flow depending on the inside of the mold. FIG. 5 is a cross-sectional explanatory diagram showing an injection method for obtaining the stirring flow shown in FIG. 4, and FIG. 6 is a macroscopic structure diagram of a slab obtained by the present invention. A, B...measurement point, C...coil position, D...tank, E...
・Low melting point alloy, 1..Tandish, 2..Tandishka, 3..Vibration device, 4..Frame, 5..
Mold, 6. Lifting device, 7. Magnetizing [P device, 8. Apron frame, 9. Skid, 10. Guide roller, 11. Slab, 12. Molten metal surface, 13. Injection Flow, 1
4. Scum, 15-. Molten metal, 16.. Powder, 17
...Immersion nozzle.

Claims (1)

[Claims] (1) When applying a moving magnetic field that moves in the slab width direction to the slab hand 3AL using an electromagnetic coil that generates a moving magnetic field in continuous slab casting, the center position of the electromagnetic coil is below the surface of the molten metal in the mold ( 0,7～
1.3) An electromagnetic stirring device for continuous casting, characterized in that it is installed so as to be X-. (21% In the electromagnetic stirring device of claim 1,
The electromagnetic coil that generates the moving magnetic field is installed in sufficient contact with the mold, and the electromagnetic coil is movable so that the installation position in the slab advancement direction can be changed based on the conditions limited by the hook size. An electromagnetic stirring device for continuous slab casting, characterized in that it is installed.