JP5691353B2 - Continuous casting mold - Google Patents

Description

  The present invention relates to a continuous casting mold (mold) of steel, and more specifically to a continuous casting mold for continuously casting steel while applying electromagnetic force to molten steel injected into the mold by an electromagnetic stirring device. It is.

  A mold (mold) that continuously casts molten steel to form a slab that is a steel material is disposed so as to be capable of varying the facing distance between a pair of opposed long-side mold copper plates and the long-side mold copper plates. A mold inner wall composed of a pair of short-side mold copper plates, and a steel mold frame applied to the outside of each of the long-side mold copper plates and the short-side mold copper plates. In general, a cooling slit is formed on the back surface (mold frame side), and cooling water is introduced therein to cool the mold copper plate.

  Also, recently, in order to improve the quality of continuously cast slabs, an electromagnetic stirrer was installed in the continuous casting mold, and Lorentz force (electromagnetic force) was applied to the molten steel, which was injected into the mold from the immersion nozzle. Brake is applied to the molten steel discharge flow, or the molten steel in the mold is agitated to promote the floating of inclusions. In addition, in the said electromagnetic stirring apparatus, there exist what uses an alternating current as a current to apply, and a thing using a direct current.

  In the case of a continuous casting mold for slabs, the electromagnetic stirring device is arranged along the mold copper plate 1 inside the long side mold frame 2 having a U-shaped cross section (box shape) as shown in FIG. Usually, an electromagnetic coil 3 is installed so that an electromagnetic force is applied to the molten steel 4 in the mold. However, in the conventional continuous casting mold, from the viewpoint of securing the mold rigidity, the mold frame in contact with the mold copper plate 1 is made thick, and the electromagnetic coil and the mold copper plate are largely separated from each other. The magnetic force emitted from the coil was attenuated, and sufficient stirring force for molten steel was not obtained. Therefore, along with the stricter demands for steel quality in recent years, there has been a demand for further improvement in the capacity of the electromagnetic stirring device.

  As a method for improving the electromagnetic stirring ability, it is conceivable to increase the size and power of the stirring device, but there is a limit due to space limitations of installing in the mold frame of the mold. Therefore, it has been studied to reduce the attenuation of magnetic force by installing the electromagnetic coil of the electromagnetic stirring device closer to the molten steel. However, in order to bring the electromagnetic coil closer to the molten steel, it is necessary to reduce the distance between the mold copper plate and the electromagnetic coil. For this purpose, it is necessary to reduce the thickness of the mold frame existing between the mold copper plate and the electromagnetic coil. is there.

  Here, since the mold frame plays a role of reinforcing the deformation due to the static iron pressure that the mold copper plate receives from the molten steel and the thermal strain due to the molten steel from the back, reducing the thickness of the steel material that constitutes the mold frame, This causes a serious problem that the mold strength (rigidity) is reduced. As a technique for solving this problem, Patent Document 1 discloses that a reinforcing rib (reinforcing material) having a thickness of 60 mm is disposed inside a mold frame on the back surface of a long side mold copper plate, and between the reinforcing materials. A technique for reducing the thickness of the mold frame without lowering the rigidity of the long-side mold frame is disclosed by installing an electromagnetic coil.

JP 2009-279599 A

  By installing the reinforcing material in the mold frame, it is possible to maximize the capability of the electromagnetic stirring device without increasing the size of the electromagnetic stirring device and increasing the output. However, according to the investigation by the inventors, when the reinforcing material is installed, the magnetic flux generated from the electromagnetic coil also flows to the reinforcing material, and an eddy current is generated inside the reinforcing material and the reinforcing rib generates heat. In particular, the heat generation is large when electromagnetic stirring is performed using an alternating current in which magnetic flux easily flows through the reinforcing material, and the heat generation temperature rises as the number of charges continuously cast increases, sometimes from 500 ° C. to 700 ° C. It has become clear that it may be heated to a temperature of ° C.

  When the above heat generation of 500 ° C. or more is repeatedly caused, the reinforcing material repeats thermal expansion and contraction, and as a result, the joint portion of the reinforcing material attached by welding inside the mold frame is destroyed and peeling occurs. As a result of the mold frame supporting the mold copper plate being deformed under the influence of thermal expansion and contraction of the reinforcing material or the flatness of the mold copper plate itself being lost, there arises a problem that the mold life is remarkably reduced.

  The present invention has been made in view of the above problems of the prior art, and its purpose is to prevent the breakage and deformation of the continuous casting mold by extending the temperature of the reinforcing material to extend the mold life. At the same time, it is to stably realize a continuous casting operation that maximizes the electromagnetic stirring ability.

  The inventors have conducted intensive studies on means for solving the above problems. As a result, it has been found that it is desirable to cool the reinforcing material installed inside the mold frame by providing a cooling device, and it is desirable that the temperature of the reinforcing material is preferably 200 ° C. or less by the cooling device, and the present invention is completed. It came to do.

That is, the present invention provides a mold inner wall composed of a long-side mold copper plate arranged opposite to each other and a short-side mold copper plate arranged oppositely between the long-side mold copper plate, and the respective mold copper plates constituting the mold inner wall. A cross-section composed of a side plate, an upper plate and a lower plate disposed outside the U-shaped mold frame is installed inside the U-shaped mold frame , and the upper plate. In a continuous casting mold having an electromagnetic stirring function composed of a reinforcing material joined to the lower surface plate and an electromagnetic coil disposed in a portion excluding the reinforcing material in the mold frame, cooling water is jetted from the nozzle to the reinforcing material. And a continuous casting mold characterized in that a cooling device for directly cooling is provided.

  The water cooling device provided in the continuous casting mold of the present invention is characterized in that the temperature of the reinforcing material is cooled to 200 ° C. or lower.

  According to the present invention, it is possible to suppress the temperature rise of the reinforcing material in the continuous casting mold having the electromagnetic stirring device in which the mold frame of the continuous casting mold is thinned and the electromagnetic coil is brought close to the molten steel. Since the maximum electromagnetic force can be applied to the molten steel without being damaged or deformed, a high quality steel material can be stably manufactured.

It is a figure explaining the continuous casting mold which has the conventional electromagnetic stirring apparatus. It is a figure explaining the continuous casting mold which has an electromagnetic stirrer of patent documents 1. It is a graph which shows the relationship between the number of continuous casting charges, and the temperature of a reinforcing material. It is a figure explaining the temperature measurement position of a reinforcing material. It is a figure explaining one Example of the continuous casting mold of this invention. It is a graph which shows the change of the temperature of the reinforcing material by the presence or absence of water cooling.

Embodiments of the present invention will be described below.
FIG. 2 schematically shows the continuous casting mold disclosed in Patent Document 1. As shown in FIG.
The electromagnetic coil 3 of the electromagnetic stirring device is installed inside the mold frame 2 so as to sandwich a pair of long-side mold copper plates 1 constituting the inner wall of the mold from both sides. The electromagnetic coil 3 generates a high-output magnetic force at a low frequency, and this is applied to the continuous casting material (molten steel) 4 to control the molten steel flow discharged from the immersion nozzle, It stirs and promotes the floating of inclusions in the molten steel.
In the mold shown in FIG. 2, reinforcing ribs (reinforcing materials) 5 that are joined to the upper surface plate 2 a and the lower surface plate 2 b are further arranged inside the mold frame 2, and divided between the reinforcing materials 5. An electromagnetic coil is provided. Thus, the side plate 2c on the molten steel surface side (mold copper plate side) of the mold frame 2 is thinned to bring the electromagnetic coil closer to the molten steel, thereby improving the stirring function and preventing the mold rigidity from being lowered due to the thinning.

  The mold frame 2 and the reinforcing material 5 are manufactured using steel such as SUS304 in order to ensure strength. Therefore, in the case of continuous casting with electromagnetic stirring using the continuous casting mold used in FIG. 2, the magnetic flux generated from the electromagnetic coil is not only in the molten steel 4 but also on the side of the reinforcing material 5 installed between the electromagnetic coils. An eddy current flows and flows, and the temperature of the reinforcing material 5 rises by induction heating.

  FIG. 3 is a view showing the relationship between the electromagnetic coils 3 when the continuous casting mold shown in FIG. 2 is used and continuous charging of 4 charges is performed while applying an AC magnetic field at a frequency of 3.5 Hz and an AC current of 1000 A while performing electromagnetic stirring. The temperature change of the installed reinforcing material 5 shows the result of having installed the thermocouple in the position of AC shown in FIG. 4, and measuring it. From this figure, after 4 charges, the maximum reached temperature of the reinforcing material has reached 500 ° C, and if the number of charges further increases or the frequency and current value of electromagnetic stirring are further increased, the temperature further increases. Was expected to rise.

  When heating and cooling are repeated as described above, thermal fatigue due to thermal expansion and contraction causes peeling of the joint between the reinforcing material and the mold frame (welded part) or deformation of the mold frame due to thermal strain. As a result, the flatness of the mold copper plate is impaired, and normal casting cannot be performed. As a result, not only the mold life is reduced, but also the surface quality and internal quality of the cast slab are adversely affected.

Therefore, the present invention proposes to install a cooling device in the heat generating portion of the reinforcing material in order to suppress the temperature rise of the reinforcing material.
FIG. 5 is a schematic view showing a continuous casting mold according to one embodiment of the present invention, in which nozzles are installed on both sides in the vicinity of the portion C (see FIG. 4) of the reinforcing material having the largest temperature rise in FIG. Cooling water is ejected from this nozzle to achieve cooling.

  The cooling device is preferably capable of cooling the maximum reached temperature of the reinforcing material to 200 ° C. or lower. This is because if it is 200 ° C. or lower, the adverse effects due to thermal expansion are negligible. More preferably, it is 150 degrees C or less.

  The cooling device is not particularly limited in type and type as long as the temperature of the reinforcing material can be cooled to 200 ° C. or lower. Therefore, the method is not limited to the method of directly cooling the nozzle by ejecting the cooling water as described above. For example, a water-cooled pipe is provided on the surface of the reinforcing material to indirectly cool, or the mold copper plate is cooled. As described above, a groove for flowing cooling water may be provided inside the reinforcing material so that the cooling water flows. Further, the cooling medium is not limited to water.

It has a cross-sectional area of a maximum casting width of 2000 mm and a thickness of 260 mm. Continuous casting is performed using the continuous casting mold of the present invention shown in FIG. 5, and cooling water is ejected from the water-cooling nozzle shown in FIG. The temperature change of the reinforcing material was measured when cooled and not cooled. During continuous casting, an alternating current of 600 A was applied to the electromagnetic stirrer at a frequency of 3.4 Hz, and the magnetic flux density on the long side mold copper plate surface at this time was 450 gauss. The temperature of the reinforcing material was measured at the position C in FIG.
As a result of the above measurement, as shown in FIG. 6, when the reinforcing material was not cooled, the temperature of the reinforcing material rose to 600 ° C. or higher, but the cooling device (water cooling nozzle) of the present invention should be used. Thus, it was confirmed that the temperature of the reinforcing material can be maintained at 200 ° C. or lower.

  The technique of the present invention can be applied to any type of continuous casting mold such as a curved type or a vertical type as long as it is an electromagnetic stirring device that electromagnetically stirs molten steel in the mold described above. Further, the technology of the present invention is not limited to a continuous casting mold for slabs, but can be applied to a continuous casting mold for bloom or billet.

1: Mold copper plate 2: Mold frame 2a: Upper surface plate of mold frame 2b: Lower surface plate of mold frame 2c: Side plate of mold frame 3: Electromagnetic coil of electromagnetic stirrer 4: Cast material (molten steel)
5: Reinforcing material (reinforcing rib)
6: Cooling device (water cooling nozzle)

Claims (2)

A mold inner wall composed of a long-side mold copper plate and a short-side mold copper plate arranged opposite to each other,
A mold frame having a U-shaped cross-section composed of a side plate, an upper surface plate and a lower surface plate, disposed on the outer side of each mold copper plate constituting the mold inner wall;
Installed inside the shape of the mold frame of the co and a reinforcing member joined to the top plate and bottom plate,
In a continuous casting mold having an electromagnetic stirring function composed of an electromagnetic coil disposed in a portion excluding the reinforcing material in the mold frame,
A continuous casting mold, wherein the reinforcing member is provided with a cooling device that directly cools the nozzle by cooling water from a nozzle. The continuous casting mold according to claim 1, wherein the water cooling device cools the temperature of the reinforcing material to 200 ° C or lower.

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