JPS5842780B2 - Electromagnetic stirring method and device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method and device for stirring molten metal such as molten steel in a mold, and an electromagnetic stirring method and device using permanent magnets that are excellent not only in stirring power but also in removing inclusions from molten steel. Regarding.

Generally, center segregation and center porosity are observed in slabs produced using continuous casting machines.

This is affected not only by metallurgical factors but also by mechanical factors of the casting machine, and the main cause is said to be insufficient supply of molten steel due to so-called bridging that occurs during solidification of molten steel.

It is known that electromagnetic stirring is extremely effective in solving these problems.

That is, the solidified tip of the slab is fluidly stirred, the bridge is forcibly separated by the stirring flow, the supply of molten steel is completed, and the number of equiaxed crystals can be increased, thereby reducing segregation and center porosity.

Furthermore, inclusions are internal defects in slabs, and they are classified into large spherical Mn silicate-based inclusions and alumina clusters based on their morphology.

This electromagnetic stirring is also said to be effective against inclusions.

In the well-known induced rotating magnetic field method using electromagnets, molten steel is rotated and flowed in a plane perpendicular to the drawing direction, and inclusions with small specific gravity are inevitably drawn to the center of the slab, resulting in solidification due to the flow. Combined with the cleaning effect on the interface, it is effective in removing inclusions directly under the epidermis.

In general, inclusions collected at the center of a slab tend to aggregate, become coarse, and float, so electromagnetic stirring is effective.

However, in reality, there are few cases in which the floating speed of coarse inclusions is faster than the drawing speed of the slab, and most of the inclusions remain without being removed, resulting in quality problems when the resulting slab is turned into a product. may occur.

In an electromagnetic stirring device using an induced rotating magnetic field, the electromagnet that generates the alternating current rotating magnetic field is large, so the equipment is large and expensive, and it may not be possible to install it depending on the size of the continuous casting machine.

In addition, there is a limit to the penetration depth of induced current in molten steel, and in the case of large molds, a low frequency converter is used to convert the current to several Hz.
The equipment is expensive due to the need to use low frequencies.

Furthermore, the loss in the coil and iron core of the power consumed is large and is extremely uneconomical.

This invention proposes an electromagnetic stirring method that provides rotational flow and simultaneous convection to molten steel in a mold in a continuous casting machine, and is highly effective in reducing center segregation and center porosity of slabs and removing inclusions. The equipment used to carry out this method has a simple configuration, can be manufactured compactly and at low cost, and the magnetic field at the center of the mold is strong, allowing sufficient stirring force to be obtained even at low speed rotation. Intended as an electromagnetic stirring device.

That is, the gist of this invention is to install a spirally magnetized permanent magnet around a mold, rotate it in the circumferential direction of the mold, and apply a rotating magnetic field and a traveling magnetic field depending on the rotation angle of the magnet to the molten metal in the mold. This is an electromagnetic stirring method and device that is excellent in removing inclusions.

The method of this invention will be explained below based on the drawings.

This electromagnetic stirring method involves installing a permanent magnet around the mold so that the magnetic flux that crosses the mold changes its position in a spiral pattern in the vertical direction of the mold, changing the direction of the magnetic flux, and rotating the permanent magnet in the circumferential direction of the mold. , a rotating magnetic field caused by magnetic flux crossing the mold and a traveling magnetic field caused by the rotation angle of the magnet are applied to the molten metal in the mold.

Any magnet having the above-mentioned structure can be used as the permanent magnet, and for example, a single spiral permanent magnet or a spirally magnetized cylindrical magnet can be used.

In the latter case, magnets 1 are spirally attached to the inner surface of a cylinder made of non-magnetic material, and when it is unfolded, one strip of magnet 1 appears alternately with 2 parts of non-magnetic material and traverses the cylinder, as shown in Figure 1. produces a unidirectional magnetic field.

Furthermore, a member (spacer) made of a non-magnetic material may be inserted into the space between the spiral magnets to form a cylindrical shape.

It is also possible to use a cylindrical magnet in which two magnet strips are magnetized in a spiral manner so that the non-magnetic material portions appear alternately, and the same applies even if there are multiple strips.

Next, the magnetic flux at a certain point P on the circumferential surface of the cylindrical magnet moves by rotating the cylindrical magnet in the circumferential direction φ and the axial direction Z, and a traveling magnetic field is generated due to the progress of the rotating magnetic field and the rotation angle. (Figure 2).

Therefore, the slab 3 surrounded by the magnet 1 is given a rotational force by the rotating magnetic field and a convection by the traveling magnetic field, and the inclusions in the molten steel are given this lifting force and obtain a floating speed that is higher than the drawing speed of the slab. surface.

Therefore, according to this electromagnetic stirring method, bridging can be prevented by rotational force, center segregation and center porosity can be reduced, and a sufficient floating speed can be given to inclusions by the traveling magnetic field, resulting in an excellent effect in removing inclusions. be able to.

Next, an example of an electromagnetic stirring apparatus for carrying out the method of this invention will be explained based on the drawings.

FIG. 5 is a longitudinal sectional view of the continuous casting machine.

To explain the case where a rotating permanent magnet is provided in the cooling zone of a continuous casting machine, a cooling water channel surrounds the outside of the mold 4 and water is sent from a lower cooling water port 10a to an upper cooling water outlet 10b. A rotating permanent magnet is provided around the band.

For the permanent magnet 1, here, a spacer made of a suitable non-magnetic material is used to fill in the space between the spiral magnets to form a cylinder, and a yoke 5 is provided on the outer periphery of the cylinder. The permanent magnet is supported by a bearing 7 to enable rotation of the entire permanent magnet.

It is also advisable to attach a protective ring made of a non-magnetic material to the inner surface of the permanent magnet 1 for protection.

The lower end of the yoke 5 holding the permanent magnet 1 is supported by a bearing 7, and the bearing 7 is provided on the floor above the mold mount 11.

As the rotation mechanism of the permanent magnet 1, a mechanism consisting of a spur gear 6 provided on the outer periphery of the yoke 5 and a motor 8 that drives a driving gear 9 that meshes with the spur gear 6 can be used. Various drive mechanisms can be used.

An electric motor, a hydraulic motor, etc. can be used as the motor.

The hot water level 12 is shown for reference.

As described above, the electromagnetic stirring device according to the present invention is installed by changing its structure depending on the type, size, etc. of the continuous casting machine and the installation location.
By adopting a driving configuration, it has the same functions and effects as the above-mentioned invention device.

Next, an example according to the present invention will be shown to clarify its effects.

The electromagnetic stirring device of the present invention, which consists of a rotating permanent magnet having the above-mentioned configuration and its rotational drive device, is used for a 180 mm diameter billet, 4 mm.
Installed in continuous strand casting machine.

The spirally magnetized cylindrical permanent magnet has an inner diameter of 360 mm.
A 5US304 material was used for the spacer with an outer diameter of 440 m1φ to fill between the spiral magnets, and a 5S41 material was used for the yoke, with a total outer diameter of 520 mm and a height of 300 mm.

The magnet is a samarium cobalt magnet with a maximum energy product of 2
0 MGOe and a magnetic flux density of 980 G at the center of the magnet were used, and the driving rotation speed was 100 to 25 Orpm.

Using this continuous casting machine, two of the strands were subjected to electromagnetic stirring according to the method of the present invention, and the remaining two strands were cast without stirring at a drawing speed of 1.5 m/min.

The composition of molten steel in weight% is C0.43% S
i0.27% Mn 0.65% P 0.019%so, oio
% 5olAl 0.029% balance Fe.

Test pieces were cut out from the billet positions corresponding to the casting amounts of 10t and 30t of the latter strands at the start of casting, and the macrostructure,
The component segregation and number of inclusions were investigated.

As a result, the interior of the cast slab subjected to electromagnetic stirring using the apparatus of this invention (Fig. 6a) became almost equiaxed crystals, and the reduction of center segregation and the disappearance of center porosity showed great effects.

On the other hand, in the conventional non-stirred material, there were few equiaxed crystals and most of the crystals were columnar crystals (Fig. 6b).

Regarding center segregation, FIG. 4 shows a graph of the component ratios (wt%) of S and C from the surface of the slab to the center.

In the figure, line A is the unstirred material, and line B is the slab that has been stirred by the method and apparatus of the present invention, and it can be seen that center segregation has been significantly reduced.

Further, the number of inclusions decreased from 13/m' in the non-stirred material to 2/m' in the stirred material produced by the method of the present invention, which indicates that the method of the invention is superior in removing inclusions.

In addition, in the conventional stirring device using an electromagnet, the magnetic field at the center was about 4000 at most, but with the device of the present invention, not only can it easily obtain a magnetic field of <IKG or more as shown in the above embodiment, but also its configuration is Due to its simplicity, it could be made small and inexpensive.

As described above, the electromagnetic stirring method according to the present invention uses a simple device in which a spirally magnetized permanent magnet is placed around the mold and rotated in the circumferential direction. This electromagnetic stirring method is excellent in improving the quality of slabs because it provides a rotational force that is effective for eliminating inclusions and a convection stirring force that is effective for removing inclusions.

[Brief explanation of drawings]

Fig. 1 is a developed view of a cylindrical permanent magnet according to the present invention, Fig. 2 is a schematic diagram showing changes in the magnetic field due to rotation of the permanent magnet,
Fig. 3 is a schematic diagram showing the stirring flow of molten steel by the method of the invention, Fig. 4 is a graph showing the center segregation of the slab, Fig. 5 is a vertical cross-sectional view showing an example of the inventive device, and Fig. 6 is the slab This is a cross-sectional macrostructure diagram, in which the x mark indicates an equiaxed crystal region and the surrounding area indicates a columnar crystal region, the same figure a shows the case of a stirred material, and the same figure shows the case of a non-stirred material. In the figure 1... Permanent magnet, 2... Non-magnetic material, 3... Slab, 4... Mold, 5... Yoke, 6... Spur gear, 7
... bearing, 8 ... motor, 9 ... drive gear, 10a ... cooling water inlet, 10b ... cooling water drain, 11 ... mold mount, 12 ... hot water surface.

Claims (1)

[Claims] 1. A spirally magnetized permanent magnet is installed around the mold,
An electromagnetic stirring method in which the molten metal in the mold is rotated in the circumferential direction of the mold, and a rotating magnetic field and a traveling magnetic field due to the rotation angle of the magnet are applied to the molten metal in the mold. 2. An electromagnetic stirring device consisting of a mechanism in which a spiral permanent magnet or a spirally magnetized cylindrical permanent magnet is arranged around a mold and is rotatable in the circumferential direction of the mold.