JPH0824998B2 - Method and apparatus for manufacturing semi-solidified metal by electromagnetic stirring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an electromagnetic induction stirring method for a solid-liquid metal mixture in which non-dendritic primary crystals are dispersed in a metal melt (referred to as a semi-solid metal for simplicity). The present invention relates to a method and a device manufactured by.

As a method for producing a semi-solid metal, a mechanical stirring method and an electromagnetic induction stirring method are roughly classified. The electromagnetic induction stirring method (which is called electromagnetic stirring for simplicity) has a lower stirring efficiency than the mechanical stirring method, but has the advantage that it has less restrictions on equipment materials and high productivity. Has been done.

(Prior Art) Japanese Patent Publication No. 61-7148 and Japanese Patent Publication No. 62-25464 disclose methods for continuously or semi-continuously producing a metal slurry in a semi-solidified state by an electromagnetic stirring method, and the latter publication. Further discloses a device therefor.

The contents of these disclosures use electromagnetic stirring means for generating a rotating magnetic field by a two-pole motor stator or the like, and install a mold having a cooling means inside thereof, and supply molten metal from above into the mold to cool it at the same time. It is intended to obtain a metal slurry of a semi-solidified metal in which primary solid particles of dendrites which are agitated and degenerate are dispersed in a molten metal by rotating and flowing by a rotating magnetic field.

As conditions for producing a metal slurry in a good semi-solidified state here, strong cooling for obtaining sufficiently small solid particles and intense stirring strength for shearing dendrite are necessary. Since the two conditions are in conflict with each other, the above conventional method and apparatus are not always satisfactory.

(Problems to be Solved by the Invention) Problems with the conventional method and apparatus for producing semi-solidified metal by the electromagnetic stirring method will be described below.

(1) In order to produce a good semi-solid metal, it is necessary to give a strong stirring effect while cooling the molten metal.
Aiming for strong stirring, that is, high-speed rotation flow, with the electromagnetic stirring method,
Due to centrifugal force, a large vortex dent is generated on the surface of the molten metal at the center of the rotational flow, while the outer periphery becomes bulky, so the molten metal is scattered from the upper part of the cooling and stirring tank, and the entrainment of gas is increased. This makes stable operation impossible. Therefore, it is not possible to aim for a high-speed rotation flow, that is, a strong stirring effect.

(2) The central part of the rotational flow of the molten metal is rotating at high speed, but there is almost no stirring effect, and therefore the stirring effect in the cross section is non-uniform. In addition, there is a characteristic that the rotation speed, that is, the stirring effect depends on the viscosity of the molten metal, and when the apparent viscosity becomes high in a semi-solidified state, the stirring effect decreases, and there is no mixing effect especially at the center of rotation. The risk of segregation increases.

(3) In order to produce a good semi-solid metal, strong cooling is required to obtain sufficiently small solid particles, but in the case of the electromagnetic stirring system, the inner wall surface of the cooling stirring tank, that is, the area of the cooling wall, is required. On the other hand, since the internal volume is large, the heat capacity of the molten metal is large, and the heat generated by the electric current generated by the rotating magnetic field makes it impossible to increase the cooling rate too much.

When a water-cooled copper plate is used for the inner wall surface and strong cooling is performed, solidified shells adhere and grow on the inner wall surface, the magnetic flux of the rotating magnetic field is greatly attenuated, and the rotation speed, that is, the stirring effect is greatly reduced. There is a limit to increasing the cooling strength of the wall surface.

(4) The central part of the rotational flow of the molten metal in the electromagnetic stirring system, that is, the central part of the cooling stirring tank is a dead space for producing semi-solidified metal, which is harmful and useless.

As described above, the present invention aims to effectively solve the various problems remaining in the prior art, eliminates the scattering of molten metal, does not involve gas and the like, enhances the stirring and cooling effect, and stabilizes The priority item was to enable operation.

(Means for Solving the Problem) In order to solve the above-mentioned problems, it is most preferable to eliminate the molten metal in the central portion of the rotational flow of the molten metal, that is, the central portion of the cooling and stirring tank, which is hardly involved in the cooling and stirring effect. The present invention was achieved as a result of repeated experiments and studies, which were considered to be effective. The summary is as follows.

1. The molten metal is stored in a cooling and stirring tank, and while cooling by heat removal from the inner wall surface of the cooling and stirring tank, stirring is performed by rotating and flowing the molten metal by a rotating magnetic field that operates across the cross section of the cooling and stirring tank. In addition, in the method for producing semi-solidified metal, the molten metal is swirled between the outer wall surface of the non-magnetic and non-conductive core provided at the center of the cooling and stirring tank and the inner wall surface of the cooling and stirring tank. A method for producing a semi-solidified metal by an electromagnetic stirring method, which comprises:

2. A cooling and stirring tank having a means for cooling the molten metal and an electromagnetic induction coil that generates a rotating magnetic field that works across the cross section of the cooling and stirring tank are provided, and the molten metal supplied into the cooling and stirring tank is rotated by the rotating magnetic field. An apparatus for producing a semi-solid metal by an electromagnetic stirring method, characterized in that a non-magnetic, non-conductive core is provided in a central portion of a cooling and agitating tank in an apparatus for producing a semi-solid metal which is agitated by forcing a flow.

In the above method, it is preferable in practice that the swirling flow of the molten metal includes a displacement flow due to the up-and-down movement of the core, and the above-mentioned device enables the core to be repeatedly moved up and down in the cooling and stirring tank. It is preferable that the core is rotatably supported and fixed via a torque meter, and that the outer diameter of the core is within the range of 30 to 60% of the inner diameter of the cooling and stirring tank with a cylindrical core. .

The shape of the inner wall surface of the cooling stirring tank is preferably cylindrical.
The outer wall of the core is basically cylindrical, but other shapes may be used to improve the stirring effect, and the position of the core does not always coincide with the center axis of the cooling stirring tank and the center axis of the core. You don't have to.

(Operation) In the present invention, when the semi-solidified metal is manufactured by cooling the molten metal and stirring by the rotational flow in the rotating magnetic field, the non-magnetic, Molten metal is excluded from the dead space at the center of rotation by providing a core of non-conductive material, such as refractory or ceramic.

By doing so, the molten metal is stirred by the swirling flow between the outer wall surface of the core and the inner wall surface of the cooling stirring tank. The rotation speed of this swirling flow is smaller than when the core is not used, but the vortex dent on the surface of the molten metal is reduced to a practical range, stable operation is possible without the molten metal scattering, and an appropriate size is achieved. It was also clarified that by selecting the core, the stirring effect does not decrease even though the rotation speed decreases. Also, by moving the core up and down, the mixing and stirring by the displacement flow is performed,
A homogeneous semi-solid metal can be produced.

Next, the first embodiment of the apparatus for producing semi-solidified metal according to the present invention
It will be described with reference to the drawings. Figure 1 is an overall view, and the cooling and stirring tank is
It is composed of a cooling cylinder 2 and a water cooling jacket 3, and an electromagnetic induction coil 4 is installed on the outer circumference thereof. The cooling cylinder 2 and the water cooling jacket 3 are made of a thin non-magnetic metal plate in order to minimize the attenuation of the magnetic flux penetrating therethrough. The cooling water 13 is supplied from the lower portion, the outer surface of the cooling cylinder 2 is passed through at a high speed, and the draining water 13 is discharged from the upper portion, so that an appropriate cooling effect is provided. The inner wall surface of the cooling cylinder 2 may be coated with a refractory material having an appropriate thickness.
In many cases, the stator coil of a two-pole three-phase induction motor is used as the electromagnetic induction coil 4, and a rotating magnetic field penetrating the center is obtained by energizing a three-phase alternating current 14, and a rotating torque proportional to the magnetic flux density. Thereby, the molten metal in the cooling stirring tank is rotatively flowed and stirred.

A hot water receiving tundish 1 lined with a refractory material 1'is connected to the upper end of this cooling and stirring tank, and a discharge nozzle 5 is provided at the bottom.
Is provided.

Next, a core 6 made of a non-magnetic non-conductive material such as a refractory material is provided at the center of the cooling and stirring tank. It is preferable that the core 6 is rotatably supported by a support arm 8 via a bearing 7 as shown in the drawing, and the support arm 8 is mounted on a support base 11 so as to be capable of moving up and down via a lifting means such as a hydraulic cylinder 12.

Further, it is preferable that the core 6 is connected and fixed to the torque meter 10 via the connecting shaft 9.

Now, the molten metal 15 is continuously supplied to the hot water receiving tundish 1 and flows into the cooling and stirring tank. This molten metal is being stirred by an appropriate cooling action in the cooling and stirring tank and is swirling between the outer wall surface of the core and the inner wall surface of the cooling stirring tank by the rotating magnetic field generated by the electromagnetic induction coil 4 and is being generated. The dendritic primary crystals are converted into a rounded form by disappearing or reducing the branches, and the semi-solidified metal 15 'is continuously discharged from the discharge nozzle 5 at the bottom. In this case, core 6
May be fixed at a fixed position, but may be moved up and down for the purpose of promoting mixing and stirring by the displacement flow. It is also possible to measure the viscous torque of the semi-solidified metal 15 ′ acting on the core by the torque meter 10 directly connected to the core 6 to estimate the properties and stirring condition of the semi-solidified metal.

When the operation is completed, the core 6 is retracted upward by the hydraulic cylinder 12 via the support arm 8, and the support arm 8 is further swung to facilitate maintenance and inspection of the cooling and stirring tank.

Next, the characteristics of the stirring action will be described. FIG. 2 is a principle diagram showing the stirring action of the conventional electromagnetic stirring system, and FIG. 3 is a principle diagram showing the stirring action of the electromagnetic stirring system according to the present invention, and FIG. 4 is a graph showing the stirring effect numerically. In FIGS. 2 and 3, the cooling and stirring tank composed of the metal cooling cylinder 2 and the water cooling jacket 3 and the electromagnetic induction coil 4 arranged on the outer circumference thereof are common, but in FIG. 3, the core 6 is cooled. It is in the stirring tank. In the conventional apparatus shown in FIG. 2, the stronger the stirring by the rotating magnetic field, the more molten metal in the cooling stirring tank.
15 rotates at a high speed, and its rotation speed (Ω) becomes maximum at the center as shown in Fig. 4, and a large vortex dent (H _o ) is generated at the center by the centrifugal force. If this vortex dent (H _o ) becomes too large, problems such as the scattering of molten metal from the upper part of the cooling and stirring tank and the entrainment of gas will occur, and it will not be practically applicable. Although the central portion rotates at a very high speed, it has a drawback that the shearing force necessary for changing the dendrites is small, that is, there is almost no stirring effect. Therefore, in the present invention, as shown in FIG. 3, a core 6 made of a refractory material having a cylindrical shape with a radius r _{1 is provided in} the center of the cooling and stirring tank. When the rotating magnetic field having the same strength as that of the conventional method is applied to the method of the present invention, the rotational speed (Ω) of the swirling flow generated in the molten metal 15 is different between the inner wall surface of the cooling cylinder 2 and the outer wall surface of the core 6. It becomes 0, and the maximum rotation speed also decreases.
Therefore, vortex dent due to centrifugal force (H _o becomes considerably small,
Practical problems are solved. And the stirring effect generated in the cross section, that is, the shear stress, is
Even though the rotation speed is low, the average value in the cross section is almost the same, which means that the stirring effect is effectively given.

In the electromagnetic stirring method, the rotating speed of the molten metal or the semi-solidified metal, that is, the stirring effect itself, is the viscosity of the molten metal or the semi-solidified metal because the molten metal itself rotates by the rotational force of electromagnetic induction generated in the molten metal. Although it is difficult to grasp the rotation speed, that is, the stirring effect, it is possible to estimate the stirring effect from the viscous torque by the torque meter directly connected to the core 6, which is a great advantage of the present invention. Is.

Next, the relationship between the inner diameter of the cooling stirring tank (cooling cylinder 2) and the outer diameter of the core for giving an effective stirring effect will be described.
A rotating magnetic field of 600 Gauss is applied to a cooling stirring tank with an inner diameter of 170 mm,
Figures 5 (a), 5 (b) and 6 show the calculation results when the center axis of the inner surface of the cylinder of the cooling and stirring tank and the center axis of the outer surface of the cylinder of the core are aligned and the core is provided in the cooling and stirring tank. Show. 5 (a) and 5 (b) respectively show the core radius and the shear strain rate on the inner wall surface of the cooling and stirring tank and the outer wall surface of the core with the solid fraction f _s as a parameter, and FIG. 6 shows the core radius. the relationship between the vortex dent H _o in the core outer wall surface showed solid fraction f _s as a parameter. The shaded area in these figures shows the optimum core radius range where the vortex dent is small and is practical, and the shear strain rate is large. In this range, the outer diameter of the core is 30 to 60 of the cooling stirring tank inner diameter. Equivalent to%.

(Example) A case will be described in which a rotating magnetic field having a central magnetic flux density of 800 gauss is generated by a 2-pole 3-phase stirring coil in a cylindrical cooling stirring tank having an inner diameter of 170 mm (r ₂ = 85 mm).

In the conventional method, the rotation speed of the molten metal is 10 at maximum at the center.
00r.pm next, eddy dent H _o of the rotation center portion reaches 1200 mm.

On the other hand, in the method of the present invention provided with a cylindrical core having an outer diameter of 100 mm (r ₁ = 50 mm), the rotation speed of the molten metal becomes maximum at the midpoint between the outer surface of the core and the inner surface of the cooling stirring tank.
about rpm, the maximum indentation H _o in the core surface is depleted in 70 mm, it has become possible stable operation.

Furthermore, when the theoretical estimation calculation is performed by expressing the stirring effect in terms of shear strain rate, in the case of the conventional method, the center of rotation becomes 0 at a maximum of 250 sec ⁻¹ on the inner surface of the cooling stirring phase, whereas in the case of the method of the present invention, It was clarified that a maximum of 230 sec ^-1 is generated on the inner wall surface of the cooling and stirring phase and the outer wall surface of the core, which gives an effective stirring effect.

(Effects of the Invention) The following effects are expected by using the method and apparatus of the present invention in the production of semi-solidified metal by the electromagnetic stirring method.

(1) Vortex dents are small even when agitated by a powerful swirling flow, and there is no danger of molten metal splashing from the upper part of the cooling and stirring tank, and stable and practical operation is possible.

(2) For the same rotating magnetic field, the stirring effect is almost the same even if the rotating speed is reduced. Rather, in the conventional method, the rotating center portion becomes a dead space with almost no stirring effect. A uniform stirring effect can be obtained.

(3) The amount of molten metal corresponding to the volume of the core in the molten metal is eliminated, and the heat capacity corresponding to this is reduced, so the cooling rate of the molten metal is improved even with the same cooling capacity, and the semi-solidified metal with a smaller particle size is used. Can be manufactured.

As described above, the present invention is very useful for practical application of semi-solidified metal production by the electromagnetic stirring system.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the entire structure of the present invention in cross section, FIG. 2 is a principle diagram showing the stirring action of a conventional electromagnetic stirring system, and FIG. 3 is a principle diagram showing the stirring action of the electromagnetic stirring system according to the present invention. Fig. 4 is a graph showing the stirring effect of the conventional method and the present invention in numerical form, and Figs. 5 (a) and 5 (b) are core radii and shear strains on the inner wall surface of the cooling stirring tank and the outer wall surface of the core. Relationship with speed,
FIG. 6 is a graph showing the relationship between the core radius and the vortex depression. 1 ... Receiving hot water tundish 1 '... Lined refractory material 2 ... Cooling cylinder 3 ... Water cooling jacket 4 ... Electromagnetic induction coil 5 ... Discharge nozzle, 6 ... Core 7 ... Bearing, 9 ...... Coupling shaft 10 …… Torque meter, 11 …… Support base 12 …… Hydraulic cylinder

Claims (6)

[Claims] 1. A molten metal is contained in a cooling and stirring tank, and while being cooled by removing heat from the inner wall surface of the cooling and stirring tank, the molten metal is rotatively fluidized by a rotating magnetic field that operates across a cross section of the cooling and stirring tank. In the method of producing semi-solidified metal by adding the stirring by the method, the molten metal is swirled between the outer wall surface of the non-magnetic and non-conductive core with the central portion of the cooling stirring tank and the inner wall surface of the cooling stirring tank. A method for producing a semi-solid metal by an electromagnetic stirring method, which is characterized by flowing. 2. The method for producing a semi-solid metal by electromagnetic stirring according to claim 1, wherein the swirling flow of the molten metal includes a displacement flow caused by a lifting motion of the core. 3. A cooling and stirring tank having a means for cooling the molten metal, and an electromagnetic induction coil for generating a rotating magnetic field that works across the cross section of the cooling and stirring tank, and rotating the molten metal supplied into the cooling and stirring tank. In a semi-solid metal manufacturing apparatus that applies stirring by forcing a rotational flow by a magnetic field, a semi-solid metal is manufactured by an electromagnetic stirring method characterized by having a non-magnetic, non-conductive core in the center of a cooling and stirring tank. apparatus. 4. An apparatus for producing a semi-solid metal by an electromagnetic stirring system according to claim 3, wherein the core is arranged so as to be able to repeatedly move up and down in the cooling stirring tank. 5. An apparatus for producing a semi-solidified metal by an electromagnetic stirring system according to claim 3 or 4, wherein the core is rotatably supported and is fixed via a torque meter. 6. The core according to claim 3, wherein the core has a cylindrical shape and the outer diameter thereof is in the range of 30 to 60% of the inner diameter of the cooling and stirring tank.
An apparatus for producing a semi-solid metal by the electromagnetic stirring method described in the item 4, item 4 or item 5.