JPS5935865A - Electromagnetical casting of metal - Google Patents

Abstract

1. A process for the casting of metals wherein one electromagnetic confinement field generated by the inductor (3) applied to the liquid metal (2) and a stationary magnetic field generated by an annular coil (7) and a variable magnetic field generated by an annular coil (8) both applied above the level of liquid metal are caused to act simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a confining magnetic field.
It relates to an electromagnetic metal casting method in which at least one magnetic field different from the ment) is applied.

The fact that steel ingots or aluminum ingots can be formed by electromagnetic casting is disclosed in French Patent No. 1.509.
Already known from No. 962.

This technique uses an annular inductor to generate an alternating electromagnetic field around a molten metal column, but under the action of such a magnetic field, a centripetal force is generated within the metal, causing the metal to flow (5talement). It will have a specific geometric form without being

The encapsulated metal in this way (metal conf
When the metal is cooled with a suitable coolant, the metal solidifies according to the shape imposed by the magnetic field.

In contrast to conventional casting methods, solidification in this case does not take place by contact with the mold walls, but without any contact with the solid material.

This generally results in ingots with a better surface condition, and in some cases these ingots can also be directly deformed without special surface treatments such as scalpage.

However, the aforementioned techniques are not without drawbacks. In fact, it has been found that the enclosed electromagnetic field creates vortices and agitates the liquid metal excessively. This phenomenon destabilizes the crystallization process during cooling, resulting in a non-uniform structure and irregular particle shapes.

This phenomenon also causes pinholes on the surface of the ingot, due in part to the breakdown of the oxide film covering the metal, dispersing particles of this film throughout the still liquid metal.

The applicant has sought a method of eliminating the above-mentioned drawbacks while keeping in mind the advantages of this electromagnetic casting method.

As a result of many experiments, the present applicant has developed a casting method in which at least one magnetic field different from the enclosed variable magnetic field is applied.

This method is characterized by simultaneously applying a steady magnetic field and a variable magnetic field with an appropriate frequency to generate radial vibrations inside the unsolidified metal and to limit the above-mentioned stirring.

In the electromagnetic casting method, the liquid metal is encapsulated and held by the action of an electromagnetic field generated in a ring-shaped inductor through which an alternating current having a frequency of usually 500 to 5000 hertz flows. This inductor acts on the liquid metal which, after being introduced by the feeding device, flows out in a column from the lower part of the screen (ecran), which has approximately the same cross-sectional area as the ingot to be cast and is coaxial with the ingot.

This action has the effect of imparting a rotational movement to the liquid metal at the periphery of the ingot in a plane that passes through the axis of the ingot and is oriented downwards when viewed away from this axis. It also has

In the method of the present invention, a steady magnetic field and a variable magnetic field varying with an appropriate frequency are simultaneously applied to generate radial vibrations inside the unsolidified metal and to limit stirring.

The stationary magnetic field has a substantially perpendicular direction and is generated by a DC toroidal coil. This coil has a sufficient number of turns to obtain a value of less than 0.5 Tesla, has a horizontal cross section approximately equal to the cross section of the screen, and is placed concentrically with the axis of the ingot above the core screen. The magnetic field can be changed by providing an annular iron core inside the coil.

The combination of the effects of this constant magnetic field and the enclosed magnetic field alone has a beneficial effect on the surface condition and structure and homogenizes the metal of the shell of the cast product.

However, the present invention uses not only a steady magnetic field but also an η electromagnetic field of an appropriate frequency to generate radial vibrations and limit agitation.

This variable magnetic field parallel to the axis of the ingot has a low frequency i.e. 5
It is generated by a coil through which an alternating current of 100 to 100 hertz flows. The frequency of the alternating current is generally the industrial frequency of 50 Hz.
It is convenient to do so.

This coil is annular and is arranged concentrically with the DC coil at an intermediate height within the DC coil at a boundary between the screen and the DC coil. If alternating current is passed directly through the screen, the screen itself becomes a variable magnetic field generating means, so in that case, the alternating current coil can be omitted, and it is easier to introduce the iron core into the direct current coil.

Due to the low frequencies used, the variable magnetic field generated by the coil or screen exerts an electromagnetic effect over the entire liquid metal, so that the rotational movement of the metal is similar to the case of an enclosed magnetic field, and the variable magnetic field produced by the coil or screen exerts an electromagnetic effect on the ingot periphery, as in the case of an enclosed magnetic field. It spreads out to the axis of the ingot without staying in the vicinity. Additionally, because this rotational motion is in the opposite direction to that of the enclosing magnetic field, this antagonistic effect reduces the magnitude of vortices and agitation seen in conventional electromagnetic casting processes.

This electromagnetic effect therefore spreads over the entire ingot cross section, resulting in finer grains and more uniform crystallization.

Furthermore, in connection with this, the metal movement speed within the cavity is reduced, and although the phenomenon of collapse of the oxide film is not completely eliminated, the pinhole phenomenon is also reduced because particles of the film are no longer dispersed into the metal.

The variable magnetic field also performs other functions, such as generating induced currents with concentric lines of force in the metal.

The combination of the effects of the steady magnetic field and this induced current generates a force in the radial direction with a frequency N equal to the frequency of the variable magnetic field.

Similarly, the interaction between a variable magnetic field and an induced current, both of which have a frequency N, also produces a variable force in the radial direction, but the frequency of this force is 2N.

These forced vibrations have a particle refining effect.

In a variant of the invention, the variable magnetic field can be generated by a coil carrying an alternating current at a frequency of more than 100 hertz. In this case, as the value of the frequency increases, the degree of penetration of the electromagnetic field into the metal is limited, so the cooperative action between the steady magnetic field and the induced current is significantly reduced, and forced vibrations are virtually non-existent. However, if the resonance phenomenon is used, a vibration effect can be obtained even in this case. That is, depending on the dimensions of the cast product, the casting speed, and the type of alloy used, there will be a natural frequency of the liquid metal, forming dendrites, or solid metal mass.

Its value can be calculated or estimated using suitable detection equipment, and adjusting the frequency of the variable magnetic field to the value of these fundamental or harmonic frequencies results in resonant oscillations. This vibration also has a remarkable effect on particle refinement.

In this case it is not necessarily necessary to use special coils to generate the variable magnetic field. This is because under certain conditions this resonance phenomenon can also be obtained from the enclosed electromagnetic field itself.

In order to better understand the present invention, a detailed description will be given below based on the accompanying drawings.

Figure 1 shows a metal ingot 1 whose upper part 2 is still in a liquid state.
It shows. The ingot has an inductor 3 and a screen 4
and a cooling device 5, and a vortex 6 is generated in the liquid metal by the enclosed electromagnetic field generated by the inductor 3.

FIG. 2 shows an apparatus in which the means of the invention, namely a DC coil 7 and an AC coil 8, are added to the means of FIG. In this case, the magnetic field generated by the alternating current coil 8 causes the metal to circulate along the track 9, while radial vibrations are also generated, as indicated by 1o.

The invention will be better understood through the following examples.

After refining aluminum alloy 2024 containing aluminum at a ratio of I Ky / ) with AT5B, 5135 (
It was cast into a lu+ billet. The first part was cast under an enclosed magnetic field of frequency 2000 Hertz generated under a voltage of 28 volts and a current strength of 4900 amperes. The method of the present invention was applied to the second part. That is, by passing a current of 17,500 ampere turns through a toroidal coil placed above the screen under a continuous voltage of 24 volts,
A constant magnetic field of 4 Tesla was generated, and a variable magnetic field was generated by passing a current of 3800 ampere turns at 50 Hz under a voltage of 75 volts through another coil located within the coil at the same height as the screen. Ta.

As a result, the second part of the billet contains dendritic equiaxed particles (g
rains equiaxes dendritic
It was found that only equiaxed but dendrite-free particles were present in the first part.

Although the number of particles was eight times as large, the surface condition of the second part was much better, with no pinholes or roughness.

The invention can be used in the electromagnetic casting of metals and alloys into plates, billets, ingots, etc. in order to obtain cast products with good structure and good surface condition at the same time.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a prior art electromagnetic casting apparatus taken along a vertical plane passing through the axis of the ingot, and FIG. 2 is a sectional view similar to FIG. 1 showing the apparatus of the invention. DESCRIPTION OF SYMBOLS 1... Metal ingot, 2... Liquid metal, 3... Inductor, 4... Scree/, 5... Cooling device, 6... Vortex, 7... DC coil, 8... ...AC coil, 10...radial direction vibration. u1M person completed□1 unit ξnium...ζn and a half

Claims (1)

[Scope of Claims] (1) At least one magnetic field different from the enclosed electromagnetic field is applied to the solidifying metal in the ingot mold in order to generate radial vibrations in the unsolidified metal and limit agitation of the metal. An electromagnetic metal casting method characterized in that a steady magnetic field and a variable magnetic field of an appropriate frequency are applied simultaneously. (2) A method according to claim 1, characterized in that the steady magnetic field has a value smaller than 0.5 Tesla. (3) A method according to claim 1, characterized in that the steady magnetic field changes due to the presence of the iron core. (4) A method according to claim 1, characterized in that the variable magnetic field has a frequency of 5 to 100,000 hertz. (5) The method according to claim 1, wherein the variable magnetic field is an enclosed magnetic field. (6) The method according to claim 1, wherein the variable magnetic field is a magnetic field different from the enclosing magnetic field. (Force: The frequency of the variable magnetic field is from 100 to Zoo 000-
5. A method according to claim 4, characterized in that, in the case of ψ, a frequency value is selected such that it resonates with the natural frequency of the liquid metal, the forming dendrite, or the solid metal arms. 8. A method according to claim 1, characterized in that the constant magnetic field is generated by a toroidal coil whose lower part is located above the level of the liquid metal. 9. A method as claimed in claim 6, characterized in that the variable magnetic field is generated by a toroidal coil whose lower part is located above the level of the liquid metal.