RU2797968C1 - Method of mixing liquid metal in electric arc furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used for electromagnetic mixing of liquid metal in an electric arc furnace with continuous loading. At the first stage of the cycle - loading - the first electromagnetic field creates mixing forces in the liquid metal, having an inconsistent orientation relative to each other, and at the second stage of the cycle (refining) the second electromagnetic field creates forces acting on the liquid metal, having a coordinated orientation relative to each other. During the loading and refining steps, the control unit sends a control signal to the power supply device, which supplies the first electromagnetic stirrer with a first electric current and the second electromagnetic stirrer with a second electric current, creating said first and second electromagnetic fields, which are directed appropriately in accordance with one or the other of the specified stages. During these stages of loading and refining, the first and second electric currents have the same intensity.

EFFECT: invention prevents problems of differentiated wear on the walls and bottom of the furnace and makes the temperature uniform throughout the mass of liquid metal.

6 cl, 4 dwg

Description

The field of technology to which the invention belongs

The present invention relates to a method for electromagnetically stirring liquid metal in an electric arc furnace suitable for use in substantially continuous-feed processes for melting metallic material.

State of the art

Plants for the melting of metallic material with continuous loading are known, which contain an electric arc furnace equipped with at least one housing, or casing, inside which the metal charge is melted.

The electric arc furnace also includes a roof dome having holes for the passage of electrodes that enter the casing to allow an electric arc to be generated to melt the metal charge. The dome also has openings for the removal of exhaust gases, while there are usually means in the bottom or side of the casing for the release of liquid metal.

The electric arc furnace is associated with metal material supply means, which may be continuous loading systems.

In continuous loading solutions, to perform the first start-up with the furnace turned off, a basket loading system is typically used to create a mass of metallic material at the bottom of the furnace to be melted at the beginning of the cycle. Usually, when this mass is completely melted, the process of continuous loading of scrap (scrap metal) into the furnace is started.

In the most common solutions, the electric arc furnace has a decentered drain hole in the bottom of the shell, called "Eccentric Bottom Tapping" (EBT), or alternatively, a drain chute to drain the molten metal from the shell during the drain stage.

The draining step follows the refining step, during which certain elements are introduced into the molten metal to improve its quality or to give it the required properties, depending on the composition of the resulting steel.

One of the most common drawbacks in this type of melting process is the temperature equalization of the molten metal within the shell.

Lack of temperature uniformity in the body of molten metal can lead to problems such as undesirable concentrations of certain elements, incorrect measurements of process parameters, localized temperature peaks, premature wear of components, or other problems known in the art.

To solve these problems, it is known to use electromagnetic stirrers, usually located under the bottom of the furnace or, at most, associated with its side walls.

For example, WO 2018/145754 discloses an electric arc furnace that has an electromagnetic stirrer located at a substantially central position under the bottom of the casing and having an electromagnetic stirring axis that intersects a central vertical plane passing through the center of the casing and a drain hole or chute.

Also known is EP 2616560 B1, which discloses an electric arc furnace equipped with two electromagnetic stirrers located opposite each other relative to the central axis of the furnace.

Also known is US 3,409,726, which generally states that the direction of movement of the molten metal can be easily reversed by reversing the polarity of the direct current through the molten metal, or the excitation current of the electromagnet. US'726 discloses the use of a magnetic pole coaxial with the center of the bottom of the casing or, in addition to this central magnetic pole, three magnetic poles arranged radially and equidistant around the circumference of the electric furnace.

JP 62-73591 discloses a magnetic stirrer for electric arc furnaces. This device contains an electromagnetic stirrer that can move under the furnace, taking on variable positions in relation to the various stages of the melting cycle.

Solutions that use stirrers to stir the molten metal inside the furnace usually do not provide a correlation between the action of the stirrers themselves and the steps in the melt cycle.

This can entail excessive wear on the inner walls of the casing where the liquid metal has a higher velocity and the formation of dead zones where the liquid metal tends to stagnate without optimally combining with the surrounding liquid metal.

Thus, it is necessary to improve the method of electromagnetic stirring of liquid metal in an electric arc furnace, which can overcome the shortcomings of the prior art.

In particular, one of the objectives of the present invention is to improve the method of electromagnetic stirring of liquid metal in an electric arc furnace, which prevents problems of differential wear on the walls and bottom of the furnace, makes the temperature uniform throughout the body of the liquid metal, and improves the efficiency of the melting and refining steps inside the furnace.

The applicant has developed, tested and implemented the present invention to overcome the shortcomings of the prior art and achieve these and other objects and advantages.

Disclosure of the essence of the invention

The present invention is set forth and characterized in an independent claim. The dependent claims disclose other features of the present invention or variants of the main inventive idea.

In accordance with the above object, the present invention relates to a method for electromagnetic stirring of liquid metal in combination with a melting cycle in an electric arc furnace, which provides at least one charging step in which a metal charge is introduced into the furnace, a melting step and a liquid metal refining step in an electric arc furnace. ovens.

In accordance with one aspect of the present invention, such electromagnetic stirring is applied to a continuous electric arc furnace in which at least one first electromagnetic field is generated along the first axis of electromagnetic stirring by at least two electromagnetic stirrers located under the hearth or bottom of the furnace and at least one second electromagnetic field along the second electromagnetic mixing axis.

According to one aspect of the invention, at least in the first stage of the furnace cycle, the first electromagnetic field and the second electromagnetic field create mixing forces acting on the liquid metal having a mismatched orientation relative to each other, and at least in the second stage of the furnace cycle, electromagnetic fields create the mixing forces acting on the liquid metal. metal forces having a consistent orientation relative to each other.

The term "inconsistent", hereinafter in the description, indicates that the axis of the mixing forces generated by the first electromagnetic stirrer has the opposite orientation relative to the axis of the mixing forces generated by the second electromagnetic stirrer; the term "matched", on the contrary, indicates that the axes of the mixing forces generated by both electromagnetic stirrers have the same orientation, that is, they have the same direction.

Thus, when the orientations of the axes of the forces are inconsistent, or opposite, there is a mixing of the steel, which prevails over the entire periphery of the casing, with a substantially circular and tangential movement of the steel relative to the heat-resistant wall of the casing.

When, on the other hand, the axes of the electromagnetic forces have a consistent orientation, both agitators contribute to the movement of the steel towards the same peripheral zone of the furnace, and the steel bounces around the perimeter and returns to the center.

Differentiating the mixing action with respect to the steps of the melting process makes it possible, in addition to obtaining a liquid metal having very uniform thermal and chemical characteristics, also to optimize the overall energy consumption of the electric arc furnace and reduce the overall cycle time.

Brief description of the drawings

These and other aspects, features and advantages of the present invention will become apparent from the following disclosure of some embodiments, given as a non-limiting example with reference to the accompanying drawings, in which:

- in Fig. 1 is a schematic sectional view of an electric arc furnace in which the electromagnetic stirring method of the present invention is applicable;

- in Fig. 2 and FIG. 3, respectively, is a schematic representation of the mixing method according to the present invention.

- in Fig. 4a-4f are schematic representations of possible alternative arrangements of electromagnetic stirrers in an electric arc furnace in which the electromagnetic stirring method of the present invention is applicable.

For ease of understanding, where possible, the same reference numbers have been used to refer to identical common elements throughout the drawings. It is clear that the elements and features of one embodiment can be easily included in other embodiments without further explanation.

Implementation of the invention

We will now consider in detail possible embodiments of the invention, one or more examples of which are shown in the accompanying drawings. Each example is given as an illustration of the invention and should not be understood as limiting it. For example, features shown or disclosed insofar as they are features of one embodiment may be modified or adopted in, or in combination with, other embodiments to provide other embodiments. The present invention is intended to include all such modifications and variations.

Prior to the disclosure of these embodiments, we should also clarify that the present description is not limited in its application to the details of construction and arrangement of components as disclosed in the following description using the accompanying drawings. The present description may provide for other embodiments and may be obtained or performed in various other ways. We should also clarify that the phraseology and terminology used here is for descriptive purposes only and should not be considered restrictive.

The embodiments disclosed in the accompanying drawings relate to an electric arc furnace, indicated generally with reference numeral 10, inside which liquid metal L is agitated in accordance with the electromagnetic agitation method of the present invention.

The electric arc furnace 10 can be driven by alternating current AC, characterized by the presence of three or more electrodes 14, between which an electric arc is ignited to start and/or continue the melting process, or by direct current DC, characterized by the presence of one or two electrodes 14 located in the center , which function as a cathode interacting with the anodes located at the bottom of the electric arc furnace 10 to create an electric arc.

Although we refer to the AC electric arc furnace 10 in the drawings herein, it will be appreciated that the concepts disclosed below also apply to the DC electric arc furnace 10 .

According to the embodiment shown in FIG. 1, the electric arc furnace 10 comprises, among its main parts, a casing or casing 11 and a covering element or dome 12 located on top and covering the casing 11.

Associated with the electric arc furnace 10 are means 13 for continuously supplying a metal charge 25, which may include, for example, scrap S.

The feed means 13 are capable of moving the metal charge 25 in accordance with a predetermined feed Z-axis.

According to some embodiments, the feed means 13 may be positioned laterally, see FIG. 1-3, to introduce the metal charge 25 through the side of the electric arc furnace 10, or from above, to introduce the metal charge 25 through the hole made in the roof 12.

The metal charge 25 is arranged in a known manner on the supply means 13 and can have predetermined dimensions, which can even be highly variable.

Roof 12 is provided with an opening(s) for accommodating and/or positioning electrodes 14 capable of creating an electric arc to melt the metal charge present in casing 11.

Roof 12 and electrodes 14 are connected to lifting and turning devices which are capable of raising roof 12 and electrodes 14 even independently of each other.

The casing 11 is provided with a bottom or hearth 15 and a side wall 16 made at least in part of a heat-resistant material in order to withstand the high temperatures reached during the melting stage and the highly reactive environment.

The bottom 15 may be provided with a decentered drain 17, also referred to as an "eccentric bottom drain" (EBT), or alternatively or additionally, with a drain chute for extracting molten metal from the casing 11 during the drain step.

The shroud 11 is mounted on supports which are not visible in the drawings, and actuating means are usually provided for turning the shroud 11 itself about a predetermined axis of rotation.

The furnace 10 also includes a lining 18 having a bottom edge 19 resting on the top edge of the casing 11.

Lining 18, usually consisting of cooled panels, is located essentially in the continuation of the walls of the casing 11, and above it is the roof 12, ensuring the closure of the latter.

The lining 18 is provided with a first opening 20 through which the supply means 13 are positioned for supplying the metal charge 25, and with a second opening through which slag tapping operations can be performed.

Inside the casing 11, under the first opening 20, there is a loading zone 28, where the newly introduced metal charge 25 accumulates.

The loading zone 28 is located in a peripheral position relative to the central zone of the electric arc furnace 10 where the electrodes 14 are present.

The second opening can be selectively rendered accessible/inaccessible by means of the slag outlet door 22, which is generally located in an opposite position to the drain opening 17, see FIG. 2-3.

In accordance with some embodiments shown in FIG. 2 and 3, the electric arc furnace 10 under the casing 11 is equipped with two electromagnetic stirrers 23, 24 configured to generate stirring forces F1, F2 in the liquid metal L present inside the casing 11 during the melting process.

As shown in the drawings, the electromagnetic stirrers 23, 24 can be arranged in opposite and mirror ways in order to create a pair of electromagnetic stirrers with respect to the central plane P.

The electric arc furnace 10 includes a power supply device 26 configured to power the electromagnetic stirrers 23, 24, and a control unit 27 functionally connected to the power supply device 26 to control the drive of the electromagnetic stirrers 23, 24.

In accordance with some embodiments, each electromagnetic stirrer 23, 24 includes a housing made of magnetic material around which coils of electrically conductive material are wound. The coils are made with the possibility of their supply with electric current from the power supply device 26, with the creation of a magnetic field in the direction of the electromagnetic stirring axis of the electromagnetic stirrer 23, 24.

In accordance with some embodiments, power supply means 13 and electrodes 14 may also be operatively associated with the control unit 27.

The first electromagnetic stirrer 23 is energized so that a first electromagnetic field is generated along the first electromagnetic stirring axis X1.

The second electromagnetic stirrer 24 is energized so that a second electromagnetic force field is generated along the second electromagnetic stirring axis X2.

According to the following embodiments shown in FIG. 4, the number of electromagnetic stirrers 123, 124 may be more than two in order to generate a corresponding number of electromagnetic fields along the electromagnetic stirring axis X.

In some embodiments, the electromagnetic stirrers 123, 124 may be arranged to form pairs of electromagnetic stirrers, eg two pairs (FIGS. 4a, 4d) or more, eg three pairs (FIG. 4e).

Alternative embodiments may provide that pairs of opposing electromagnetic stirrers 123 are offset (FIG. 4d) or aligned (FIG. 4e) with respect to the central plane P.

According to other embodiments, electromagnetic stirrers 123, 124 of the same pair may be positioned to have different distances from the central plane P (FIG. 4d).

In other embodiments, different pairs of electromagnetic stirrers 123, 124 may have different distances from the central plane P (FIG. 4a).

The following embodiments may include an odd number of electromagnetic stirrers 123, 124, such as 3 or 5 (FIGS. 4b, 4c).

In embodiments having an odd number of electromagnetic stirrers 123, 124, at least two stirrers may be arranged in a pair opposing the central plane P (FIG. 4b).

In some embodiments, one or more electromagnetic stirrers 123, 124 can be positioned substantially in accordance with the central plane P (FIGS. 4b, 4c).

Some embodiments may provide that the central plane P divides the number of electromagnetic stirrers 123, 124 asymmetrically (FIG. 4c).

In other embodiments, the electromagnetic stirrers 123, 124 may be positioned so that their mixing axis X is at an angle with respect to the central plane P, for example orthogonally (FIG. 4f).

According to further embodiments, which are not shown here, the electric arc furnace 10 can be provided with electromagnetic stirrers 123, 124 with mixing axes X differently oriented relative to each other.

According to some embodiments, the electromagnetic stirrers 123, 124 may be suitably sized relative to the size of the housing 11 and/or the desired location.

Some embodiments, not shown here, may include an electric arc furnace 10 equipped with electromagnetic stirrers 123, 124 of various sizes relative to each other.

In accordance with some embodiments, the first electromagnetic stirring axis X1 and the second electromagnetic stirring axis X2 are parallel to each other and about the center plane P.

The central plane P is vertical and passes through the center of the bottom 15 of the casing 11 and through the drain hole 17 or, alternatively, through the drain chute.

The central plane P may be a plane of symmetry for at least the casing 11.

In accordance with some embodiments, the housing 11 has an upper plan section which may have a curvilinear shape, for example, formed by the connection of one or more curves suitably selected from the group consisting of a circle, a parabola, an ellipse, a line.

In accordance with some embodiments, the casing 11 has an elongated curvilinear shape towards the drain hole 17, which, as a result, is located at a large distance from the center of the casing 11.

As an example, in FIG. 2-3 disclose a method for electromagnetic stirring of liquid metal L in an electric arc furnace 10.

Inside the electric arc furnace 10, a melting process takes place, which includes at least one charging step, in which the metal charge 25 is introduced and melted, which is added to the liquid metal L, already pre-melted, followed by the stage of refining the liquid metal L in the electric arc furnace 10.

In the method of electromagnetic stirring of liquid metal in the continuous electric arc furnace 10 according to the invention, a first electromagnetic field is generated along the first electromagnetic stirring axis X1 and a second electromagnetic field along the second electromagnetic stirring axis X2.

According to one aspect of the invention, at the first stage, said first electromagnetic field and said second electromagnetic field create mixing forces F1, F2 acting on the liquid metal L, having an inconsistent orientation relative to each other, and at the second stage, said electromagnetic fields create forces acting on the liquid metal L F1, F2, having a consistent orientation relative to each other.

In one preferred solution, said first step is a loading step and said second step is a refining step.

In accordance with some embodiments shown in FIG. 2-3, both during at least one loading step and the refining step, the first electromagnetic stirring axis X1 and the second electromagnetic stirring axis X2 are parallel to each other and with respect to a central vertical plane P passing through the center of the electric arc furnace 10 and through the overflow opening 17 of the electric arc furnace 10.

In accordance with some embodiments, during at least one loading step, agitating forces F1, F2 establish the flow of liquid metal L in a peripheral counter-clockwise direction, see FIG. 2.

In other words, at the loading stage, as mentioned above, the axes of generating the stirring forces F1, F2, respectively, of the first electromagnetic stirrer 23 and the second electromagnetic stirrer 24, are directed in the opposite or inconsistent direction relative to each other. In FIG. The 2 opposite force generation orientations are labeled F3 for the electromagnetic stirrer 23 and F4 for the electromagnetic stirrer 24.

Thus, there is a mixing of steel, prevailing over the entire periphery of the casing 11, with the movement of the liquid metal L essentially circular and tangential relative to the heat-resistant wall of the casing 11.

In other embodiments, the mixing forces F1, F2 set the flow of liquid metal L in a clockwise direction in a peripheral direction (not shown).

The position of the magnetic stirrers 23, 24 and the opposite and inconsistent direction of their mixing action, determined by the corresponding axes X1, X2 of electromagnetic mixing, allows you to optimally influence the metal charge 25 introduced and accumulated in accordance with the loading zone 28. Due to the direction of the mixing forces, the introduced new metal charge 25 is gradually included in the previous one, thereby contributing to temperature uniformity also in accordance with the zone of the drain hole 17, which is located at a distance from the center of the electric arc furnace 10.

In addition, such a configuration and driving mode of the electromagnetic stirrers 23, 24 provide a more uniform velocity distribution, preventing turbulence and/or instability in the flow of liquid metal L.

In this case, the flow of liquid metal L, since it is essentially circular and tangential with respect to the side wall 16 of the casing 11, has a reduced radial momentum component. This helps to limit erosive action on the sidewall 16 and therefore reduce the need for frequent maintenance and repair.

In accordance with some embodiments, during the refining step, the mixing forces F1, F2 have a consistent orientation, that is, the electromagnetic stirrers 23 and 24 are driven in such a way that the axes of the generated electromagnetic forces (indicated in Fig. 3 by the arrow F5 for the electromagnetic stirrer 23 and arrow F4 for electromagnetic stirrer 24) have the same direction and orientation.

In this case, both agitators 23, 24 promote the movement of the liquid metal L towards the same peripheral zone of the furnace 10, in particular towards the decentered outlet 17, and the liquid metal L then bounces around the perimeter and returns to the center, moving towards the door 22 for the release of slag, see fig. 3.

This also makes it possible to equalize the temperature in the central region of the casing 11, which is barely agitated during the charging phase, in which the flow of liquid metal L moves at a higher speed in accordance with the side wall 16 of the casing 11.

In accordance with some embodiments, during at least one loading step and a refining step, the control unit 27 sends a control signal to the power supply device 26, which supplies the first electromagnetic stirrer 23 with a first electric current and the second electromagnetic stirrer 24 with a second electric current so that create, respectively, the first electromagnetic field and the second electromagnetic field, as indicated above, respectively directed in a mutually inconsistent, or opposite, orientation, or in a consistent orientation, that is, with the same direction, depending on one or the other of these steps.

In accordance with some embodiments, the control unit 27 may receive a loading signal from the supply means 13 proportional to the amount of metal charge 25 introduced into the electric arc furnace 10, and send a control signal to the power supply device 26 so as to set the first current and the second current based on the amount of introduced metal charge 25.

The greater the amount of metal charge 25 introduced, the greater the intensity of electric currents, because the corresponding mixing forces F1, F2 must stir a greater amount of liquid metal L.

This makes it possible to automatically regulate the mixing action of the electromagnetic stirrers 23, 24, always obtaining an ideal and uniform mixing of the liquid metal L.

In accordance with some embodiments, during at least one loading step and a refining step, the first electrical current and the second electrical current may have the same intensity.

According to the following embodiments, during at least one loading step and a refining step, the first electric current and the second electric current may have different intensity.

In particular, during the loading step, it can be ensured that the electrical currents have a greater intensity than the electrical currents during the refining step.

In fact, the presence of a metal charge 25 that is partially molten and/or in a solid state requires stirring forces F1, F2 greater than those required to stir the liquid metal L at the end of the melting process and during the refining step.

Changing the intensity of electric currents in relation to the stages of loading and refining, as indicated above, and/or in accordance with the amount of metal charge 25 introduced, allows you to optimize the overall energy consumption of the electric arc furnace 10.

It is clear that changes and/or additions to the steps can be made to the method of electromagnetic stirring of liquid metal in an electric arc furnace disclosed above without departing from the scope and scope of the present invention.

It is also clear that, although the present invention has been disclosed with reference to some specific examples, a person skilled in the art should certainly be able to obtain many other equivalent forms of the method of electromagnetic stirring of liquid metal in an electric arc furnace having the features set forth in the claims, and , therefore, all of them are included in the scope of protection defined by it.

In the following claims, the sole purpose of the reference numbers in parentheses is to facilitate reading: they are not to be considered as limiting factors as to the scope of protection claimed in the claims.

Claims (6)

1. A method for electromagnetic stirring of liquid metal in an electric arc furnace (10) with continuous loading, in which, by means of electromagnetic stirrers (23, 24; 123, 124), at least one first electromagnetic field is created along the first axis (X1) of electromagnetic stirring and at least least the second electromagnetic field along the second axis (X2) of electromagnetic mixing, characterized in that at the first stage of the furnace cycle, the specified first electromagnetic field and the specified second electromagnetic field create mixing forces (F1, F2) in the liquid metal (L) having an inconsistent orientation relative to each other, and in the second stage of the furnace cycle, said electromagnetic fields create forces (F1, F2) acting on the liquid metal (L) having a consistent orientation relative to each other, wherein said first stage is a loading stage, and said second stage is a refining stage; in that during said at least one loading stage and said refining stage, the control unit (27) sends a control signal to the power supply device (26), which supplies at least one first electromagnetic stirrer (23) with the first electric current and at least one second electromagnetic stirrer (24) with a second electric current to respectively create said first electromagnetic field and said second electromagnetic field directed appropriately in accordance with one or the other of said steps; and in that during said at least one loading step and said refining step, said first electric current and said second electric current have the same intensity. 2. Method according to claim 1, characterized in that both during said at least one loading step and during said refining step, said first electromagnetic stirring axis (X1) and said second electromagnetic stirring axis (X2) are parallel to each other. to each other and relative to the vertical central plane (P) passing through the center of the electric arc furnace (10) and through the drain hole (17) of the specified electric arc furnace (10). 3. A method according to any one of the preceding claims, characterized in that during said at least one charging step, said mixing forces (F1, F2) establish a flow of liquid metal (L) in a circumferential counter-clockwise direction. 4. Method according to any one of the preceding claims, characterized in that during said at least one charging step, said stirring forces (F1, F2) establish a flow of liquid metal (L) in a peripheral clockwise direction. 5. Method according to any one of the preceding claims, characterized in that, in said refining step, said mixing forces (F1, F2) set the flow of liquid metal (L) towards said drain hole (17) and then in the opposite direction to the central zone of said electric arc furnace (10). 6. The method according to claim 1, characterized in that said control unit (27) receives from the supply means (13) a load signal proportional to the amount of metal charge (25) introduced into said electric arc furnace (10) and sends a control signal to said power supply device (26), so that said first electric current and said second electric current have an intensity proportional to the specified amount of the introduced metal charge (25).

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