ES2998453T3 - Magnetic stirrer for furnace containing molten metal and furnace provided with such a stirrer - Google Patents

Abstract

1. Magnetic device (11) for a furnace (1) containing molten metal, such as aluminum or the like, said furnace comprising a hollow body (2) with side walls (3) and a bottom wall (4), said furnace (1) being lined with refractory material and having a portion (6) thereof normally present in the bottom wall or in one of said walls (3, 4) which is made of metal permeable to magnetic fields and coated with a refractory layer, the device (11) acting as a magnetic stirrer for the metal placed in the furnace being present in said wall portion (6), said device (11) being movable frontally and along said portion (6) permeable to magnetic fields and comprising rotating magnetic field generating means adapted to generate a magnetic flux within the metal placed in the furnace body (1), said generating means (13) also preferably translating in front of said wall portion (6) along predefined guides (19). Said generating means consist of a plurality of permanent magnets (15) supported by a supporting element (13) that rotates around an axis (M, 57) thereof during said rotation and/or translation. An oven with said stirring device is also described and claimed. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Magnetic stirrer for furnace containing molten metal and furnace provided with such stirrer

The object of the present invention is a magnetic stirring device for a furnace containing molten metal and a system comprising a furnace with such a magnetic stirring device according to the corresponding independent claims.

The use of devices (or agitators) is known, which are adapted to generate a magnetic field within a molten metal contained in a furnace that has a hollow body or tank with side walls and a bottom wall.

The body mentioned above is covered internally with refractory material and has a lower wall portion made of a material, such as stainless steel, that is permeable to the magnetic field generated by a device placed on said wall. Solutions are also known in which such a device or stirrer (as will be indicated later in this document) is also placed on a side wall of the furnace body (which in this case has a portion made of magnetic material permeable to the magnetic field).

The furnace can be a melting furnace or a support furnace.

The aforementioned magnetic stirrer may be stationary or movable along one or more guides provided beneath the wall of the furnace body in which such stirrer is placed. For example, if the stirrer is placed beneath the bottom wall, a well containing the stirrer and having the aforementioned guides is typically provided beneath the furnace, if it is of the movable type. In the movable version, the translational motion of the stirrer may be generated by drive means separate from the stirrer (such as drive elements associated with the well) or integral with the stirrer (for example, one or more electric motors moving it along the guide or guides).

The function of the known agitator is to create oscillating or wave-like movements within the mass of molten metal present in the furnace in order to remix it, making the surface temperature of said mass uniform and also preventing the creation or deposit of solid parts in it.

Magnetic stirrers for molten metals are known in the art, as disclosed in documents US 2011 19779, JP 2008 164249, CN 204255 119 or CN 201 735366.

State-of-the-art agitators are typically manufactured using electromagnets and have several drawbacks.

For example, they must be cooled. The solution of placing the stirrer inside the cooling liquid chamber (usually water) has proven to be improvable, as it presents several drawbacks. First, the stirrer is submerged in the cooling water, which requires adequate electrical insulation of such a device (comprising a series of coils through which a high current circulates) from the aforementioned fluid in order to prevent obvious inconveniences, which could generate electrical safety issues and considerable damage to the power plant and the electrical distribution network where billet production takes place, even to the point of complete shutdown of the production.

To remedy this problem, an isolation transformer is usually used, which in any case is quite bulky, requires high power and is therefore expensive.

This also negatively affects system performance and plant layout.

Furthermore, the cooling water must be demineralized (which in any case represents a significant cost) to control its conductivity (which must never exceed 220 |iS/cm), to prevent the water itself from becoming an electrical conductor due to the presence of the agitator in it.

Furthermore, known agitators operate with very high currents. This requires the use of electrical components (inverters) to drive and control the agitators, which are large and expensive, as they are designed for the high currents they must control. Furthermore, the known solutions mentioned above generally have very low efficiency due to the necessary magnetizing currents and the dispersion of the electromagnetic field generated by the agitator, the heating of the coils and the relative magnetic poles made of magnetic foil, and the agitator's shielding.

In addition, there are also problems related to the need to electrically connect the agitator (placed in the chamber where the cooling fluid is present) to a power source, and with the need to cool the agitator windings.

The objective of the present invention is to provide a magnetic stirrer for a furnace for molten metal (melting or support furnace) that is improved with respect to known analogous furnaces.

Another objective is to provide an agitator of the aforementioned type that has lower manufacturing and operating costs than known analogous agitators and that presents better results than the latter with respect to performance, energy consumption, compactness and the mixing obtained within the mass of molten metal present in the furnace.

A further objective is to provide a system comprising a furnace and the aforementioned magnetic device or stirrer provided for creating agitation within the mass of molten metal contained in the furnace, wherein the action of such stirrer is more effective with respect to known analogous devices for creating stirring movements within said mass of metal.

In particular, one objective of the invention is to provide a system comprising a furnace and a magnetic stirrer of the aforementioned type, in which there is effective control of the fluid waveforms developing in the molten metal to obtain waveforms with wave and spiral progression that are not possible with conventional stirrers. A suitable control panel and specific software allow adjustment of the generated waveforms and, consequently, the progression of the molten metal flows present in the furnace.

Another objective is to provide a device or stirrer of the aforementioned type which exhibits high efficiency, greater than that of known stirrers, and which exhibits lower energy consumption than that of known stirrers using electromagnets, and in particular which operates with an installed power less than half of that required for a normal electromagnetic stirrer.

A further objective is to provide a device or agitator that exhibits a reduced dispersion of the electrical power supplied for its operation, that does not require the use of isolation transformers, that does not use large inverters with high currents required to drive the electromagnetic coils provided with normal agitators, and that does not require expensive devices to filter harmonics or phase the power supply network.

Another objective is to provide a device or agitator of the aforementioned type that creates various controlled movements along different directions within the mass of metal placed in the furnace. A further objective is to provide a device or agitator of the aforementioned type that can be easily adapted both during construction and by means of control management software based on the type, size, structural form of the furnace, and the thickness of the furnace refractory material with which it is to be associated.

These and other objectives that will be evident to the person skilled in the art are achieved by means of a magnetic stirrer device and by means of a system comprising a furnace containing molten metal and said magnetic stirrer according to the appended claims.

For a better understanding of the present invention, the following drawings are attached merely by way of example, in which:

Figure 1 shows a perspective view from below of an oven according to the invention;

Figure 2 shows a perspective view from above, partially in section and with some parts removed for clarity, of the lower part of Figure 1 and of a device according to the invention;

Figure 3 shows a schematic side perspective view of the oven of Figure 1 and of the device according to the invention;

Figure 4 shows a top perspective view of a part of the magnetic stirring device housed in its receptacle;

Figure 5 shows a view analogous to that of Figure 2, but representing a further variant of the magnetic stirring device associated with a furnace containing molten metal, this variant not being within the scope of the present invention as claimed;

Figure 6 shows a partially sectional view of the oven and the device of Figure 5;

Figure 7 shows a perspective view of the magnetic stirring device of Figure 5, with some parts removed for better clarity.

With reference to the figures mentioned above, the furnace tub containing molten metal is generically indicated by 1. It comprises a body 2 having side walls 3 and a bottom wall 4, while being open at the top. The body 2 is generally completely covered with refractory material which, in turn, can be contained in any known metal structure, except for a portion or "window" 6 generally provided in the bottom wall 4 and occupying a more or less large (longitudinally) portion of the latter. The furnace tub or simply the furnace 1 can be a melting furnace or a holding furnace, known per se.

The part or window 6 below the refractory material is covered with material permeable to the magnetic field, such as stainless steel or equivalent material.

Below the oven 1, a well 10 is present in which a magnetic stirring device or stirrer 11 is placed, which, in one embodiment of the invention, can move along and frontally with respect to the window 6 of the bottom wall 4 (or can move along the longitudinal axis of such a wall).

More particularly, such a magnetic device or stirrer 11 comprises a support 12 for the load-bearing elements 13 which is associated with a plurality of permanent magnets 15. In Figures 1 to 4, such load-bearing elements 13 are discs made of iron or magnetic material, while in the solution according to Figures 5 to 7 (which does not form part of the present invention), such elements are cylindrical drums, also made of iron or an appropriate magnetic material.

The support 12 is a surface associated with a carriage 18 that can move in a guided manner along guides or tracks 19 placed on a bottom or surface 20 of the well 10. Such movement is generated by at least one electric motor 21 that operates on at least one wheel 23 that can move along a corresponding guide of such guides 19.

In a known manner, the support 12 is subjected to the action of a scissor lift, screw lift or other lifting system 26, supported by the carriage 18 and driven by the electric motor 27 or by a hydraulic or pneumatic cylinder integral with the latter and operating, by means of the worm screw 28, on such lift 26. By driving the motor 27, the lift rises or lowers in a manner known per se with respect to the carriage 18 which carries the support 12 close to the lower wall 4 of the oven 1 or moves it away from it.

With reference to the aforementioned Figures 1 to 4 related to the invention, the permanent magnets 15 are carried by the element 13 (or load-bearing disc). According to the invention, two elements or discs 13 are associated with the support 12 and positioned with median axes M orthogonal to the corresponding load-bearing disc (and therefore to the bottom 20 on which the carriage 18 moves as well as to the wall 4 of the furnace). Each disc can rotate around its median axis M driven by an electric motor (gear motor) 30; or a single motor 30 associated with the support 12 drives both discs 13. Naturally, each disc can be provided with an electric motor thereof (or in general an electric actuator) that generates the rotary motion thereof, by means of mechanical couplings known per se (providing gears and transmissions in mutual coupling and integral with the motor and the disc).

In one embodiment, shown in Figures 2 and 3, the permanent magnets 15 are arranged on a face 13A of the corresponding disk 13 facing the wall 4, so as to form a magnetic annular disk. In the embodiments of Figure 4, however, they occupy almost the entire surface of the corresponding disk 3 with a precise magnetic orientation.

Each magnet 15 consists of a single body or two or more stacked magnets. Furthermore, on the discs 13, the magnets are arranged so as to form two "groups" or portions with different polarities directed upwards (i.e., toward the wall 4 of the oven 1). A first group of magnets is directed with the north polarity upwards, and the other with the south polarity upwards; each such group occupies approximately half of the disc 13 (as shown in Figure 4, where the group of magnets, indicated by N and S depending on the polarity directed upwards, are separated by the line K).

The adjacent magnets 15 are inserted into respective seats 40 fixed to the disc 13 made of Teflon or similar non-magnetic material, so that it can be easily associated with the aforementioned disc.

As indicated, each disk 13 moves around its axis M. Such movement may be at a uniform or variable speed (for example, between 1 and 20 revolutions/min); the rotational speed may be the same for both disks or different.

Such disks can rotate in the same or opposite directions, continuously or alternately over time. Furthermore, they can rotate in phase or out of phase with each other, in order to determine the specific lines of force that move the liquid material contained in the molten pool, achieving precise and programmed fluid progressions.

Due to the solution shown in the examined figures, by actuating the motor 21 so as to move the carriage 18 along the tracks 19 with a reciprocating motion from one end of the furnace to the other or vice versa, and simultaneously actuating the motor(s) 30 which rotate(s) the discs 13, it is possible to generate convective and wave-like movements with spiral progression in the molten metal (e.g. aluminum) placed in the furnace 1. Such movements continuously remix the molten metal, preventing the formation of oxides therein and thereby increasing its purity (and the ability to present a high purity, which translates into final products with greater aesthetic value and greater resistance to mechanical stress).

Magnets 15 are placed on discs 13 (shown in figures 2, 3 and 4), and spiral movements are generated in the metal when the carriage 18 moves along the tracks 20.

The number and size of the magnets 15 can be varied to modify the shape and intensity of the generated magnetic field and, therefore, the mixing force generated in the molten metal and the energy dissipated therein. The rotational speed of the discs and the translational speed combined cause a longitudinal or transverse, convergent or divergent spiral progression of the fluid.

The greater the number and magnetic grade of the magnets, in particular, the greater the movement of the metal within the furnace 1.

In Figures 5 to 7, which show an embodiment not forming part of the present invention, the parts corresponding to those of Figures 1 to 4 are indicated by the same reference numerals; in this embodiment, which is not within the scope of the claimed invention, the permanent magnets 15 are supported by load-bearing elements 13 in the form of drums or cylinders. Such elements or cylinders 13 have seats 40 for the magnets 15 arranged on the surface and along generatrices of the cylinders. Furthermore, at one end 50 of each element or cylinder 13, there is a disc 54, driven by means of a belt 55 by an electric motor 30. Naturally, one motor may drive multiple cylinders 13, or each of these may have its own motor.

Each cylinder is supported laterally by panels 56 integral with the support 12, which rotate on bearings (not shown) that restrict an axis 57 of each cylinder (around which it rotates) to said panels. This axis is parallel to the bottom 20 on which the carriage 18 moves, that is, to the longitudinal axis of the wall 4 of the furnace 1.

It should be noted that with the axis of rotation parallel to the wall 4 (towards which the magnets 15 are oriented) or orthogonal to such wall 4, reference is made not only to the case in which such axis is perfectly orthogonal or parallel to the wall, but also to the case in which such axis forms an angle of several degrees incident on the aforementioned wall (and therefore not perfectly parallel to it) or in which such axis forms an angle other than 90°, close to it, with said wall 4.

The term “face” mentioned above also indicates the position of the magnets 15 such that it directs the magnetic field generated in this way towards the adjacent part of the oven 1.

In the case examined, the magnetic field depends not only on the number of permanent magnets 15, but also on the size of the cylinder 13 along the axis 57.

Also in this case, according to the embodiment examined, which is not part of the invention, the actuation of the motor 21 and of each motor 30 leads to the movement of the carriage 18 (with the modes described for the discs of figures 1 to 4) of the cylinders 13, which therefore involves the generation of additional forces in the molten metal, causing a translational and wave-like movement of the same in the furnace 1.

An embodiment of the invention is described in Figures 1 to 4. However, others are still possible: for example, on each load-bearing element 13, the magnets can be arranged (e.g., in the form of a cross on the disc in Figures 1 to 4), with a number of them and a height such as to create a magnetic flux of sufficient intensity to extend beyond the lower wall 4 of the furnace, so as not to be enclosed by the refractory material of the body 2 and to generate the desired "moving" force in the molten metal.

Furthermore, the invention described provides that the device 11 is placed in the well 10; however, such a device may be placed on one or more side walls 3 of the body 2 of the oven and, in such a case, the magnets 15 with the relative load-bearing element 13 may have an arrangement such as to generate the magnetic field towards said wall (which has a window analogous to the 6 described above).

Finally, a stirring device has been described that can move longitudinally along a furnace wall, which has permanent magnets supported by at least one load-bearing element comprising two disc-shaped bodies rotating around an axis M thereof (orthogonal or parallel to said wall). However, other embodiments are also possible in which such a stirring device does not move along the furnace wall, but rather has each load-bearing element that can move in a rotary motion around the axis M.

It should also be considered that such solutions fall within the scope of the present invention as defined by the following claims.

Claims (13)

1. System comprising a furnace (1) and a magnetic stirring device for molten metal contained in said furnace (1), said molten metal being aluminum or the like, the furnace (1) comprising a hollow body (2) with side walls (3) and a bottom wall (4), said furnace (1) being covered with refractory material and having a wall portion (6), present in one of said walls (3, 4), which is made as a metal sheet permeable to magnetic fields, the magnetic stirring device (11) for the metal placed in the furnace (1) being present in such wall portion (6), said device (11) comprising magnetic field generating means adapted to generate a magnetic flux within the metal placed in the furnace body (1), such generating means being a plurality of permanent magnets (15) supported by at least one load-bearing element (13) and placed on said wall portion (6), said load-bearing element (13) being rotatable about an axis (M, 57) thereof, characterized in that said load-bearing element (13) is provided as two discoidal bodies (13) which are adjacent and which rotate around their median axes (M) orthogonal to the wall (4) of the furnace (1), said rotation being obtained alternately in the same direction for both discoidal bodies (13) or with opposite rotation directions, with the same speed or with different speeds, with phasing or phase shifting in the rotation of said discoidal bodies (13), the permanent magnets (15) associated with each discoidal body (13) being arranged so as to form two parts or groups of magnets (N, S) which are separated from each other, a first part (N) of the magnets arranged in such a discoidal body (13) being provided with a first polarity directed towards the outside of the discoidal body (13), a second part (S) of the magnets being provided such that its second polarity is directed towards the outside of the discoidal body (13), the first polarity of such second part (S) of magnets being directed towards the discoidal body (13), each of said groups of magnets (N, S) occupying approximately half of the corresponding discoidal body (13), the groups of magnets (N, S) being separated from each other by a line (K). 2. System according to claim 1, characterized in that said permanent magnets (15) are arranged alternately as a disc or ring in the corresponding discoidal body (13), and substantially cover the entirety of such body (13). 3. System according to claim 1, characterized in that each middle axis (M) of the discoidal body (13) defines the axis of rotation of the magnetic field generating means, said discoidal body (13) being associated with a support (12) of a carriage (18) that can move with respect to the wall (4) of the oven (1), said carriage (18) moving along tracks or guides (19) so that each load-bearing element (13) and therefore the supported permanent magnets (15) can rotate and move simultaneously with respect to said wall (4). 4. System according to claim 3, characterized in that said carriage (18) supports electric actuators (21, 30) for the movement of the carriage itself along such guides (19) and of the discoidal body (13) around its median axis (M). 5. System according to claim 3, characterized in that the load-bearing elements (13) are associated with a lifting system (26) supported by the carriage (18) and actuated by an actuator (27), said load-bearing elements (13) and therefore the supported permanent magnets (15) being able to be raised or lowered with respect to the carriage (18). 6. System according to claim 3, characterized in that said tracks or guides (19) are placed on a lower surface (20) of a well (10) present below the oven (1), said magnetic field generating means (15) being able to move in and/or along a surface (20) present below the oven (1). 7. System according to claim 1, characterized in that said wall portion (6) is provided within a side wall (3) of the body (2) of the oven (1). 8. System according to claim 1, characterized in that each permanent magnet (15) is defined by one or more superimposed and stacked magnetic elements. 9. System according to claim 1, characterized in that the magnetic field generating means generate waveforms with spiral progression, linear progression, transverse progression, wave progression, translational progression, in phase or out of phase in the molten metal contained in the furnace. 10. Magnetic stirring device suitable for use in the system according to claim 1, said device (11) comprising magnetic field generating means adapted to generate a magnetic flux within the metal placed in the furnace body (1), said generating means being a plurality of permanent magnets (15) supported by at least one load-bearing element (13) and placed on said wall portion (6), said load-bearing element (13) being rotatable about an axis (M, 57) thereof, characterized in that said load-bearing element (13) is provided as two discoidal bodies (13) being adjacent and rotating about their median axes (M), said rotation being obtained alternately with the same direction for both bodies (13) or with opposite directions of rotation, with the same speed or with different speeds, with phasing or out-of-phase in the rotation of said discoidal bodies (13), the permanent magnets (15) being arranged associated with each discoidal body (13) so as to form two parts or groups of magnets (N, S) which are separated from each other, a first part (N) of the magnets (15) arranged in said discoidal body (13) being provided with a first polarity directed towards the outside of the discoidal body (13), a second part (S) of the magnets being arranged such that its second polarity is directed towards the outside of the discoidal body (13), the first polarity of said second part (S) of magnets being directed towards the discoidal body (13), each of said groups of magnets (N, S) occupying approximately half of the corresponding discoidal body (13), the groups of magnets (N, S) being separated from each other by a line (K). 11. Device according to claim 10, characterized in that said permanent magnets (15) are arranged alternately as a disc or ring in the corresponding discoidal body (13), and substantially cover the entirety of such body (13). 12. Device according to claim 10, characterized in that each permanent magnet (15) is defined by one or more superimposed and stacked magnetic elements. 13. Device according to claim 10, characterized in that the discoidal bodies (13) are associated with a support (12) supported by a carriage (18) that can move in a guided manner along tracks or guides (19), a drive motor (21) being provided for moving the carriage (18) along said tracks or guides (19) with reciprocating movement, the discoidal bodies (13) being rotated by at least one electric motor (30), the reciprocating movement of the carriage (18) and the rotation of the discoidal bodies (13) being simultaneous.