DESCRIPTION

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

It is known to use devices (or stirrers) that are adapted to generate a magnetic field within a molten metal contained in a furnace having a hollow body or tank with lateral walls and a bottom wall.

The aforesaid body is internally covered with refractory material and has a portion of the bottom wall which is made of material, such as stainless steel, that is permeable to the magnetic field generated by a device placed at such wall. Also known are solutions in which such device or stirrer (as it will be indicated in the course of the present document) is (also) placed at a lateral wall of the body of the furnace (which in such case has a portion made of magnetic material permeable to the magnetic field).

The furnace can be a smelting furnace or a holder furnace.

The abovementioned magnetic stirrer can be fixed or movable along one or more guides provided below the wall of the body of the furnace at which such stirrer is placed. For example, if the stirrer is placed below the lower wall, a well is normally provided below the furnace that contains the stirrer and which has the abovementioned guides, if it is of movable type. In the movable version, the translation movement of the stirrer can be generated by actuator means separate from the stirrer (such as drive members associated with the well) or integral with the stirrer (e.g. one or more electric motors that move it along the guide or guides).

The function of the known stirrer is that of creating oscillating or wave motions within the mass of the molten metal present in the furnace in order to remix it, making the surface temperature of such mass uniform and also preventing the creation or deposit of solid parts therein.

The stirrers of the state of the art are normally made by means of the use of electromagnets and have various drawbacks.

For example, they must be cooled. The solution of providing for the stirrer inserted in the chamber of the cooling liquid (usually water) has demonstrated that it can be improved, since it has various drawbacks. First of all, the stirrer is immersed in the cooling water, which requires a suitable electrical isolation of such device (comprising a series of coils in which high current circulates) from the aforesaid fluid in order to prevent obvious drawbacks, which could generate problems of electrical safety and considerable damage to the electrical plant and power grid where the production of billets occurs, even up to the complete stoppage thereof.

In order to remedy this problem, an isolation transformer is normally employed, which is in any case quite bulky, requires high power and hence is costly.

This also negatively affects the performance of the system and the layout of the plant.

In addition, the cooling water must be demineralized (which in any case has a non-negligible cost) in order to have a conductivity thereof (which must never exceed 200uS/cm) that is controlled, so to prevent the water itself from becoming an electrical conductor due to the presence of the stirrer therein. In addition, known stirrers operate with very high intensity currents. This involves the use of electrical components (inverters) for driving and controlling the stirrers which have large size and high costs, since they are sized for the high currents that they must control. In addition, the abovementioned known solutions generally have very low efficiency due to the necessary magnetizing currents and dispersions of the electromagnetic field generated by the stirrer, the heating of the coils and the relative magnetic poles made of magnetic sheet and the shielding of said stirrer.

In addition, there are also problems tied to the need to electrically connect the stirrer (placed in the chamber where the cooling fluid is present) to an electrical power supply, and to the need to cool the windings of the stirrer.

Object of the present invention is to provide a magnetic stirrer for a furnace for molten metal - smelting or holder furnace - which is improved with respect to analogous known furnaces.

Another object is to provide a stirrer of the abovementioned type which has lower manufacturing and management costs than those of analogous known stirrers and which have better results than the latter regarding performance, energy consumption, compactness and mixing obtained within the mass of molten metal present in the furnace.

A further object is to provide a furnace comprising the aforesaid magnetic device or stirrer in order to create a stirring within the mass of molten metal contained in the furnace, in which the action of such stirrer is more effective with respect to known analogous devices in creating stirring motions within such metal mass. In particular, one object of the invention is to provide a first furnace of the abovementioned type in which there is an effective control of the fluid wave forms which are developed in the molten metal so as to obtain wave forms with spiral and wave progression that are not possible with normal stirrers. A suitable control panel and a specific software provide for setting the generated wave forms and consequently the progression of the flows of molten metal present in the furnace.

Another object is to provide a device or stirrer of the abovementioned type which has high efficiency, greater than that of known stirrers, and which has an energy consumption lower than that of known stirrers which make use of electromagnets, and in particular operating with an installed power of less than half that required for a normal electromagnetic stirrer.

A further object is to provide a device or stirrer which has a reduced dispersion of electrical power supplied for the operation thereof, which does not require the use of isolation transformers, which does not use large-size inverters with high currents required for driving the electromagnetic coils provided with normal stirrers, and which does not require costly devices for filtering the harmonics or rephasing of the power supply network.

Another object is to provide a device or stirrer of the abovementioned type which creates diverse controlled motions along different directions within the mass of metal placed in the furnace.

A further object is to provide a device or stirrer of the abovementioned type which can be easily adapted both during construction and by means of the control management software as a function of the type, size, structural form of the furnace and thickness of the refractory material of the furnace with which it must be associated.

These and other objects which will be clear to the man skilled in the art are achieved by a magnetic stirrer device and by a furnace containing molten metal according to the enclosed claims.

For an improved comprehension of the present invention, the following drawings are enclosed merely by way of example, in which:

figure 1 shows a bottom perspective view of a furnace according to the invention;

figure 2 shows a top perspective view, partially sectional and with some parts removed for better clarity, of the bottom of figure 1 and of a device according to the invention;

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

figure 4 shows a top perspective view of a part of the magnetic stirrer device housed in its container;

figure 5 shows a view analogous to that of figure 2, but representing a further variant of the magnetic stirrer device associated with a furnace containing molten metal;

figure 6 shows a partially sectional view of the furnace and of the device of figure 5;

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

With reference to the abovementioned figures, the basin of a furnace containing molten metal is generically indicated with 1 . It comprises a body 2 having lateral walls 3 and a bottom wall 4, while it is open on the upper part. The body 2 is generally entirely covered with refractory material which in turn can be contained in any known metallic structure, except for a portion or "window" 6 generally provided in the bottom wall 4 and occupying a part, more or less (longitudinally) large, of the latter. The basin of the furnace or simply furnace 1 can be a smelting furnace or a holding furnace, per se known.

The portion 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 furnace 1 , a well 10 is present in which a magnetic stirrer device or stirrer 1 1 is placed which, in one embodiment of the invention, is movable along and frontally with respect to the window 6 of the bottom wall 4 (or it is movable along the longitudinal axis of such wall).

More particularly, such device or magnetic stirrer 1 1 comprises a support 12 for load-bearing members 13 which is associated with a plurality of permanent magnets 15. In figures 1 -4, such load-bearing members 13 are discs made of iron or magnetic material, while in the solution pursuant to figures 5-7 such members are cylindrical drums, also made of iron or an appropriate magnetic material.

The support 12 is a surface associated with a trolley 18 movable 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 operating on at least one wheel 23 movable along a corresponding guide of such guides 19.

In a known manner, the support 12 is subjected to the action of a scissors lift, screw lift or another lifting system 26, carried by the trolley 18 and actuated by electric motor 27 or by hydraulic or pneumatic cylinder integral with the latter and operating, by means of worm screw 28, on such lift 26. By actuating the motor 27, the lift is raised or lowered in a per se known manner with respect to the trolley 18 carrying the support 12 close to or moving it away from the bottom wall 4 of the furnace 1 .

With reference to the abovementioned figures 1 -4, the permanent magnets 15 are carried by the member (or load-bearing disc) 13. Preferably and advantageously, two members or discs 13 are associated with the support 12 and placed with median axes M orthogonal to the corresponding load-bearing disc (and hence to the bottom 20 on which the trolley 18 is moved as well as to the wall 4 of the furnace). In one embodiment, 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 moves both discs 13. Of course, each disc can provide for an electric motor thereof (or in general an electric actuator) that generates the rotary movement thereof, by means of per se known mechanical couplings (which provide for gears and transmissions in mutual coupling and integral with the motor and disc).

In one embodiment, shown in figures 2 and 3, the permanent magnets 15 are placed on a face 13A of the corresponding disc 13 directed towards the wall 4, so as to form a magnetic annular disc. In the embodiments of figure 4, they instead occupy nearly the entire surface of the corresponding disc 3 with a precise magnetic orientation.

Each magnet 15 is constituted by a single body or by two or more stacked magnets. On the discs 13, moreover, the magnets are arranged so as to form two "groups" or portions with different polarities directed upward

(i.e. towards the wall 4 of the furnace 1 ). A first group of magnets is directed with the north polarity upward and the other with the south polarity upward; each of such groups occupies about half of the disc 13 (as shown in figure 4 where the group of magnets, indicated with N and S as a function of the polarity directed upward, are separated by the line K).

The adjacent magnets 15 are inserted in respective seats 40 fixed to the disc 13 made of Teflon or similar non-magnetic material, so as to be easily associable with the aforesaid disc.

As stated, each disc 13 is moved around its axis M. Such movement can be at uniform or variable speed (for example between 1 and 20 rev/min); the rotation speed can be the same for both discs or different.

Such discs can rotate in the same direction or in opposite directions, continuously or alternated over time. In addition, such discs can rotate in phase or out of phase with each other, in order to determine the particular force lines that move the liquid material contained in the melting bath, obtaining precise and programmed fluidic progressions.

Due to the solution shown in the figures under examination, by actuating the motor 21 so as to move the trolley 18 along the tracks 19 with an alternated movement from one end of the furnace to the other or vice versa, and simultaneously actuating the motor(s) 30 which rotate the discs

13, it is possible to generate convective and wave motions with spiral progression in the molten metal (e.g. aluminum) placed in the furnace 1 .

Such motions continuously remix the molten metal, preventing the formation of oxides therein and thus increasing the purity thereof (and the capacity to have a high purity, which translates into final products with increased aesthetic value and greater mechanical stress resistance).

In particular, the magnets 15 are placed on the discs 13 (as in figures 2, 3 and 4), and spiral motions are generated in the metal when the trolley 18 is moved along the tracks 20.

The number and size of the magnets 15 can vary in order to modify the shape and intensity of the generated magnetic field and hence the remixing force that is generated in the molten metal and the energy that is dissipated therein. The rotation speed of the discs and the translation speed combined together cause a convergent or divergent longitudinal or transverse spiral progression of the fluid.

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

In figures 5-7, where parts corresponding to those of figures 1 -4 are indicated with the same reference numbers, the permanent magnets 15 are carried by load-bearing members 13 in the form of drums or cylinders. Such members or cylinders 13 have the seats 40 for the magnets 15 arranged on the surface and along generatrices of the cylinders. In addition, at one end 50 of each member or cylinder 13, a disc 54 is present, moved by means of belt 55 by the electric motor 30. Of course, a motor can move multiple cylinders 13 or each of these can have its own motor.

Each cylinder is laterally supported by panels 56 integral with the support 12, rotating on bearings (not shown) which constrain an axle 57 of each cylinder (around which it rotates) to said panels. Such axle is parallel to the bottom 20 on which the trolley 18 is moved, i.e. to the longitudinal axis of the wall 4 of the furnace 1 .

It should be noted that with the rotation axis parallel to the wall 4 (towards which the magnets 15 face) or orthogonal to such wall 4, reference is not only made 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 decrees incident on the aforesaid wall (and hence not perfectly parallel thereto) or in which such axis forms an angle different from 90 °, close thereto, with said wall 4.

With the abovementioned term "face", moreover, it is indicated the position of the magnets 15 such to direct the magnetic field generated thereby towards the adjacent part of the furnace 1 .

In the case under examination, 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 under examination, the actuation of the motor 21 and of each motor 30 leads to the movement of the trolley 18 (with the modes described for the discs of figures 1 -4) of the cylinders 13, which thus involves the generation of further forces in the molten metal, causing a translational and wave movement thereof in the furnace 1 .

Various embodiments of the invention have been described. Still others are nevertheless possible: for example, on each load-bearing member 13, the magnets can be arranged (e.g. cross-like on the disc of figures 1 -4), with a number thereof and height such to create a magnetic flux with intensity sufficient to go beyond the bottom wall 4 of the furnace, to not be shut on the refractory material of the body 2 and to generate the "moving" force desired in the molten metal; or, in the embodiment of figures 5-7, the cylinders which carry the magnets can be moved by motors directly fit on the axle 57.

In addition, the described invention provides for the device 1 1 placed in the well 10; nevertheless, such device can be placed at one or more lateral walls 3 of the body 2 of the furnace and in such case the magnets 15 with the relative load-bearing member 13 can have an arrangement such to generate the magnetic field towards said wall (which has a window analogous to that 6 described above).

Finally, a stirrer device was described that is longitudinally movable along a wall of the furnace, having permanent magnets carried by at least one load-bearing member rotating around an axis M thereof (orthogonal or parallel to such wall). However, other embodiments are also possible in which such stirrer device does not translate along the wall of the furnace, but rather has each load-bearing member movable with rotary motion around the axis M; or the embodiment is possible according to which there is a translation of the device along the furnace, but the permanent magnets are associated with a fixed load-bearing member (non-rotating) - even if such magnets are mounted on rotary tables, they do not rotate during the translation.

Also such solutions are to be considered as falling within the scope of the present invention as defined by the following claims.