Patent Description:
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.

Magnetic stirrers for metal melts are known in the art, such as disclosed by <CIT>, <CIT>, <CIT> or <CIT>.

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 <NUM>/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 system comprising a furnace and the aforesaid magnetic device or stirrer provided 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 system comprising a furnace and a magnetic stirrer 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 system comprising a furnace containing molten metal and said magnetic stirrer 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:.

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

The portion or window <NUM> below the refractory material is covered with material permeable to the magnetic field, such as stainless steel or equivalent material.

Below the furnace <NUM>, a well <NUM> is present in which a magnetic stirrer device or stirrer <NUM> is placed which, in one embodiment of the invention, is movable along and frontally with respect to the window <NUM> of the bottom wall <NUM> (or it is movable along the longitudinal axis of such wall).

More particularly, such device or magnetic stirrer <NUM> comprises a support <NUM> for load-bearing members <NUM> which is associated with a plurality of permanent magnets <NUM>. In <FIG>, such load-bearing members <NUM> are discs made of iron or magnetic material, while in the solution pursuant to <FIG> (which does not form part of the present invention) such members are cylindrical drums, also made of iron or an appropriate magnetic material.

The support <NUM> is a surface associated with a trolley <NUM> movable in a guided manner along guides or tracks <NUM> placed on a bottom or surface <NUM> of the well <NUM>. Such movement is generated by at least one electric motor <NUM> operating on at least one wheel <NUM> movable along a corresponding guide of such guides <NUM>.

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

With reference to the abovementioned <FIG> relating to the invention, the permanent magnets <NUM> are carried by the member (or load-bearing disc) <NUM>. According to the invention, two members or discs <NUM> are associated with the support <NUM> and placed with median axes M orthogonal to the corresponding load-bearing disc (and hence to the bottom <NUM> on which the trolley <NUM> is moved as well as to the wall <NUM> of the furnace). Each disc can rotate around its median axis M driven by an electric motor (gear motor) <NUM>; or a single motor <NUM> associated with the support <NUM> moves both discs <NUM>. 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 <FIG> and <FIG>, the permanent magnets <NUM> are placed on a face 13A of the corresponding disc <NUM> directed towards the wall <NUM>, so as to form a magnetic annular disc. In the embodiments of <FIG>, they instead occupy nearly the entire surface of the corresponding disc <NUM> with a precise magnetic orientation.

Each magnet <NUM> is constituted by a single body or by two or more stacked magnets. On the discs <NUM>, moreover, the magnets are arranged so as to form two "groups" or portions with different polarities directed upward (i.e. towards the wall <NUM> of the furnace <NUM>). 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 <NUM> (as shown in <FIG> 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 <NUM> are inserted in respective seats <NUM> fixed to the disc <NUM> made of Teflon or similar non-magnetic material, so as to be easily associable with the aforesaid disc.

As stated, each disc <NUM> is moved around its axis M. Such movement can be at uniform or variable speed (for example between <NUM> and <NUM> 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 <NUM> so as to move the trolley <NUM> along the tracks <NUM> with an alternated movement from one end of the furnace to the other or vice versa, and simultaneously actuating the motor(s) <NUM> which rotate the discs <NUM>, it is possible to generate convective and wave motions with spiral progression in the molten metal (e.g. aluminum) placed in the furnace <NUM>. 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).

The magnets <NUM> are placed on the discs <NUM> (shown in <FIG>, <FIG> and <FIG>), and spiral motions are generated in the metal when the trolley <NUM> is moved along the tracks <NUM>.

The number and size of the magnets <NUM> 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 <NUM>.

In <FIG>, showing an embodiment which is not part of the present invention, parts corresponding to those of <FIG> are indicated with the same reference numbers; in this embodiment which is not into the scope of the claimed invention, the permanent magnets <NUM> are carried by load-bearing members <NUM> in the form of drums or cylinders. Such members or cylinders <NUM> have the seats <NUM> for the magnets <NUM> arranged on the surface and along generatrices of the cylinders. In addition, at one end <NUM> of each member or cylinder <NUM>, a disc <NUM> is present, moved by means of belt <NUM> by the electric motor <NUM>. Of course, a motor can move multiple cylinders <NUM> or each of these can have its own motor.

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

It should be noted that with the rotation axis parallel to the wall <NUM> (towards which the magnets <NUM> face) or orthogonal to such wall <NUM>, 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 <NUM>°, close thereto, with said wall <NUM>.

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

In the case under examination, the magnetic field depends not only on the number of permanent magnets <NUM> but also on the size of the cylinder <NUM> along the axis <NUM>.

Also in this case, according to the embodiment under examination, which does not form a part of the invention, the actuation of the motor <NUM> and of each motor <NUM> leads to the movement of the trolley <NUM> (with the modes described for the discs of <FIG>) of the cylinders <NUM>, which thus involves the generation of further forces in the molten metal, causing a translational and wave movement thereof in the furnace <NUM>.

One embodiment of the invention has been described in <FIG>. Still others are nevertheless possible: for example, on each load-bearing member <NUM>, the magnets can be arranged (e.g. cross-like on the disc of <FIG>), with a number thereof and height such to create a magnetic flux with intensity sufficient to go beyond the bottom wall <NUM> of the furnace, to not be shut on the refractory material of the body <NUM> and to generate the "moving" force desired in the molten metal.

In addition, the described invention provides for the device <NUM> placed in the well <NUM>; nevertheless, such device can be placed at one or more lateral walls <NUM> of the body <NUM> of the furnace and in such case the magnets <NUM> with the relative load-bearing member <NUM> can have an arrangement such to generate the magnetic field towards said wall (which has a window analogous to that <NUM> 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 comprising two discoid bodies 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.

Claim 1:
A system comprising a furnace (<NUM>) and a magnetic stirrer device for molten metal contained in said furnace (<NUM>), said molten metal being aluminum or the like, the furnace (<NUM>) comprising a hollow body (<NUM>) with lateral walls (<NUM>) and a bottom wall (<NUM>), said furnace (<NUM>) being covered with refractory material and having a wall portion (<NUM>), present in one of such walls (<NUM>, <NUM>), which is made as a metal sheet permeable to the magnetic fields, the magnetic stirrer device (<NUM>) for the metal placed in the furnace (<NUM>) being present at such wall portion (<NUM>), said device (<NUM>) comprising magnetic field generator means adapted to generate a magnetic flux within the metal placed in the body of the furnace (<NUM>), such generator means being a plurality of permanent magnets (<NUM>) carried by at least one load-bearing member (<NUM>) and placed at said wall portion (<NUM>), said load-bearing member (<NUM>) being rotating around an axis (M, <NUM>) thereof, characterized in that said load-bearing member (<NUM>) being provided as two discoid bodies (<NUM>) which are adjacent and rotating around their median axes (M) orthogonal to the wall (<NUM>) of the furnace (<NUM>), said rotation being alternatively obtained with the same sense for both discoid bodies (<NUM>) or with opposite rotation senses, with the same speed or with different speeds, with phasing or dephasing in the rotation of said discoid bodies (<NUM>), the permanent magnets (<NUM>) associated with each discoid body (<NUM>) being arranged in a manner such to form two portions or groups of magnets (N, S) that are separate from each other, a first portion (N) providing for the magnets arranged on such discoid body (<NUM>) with a first polarity directed towards the exterior of the discoid body (<NUM>), a second portion (S) providing for the magnets arranged in a manner such that their second polarity is directed towards the exterior of the discoid body (<NUM>), the first polarity of such second portion (S) of magnets being directed towards the discoid body (<NUM>), wherein that each of said groups of magnets (N, S) occupies about half of the corresponding discoid body (<NUM>), the groups of magnets (N, S) being separated each other by a line (K).