Patent Description:
The technology commonly known as Twin Roll Casting is widely used in the production of aluminum strips and is characterized by the direct feeding of the liquid aluminum between two counter-rotating steel rolls, which are cooled, e.g. by water. In particular, this process requires a lateral containment of the cast aluminum in order to increase productivity and avoid material accumulation on the edges, with the consequent need to clean the solidified material waste from the edges themselves.

This can be achieved, for example, by simultaneously using a mechanical lateral containment device, or mechanical edge dam, and an electromagnetic lateral containment device, or electromagnetic edge dam.

However, many drawbacks occur using the solutions of the prior art, such as:.

Some examples of an electromagnetic device for laterally containing liquid aluminum in a twin roll caster are disclosed in the following documents:.

The need for an electromagnetic containing device capable of solving the aforesaid drawbacks is therefore felt.

It is an object of the present invention to make an electromagnetic device for laterally containing liquid aluminum, in a horizontal or vertical casting of strips according to the Twin Roll Casting technology, which is able to improve performance in terms of both containment of liquid aluminum at high pressures and extension of the lateral containment region.

It is another object of the present invention to make an electromagnetic liquid aluminum containment device which is flexible, allowing different strip widths to be cast with the same steel rolls.

The present invention achieves at least one of such objects, and other objects which will be apparent in light of the present description, by means of an electromagnetic device for laterally containing liquid aluminum or a liquid alloy thereof, having a first electrical conductivity in a range from about <NUM> to <NUM>/m at a first temperature in a range from about <NUM> to <NUM>, at one open side end of a passage defined between two counter-rotating casting rolls, said device comprising.

wherein said at least one plate is made of a second material having a third electrical conductivity of at least <NUM>/m, at said second temperature, greater than said first electrical conductivity at said first temperature, whereby said at least one plate electromagnetically shields said inner surfaces with respect to each other.

Another aspect of the invention relates to a casting machine for casting flat products made of aluminum or alloys thereof, comprising.

preferably wherein said casting machine is a horizontal casting machine, said two counter-rotating casting rolls are superposed, and said feeding means are adapted to feed the liquid aluminum horizontally in the space between the two casting rolls.

A further aspect of invention relates to a casting process for casting flat products made of aluminum or alloys thereof, performed by means of the aforesaid casting machine, the process comprising the following steps:.

Advantageously, the solution of the electromagnetic device or edge dam of the invention allows to meet the following requirements:.

The casting machine of the invention further exploits the magnetic properties of the casting rolls, preferably made of steel (at least on the outer part thereof, in contact with the product to be solidified), to convey the magnetic field generated by the at least one coil, first between said coil and a casting roll and then between the casting roll and the aluminum product in the step of casting, thus generating eddy currents by induction, which, by interacting with the magnetic field, produce the Lorentz forces capable of contrasting the liquid aluminum head on the edge of the aluminum product.

The magnetic yoke can be made in a single piece of ferromagnetic material or made of a plurality of ferromagnetic sheets arranged on top of each other, or side by side, and electrically insulated from one another.

In both variants, the choice of the magnetic yoke material is important because the magnetic yoke as a whole must have a low electrical conductivity which significantly reduces the generation of eddy currents and therefore the need to cool the yoke intensively.

The presence of at least one plate, made of said second material, between the two wedge-shaped ends allows to:.

A better heat exchange between the metal of the casting product and the casting roll allows higher productivity (e.g. <NUM>/min for aluminum strip thicknesses of <NUM>) and greater flexibility in production control.

Further features and advantages of the present invention will become more apparent in light of the detailed description of preferred, but not exclusive embodiments.

The dependent claims describe particular embodiments of the invention.

The description of the invention refers to the accompanying drawings, which are provided by way of non-limiting example, in which:.

<FIG> shows an example of a horizontal casting machine comprising a pair of electromagnetic devices <NUM>, <NUM>, which are the object of the present invention. However, the electromagnetic devices of the present invention can also be used in vertical casting machines.

The casting machine, in the horizontal version of which is illustrated in the Figures, for casting flat products, e.g. strips, made of aluminum or alloys thereof, comprises:.

In this description, the term "aluminum" means both pure aluminum and any aluminum alloy with at least one metal, e.g. copper, zinc, manganese, silicon, or magnesium.

Advantageously, the aforesaid casting machine can not be equipped with any mechanical lateral containment device.

It is sufficient to use only one electromagnetic device if it is necessary to contain the liquid aluminum laterally only at one of the two side ends of said passage.

Preferably, at least the outer surfaces of the casting rolls <NUM>, <NUM>' are made of a ferromagnetic material, e.g. ferromagnetic steel.

The feeding means, known in themselves, comprise:.

Moving means <NUM> can be provided for moving the first electromagnetic device <NUM> and/or the second electromagnetic device <NUM> so as to adjust the distance from one another along a direction Z (<FIG>) parallel to a plane containing the rotation axes of the two casting rolls <NUM>, <NUM>'. Such moving means <NUM> can be, for example, linear, hydraulic, pneumatic, mechanical, pneumatic actuators, combinations thereof or the like.

This allows to cast different widths of aluminum product, e.g. strips, without needing to replace the casting rolls. The transition from one strip size to be produced to another only requires the lateral displacement of at least one of the two electromagnetic lateral containment devices, with respect to the casting rolls, along the Z direction. This can also apply to only one electromagnetic device.

Therefore, the width of the casting rolls being the same, said width being fixed, the electromagnetic lateral containment device can be moved so as to define different widths of the strip to be cast, and therefore it is not necessary to have dedicated sets of rolls as in the prior art, in which the electromagnetic device cannot be displaced laterally and, therefore, the casting rolls must be changed whenever it is necessary to cast strips of different widths.

Each electromagnetic device <NUM>, <NUM>, suited for the lateral containment of the liquid aluminum during casting, at the respective open side end of the passage defined between the two casting rolls <NUM>, <NUM>', comprises:.

The outer surfaces <NUM>, <NUM>' of the two wedge-shaped ends <NUM>, <NUM>' are shaped so that both said wedge-shaped ends <NUM>, <NUM>' can be inserted at least partially between the two casting rolls <NUM>, <NUM>'.

In the step of casting, the temperature of aluminum and alloys thereof is comprised in the range from about <NUM> to <NUM>. At this temperature the electrical conductivity of aluminum and alloys thereof is in the range from about <NUM> to <NUM>/m.

More specifically, the temperature of the aluminum in the step of casting is in the range from about <NUM> to <NUM>. At this temperature, the electrical conductivity of aluminum is comprised in the range from <NUM> to <NUM>/m.

Therefore, it is important to choose the materials of magnetic yoke <NUM> and plate <NUM> in order to satisfy the following relationship during the step of casting of aluminum or alloy thereof <MAT> wherein σAl is the electrical conductivity of aluminum or of an alloy thereof.

Preferably, the plate <NUM> is made of a material chosen from the following: copper, silver or other suitable metal.

The electrical conductivity of the material of the plate <NUM> during said step of casting is at least <NUM>/m, e.g. about <NUM>/m.

The temperature of the plate <NUM> is kept in the range from about <NUM> to <NUM>, during the casting of the aluminum or an alloy thereof.

Preferably, the magnetic yoke <NUM> is made of a ferromagnetic material, e.g. chosen from the following: silicon steel, "Fluxtrol" materials, e.g. Fluxtrol <NUM>, or "Grey T Type" made by MagShape, or anyway materials having magneto-dielectric properties, due to the doping between iron elements and plastic elements constituting the magnetic yoke <NUM>, which imply the reduction of the internal heating phenomenon due to the formation of eddy currents.

The electrical conductivity of the ferromagnetic material of the magnetic yoke <NUM> during the aforesaid step of casting is less than or equal to <NUM>/m, preferably less than or equal to <NUM>/m.

The temperature of the magnetic yoke <NUM> is kept in the range from about <NUM> to <NUM>, during the casting of aluminum or an alloy thereof.

Advantageously, each electromagnetic device <NUM>, <NUM>, and thus the respective magnetic yoke <NUM>, is positioned laterally and in an outer position, e.g. completely outside, with respect to the zone occupied by the unloader or the feed tip <NUM>.

Furthermore, the magnetic yoke <NUM> is not profiled to adapt to the unloader <NUM>. The magnetic yoke <NUM> is instead profiled to define the aforesaid gap <NUM> in which the plate <NUM> is inserted, said plate being made of a conductive and magnetic material such as to electromagnetically shield the inner surfaces <NUM>, <NUM>', which are preferably flat and substantially parallel to each other. Therefore, the plate <NUM> is not transparent to the magnetic fields generated by the electromagnetic device.

Preferably, the gap or distance <NUM> between the inner surfaces <NUM>, <NUM>', facing each other, of the two wedge-shaped ends <NUM>, <NUM>' is in a range from <NUM> to <NUM>, preferably <NUM> to <NUM>. Optionally, the plate <NUM>, or at least the part of plate <NUM> arranged between the two inner surfaces <NUM>, <NUM>', has a thickness in the range from <NUM> to <NUM>, preferably from <NUM> to <NUM>. Therefore, due to the shape of the outer surfaces <NUM>, <NUM>' of the wedge-shaped ends <NUM>, <NUM>', and due to the fact that the gap <NUM> and, therefore, the plate <NUM> are very thin, the magnetic field flux, appropriately diverted by the plate <NUM>, enters into a casting roll and crosses the space between the casting rolls, crossing the aluminum to be cast, in a point in which this space is very narrow. For example, considering a casting roll diameter of <NUM>, the magnetic field flux between the casting rolls makes a path of about <NUM>-<NUM> when it exits the wedge-shaped end <NUM> and then closes in the other wedge-shaped end <NUM>'. Preferably, the two wedge-shaped ends <NUM>, <NUM>' are arranged symmetrically with respect to a symmetry plane lying in the gap <NUM>, with the respective inner surfaces <NUM>, <NUM>' substantially parallel and proximal to said symmetry plane, and the respective outer surfaces <NUM>, <NUM>', flat or curved, distal from the symmetry plane but substantially converging towards said symmetry plane so as to define the wedge shape.

In a variant, the outer surfaces <NUM>, <NUM>' of the wedge-shaped ends <NUM>, <NUM>' are curvilinear with a radius of curvature substantially equal to the outer radius of the corresponding casting roll. Each wedge-shaped end <NUM>, <NUM>' is also provided with two further lateral surfaces <NUM> that are transverse, preferably perpendicular, to the inner surface <NUM>, <NUM>', and joining the inner surface <NUM>, <NUM>' to the respective outer surface <NUM>, <NUM>'.

Advantageously, the lateral containment of the liquid aluminum is achieved by supplying electrical current to at least one coil <NUM> so that, by virtue of the magnetic properties of the materials of some components of the casting machine and the relation between the electrical conductivities of the different materials used, the magnetic field flux produced by the coil <NUM> passes in succession, as shown in <FIG>:.

Preferably, if the casting process is performed by means of a horizontal casting machine, the passage of the magnetic field flux from the first roll <NUM> to the second roll <NUM>' is substantially vertical; while, if the casting process is performed by means of a vertical casting machine, the passage of the magnetic field flux from the first roll <NUM> to the second roll <NUM>' is substantially horizontal.

By way of example only, during the operation of the device of the invention, the minimum distance between the electromagnetic device and the casting roll, i.e. the minimum distance between the outer surfaces <NUM>, <NUM>' of the wedge-shaped ends <NUM>, <NUM>' and the corresponding casting roll, is about <NUM>-<NUM>, e.g. about <NUM>. Preferably, the distance between the electromagnetic device and the liquid aluminum is about <NUM>-<NUM>, e.g. <NUM>.

Advantageously, the electrical conductivity of the material of the plate <NUM> prevents the magnetic field from closing in the yoke itself, thereby conveying the magnetic field flux from the wedge-shaped end <NUM> towards the surface of the proximal casting roll <NUM>, made of ferromagnetic material, thus promoting the containment force.

A solidification process of the liquid aluminum through the casting machine is shown in <FIG>. In this process, the products, e.g. strips or sheets, are cast directly by means of the liquid aluminum feed, through the unloading device <NUM>, between two cooled and counter-rotating casting rolls <NUM>, <NUM>'. A cross-section of the solidification region is shown in <FIG>. As soon as the liquid aluminum touches the rolls <NUM>, <NUM>', a solid shell starts forming, growing towards outlet passage <NUM>. The solid shells adhering to the upper roll <NUM> and to the lower roll <NUM>' meet in a solidification point <NUM> just before the outlet passage <NUM> (usually the total solidification length is about <NUM>-<NUM> for a conventional process with a casting speed of about <NUM>/min and a aluminum sheet thickness of <NUM>) and from there the aluminum product is deformed by the casting rolls <NUM>, <NUM>', obtaining the cast product <NUM>. With reference to <FIG>, the electromagnetic device or edge dam <NUM> is used to handle the aluminum by applying pressure along the sump depth <NUM> (<FIG>, corresponding to the actual solidification length) during casting. This pressure, by virtue of the aforesaid Lorentz Forces, controls the position of the side edge of the aluminum in the region between the unloader <NUM> and the outlet passage <NUM>, where a real physical containment is absent. Diagrammatically in <FIG>, in which the direction of casting is indicated by reference numeral <NUM>, the region in which the liquid aluminum is physically contained inside the unloader <NUM> is indicated by reference numeral <NUM>; the solidification region in which the liquid aluminum is not physically contained laterally is indicated by reference numeral <NUM>; the region in which the cast product is completely solid and reduced in thickness is indicated by the reference numeral <NUM>; and the lateral region (circled in <FIG>) in which the liquid aluminum is contained by the Lorentz Forces, by means of the electromagnetic device <NUM>, is indicated by the reference numeral <NUM>.

Preferably, as shown in <FIG> and <FIG>, the magnetic yoke <NUM> has the body <NUM> provided with two arms <NUM>, <NUM>', each arm ending with the respective wedge-shaped end <NUM>, <NUM>'.

In the case of horizontal casting, the two wedge-shaped ends <NUM>, <NUM>' are arranged one above the other.

In a variant, shown in <FIG>, the arms <NUM>, <NUM>' comprise:.

The body <NUM> is provided with an further stretch <NUM> connecting the first stretches <NUM>, <NUM>' and arranged in a distal position from the wedge-shaped ends <NUM>, <NUM>'.

Preferably, the first stretches <NUM>, <NUM>' and second stretches <NUM>, <NUM>' are arranged along a first plane, and third curved stretches <NUM>, <NUM>' are provided which connect a respective second stretch <NUM>, <NUM>' to the respective wedge-shaped end <NUM>, <NUM>'. The two wedge-shaped ends <NUM>, <NUM>' are therefore arranged along a second plane which is inclined with respect to the first plane by an angle greater than <NUM>°, preferably between <NUM> and <NUM>°.

In an embodiment of the present invention, the body <NUM> of magnetic yoke <NUM>, having the shape described above, is made of a ferromagnetic material, e.g. silicon steel, and can be formed by a single solid piece of such ferromagnetic material. In another embodiment, the body <NUM> of the magnetic yoke <NUM> can be formed by a series of ferromagnetic sheets which are bent and fixed together, using mechanical means, an adhesive or similar means to provide the desired configuration, said ferromagnetic sheets being insulated from each other by means of insulators, using a technology similar to that used for the composition of the ferromagnetic cores of the transformers.

Preferably, the at least one plate <NUM>, preferably a single plate <NUM>, in the variant shown in <FIG>, comprises a flat part <NUM> arranged between the inner surfaces <NUM>, <NUM>' of the wedge-shaped ends <NUM>, <NUM>'. The thickness of said flat part <NUM> is preferably in the range from about <NUM> to <NUM>, e.g. from <NUM> to <NUM>.

Optionally, said flat part <NUM> is provided, at one end thereof, with a bifurcation with diverging stretches <NUM>, <NUM>' substantially parallel to the second stretches <NUM>, <NUM>' of the arms <NUM>, <NUM>' of the magnetic yoke <NUM>. The space between the two diverging stretches <NUM>, <NUM>' can be either empty, as shown in the Figures, or full whereby a material block is provided having the aforesaid diverging stretches <NUM>, <NUM>' as two opposite surfaces. Preferably, the flat part <NUM> has a curved end stretch <NUM> arranged between the third curved stretches <NUM>, <NUM>' of the magnetic yoke and connected to the diverging stretches <NUM>, <NUM>'.

The plate <NUM> is preferably also provided, at a side edge <NUM> thereof (<FIG>), with a wall <NUM> (<FIG>) which is transversal, preferably orthogonal, to the flat part <NUM> and shaped to cover a side surface <NUM> of both the wedge-shaped ends <NUM>, <NUM>'.

The wall <NUM> is also provided with a respective bifurcation with respective diverging stretches <NUM>, <NUM>' which are transversal, preferably perpendicular, to the diverging stretches <NUM>, <NUM>' of the plate <NUM> and shaped so as to cover a flank of said second stretches <NUM>, <NUM>' of the body <NUM> of the magnetic yoke <NUM>. Preferably, a curved stretch <NUM>' connects the main body of the wall <NUM> to the diverging stretches <NUM>, <NUM>'.

Preferably, the plate <NUM> is fixed to the magnetic yoke <NUM>, e.g. by means of an adhesive binder. Any epoxy adhesive which has the following characteristics can be used:.

In particular, the flat part <NUM>, e.g. rectangular, is fixed to the inner surfaces <NUM>, <NUM>' of the wedge-shaped ends <NUM>, <NUM>'; the diverging stretches <NUM>, <NUM>' are fixed to the respective second stretches <NUM>, <NUM>' of the body <NUM>; the curved end stretch <NUM> is fixed to the third curved stretches <NUM>, <NUM>'; the wall <NUM> is fixed to the side surfaces <NUM> of both wedge-shaped ends <NUM>, <NUM>'. Furthermore, in particular, the curved stretch <NUM>' of the wall <NUM> is fixed to the inner surfaces of the curved stretches <NUM>, <NUM>' of the body <NUM>, while the diverging stretches <NUM>, <NUM>' of the wall <NUM> are fixed to a flank of the corresponding second stretch <NUM>, <NUM>' of the body <NUM>.

Advantageously, the plate <NUM> can be provided with cooling means. These cooling means comprise at least one channel <NUM> made inside the plate <NUM>, and which can be connected to a supply circuit of cooling liquid, e.g. water.

In a variant shown in the partially sectioned view of <FIG>, in which for a better understanding the upper part of the wall <NUM> is not visible, a channel <NUM>, inside the plate <NUM>, is made in proximity of two edges of the plate <NUM>, and in particular along the edge <NUM>, corresponding to the tip of the wedge-shaped ends <NUM>, <NUM>', and along the edge <NUM>, i.e. the edge of the plate <NUM> which in operating position is proximal to the lateral end of the passage of the product to be cast, and therefore distal from wall <NUM>. This configuration allows the removal of the heat generated by the Joule effect in the part of the magnetic yoke <NUM> proximal to the passage of the product to be cast, keeping the yoke temperature below about <NUM>.

Preferably, the channel <NUM> has substantially a L-shape in plan, with the short stretch along the edge <NUM> and the long stretch along the edge <NUM>. Preferably, the cooling liquid, supplied by the supply circuit (not shown), enters the channel <NUM> from an end of the edge <NUM> and exits the channel <NUM> from an end of the edge <NUM>. In particular, the wall <NUM> is provided with a slot <NUM> (<FIG>) to let the cooling liquid into the channel <NUM>, at the end of the edge <NUM>.

The long stretch of the channel <NUM>, along the edge <NUM>, can have a curved end <NUM> at the curved end stretch <NUM> of the flat part <NUM> of the plate. Preferably, in this case, the cooling liquid, supplied by the supply circuit, enters the channel <NUM> from an end of the edge <NUM>, proximal to the wall <NUM>, and exits the channel <NUM> from the curved end thereof, distal from the edge <NUM>.

In addition to the channel <NUM>, suitable cooling systems can be provided to cool the outer walls of the entire wall <NUM> and of the diverging stretches <NUM>, <NUM>' of the plate <NUM>.

In a variant shown in <FIG>, there are provided two coils <NUM>, <NUM>' connected in series, each coil <NUM>, <NUM>' being wound on a first stretch <NUM>, <NUM>' of a respective arm <NUM>, <NUM>' of the magnetic yoke <NUM>. The use of more than two coils is not excluded. The coils, e.g. made of copper, are preferably hollow and/or preferably internally watercooled.

Advantageously, at least one cooling circuit can be provided which runs through at least one first stretch <NUM>, <NUM>' of the arms <NUM>, <NUM>'.

Preferably, as shown in <FIG>, two cooling circuits are provided, one passing through at least the first stretch <NUM> of the arm <NUM> on which the coil <NUM> is wound, and the other passing through at least the first stretch <NUM>' of the arm <NUM>' on which the coil <NUM>' is wound.

Claim 1:
An electromagnetic device (<NUM>) for laterally containing liquid aluminum or a liquid aluminum alloy, having a first electrical conductivity in a range from about <NUM> to <NUM>/m at a first temperature in a range from about <NUM> to <NUM>, at one open side end of a passage defined between two counter-rotating casting rolls (<NUM>, <NUM>'), said device comprising
- a magnetic yoke (<NUM>) made of a first material having a second electrical conductivity either less than or equal to <NUM>/m, at a second temperature comprised in a range from about <NUM> to <NUM>, lower than said first electrical conductivity, said first material being ferromagnetic material and said magnetic yoke ending with two mutually proximal wedge-shaped ends (<NUM>, <NUM>'), said wedge-shaped ends having respective inner surfaces (<NUM>, <NUM>'), facing each other and defining a gap (<NUM>), and respective outer surfaces (<NUM>, <NUM>'), arranged one on one side and the other on the other side with respect to a plane lying in said gap;
- at least one coil (<NUM>) wound on at least one stretch of the magnetic yoke (<NUM>) and adapted to be supplied by electric current;
- at least one plate (<NUM>) inserted in said gap (<NUM>);
characterized in that said at least one plate (<NUM>) is made of a second material having a third electrical conductivity of at least <NUM>/m, at said second temperature, greater than said first electrical conductivity at said first temperature, whereby said at least one plate (<NUM>) can electromagnetically shield said inner surfaces (<NUM>, <NUM>') with respect to each other.