TECHNICAL FIELD This invention relates to controlling the flow of molten metal through the outlet channel of a furnace or a vessel containing molten metal, particularly to a device and to a process for braking and stopping the flow of molten metal using an electromagnetic brake.

BACKGROUND OF THE INVENTION When transferring high temperature molten metal (approximately 1500°C) from a melting furnace, or from a treating or collecting vessel, to another receptacle, it is important to keep the closing phase of the transfer operation as short as possible to minimize the passage of slag from one vessel to another, to improve the control of the transferred material, and to reduce damage to the mechanism which closes off the flow of molten metal. It is also important to ensure the successful transfer of the molten metal during the operational cycle, to limit maintenance and prolong the life of the melting and transfer equipment.

Several ways of intercepting the high temperature molten metal in the transfer operations are known. These systems use mechanical means to interrupt the flow of molten metal.

Examples include the use of plugging devices in the discharge ports, such as stoppers

(refractory or mechanical cones plugging the discharge port) or plates which, by sliding one onto another, can open or plug the discharge ports and thereby act as slide gates.

The flow of molten metal can also be mechanically interrupted by rotating the vessel itself, so that the molten metal flows away from the discharge port, and then filling the tap hole with sand.

These mechanical devices can be positioned in several locations on the vessel, including on the vessel side or the vessel bottom. Placing them on the side substantially lightens the mechanical loads produced by the molten metal pressure but causes a more consistent drop in molten metal temperature. Side placement also requires a continuous rotation of the transferring vessel and a repositioning of the receiving vessel because the parabolic path of the. flowing molten metal keeps changing during outflow operations.

Placing the mechanical flow interruption devices on a vessel bottom subjects them to heavier static and dynamic loads but does not necessarily require rotation of the vessel.

It also reduces the amount of slag that might escape through the tap hole.

All of these interruption systems require the rotation of the vessel to stop the flow or the plugging of the hole by mechanical means, the discharge of any remaining molten metal in the outlet channel, the filling of the outlet channel with refractory materials (like sand), and the return of the vessel to normal operating conditions. These limitations (1) do not control the passage of slag into the receiving vessel; (2) delay the transfer process and thereby substantially diminish the furnace coefficient of utilization ; (3) expose the containment refractory materials to strong thermal cycles, causing their quick deterioration and consequent consumption; and (4) for some operations (like filling the channel with sand), require the presence of operators in the furnace area, which may expose them to potentially dangerous safety conditions.

SUMMARY OF THE INVENTION Our invention makes possible the efficient control and braking of molten metal as it

passes through the outlet channel of a furnace or a vessel containing molten metal by applying an electromagnetic brake to the metal flow.

Our invention comprises a process for braking and stopping the flow of molten metal in the outlet channel of a melting furnace or a vessel containing molten metal, comprising the steps of imposing a magnetic field perpendicularly to the flow of molten metal in the outlet channel of a melting furnace or a vessel containing molten metal, and injecting an electric current perpendicularly to the flow of metal and to the magnetic field in the area of the field to reduce or stop the flow of metal through the outlet channel. The magnetic field may be carried out using an electromagnet, and the functioning of the electromagnet can be initiated by means of a slag sensor. A heat system also may be employed in the channel, using temperature detectors, to provide added flexibility and control over the metal solidification process.

Our invention optionally uses a cusp scheme of a magnetic field, in which the tapping hole is encircled by a series of coils through which passes an electric current to produce a magnetic field gradient which, interacting with the molten metal in motion, creates a sufficient opposing force to brake the flow of molten metal.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view partly in perspective and partly diagrammatic of a preferential, but not exclusive, configuration of our invention, showing the electromagnetic brake and its arrangement with respect to the outlet channel of a melting furnace. No molten metal is shown in this depiction.

Figure 2 is a sectioned view of the outlet channel and electromagnetic brake of Figure 1.

Figure 3 is the opposing section of the sectional view of Figure 2.

Figure 4 is a top view of the electromagnetic brake of Figure 1 and its arrangement with respect to the outlet channel.

Figure 5 is the same as Figure 1, showing the slag sensor and a temperature detector placed at the outlet channel.

Figure 6 is a diagrammatic view illustrating an embodiment of this invention.

Figure 7 is a diagrammatic illustration of a section of an embodiment of this invention.

Figure 8 is a graphical representation of the main working parameters of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to Figure 1, molten metal flows through the tap hole 1 of a melting furnace outlet channel 2, in the direction of the arrows 3, when the furnace is tapped.

The melting furnace is not shown in the drawings, but it may be one of any number of furnace types available. A magnet 4 of suitable size, configuration, and strength, and having an opposite north pole 5 and south pole 6, is positioned adjacent and perpendicular to the outside wall of the outlet channel 2, as shown in Figures 1 and 2.

The poles 5 and 6 of the magnet are suitably shaped to optimize the distribution of a magnetic field 7 inside the tap hole 1. The magnetic field 7 is preferentially a direct current (DC) field. The magnetic field 7 is positioned perpendicular to the direction of flow of molten metal 3 within the tap hole 1. The relationship of the magnet 4 to the outlet channel 1 is also shown in sectional view in Figures 2 and 3, and in top view in Figure 4.

The magnet has a plurality of electric coils 8 wound around it at an appropriate place.

The field of an electric current 11 is established between an anode 10 and a cathode 9 across the tap hole I and is preferably positioned perpendicularly to the magnetic field 7,

in the same area of the magnetic field 7 maximum intensity, and perpendicularly to the direction of flow of molten metal 3 within the tap hole 1. The electric current 11 can be induced by either alternating current (AC) or direct current (DC), but is favorably induced by a DC electric current. To completely stop the flow of fluid inside the tap hole 1, it is necessary to induce the electric field 11.

At the moment of furnace emptying, the tap hole 1 is normally opened according to standard technologies and the molten metal is allowed to flow through the furnace outlet channel 2. Subsequently, when the tapping operations are being concluded, the magnetic field 7 is applied across the tap hole 1 perpendicular to the direction of the arrows 3 in order to perform a first braking operation by generating volume forces within the molten metal, and to fill completely the outlet channel 2, in case the liquid vein had detached from the walls. Immediately afterward, the electric current 11 is established by closing the electric circuit through the molten metal, producing a further braking action, which allows for the complete stopping of the molten metal flow through the outlet channel 2. This action then permits a mechanical device to close the tap hole 1, thereby reducing the wear on the device and prolonging its life. In another version, the magnetic field 7 and the electric current 11 can be enabled at the same time. Figure 8 illustrates graphically the main working parameters of the invention by showing speed trend as a function of the magnetic field 7 and the imposed electric current 11 in a wide range of operating conditions for liquid steel at the initial speed of 6.3 meters/second.

The possibility of braking and stopping the liquid metal by exerting a magnetic field on the fluid flow in addition to the passage of an electric current substantially, but not exclusively, perpendicular to it and to the direction of the liquid metal motion, greatly reduces all problems of duration of intercepting materials and minimizes infiltration processes of solidified steel between moving and fixed parts. In this type of application, in fact, the mechanical plugging means do not come into contact with the moving metal during the closing phase. Keeping the liquid metal inside the channel contributes to the longer duration of the refractory materials making up the tapping channel. One of the

major causes of the wear of such materials is that of being subject to thermal cycles and high temperature oxidation. However, since the channel is always kept filled with liquid metal, (and therefore, besides being at practically constant temperature, it is not exposed to the oxidizing action of air), these factors are avoided and the life of the device is therefore prolonged. The possibility of slowing down and even stopping the fluid flow . by means of an external static magnetic field used in conjunction with a mechanical interception system permits substantial improvement in the duration of performances of the mechanical intercepting and plugging elements, thus making the action itself simpler and safer. Thanks to the complete automation of the process, man's presence in the furnace area during normal tapping operations is not necessary.

In another embodiment of the invention, illustrated in Figure 5, a slag sensor 12 may be suitably placed in the melting furnace outlet channel 2. The slag sensor 12 may be set up to actuate the electromagnet as soon as the sensor detects slag passing through the tap hole 1, thereby initiating the end-of-tapping procedure and stopping the arrows.

It is well known in the industry that molten metal held within the outlet channel 2 tends to solidify more or less quickly, causing the formation of a solid plug which might hinder the functioning of the melting furnace or even stop the outflow of molten metal from the vessel. Our invention can be configured in several ways to prevent the solidification of molten metal in the outlet channel 2 through the use of temperature detectors 13 and a heat source. The temperature detectors 13 can be suitably placed along the outside of the outlet channel 2 at the downstream end of the direction of molten metal flow 3, as shown in Figure 5. The temperature detectors 13 would monitor the position of the solidification front and activate a heating system, which preferably is an induction device consisting of a tiessun rmmero per il winding through which passes an alternating current of suitable frequency and which may be located around the same magnetic yoke 4 used to convey the magnetic field 7. The winding is wound around an area easily accessible and not dangerous for the possible presence of a water cooling system. Another heating system can be established through the Joule effect produced by

passing an electric current through the tap hole 1 by the cathode 9 and anode 10. In DC furnaces, cathode 9 and anode 10 may be used together as an electrode (usually an anode) for the main melting current..

In the embodiment of the invention shown in Figure 6, there is a first area of magnetic field 20 substantially as described above and a second area of magnetic field 21 located immediately beneath the first area 20. The magnetic poiarity is inverted in the second area 21 from the first area 20, which increases the braking effect. A DC electric current can be applied to this embodiment to aid in the braking action by creating a force opposite to that of gravity.

In the embodiment of the invention diagrammatically illustrated in Figure 7, the outlet channel 2 is encircled by a series of coils 23 through which passes an electric current, such that each coil supports a current circulation 24 opposite to that of the previous and of the successive coils 23, creating a magnetic field which, at the axis of the outlet channel, is directed mainly along it. In this way, a strong magnetic gradient is produced which, by interacting with the liquid metal flowing in the tap channel 2, creates a force of opposite direction to the outflow speed whose effect is to brake the flow of molten metal.