IMPROVEMENTS IN AND RELATING TO STIRRING OF MOLTEN METALS IN COMPLEX STRUCTURES

Abstract

Apparatus and methods for stirring a molten metal are provided. The apparatus comprising: two or more discrete units, each unit including a core (7), the core (7) being provided with two or more teeth (5, 13, 17), the core (7) being provided with at least one electrically conducting coils (3, 15,19); in use, mounting a first discrete unit in proximity to the container (23) at a first location; in use, mounting a second discrete unit in proximity to the container (23) at a second location; electrical connections between the two or more discrete units and a common control unit, thereby providing an electromagnetic stirrer. The apparatus format allows the discrete units to be position between different pairs of elements or parts of furnaces and the like to allow retrofitting of electromagnetic stirring where access is restricted.

Claims

1. Apparatus for stirring a molten metal in a container, the apparatus comprising: two or more discrete units, each unit including a core, the core being provided with two or more teeth, the core being provided with at least one electrically conducting coil; in use, mounting a first discrete unit in proximity to the container at a first location; in use, mounting a second discrete unit in proximity to the container at a second location; electrical connections between the two or more discrete units and a common control unit, thereby providing an electromagnetic stirrer.

2. Apparatus according to claim 1, wherein the two or more teeth have an end proximal the core and an end distal the core, the end distal the core defines a tooth end face, the tooth end face for at least one of the teeth not being aligned with the tooth end face for at least one of the other teeth.

3. (canceled)

4. Apparatus according to claim 1, wherein the first location and second location are different in terms of being spaced along a wall or along the perimeter of the container.

5. Apparatus according to claim 4, wherein a part or element are interposed between the first discrete unit and the second discrete unit, the part or element is interposed in terms of obscuring and/or intersecting a direct line from at least a part the first discrete unit to at least a part of the second discrete unit.

6. Apparatus according to claim 4, wherein a part or element are interposed between the first discrete unit and the second discrete unit, the part or element is interposed in terms of obscuring and/or intersecting a direct line from the centre of the first discrete unit to the centre of the second discrete unit.

7. Apparatus according to claim 5, wherein the part is one or more of: a projection; a profile; an element; a plate; an integral part of the container.

8. Apparatus according to claim 5, wherein the element is one or more of: a stay; a support; a projection; a framework; a structural element; an element connected to or contacting the container.

9. (canceled)

10. Apparatus according to claim 4, wherein a discrete unit is placed in each of a series of gaps along the perimeter of the container.

11. Apparatus according to claim 1, wherein the phasing of the discrete units is controlled to determine the magnetic force generated.

12. Apparatus according to claim 1, wherein the tooth end face for at least one of the teeth is considered not aligned with the tooth end face for at least one of the other teeth when one of the following apply: 1) one or more tooth end faces are inclined at an angle relative to one or more another tooth end faces; 2) one or more tooth end faces are inclined at an angle relative to a face of the base connector which connects two or more of the teeth together; 3) one or more tooth end faces are inclined at an angle relative to one or more another tooth end faces and one or more tooth end faces are parallel to a face of the base connector which connects two or more of the teeth together; 4) one or more tooth end faces are parallel to, but not coplanar with one or more another tooth end faces; 5) one or more tooth faces are parallel to, but not coplanar with one or more another tooth end faces and are parallel to, but not coplanar with a face of the base connector.

13. (canceled)

14. (canceled)

15. (canceled)

16. Apparatus according to claim 1, wherein one or more or all of the teeth extend perpendicular to the base connection, each tooth having an extent away from the base connection, one or more of the teeth having a greater extent that one or more of the other teeth.

17. Apparatus according to claim 16, wherein the outermost tooth on one side of the set of teeth, have a greater extent than one or more of the other teeth.

18. Apparatus according to claim 17, wherein the extent of the outermost teeth is the same, the inner most tooth for an odd number of teeth and the innermost pair of teeth for an even number of teeth have a lesser extent than one or more of the other teeth.

19. Apparatus according to claim 18, wherein teeth intermediate the outermost and the innermost teeth or pair of teeth have an intermediate extent.

20. Apparatus according to claim 1, wherein one or more or all of the tooth end faces are provided such that the air gap between the end face and the outer wall of the opposing part of the container for the molten metal is less than 10 cm.

21. Apparatus according to claim 1, wherein one or more of the tooth end faces are inclined and/or orientated and/or profiled so as to provide all of the tooth end face within a maximum air gap value, the maximum air gap value being less than 10 cm

22. (canceled)

23. A method of stirring molten metal within a container, the method including: providing two or more discrete units, each unit including a core, preferably the core being provided with two or more teeth, the core being provided with at least one electrically conducting coils; mounting a first discrete unit in proximity to the container at a first location; mounting a second discrete unit in proximity to the container at a second location; electrically connecting the two or more discrete units to a common control unit, thereby providing an electromagnetic stirrer, the common control unit applying a current to at least one of the electrically conducting coils at a first time to generate a first magnetic field configuration; the common control unit applying a current to at least one of the other electrically conducting coils at a second time to generate a second magnetic field configuration, such that the changes in magnetic field configuration cause movement of the molten metal within the container; wherein the first location and the second location are different, wherein a part of the container or an element connected to the container is interposed between the first location and the second location.

24. (canceled)

25. Apparatus according to claim 6, wherein the element or part is one or more of: a projection; a profile; an element; a plate; an integral part of the container.

26. Apparatus for stirring a molten metal in a container, the apparatus comprising: two or more discrete units, each unit including a core, the core being provided with two or more teeth, the core being provided with at least one electrically conducting coil; in use, mounting a first discrete unit in proximity to the container at a first location; in use, mounting a second discrete unit in proximity to the container at a second location; electrical connections between the two or more discrete units and a common control unit, thereby providing an electromagnetic stirrer; wherein the first location and second location are different in terms of being spaced along a wall or along the perimeter of the container; wherein a part or element are interposed between the first discrete unit and the second discrete unit, the part or element is interposed in terms of obscuring and/or intersecting a direct line from at least a part the first discrete unit to at least a part of the second discrete unit; wherein the part is one or more of an integral part of the container; or wherein the element is connected to or contacting the container.

Description

[0074] Various embodiments of the invention will not be described, with reference to the accompanying drawings by way of example only, in which:

[0075] FIG. 1 illustrates a prior art planar electromagnetic stirrer configuration; and

[0076] FIG. 2 illustrates in plan view a first embodiment of the present invention deployed relative to a furnace with external bracing;

[0077] As illustrated in FIG. 1, an electromagnetic stirrer 1 comprises a closely coiled electrical conductor 3 wrapped around a first tooth 5 of a core 7. In such an arrangement the tooth can be considered as a pole and the terms can be used interchangeably. The conductor 3 is connected to a power supply 9 via a control system 11. The control system 11 determines the timing, current, voltage and other operating conditions applied to the electrical conductor 3 and hence the resultant magnetic field generated by the electrical conductor 3.

[0078] The core 7 is generally of a ferromagnetic or ferromagnetic material, such as iron, and is crucial to concentrating the magnetic flux and hence the generation of a more powerful magnetic field than would be achieved without the core 7. Typically a thousand time increase in the strength of the magnetic field is possible through the use of the core 7.

[0079] The magnetic field arises which a current passes through the conductor 3 and disappears when the current is removed. This occurs quickly and so makes the use of electromagnets beneficial where a changing magnetic field is required.

[0080] As shown in FIG. 1, the second tooth 13 has a second coil 15 and the third tooth 17 has a third coil 19. The control system 11 ensures that current can be fed to the first coil 7, second coil 15 and third coil 19 at different times. The use of different phases means that the configuration of the overall magnetic field arising changes with time. Correct configuration of the operating conditions, including the phase for the coils, ensures that the resultant magnetic field serves to move molten metal 21 (for instance aluminium) within the container 23 which the electromagnetic stirrer 1 is provided for.

[0081] In the FIG. 1 embodiment, the core 7 forms a continuous mass throughout the first tooth 5, second tooth 15, third tooth 17 and the connecting base 25. The connecting base 25 links the three poles and also provides a first side extension 27 and a second side extension 29 at the two ends. As a result, the first tooth 5, second tooth 15 and third tooth 17 are effectively individual teeth extending from the connecting base 25.

[0082] In effect, the core 7 and the molten metal 21 form a magnetic circuit with relatively low reluctance. The air gap AG has a higher reluctance but is kept small by the relative deployment of the electromagnetic stirrer 1 and the container 23.

[0083] As shown, the electromagnetic stirrer 1 is provided in proximity with a planar wall 31 of the container 23. The casing 33 provided around the electromagnetic stirrer 1 has a planar wall 35 facing the planar wall 33 of the container 23. The end faces 37a, 37b and 37c of the three poles are also aligned in a common plane (extending left to right in the illustration) and the connecting base 25 of the core 7 also means that the connecting base 25 and the ends 35a, 35b and 35c of the three poles distal to the planar wall 35 also occupy a separate common plane (extending left to right in the illustration).

[0084] In very many cases, the container 23 in which molten metal 21 is to be stirred features a planar wall 31, for instance as a side wall or a base wall, for the container 23 and so the planar wall 35 of the casing 33 can be placed close to the planar wall 31 of the container. This means that the total air gap AG is kept low.

[0085] As illustrated in FIG. 2, there are containers 200 which contain molten metal 202 and which require stirring, but which feature curved walls 204 and/or complex structures 206 associated with those walls 204. In the FIG. 2 embodiment, the container 200 is a circular furnace and as such has a substantial diameter, for instance greater than 4 m, and hence a substantial circumference. The overall mass and/or size of the circumference means that furnace is not moveable and that a stirrer cannot encircle the container. Curved surfaces are also encountered in rotary furnaces and other such containers for molten metal. As illustrated in FIG. 2, to support the mass of molten metal 202 within the container 200 a series of stays 206 are provided on the curved wall 204 to give sufficient structural strength.

[0086] If it is desired to conduct electromagnetic stirring on such a container 200 then there are problems for existing approaches. Firstly, the gap 208 between adjacent stays 206a and 206b, for instance, is insufficient to allow the introduction of an electromagnetic stirrer such as that illustrated in FIG. 1. Scaling down the electromagnetic stirrer to fit the gap 208 available is not a viable option due to the limited magnetic forces that could be applied to the molten metal 202 as a result. Removing one or more of the stays 206 is not a cost effective solution because of the scale of the task involved and indeed may not be possible whilst still retaining the necessary structural properties for the container 200.

[0087] FIG. 2 shows one embodiment of a solution provided according to the present invention. A first inductor 220 is provided within a first unit 222 between a first stay 206a and a second stay 206b. A second inductor 224 is provided within a second unit 226 between the second stay 206b and a third stay 206c. A third inductor 228 is provided within a third unit 230 between the third stay 206c and a fourth stay 206d.

[0088] A common controller 232 acts on the electrical connection 234a, 234b, 234c to the three separate units 222, 226, 228 so as to separately control the application of the electric current to each and hence the magnetic field generated.

[0089] In this embodiment, each inductor is formed of core 236 which provides a pair of teeth 238 which extend towards the container 200. The teeth 238 and the core 236 are formed of a common material offering low reluctance. The teeth 238 are each provided with an electrically conductive coil (not shown for clarity purposes).

[0090] The common controller allows the application of current to an inductor, the build-up of the magnetic field as a result and the withdrawal of the current and hence the magnetic field. The common controller also allows the sequence of these steps, the firing of the phases, to be controlled for the three separate inductors such that they work in a sequential manner to apply force to the molten metal 202 in the container 200 and hence stir the contents of the container 200.

[0091] The overall effect is similar to that from the stirrer of FIG. 1, but the effect is achieved using a series of separate inductors 220, 226, 228 mounted between the obstructions such as the stays 206.

[0092] In further embodiments, more complex arrangements for the electrically conductive coils may be provided. For instance, two or more coils may be provided on a single tooth, for one or more or all of the teeth. Those two or more coils may be interleaved. It is also possible for the electrically conductive coil of one inductor to be interleaved with an adjacent inductor. For instance, moving left to right: the first tooth of the first inductor may be provided with its own coil; the second tooth may be provided with a coil which interleaves with the first tooth of the second inductor; the second tooth of the second inductor may be provided with a coil which interleaves with the first tooth of the third inductor; the second tooth of the third inductor may be provided with its own coil. In such arrangements low reluctance material may be provided to bridge the gap between the cores/teeth for the interleaved coils.