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 being provided with two or more teeth, the core being provided with at least one electrically conducting coils; 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. 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 curved container having a plurality of stays, the apparatus comprising: a first discrete unit and a second discrete unit, each unit including a core having two or more teeth and at least one electrically conducting coil; a common controller coupled to the first discrete unit and the second discrete unit via electrical connections; and wherein the first discrete unit is configured to be coupled to a curved wall of the curved container at a first location between a first pair of the plurality of stays and the second discrete unit is configured to be coupled to the curved wall of the curved container at a second location between a second pair of the plurality of stays; and wherein a first stay is disposed between the first discrete unit and the second discrete unit, such that the first stay is intersected by a direct line extending from the first discrete unit to the second discrete unit.

2. Apparatus according to claim 1, wherein: the two or more teeth have a first end proximal the core and a second end distal the core, the second end defines a tooth end face, and the tooth end face of a first tooth of the two or more teeth is not aligned with the tooth end face of a second tooth of the two or more teeth.

3. Apparatus according to claim 1, wherein the first stay of the plurality of stays is interposed between the first discrete unit and the second discrete unit, such that the first stay is intersected by a direct line from a centre of the first discrete unit to a centre of the second discrete unit.

4. Apparatus according to claim 1, wherein the plurality of stays extend away from an outer surface of the curved wall and comprise: a projection; a profile; an element; a plate; an integral part of the container, or combination thereof.

5. Apparatus according to claim 1, wherein the plurality of stays contact the container.

6. Apparatus according to claim 1, further comprising: a plurality of discrete units, including the first and second discrete units; and wherein: a respective discrete unit of the plurality of discrete units are positioned in each of a series of gaps defined by two adjacent stays of the plurality of stays positioned along the perimeter of the container.

7. Apparatus according to claim 1, wherein the common controller is configured to independently control a phasing of the discrete units to determine a magnetic force generated by the first and second discrete units.

8. Apparatus according to claim 2, 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 a 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.

9. Apparatus according to claim 1, wherein one or more or all of the teeth extend perpendicular to a 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.

10. Apparatus according to claim 9, wherein a first outermost tooth has a greater extent than one or more of the other teeth.

11. Apparatus according to claim 10, wherein: based on a number of teeth being an odd number, the extent of the first outermost tooth is the same as an innermost tooth; and based on a number of teeth being an even number, an innermost pair of teeth have a lesser extent than one or more of the other teeth.

12. Apparatus according to claim 11, wherein teeth intermediate the outermost tooth and the innermost tooth or pair of teeth have an intermediate extent.

13. Apparatus according to claim 2, wherein one or more or all of the tooth end faces are provided such that an air gap between the end face and an outer wall of the container is less than 10 cm.

14. Apparatus according to claim 2, 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.

15. A method of stirring molten metal within a curved container, the method including: mounting a first discrete unit on a curved wall of the curved container at a first location; mounting a second discrete unit on the curved wall of the curved container at a second location; applying, via a controller, a first current to one or more first electrically conducting coils of the first discrete unit at a first time to generate a first magnetic field configuration; and applying, via the controller, a second current to one or more second electrically conducting coils of the second discrete unit at a second time to generate a second magnetic field configuration, such that changes in magnetic field configuration cause movement of the molten metal within the curved container; wherein the first location and the second location are different, and wherein a stay is interposed between the first location and the second location such that the stay is intersected by a direct line extending from the first discrete unit to the second discrete unit.

16. The method of claim 15, further comprising: mounting a third discrete unit on the curved wall of the curved container at a third location; and applying, via a controller, a third current to one or more third electrically conducting coils of the third discrete unit at a third time to generate a third magnetic field configuration.

17. Apparatus for stirring a molten metal in a container having a plurality of stays that define a series of gaps on an outer surface of the container, the apparatus comprising: a first discrete unit and a second discrete unit, each unit including a core having two or more teeth and at least one electrically conducting coil a common controller; and electrical connections extending between the first and second discrete units and the common controller; wherein the first discrete unit is configured to abut the container at a first location within a first gap of the series of gaps and the second discrete unit is configured to abut the container at a second location within a second gap of the series of gaps such that at least one stay of the plurality of stays intersects a direct line extending from a first portion of the first discrete unit to a first portion of the second discrete unit; wherein the first location and second location are different in terms of being spaced along a perimeter of the container; and wherein a stay is interposed between the first discrete unit and the second discrete unit, such that the stay intersects a direct line extending from a first portion of the first discrete unit to a first portion of the second discrete unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the invention will not be described, with reference to the accompanying drawings by way of example only, in which:

(2) FIG. 1 illustrates a prior art planar electromagnetic stirrer configuration; and

(3) FIG. 2 illustrates in plan view a first embodiment of the present invention deployed relative to a furnace with external bracing;

DETAILED DESCRIPTION OF THE INVENTION

(4) As illustrated in FIG. 1, an electromagnetic stirrer 1 comprises a closely coiled electrical conductor 3 (e.g., coil 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.

(5) 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.

(6) 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.

(7) 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 3, 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.

(8) In the FIG. 1 embodiment, the core 7 forms a continuous mass throughout the first tooth 5, second tooth 13, 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 13, and third tooth 17 are effectively individual teeth extending from the connecting base 25.

(9) 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.

(10) 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 31 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 of the three poles distal to the planar wall 35 also occupy a separate common plane (extending left to right in the illustration).

(11) 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.

(12) 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 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 meters (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.

(13) 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.

(14) 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.

(15) A common controller 232 acts on the electrical connection 234a, 234b, 234c to the three separate units 222, 226, 230 so as to separately control the application of the electric current to each and hence the magnetic field generated.

(16) 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).

(17) 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.

(18) 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, 224, 228 mounted between the obstructions such as the stays 206.

(19) 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.