ELECTROMAGNETIC DEVICE AND SYSTEM FOR PUMPING, CIRCULATING OR TRANSFERRING NON-FERROUS MOLTEN METAL

Abstract

An electromagnetic device for pumping, circulating or transferring non-ferrous molten metal has a duct made of a refractory material with a first aperture at a first end of the duct and a second aperture at a second end of the duct. The duct conveys a body of non-ferrous molten metal between the first and second apertures. The duct encloses the body of non-ferrous molten metal between the first and second apertures. The duct has opposing first and second external side surfaces. A first inductor assembly extends adjacent to the first side surface. The first inductor assembly comprises a plurality of inductors arranged along a length of the duct adjacent to the first side surface. An electronic circuit generates direct current pulses that energise each inductor of the plurality of inductors in a sequence, so as to generate a moving magnetic field within the body of non-ferrous molten metal which propels the body of non-ferrous molten metal along the duct.

Claims

1. An electromagnetic device for pumping, circulating or transferring non-ferrous molten metal, the electromagnetic device comprising: a duct made of a refractory material, the duct having a first aperture at a first end of the duct and a second aperture at a second end of the duct, the duct configured to convey a body of non-ferrous molten metal between the first and second apertures, the duct configured to enclose the body of non-ferrous molten metal between the first and second apertures, and the duct having opposing first and second external side surfaces; a first inductor assembly extending adjacent to the first side surface, wherein the first inductor assembly comprises a plurality of inductors arranged along a length of the duct adjacent to the first side surface; and an electronic circuit configured to generate direct current pulses that energise each inductor of the plurality of inductors in a sequence, so as to generate a moving magnetic field within the body of non-ferrous molten metal which propels the body of non-ferrous molten metal along the duct.

2. The electromagnetic device of claim 1, wherein a cross-section through the duct has a height and a width, wherein the height is defined by a distance between the first and second side surfaces and the height is less than the width.

3. The electromagnetic device of claim 2, wherein the width of the cross-section is at least the width of the inductors of the first inductor assembly.

4. The electromagnetic device of claim 2, wherein the height is based on the penetration depth of the magnetic field.

5. The electromagnetic device of claim 1, wherein the distance between the first inductor assembly and the second side surface is less than the penetration depth of the magnetic field.

6. The electromagnetic device of claim 5, wherein the penetration depth of the magnetic field is at least one of: 50 mm, 100 mm, 200 mm, 300 mm, 400 mm, 500 mm and 1000 mm.

7. The electromagnetic device of claim 1, wherein a cross-section through the duct is substantially rectangular.

8. The electromagnetic device of claim 1, wherein a gap between the body of non-ferrous molten metal and the first inductor assembly is more than one of: 75 mm, 100 mm, 150 mm, 200 mm and 250 mm.

9. The electromagnetic device of claim 1, further comprising a second inductor assembly extending adjacent to the opposing second side surface, wherein the second inductor assembly comprises a plurality of components arranged along a length of the duct adjacent to the second side surface, wherein each of the components is one or more of an inductor and a magnetic core.

10. (canceled)

11. The electromagnetic device of claim 9, wherein each of the inductors adjacent to the first side surface opposes one of the components adjacent to the second side surface.

12. The electromagnetic device of claim 1, wherein each inductor comprises a coil wrapped around a magnetic core, wherein each of the inductors on a side of the duct is wrapped around a single magnetic core that extends along the length of that side of the duct.

13. (canceled)

14. (canceled)

15. The electromagnetic device of claim 11, wherein the single magnetic core comprises a base that extends along the length of the side of the duct and a plurality of projections extending from the base, wherein each coil extends around one of the projections.

16. (canceled)

17. The electromagnetic device of claim 15, wherein the coils extending around neighbouring projections are offset or diagonally offset.

18. (canceled)

19. The electromagnetic device of claim 12, wherein the magnetic core has a laminated structure comprising sheets of magnetic material separated by an insulating material, optionally wherein the insulating material comprises one or more of air, silicates and/or polymers.

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. The electromagnetic device of claim 1, wherein the direct current pulses are asymmetrical.

25. The electromagnetic device of claim 1, wherein each direct current pulse has a pulse length in the range of 10 and 10000 milliseconds.

26. The electromagnetic device of claim 25, wherein the electronic circuit generates between 0.5 and 100 direct current pulses per second, preferably 0.1 to 100 direct current pulses per second.

27. The electromagnetic device of claim 1, wherein the inductor assembly is not physically coupled to the duct or to insulation surrounding the duct.

28. (canceled)

29. (canceled)

30. (canceled)

31. A system comprising a vessel for holding a body of non-ferrous molten metal and a channel connected by at least one end to a first opening in the vessel, and an electromagnetic device according to claim 1, wherein the electromagnetic device is configured to cause molten metal to flow along the channel.

32. The system of claim 19, wherein the first aperture of the electromagnetic device is connected to a second opening in the vessel and the second aperture of the electromagnetic device is connected to the channel, wherein the electromagnetic device is configured to propel the body of non-ferrous molten metal along the duct towards the first aperture.

33. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention shall now be described, by way of example only, with reference to the accompanying drawings in which:

[0057] FIG. 1 illustrates a three-dimensional cross-section view of an electromagnetic device for pumping, circulating or transferring non-ferrous molten metal according to an embodiment of the invention;

[0058] FIG. 2 illustrates a side view of the cross-section of FIG. 1;

[0059] FIG. 3 illustrates an assembly comprising a plurality of inductors made up of coils wrapped around a magnetic core;

[0060] FIG. 4 illustrates an example of the construction of the magnetic core in more detail;

[0061] FIG. 5 illustrates an electronic circuit for energising the inductors to generate a moving magnetic field that propels a body of non-ferrous molten metal;

[0062] FIG. 6 illustrates an example of a moving magnetic field;

[0063] FIG. 7 illustrates penetration depth of a magnetic field as a function of frequency for a number of materials; and

[0064] FIG. 8 illustrates a plan view of the electromagnetic device of FIG. 1 connected to a chamber and a channel for pumping, circulating or transferring non-ferrous molten metal.

DETAILED DESCRIPTION

[0065] FIGS. 1 and 2 illustrate a cross-section through the centre of an electromagnetic device 100 for pumping, circulating or transferring non-ferrous molten metal. The electromagnetic device 100 has a duct 102 formed of a refractory material 108 such as silicon carbide, which is able to resist the heat of the molten metal without melting or damage. The refractory material 108 is housed within a holder 110. The holder 110 protects the refractory material 108 from damage and provides a way for mounting refractory material 108 in the electromagnetic device 100. The holder 110 is made from metal and in this example is formed in two parts (an upper part and a lower part) to facilitate mounting around the refractory material 108.

[0066] The duct 102 has a first aperture 104 at a first end of the duct 102 and a second aperture 106 at the opposite end of the duct 102. The duct 102 has opposing first and second external side surfaces 112, 114. A first inductor assembly 116 extends adjacent to only the first external side surface 112. A second inductor assembly 118 extends adjacent to only the second external side surface 114.

[0067] Ceramic insulation material 109 is placed between the duct 102 and the surfaces of the holder 110 adjacent to the first and second inductor assemblies 116, 118, in order to protect the first and second inductor assemblies 116, 118 from the heat of the molten metal in the duct 102.

[0068] Each of the inductor assemblies 116, 118 comprise a plurality of inductors 120 arranged along the length of the duct adjacent to the respective side surface. For example, first inductor assembly 116 comprises a plurality of inductors 120a, 120b, 120c adjacent to the first side surface 112 of the duct 102. Second inductor assembly 118 comprises a plurality of inductors 120a, 120b, 120c which mirror the inductors in the first inductor assembly 116. That is, each inductor 120 in the first inductor assembly 116 has a corresponding inductor 120 in the second inductor assembly 118 that opposes it on the opposite side of the duct 102. Specifically, inductor 120a in the first inductor assembly 116 opposes inductor 120a in the second inductor assembly 118, inductor 120b in the first inductor assembly 116 opposes inductor 120b in the second inductor assembly 118, and inductor 120c in the first inductor assembly 116 opposes inductor 120c in the second inductor assembly 118

[0069] An electronic circuit (shown in detail in FIG. 5) energises each of the inductors 120a, 120b and 120c in turn in order to generate a moving magnetic field which moves along the length of the duct (as illustrated by FIG. 6) in order to propel a body of non-ferrous molten metal along the duct 102 between the first aperture 104 and the second aperture 106.

[0070] By having a plurality of inductors 120 extending along only the top and bottom external side surfaces 112, 114 of the duct 102, rather than having the inductors as coils wrapped around the entire outer circumference of the duct 102, the duct 102 no longer needs to have a circular cross-section dictated by the coil geometry. Instead, the duct 102 can have a cross-sectional shape which is optimised for both penetration depth and pumping capacity simultaneously. In this example, the duct 102 has a substantially rectangular cross-section where the inductor assemblies 116, 118 are adjacent to the longer sides (width) of the rectangular cross section of the duct 102, to maximise overlap between the inductor assemblies 116, 118 and the side surfaces 112, 114 respectively. The shorter sides 119 (height) of the cross-section of the duct 102 can be selected according to the penetration depth of the magnetic field generated by the inductors 120 (to allow the magnetic field to penetrate through the entire duct 102).

[0071] You will note that in this example, the refractory material 108 of the duct 102 has rounded internal corners. The rounded internal corners improve flow of the molten metal along the duct 102, reducing regions with little or no flow, and avoiding sharp corners to reduce the likelihood that the refractory material will crack under the intense heat of the molten metal (thermal shock).

[0072] The first and second inductor assemblies 116, 118 may be fitted to sliders (not shown) which allow them to be slid easily in and out of position to facilitate maintenance. Although the device 100 is shown with two inductor assemblies in place, the device 100 can work adequately with only a single inductor assembly in place. Therefore, one of the inductor assemblies can be removed for maintenance without having to decommission the entire process the device is connected to.

[0073] The duct 102 is configured to surround and enclose the body of non-ferrous molten metal on all sides, all the way around the circumference of the duct 102, with the only openings being the first and second apertures 104, 106 at either end of the duct 102. This contrasts to the open-topped launder design seen in other circulating devices where inductors are placed adjacent to the base and one or more sides of an open-topped launder. However, in an open-topped launder, it is not possible to generate pressure in the molten metal required for transferring the molten metal. Applying a force to molten metal in an open-topped launder just tends to generate velocity and waves which could cause molten metal to splash over the top of the launder. In contrast, having the duct 102 enclose the body of molten metal on all sides, the magnetic field acts like a piston pushing the molten metal out of the exit aperture, which acts to cause a pressure head of molten metal at the exit aperture.

[0074] As shown in FIG. 3, the inductors 120 are formed from coils of wire wrapped around magnetic core 130. Specifically, the electromagnetic device 100 has a single magnetic core 130 formed from a ferromagnetic or ferrimagnetic material, such as ferritic steel, with a base 132 that extends along the length L of the duct 102. Finger-like projections 133 extend from the base 132, towards the side surfaces 112, 114. The coils are wrapped around the projections 133, with sufficient turns of wire forming a coil around each of the projections 133. The number of turns depends on the design criteria for the electromagnetic device, but is usually in the range of 50-200 turns. The coils are formed from wire, such as copper wire, or material with similarly good electrical conductivity. The coils are embedded in a glassy silica fibre sleeve, soaked with a resin such as epoxy to give the coil physical protection and electrical insulation. The coils may also be placed into a non-conductive temperature resistant polymer box and cast into a non-conductive temperature resistant rubber.

[0075] The magnetic core 130 has a laminate construction, as shown in FIG. 4, where thin sheets of magnetic material 134 (such as ferromagnetic or ferrimagnetic material, like ferritic steel) are stacked with air gaps 136 (or other insulating material) in between. Spacers 138 made of an insulating material, such as non-conductive polymer, hold the sheets of magnetic material 134 apart to form the air gaps 136. Holes extend through the projections 133 and base 132, typically passing through the spacers 138. Through these holes, a threaded connecting rod 140 is passed. Fasteners, such as nuts 142, in either end of the connecting rod 140 hold the magnetic core 130 together.

[0076] The laminated structure of the magnetic core 130 has been designed to suit the applied current source. The laminated design, where the air gap 136 is around the same thickness as the sheet of magnetic material 134, significantly reduces the total weight of each of the assemblies 116, 118. This is important since the assemblies have to be held in place above and below the duct 102.

[0077] The coils extending around neighbouring projections 133 are offset diagonally. That is, the position of a particular coil along a first side of projection 133 is different to the position of the same coil on the opposite side of the projection 133. The position of a particular coil on the first side of projection 133 matches the position of the neighbouring coil on the first side of the neighbouring projection. Likewise, the position of the particular coil on the second opposite side of projection 133 matches the position of the coil on the second opposite side of the neighbouring projection 133.

[0078] Inlets 152 and outlets 154 are provided for attachment to a liquid cooling supply. Cooling liquid passes around the inductor coil 120 and optionally the magnetic core 130. The coils generate resistive heat in operation and while the design of the magnetic core has been considered to reduce any currents and therefore waste heat, nevertheless some waste heat will still be produced that is removed by the liquid cooling fluid. The liquid coolant has a low conductivity and is designed to not be hazardous in order to not cause explosion of any exposed liquid aluminium.

[0079] FIG. 5 illustrates an electronic circuit 180 which is designed to energise each of the inductors 120a, 120b and 120c in a sequence so as to generate a moving magnetic field which propels a body of non-ferrous molten metal along the duct 102. The electronic circuit 180 takes a mains alternating current supply 182 (which is typically at 380 V-480 V, 50 Hz-60 Hz) and converts it into direct current using input rectifier 184. There is a DC-DC converter 186a, 186b and 186c for each of the inductors 120a, 120b, and 120c fed from the direct current generated by the input rectifier 184. Each DC-DC converter 186a, 186b and 186c generates the pulse required to operate each of the inductors 120a, 120b and 120c and generate the moving magnetic field.

[0080] Power to each of the inductors 120 is turned on for a period of between 10 and 10000 milliseconds before being turned off. The inductors 120 are turned on and off in a sequence to generate the desired moving magnetic field. For example, first inductor 120a is turned on generating a magnetic field shown in FIG. 6a, then inductor 120a is turned off and inductor 120b is turned on generating a magnetic field that has moved along the length of the duct 102, as shown in FIG. 6b. Finally, inductor 120b is turned off and inductor 120c is turned on. This generates a magnetic field which has moved further along the length of the duct, as shown in FIG. 6c. This moving magnetic field propels the body of non-ferrous molten metal along the duct in the direction of the moving magnetic field. The process is repeated by turning off inductor 120c and turning on inductor 120a and repeating the cycle. The direction of travel can be changed by reversing the sequence in which the inductors 120a, 120b and 120c are turned on and off.

[0081] The applied pulsing rate is around 0.5 to 100 pulses per second. This correlates to the effect that would be expected from a frequency in the range of around 0.16 Hz-33.3 Hz. The higher the pulsing rate the lower the penetration depth, but the higher the interaction of the magnetic field with the molten metal. The ability to vary the pulsing rate allows to adjust the performance of the electromagnetic device 100 to be adjusted to suit different requirements, for example, to suit the needs of circulation or transfer.

[0082] FIG. 7 illustrates the penetration depth of a magnetic field into a number of materials as a function of frequency. As can be seen from FIG. 7, lower frequency pulses that can be generated by the electronic circuit 180 provide for a much a higher penetration depth which can easily be tuned when compared with typical mains frequencies (fixed at 50-60 Hz). This increased penetration depth, combined with a duct geometry which reduces the required penetration depth, allows the inductor assemblies 116, 118 to be spaced apart from the duct 102 to reduce heat loading on the inductors by providing space for more insulation 109 and allowing the inductor assemblies 116, 118 to be physically separated from the duct 102 and insulation 109 for easier maintenance.

[0083] FIG. 8 illustrates a system comprising a vessel 170 for holding a body of non-ferrous molten metal, for example, when melting metal for production or recycling. A channel 160 such as an open-topped launder is connected at a first end to an opening 172 in the vessel 170. The electromagnetic device 100 is connected by its second aperture 106 to a second opening 174 in the vessel 170. In this way, the electromagnetic device being operated as described above is configured to propel the body of non-ferrous molten metal along the duct 102 towards its second aperture 106 into the vessel 170, causing non-ferrous molten metal to circulate in the vessel 170 and back into the channel 160 via opening 172. This acts to stir the molten metal in the vessel helping to make the temperature distribution in the vessel 170 more homogeneous, ensuring thorough mixing of alloys, reducing dross formation and improving melting efficiency.

[0084] The channel can also have an outlet 164 with a dam that can allow molten metal to be selectively removed from the channel 160 and the electromagnetic device 100 can pump the molten metal around channel 160 towards the outlet 164. In transfer operations such as this, the electromagnetic device 100 may operate in the opposite direction, propelling the body of non-ferrous molten metal along the duct 102 towards its first aperture 104 and into the channel 160.

[0085] Although the invention has been described in certain terms of a particular preferred embodiment, the skilled person will appreciate that there are modifications that could be made without departing from the scope of the claimed invention.

[0086] For example, the invention has been shown as having corresponding pairs of inductors 120 and magnetic cores 133 on either side of the duct 104. However, the skilled person will appreciate that only a first inductor assembly may be provided on one side of the duct, either permanently or just during maintenance operations. That is, there does not need to be a second inductor assembly on the other side of the duct. If a second inductor assembly is provided, the skilled person will appreciate that it could have an inductor with a magnetic core, or just a magnetic core by itself.

[0087] The invention has been illustrated in terms of three inductors. The skilled person will appreciate that as long as at least two inductors are provided, any number of inductors can be provided which produce the desired moving magnetic field to propel the molten metal along the duct.

[0088] Although the inductors have been illustrated as comprising coils, any kind of inductor known to the skilled person could be used instead, such as a flat plate inductor.

[0089] The coils have been illustrated as being diagonally offset. However, the coils could be offset in some other arrangement or not offset at all, particularly if the overall length of the device is not critical.