The present invention relates to a refractory well for melting scrap metal pieces into a molten metal bath.

The present invention seeks to provide an improved refractory well for melting scrap metal pieces into a molten metal bath.

Accordingly, the present invention provides a refractory well for melting scrap metal pieces into a molten metal bath, comprising: an inlet for introducing metal into said well, said inlet being located so as to cause a circular flow of molten metal in said well; an outlet for the flow of metal from said well; and an electromagnetic pump located beneath the refractory well for pumping said molten metal from said well through said outlet.

In a preferred form of the invention the electromagnetic pump is located so as to apply a force to said metal downstream of at least one of said inlet and said outlet (19) thereby to draw said metal through said well.

Preferably an outlet passage connects with said outlet and the electromagnetic pump is located adjacent the outlet or outlet passage of said well.

Preferably an outlet passage connects with said outlet and the electromagnetic pump is located vertically below at least one of the outlet and outlet passage of said well.

Preferably the inlet is arranged to direct molten metal into said well tangentially thereof so as to create a vortex in said metal in said well.

The inlet may be formed as an elongate opening extending at least a portion of the height of the cavity, as an elongate opening extending from adjacent the base of the cavity, or as an elongate opening extending the height of the cavity.

Preferably the outlet is formed as a horizontal rectangular slot located at or adjacent the bottom of said cavity, or as a horizontal rectangular slot located adjacent the base of said cavity, or as a horizontal rectangular slot opening into a side wall of said cavity. Preferably the outlet extends downwardly from the base of said cavity.

Preferably the well further comprises bypass means for conducting molten metal past said outlet, said bypass means being arranged so as to enable heat transfer from metal in said bypass to said well at or adjacent said outlet thereby to minimise the risk of metal blockage in said outlet.

Preferably said outlet and said bypass open into said outlet passage adjacent one another.

Advantageously said outlet is formed in a lower wall of said well opening into said outlet passage and said bypass is formed by said inlet extending across said wall and opening into both said well and said outlet passage.

The present invention also provides a method of melting scrap metal comprising: providing a refractory well having an inlet for introducing metal into said well and an outlet for the flow of metal from said well; causing a downward, circular flow of molten metal in said well towards said outlet of said well; introducing the scrap metal into said molten metal flow; and applying a pumping force to said molten metal at a location thereby to cause said metal to be drawn and not pushed through said outlet.

Conveniently the electromagnetic pump is located so as to apply a force to said metal downstream of at least one of said inlet and said outlet thereby to draw said metal through said well.

Preferably the method comprises directing molten metal into said well tangentially thereof so as to create a vortex in said metal in said well.

Advantageously the molten metal is directed into said well tangentially thereof along at least a portion of the height of the cavity, or adjacent the base of the cavity, or over the height of the cavity.

Preferably the method further comprises conducting molten metal through a bypass past said outlet, so as to enable heat transfer from metal in said bypass to said well at or adjacent said outlet thereby to minimise the risk of metal blockage in said outlet. Preferably said outlet and said bypass open into said outlet passage adjacent one another.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a plan view of the apparatus according to an embodiment of the present invention;

Figure 2 shows a perspective view of the embodiment of Figure 1 ;

Figure 3 shows a side elevation of the embodiment as shown in Figure 1 ;

Figure 4 shows a further side elevation of the embodiment shown in Figure 1 ;

Figure 5 shows a further embodiment of the present invention;

Figure 6 shows a rear view of the embodiment as shown in Figure 5;

Figure 7 shows a section through A-A of Figure 6;

Figure 8 shows a section through C-C;

Figure 9 shows an end view of the embodiment of Figure 5;

Figure 10 shows a section B-B of the Figure 6;

Figure 11 shows a perspective cut-away view of the embodiment of Figure 5;

Figure 12 shows a front view of the embodiment of Figure 5;

Figure 13 shows a further embodiment of refractory well in plan view;

Figure 14 shows a perspective view of the refractory well of Figure 13; Figures 15 to 17 show various side elevations of the refractory well as shown in Figure

13;

Figure 18 shows a further embodiment of refractory well;

Figure 19 shows a perspective view of the refractory well of Figure 18;

Figures 20 and 21 show side views of the refractory well of Figure 18;

Figure 22 shows a further embodiment of refractory well;

Figure 23 shows a section A-A of Figure 22;

Figure 24 shows a perspective view of the refractory well of Figure 22; and

Figures 25 and 26 show side views of the refractory well of Figure 22.

Figure 1 shows an aluminium recycling furnace 10 comprising a main chamber 12 connected to a dross well 14 and a refractory well 16, sometimes referred to as a vortex bowl. The main chamber is a main furnace chamber which contains molten hot metal such as molten aluminium. Molten metal is allowed to flow into the refractory well 16 via an inlet 18 and then from the refractory well 16 into the dross well 14 via an outlet 19 of the well 16 into an outlet passage 20. The metal then flows back into the main chamber 12 via an outlet 21. The outlet passage 20 is shown with its axis horizontal but any angle which allows metal flow would be suitable.

The refractory well 16 is generally cylindrical in shape and the inlet 18 is generally tangential to the well 16 such that as the molten metal flows into the chamber 12 it tends to cause circulatory motion typically in the form of a vortex in the well 16. Scrap metal such as aluminium chips are fed into the well 16 from above, typically from a conveyor (not shown). Although the well 16 is shown as cylindrical it will be appreciated that any suitable shape may be used. For example, the base of the well may be curved or funnel shaped to direct metal flow towards and through the outlet. The outlet of the well 16 may also be shaped or restricted in cross section to assist in the formation of the vortex. The metal movement in the refractory well produces a downward vortex action for the metal flow. This metal flow pattern forces the scrap materials, which are continuously introduced into the top of the refractory well 16, to become quickly submerged below the metal surface. Because generally the surface area to volume ratio of the scrap materials is quite high, the scrap would otherwise tend to sit on the surface of the molten metal and be subject to oxidisation. The conveyor feeds scrap into the refractory well at a uniform rate which is less than or equal to the thermal capacity of the furnace in order to maintain the temperature of the metal at a suitable level.

The molten metal then flows from the refractory well 16 through the outlet passage 20 to the dross well 14. In the dross well 14, further metal processing or treatment can be carried out before the molten metal is passed back into the main chamber for final heating to the furnace operating temperature. The outlet 20 of the well 16, in the illustrated embodiment, is located in the side wall of the well 16 although it could also equally be located in the base of the well 16 allowing the metal to flow downwardly, out of the well 16, to assist in the production of a vortex motion.

In order to pump the molten metal from the refractory well 16 to the dross well 14, the metal melting apparatus is provided with an electromagnetic pump 22 which is located under the refractory well 16. The apparatus may be supported in a manner allowing it to be tilted around axis X in order to allow access to the electromagnetic pump 22 for servicing and the like.

The passage 21 between the dross well 14 and the main chamber 12 is provided at or adjacent the bottom of the dross well 14 at an end or location preferably remote from the outlet passage 20 of the refractory well 16.

The molten metal in the main chamber 12 is generally hottest at its uppermost surface and coolest at its lowermost surface.

The inlet 18 to the well 16 can be of any suitable shape but preferably is generally elongate, extending vertically. The inlet 18 may extend for part or the whole of the height of the well 16 and ideally extends the full height. This allows the molten metal to flow freely into the well 16 and also enables the furnace to continue operating with relatively low levels of molten metal, even when dross is formed on the molten metal surface.

By providing the pump 22 under the refractory well 16, it is possible for high quantities of molten metal levels to be pumped from the refractory well 16 to the dross well 14. The pump 22 can be located immediately beneath the outlet 19 or outlet passage 20 or downstream of the outlet 19 or outlet passage 20. The electromagnetic pump 22 is thus located so as to apply a movement force to the molten metal which lies upstream of the inlet 18 to the well 16, and preferably upstream of the outlet 19 or outlet passage 20, such that the molten metal is drawn through the well 16 rather than pushed. In effect, the pump applies a tensile force to the molten metal to draw it through the outlet 19 and preferably outlet passage 20. In this way, blockages in the inlet 18 or outlet 19 or outlet passage 20 which could cause overflow in the well 16 are avoided. The location of the pump externally of the well also makes maintenance and repair of the pump relatively easy.

Figures 5 to 12 show a second embodiment of the apparatus of the present invention. The apparatus comprises a main chamber 112, a refractory well 116 and a dross well 114. In the embodiment shown, the dross well comprises a door 110 located at one end of the dross well 114. In the embodiment shown, the refractory well 116 has a connection or passageway 120 between the refractory well 116 and the dross well 114 which is located midway along one side of the dross well 114.

As shown in Figure 6, flues 111A and 111B are provided and connected to main chamber 112 and dross well 114 respectively to allow any gases to escape from the main chamber and the dross well, which as can be seen in Figure 11 are closed units.

An electromagnetic pump 122 is provided under the refractory well 116 in the area under the connection between the refractory well 116 and the dross well 114. In figure 7, the flow of molten metal can be seen as indicated by the arrows which show a flow of molten metal from the main chamber 112 through the refractory well 116 to the dross well 114 and returning to the main chamber 112.

As shown in Figure 11 , each of the main chamber 112 and the dross well 114 are substantially box shaped, having planar side walls and planar upper and lower walls respectively. As shown in Figure 11 , which is a cut away image of the embodiment of Figure 5, the levels of the molten metal 111, 113 can be seen in each of the main chamber 112 and the dross well 114 respectively.

Figures 13 to 17 show a further embodiment of refractory well 216 which comprises a tangential inlet 218 and outlet 220. An electromagnetic pump 222 is provided under the refractory well 216. In this alternative refractory well 216, both the inlet 218 and the outlet 220 are provided on the same side of the refractory well 216. This alternative refractory well 216 may be used as a bolt on option to a metal melting apparatus.

Figures 18 to 21 show a further embodiment of refractory well 316 which shares a number of features in common with the embodiments shown in Figures 1 to 17. In particular, the refractory well comprises a cylindrical well or cavity 317 and also an inlet 318 formed as an elongate slot. The inlet 318 when provided with the long slot ensures that molten metal from both the top and bottom of the main chamber can be drawn into the refractory well 316. The outlet 319 of the refractory well 316 is formed as a rectangular, horizontally aligned slot. The electromagnetic pump 322 is located under the refractory well 316 and preferably under the outlet 319 or just downstream of the outlet 319 or outlet passage 320. The outlet 3219 is located at the bottom of the refractory well 316.

Figure 22 shows a further embodiment of refractory well 416 comprising an inlet slot 418, an outlet 419 and an outlet passage 420. An electromagnetic pump 422 is provided and located under the refractory well 416, preferably under the outlet 419 and/or outlet passage 420 or just downstream of the outlet 419 or outlet passage 420. As shown in Figure 23 which is a Section on A-A of Figure 22, the outlet 419 of the well 416 is in the form of a restriction at the bottom of the cylindrical chamber 417 of the well 416 which assists in the formation of the vortex produced by the flow of molten metal through the inlet 418.

As can be seen in Figure 23, a bypass is formed from the inlet 418 to the outlet passage 420, bypassing the outlet 419. This is effected conveniently by extending the inlet 418 from the top of the well down to the outlet passage 420. This arrangement allows some of the molten metal from the main chamber to bypass the well 416 and outlet 419 and flow directly past the outlet 419 into the outlet passage 420, preferably mixing with molten metal passing through the outlet 419. This has the advantage of heating metal in and around the outlet 419. In instances where the solid metal dropped into the well does not melt sufficiently before entering the outlet 419 the outlet can become partially or fully blocked. Providing a bypass adjacent the outlet to allow molten metal to flow past the outlet results in heat being applied to the metal around the outlet, preventing a blockage from forming. It will be appreciated that provided the separation of the bypass metal and the outlet 419 is small enough to allow heat transfer from the bypass metal to the metal in the outlet419, the risk of blockage is minimised.

The above described preferred embodiments of the invention have advantages over the known art in that, firstly, in the known art generally high levels of molten metal have to be maintained in the main chamber whereas with the present invention, quite low levels of molten metal can be accommodated and processed.

The positioning of the electromagnetic pump, drawing the molten metal out of the refractory well avoids blockages in the outflow which tend to occur when the molten metal is "pushed" through the outlet, resulting in overflowing of the refractory well.

In the present invention, the pump can be located immediately beneath the outlet, where this is to one side of the refractory well or in the base, which is simply not possible in the conventional apparatus.

The positioning of the electromagnetic pump also provides for a more efficient operation and faster transfer of molten metal through the outlet of the refractory well.

It will be appreciated by those skilled in the art that features of any of the embodiments described are interchangeable between embodiments and any feature of any embodiment may be combined with features of any other embodiment.

A major disadvantage of known apparatus is the tendency of the molten metal inlet to the refractory well to become blocked with dross which always forms in the aluminium furnace 12. Furnace designers and furnace operators, therefore, try to minimise the amount of dross and its negative impact on the furnace operation. The dross formed in the main chamber 12 typically floats on the surface of the molten metal in the main chamber 12 due to the lower density of the dross. As a result, this floating dross is drawn by the movement of the hot metal through the inlet 18 into the refractory well 16.

However, in the present invention as described above, since the dross floats on the surface of the metal it will only block the upper portion of the vertical slot of the inlet 18, and the well 16 will continue to receive molten metal through the lower part of the inlet 18. As a result, the refractory well and the vortex continue to operate efficiently.

The partial blockage of the inlet 18 does not hinder the vortex well operation but in fact enhances its operation for the following reasons:

1 It creates an even faster flow of molten metal in the subsurface of the vortex well (to compensate for the blocked upper portion of the inlet 18). This higher velocity enhances the heat transfer into the well 16 and enhances the re-melting process of scrap material.

2 The blockage forces results in the movement of molten metal from the main chamber 12 being from beneath the metal surface i.e. the movement is a subsurface movement. This creates less disturbance to the metal surface in main chamber. This typically leads to less oxidization of the aluminium in the main chamber and the formation of less dross.

3 The blockage of the upper portion of the inlet 18 also leads to less disturbance of the main vortex surface in the well 16. This lowering of the disturbance of the surface of the molten metal in the vortex leads to a combination of less oxidization in the vortex well. It also creates a heat shield in the vortex well, leading to less heat dissipation from the vortex well during operation.

4 The movement of the molten metal in the main chamber subsurface leads to less stratification of the metal bath. This leads to a more uniform temperature distribution in the main chamber 12 which in turn leads to better quality metal produced by the furnace.