Technical Field of the Invention

The present application relates to an apparatus and method for submerging materials, especially solid-phase materials, into a bath of molten material. Background to the Invention

It is known to provide furnaces for the melting and refining of metal materials, including aluminium. It is also known to introduce solid-phase materials into a bath of molten metal contained in a furnace or the like. Such materials may be in granular form and may include alloying elements, metallurgical agents (fluxes) to aid production, or lightweight scrap pieces/fragments that are being recycled back into the melting process. It is generally desirable to submerge any added solid-phase materials below the surface and into the body of the bath as quickly as possible to improve process efficiency, material utilisation and to minimise losses through oxidation from the furnace atmosphere. Known methods for submerging solid-phase materials in a bath of molten metal, include: i) Manual agitation and pushing of the material below the surface by means of a paddle or similar hand tool. This tends to be very inefficient and has safety issues for the operator. ii) Use of mechanical devices such as pumps to create a vortex or "whirlpool" into which the added material is charged. These tend to be maintenance intensive and can produce excessive agitation and metal dross (oxidation). iii) Use of electromagnetic induction stirring devices. Many known arrangements do not submerge the added material directly but are used to direct a flow of molten metal over heavier materials that have been placed into the furnace hearth during initial charging or contained within a cage lowered into the metal bath. The applicant has previously proposed in WO 03/106908 Al use of an electromagnetic induction device mounted to an inclined wall of a furnace to create a flow of the molten metal in a furnace chamber having a vertical component for submerging materials introduced onto the top of the molten metal bath. The electromagnetic stirring device can be mounted to an inclined lower wall of the furnace chamber itself or to an inclined lower wall of a port or cradle fluidly connected with a furnace chamber. The lower wall is inclined at an angle 30° to 60°, typically 45° to 55°, and the electromagnetic induction device can be operated at speeds up to 50Hz in order to set up fast flow rates in the vertical plane in the molten metal bath so that materials introduced on top of the bath are rapidly dragged down and submerged.

Whilst the arrangements disclosed in WO 03/106908 Al have been found to work well, it would be advantageous if the known apparatus and methods could be improved to further increase the speed and effectiveness with which solid-phase materials are submerged into the molten bath.

It is also known to use an electromagnetic induction device mounted to an inclined lower wall of a furnace port to induce an upward flow of the molten metal so as to draw molten metal out of a furnace chamber through the port for casting. In order to create a flow, the upward forces induced in the molten metal have to overcome frictional resistance and gravitational forces. In the known arrangements this requires the use of a channel plate mounted parallel to but closely spaced from the inclined inner surface of the lower wall. The channel plate defines a restricted extraction channel between itself and the inclined lower wall of the port through which the molten metal can be pumped by the electromagnetic induction device. Known channel plates extend across the full extent of the internal width of the port and for a distance beyond the upper surface of the molten metal bath to the upper end of the inclined inner surface of the port where the molten metal enters a channel or feed launder along which it can flow, usually by means of gravitational forces.

The presence of a channel plate makes it difficult to also use the electromagnetic induction device to stir the molten metal in the furnace chamber as it disrupts the circulation of the molten metal. To overcome this issue, the applicant has previously proposed in WO 2012/120276 Al apparatus comprising a bi-directional electromagnetic induction device mounted to an inclined lower wall of a furnace port and a retractable channel plate apparatus. This allows the channel plate to be retracted out of the port and the electromagnetic induction device operated in a first direction to induce a downward flow in the molten metal in the port so as to create a flow of the metal bath in the furnace chamber for stirring. When material is to be extracted from the furnace, the channel plate is introduced into the port and the electromagnetic induction device operated in a second direction opposite to the first to induce un upward flow of the molten metal so that molten metal is pumped from the furnace chamber up through an extraction channel between the channel plate and the lower surface of the port. Movement of the channel plate assembly is controlled by an automatic feedback control system so that the leading edge of the channel plate is maintained just below the upper surface of the molten metal bath as the molten metal is extracted. In this arrangement, the majority of the channel plate is not submerged.

It is an objective of the present invention to provide apparatus for submerging solid-phase materials into a bath of molten material which overcomes, or at least reduces, the drawbacks of the known apparatus.

It is a further objective of the invention to provide an improved method of submerging solid-phase materials into a bath of molten material which overcomes, or at least reduces, the drawbacks of the known methods.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided apparatus for submerging materials added into a bath of molten material, the apparatus comprising a furnace having a furnace chamber, a port in fluid communication with the furnace chamber and having an inclined lower wall, an electromagnetic induction unit mounted to the inclined lower wall of the port for inducing a flow in molten material in the port at least in a generally downwards direction along the inclined lower wall of the port, a submergence plate positioned in the port in spaced relation to the inner surface of the inclined lower wall to define a submergence flow channel for the molten material between the submergence plate and the inner surface.

The maximum width of the submergence plate may be less than the internal width of the port. The maximum width of the submergence plate may be in the range of 30% to

85% of the internal width of the port.

The maximum width of the submergence plate may be in the range of 50% to 75% of the internal width of the port.

The submergence plate may be positioned in the port in use so that at least the majority of the submergence plate is submerged below the upper surface level of the bath of molten material, the vertical displacement of an upper edge of the plate relative to the upper surface level of the bath being in the range of 50mm above the upper surface level of the bath to 150mm below the upper surface level of the bath.

Where the upper edge of the submergence plate is level with or below the upper surface level of the bath, the whole, or substantially the whole, of the submergence plate is submerged below the upper surface level of the bath of molten material.

The minimum standoff distance X between the inner surface inclined lower wall and the submergence plate may be in the range of 25mm to 300mm, and more preferably in the range of 50mm to 250mm.

The submergence plate may be mounted in the port such that its position within the port is adjustable. The position of the submergence plate may be adjustable in use to maintain a vertical displacement of the upper edge of the plate relative to the upper surface level of the bath at a desired value, within predetermined tolerances, in the event that the level of the molten material bath changes. The apparatus may comprise an electronic control system for automatically adjusting the position of submergence plate or a manually operated adjustment mechanism. The submergence plate may be adjustably mounted to a support which holds the submergence plate suspended in position in the port. The support may be configured to enable the submergence plate to be retracted out of the port. The support may be configured to be introduced into the port through its open upper end.

The submergence plate may be a relatively thin, generally rectangular blade- like member having opposed major faces, an inner one of the major faces opposing in spaced relation the inner surface of the inclined lower wall of the port. The inner major face of submergence plate may be aligned generally parallel to the inner surface of the inclined lower wall of the port or it may be angled so that the inner major face of the plate and the inner surface of the inclined lower wall converge in a direction towards a lower edge of the submergence plate. The submergence plate may be located substantially centrally within the port or it may be offset to one side and/or its longitudinal axis may be angled relative to a longitudinal axis of the port.

The submergence plate may have a metal frame lined with refractory materials.

The molten material may be a molten metal material. The added materials may be solid-phase materials .

In accordance with a second aspect of the invention, there is provided a method for submerging materials added into a bath of molten material contained in a furnace having a furnace chamber and a port in fluid communication with the furnace chamber, the port having an inclined lower wall and an electromagnetic induction unit mounted to the inclined lower wall of the port for inducing a flow in the molten material in the port at least in a generally downwards direction along the inclined lower wall of the port, the method comprising: a) positioning a submergence plate in the port in spaced relation to an inner surface of the inclined lower wall to define a submergence flow channel for the molten material between the submergence plate and the inner surface; b) operating the electromagnetic induction unit to induce a flow in the molten material in the port in a generally downwards direction in the submergence flow channel between the submergence plate and the inner surface of the inclined lower wall of the port and in to the lower levels of the bath in the furnace main chamber; c) introducing materials into the upper surface levels of the bath of molten material in the port so that the materials are entrained in the flow of molten material to pass through the submergence flow channel and into the lower levels of the bath in the furnace main chamber.

The maximum width of the submergence plate may be less than the internal width of the port.

The maximum width of the submergence plate may be in the range of 30% to 85%, or 50% to 75%, of the internal width of the port;

The feed rate at which the material is added may be regulated in relation to the submergence rate.

The method may comprise positioning the submergence plate in the port so that at least the majority of the submergence plate is submerged below the upper surface level of the bath of molten material, the vertical displacement of an upper end of the plate relative to the upper surface level of the bath being in the range of 50mm above the upper surface level of the bath to 150mm below the upper surface level of the bath.

The whole of the submergence plate may be submerged in the molten material bath.

The method may comprise adjusting the position of the submergence plate as the level of the bath of molten material changes. The method may comprise adjusting the position of the submergence plate manually or by means of an automatic control system. The method may comprise positioning the submergence plate such that the minimum standoff distance X between the inner surface inclined lower wall and the submergence plate is in the range of 25mm to 300mm, and more preferably in the range of 50mm to 250mm.

The submergence plate may be a relatively thin, generally rectangular bladelike member having opposed major faces, an inner one of the major faces opposing in spaced relation the inner surface of the inclined lower wall of the port. The inner major face of submergence plate may be aligned generally parallel to the inner surface of the inclined lower wall of the port or it may be angled so that the inner major face of the plate and the inner surface of the inclined lower wall converge in a direction towards a lower edge of the submergence plate. The submergence plate may be located substantially centrally within the port or it may be offset to one side and/or its longitudinal axis may be angled relative to a longitudinal axis of the port.

The submergence plate may have a metal frame lined with refractory materials.

The molten material may be a molten metal material. The added materials may be solid-phase materials. An embodiment of the invention will now be described, by way of non- limiting example only, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal cross sectional view through part of an apparatus in accordance with the invention including a furnace having a furnace main chamber and a port in which a submergence plate is located; Figure 2 is a perspective view from the inside of a furnace port forming part of the apparatus of Figure 1, with part of the port outer lining removed to show the refractory lining;

Figure 3 is a longitudinal cross sectional view through a port forming part of the apparatus of Figure 1 but with the electromagnetic induction device omitted for clarity;

Figure 4 is a longitudinal cross sectional view through a port forming part of the apparatus of Figure 1 also illustrating a support for adjustably mounting the submergence plate in the port; and Figure 5 is a horizontal cross sectional view through the port of Figure 4 taken on line A-A.

This invention is primarily concerned with apparatus and methods for submerging solid-phase materials being introduced into a bath of molten metal. However, the invention could be extended for use with other molten materials provided they are electrically conductive. Accordingly, throughout this specification, including the claims, references to "molten material" should be understood as referring to electrically conductive molten material unless expressly stated otherwise. Furthermore, references to "metal", including "molten metal", should be understood as encompassing alloys which may include non-metallic materials or additives provided that the material as a whole remains electrically conductive.

Apparatus 10 in accordance with the invention includes a furnace 12 having a main furnace chamber 14 and a port 16 in fluid communication with the main furnace chamber 14 so that a molten metal bath 18 contained in the furnace has a common upper surface level 20 in the port 16 and the main furnace chamber 14. The furnace 12 in this embodiment forms part of apparatus for casting metals and can be of any suitable type. The port 16 is accessible from the top having a openable upper closure 17 and can be used to introduce material into the molten metal bath 18, such as additives and/or scrap metal. Such materials may be in granular form and may include alloying elements, metallurgical agents (fluxes) to aid production, or lightweight scrap pieces/fragments that are being recycled back into the meting process. The port 16 can also be used for extracting molten metal from the furnace chamber 14 for casting.

The port 16 has an inclined lower wall 22 leading to a channel member 24 at the upper, outer end of the port 16. In use, the channel member 24 can be extended outwardly by connecting additional channel members to form an extraction chute, which may be a casting feed launder. In vertical cross-section, the port 16 is shaped generally as a right-angled triangle, with the inclined lower wall 22 being angled at approximately 45° to 55° to a vertical end wall 26 of the furnace. However, the port need not be constructed as a right angled triangle and the angle of the inclined lower wall can be varied to suit the particular application and could, for example, be anywhere in the range of 30° to 70°.

The furnace main chamber 14, the port 16 and the channel member 24 are constructed from metal materials lined with refractory material 27 where they are in contact with molten metal in a known manner. Any suitable refractory materials can be used dependant on the nature of the metal material being processed and the temperatures encountered. The refractory material 27 lining the port 16 defines an interior channel 25 through which molten materials can flow. The port 16 has an interior width w which is measured between opposing inner surfaces of the refractory material 27 lining the port.

The apparatus includes an electromagnetic induction device 28 (in the form of a linear induction motor) externally mounted to the inclined lower wall 22 of the port 16 for inducing flow in the molten metal 18 in the port 16. The induction device 28 may be referred to as an induction stirring device or induction pump as its primary function is to impart a motion to the fluid metal in the port 16 and the furnace chamber 14. Whilst some heat will be generated in the molten metal, this is not the primary purpose of the induction device 28 and the induction device is not an induction heating device as such. The electromagnetic induction device 28 may be a liner motor having variable speeds of up to 50Hz or more. The electromagnetic induction device 28 is bi-directional and can be operated in a first direction to induce a downward force on the molten metal 18 in the port 16 to set up a flow of material in a downwards direction along the inclined lower wall 22 of the port or in a reverse direction to induce an upward force on the molten metal bath 18 in the port in the manner described in the applicant's earlier patent application published as WO 03/106908 Al, the contents of which incorporated by reference in their entirety.

In accordance with the present invention, the apparatus 10 includes a submergence plate or blade 30 located in the port 16 in spaced relation to the inner surface of the inclined lower wall 22 of the port 16 and positioned at a predetermined location in relation to the working face of the electromagnetic induction device 28. The submergence plate 30 is made from suitable materials for immersion in the molten metal. The plate 30 may have a metal core covered with a refractory material, for example. The submergence plate 30 is typically a thin, generally square or rectangular plate having a length L and a width W and a thickness T which is relatively small in comparison to its length and width. The plate 30 has inner and outer major faces 32, 34, the inner major face 32 opposing the inner surface 36 of the inclined lower wall 22 of the port 16 such that a void or submergence flow channel 38 is defined between the submergence plate and the inner surface 36 of the inclined lower wall of the port.

In use, with the submergence plate 30 in position in the port, electromagnetic induction device 28 is operated in a first direction to induce a downward force on the molten metal 18 in the port 16 to set up a flow in a downwards direction between the submergence plate 30 and the inclined lower wall 22 of the port and into the furnace main chamber 14 as indicated by the arrows A in Figure 3. The action of the electromagnetic induction device 28 pulls molten metal from the upper surface layers 20 of the metal bath 18 in the furnace main chamber 14 into the port 16 as indicated by the arrows B. This metal flow passes around the upper edges of the submergence plate 30 into the void 38 between the inner major face 32 of the plate and the opposed face 36 of the inclined wall of the port as indicated by the arrows C. The flow of molten metal accelerates down the void and exits the bottom of the submergence plate 30 where it is jetted into the lower layers of the metal bath 18 in the furnace main chamber 14. The general flow pattern produced is shown in by the arrows in the Figures. As the molten metal 18 enters the void 38 it changes direction and accelerates down the inclined inner face 36 of the lower wall so inducing vortices in the metal flow within the void and a strong submerging force at the upper end 40 of the submergence plate 30.

Once the flow is established, solid-phase material additions are introduced into the upper layers 20 of the metal bath in the port 16 where they are entrained and submerged by the combined action of the metal flow and the travelling magnetic field generated by the electromagnetic induction device 28, the mixture then being incorporated into and dissipated throughout the metal bath 18 in the main furnace chamber 14. The submergence of the added materials is accomplished with minimum disturbance to the surface 20 of the molten metal bath, resulting in reduced dross formation and metal loss. In use, the submergence plate 30 is positioned so that its upper end 40 is located proximal to the surface 20 of the molten metal. Typically, the vertical distance Y between the upper end 40 of the submergence plate 30 and the surface 20 of the metal is in the range of 50mm above the surface to 150mm below the surface. For ease of reference, the vertical distance Y between the upper end 40 of the submergence plate 30 and the surface 20 of the molten metal will be referred to herein as the vertical displacement of the submergence plate. It should be noted that the term "vertical displacement" is intended to include a situation where the upper end 40 of the submergence plate 30 is level with the upper surface 20 of the molten metal bath. Where the upper end 40 of the submergence plate is positioned level with or above the upper surface level 20 of the molten metal bath, the molten metal will flow about the upper regions of the side edges of the plate 30 into the void 38 between the inner major face 32 of the plate and the opposed face 36 of the inclined wall of the port.

Since it is common for the upper surface level 20 of the metal bath 18 to vary as processing proceeds, the submergence plate 30 is adjustably mounted in the port so that the its vertical displacement Y can be maintained within an acceptable tolerance of a desired value. The submergence plate 30 could, for example, be adjustably mounted to a support which can be introduced into the port 16 through its open upper end to hold the submergence plate suspended at the desired location. The arrangement can include means for adjusting the position of the submergence plate 30 relative to the support. This may be a simple mechanical arrangement in which adjustments are made manually as required or it may comprise an automated system which could include a closed loop feedback arrangement to maintain the desired vertical displacement Y of submergence plate 30. A semi-automated arrangement could also be used in which movement of the submergence plate is effected by means of an electronically controlled actuator in response to a manual input. In one embodiment as illustrated in Figures 4 and 5, the submergence plate 30 is mounted to a slide assembly 42 which is itself movably mounted on a support assembly 44, the arrangement being configured so that the slide assembly can be introduced into the port 16 through its open upper end to bring the submergence plate 30 into a desired position. In such an arrangement, all parts of the slide assembly and/or support that come into contact with the molten metal may be made from or covered with refractory material. In the embodiment illustrated, the support assembly 44 includes a fixed support 46 mounted to a wall of the furnace or other fixed member above the port and a rail assembly 48 pivotably mounted to the fixed support. The slide assembly 42 is mounted to the rail assembly 48 by means of a carriage 50 for moment longitudinally along the rail assembly by means of an electronically controlled drive mechanism or actuator 52 operationally connected with the carriage. The slide assembly 42 includes a supporting frame 54 which is mounted to the carriage and to which the submergence plate 30 is mounted. The supporting frame 54 may be a steel frame work and may be lined with refractory materials where it is submerged in the molten metal bath. The rail assembly 48 can be pivoted about a pivot point 56 between an in-use inclined position as shown and a generally upright, storage position in which it extends vertically in-line with the fixed support 46. When the rail assembly 48 is in the in-use inclined position, the submergence plate 30 is held at an appropriate angle to be positioned in the port opposite the inclined lower wall 22 and the slide assembly 42 can be advanced into the port down the rail assembly 48 to position the submergence plate in the port for use in submerging material as shown and as described herein. When the submergence plate 30 is not required, the slide assembly 42 can be retracted upwardly along the rail assembly 48 until the submergence plate is outside the port and the rail assembly pivoted upwardly to the vertical storage position to allow access to the port. Movement of the submergence plate 30 is achieved by means of the actuator 52 or other drive mechanism, operating under the control of an electronic control system. The control system may include a sensor arrangement for monitoring the level 20 of the metal bath 18 and a feedback arrangement for determining vertical displacement Y of the submergence plate 30. The control system may be configured to adjust the position of the submergence plate 30 substantially continuously as the level 20 of the metal bath changes in order to maintain the vertical displacement Y substantially at a desired value or to carry out adjustments periodically and incrementally only when the vertical displacement Y has changed to or beyond a predetermined tolerance amount from the desired value. In the later arrangement, with the vertical displacement Y of the submergence plate 30 initially set at a desired value Z, the control system can be configured to adjust the position of the submergence plate 30 to bring the vertical displacement Y back to the desired value Z only after the vertical displacement Y changes by a predetermined amount, say Z ± d.

The length L of the submergence plate 30 is less than the distance from its upper edge 40 to the lower surface 58 of the port so that fluid is able to flow out of the end of the submergence flow channel 38 and into the lower levels of the molten metal bath 18 in the furnace main chamber.

The minimum standoff distance X between the inner surface 36 of the refractory lined inclined lower wall 22 and the inner major face 32 of the submergence plate 30 may be anywhere in the range of 25mm to 300mm but is more typically in the range of 50mm to 250mm. In the embodiment illustrated, the major inner face 32 is aligned parallel to inner surface 36 of inclined lower wall 22. However, in some applications it may be desirable to angle the submergence plate 30 relative to the inner surface 36. For example, the major inner face 32 of the plate 30 may be arranged to converge towards the opposed inner surface 36 of the inclined wall 22 from its upper end 40 towards its lower end 60 so as to increase a jetting action of the metal flow between the plate and the inclined wall. The inner major face 32 of the submergence plate 30 may also be profiled so as to modify the flow of metal in the void 38 between the plate 30 and the inner surface 36 of the inclined wall 22.

As illustrated in Figures 2 and 5, unlike the known channel plates, the submergence plate 30 does not extend across the full internal width w of the port 16 but rather has a width W which is less than the width w of the port. The width W of the submergence plate may be in the range of 30% to 85% of the port internal width w, more preferably in range of 50% to 75% of the internal width w of the port, where the internal width w of the port is measured at the position of the submergence plate 30. This allows molten metal to flow between the sides of submergence plate 30 and refractory lining on either side. Whilst the submergence plate 30 will typically be generally square or rectangular, this is not essential and the width W of the submergence plate 30 can vary along its length. In some applications for example, it may be desirable that the width W of the plate increases from its upper end 40 to its lower end 60 in order to increase the submerging effect. Where the width W varies, the maximum width of the submergence plate will typically remain within the ranges indicated above. Furthermore, whilst the submergence plate 30 will normally be located substantially centrally within the interior of the port 16 with its longitudinal axis parallel to a central longitudinal axis S of the interior channel in the port, in some applications, the submergence plate 30 may be offset to one side or it may be angled relative to the longitudinal axis S of the port channel. The submergence plate 30 could be offset so that there is a clearance on one side of the plate 30 only, the plate contacting the side wall of the port on the other side.

The solid-phase materials can be introduced into the molten metal bath 18 in the port 16 at various locations depending on their nature and physical properties. For example, additional material can be introduced directly into the void 38 between the submergence plate 30 and inclined face 36 of the port 16 at the position indicated generally at 62 in Figure 2. Alternatively, material can be introduced into the upper layers of the metal bath 18 in the port in front of the submergence plate 30, as indicated at 64. These though are only typical examples of possible locations for introducing solid-phase materials and the person skilled in the art will be able to conduct trials to establish the most suitable entry position or positions for adding materials for any given application. The feed rate at which the solid-phase material is added is preferably controlled to match the submergence rate to ensure maximum efficiency and reduce the risk of blockage. The precise construction, orientation and location of the submergence plate 30 and the choice of entry location for the added material can all be varied as required to provide optimal submergence in dependence on the characteristics of the molten metal, the material being added, and taking into account the port and furnace chamber design. In preferred embodiments, the submergence plate 30 is mounted so that it can be retracted out of the port 16 to enable the electromagnetic induction device 28 to be operated in the first direction to stir the molten material in the furnace chamber 14 in a conventional manner as described in WO 03/106908 Al . Furthermore, the apparatus 10 may also be combined with a retractable channel plate assembly as described in the applicant's earlier patent application WO 2012/120276 Al so that with the submergence plate 30 removed from the port, a channel plate can be introduced and the electromagnetic induction device operated in a second direction opposite to the first to extract molten metal from the furnace chamber. The reader should refer to WO 2012/120276 Al for details of the retractable channel plate assembly. The whole contents of WO 2012/120276 Al are also hereby incorporated by reference.

Whereas the invention has been described in relation to what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed arrangements but rather is intended to cover various modifications and equivalent constructions included within the spirit and scope of the invention as defined in the accompanying claims.

Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof.