Patent Description:
The present disclosure relates to metallurgy generally and more specifically to devices and processes for furnaces, molten metal containment structures, and scrap submergence devices for mixing, conveying, treating and/or holding molten metals.

It is desirable for a number of reasons to cause material (e.g., aluminum) to flow in non-ferrous molten metal furnaces (such as a melting or holding furnace). In some cases, recycled material, such as used beverage cans (UBC) or other scrap, is melted before being combined with other sources of material before being cast as an ingot or other cast product.

Molten aluminum is a poor conductor of heat. Heat that reaches the surface of the material in the furnace is slow to reach an opposite surface of the material. Hotspots may develop on the surface increasing oxidation while solid metal stays relatively cold in other portions of the furnace. An unmixed volume of material may have a significant temperature difference between opposite sides (or between top and bottom). Stirring the material causes convection, which helps homogenize the temperature, that is, make it the same throughout. Mixing may also help melt the recycled material much faster. Mixing of solid metal into the molten bath results in high heat transfer and rapid melting of the solids. Simultaneous flux addition removes contaminants and oxides from the metal, resulting in improved metal quality and metal recovery.

The term embodiment and like terms are intended to refer broadly to all of the subject matter of this disclosure and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the claims below. Embodiments of the present disclosure covered herein are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the disclosure and introduces some of the concepts that are further described in the Detailed Description section below. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings and each claim. <CIT> discloses a side well for a metal melting furnace. The side well includes an insulated body having a front wall forming a part of an insulated side wall of a metal melting furnace and a top. A cavity within the body includes a single upright well having a cylindrical wall adjacent to a closed bottom of the cavity, an entrance to the cavity at the top of the insulated body, a metal inlet channel leading directly into the cavity from an inlet aperture in the front wall, and a metal outlet channel leading directly from the cavity to a metal outlet aperture in the front wall. The side well includes a rotatable impeller having a vertical rotatable shaft and at least one vaned section positioned at a lower end of the rotatable shaft. The impeller extends into the cavity with its vaned section positioned in the well adjacent to the cylindrical wall. <CIT> discloses a dual-function impeller for rotation in molten metal in a direction of rotation, as part of a rotary injector. The impeller includes a body having an axis, multiple blades circumferentially interspaced around the axis, and an aperture coinciding with the axis. <CIT> discloses a blowing spiral stirrer for hot metal desulfurization, including a porous blowing head and a spiral stirring blade provided on a stirring shaft. The stirring blades of the spiral stirrer are uniform in size, revolve around each other around the stirring shaft, and are evenly spaced in the circumferential direction. An aluminium metal furnace is known from <CIT>, including a heating chamber provided with a heating unit for heating molten aluminum. The furnace further includes a raw material supply unit for injecting aluminum scrap into the molten aluminum, a stirring unit for stirring the molten aluminum, and a flow of the molten aluminum flowing in from the heating chamber and a flow of the molten aluminum formed by the stirring unit in advance.

In view of the problems mentioned above in the state of the art devices/apparatus in this technical field, the present invention provides a scrap submerge device in accordance with the subject matter of independent claim <NUM>.

According to certain embodiments not part of the present invention, a molten metal recycling system comprises: a furnace comprising a main hearth, a sidewell, and a divider wall separating the main hearth from the sidewell, wherein the divider wall comprises (i) an entrance port where molten metal enters the sidewell and (ii) an exit port where molten metal exits the sidewell; and a scrap submergence device for mixing molten metal in the furnace, the scrap submergence device comprising: an upper structure; a shaft extending down from the upper structure; and an impeller at a lower end of the shaft, wherein the impeller is arranged within the sidewell such that: a radial flow path of the impeller is offset approximately <NUM>" to <NUM>" (<NUM> centimeter to <NUM> centimeter) from a deflector block; and a forward edge of the radial flow path of the impeller is aligned with an edge of the entrance port.

Other objects and advantages will be apparent from the following detailed description of non-limiting examples.

The subject matter of embodiments of the present disclosure is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. Directional references such as "up," "down," "top," "bottom," "left," "right," "front," and "back," among others, are intended to refer to the orientation as illustrated and described in the figure (or figures) to which the components and directions are referencing.

All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of "<NUM> to <NUM>" should be considered to include any and all subranges between (and inclusive of) the minimum value of <NUM> and the maximum value of <NUM>; that is, all subranges beginning with a minimum value of <NUM> or more, e.g., <NUM> to <NUM>, and ending with a maximum value of <NUM> or less, e.g., <NUM> to <NUM>.

As used herein, the meaning of "a," "an," and "the" includes singular and plural references unless the context clearly dictates otherwise.

<FIG> illustrates a scrap submergence device <NUM>, which may include an impeller <NUM>, a shaft <NUM>, an upper structure <NUM>, and a counterweight <NUM>. The scrap submergence device <NUM> is disposed adjacent to a furnace <NUM> (see <FIG>). The scrap submergence device <NUM> may be combined with the furnace <NUM> as components of a recycling system. A controller (not illustrated) may be provided with the scrap submergence device <NUM> and/or the recycling system and may be communicatively coupled to various components or subcomponents of the scrap submergence device <NUM> and/or the recycling system (or other system utilizing the scrap submergence device <NUM>) to control various aspects of the scrap submergence device <NUM> and/or the recycling system during use. As some non-limiting examples and as discussed in detail below, the controller may be utilized to control aspects of the scrap submergence device <NUM> and/or the recycling system such as a mass flow rate, a rotational speed of the scrap submergence device <NUM>, a height of the scrap submergence device <NUM> within molten metal, a height of the scrap submergence device <NUM> relative to a surface of the furnace <NUM>, an angle of the scrap submergence device <NUM>, a location of the scrap submergence device <NUM> relative to other components, a pumping number of the impeller (which provides a measure of the efficiency of the impeller <NUM>), a pumping rate of the impeller, combinations thereof, or other suitable aspects of the scrap submergence device <NUM> and/or the recycling system.

In some cases, the scrap submergence device <NUM> raises and lowers the impeller <NUM> and at least a portion of the shaft <NUM> into and out of a sidewell <NUM> of the furnace <NUM>. The scrap submergence device <NUM> may have an operating position where the impeller <NUM> is submerged in molten metal in the sidewell <NUM> and a retracted position where the impeller <NUM> is raised out of the sidewell <NUM> so it is not in contact with molten metal in the sidewell <NUM>. As described in greater detail below, the impeller <NUM> includes at least one blade <NUM> such that the impeller <NUM> and blade(s) <NUM> rotate about an axis V of the shaft <NUM>. The rotation of the impeller <NUM> and blade(s) <NUM> mixes and submerges shredded UBC or other scrap material in the molten aluminum within the sidewell <NUM>.

As shown in <FIG>, the furnace <NUM> may include a divider wall <NUM> separating a main hearth <NUM> of the furnace <NUM> from the sidewell <NUM>. The divider wall <NUM> may include an entrance port <NUM> and an exit port <NUM> to allow molten metal to move between the main hearth <NUM> and the sidewell <NUM>. The main hearth <NUM> may include a main hearth ramp <NUM> (see <FIG>). In some examples, the entrance port <NUM> is disposed near a deflector block <NUM>. <FIG> shows a top view of the sidewell <NUM> and illustrates a radial flow path <NUM> created by the impeller <NUM> (i.e., showing the full motion path of the impeller <NUM>). In some examples, the impeller <NUM> is disposed closer to the entrance port <NUM> than the exit port <NUM>. The furnace <NUM> may contain molten aluminum that is at a temperature of approximately <NUM> to <NUM>, although other temperatures may be used. In various examples, and as best illustrated in <FIG>, <FIG>, and <FIG>, a portion <NUM> of the sidewell <NUM> downstream from the entrance port <NUM> may optionally have a radiused surface. In certain aspects, the portion <NUM> of the sidewell <NUM> may be proximate to the deflector block <NUM>. The radiused surface of the portion <NUM> may direct and/or promote flow of molten metal into the impeller <NUM> and may reduce potential dead zones in the molten metal (i.e., regions where the flow is reduced).

In some examples, the deflector block <NUM> may be attached to the divider wall <NUM> and may have an approximately flat surface <NUM> that faces the impeller <NUM> (<FIG>). As shown in <FIG>, the deflector block <NUM> may also have a leading surface <NUM> and a trailing surface <NUM>. In some examples, the relative location between the impeller <NUM> and the deflector block <NUM> is controlled to optimize the flow of molten metal in the sidewell <NUM>. For example, as shown in <FIG>, a distance between the impeller <NUM> (or a blade <NUM> of the impeller <NUM>) and the approximately flat surface <NUM> of the deflector block <NUM> is defined as distance X. In some cases, the forward-most point of radial flow path <NUM> of the impeller <NUM> (or a blade <NUM>) (see point Z in <FIG>) is approximately aligned with the leading surface <NUM> of the deflector block <NUM>. The leading surface <NUM> may also be aligned with one edge of the entrance port <NUM> such that the forward-most point of radial flow path <NUM> of the impeller <NUM> is aligned with an edge of the entrance port <NUM>. In some examples, the distance X is approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other distances may be used depending on the overall configuration and size of the furnace <NUM> and sidewell <NUM>. In some cases, the distance X is approximately <NUM>" to <NUM>" (<NUM> to <NUM>). In some examples, the distance X is approximately <NUM>" to <NUM>" (<NUM> to <NUM>).

Optimizing the location of the impeller <NUM> relative to the deflector block <NUM> can affect at least one of the following: the mass flow of molten metal flowing into the sidewell <NUM> (in some cases, the metal will appear orange in color); the size of the vortex (which affects submergence efficiency such that scrap should be pulled downward but not so large as to create excess oxidation); the size of dross balls being produced, as explained in more detail below; and/or the pattern of flow of the molten metal within the sidewell <NUM>. In addition, the optimum location of the impeller <NUM> may change over time due to erosion of the deflector block <NUM> and build-up of material in the sidewell <NUM>. Based on erosion, in some cases, the impeller <NUM> (or at least one blade <NUM>) should be replaced approximately every <NUM> to <NUM> days of operation. As shown in <FIG>, the sidewell <NUM> may include a hearth ramp <NUM> at an opposite end of the sidewell <NUM> from the impeller <NUM> beyond the exit port <NUM>.

The entrance port <NUM> and the exit port <NUM> may each have dimensions and cross-sectional areas that optimize flow of molten metal through the sidewell <NUM> (see <FIG>). In some examples, the entrance port <NUM> has an entrance width Wi that is approximately <NUM>" to <NUM>" (<NUM> to <NUM>) and an entrance height Hi that is approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other widths and heights are envisioned. In some cases, the entrance width Wi is approximately <NUM>" to <NUM>" (<NUM> to <NUM>) and the entrance height Hi is approximately <NUM>" to <NUM>" (<NUM> to <NUM>). The entrance width Wi may be approximately <NUM>" (<NUM>) and the entrance height Hi may be approximately <NUM>" (<NUM>). In some examples, the exit port <NUM> has an exit width We that is approximately <NUM>" to <NUM>" (<NUM> to <NUM>) and an exit height He that is approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other widths and heights are envisioned. In certain examples, the exit height He is optionally less than the entrance height Hi. In various aspects, the exit height He and the entrance height Hi are each less than a lowest molten metal level within the furnace. In some cases, the exit width We is approximately <NUM>" to <NUM>" (<NUM> to <NUM>) and the exit height He is approximately <NUM>" to <NUM>" (<NUM> to <NUM>). The exit width We may be approximately <NUM>" (<NUM>) and the exit height Hie may be approximately <NUM>" (<NUM>).

In some examples, the entrance port <NUM> has an entrance width Wi that is approximately <NUM>" (<NUM>) and an entrance height Hi that is approximately <NUM>" (<NUM>) where the upper corners may each include a fillet with a <NUM>" radius (upper corners <NUM> as shown in <FIG>). In some cases, the exit port <NUM> has an exit width We that is approximately <NUM>" (<NUM>) and an exit height He that is approximately <NUM>" (<NUM>) where the upper corners may each include a fillet with a <NUM>" radius (upper corners <NUM> as shown in <FIG>). As shown in <FIG> and <FIG>, the exit port <NUM> may be angled at an angle θ relative to the divider wall <NUM> such that the exit port <NUM> is not perpendicular to the divider wall <NUM> and at least a portion of the flow through the exit port <NUM> is directed up the main hearth ramp <NUM>. In certain cases, the entrance port <NUM> is substantially perpendicular to the divider wall <NUM>, and the exit port <NUM> extends at the angle θ relative to the entrance port <NUM> such that a central axis of the exit port <NUM> is not parallel with a central axis of the entrance port <NUM>. In some cases, the angle θ is from greater than about <NUM>° to about <NUM>°, although other suitable angles may be used. For example, in other cases, the angle θ is from about <NUM>° to about <NUM>°. In one non-limiting example, the angle θ is approximately <NUM>°. In certain aspects, the angle θ may promote the flow of the molten metal back into the main hearth. In some aspects, the angle θ may depend on a volume or surface area of the sidewell <NUM> and a volume or surface area of the main hearth <NUM>.

There may be a ratio between the area of the entrance port <NUM> and the area of the exit port <NUM>. The areas for the entrance port <NUM> and the exit port <NUM> may be calculated based on the product of the respective width and the height, which are described above. In some examples, to optimize the circular flow within the sidewell <NUM>, the area of the exit port <NUM> (exit width We x exit height He) is smaller than the area of the entrance port <NUM> (entrance width Wi x entrance height Hi). For example, the area of the exit port <NUM> may be approximately <NUM>%-<NUM>% the area of the entrance port <NUM>, such as from approximately <NUM>%-<NUM>% the area of the entrance port <NUM>. Constructing the exit port <NUM> to be smaller than the entrance port <NUM> may create back pressure in the sidewell <NUM> to allow for better stirring of the molten metal within the sidewell <NUM>. In some cases, the area of the exit port <NUM> is approximately <NUM>% to <NUM>% of the area of the entrance port <NUM>, although other ratios may be used. The area of the exit port <NUM> may be approximately <NUM>% of the area of the entrance port <NUM>. Based on experimentation, it has been determined that too large of an exit port <NUM> may produce low velocities in the main hearth <NUM> and high mass flow in sidewell <NUM>. Too small of an exit port <NUM> may produce high velocities in the main hearth <NUM> and low mass flow in sidewell <NUM>.

Compared to a sidewell <NUM> that does not include a deflector block, the addition of deflector block <NUM> may increase mass flow rate during operation of the scrap submergence device <NUM>, such as <NUM>-<NUM>% or greater. In some cases, the addition of deflector block <NUM> increases mass flow rate during operation of the scrap submergence device <NUM> by approximately <NUM>%. This effect is because, without the deflector block <NUM>, the impeller <NUM> causes a vortical flow just downstream of the entrance port <NUM>, which reduces the mass flow rate as molten metal flow moves upward toward the free surface due to viscous dissipation and momentum transfer. Adding the deflector block <NUM> reduces the vortical flow just downstream of the entrance port <NUM> thus directing the molten metal more uniformly toward the impeller <NUM>.

As shown in <FIG>, in some examples, the deflector block <NUM> may be replaced with a curved deflector block 12a. The curved deflector block 12a is similar to the deflector block <NUM> except that the approximately flat surface <NUM> of the deflector block <NUM> (offset by distance X from impeller <NUM>) is replaced with a curved surface 12a. In some cases, the curvature of the curved surface 12a. <NUM> is not related to the curvature of the impeller <NUM>. In other examples, the curvature of the curved surface 12a. <NUM> approximately matches the curvature of the impeller <NUM> such that the curved surface 12a. <NUM> is centered about the center of the impeller <NUM> and the radius of the curved surface 12a. <NUM> is slightly larger than the radius of the impeller <NUM>. Based on such a relationship between the curved surface 12a. <NUM> and the impeller <NUM>, in some cases, the offset distance between the curved surface 12a. <NUM> and the impeller <NUM> (e.g., see distance X in <FIG>) would be approximately constant along the length of the curved surface 12a. In some examples, the curved deflector block 12a has an improved service life compared to that of the deflector block <NUM>.

As illustrated in <FIG>, the deflector block <NUM> (or deflector block 12a) may be attached to the scrap submergence device <NUM> such that the deflector block <NUM> is removable from the sidewell <NUM> of the furnace <NUM>. In some examples, an arm <NUM> extends from the upper structure <NUM> and the deflector block <NUM> is removably attached to the arm <NUM>. In some examples, the arm <NUM> is removably attached to the upper structure <NUM>. Based on this arrangement, the deflector block <NUM> can be replaced without emptying the furnace of molten metal (i.e., on the fly), which reduces down time and increases overall efficiency of the recycling process. In addition, mounting the deflector block <NUM> (or deflector block 12a) relative to the scrap submergence device <NUM> allows for a repeatable, constant, and predictable location for the deflector block <NUM>. As described above, in some cases, the relative location between the deflector block <NUM> (or deflector block 12a) and the impeller <NUM> affects the flow of molten metal and the overall efficiency of the recycling system.

In some cases, the material of the deflector block <NUM> (or deflector block 12a) includes a precast refractory composite material that includes low cement refractory slurry and stainless steel fiber or carbon fiber. In some examples, the material of the deflector block <NUM> (or deflector block 12a) includes a ceramic and a metal material. Oxide-based refractory materials have reasonable chemical/metallurgical resistance relative to molten aluminum, but may not have sufficient strength to sufficiently support the deflector block <NUM> (particularly when the deflector block <NUM> is attached to the scrap submergence device <NUM> and separate from the furnace <NUM>, as described above). In some cases, the deflector block <NUM> (or deflector block 12a) includes a metallic preform acting as a skeleton that is at least partially encapsulated by an oxide-based refractory material. The metallic preform may be steel, stainless steel, iron, cast iron, titanium, magnesium, Inconel, or any other appropriate material. In some cases, the metallic preform is <NUM> stainless steel. By encapsulating a metal alloy preform within an oxide-based refractory material, the block can be fabricated to have both the required mechanical strength and the required chemical/metallurgical resistance.

Various examples of impellers <NUM> are shown in <FIG>. Although the illustrated examples of the impellers <NUM> include three blades <NUM>, the impeller <NUM> may include any number of blades <NUM> including as few as one. The impeller <NUM> may be attached near a lower end of the shaft <NUM> such that the blade(s) <NUM> extend radially from the shaft <NUM>. In some examples, the impeller <NUM> includes a plate <NUM> that connects the blade(s) <NUM>. As shown in <FIG>, the plate <NUM> may be attached to the lower edge(s) of the blade(s) <NUM> such that a lower surface of the plate <NUM> is aligned with a lower surface of the blade(s) <NUM>. In other examples, the plate <NUM> is attached to other portion(s) of the blade(s) <NUM>. For example, as shown in <FIG>, the plate <NUM> may be attached approximately halfway between the lower edge(s) and the upper edge(s) of the blade(s) <NUM>. The plate <NUM> may have any appropriate shape including, for example, triangular, rectangular, or square. As shown in <FIG>, the plate <NUM> may have a circular disk shape. The width/diameter of the plate <NUM> may be equal to the total diameter D of the blade(s) (see <FIG> and <FIG>) such that the plate <NUM> extends to an outermost edge of each blade <NUM> or, as shown in the drawings, the width/diameter of the plate <NUM> may be less than the total diameter D of the blade(s) <NUM> such that the plate <NUM> does not extend to an outermost edge of each blade <NUM>. In some examples, the width/diameter of the plate <NUM> is approximately half of the total diameter D of the blade(s) <NUM>. The plate <NUM> adds strength to the blades <NUM> and the impeller <NUM> as a whole while also minimizing upward vortices in the molten metal such that a downward vortex can be induced to help submerge and mix the recycled material (e.g., shredded UBC or other scrap).

As shown in <FIG> and <FIG>, the shaft <NUM> may include a shoulder <NUM> and a coupling <NUM>. The coupling <NUM> allows the impeller <NUM> to be removably attached to the upper structure <NUM>. The shoulder <NUM> protects the coupling <NUM> and reduces the splashes of molten metal that reach the coupling <NUM>. In some examples, the coupling <NUM> includes a threaded hole <NUM> for attachment to the upper structure <NUM>.

In some cases, the material of the impeller <NUM> and the blades <NUM> includes (<NUM>) an inner skeleton and (<NUM>) an outer coating where at least a portion of the inner skeleton is encapsulated by the outer coating. As shown in <FIG>, the inner skeleton may include a shaft skeleton <NUM>, at least one blade skeleton <NUM>, and a plate skeleton <NUM>. The outer coating may include a shaft coating <NUM>, at least one blade coating <NUM>, and a plate coating <NUM>. Each blade skeleton <NUM> may include at least one hole <NUM> such that the material of the outer coating flows through the at least one hole <NUM> to enhance the strength/integrity of the attachment between the inner skeleton and the outer coating. In some examples, the inner skeleton is steel, stainless steel, iron, titanium, magnesium, Inconel, or any other appropriate material. In some cases, the inner skeleton is cast iron. The outer coating may be a refractory composite material that includes low cement refractory slurry and a metal material (e.g., stainless steel fibers or needles). In some examples, the material of the impeller <NUM> and the blades <NUM> includes a ceramic and a metal material. In some cases, the material of the impeller <NUM> and the blades <NUM> includes approximately <NUM>% to <NUM>% stainless steel needles. The stainless steel may include <NUM> stainless steel or any other appropriate stainless steel.

In some examples, the scrap submergence device <NUM> creates agitation in the sidewell <NUM>, which aids in mixing and melting the recycled material with the molten metal. The impeller <NUM> may be inserted into the molten metal and rotated to cause both bulk motion and small-scale motion eddies in the molten metal adjacent each impeller blade <NUM> (assuming turbulent flow). Mechanical energy is required to rotate the impeller <NUM> which transmits energy into the molten metal.

The impeller <NUM> may be designed to cause primarily radial flows in the molten metal because each blade <NUM> is designed such that a central plane of the blade <NUM> intersects (and/or is coplanar with) the axis V of the impeller <NUM> (see <FIG>). Radial flow described herein refers to flows that occur within a plane that is perpendicular to the axis V of the impeller <NUM>. Alternative impeller configurations include, for example, pitched blades (which would not have a central plane of the blade <NUM> that intersects or would not be coplanar with the axis V of the impeller <NUM>). Pitched blade configurations would create flows with more axial components such that more significant portions of the flow would be parallel to the axis V of the impeller (e.g., a boat propeller). <FIG> shows another example of an impeller <NUM> where the diameter of the shaft <NUM> of the impeller <NUM> changes along its length. As shown in <FIG>, the diameter of the shaft <NUM> may taper such that the diameter increases near the shoulder <NUM>.

<FIG> shows a schematic top view of an impeller <NUM> that includes three blades <NUM>. Clockwise rotation of the impeller <NUM> creates increased (positive) pressure in the molten metal adjacent to the leading face <NUM> of each blade <NUM> and decreased (negative) pressure in the molten metal adjacent to the trailing face <NUM>. As the impeller <NUM> rotates, fluid (molten metal) flows along the surface of each blade <NUM> in the radial direction around the outermost tip <NUM> (or outermost edge) of the blade <NUM>, the fluid mixes with other fluid having a lower velocity, which may create free vortices <NUM>. Because the impeller <NUM> is submerged (closer to the floor <NUM> of the sidewell <NUM> than the surface of the molten metal, as described below), at least some of the fluid is pulled downward toward the impeller <NUM>. This downward flow may be observed such that recycled material (e.g., shredded UBC or other scrap) is pulled downward from the surface of the molten metal. In some cases, the downward flow also includes vortices that are centered around the shaft <NUM> and/or axis V (see <FIG>). In addition to flow that moves in the radial direction around the outermost tip <NUM> of the blade <NUM>, each blade <NUM> may also induce tangential flow that moves over the upper edge of the blade <NUM> or over the lower edge of the blade <NUM> (such as from the leading face <NUM> of the blade <NUM> to the trailing face <NUM> of the blade <NUM>). In some cases, the flow over the top and/or bottom of the blade <NUM> creates linear vortices. In some non-limiting examples, for blades <NUM> that have a height C (see <FIG>) equal to less than approximately <NUM>", the flow is approximately balanced between portions that flow over the top of the blade <NUM> and portions that flow under the blade <NUM>. In some non-limiting examples, blades <NUM> that have a height C equal to greater than approximately <NUM>", a higher percentage of the flow is moves over the top of the blade <NUM> compared to the flow that moves under the blade <NUM>. In some cases, increased blade height (i.e., height C) leads to increased vorticity at the trailing face <NUM> of the blade <NUM>, which draws in additional molten metal from the leading face <NUM> of the subsequent blade resulting in increased downward submergence at the uppermost surface of the metal.

In some cases, flows moving toward the bottom of the blade <NUM> (due to the distance between the bottom of the blade <NUM> and the floor <NUM> of the sidewell <NUM>) are re-directed upwards from the trailing face <NUM> to the leading face <NUM> of the next blade <NUM> and over the top. In addition, some of the flow moving toward the bottom of the blade <NUM> interacts with the plate <NUM> and is redirected to the lower radial tip of the blade <NUM> (i.e., the bottom of outermost tip <NUM>) which increases overall efficiency.

The dimensionless pumping number provides a measure of the efficiency of the impeller <NUM>. In some examples, the pumping number Np is defined as: <MAT> where Q is the impeller pumping rate (m<NUM> /minute), N is the speed (RPM) of the impeller, and D is the diameter (meter) of the impeller.

The shape of the impeller <NUM>, including the blade(s) <NUM>, can be adjusted to optimize efficiency of the scrap submergence device <NUM>. For example, the radius of each blade or the length (radial dimension) from the outer surface of the shaft <NUM> to the outermost tip <NUM> of each blade <NUM> (see radii A and B in <FIG>, and <FIG>) can be changed to accommodate characteristics of the particular furnace <NUM> and/or to optimize performance of the scrap submergence device <NUM>. In some cases, as shown in <FIG>, the radius A is approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other suitable dimensions can be used. The overall diameter of the impeller may be approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other suitable diameters can be used. In some examples, the radius A is approximately <NUM>" (<NUM>), and the total diameter D of the impeller is approximately <NUM>" (<NUM>) although other suitable dimensions can be used. The radius A may be approximately <NUM>" (<NUM>). In some cases, as shown in <FIG>, the radius B is approximately <NUM>" to <NUM>" (<NUM> to <NUM>) although other suitable lengths can be used. The total diameter D of the impeller may be approximately <NUM>" to <NUM>" (<NUM> to <NUM>) although other suitable dimensions can be used. In some examples, the radius B is approximately <NUM>" (<NUM>), and the total diameter D of the impeller is approximately <NUM>" (<NUM>). The diameter of the shaft <NUM> may be approximately <NUM>" to <NUM>" (<NUM> to <NUM>) although other suitable dimensions can be used. In some examples, the diameter the of shaft <NUM> is approximately <NUM>" (<NUM>). In some cases, the diameter of the shaft <NUM> is approximately <NUM>" (<NUM>). As shown in <FIG>, in some cases, the diameter of the shaft <NUM> varies along the length of the shaft and generally increases when moving up toward the shoulder <NUM>.

The height (vertical dimension) of each blade <NUM> can also vary to suit specific needs for a particular furnace <NUM> and/or to optimize performance of the scrap submergence device <NUM>. In some cases, the height C (see <FIG> and <FIG>) is approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other suitable heights may be used. In some examples, the height C is approximately <NUM>" (<NUM>). In some cases, the height C is approximately <NUM>" (<NUM>). In some examples, the height C is approximately <NUM>" (<NUM>). In some cases, increasing the height of the blade <NUM> causes better results related to mass flow rate through the sidewell <NUM> and the ability to mix and melt solid pieces of recycled material in the molten metal. Increasing the height of the blade <NUM> may also contribute to stronger vortices both in the sidewell <NUM> and in the main hearth <NUM>, which improves the melting rate. The vortices formed near the entrance port <NUM> may contribute to reduced mass flow rate through the sidewell <NUM> and the formation of such vortices may increase with blade height. In some examples, when various factors (e.g., geometry, impeller speed, etc.) are adjusted, the mass flow rate through the entrance port <NUM> pulsates such that a combination of impeller geometry, impeller position, deflector block position, and molten metal level can excite a resonance behavior, which causes a corresponding increase in furnace performance. In some cases, higher velocities closer to the floor <NUM> and under the impeller <NUM> may increase the flow through the sidewell <NUM>.

The ratio of blade height C to blade radius (i.e., radius A or radius B) may be approximately <NUM> to approximately <NUM>, or other suitable ratios. The present invention discloses that the ratio of blade height C to blade radius is <NUM> to <NUM>, such as approximately <NUM> to approximately. In some cases, the ratio of blade height C to blade radius is approximately <NUM>.

As shown in <FIG>, the blades <NUM> includes additional features designed to increase efficiency of the molten metal flow adjacent to the impeller <NUM>. The blade <NUM> includes a radial extension <NUM> at the outermost tip <NUM>. The radial extension <NUM> extends in a tangential direction from the leading face <NUM> of the blade <NUM>. The radial extension <NUM> decreases the losses at the outermost tip <NUM> (associated with the free vortices) thus increasing the pumping number. In some examples, the radial extension <NUM> has a sharp knife edge at the tip of the leading face <NUM>. As shown in <FIG>, the impeller <NUM> may include a ring <NUM> extending around a full perimeter of the impeller <NUM> that attaches to the outermost tip <NUM> of each blade <NUM>. In some cases, as illustrated, the ring <NUM> is attached to the bottom of outermost tip <NUM> and provides reinforcement for this portion of the blade <NUM>. As shown in <FIG>, a blade <NUM> may include an upper extension <NUM> at the upper edge of the blade <NUM>. The upper extension <NUM> may extend in an approximately tangential direction from the leading face <NUM> of the blade <NUM>. The upper extension <NUM> may decrease the losses at the upper edge of the blade <NUM> thus increasing the pumping number. In some examples, the upper extension <NUM> has a curved geometry, a peaked geometry or a sharp knife edge at the tip of the leading face <NUM>. Although <FIG> illustrates an example that includes both the upper extension <NUM> and the radial extension <NUM> but does not include the ring <NUM>, the impeller <NUM> may include any combination of these features (e.g., any combination of one, two, or all three of these features). The configuration of <FIG>, where the radial extension <NUM> extends along the side of the blade <NUM> and the upper extension extends along the upper edge of the blade <NUM>, increases pressure on the molten metal as the impeller <NUM> rotates.

The addition of salt flux (also referred to as salt) to the sidewell <NUM> of the furnace <NUM> increases the efficiency of the furnace <NUM> and the recycling process. The salt may be added through a salt feed tube <NUM> (see <FIG>). In some examples, the salt feed tube <NUM> is located at the divider wall <NUM> between the entrance port <NUM> and the exit port <NUM>. In some cases, the salt may be mixed with shredded material. In some cases, the salt may be added through a hollow impeller. In such an example, the shaft of the impeller may be hollow and may allow for salt to be injected by the hollow shaft. In some cases, the amount of salt added is approximately <NUM>% to <NUM>% of the charge input weight. In some examples, the amount of salt added is approximately <NUM>% to <NUM>% of the charge input weight. In some cases, the amount of salt added is approximately <NUM>% of the charge input weight.

To maximize efficiency in the recycling process, impurities (such as dross) should be removed from the molten metal, to the extent possible while simultaneously minimizing the amount of molten metal removed from the furnace. The scrap submergence device <NUM> and the related fluid flow created by the scrap submergence device <NUM> circulates the molten metal and causes the dross to accumulate. In some cases, the dross accumulates in the form of spherical shapes (also referred to as dross balls). The dross balls may primarily contain salts, oxides, oxide skins, spinel, and silicates. In some cases, salt flux input should be adapted based on the characteristics of the dross balls such that (i) if the dross balls are completely covered in molten metal (e.g., aluminum), more salt is needed and (ii) if the dross balls are completely dewetted of aluminum, salt addition should be suspended. Excessive salt can lead to dross balls sticking and clumping together. The salt may have a lower melting point (approximately <NUM>) compared to that of the molten metal. However, when added to the furnace, the salt does not immediately break down and/or melt. Adding salt to the dross layer gives the salt time to melt near the recycled material at the impeller <NUM> to start producing dross balls. In some examples, the frequency and location of the salt additions can also affect efficiency of the recycling process. In some cases, the salt includes NaCl and/or KCl and may also include an active fluoride component. In some examples, the salt includes <NUM>% sodium chloride, <NUM>% potassium chloride, and <NUM>% cryolite.

To optimize the dross balls (i.e., maximize the impurities removed from the furnace while also minimizing the molten metal removed from the furnace), in some cases, the dross balls are pushed into the vortex created near the impeller <NUM> at least once after being formed, which increases the amount of oxides collected in each ball. In some examples, the dross balls accumulate near the hearth ramp <NUM> of the sidewell <NUM> (see <FIG>). The diameter of the dross balls may be approximately <NUM>" to <NUM>" (<NUM> to <NUM>), although other sizes are envisioned. In some examples, the average dross ball size is approximately <NUM>" to <NUM>" (<NUM> to <NUM>). In some cases, the average dross ball size is approximately <NUM>". Size of the dross ball may be affected by quantity of salt input, magnitude of gap between the impeller <NUM> and the deflector block <NUM>, rotational speed of the scrap submergence device <NUM>, and other factors. In some examples of molten aluminum furnaces as disclosed herein, the dross balls contain small amounts of aluminum, in some cases, approximately <NUM>% aluminum. In some examples, the dross balls contain <NUM>%-<NUM>% aluminum. In some cases, the dross balls contain <NUM>%-<NUM>% aluminum. This is significantly lower than dross from conventional aluminum furnaces (e.g., that include a circulation pump and a separate mixing device), where dross collected will include <NUM>%-<NUM>% aluminum. These conventional furnaces may produce dross but do not produce dross balls. Dross balls are easy to handle and separate from molten metal (compared to dross collected in conventional furnaces) because of their lower aluminum amount. In addition, dross balls do not fume or thermite. In some cases, the average composition of the dross balls is: <NUM>% solids (including, for example, spinel, aluminum oxide, silicates), <NUM>% aluminum, <NUM>% salt (for example, NaCl, KCl, trace fluoride), <NUM>% Al<NUM>C<NUM>, and AlN may or may not be detected. The significantly lower amount of aluminum in the dross balls compared to conventional dross reduces the cost and energy required for producing aluminum.

The dross balls may accumulate and form a deep layer of dross balls near the hearth ramp <NUM>. The area adjacent to the impeller <NUM> may have the lowest concentration of dross balls or a thin layer of dross balls. The volume of molten metal within the furnace <NUM> may be controlled such that the surface of the metal (where the dross balls are located) remains above the exit port <NUM> to prevent the dross balls from moving into the main hearth <NUM>. During operation of the scrap submergence device <NUM>, it may be helpful to remove the larger dross balls while leaving the smaller balls because the smaller balls are more effective in removing oxides and absorbing salt. The dross balls are larger at the bottom of the dross layer. Therefore, to remove the larger dross balls, it may be necessary to push the small dross ball layer on the surface aside to expose the larger balls underneath.

During operation of the scrap submergence device <NUM>, location and rotational speed of the impeller <NUM> can be adjusted to optimize mixing and overall efficiency of the recycling process. In some cases, the speed of the impeller <NUM> is varied based on the amount of metal in the furnace. In some cases, the speed of the impeller <NUM> may be from <NUM>-<NUM> RPM. When the amount of molten metal in the furnace is low, the impeller <NUM> is located lower within the sidewell <NUM> (i.e., closer to the floor <NUM> of the sidewell <NUM>). As the volume of molten metal in the furnace increases, the impeller <NUM> is raised away from the floor <NUM>. The rotational speed of the impeller <NUM> will also need to increase with increased volume of molten metal. In one non-limiting example, in some cases where recycled material (e.g., shredded UBC or other scrap) is added to the furnace at a rate of approximately <NUM>,<NUM> lb/hr, for a depth of approximately <NUM>" (<NUM>) of molten metal, the impeller <NUM> may rotate at approximately <NUM>-<NUM> RPM, although other speeds may be utilized. In another non-limiting example, in some cases, for a depth of approximately <NUM>" (<NUM>) of molten metal, the impeller <NUM> may rotate at approximately <NUM>-<NUM> RPM (at the same feed rate of approximately <NUM>,<NUM> lb/hr), although other speeds may be utilized. The speed of the impeller <NUM> may also need to increase with higher feed rates. In one non-limiting example, in some cases where recycled material (e.g., shredded UBC or other scrap) is added to the furnace at a rate of approximately <NUM>,<NUM> lb/hr to <NUM>,<NUM> lb/hr, for a depth of approximately <NUM>" (<NUM>) of molten metal, the impeller <NUM> should rotate at approximately <NUM>-<NUM> RPM, although other speeds may be utilized. In another non-limiting example, in some cases, for a depth of approximately <NUM>" (<NUM>) of molten metal, the impeller <NUM> should rotate at approximately <NUM>-<NUM> RPM (at the same feed rate of approximately <NUM>,<NUM> lb/hr to <NUM>,<NUM> lb/hr), although other speeds may be utilized. The higher feed rate (approximately <NUM>,<NUM> lb/hr to <NUM>,<NUM> lb/hr) causes more shredded material to be present on the surface of the molten metal, which has a stabilizing effect resulting in fewer vortices formed and less splashing at the surface of the molten material thus allowing for higher rotational speeds for the impeller <NUM>. In some examples, for a given feed rate, the maximum rotational speed of the impeller <NUM> and the depth of molten metal in the sidewell <NUM> have an approximately linear relationship. In various cases, the rotational speed of the impeller <NUM> may be controlled based on a depth of the molten metal in the sidewell <NUM>. In some examples, the rotational speed of the impeller <NUM> may optionally be increased when the depth of the molten metal is higher and may optionally be decreased when the depth of the molten metal is lower. In some cases, the bottom of the impeller <NUM> is located approximately <NUM>" to <NUM>" (<NUM> to <NUM>) from the floor <NUM> of the sidewell <NUM>. In some examples, the bottom of the impeller <NUM> is located approximately <NUM>" (<NUM>) from the floor <NUM> of the sidewell <NUM>. In other words, the impeller <NUM> is typically arranged such that the center of the height of the impeller <NUM> is located below the halfway point of the depth of the molten metal (i.e., the impeller is submerged below the center of the depth of the molten metal).

In some cases, a height of the impeller <NUM> above a floor of the sidewell <NUM> (or a distance from the floor of the sidewell <NUM> to the impeller <NUM>) may be controlled based on the amount of molten metal in the sidewell <NUM>. As a non-limiting example, the impeller <NUM> may be controlled such that the height of the impeller <NUM> is increased when the amount or depth of the molten metal in the sidewell <NUM> is higher and decreased when the amount or depth of the molten metal in the sidewell <NUM> is lower.

In addition, the location of the impeller <NUM> relative to the deflector block <NUM> (or deflector block 12a) may also need to change during operation of the scrap submergence device <NUM>. For example, as material accumulates or builds up on the various surfaces in the sidewell <NUM>, the impeller <NUM> may need to move away from the deflector block <NUM> (or deflector block 12a) to ensure optimum offset between these components (e.g., distance X described above).

A method of operating the scrap submergence device <NUM> with a furnace <NUM> may include adding molten metal to the furnace <NUM>, inserting the impeller <NUM> into the molten metal in the sidewell <NUM>, adding recycled material into the sidewell, and rotating the impeller <NUM> about its vertical axis V. In some embodiments, salt flux may added in proportion to the amount of recycled material. A deflector block <NUM> (or deflector block 12a) may be arranged relative to the impeller <NUM> and/or relative to an entrance port <NUM> in the divider wall <NUM> between the main hearth <NUM> and the sidewell <NUM>. In some cases, the deflector block <NUM> (or deflector block 12a) may be attached to the divider wall <NUM> while in other examples, the deflector block <NUM> (or deflector block 12a) is attached to an arm <NUM> that extends down from the upper structure <NUM>.

<FIG> illustrate another example of a furnace <NUM> according to embodiments. The furnace <NUM> includes a main hearth <NUM> and a sidewell <NUM>, which may be similar to the main hearth <NUM> and the sidewell <NUM> of the furnace <NUM>. Similar to the furnace <NUM>, the furnace <NUM> includes a main hearth ramp <NUM>. Heating elements <NUM> (including but not limited to burners) may be supported relative to the main hearth <NUM> and direct heat into the main hearth <NUM>.

A divider wall <NUM> separates the main hearth <NUM> from the sidewell <NUM>. The divider wall <NUM> includes an entrance port <NUM> and an exit port <NUM>, which may be sized, dimensioned, or otherwise controlled as discussed previously with respect to the entrance port <NUM> and the exit port <NUM>. Similar to the sidewell <NUM>, and as best illustrated in <FIG> and <FIG>, the sidewell <NUM> includes the portion <NUM> with the radiused surface to direct and/or promote flow of molten metal to an impeller (the impeller is not shown in <FIG> for simplicity). Similar to the sidewell <NUM>, the sidewell <NUM> may include a hearth ramp <NUM> at an opposite end of the sidewell <NUM> from the entrance port <NUM> and optionally beyond the exit port <NUM>. As best illustrated in <FIG>, the distal wall <NUM> of the sidewell <NUM> does not include a ramp (such as the ramp <NUM>). In other words, the distal wall <NUM> extends all the way across and does not include an offset portion.

As best illustrated in <FIG>, in various examples, the sidewell <NUM> includes a divider wall <NUM> within the sidewell <NUM> between the entrance port <NUM> and the exit port <NUM>. The divider wall <NUM> may include a curved or radiused surface <NUM>. In some examples, the curvature of the surface <NUM> may depend on the curvature of the impeller, although it need not in other examples. The divider wall <NUM> may extend a predetermined distance into the sidewell <NUM> (and away from the divider wall <NUM>) such that the divider wall <NUM> defines a flow passage <NUM> between an end <NUM> of the divider wall <NUM> and a wall <NUM> of the sidewell <NUM> that molten metal flows through after being mixed by the impeller and before exiting via the exit port <NUM>. The flow passage <NUM> has a passage width <NUM> that is less than a width <NUM> of the sidewell <NUM>. In various examples, the curvature of the surface <NUM> of the divider wall <NUM> and the flow passage <NUM> defined by the divider wall <NUM> may improve the mixing of molten metal by the impeller and may improve the overall flow of molten metal through the sidewell <NUM>.

Claim 1:
A scrap submergence device (<NUM>) for mixing molten metal in a furnace (<NUM>), the scrap submergence device (<NUM>) comprising:
an upper structure (<NUM>);
a shaft (<NUM>) extending down from the upper structure (<NUM>); and
an impeller (<NUM>) at a lower end of the shaft (<NUM>), the impeller (<NUM>) comprising:
a plurality of blades (<NUM>), each of the plurality of blades (<NUM>) having a blade height and a blade radius; and
a plate (<NUM>),
wherein a ratio of the blade height to the blade radius is <NUM> to <NUM>, and at least one of the plurality of blades (<NUM>) comprises a radial extension (<NUM>) extending in a tangential direction from an outermost edge (<NUM>) on a leading face (<NUM>) of the at least one of the plurality of blades (<NUM>).