ELECTRIC IMMERSION ALUMINUM HOLDING FURNACE WITH CIRCULATION MEANS AND RELATED METHOD

Abstract

A process to hold molten aluminum alloy in a refractory lined vessel using heating elements disposed within ceramic immersion heating tubes to provide accurate temperature metal for the casting industry. The vessel is lined with multi thicknesses of high insulating refractory materials to minimize heat loss with contoured corners to allow smooth flow of circulating metal provided by a gear drive with rotary shaft and impeller. The heating elements are housed in a ceramic protection tube to prevent aluminum leakage which would result in element failure. The receiving and outlet wells are separated by refractory arches. An insulated inert gas purged cover is used over the heat chamber to reduce heat loss and allow for an inert purge gas to minimize surface oxidation. A thermocouple for temperature control is positioned in the exit chamber. A ceramic drain plug is provided to remove metal for maintenance.

Claims

1. A system comprising: an electric immersion holding furnace having refractory walls engaging an insulated floor, wherein the refractory walls engaging the insulated floor define a holding chamber; a heating element disposed within an immersion tube, wherein the immersion tube extends into the holding chamber; and means for circulating molten metal within the electric immersion holding furnace in a substantially horizontal direction.

2. The system of claim 1, wherein the immersion tube further comprises silicon nitride.

3. The system of claim 1, wherein the immersion tube further comprises silicon carbide.

4. The system of claim 1, wherein the immersion tube further comprises silicon nitride and a compound configured to withstand the heat of the electric immersion holding furnace.

5. An electric immersion holding furnace comprising: refractory walls operatively connected to an insulated floor, wherein the refractory walls and insulated floor define a holding chamber; an immersion tube, extending through a refractory wall and disposed within the holding chamber; a motor operatively engaged to a first end of a shaft, wherein the motor is disposed outside of the electric immersion holding furnace; a shaft having the first end, a second end, and a body engaging the first end and second end, the body extends into the holding chamber below the immersion tube, and the second end engages an impeller suspended in the holding chamber below the immersion tube, wherein the motor rotates the shaft and impeller such that the impeller circulates liquid metal throughout the holding chamber and across the immersion tube in a substantially horizontal direction.

6. The electric immersion holding furnace of claim 5, further comprising a gearbox engaged to the motor, wherein the gearbox is a variable speed gearbox and the motor is a bi-directional motor.

7. The electric immersion holding furnace of claim 5 further comprising arches that extend into the holding chamber to create holding spaces.

8. The electric immersion holding furnace of claim 5 further comprising a plurality of immersion tubes, wherein an electric heater is disposed within each of the plurality of immersion tubes, and wherein the plurality of immersion tubes are disposed horizontally with the holding chamber.

9. The electric immersion holding furnace of claim 8, wherein a gearbox is configured to adjust a length of the shaft extending into the holding chamber.

10. The electric immersion holding furnace of claim 5, wherein the motor is disposed on a top of the electric immersion holding furnace such that the shaft body extends through the top of the electric immersion holding furnace and the second end engages the impeller below the immersion tube.

11. The electric immersion holding furnace of claim 5, wherein the motor, shaft, and impeller comprise a stirring assembly and wherein the electric immersion holding furnace further comprises multiple stirring assemblies.

12. The electric immersion holding furnace of claim 5, wherein the immersion tubes contain either silicon nitride or silicon carbide and shaft is comprised of a material selected from the group consisting of graphite, castable refractory, silicon nitride, and silicon carbide.

13. The electric immersion holding furnace of claim 5, wherein the impeller further comprises a plurality of arms, wherein the arms comprise a surface having a negative slope defined by a slope angle, and wherein the slope angle is the angle of the surface relative to a vertical line extending from a top corner of an arm to the bottom on the arm.

14. The electric immersion holding furnace of claim 13, wherein the slope angle is in the range of 15 degrees to 45 degrees.

15. The electric immersion holding furnace of claim 5, wherein the impeller further comprises paddles extending radially from the shaft.

16. The electric immersion holding furnace of claim 15, wherein the paddles further comprise a concave end distally disposed from the shaft.

17. A method for preventing sludge and corundum accumulation on immersion tubes in an electric immersion holding furnace comprising: circulating the metal in a horizontal plane in a holding chamber disposed within an electric immersion holding furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The foregoing will be apparent from the following more particular description of exemplary embodiments of the disclosure, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the disclosed embodiments.

[0034] FIG. 1 is a perspective view of an exemplary electric immersion holding furnace.

[0035] FIG. 2 is a cross-sectional side view that shows the length of an exemplary electric immersion holding furnace while depicting the stirring assembly disposed below horizontal heating elements.

[0036] FIG. 3. is a perspective view of an exemplary stirrer assembly depicting an exemplary impeller configured to move the metal in a substantially horizontal manner

[0037] FIG. 4 is a cross-sectional side view that depicts the width of an exemplary electric immersion holding furnace, while showing a horizontal heating element extending partially into the holding chamber above the stirring assembly.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The following detailed description of the preferred embodiments is presented only for illustrative and descriptive purposes and is not intended to be exhaustive or to limit the scope and spirit of the invention. The embodiments were selected and described to best explain the principles of the invention and its practical application. One of ordinary skill in the art will recognize that many variations can be made to the invention disclosed in this specification without departing from the scope and spirit of the invention.

[0039] Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate embodiments of the present disclosure, and such exemplifications are not to be construed as limiting the scope of the present disclosure in any manner.

[0040] It will be understood that aluminum may refer to either pure elemental aluminum or alloys comprising aluminum unless otherwise specifically stated in an example.

[0041] References in the specification to one embodiment, an embodiment, an exemplary embodiment, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0042] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiment selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure.

[0043] The singular forms a, an, and the include plural referents unless the context clearly dictates otherwise. Numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the states value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0044] All ranges disclosed herein are inclusive of the recited endpoint and are independently combinable (for example, the range from 2 degrees to 10 degrees is inclusive of the endpoints, 2 degrees and 10 degrees, and all intermediate values.

[0045] As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as about and substantially, may not be limited to the precise values specified. The modifier about should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example the expression from about 2 to about 4 also discloses the range from 2 to 4.

[0046] It should be noted that many of the terms used herein are relative terms. For example, the terms upper and lower are relative to each other in location, i.e. an upper component is located at a higher elevation than a lower component in a given orientation, but these terms can change if the device is flipped. The terms inlet and outlet are relative to a fluid flowing through them with respect to a given structure, e.g. a fluid flows through the inlet into the structure and flows through the outlet out of the structure. The terms upstream and downstream are relative to the direction in which a fluid flows through various components, i.e. the flow of fluids through an upstream component prior to flowing through the downstream component.

[0047] The terms horizontal and vertical are used to indicate direction relative to an absolute reference, i.e. ground level. However, these terms should not be construed to require structure to be absolutely parallel or absolutely perpendicular to each other. For example, a first vertical structure and a second vertical structure are not necessarily parallel to each other. The terms top and bottom or base are used to refer to locations/surfaces where the top is always higher than the bottom/base relative to an absolute reference, i.e. the surface of the Earth. The terms upwards and downwards are also relative to an absolute reference; an upwards flow is always against the gravity of the Earth.

[0048] The term directly, wherein used to refer to two system components, such as valves or pumps, or other control devices, or sensors (e.g. temperature or pressure), may be located in the path between the two named components.

[0049] An aluminum melting furnace, which is also known as an aluminum smelting furnace, generally melts aluminum prior to the aluminum entering one or more electric immersion holding furnaces. The melting furnace may produce melt zone temperatures upwards of 2,100 F. with metal temperatures upwards of 1,500 F. By contrast, an electric immersion holding furnace is generally designed to store the aluminum and aluminum alloys in liquid form while the metal awaits further processing. An electric immersion holding furnace may generate temperatures ranging from about 1,200 F. to about 1,400 F. The desired aluminum generally resides at the bottom of the furnace where troughs or large buckets may convey the molten aluminum to one or more holding furnaces.

[0050] Generally, an electric immersion holding furnace is associated with a caster.

[0051] Occasionally, one electric immersion holding furnace may be associated with two or possibly three casters, but it is generally uncommon in the industry to have a single electric immersion holding furnace connected to more than three casters. As a result, in production facilities that utilize many casters, it is common to have about as many electric immersion holding furnaces configured to supply liquid metal to the associated caster.

[0052] An exemplary electric immersion holding furnace with exemplary circulating means as disclosed herein may be configured to be used with any commonly used casting techniques. These techniques may include for example, high pressure die casting, low pressure die casting, permanent molding, sand molding, lost foam molding, the V process, and investment casting.

[0053] In die casting, a reusable steel mold forms aluminum into castings under high pressure. Operators or equipment generally inject molten metal in to the die (mold) where the metal is rapidly chilled. The die cast machines are normally classified as horizontal or vertical

[0054] In low pressure casting, pressurized air in an air tight furnace containing molten metal forces the metal up a refractory tube and into a permanent mold mounted over the furnace. The pressure is typically less than 15 pounds per square inch (PSI). This casting process typically eliminates the need for risers and heavy gating. Aluminum wheels are commonly produced by a low pressure casting system.

[0055] Permanent mold castings represent about 15% of the casting poured. In permanent mold casting, operators and equipment pour aluminum into permanent metal molds under gravity. Metal molds are made of high alloy iron or steel and have typically production life of upward 125,000 castings.

[0056] In sand mold casting, operators and equipment pour molten aluminum into green sand molds or chemically bonded molds. This is considered a gravity pour casting, like permanent mold, but more complex castings can be produced in sand using sand cores.

[0057] Aluminum sand castings represent about 11% of the aluminum castings produced in the world. The sand mold generally cannot be reused.

[0058] In lost foam casting, operators and equipment use gravity to pour aluminum into an unbounded sand flask formed around a polystyrene mold. The foam pattern is a duplicate of the castings to be produced. As the aluminum is poured into the sand flask, the polystyrene mold evaporates and the aluminum sets in the form of the foam pattern. This is process is also called EPC which represents expendable pattern castings.

[0059] In investment casting, a wax pattern stands in for the final aluminum casting and a plaster mold is created around the wax pattern. The plaster mold is a refractory mold that as the inverse shape of the final aluminum casting. Prior to adding the aluminum, operators and equipment burn out the wax, thereby leaving the refractory plaster or ceramic mold in the exact shape of the casting to be produced. The molten aluminum is then poured into the refractory mold to produce high tolerance castings.

[0060] The following detailed description of the preferred embodiments is presented only for illustrative and descriptive purposes and is not intended to be exhaustive or to limit the scope and spirit of the invention. The embodiments were selected and described to best explain the principles of the invention and its practical application. One of ordinary skill in the art will recognize that many variations can be made to the invention disclosed in this specification without departing from the scope and spirit of the invention.

[0061] Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate embodiments of the present disclosure, and such exemplifications are not to be construed as limiting the scope of the present disclosure in any manner.

[0062] FIG. 1 is a perspective view of an electric immersion holding furnace 10. Operators may pour molten metal into an inlet 25 in the top 70 of the electric immersion holding furnace 10. The electric immersion holding furnace 10 comprises Refractory walls 15 bounded by supports 20. Exemplary electric immersion holding furnaces 10 typically resemble a rectangular prism, but nothing in this disclosure limits the shape of the electric immersion holding furnace 10 or the holding chamber 55. In the depicted embodiment, a first small refractory wall 15.sub.a is disposed opposite a second small refractory wall 15.sub.c. Together, the first small refractory wall 15.sub.a and the second small refractory wall 15.sub.c define a width W of the electric immersion holding furnace 10. Likewise a first large refractory wall 15.sub.b is disposed opposite to a second large refractory wall 15.sub.d. Together, the first large refractory wall 15.sub.b and the second large refractory wall 15.sub.d define a length L of the electric immersion holding furnace 10. The refractory walls 15 engage the insulated floor 72 of the electric immersion holding furnace 10 to define a holding chamber 55 (FIG. 2). The holding chamber 55 may further comprise a top 70 of the electric immersion holding furnace 10 disposed above arches 60 (FIG. 2) extending into the holding chamber 55. To facilitate horizontal movement of the metal 51 (FIG. 2) within the holding chamber 55 in accordance with the exemplary embodiments disclosed herein, a stirrer assembly 40 (see FIG. 3 for more detail) is provided. The stirrer assembly 40 may comprise a motor 45 disposed in or atop a gearbox 41. The gearbox 41 may engage the top 70 of the electric immersion holding furnace 10 directly. The motor 45 and gearbox 41 are preferably disposed outside of the holding chamber 55. The metal 51 within the holding chamber 55 may be aluminum, an aluminum alloy, or other molten metal or metal alloy used in metal casting.

[0063] The electric immersion holding furnace 10 may further comprise a thermocouple 80. The thermocouple 80 extends into the holding chamber 55 to regulate the metal's temperature. When the metal 51 is needed for further processing, dip ladles (not depicted) collect the molten metal through an outlet 27 in the top 70 of the electric immersion holding furnace 10. Lifting brackets 75 may be used to raise the cover 73 for cleaning.

[0064] Electric immersion holding furnaces 10 typically heating elements that provide less radiant and convection heat than melting furnaces. When the electric immersion holding furnace is configured to hold aluminum, the electric immersion holding furnace 10 may maintain temperatures above 1,150 degrees Fahrenheit ( F.) and typically between 1,200 F. to 1,400 F. depending on the aluminum or aluminum alloy to keep the aluminum or aluminum alloy at the desired casting temperature. Electric immersion holding furnaces 10 typically have electric heating elements placed in immersion tubes 50. The immersion tubes 50 typically extend through the holding chamber 55 any may contact the molten metal 51 in the holding chamber 55. Operators can adjust the heat output of the electric heating elements and thereby regulate the temperature in the electric immersion holding furnace 10 to control the metal's consistency prior to casting.

[0065] FIG. 2 is a cross sectional side view of an exemplary electric immersion holding furnace 10 bisected along the length L (FIG. 1). In this exemplary embodiment, the heating elements and immersion tubes 50 are horizontally disposed. In other exemplary embodiments, the immersion tubes 50 may extend into the holding chamber 55 at an angle relative to a horizontal line. Although the immersion tube 50 depicted appears generally cylindrical with a domed end, it will be understood that an immersion tube 50 may be polyhedral in shape, including but not limited to a rectangular polyhedron, have a generally oval profile, extend into the metal as a helix, or have helical sections, be generally conical in shape, or otherwise configured to encompass a heating element. Molten metal 51 immerses the immersion tubes 50. Arches 60 partially divide the holding chamber 55. The arches 60 may comprise the same material as the refractory walls 15. The refractory walls 15 are generally insulated walls and may comprise castable refractory, brick, or other material configured to withstand the pressures and temperatures within the electric immersion heating furnace 10. The metal 51 generally defines a level 52 with a pocket of gas 53 above the level 52. The stirring assembly 40 generally comprises the motor 45 communicating with a gearbox 41, shaft 35 and impeller 30. In certain exemplary embodiments, the shaft 35 may be a silicon nitride shaft. In other exemplary embodiments, the shaft 35 may be a silicon carbide shaft. In other exemplary embodiments, the shaft 35 may be comprised of graphite. In still other exemplary embodiments, the shaft 35 may comprise a material configured to withstand the pressure and heat in the holding chamber 55 (e.g. concrete graphite, an alloy or composite material containing silicon carbide or silicon nitride). The impeller 30 extends below the immersion tubes 50 and may rotate in a clockwise or counter clockwise direction. The rate at which the impeller 30 rotates may vary depending on the configuration of the gearbox 41. The impeller 30 is configured to move the liquid metal 51 under and around the immersion tubes 50, preferably horizontally. In certain exemplary embodiments, the impeller 30 may rotate substantially constantly while metal 51 is in the electric immersion holding furnace 10. In other exemplary embodiments, the impeller 30 may rotate intermittently. In exemplary embodiments in which the impeller 30 rotates intermittently, the impeller 30 may rotate at predetermined internals. In other exemplary embodiments, the electric immersion holding furnace 10 may further comprise a sludge detector and the impeller 30 may rotate in response to detected sludge accumulations around the immersion tubes 50.

[0066] FIG. 3 is a perspective view of an exemplary stirring assembly 40. The motor 45 is disposed within a motor housing 28. The motor 45 is a three to five horse power motor 45 and the shaft 35 is comprised of oxide-resistant impregnated graphite. The shaft 35 has a first end 63, a second end 67, and a body 65. In the depicted embodiment, the first end 63 engages the motor 45 directly. The body 65 extends through the top 70 of the electric immersion holding furnace 10 and into the holding chamber 55 below the immersion tube 50. The impeller 30 may rotate in a range between 150 rpm to 300 rpm

[0067] The second end 67 engages the impeller 30 suspended in the holding chamber 55 below the immersion tube 50. The second end 67 may comprise a screw and the impeller 30 may engage the second end 67 through a complementary screw. In embodiments in which the stirring assembly 40 is configured to rotate bi-directionally, the impeller 30 may be pinned to the second end 67 of the shaft 35. The motor 45 rotates the shaft 35 and impeller 30 such that the impeller 30 circulates molten metal 51, or molten aluminum across the immersion tube 50 in a substantially horizontal direction. The exemplary impeller 30 is comprised of graphite and has multiple of arms 42 configured to move the metal 51 in a horizontal direction. The arms 42 may be machined. The arms 42 may comprise a surface 46 having a negative slope s, wherein the slope s is disposed at a slope angle , and wherein the slope angle is defined by the angle of the surface 46 relative to a vertical line v extending from a top corner 56 of an arm 42 to the bottom 57 of the arm 42. The slope angle may be in a range of 15 degrees to 75 degrees with respect to the vertical line v, preferably 15 degrees to 45 degrees. The slope angle may be selected based on the dimensions of the holding chamber 55 and the position of the impeller 30 within the holding chamber 55. In the depicted embodiment, the stirring assembly 40 is disposed substantially vertically with the impeller 30 extending below the immersion tubes 50. In other exemplary embodiments, the electric immersion holding furnace may have the stirring assembly 40 disposed at an angle relative to the vertical line v. In still other exemplary embodiments, the impeller 30 may be disposed at an angle relative to the vertical line v between 0 degrees and 180 degrees. An exemplary angle may be 90 degrees.

[0068] In other exemplary embodiments a gearbox 41 or a speed controlled direct drive motor 45 may engage the body 65 of the shaft 35 to configure the shaft 35 to spin the impeller 30 at different rates of speed. In other exemplary embodiments, the gearbox 41 or a motor 45 may reverse the direction the impeller 30 spins. In still other exemplary embodiments, a stirrer adjustment mechanism may engage the shaft 35 to change the height of the shaft 35 and the location of the impeller 30 in the holding chamber 55 relative to the insulated floor 72 of the holding chamber 55. In other exemplary embodiments, the stirrer adjustment mechanism may change the position of the shaft 35 and impeller 30 within the holding chamber 55, such as by pivoting the shaft 35 around a point, by moving the shaft 35 and impeller 30 laterally within the holding chamber 55, or a combination thereof.

[0069] Alternative embodiments may have more than one immersion stirring assembly 40. Other embodiments may utilize pumps to circulate the metal 51. Means for circulating the metal 51 may include the exemplary stirring assemblies 40 embodiments described herein, exemplary impellers 30, pumps, baffles that extend partially or completely into the metal 51, immersion tubes 50 pivotally mounted the electric immersion holding furnace that vibrate or move in a linear or rotary direction, or pivotally mounted stirring mechanisms configured to allow the shaft 35 of the stirring assembly 40 to move around a fixed point.

[0070] A device that circulates the metal 51 in an electric immersion holding furnace 10 to prevent corundum accumulation around the immersion tubes and inner walls is considered to be within the scope of this disclosure.

[0071] FIG. 4 is a cross sectional side view of the electric immersion holding furnace 10 intersected along line D-D (FIG. 2). In this exemplary embodiment, the immersion tubes 50 extend into the holding chamber 55 through second large refractory wall 15.sub.d but do not contact the first large refractory wall 15.sub.b. In other exemplary embodiments, at least one of the immersion tubes 50 may contact the second large refractory wall 15.sub.d and the first large refractory wall 15.sub.b. In yet other exemplary embodiments, the immersion tubes 50 may engage one or both of the small refractory walls 15.sub.a, 15.sub.c. In still other exemplary embodiments, the immersion tubes 50 may be vertically disposed or diagonally disposed relative to a horizontal line extending through the holding chamber 55 (see the level 52, FIG. 2). In other exemplary embodiments, the immersion tubes 50 may be partially immersed within the liquid metal 51. It will be understood that any of the example embodiments disclosed herein may be used singularly or in combination with any of the other exemplary embodiments disclosed herein where such combination permits the electric immersion holding furnace 10 to function as a vessel for holding molten metal 51.

[0072] As further depicted in FIG. 4, the exemplary impeller 30 may comprise a series of paddles 31 extending radially from the shaft 35. The paddles 31 may comprise a concave end 33 distally disposed from the shaft 35. Impellers 30 configured with paddles 31 having concave ends 33 and rotating with the shaft 35 may promote horizontal movement of the metal 51 within the holding chamber 55, and desirably, uniform horizontal movement.

[0073] An exemplary system may comprise: an electric immersion holding furnace having refractory walls engaging an insulated floor, wherein the refractory walls engaging the insulated floor define a holding chamber; a heating element disposed within an immersion tube, wherein the immersion tube extends into the holding chamber; and means for circulating molten metal within the electric immersion holding furnace in a substantially horizontal direction.

[0074] An exemplary electric immersion holding furnace may comprise: refractory walls operatively connected to an insulated floor, wherein the refractory walls and insulated floor define a holding chamber; an immersion tube, extending through a refractory wall and disposed within the holding chamber; a motor operatively engaged to a first end of a shaft, wherein the motor is disposed outside of the electric immersion holding furnace; a shaft having the first end, a second end, and a body engaging the first end and second end, the body extends into the holding chamber below the immersion tube, and the second end engages an impeller suspended in the holding chamber below the immersion tube, wherein the motor rotates the shaft and impeller such that the impeller circulates liquid metal throughout the holding chamber and across the immersion tube in a substantially horizontal direction.

[0075] An exemplary electric immersion holding furnace may further comprise a gearbox engaged to the motor, wherein the gearbox is a variable speed gearbox and the motor is a bi-directional motor. An exemplary electric immersion holding furnace may further comprise a plurality of immersion tubes, wherein an electric heater is disposed within each of the plurality of immersion tubes, and wherein the plurality of immersion tubes are disposed horizontally with the holding chamber. a gearbox may be configured to adjust a length of the shaft extending into the holding chamber.

[0076] In an additional exemplary embodiment, the electric immersion holding furnace the motor is disposed on a top of the electric immersion holding furnace such that the shaft body extends through the top of the electric immersion holding furnace and the second end engages the impeller below the immersion tube. In additional embodiments, the electric immersion holding furnace may further comprise multiple stirring assemblies.

[0077] An exemplary electric immersion holding furnace may have an impeller further comprising a plurality of arms, wherein the arms comprise a surface having a negative slope defined by a slope angle, and wherein the slope angle is the angle of the surface relative to a vertical line extending from a top corner of an arm to the bottom on the arm. In other exemplary embodiments, the impeller may further comprise paddles extending radially from the shaft, wherein the paddles further comprise a concave end distally disposed from the shaft.

[0078] An exemplary method for preventing sludge and corundum accumulation on immersion tubes in an electric immersion holding furnace may comprise: circulating the metal in a horizontal plane in a holding chamber disposed within an electric immersion holding furnace.

[0079] While this invention has been particularly shown and described with references to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.