US20180354028A1

US20180354028A1 - Sludge Removal Devices, Systems, and Methods

Info

Publication number: US20180354028A1
Application number: US16/003,344
Authority: US
Inventors: Victor F. Rundquist; Kevin Scott GILL; Michael Caleb POWELL
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 2017-06-12
Filing date: 2018-06-08
Publication date: 2018-12-13
Also published as: WO2018231533A1

Abstract

Methods for removing sludge and/or impurities from a molten metal are disclosed herein, as well as sludge removal devices and systems for use in the methods. Sludge removal devices that can reduce the downstream deposition of sludge in certain process components through upstream deposition and subsequent removal from the molten metal are also disclosed.

Description

REFERENCE TO RELATED APPLICATION

Under provisions of 35 U.S.C. § 119(e), Applicants claim the benefit of U.S. Provisional Application No. 62/518,231 filed Jun. 12, 2017, which is incorporated herein by reference in its entirety.

BACKGROUND

Ultrasonic degassing methods for molten metals can produce molten metals with reduced amounts of dissolved gasses, fewer inclusions, and reduced alkali contaminants, which have led to improved quality in the articles produced therefrom. Despite the advantages of these degassing methods, the presence of trace impurities and/or the introduction of microbubbles that can remain in the molten metal after degassing can result in sludge and sludge deposits on components of downstream machinery. Ceramic foam filters have conventionally been used as a component of downstream casting machinery for filtering the molten metal prior to casting, however, these filters are not able to effectively remove the microbubbles and/or the trace impurities present in molten metals, particularly those present following an ultrasonic degassing step. Additionally, ceramic foam filters do not prevent sludge deposition on other components of the downstream machinery, and may also require interrupting the casting processes in order to replace the filter once it is saturated with sludge deposits.
Accordingly, there is a need for improved devices, systems, and methods to remove sludge from molten metals, preferably before reaching downstream machinery.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify required or essential features of the claimed subject matter. Nor is this summary intended to be used to limit the scope of the claimed subject matter.
The present invention is directed to a sludge removal device comprising a sludge deposition surface configured for contact with a molten metal, and a plurality of channels extending through the sludge removal device. In one embodiment, each of the plurality of channels can be any suitable shape or style that allows the metal to pass through the device without significant impedance, e.g., channels comprising shaped cross-sections (e.g., circular, triangular, rectangular, hexagonal, etc.) with constant, increasing, or decreasing cross-sectional area along the length of the channel. For instance, cylindrical channels may have a constant cross-sectional area, and a radius in a range from about 1/16″ to about ¾″.
The present invention also discloses a sludge removal system comprising a molten metal launder, the launder comprising a launder inlet and a launder outlet. In certain embodiments, the launder can be configured to induce a flow of molten metal from the launder inlet toward the launder outlet, when the launder is filled. The sludge removal system can further comprise a sludge removal device as described herein. One or more than one sludge removal device can be employed in the sludge removal system. For instance, multiple sludge removal devices can be arranged in series along the length of a molten metal launder.
The present invention is also directed to a method for removing impurities from a molten metal. The methods disclosed herein can comprise passing a molten metal comprising impurities through a sludge removal system, depositing at least a portion of the impurities on the sludge deposition surface of a sludge removal device, and removing the deposited impurities from the molten metal. Methods consistent with the invention disclosed herein may also comprise a step of regenerating the sludge deposition surface of the sludge removal device, or simply replacing the sludge removal device altogether, once the device has become saturated with sludge deposits.
Both the foregoing summary and the following detailed description provide examples and are explanatory only. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Further, features or variations may be provided in addition to those set forth herein. For example, certain embodiments may be directed to various feature combinations and sub-combinations described in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate various embodiments of the present invention. In the drawings:

FIG. 1 shows a perspective diagram of a sludge removal system.

FIG. 2 shows top and front views of a sludge removal device shaped to fit a launder having a trapezoidal cross-section.

FIG. 3 shows top and front views of a sludge removal device shaped to fit a launder having a rounded trapezoidal cross-section.

FIG. 4 shows top and front views of a sludge removal device shaped to fit a launder having a rounded trapezoidal cross-section, and having overflow cutouts on the top edge.

FIG. 5 shows top and front views of a sludge removal device shaped to fit a launder having a rounded trapezoidal cross-section, and having an overflow cutout on the lateral edges.

FIG. 6 shows front and lateral views of a sludge removal device having a plurality of channels configured to be substantially parallel to the direction of molten metal flow.

FIG. 7 shows front and lateral views of a sludge removal device having a plurality of channels configured to be at a 45° angle to the direction of the molten metal flow.

FIG. 8 is a bar graph of the elemental composition of sludge deposited on various components of downstream equipment in Example 1.

FIG. 9 is a photomicrograph of a cross-section of a sludge deposit collected from the sludge removal device of Example 3.

FIG. 10 is a photomicrograph of a cross-section of a sludge deposit collected from the sludge removal device of Example 4.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings. Wherever possible, the same or similar reference numbers are used in the drawings and the following description to refer to the same or similar elements. While embodiments of the invention may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the scope of the invention.
The terms “a,” “an,” and “the” are intended to include plural alternatives, e.g., at least one. For instance, the disclosure of “a sludge removal device,” “a channel opening,” “a launder outlet,” etc., is meant to encompass one, or combinations of more than one, sludge removal device (e.g., one or two or more sludge removal devices), channel opening (e.g., one or two or more channel openings), launder outlet (e.g., one or two or more launder outlets), etc., unless otherwise specified.
All publications and patents mentioned herein are incorporated herein by reference for the purpose of describing and disclosing, for example, the constructs and methodologies that are described in the publications, which might be used in connection with the presently described invention. The publications discussed throughout the text are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention.
Applicants disclose several types of ranges in the present invention. When Applicants disclose or claim a range of any type, Applicants' intent is to disclose or claim individually each possible number that such a range could reasonably encompass, including end points of the range as well as any sub-ranges and combinations of sub-ranges encompassed therein. For example, in an embodiment of the invention, the molten metal flow capacity of the sludge removal system may be in a range from about 10 to about 30 L/min. By a disclosure that the flow capacity is in a range from about 10 to about 30 L/min, Applicants intend to recite that the flow capacity may be any flow capacity in the range and, for example, may be about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 20, about 21, about 22, about 23, about 24, about 25, about 26, about 27, about 28, about 29, or about 30 L/min. Additionally, the flow capacity may be within any range from about 10 to about 30 L/min (for example, the rate is in a range from about 15 to about 25 L/min), and this also includes any combination of ranges between about 10 and about 30 L/min. Likewise, all other ranges disclosed herein should be interpreted in a similar manner.
Embodiments of the present invention may provide systems, methods, and/or devices for the removal of sludge (e.g., impurities encapsulated in microbubbles) and other impurities from molten metal. Such molten metals may include, but are not limited to, aluminum, copper, steel, zinc, magnesium, and the like, or combinations of these and other metals (e.g., alloys). Accordingly, the present invention is not limited to any particular metal or metal alloy. The processing or casting of articles from a molten metal may utilize a bath containing the molten metal, and this bath of the molten metal may be maintained at elevated temperatures. For instance, molten copper may be maintained at temperatures of around 1100° C., while molten aluminum may be maintained at temperatures of around 750° C.
As used herein, the terms “launder,” “molten metal launder,” and the like are meant to encompass any container that might contain a molten metal, inclusive of bath, vessel, crucible, launder, furnace, ladle, and so forth. The launder and molten metal launder terms are used to encompass batch, continuous, semi-continuous, etc., operations and, for instance, where the molten metal is generally static (e.g., often associated with a crucible) and where the molten metal is generally in motion (e.g., often associated with a launder).
Furthermore, molten metals may have impurities present in them, and these impurities may negatively affect the final production and casting of the desired metal article, and/or the resulting physical properties of the metal article itself. For instance, the impurity in the molten metal may comprise an alkali metal or other metal that is neither required nor desired to be present in the molten metal. As one of skill in the art would recognize, small percentages of certain metals are present in various metal alloys, and such metals would not be considered to be impurities. As non-limiting examples, impurities may comprise titanium, boron, vanadium, magnesium, sodium, and the like, or combinations or oxides thereof. In certain embodiments, impurities in the molten metal may comprise titanium, boron, and/or vanadium. Impurities may enter a molten metal bath (aluminum, copper, or other metal or alloy) from any number of sources or methods, and/or be initially present in a metal feedstock starting material used to form the molten metal bath. Even trace amounts of impurities can present problems in downstream metal casting processes, as the impurities can become deposited as sludge on downstream machinery. Sludge deposition can result in damage to the downstream machinery and require that continuous processes be pushed off-line for maintenance and/or repairs.
Known methods to reduce the amounts of impurities of molten metals in refining processes have not been completely successful. These processes have commonly involved passing the molten metal through ceramic foam filters to remove particulate matter from the molten metal. This process will be referred to as the “conventional” process throughout this disclosure. While the conventional process may be successful in reducing, for example, the amount of suspended particulate impurities in a molten metal in some situations, this conventional process has noticeable drawbacks, such as a reduced flow rate of the molten metal, a pressure drop across the filter, and the inability to remove dissolved or suspended impurities significantly smaller than the pore size of the filter. In addition, ceramic foam filters have the practical disadvantage of being difficult to separate from the metal after the filter is saturated with impurities, which can result in significant material waste. Accordingly, the devices, methods, and systems provided herein may provide an improvement over the conventional processes to remove impurities from a molten metal.

Sludge Removal Devices

The sludge removal devices contemplated herein have demonstrated exceptional and unexpected results when employed in the systems and methods described herein. Particularly the overall shape, size, and composition of sludge removal devices can affect the sludge removal from the molten metal. Without being bound by theory, the sludge removal device may provide a purified molten metal by acting as a sacrificial deposition surface for impurities in the metal collected as sludge. Accordingly, sludge removal devices contemplated herein can be any capable of removing an amount of impurities from molten metal, reduce the amount of sludge deposition on other components of downstream machinery, and are compatible with the systems and methods disclosed herein.
Sludge removal devices 124, as exemplified by FIGS. 1-7, generally can be any device comprising a body configured for contact with molten metal, and a plurality of channels extending through a width of the body. The body of sludge removal devices contemplated herein can comprise any material suitable for sustained contact with molten metal that allows or encourages sludge deposition. Suitable refractory materials can include coated metals, inorganic clays, and other refractory materials. Refractory ceramics can be especially advantageous for components that contact molten metal due to their durability, ease of manufacture and manipulation, and cost-effectiveness. In some aspects, the body of sludge removal devices contemplated herein can comprise a refractory ceramic, e.g., a marinite, a fused silica, a sialon, a silicon carbide, a boron carbide, a boron nitride, a silicon nitride, an aluminum nitride, an aluminum oxide, a zirconia, or any combination thereof. In other aspects, the body of sludge removal devices can comprise marinite A. Moreover, the body can comprise a surface portion and a separate interior portion comprising the same or different material, where the surface portion is configured for contact with the molten metal, and the interior portion can comprise a support material. The material of the surface portion can be any of those described above. For instance, the body of the sludge removal device may consist entirely of marinite A, or comprise a marinate A coated on a separate support material.
Similarly, the overall shape of the sludge removal device is not particularly limited. In general, the shape of the sludge removal device may be complementary to the walls of a molten metal launder, such as to allow the body of the sludge removal device to fit securely against the sides of the molten metal launder. In certain embodiments, the lateral edge of the body can comprise a gasket to secure the fit between the lateral edge of the sludge removal device and the wall of launder 120. As shown in FIGS. 2-7, the sludge removal device may have a generally trapezoidal shape. Alternatively, the sludge removal devices may take any number of other suitable shapes (e.g., rectangular, circular, etc.) depending on the requirements of any particular sludge removal system or method systems. Additionally, as shown in FIGS. 4-5, the body may comprise an overflow cutout configured to allow molten metal to pass around the device in the event that the plurality of channels become saturated with sludge. The overflow cutout may be configured to sit above or below a molten metal level during operation. The overflow cutout may also interrupt the continuity between the walls of the launder and the body of the sludge removal device as shown in FIG. 5, without affecting the fit of the sludge removal device within the molten metal launder.
The sludge removal device can typically comprise lateral edges (e.g., top, bottom, and/or sides), an upstream face, and a downstream face. As discussed herein, the upstream face and downstream face are meant to comprise the total area of the plane defined by the relevant portion of the sludge removal device body. Particularly, the upstream face is meant to include both the portion of each face represented by the body, and the portion of each face represented by channel openings. In certain embodiments, the upstream face and the downstream face can be substantially parallel to each other. In embodiments where the sludge removal device comprises a plane of symmetry, the upstream face and downstream face can be interchangeable.
As defined herein, the distance between the upstream face and downstream face of the sludge removal device is the width of the device. The width of the device is not limited to any particular range, but often can be at least about 0.1 inches, at least about 0.5 inches, at least about 1 inch, at least about 2 inches, at least about 3 inches, at least about 4 inches, at least about 8 inches, or at least about 12 inches. In other aspects, the width may be in a range from about 0.5 to about 12 inches, from about 0.5 to about 8 inches, from about 1 to about 6 inches, from about 1 to about 4 inches, or from about 2 to about 6 inches.
Other dimensions of the sludge removal device can also be generally any that are appropriate for the systems and methods in which they are employed. For instance, just as the shape can be dependent on the cross-sectional shape of a metal launder, the size of the sludge removal device may also match that of the launder cross-section. A height and length on the order of inches, or feet, or more is not outside the scope of the invention, so long as it is suitable for use in the systems described herein. Similarly, the plurality of channels is not limited to any particular number of channels. Rather, the effectiveness of embodiments disclosed herein may be more greatly affected by the density or shape of the channels. Any number of channels may be appropriate for a given sludge removal device (e.g., at least 10, at least 50, at least 100, at least 500). Alternatively, an effective number of channels may be limited by a minimum size of the channels (e.g. less than 500, less than 100, less than 50, or less than 10 channels).
Similar to the body of the sludge removal device, the individual characteristics of the plurality of channels also are not limited to any particular shape, size, or direction. Moreover, the characteristics of each of the plurality of channels can be the same or different as any other channel in the sludge removal device, such that any combinations of channels having differing characteristics can be suitable. Generally, any characteristics that promote the deposition of sludge and agglomeration of microbubbles present in molten metal can be advantageous. As an example, the cross-sectional shape of the channels can be independently selected from a circle, oval, rectangle, square, triangle, hexagon, octagon, honeycomb, or any regular or irregular polygon. Accordingly, in certain embodiments, each of the plurality of channels independently can be a cylindrical channel.
Further, the cross-sectional shape, size, or direction of any particular channel may be either constant or variable along its length. Accordingly, a channel may be cylindrical, conical, or both over different portions of a channel. Each of the plurality of channels extending through the body can have an upstream opening (the intersection between a channel and the upstream face) and a downstream opening (the intersection between a channel and the downstream face). Because the cross-sectional shape of any particular channel may be variable along its length, the upstream openings and downstream openings may have different cross-sectional areas. In certain aspects, a ratio of the total cross-sectional area of upstream openings to the total cross-sectional area of downstream openings can be in a range from about 100:1 to about 1:100, from about 10:1 to about 1:10, from about 5:1 to about 1:5, or from about 2:1 to about 1:2.
As discussed above, one disadvantage of conventional ceramic filters is the resulting pressure drop caused by slowing the molten metal as it passes through the filter. It follows that the channels useful for the present invention will have a cross-sectional area that may be larger than the typical pore size of ceramic foam filters such that may avoid any significant reduction in the processing speed of the molten metal. In certain embodiments, each of the plurality of channels can have an average cross-sectional area of at least about 0.01 in², at least about 0.1 in², at least about 0.5 in², at least about 1 in², at least about 2 in², at least about 3 in², at least about 5 in², or at least about 10 in². Alternatively, each of the plurality of channels can have an average cross-sectional area in a range from about 0.01 to about 10 in², from about 0.1 to about 10 in², from about 0.1 to about 5 in², from about 0.1 to about 3 in², or from about 0.1 to about 1 in². In aspects comprising cylindrical channels, the channels independently can have a radius of at least 1/16″, at least ⅛″, at least 3/16″, at least ¼″, at least ½″, or at least ¾″. In other aspects, each of the cylindrical channels independently can have a radius in a range from about 1/16″ to about ¾″, or from about ¼″ to about 1¼″.
The aggregate size of the channels also can be defined, and related to the total area of the upstream or downstream face of the sludge removal device. As defined above, the upstream and downstream faces include the entire area encompassed by the body of the sludge removal device (excluding the area of any overflow cutout, but including the area of channel openings). Thus, the total cross-sectional area of upstream openings compared to the area of the upstream face can be relevant to the expected acceleration of molten metal through the channels, and resultant sludge deposition. In certain aspects, the total cross-sectional area of upstream openings can be at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the area of the upstream face of the sludge removal device. Alternatively, the total cross-sectional area of upstream openings can be in a range from about 10% to about 90%, from about 30% to about 80%, or from about 40% to about 70% of the total area of the upstream face. The same percentages and ranges also apply to downstream openings on the downstream face of sludge removal devices contemplated herein.
The direction of the channels may also affect agglomeration of microbubbles and sludge deposition on the sludge removal device. The direction of a channel can be defined by a flow axis, or the overall direction of flow through the channel. For the purpose of this disclosure the flow axis will be defined as the axis created by connecting the center points of the upstream and downstream openings. For cylindrical channels, the flow axis will defined by the axis connecting the center points of two circles on opposite faces of the sludge removal device. In certain aspects, the flow axis of at least one of the plurality of channels can be configured to be substantially parallel to a direction of molten metal flow during operation. Alternatively, the sludge removal device may be configured such that a flow axis of at least one channel is at an angle compared the direction of molten metal flow. Such angled operation can be accomplished either by angling the entire sludge removal device, or by a sludge removal device comprising channels with an angled flow axis.
Thus, in certain aspects, sludge removal devices contemplated herein may comprise at least one channel comprising a flow axis having an angle of at least 10°, at least 20°, at least 30°, at least 45°, at least 60°, or at least 80° relative to the upstream and/or downstream face of the sludge removal device. Alternatively, at least one channel can have a flow axis having an angle in a range from about 10° to about 80°, from about 30° to about 60°, or from about 40° to about 50° relative to the upstream and/or downstream face of the sludge removal device.
The aspects discussed above may provide a sludge removal device with excellent capacity for sludge deposits, in addition to its performance in collecting impurities from a molten metal. In certain embodiments, the sludge removal device can have a sludge deposition capacity of at least 0.5 lbs, at least 1 lb, at least 2 lbs, at least 5 lbs, at least 10 lbs, or be in a range from about 0.5 lbs to about 50 lbs. Once the sludge removal device has reached its capacity (or at any intermediate point) the sludge removal device can be either replaced, or reused following regeneration of the deposition surface (e.g., by scraping, brushing, washing, etc.).

Sludge Removal Systems

Sludge removal systems for the removal of impurities and sludge from molten metal are contemplated herein. An embodiment of sludge removal systems contemplated herein is shown in FIG. 1, and generally may comprise a metal launder 120, upstream machinery 110, and downstream machinery 130.
Upstream machinery 110 is not limited to any particular kind of machinery and generally can be any machinery that prepares the metal for casting or further processing. For instance, upstream machinery 110 can comprise a molten metal degassing device to remove impurities in the metal by introducing microbubbles that adsorb impurities and carry them out of the metal due to their buoyancy and/or relative density. In certain embodiments, the degassing device can employ conventional degassing methods (e.g., rotary degassing). Alternatively, or additionally, degassing device 110 can employ ultrasonic degassing methods (e.g., degassing device 110 can employ rotary degassing and ultrasonic degassing in tandem, and in any order or sequence). In such embodiments, degassing device 110 can comprise an ultrasonic device with an integrated gas delivery system. Ultrasonic degassing of molten metals and ultrasonic degassing devices are described in detail, for instance, in U.S. Pat. Nos. 8,844,897, 8,652,397, 9,327,347, 9,382,598, and 9,617,617, all of which are incorporated herein by reference in their entirety. Any upstream machinery can be in fluid connection with launder inlet 122 of the sludge removal device. Similarly, downstream machinery 130 can be in fluid connection with a launder outlet, and is not limited as to the function of the machinery. In certain embodiments, downstream machinery 130 can comprise a metal casting machine.
The example of FIG. 1 shows molten metal launder 120. Launder 120 comprises a molten metal launder inlet 122 and launder outlet 128. Sludge removal device 124 is positioned within launder 120, and secured against the walls of the launder, such that the molten metal in launder 120 is passed through the plurality of channels 126 as it flows from the launder inlet to the launder outlet. In FIG. 1, a molten metal flow in the direction of launder outlet 128 can be achieved by positioning the launder inlet above the launder outlet. Alternatively, or additionally, a molten metal flow in the direction of launder 128 can be achieved by setting launder 120 at an angle with respect to the ground. In either case, a height differential between launder inlet 122 and launder outlet 128 may control the flow rate of the molten metal through the launder such that as the height differential is increased, the flow rate will also increase. In certain embodiments, the launder inlet can be positioned at or near the top of the launder. The launder inlet can be positioned within 1 inch, within 2 inches, or within 5 inches of the top of the launder. Similarly, the launder outlet may be positioned at or near the bottom of the launder, and on the opposite end as the launder inlet. As shown in FIG. 1, the launder outlet may be positioned as a drain on the bottom surface of the launder, and alternatively may be placed within 1 inch, within 2 inches, or within 5 inches of the bottom of launder 120, on a lateral side of the launder. These configurations of the molten metal launder can be beneficial in a molten metal launder wherein the direction of molten metal flow is substantially horizontal. However, other launder configurations are also envisioned by this disclosure, for instance where the launder is configured for a substantially vertical molten metal flow.
The molten metal launder is not limited to any particular size or shape, and may be generally any that accommodates the sludge removal devices contemplated herein, and the molten metal flow through the launder. The launder may also be constructed of any conventional material, and the launder surface configured for contact with the molten metal can be the same or different than the body of the sludge removal devices contemplated herein. Accordingly, the launder walls may accumulate sludge deposits due to contact with the molten metal. While it is preferred that the sludge accumulate mainly on the sludge removal device, some portion may be deposited on the walls of the molten metal launder during the process. In certain embodiments, launders that have a larger cross-sectional area and/or an increased flow capacity, may experience reduced deposition on the walls of the launder, compared to an amount of sludge deposited on the sludge removal device. In certain embodiments, the flow capacity of the metal launder can be at least about 1 L/min, at least about 5 L/min, at least about 20 L/min, at least about 50 L/min, or at least about 100 L/min. Alternatively, launders may have a flow capacity in a range from about 1 L/min to about 1000 L/min, from about 1 L/min to about 500 L/min, from about 1 L/min to about 100 L/min, or from about 1 L/min to about 50 L/min.
In certain embodiments, the ratio of the cross-sectional area of the launder to that of the combined plurality of channels can be greater than 1:1, greater than 2:1, greater than 3:1, greater than 4:1, greater than 5:1, greater than 10:1, greater than 20:1 or greater than 50:1. As a result, the ratio of an average flow rate of the molten metal within each of the plurality of channels to an average flow rate of the molten metal in the launder can be at least about 2:1, at least about 5:1, at least about 10:1, at least about 50:1, at least about 100:1, or at least about 1000:1. In other embodiments, a ratio of the average flow rate of the molten metal within each of the plurality of channels to an average flow rate of the molten metal in the launder can be in a range from about 1:1 to about 100:1, from about 5:1 to about 500:1, from about 20:1 to about 100:1, or from about 50:1 to about 100:1.
It may be advantageous, depending on the geometry of the sludge removal device, to employ more than one sludge removal device in the sludge removal system 100. Thus, in certain aspects, the sludge removal device can comprise two or more sludge removal devices, shown in FIG. 1 as 124 a, 124 b, and 124 c. In such cases, the plurality of sludge removal devices can be arranged serially in launder 120, wherein a first sludge removal device 124 a is upstream of at least one second sludge removal device 124 b (and 124 c in FIG. 1). Moreover, when passing from first sludge removal device 124 a to second sludge removal device 124 b, it may be advantageous that second sludge removal device 124 b has a different total cross-sectional area of channel openings 126 b than the total cross-sectional area of channel openings 126 a on first sludge removal device 124 a (e.g., the total area of channel openings on the upstream device can be greater than that of a downstream device). Accordingly, in some instances, a ratio of the total cross-sectional area of channel openings 126 a to the total cross-sectional area of channel openings 126 b can be in a range from about 1:1 to about 10:1, about 1.5:1 to about 10:1, or about 2:1 to about 5:1. For instance, at least one channel opening 126 b may be smaller than at least one channel opening 126 a. Alternatively, the plurality of channel openings 126 a, 126 b, and 126 c of the sludge removal devices 124 a, 124 b, and 124 c can be of generally the same size, shape, arrangement and amount.

Sludge Removal Methods

Methods contemplated herein can make use of the sludge removal devices and systems described above. Generally, the methods can comprise passing a molten metal comprising impurities through a sludge removal device, and depositing at least a portion of the impurities on the sludge device to form a purified molten metal. In certain embodiments, the method can further comprise removing the sludge removal device from the molten metal after a saturation period. The sludge removal device can be regenerated, then replaced in the molten metal to maintain a continuous sludge removal method. Alternately, the saturated sludge removal device can be discarded, then replaced with a new (or regenerated) sludge removal device. In certain aspects, sludge devices can be regenerated by mechanical methods (e.g., wiping, scraping, brushing, washing, cleaning, etc.).
The methods disclosed herein can be continuous. For example, molten metal can be continuously passed through a sludge removal device for a saturation period. After the saturation period, the sludge removal device can be replaced without stopping the flow of molten metal, or the sludge removal method. The saturation period for the method can be related to the capacity of the sludge removal device, as well as the amount of impurities and sludge present in the molten metal. In certain embodiments, the saturation period can be at least 3 hours, at least 6 hours, or at least 12 hours. Thus, certain embodiments described herein may be able to operate continuously for a period of operation of at least 1 hour, at least 2 hours, at least 3 hours, at least 6 hours, at least 9 hours, at least 12 hours, at least 24 hours, at least 48 hours, at least 72 hours, at least 7 days, at least 14 days, or at least 30 days, without negatively impacting the performance of the sludge removal device. Additionally, in some embodiments, the duration of the deposition step can be in a range from about 1 to about 72 hours, from about 6 to about 48 hours, from about 12 to about 72 hours, from about 24 hours to about 7 days, or from about 48 hours to about 14 days, without the need to regenerate or replace the sludge removal device.
In certain embodiments, the methods can further comprise degassing the molten metal prior to passing the molten metal through the sludge removal system. Further, the degassing step may comprise operating an ultrasonic device in a molten metal bath, and introducing a purge gas into the molten metal. Without being bound by theory, it is believed that the ultrasonic degassing step performed in this manner results in the formation of microbubbles, the microbubbles being able to encapsulate impurities present in the molten metal bath. Once the impurities are encapsulated within the microbubbles, those that are significantly less dense than the molten metal rise to the surface of the molten metal bath and are removed, while microbubbles that are significantly more dense than the molten metal bath sink to the bottom and are removed. However, microbubbles which comprise an intermediate amount of impurities may result in a density similar to that of the molten metal and may remain entrained in the molten liquid after degassing step, which may subsequently be deposited onto downstream machinery. These microbubbles may not be restrained by conventional methods, and as a result, deposits on the downstream machinery can build up over time.
In certain embodiments of the methods disclosed herein, impurities encapsulated by microbubbles in the molten metal bath can be deposited on the sludge removal device, by contacting the microbubbles with the surface of the sludge removal device. While not wishing to be bound by theory, it is believed that increasing the flow rate of the molten metal through the channels of the sludge removal device allows for greater contact between the surface of the sludge removal device and the microbubbles and/or free impurities present in the molten metal, thereby leading to greater sludge deposition than occurs on the walls of the launder under typical conditions. Accordingly, certain embodiments of the methods disclosed herein can comprise passing the molten metal through at least one of the plurality of channels of the sludge removal device. Although the fluid dynamics taking place within the channel is complex, it is believed that the reduced cross-sectional area of the plurality of channels in the sludge removal device compared to that of the molten metal launder causes the molten metal to accelerate through the plurality of channels, thereby creating turbulent flow in the molten metal as it passes through the channels of the sludge removal device.
To achieve the desired effect of acceleration and/or turbulent flow, an intra-channel flow rate of the molten metal can be greater than the general launder flow rate. In certain embodiments, a ratio of the intra-channel flow rate to the launder flow rate can be at least about 1.5:1, at least about 2:1, at least about 5:1, or at least about 10:1. In other embodiments, the ratio of the intra-channel flow rate to the launder flow rate can be in a range from about 1.1:1 to about 100:1, from about 1.1:1 to about 50:1, from about 1.1:1 to about 20:1, from about 1.1:1 to about 10:1, or from about 2:1 to about 10:1. The flow rate of the molten metal through a center region of at least one of the plurality of channels also can be greater than a flow rate of the molten metal through an edge region of the at least one channel. In such embodiments, the flow rate of the molten metal near the edge of the channel can approach zero, allowing for the impurities present in the molten metal to have an extended interaction with the surface of the channel and eventually the downstream face of the sludge removal device. Such extended interactions may further increase the chances that the microbubbles and impurities contained within will be deposited as sludge on the sludge removal device.
In certain embodiments, the interaction between the molten metal and the sludge removal device may cause the temperature of the molten metal to drop as it passes through the device. This may be due to the increased contact with the sludge removal device, or the general dispersion of heat from the molten metal as it passes through the launder. This cooling effect may be mitigated by superheating the molten metal before entering the launder, or by maintaining the temperature of the molten metal as it flows through the launder. Ultimately, the required temperature of the molten metal will depend on its composition. For instance, molten copper may be maintained at temperatures of around 1100° C., while molten aluminum may be maintained at temperatures of around 750° C. In certain embodiments, the molten metal may be maintained at a temperature of at least 250° C., at least 400° C., at least 500° C., at least 600° C., at least 700° C., at least 1000° C., or at least 1250° C. Alternatively, the temperature of the molten metal can be above the melting point of the molten metal by less than 20° C., less than 50° C., or less than 100° C. above the melting point of the molten metal. The composition of the molten metals suitable for the methods described herein is not limited to any particular metal, or metal alloy. In certain embodiments, the molten metal can comprise aluminum, copper, zinc, steel, brass (e.g., red brass, yellow brass), bronze, aluminum bronze, chromium, cobalt, nickel, gold, iridium, iron, lead, magnesium, manganese, platinum, palladium, rhenium, rhodium, silver, tin, tungsten, or combinations thereof. In other embodiments, the molten metal can comprise aluminum, copper, zinc, steel, or any combination thereof. In certain aspects of the methods disclosed herein, the molten metal can comprise aluminum. In certain aspects of the methods disclosed herein, the molten metal can comprise copper.
Any of the above mentioned metals may also be considered as impurities, dependent on the context of the method being employed. As an example, zinc can be the molten metal to be purified, but also can be an impurity in the molten metal (e.g., aluminum) to be removed by the sludge removal methods disclosed herein. Examples of impurities can include, but are not limited to, metals and/or metal oxides, such as titanium compounds, boron compounds, vanadium compounds, magnesium compounds, sodium compounds, or any combination thereof. The total amount of impurities initially present in the molten metal is not particularly limited, but can be in a range of at least about 3 ppm, at least about 4 ppm, at least about 10 ppm, at least about 20 ppm, or in a range from about 1 to about 100 ppm, from about 3 to about 10 ppm, from about 5 to 20 ppm, or from about 3 to 50 ppm, and the like. Unexpectedly, certain embodiments of the methods disclosed herein may be capable of reducing a total amount of impurities in the molten metal to less than 1000 ppm (by weight), less than 100 ppm, less than 50 ppm, less than 20 ppm, less than 10 ppm, less than 5 ppm, less than 2 ppm, less than 1 ppm, or less than 0.1 ppm.
Accordingly, in certain embodiments, the total amount of impurities removed from the molten metal can be at least 50 wt. %, at least 60 wt. %, at least 70 wt. %, at least 75 wt. %, at least 80 wt. %, at least 85 wt. %, at least 90 wt. %, or at least 95 wt. %, based on the initial weight of impurities present in the molten metal. Additionally, the methods disclosed herein may reduce an amount of a particular impurity in the molten metal (e.g., vanadium), by any of the absolute or relative amounts listed above, independent from the total amount of impurities removed. For instance, at least 95 wt. % of the vanadium may be removed from the molten metal, while less than 50 wt. % of other impurities (either independently, or as a whole) are removed.
The amount of impurities in a given molten metal sample may be too low to directly detect in the melt by convenient analytical methods. Thus, the effectiveness of the devices, systems, and methods described herein also can be determined by the amount and location of impurities deposited as sludge on components of the sludge removal system, including metal casting machinery downstream of the molten metal launder. Certain embodiments disclosed herein may reduce the amount of sludge deposition on downstream machinery, or specific components thereof, over a period of operation by at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98%, or at least 99%.
In certain embodiments, the method further comprises casting the purified molten metal to form a metal article. The casting machinery and methods are not limited, and generally can be any that are suitable to produce a desired article. Such articles may include cast metal rods, cast metal bars, or articles that have further machined (e.g., wire, machine parts), or any other products or components of products comprising metal.

EXAMPLES

The examples below were conducted to demonstrate the efficacy of the sludge removal devices, systems, and methods disclosed herein, particularly in comparison to the conventional method of filtering molten metal using a ceramic foam filter. In each example, molten aluminum was subjected to ultrasonic degassing with an ultrasonic degassing device. Generally, molten aluminum was subjected to ultrasonic degassing using an ultrasonic device operated at 20,000 Hz while the molten aluminum was purged with argon gas at a rate of about 56 standard liters per minute (L/min). The argon was injected along the tip of the ultrasonic device. Following the degassing procedure, the molten aluminum was passed into a launder configured as shown in FIG. 1. Example 1 did not employ a sludge removal device, and Examples 2-4 employed a single sludge removal device arranged in the launder, as depicted in FIG. 1. After passing through the sludge removal device, and exiting the launder, the molten aluminum proceeded from the launder to a metal casting machine comprising a ceramic foam filter, a cast spout, and a downspout. For each example, the amount, placement, and composition of the resulting sludge deposition on the launder walls, the sludge removal device (where applicable), and the downstream equipment was observed. Sludge deposits from Example 1 were analyzed by X-ray diffraction using a scanning electron microscope (SEM); results are shown in FIG. 8.

Example 1

Molten aluminum was subjected to ultrasonic degassing as described above, then passed into a metal launder without a sludge removal device. The molten aluminum was allowed to exit the launder into the metal casting machine. After 6 hours, the process was stopped due to the presence of significant sludge deposits on critical components of the metal casting machine. As expected, and discussed above, the ceramic foam filter collected some deposits, but was ineffective in preventing sludge deposition on either cast spout. The total amount of sludge deposits on the components of the metal casting machine was estimated to weigh between about 1 to about 5 lbs.
Deposits on the cast spout (top and bottom), ceramic foam filter, and downspout of the metal casting machine were collected. Sludge deposits were also collected from the walls of the launder, before entering the metal casting machine. The composition of each of the collected deposits was analyzed as described above (FIG. 8). While minor differences in the composition of each sludge deposit were observed, the sludge deposits collected from within the launder (TRC #1 and TRC #2) were generally the same as those collected from the downstream metal casting machine (cast spout top and bottom, filter, and downspout). Because there is little difference between the sludge removed from the launder and the downstream machinery, removing the sludge from within the launder can prevent sludge deposition on downstream equipment.
Unexpectedly, a significant amount of the sludge was vanadium, which can be difficult to remove from molten metals by conventional methods. Accordingly, the disclosed systems and methods may offer an efficient means for removing impurities that are particularly difficult to remove from molten metal by conventional methods.

Example 2

Example 2 was performed identically to Example 1, except that a sludge removal device was employed within the metal launder to collect the sludge formed. A sludge device was prepared from a 1″ wide block of marinite A, by drilling holes spaced as depicted in FIG. 2 (⅜″ diameter). The sludge removal device was positioned within the launder so that the molten metal flowed through the plurality of channels of the sludge removal device upstream of the metal casting machine. The aluminum casting process was again operated continuously and the sludge removal device and certain components of the aluminum casting machine were examined intermittently for deposition of sludge.
Surprisingly, after 6 hours, no noticeable sludge deposits were present on the cast spout (top and bottom) and downspout components of the metal casting machine. Instead, and unexpectedly, sludge deposits were found almost exclusively on the sludge removal device. At this point, the sludge removal device was removed from the launder and the sludge deposits were scraped from the device. The sludge removal device was replaced within the launder and the metal casting operation continued without interruption.
Operating in this manner, the sludge removal device remained effective in preventing deposition of impurities in the downstream machinery, even after continuous operation for 3 days. The sludge removal device was able to prevent time-consuming cleaning steps from interrupting the continuous metal casting process. As shown in FIG. 8, the composition of the sludge collected by the sludge removal device is comparable to sludge deposited elsewhere in the process, where the sludge removal device was not employed.

Example 3

Example 3 was performed as above for Example 1, using the sludge removal device shown in FIG. 6, having horizontal channels substantially parallel to the direction of flow of the molten metal through the launder. The metal casting process was again conducted for 6 hours before the sludge removal device was removed from the launder to examine the effect of positioning the channels of a sludge removal device at an angle, with respect to the flow of the metal in the launder, compared to methods where the channels of the sludge removal device are parallel to the direction of flow. Sludge deposits were removed from the device, sectioned, and analyzed under microscope. A photomicrograph of the sludge cross-section is shown in FIG. 9. Many gas porosities (dark circles) are present in the cross-section of the aluminum sludge deposit (light gray). Relatively few oxide films (dark striations) are seen within the deposit.

Example 4

Example 4 was conducted identically to Example 3, except that the sludge removal device depicted in FIG. 7 was employed. Notably, the sludge removal device in FIG. 7 differs from that used in Example 3 by having channels that are angled at 45° relative to the upstream face of the device and the direction of flow of the molten metal through the launder. As in Example 3, the sludge removal device was removed from the molten metal launder after conducting the aluminum casting process continuously for 6 hours. The sludge deposited on the surface of the sludge removal device was removed, cross-sectioned, and examined under microscope. FIG. 10 represents a photomicrograph of the cross-section.
Surprisingly, comparing the photomicrographs from Examples 3 and 4 reveal that the angled channels were able to remove more impurities from the molten metal, in addition to removing microbubbles from the melt. In each photomicrograph, the light grey segments represent the cross-sectioned aluminum sludge deposit removed from the sludge removal device, and the dark striations within the sludge deposit represents impurities in the form of oxide films containing adhered particles. The dark circles within the cross section represent gas porosities entrapped within the sludge deposit.
As is shown in FIG. 10, the photomicrograph of Example 4 shows a greatly increased amount of oxide films (dark striations) in the sludge deposit. In comparison, FIG. 9 shows relatively few dark striations, and thus relatively few impurities that have been sequestered from the molten metal. Further, the angled channels produced a sludge cross-section having a much lower amount of gas porosities. Comparing FIGS. 9-10, the amount of gas porosities (round dark spots) in the sludge cross section is drastically reduced by using angled channels. Without being bound by theory, it is believed that the angled channels allow the microbubbles within the molten metal to agglomerate within the channel, and that the larger bubbles are then able to drift toward the surface of the launder due to their natural buoyancy. In doing so, it appears the impurities encapsulated by the bubbles are either carried along to the top of the melt and removed, or deposited within the sludge deposit. In either case, the impurities are removed from the molten metal, and not collected on downstream machinery. In Examples 3-4, no observable deposition of sludge occurred on the downstream metal casting machinery.

Claims

What is claimed is:

1. A sludge removal device comprising:

a body configured for contact with a molten metal; and

a plurality of channels extending through a width of the body;

wherein:

the device comprises an upstream face and a downstream face;

each of the plurality of channels comprises an upstream opening on the upstream face of the device, and a downstream opening on the downstream face of the device; and

each of the plurality of channels independently has an average cross-sectional area from about 0.01 to about 10 square inches.

2. The device of claim 1, wherein the body comprises a marinite, a fused silica, a sialon, a silicon carbide, a boron carbide, a boron nitride, a silicon nitride, an aluminum nitride, an aluminum oxide, or a zirconia.

3. The device of claim 2, wherein the body comprises marinite A.

4. The device of claim 1, wherein:

the width of the body is in a range from about 0.5 to about 8 inches; and

the body is shaped to fit securely against the sides of a molten metal launder.

5. The device of claim 1, wherein:

a total cross-sectional area of upstream openings is in a range from about 10% to about 90% of the total surface area of the upstream face; and

a total cross-sectional area of downstream openings is in a range from about 10% to about 90% of the total surface area of the downstream face.

6. The device of claim 1, wherein a cross-sectional shape of each of the plurality of channels is independently selected from a circle, oval, rectangle, square, triangle, hexagon, octagon, honeycomb, regular or irregular polygon, or any combination thereof.

7. The device of claim 6, wherein each of the plurality of channels is cylindrical, and has a radius in a range from about 1/16 to about ¾ inches.

8. The device of claim 1, wherein a flow axis of at least one of the plurality of channels is configured to be substantially parallel to a molten metal flow direction.

9. The device of claim 1, wherein a flow axis of at least one of the plurality of channels is configured to be at an angle relative to a molten metal flow direction.

10. The device of claim 9, wherein the angle is in a range from about 10° to about 80°.

11. The device of claim 9, wherein the angle is in a range from about 30° to about 60°.

12. A sludge removal system comprising:

a molten metal launder configured to generate a molten metal flow between a launder inlet and a launder outlet; and

a first sludge removal device positioned within the molten metal launder and between the launder inlet and the launder outlet;

wherein the sludge removal device comprises:

a body configured for contact with a molten metal; and

a plurality of channels extending through a width of the body.

13. The system of claim 12, further comprising:

a molten metal degassing device in fluid connection with the launder inlet; and

a metal casting machine in fluid communication with the launder outlet.

14. The system of claim 12, further comprising a second sludge removal device arranged serially in the molten metal launder, downstream of the first sludge removal device;

wherein a total cross-sectional area of the plurality of channels on the first sludge removal device is greater than that of the second sludge removal device.

15. The system of claim 12, wherein:

a cross-sectional area of the launder is in a range from about 1 to about 50 ft²

a flow capacity of the molten metal launder is in a range from about 1 L/min to about 50 L/min.

16. A method for removing impurities from a molten metal, the method comprising:

flowing a molten metal comprising impurities through a sludge removal device, the sludge removal device comprising:

a body configured for contact with a molten metal; and

a plurality of channels extending through a width of the body; and

depositing at least a portion of the impurities on the sludge removal device to form a purified molten metal;

wherein the molten metal comprises aluminum, copper, zinc, steel, or a combination thereof.

17. The method of claim 16, further comprising:

removing the sludge removal device from the molten metal after a saturation period; and

regenerating the sludge removal device by mechanically removing the deposited impurities from a surface of the sludge removal device.

18. The method of claim 16, wherein:

the molten metal comprises impurities in a range from about 1 ppm to about 100 ppm;

at least 80 wt. % of the impurities are removed from the molten metal; and

the impurities comprise a metal and/or metal oxide.

19. The method of claim 16, further comprising:

degassing the molten metal prior to flowing the molten metal through the sludge removal device; and

casting the purified molten metal.

20. The purified molten metal produced by the method of claim 16.

21. A cast metal article comprising the purified molten metal of claim 20.