Method and apparatus for improving aluminum degassing efficiency

Abstract

A method for treating molten aluminum as it passes between a melting furnace and a casting apparatus, the method including the steps of monitoring a hydrogen concentration in the molten aluminum, correlating the hydrogen concentration with the use of an inert gas concentration; and automatically adjusting the inert gas output from a degasser and the degasser rotor speed to provide a consistent desired hydrogen concentration for the molten aluminum entering the casting apparatus.

Description

[Background technology]

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 311,309, filed February 17, 2022, the contents of which are incorporated herein by reference.

[0002] The exemplary embodiment relates to a method and apparatus for improving the quality of aluminum, and more particularly to a method and apparatus for treating molten aluminum with a gas prior to casting and solidification. It finds particular application in connection with the casting of aluminum pieces and will be described with particular reference thereto. However, it will be understood that the exemplary embodiment is applicable to other similar applications.

[0003] When many molten metals are used in casting and similar processes, they must undergo preliminary treatment to remove unwanted components that may adversely affect the physical or chemical properties of the resulting cast product. For example, molten aluminum is so reactive that when it comes into contact with moist air or wet tooling, the water decomposes and releases hydrogen into the melt. Hydrogen solubility decreases rapidly when the metal freezes during casting, causing the hydrogen to leave the solution. This can result in problems such as twisting or delamination of the extrudate in thin-walled sections and blistering of the cast product.

[0004] Therefore, hydrogen removal and control is an important part of the metal processing process in aluminum casting. The aluminum melt is constantly interacting with the atmosphere, and an equilibrium is formed between gaseous hydrogen in the air and hydrogen dissolved in the molten aluminum. The partial pressure (i.e. amount) of hydrogen in the atmosphere is largely irrelevant. Rather, hydrogen originates from water vapor in the atmosphere.

[0005] Dissolved hydrogen levels must be controlled to minimize scrap and waste, therefore metal casters must prevent and minimize the introduction of hydrogen into the melt and remove it prior to pouring.

[0006] Degassing of molten aluminum is usually accomplished using a purge (inert) gas introduced into the melt by a rotary degasser. This process of removing hydrogen is often referred to as "metal degassing."

[0007] In-line degassing systems are often installed between the holding furnace and the casting station. A standard degassing system injects the inert gas using one or more injectors or injection devices such as a spinning rotor device. The injectors typically introduce the inert gas, such as argon, into the molten metal in the form of bubbles that the injectors shear and disperse into the molten metal to saturate the molten metal with the inert gas. Many degassing systems function automatically without much operator attention. This results in inefficient use of purge gas and costs associated with other downstream in-line processes such as filtration. An in-line degassing apparatus and process for in-line aluminum processing is disclosed in U.S. Pat. No. 8,025,712, the disclosure of which is incorporated herein by reference.

[0008] It is also desirable to reduce the non-metallic impurity content of the molten aluminum being cast. This is typically accomplished by utilizing one or more of a variety of fluxing techniques in which the molten metal is contacted with a reactive gas or solid fluxing agent (such as a halogen). For example, chlorine gas can be utilized to remove non-metallic impurities.

[0009] The degassing process is limited by thermodynamic laws. When dry purge gas bubbles are introduced into the melt, they collect hydrogen as they float towards the surface. A local equilibrium is rapidly established between the H2 concentration in the melt boundary layer and the H2 partial pressure in the purge gas bubbles. The diffusion of hydrogen from the bulk to the boundary layer is rate limiting, but the recombination of atomic hydrogen to molecular hydrogen is very fast. The process efficiency is thermodynamically approximately 100%. However, as the gas content in the melt decreases, the equilibrium pressure of hydrogen in the bubbles also decreases. Therefore, the amount of purge gas required to remove the residual hydrogen must increase.

[0010] Currently, there are no in-line degassing systems that automatically adjust speed and gas flow rates. Rather, it is widely accepted in foundries that degassing equipment is set to one pre-identified setting and will maintain that setting for almost every drop, regardless of metal flow, incoming hydrogen level, alloy type, or season.

[0011] Thus, a typical foundry approach involves the use of excessive amounts of inert gas to achieve the desired hydrogen levels. Of course, this inefficiency leads to unnecessary increased costs and wasted resources. Thus, there is a need for a metal processing method and apparatus that provides effective processing in real time with a correspondingly low gas consumption. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention relates to a method and apparatus for monitoring and reducing undesirable impurities in molten metal. For convenience, the following description is directed to the processing of aluminum, although other molten metal systems may benefit from the use of the disclosed system. [Means for solving the problem]

[0013] According to one aspect of the present invention, a method for treating molten aluminum as it passes between a melting furnace and a casting apparatus is provided, the method including monitoring a hydrogen concentration in the molten aluminum and calculating an amount of inert gas required to achieve a target hydrogen concentration in the molten aluminum, the method further including automatically adjusting an amount of inert gas injected into the molten aluminum based on the calculation.

[0014] In one aspect of the invention, the degasser automatically adjusts the inert gas concentration and rotor speed output from the degasser to maintain a constant hydrogen level as the molten aluminum enters the casting apparatus.

[0015] In accordance with another aspect of the invention, an analyzer is used to monitor the inflow and outflow hydrogen levels in the molten metal and to signal the degasser to make adjustments accordingly during the casting process.

[0016] According to one aspect of the invention, the monitoring of the hydrogen concentration is continuous. According to another aspect of the invention, the monitoring of the inert gas concentration is continuous. In one embodiment of the invention, the hydrogen concentration and the inert gas concentration are measured. In another embodiment of the invention, the monitoring of the hydrogen concentration and / or the inert gas concentration is performed periodically.

[0017] According to another aspect of the present invention, a method is provided for measuring the gas content of molten metal using a gas measurement system that includes monitoring the hydrogen concentration in the molten metal and correlating the use of an inert gas concentration with the hydrogen concentration in the molten metal, and a degasser unit automatically adjusts the output of the degasser unit to maintain a substantially constant hydrogen content level in the molten metal being cast in real time. As used herein, "substantially constant" means a variation in hydrogen concentration during casting of less than 10%, less than 5%, or less than 1%. The hydrogen concentration is continuously measured by an analysis unit. The analysis unit may also continuously measure the inert gas. In some embodiments, the inert gas is argon, although other inert gases such as nitrogen may be used.

[0018] Also disclosed herein is an apparatus for receiving a gas concentration supply and conditioning a melting furnace, the apparatus including a degassing station including a first sensor for measuring a hydrogen concentration in the molten metal and a second sensor for measuring an inert gas concentration.

[0019] In some preferred embodiments, the first sensor for measuring the hydrogen concentration in the molten metal and the second sensor for measuring the inert gas concentration are the same sensing device. In other preferred embodiments, the first sensor and the second sensor are the same sensor, which simultaneously measures the hydrogen concentration and the inert gas concentration. Other aspects of the device include a control unit (e.g., a programmable logic controller "PLC") for receiving the gas concentration measurements.

[0020] In some embodiments of the invention, the control unit correlates the hydrogen concentration in the molten metal with the inert gas concentration introduced into the molten metal and / or into the degassing unit, while in other embodiments the control unit balances the correlated hydrogen concentration with the inert gas concentration to maintain a constant outlet hydrogen content.

[0021] Sensor devices according to embodiments of the present invention may be contacted with molten metal, such as aluminum or as disclosed, for example, in US Pat. No. 6,216,525.

[0022] Analytical devices according to embodiments of the present invention may be contacted with molten metal, such as aluminum or as disclosed, for example, in US Pat. No. 4,907,440.

[0023] In some embodiments, the degassing unit is an in-line degassing system. In some embodiments, the in-line degassing system can be located between the holding furnace and the casting station.

[0024] One suitable molten aluminum degassing or metal refining system is offered by Pyrotek under the SNIF trademark. References and information regarding Pyrotek products can be found on their website at www.pyrotek-inc.com.

[0025] U.S. patents that refer to such systems include U.S. Patent No. 9,127,332 for a molten aluminum refining and gas distribution system, U.S. Patent No. 5,198,180 for a gas distribution apparatus with rotor and stator for molten aluminum refining, U.S. Patent No. 5,846,481 for a molten aluminum refining apparatus, U.S. Patent No. 3,743,263 for a molten aluminum refining apparatus, and U.S. Patent No. 4,203,581 for a molten aluminum refining apparatus, all of which are incorporated herein by reference. [Brief description of the drawings]

[0026] The following is a brief description of the drawings, which are presented for purposes of illustrating exemplary embodiments disclosed herein and not for purposes of limiting same.

[0027] [Figure 1] FIG. 1 illustrates a process flow for an exemplary degassing method for an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a schematic diagram of an exemplary degassing apparatus according to an embodiment of the present disclosure. [Figure 3a] FIG. 1 is a front view of an aluminum casting showing the effect of hydrogen concentration. [Figure 3b] FIG. 3b is a diagram of the aluminum casting of FIG. 3a. [Figure 3c] FIG. 3b shows hydrogen concentration levels in the aluminum casting of FIG. [Figure 3d] FIG. 1 is a front view of hydrogen concentration in an aluminum casting with a diagram showing hydrogen concentration levels. [Figure 4] 1 is a perspective view of an exemplary in-line metal processing system with a baffle and rotating dispenser according to the prior art. [Diagram 5] FIG. 1 is a perspective cutaway view of a prior art degassing rotor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Many of the components utilized in the present invention are widely known and used in the field of the invention described, and their exact nature or type is not necessary for the understanding and use of the present invention by those skilled in the art. Therefore, they will not be described in detail. A more complete understanding of the components, processes and devices disclosed herein can be obtained by referring to the attached drawings. The drawings are merely schematic representations and are provided for convenience and ease of describing the present disclosure, and are therefore not intended to show the relative size and dimensions of the device or its components and / or to define or limit the scope of the exemplary embodiments.

[0029] Although specific terms are used in the following description for clarity, these terms are intended to refer only to the particular structures of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the following drawings and the following description, like numbers should be understood to refer to components of like function.

[0030] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0031] As used in this specification and claims, the terms "comprise," "include," "have," "having," "capable," "comprising," and variations thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named components / steps and allow for the presence of other components / steps. However, such descriptions should also be construed as describing a kit or apparatus or method as "consisting of" and "consisting essentially of" the recited components / steps, which allows for the presence of only the named components / steps and excludes other components / steps.

[0032] Numerical values ​​in this specification and the claims herein should be understood to include numerical values ​​that are the same when reduced to the same number of significant figures, and numerical values ​​that differ from the stated value by less than experimental error of conventional measurement techniques of the type described herein to determine the value.

[0033] All ranges disclosed herein are inclusive of the recited endpoints and are independently combinable (e.g., the range "from 2g to 10g" includes the endpoints 2g and 10g, as well as all intermediate values).

[0034] Values ​​modified by one or more terms such as "about" and "substantially" may not be limited to the exact value specified. The modifier "about" should also be considered to disclose a range defined by the absolute values ​​of the two endpoints. For example, the expression "about 2 to about 4" also discloses the range "2 to 4." The term "about" can refer to plus or minus 10% of the specified number.

[0035] The terms "upper" and "lower" relate to one another in location, i.e., an upper component is located at a higher elevation than a lower component.

[0036] The terms "horizontal" and "vertical" are used to indicate orientation relative to an absolute reference, i.e., the earth's surface. However, these terms should not be interpreted as requiring that similarly described structures be perfectly parallel or perfectly perpendicular to one another.

[0037] Examples 1 and 2 below show that the hydrogen concentration of the aluminum leaving the furnace is generally highest at the beginning of the process and gradually decreases during casting. If the degasser is set to one fixed parameter, the hydrogen concentration after the degasser also follows the same path as the inlet hydrogen, and the hydrogen removal efficiency remains at approximately the same level. This approach produces solids, slabs or billets with different hydrogen concentrations depending on the set parameters of the furnace outlet and the degasser. If the degasser is set to one fixed parameter, it is almost always set during the season when the metal flow rate is highest, the humidity is highest, and alloy removal is difficult. As a result, casting operations almost without exception overprocess the molten aluminum.

[0038] JPEG2025507583000002.jpg85153

[0039] JPEG2025507583000003.jpg94153

[0040] Examples 3-6 below show data collected from two separate castings with no changes to the degasser parameters. The ALSCAN tests were each conducted on two separate days. Examples 3 and 4 are test results conducted on day 1. Examples 5 and 6 are test results conducted on day 3. The only changes that occurred were the inlet metal temperature and metal levels in the washer. This process can result in inlet metal hydrogen content levels being higher than expected. However, in both cases, hydrogen levels were observed to decrease over time despite the potentially lower inlet hydrogen content levels.

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[0042] JPEG2025507583000005.jpg86153

[0043] JPEG2025507583000006.jpg97153

[0044] JPEG2025507583000007.jpg97153

[0045] The results of the experiment are shown in Figures 3a, 3b and 3c. If the metallurgist of the foundry collects the ALSCAN numbers at a point near the end of the casting, despite the selection of the degasser according to the hardest alloy, the highest metal flow rate, the most humid season, etc., the hydrogen concentration is relatively low relative to the beginning of the casting. In this case, a weak parameter set can be selected as the standard configuration for all drips. This is important in the first half of the casting, since the hydrogen level may exceed the acceptable range. Similarly, as can be seen in Figure 3d, if the same measurements are obtained at the beginning of the casting and the parameters of the degasser are set accordingly, the degassing will be efficient only at the beginning, but very strong in the rest of the casting. In this case, an unnecessary use of argon will be made, which is undesirable for the foundry's economy.

[0046] FIG. 1 illustrates a process flow for an exemplary degassing method. Process 100 illustrates a method for treating molten aluminum as it passes between a melting furnace and a casting apparatus. Process 100 includes steps 102 of monitoring hydrogen concentration in the molten aluminum and 104 of monitoring inert gas concentration in the molten aluminum. Process 100 further includes step 106 of correlating the use of gas concentration with hydrogen concentration. In one embodiment, a degasser is used at degassing station 202, and the degasser includes a controller that automatically adjusts 106 the inert gas concentration output from the degasser to maintain a constant hydrogen level as the molten aluminum enters the casting apparatus.

[0047] FIG. 2 shows a schematic diagram of an exemplary degassing apparatus. The apparatus 200 includes a degassing station 202. The degassing station 202 includes a first sensor 204a for measuring hydrogen concentration in the molten metal and an optional second sensor 204b for measuring inert gas concentration. After the hydrogen and inert gas are measured, the information is sent to a control unit 212. The control unit 212 is configured to receive the inert gas concentration measurements (206). The control unit 212 correlates the hydrogen concentration in the molten metal with the inert gas concentration in the molten metal. The control unit 212 balances the correlated hydrogen concentration (208) with the inert gas concentration to maintain a constant outlet hydrogen content level. The control unit 212 is configured to automatically adjust the hydrogen output (210) based on the inert gas concentration.

[0048] 4, there is shown an embodiment of the prior art disclosed in U.S. Patent No. 5,718,416. The lower portion of the refining vessel is commonly referred to as the tub assembly 301. The tub assembly 301 is a two-stage refining vessel where aluminum or other molten metal is introduced into the first refining stage or section of the vessel via metal inlet 302.

[0049] After being refined in the first refining section, the metal flows to the second refining section where it is further refined before exiting through metal outlet 303. The design of the refining vessel is such that the metal inlet and outlet can be reversed to suit the specifics of the facility in which it is used. That is, metal inlet 302 can be used as the outlet and metal outlet 303 can be used as the inlet. The first refining section then becomes the second refining section and vice versa. In general, the trough transports the molten material from a furnace configured to melt the aluminum material into a molten metal alloy to a casting mechanism that forms the molten material into a desired shape.

[0050] The dome lid assembly 305 may be securely and sealably attached to the upper exterior surface of the containment tub assembly 301 by a number of different known means. The dome lid 306 has four exterior walls: a lid front wall 306a, two lid side walls 306b, and a lid rear wall (not shown), in addition to a lid roof 306d. Figure 4 shows that the lid front wall 6a and the two lid side walls 306b are angled inwardly.

[0051] The front access door 307a has a significant area on the dome lid front wall 306a and therefore can be quite heavy. To open the front access door 307a more easily, a hydraulic cylinder assembly 8 is provided. The side access door 307b is smaller than the front access door 307a and is much easier to operate by an operator, therefore a handle 309 is provided to open the side access door 307b without the need for mechanical assistance.

[0052] The cap roof 306d is fitted with two rotating gas distributors 312, one for each purification section or stage.

[0053] Figure 5 is a perspective cross-sectional view of one embodiment of a molten metal purification gas dispersion apparatus 660 contemplated by the present invention. Figure 6 shows an injector, in this embodiment, including a stator 662, a rotor shaft 661, and a passageway between the stator 662 and the rotor shaft 661 through which gas 664 passes. A spinning rotor 667 includes blades 670 (or vanes) having a space or distance 671 between them. Gas-laden bubbles 677 are released into the molten aluminum for dispersion, as indicated by arrows 669 and 673.

[0054] Figure 6 also shows a central passage 666 (or conduit) through which gas and flux are introduced from an external source 678 that is injected or pumped into the central passage 666 as shown by arrows 663. Figure 3 also shows a gas passage 659 between the stator 662 and the rotor shaft 661 through which gas is introduced into the injector 660 or molten metal refining system (preferably molten aluminum). Typically, the flux is provided in a powder or other solid form and may be mixed with a gas for injection into the molten metal, although there are applications such as future applications in which a liquid or gas form of the flux may be utilized.

[0055] Those skilled in the art will appreciate that any of a number of different spinning rotors may be utilized depending on the particular application of the embodiment of the invention being implemented, without any being specifically required to practice the invention, all within the contemplation of the invention.

[0056] As can also be seen in FIG. 6, the rotor shaft 661 is rotatably disposed within an internal cavity within the stator 662 such that it may be driven by a motor or other drive within the cavity of the stator 662. The rotor shaft 661 is operably attached to the spinning rotor 667 such that the nozzles rotate with the rotor shaft 661. Gas passages are also provided between the internal cavity surface of the stator 662 and the outer surface of the rotor shaft 661 such that the gas 664 may pass through the passages before being discharged between the bottom of the stator 662 and the top of the spinning rotor 667. The gas is discharged and preferably sheared between the top of the spinning rotor 667 and the bottom of the stator 662, and the vanes 670 of the spinning rotor 667 contribute to the shearing and dispersion of gas bubbles 677 within the molten metal surrounding the spinning rotor 667. The stator 662 may be smooth, may include vanes 670, or may include any of a number of different surfaces and configurations on its exterior surface, none of which are particularly required to practice the present invention.

[0057] FIG. 6 also shows where the outer surface of rotor shaft 661 interacts with the inner surface of stator 662, the intersection identified as item 679 and also referred to as gap 679. The area of ​​intersection 679 may be referred to as a bushing, bearing, or using other terms, and in some embodiments there may be a few thousandths of an inch of clearance between the two components. It is generally desirable to maintain some gas pressure in gap 679 to keep molten metal from entering gap 679 at its lower end near rotating rotor 667. It is generally desirable to maintain some gas pressure below gap 679 to keep molten metal from entering gap 679 at its lower end near rotating rotor 667.

[0058] In a typical application using gap 679, only gas is used in connection with the stator and rotor configuration, with the desired flux being added via a separate injector. However, in an embodiment of the present invention, flux can be introduced into a molten metal processing system using a rotating rotor and shaft within the stator.

[0059] As will be appreciated by those skilled in the art, the gas and flux flow rates depend on the metal flow rate, impurities in the inlet metal in a given application, and the desired quality of the output metal. However, in one example, the gas flow rate ranges up to 5 cfm (8 Nm3 / h), with a typical range being 2 to 4 and 1 / 2 cfm (3 to 7 Nm3 / h). Flux material in a typical application may utilize 20 g / m or more. The flow rates described herein are per nozzle and are provided as examples, and are not intended to limit the invention as they are not dependent on any particular range or set of parameters in a metal processing system.

[0060] The preferred gas for use in conjunction with the present invention in certain embodiments is argon, although nitrogen, or others, may also be utilized. Although the present invention is not limited to any particular flux material, the preferred flux material in certain embodiments may be a eutectic mixture of magnesium chloride and potassium chloride (commonly known by the trademarks ProMag and Zendox).

[0061] The exemplary embodiments have been described with reference to preferred embodiments. Modifications and alterations will occur to others upon reading and understanding the above detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or equivalents thereof.

Claims

1. 1. A method for treating molten aluminum as it passes between a melting furnace and a casting apparatus, comprising the steps of: Measuring the hydrogen concentration in the molten aluminum; and Correlating the inert gas concentration usage with the hydrogen concentration; and and automatically adjusting the inert gas output from a degasser and the degasser rotor speed to provide a substantially constant hydrogen level in the molten aluminum as the inert gas enters the casting apparatus.

2. 2. The method of claim 1, wherein the hydrogen concentration is measured continuously.

3. 2. The method of claim 1, wherein said hydrogen concentration is measured periodically during a particular cast.

4. 2. The method of claim 1, wherein the inert gas is argon.

5. 2. The method of claim 1, wherein the inert gas is nitrogen.

6. 2. The method of claim 1, wherein the degasser comprises an inert gas dispersion rotor.

7. 2. The method of claim 1, wherein chlorine gas is introduced into the molten aluminum.

8. 10. The method of claim 1, wherein the PLC sets the degasser inert gas level and rotor speed based on a molten metal recipe and machine learning from previous casts.

9. 1. An apparatus for adjusting a melting furnace receiving a gas concentration supply, the apparatus comprising: a degassing station including a first sensor for measuring a hydrogen concentration in the molten metal; an optional second sensor for measuring an inert gas concentration in the molten metal; a control unit for receiving the gas concentration measurements; and a rotor for dispersing, the control unit balancing the inert gas concentration relative to the hydrogen concentration, the control unit automatically adjusting hydrogen output.

10. 10. The apparatus of claim 9, wherein the degasser maintains a constant outlet hydrogen content level.

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