US20250178076A1

US20250178076A1 - Method and apparatus for improving aluminum degassing efficiency

Info

Publication number: US20250178076A1
Application number: US18/838,976
Authority: US
Inventors: Mike Klepacki; Ozgur Cakmak; Stam Bisotis
Original assignee: Pyrotek Inc
Current assignee: Pyrotek Inc
Priority date: 2022-02-17
Filing date: 2023-02-16
Publication date: 2025-06-05
Also published as: CN118973740A; JP2025507583A; MX2024010040A; EP4479205A1; KR20240150478A; WO2023158747A1; AU2023221966A1; CA3251253A1

Abstract

A method for treating molten aluminum as it passes between a melting furnace and a casting apparatus. The method includes monitoring hydrogen concentration in the molten aluminum; correlating an inert gas concentration usage with the hydrogen concentration; and automatically adjusting the inert gas output from a degasser and the rotor rpm of the degasser to yield a consistent and desired hydrogen concentration for the molten aluminum entering the casting apparatus.

Description

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

BACKGROUND

The present exemplary embodiment relates to a method and apparatus for improving the quality of aluminum, more particularly, to the treatment of molten aluminum with a gas prior to casting and solidification. It finds particular application in conjunction with casting of aluminum pieces and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
When many molten metals are used for casting and similar processes, they must be subjected to a 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 extremely reactive, therefore, when it comes into contact with moist air or wet tools, the water decomposes to release hydrogen in the melt. Hydrogen solubility decreases rapidly as the metal freezes during casting, causing the hydrogen to leave the solution. Casting problems such as twisting and flaking in thin section extrusions and blisters on cast products can result.
Thus, hydrogen removal and control are a vital part of the metal treatment process in aluminum casting. The aluminum melt is always in interaction with the atmosphere, to a point where an equilibrium is formed between gaseous hydrogen in the air and hydrogen dissolved in molten aluminum. Partial pressure (i.e. amount) of hydrogen in the atmosphere is almost irrelevant. Rather, hydrogen comes from the water vapor in the atmosphere.
Dissolved hydrogen levels must be controlled to minimize scrap and waste. Accordingly, metal casters must prevent and minimize introduction of hydrogen in the melts and remove the hydrogen prior to pouring.
Degassing molten aluminum is generally accomplished by using a purge (inert) gas, typically introduced into the melt by a rotary degassing unit. This process of removing hydrogen is often referred to as “metal degassing”.
In-line degassing systems are often installed between a holding furnace and a casting station. A standard degassing system involves the injection of an inert gas utilizing one or more injectors or injection devices, such as spinning rotor devices. The injector would typically introduce the inert gas, such as Argon, into the molten metal in the form of bubbles that the injector may sheer and disperse into the molten metal in order to saturate the molten metal with the inert gas. Many degassing systems function automatically and without much attention by the operator. This has led to inefficient purge gas usage and expenses relating to other downstream in-line processes, such as filtration. An in-line degassing apparatus and process for in-line aluminum treatment is disclosed in U.S. Pat. No. 8,025,712, the disclosure of which is herein incorporated by reference.
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 various fluxing processes, wherein the molten metal is contacted with either reactive gaseous or solid fluxing agents (such as halogens). For instance, chlorine gas may be utilized in the removal of the non-metallic impurities.
The degassing process is limited by thermodynamic laws. When dry, purge gas bubbles are introduced to the melt, they collect hydrogen as they float towards the surface. A local equilibrium is rapidly established between H₂concentration in the molten boundary layer and the partial pressure of H₂in the purge gas bubble. The diffusion of hydrogen from the bulk into the boundary layer is rate limited, while the recombination of atomic to molecular hydrogen is very rapid. The process efficiency is about 100% from the thermodynamic point of view. But as the gas content in the melt drops, so does the equilibrium pressure of hydrogen in the bubbles. Accordingly, the amount o purge gas required to remove the remaining hydrogen must increase.
There is currently no in-line degassing system that adjusts speed and gas flow automatically. Rather, it is widely accepted among cast houses that degassers are set to one-previously-verified-confirmed setting, and kept that way for almost all drops, regardless of the metal flow, incoming hydrogen level, alloy types, or the season.
Accordingly, the typical cast house approach uses too much inert gas to achieve a desired hydrogen level. Of course, this inefficiency leads to unnecessary increased cost and squandering of resources. Thus, there is a need for a metal treatment method and apparatus that provides effective treatment in real-time, with correspondingly small amounts of gas consumption.

BRIEF DESCRIPTION

The present invention relates to methods and apparatus for monitoring and reducing undesirable impurities in molten metals. For convenience, the following description will be directed to the treating of aluminum although other molten metal systems may benefit using the system of the present disclosure.
According to one aspect of the invention, there is provided a method for treating molten aluminum as it passes between a melting furnace and a casting apparatus. The method includes monitoring the hydrogen concentration in the molten aluminum and calculating the quantity of inert gas required to achieve a target hydrogen concentration in the molten aluminum. The method further includes automatically adjusting the quantity of inert gas injected into the molten aluminum based on the above calculation.
In one embodiment of the present invention, the degasser automatically adjusts the inert gas concentration output from the degasser and rotor speed to maintain a constant hydrogen level as the molten aluminum enters the casting apparatus.
According to another aspect of the invention, an analyzer is used to monitor the incoming and outgoing hydrogen levels in the molten metal and signals the degasser to make adjustments accordingly during the casting process.
According to one aspect of the present invention, 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 present invention, monitoring of the hydrogen concentration and/or the inert gas concentration occurs periodically.
According to another aspect of the invention, there is provided a method of measuring the gas content of molten metal using a gas measurement system comprising monitoring the hydrogen concentration contained in the molten metal and correlating the inert gas concentration usage with the hydrogen concentration contained in the molten metal, wherein a degasser unit automatically adjusts the degasser unit's output to maintain a substantially constant hydrogen content level in the molten metal be cast in real-time. As used herein “substantially constant” means a variation of hydrogen concentration over the cast of less than 10%, or less than 5% or less than 1%. The hydrogen concentration is measured continuously by an analyzing unit. The analyzing unit can also continuously measures the inert gas. In some embodiments, the inert gas is argon, however other inert gases, such as nitrogen, may be used.
Also disclosed herein is an apparatus for receiving a gas concentration feed and adjusting a melting furnace. The apparatus comprises a degassing station that includes a first sensor for measuring hydrogen concentration in molten metal and a second sensor for measuring inert gas concentration.
In some preferred embodiments, the first sensor for measuring hydrogen concentration in molten metal and the second sensor for measuring inert gas concentration is the same sensing device. In other preferred embodiments, the first sensor and the second sensor are the same sensor and measures the hydrogen concentration and the inert gas concentration at the same time. Other aspects of the apparatus include a control unit (e.g. a programmable logic controller “PLC”) for receiving the gas concentration measurement.
In some embodiments of the present invention, the control unit correlates the hydrogen concentration within the molten metal with the inert gas concentration within the molten metal and/or being introduced to the degassing unit. In other embodiments, the control unit balances the inert gas concentration with the correlated hydrogen concentration to maintain a constant outlet hydrogen content.
Sensor devices in accordance with embodiments of this invention may be in contact with molten metals such as aluminum or, for example, as disclosed in U.S. Pat. No. 6,216,525, which is incorporated herein by reference.
Analyzing devices in accordance with embodiments of this invention may be in contact with molten metals such as aluminum or, for example, as disclosed in U.S. Pat. No. 4,907,440, which is incorporated herein by reference.
In some embodiments, the degassing unit is an in-line degassing system. In some embodiments, the in-line degassing system may be located between the holding furnace and the casting station.
One suitable molten aluminum degassing or metal refining systems are offered by Pyrotek under the SNIF trademark. References and information relative to the Pyrotek products may be found at its website at www.pyrotek-inc.com
United States patents referring to such systems include the following: U.S. Pat. No. 9,127,332 for Molten Aluminum Refining and Gas Dispersion System; U.S. Pat. No. 5,198,180, for a Gas Dispersion Apparatus with a Rotor and Stator for Molten Aluminum Refining; U.S. Pat. No. 5,846,481, for a Molten Aluminum Refining Apparatus; U.S. Pat. No. 3,743,263, for an Apparatus for Refining Molten Aluminum; and U.S. Pat. No. 4,203,581, for an Apparatus for Refining Molten Aluminum; all of which are hereby incorporated by this reference.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 illustrates a process flow of an exemplary degassing method to the embodiments of the disclosure;

FIG. 2 illustrates a schematic diagram of an exemplary degassing apparatus according to the embodiments of the disclosure;

FIG. 3 a is a front view of a representation aluminum cast illustrating effects of hydrogen concentration;

FIG. 3 b is a view of the aluminum cast of FIG. 3 a;

FIG. 3 c is a graphic displaying the hydrogen concentration level contained in the aluminum cast of FIG. 3 b.

FIG. 3 d is a front view of the hydrogen concentration contained in an aluminum cast with a graphic displaying the hydrogen concentration level.

FIG. 4 is a perspective view of a representation in-line metal treatment system; and with baffles and a rotary dispenser in accordance with the prior art;

FIG. 5 is a perspective cutaway view of a prior art degassing rotor.

DETAILED DESCRIPTION

Many of the components utilized in this invention are widely known and used in the field of the invention described, and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art or science; therefore, they will not be discussed in significant detail. A more complete understanding of the components, processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawings. The figures, which are merely schematic representations, are provided for convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.
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 embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.
The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
As used in the specification and in the claims, the terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants 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 permit the presence of other components/steps. However, such description should be construed as also describing kits or devices or methods as “consisting of” and “consisting essentially of” the enumerated components/steps, which allows the presence of only the named components/steps, and excludes other components/steps.
Numerical values in the specification and claims of this application 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 stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.
All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 2 grams to 10 grams” is inclusive of the endpoints, 2 grams and 10 grams, and all the intermediate values).
A value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value 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.” The term “about” may refer to plus or minus 10% of the indicated number.
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.
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 similarly-described structures to be absolutely parallel or absolutely perpendicular to each other.
Examples 1 and 2, below, demonstrate that hydrogen concentration of aluminum leaving a furnace is typically the highest at the beginning of the process and will gradually decrease during casting. When a degasser is set to one-fixed-parameter, the hydrogen concentration after the degasser will also follow the same path as the inlet hydrogen, and hydrogen removal efficiency will remain around the same level. This approach creates a solid, slab, or billet with a different concentration of hydrogen depending on the furnace outlet and the preset parameters of the degasser. When a degasser is set to one-fixed-parameter, most of the time it is set to highest metal flow, most humid season, hard to remove alloy. As a consequence, casting operations almost universally over treat molten aluminum.


H2		H2		H2
Level	Temper-	Level	Temper-	Level	Temper-
AA-9-	ature	AA10-	ature	AA11-	ature
i	T-AA9	i-1	T-AA10	i-1	T-AA11

14:20	0.462	769
14:35	0.438	760
14:48	0.42	770
15:07	0.371	735
18:13			0.45	773
18:26			0.429	760
18:38			0.415	755
18:52			0.411	747
11:26					0.496	755
11:39					0.456	747
11:51					0.449	747
12:04					0.44	748
12:04					0.437	743
12:29					0.438	757

Example 2

Examples 3-6, below, display data collected from two separate casts without changing the parameter on the degasser. ALSCAN tests were performed respectively on two separate dates. Examples 3 and 4 are test results taken on day 1. Examples 5 and 6 are test results taken on day 3. The only change that occurred was the incoming metal temperature and the metal level in the launders. This process makes the incoming metal hydrogen content levels occasionally go higher than expected. However, even though incoming hydrogen content levels could be lower, in both cases, it was observed that hydrogen levels decrease in time.
The result of the Experimentation is shown in FIGS. 3 a, 3 b, and 3 c . Even though a degasser was selected according to the hardest alloy, highest metal flow rate, and most humid seasons, etc, when a cast house metallurgical engineer collects ALSCAN numbers, at a time closer to the end of the cast, hydrogen concentration is relatively low with respect to the beginning of the cast. In this case, a weak set of parameters may be selected as the standard configuration for all drops. This may be critical for the first half of the cast, because hydrogen levels may be higher than acceptable. Likewise, as seen in FIG. 3 d , if the same reading is taken at the beginning of the cast, and the degasser parameters are set accordingly, degassing would be efficient only initially, but would become very strong for the rest of the cast. In this case, unnecessary Argon usage takes place that is not desired for cast house economy.
FIG. 1 illustrates a process flow of an exemplary degassing method. Process 100 shows a method for treating molten aluminum as it passes between a melting furnace and a casting apparatus. The method 100 includes monitoring the hydrogen concentration in the molten aluminum 102 and monitoring the inert gas concentration in the molten aluminum 104. The process 100 further includes correlating the gas concentration usage with the hydrogen concentration 106. In one embodiment of the, a degasser is used at the degassing station 202 and the degasser includes a controller to automatically adjust the inert gas concentration output from the degasser 106 to maintain a constant hydrogen level as the molten aluminum enters a casting apparatus.
FIG. 2 illustrates a schematic diagram of an exemplary degassing apparatus. The apparatus 200 includes a degassing station 202. The degassing station 202 includes a first sensor for measuring hydrogen concentration in molten metal 204 a, and an optional second sensor for measuring inert gas concentration 204 b. After the hydrogen and the inert gas are measured, the information is sent to a control unit 212. The control unit 212 is configured for receiving the inert gas concentration measurement 206. The control unit 212 correlates the hydrogen concentration within the molten metal with the inert gas concentration within the molten metal. The control unit 212 balances the inert gas concentration with the correlated hydrogen concentration 208 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.
With reference to FIG. 4 , a prior art embodiment as disclosed by U.S. Pat. No. 5,718,416 is illustrated. The lower part of the refinement vessel is generally referred to as the tub assembly 301. The tub assembly 301 is a two stage refining vessel wherein the aluminum or other molten metal is introduced into the first refinement stage or first refinement compartment of the vessel through metal inlet 302.
After being refined in the first refinement compartment, the metal flows to the second refinement compartment, where it is further refined before exiting through the metal outlet 303. The design of the refinement vessel is such that the inlet and outlet for the metal can be reversed to accommodate the particulars of the facility in which it is used, i.e. the metal inlet 302 can be used as an outlet and the metal outlet 303 can be used as an inlet. The first refinement compartment then becomes the second and visa versa. Generally, the trough transfers the molten material from a furnace, configured to melt the aluminum material into the molten metal alloy, to a casting mechanism to form the molten material into a desired shape.
The dome lid assembly 305 can be securely and sealably attached to the upper outer surface of the containment vessel tub assembly 301 by numerous different known means. The dome lid body 306 has four outer walls, a lid body front wall 306 a, two lid body side walls 306 b and a lid body rear wall (not shown), in addition to the lid body roof 306 d. FIG. 4 illustrates how the lid body front wall 6 a and the two lid body side walls 306 b are inwardly sloping.
The front access door 307 a comprises a substantial area on the dome lid front wall 306 a and can consequently be very heavy. In order to more easily open the front access door 307 a. A hydraulic cylinder assembly 8 is provided. The side access doors 307 b are smaller than the front access door 307 a and much more easily handled by workmen and handles 309 are therefore provided to open the side access doors 307 b, without the need for mechanical assistance.
Mounted on the lid body roof 306 d are two rotary gas dispersion devices 312, one for each refining compartment or stage.
FIG. 5 is a perspective cutaway view of one embodiment of a molten metal refining gas dispersing device 660 contemplated by this invention. FIG. 6 illustrates an injector which in this embodiment includes stator 662, rotor shaft 661, passageway between the stator 662 and the rotor shaft 661 through which gas 664 is passed through. Spinning rotor 667 includes blades 670 (or vanes) with space or distance 671 there-between. Gas bubbles 677 which include gases are released as indicated by arrows 669 and 673 into the molten aluminum for dispersion.
FIG. 6 also illustrates a central passageway 666 (or conduit) through which gas and flux are introduced as indicated by arrow 663 from an external source 678, which is being injected or pumped into central passageway 666. FIG. 3 also shows gas passageway 659 between stator 662 and rotor shaft 661, and through which gas is introduced into the injector 660 or molten metal refining system (preferably molten aluminum). While typically flux may be provided in powder or other solid form and mixed with gas to inject it into the molten metal, there may also be applications such as future applications wherein a flux in liquid or gaseous form is utilized.
It will be appreciated by those of ordinary skill in the art that any one of a number of different spinning rotors may be utilized with no one in particular being required to practice this invention, all within the contemplation of this invention and depending upon the specific application of the embodiment of this invention being practiced.
As can also be seen from FIG. 6 , the rotor shaft 661 is rotatably positioned within the internal cavity within stator 662 such that it may be driving by a motor or other drive within the stator 662 cavity. The rotor shaft 661 is operably attached to the spinning rotor 667 such that the nozzle rotates with the rotor shaft 661. A gas passageway is also provided between the internal cavity surface of the stator 662 and the outer surface of the rotor shaft 661 such that gasses 664 may pass through the passageway 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 sheering of the gas bubbles 677 and dispersion thereof within the molten metal surrounding the spinning rotor 667. The stator 662 may be smooth, include vanes 670, or include any one of a number of different surfaces and configurations on the outer surface thereof, with no one in particular being required to practice this invention.
FIG. 6 also illustrates where the outer surface of the rotor shaft 661 interacts with the interior surface of the stator 662, with that intersection identified as item 679, which may also be referred to as gap 679. The area of that intersection 679 may be referred to as a bushing, a bearing, or using other terms, and there may in some embodiments be a two to four one-thousandths of an inch clearance between the two components. It is typically desirable to maintain a certain pressure of gas in that gap 679 so that molten metal does not enter the gap 679 at the lower end near the rotating rotor 667. It is typically desirable to maintain a certain pressure of gas below that gap 679 so that molten metal does not enter the gap 679 at the lower end near the rotating rotor 667.
In typical applications utilizing the gap 679, only gas is utilized in connection with the stator and rotor configuration, with any desired flux being added through a separate injector. However, embodiments of this invention, may provide for the introduction of flux in molten metal processing systems which utilize a rotating rotor and shaft within a stator.
As will be appreciated by those of ordinary skill in the art, the gas and flux flow rates will depend on the metal flow rate, the impurities in the incoming metal in a given application, and the desired quality of the output metal. However, in one example the gas may range flow up to five cfm (eight Nm3/h), with a typical range being in the two to four and one-half cfm (three to seven Nm3/h). The flux material in typical application may utilize up to twenty g/m or higher. The flow rates given herein are per nozzle and are given as examples and not to limit the invention in any way as it is not dependent on any particular range or set of parameters in the metal processing system.
While the preferred gas used in combination with this invention in a given embodiment is argon, nitrogen, or others may also be utilized. Although this invention is not limited to any particular flux material, a preferred flux material in a given embodiment may be a eutectic mixture of magnesium chloride and potassium chloride (which is commonly known by trademarks ProMag and Zendox).
The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A method for treating molten aluminum as it passes between a melting furnace and a casting apparatus, the method comprising:

determining hydrogen concentration in the molten aluminum; and

correlating the inert gas concentration usage with the hydrogen concentration; and

automatically adjusting the inert gas output from a degasser and a rotor rpm of the degasser to supply a substantially constant hydrogen level in the molten aluminum as it enters the casting apparatus.

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

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

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

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

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

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

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

9. An apparatus for receiving a gas concentration feed and adjusting a melting furnace comprising: a degassing station that includes a first sensor for measuring hydrogen concentration in molten metal, an optional second sensor for measuring inert gas concentration in molten metal, a control unit for receiving the gas concentration measurement, and a rotor for dispersing, wherein the control unit balances the inert gas concentration correlated with the hydrogen concentration, and wherein the control unit automatically adjusts a hydrogen output.

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