Patent Application
20250178076
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 H2 concentration in the molten boundary layer and the partial pressure of H2 in 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.
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.
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.
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.
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
With reference to
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 306a, two lid body side walls 306b and a lid body rear wall (not shown), in addition to the lid body roof 306d.
The front access door 307a comprises a substantial area on the dome lid front wall 306a and can consequently be very heavy. In order to more easily open the front access door 307a. A hydraulic cylinder assembly 8 is provided. The side access doors 307b are smaller than the front access door 307a and much more easily handled by workmen and handles 309 are therefore provided to open the side access doors 307b, without the need for mechanical assistance.
Mounted on the lid body roof 306d are two rotary gas dispersion devices 312, one for each refining compartment or stage.
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
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.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2023/013233 | 2/16/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63311309 | Feb 2022 | US |
