Patent Application
20240117468
The present disclosure relates to methods for processing machining chips comprising aluminum-lithium alloy.
Machining an aluminum ingot to produce a part can generate machining chips as a byproduct. Disposing of the machining chips can be costly. Recycling or otherwise repurposing the machining chips presents challenges.
One non-limiting aspect according to the present disclosure is directed to a method for processing aluminum-lithium alloy chips. The method includes obtaining machining chips produced during machining of an aluminum-lithium alloy using a processing fluid. The method comprises cleaning a volume of the machining chips to remove at least a portion of processing fluid from the machining chips and thereby provide cleaned machining chips. A volume of the cleaned machining chips is compressed to provide a compact comprising a density of at least 70%, at least 80%, at least 90%, or at least 95% of a full theoretical density of the aluminum-lithium alloy. In certain non-limiting embodiments of the method, cleaning a volume of machining chips comprises at least one of contacting the machining chips with an aqueous solution to dissolve processing fluid on the machining chips into the aqueous solution, and heating the machining chips in an inert atmosphere to pyrolize processing fluid on the machining chips. In certain non-limiting embodiments of the method, cleaning a volume of machining chips comprises at least one of contacting the machining chips with an aqueous solution to dissolve processing fluid on the machining chips into the aqueous solution. In various non-limiting embodiments of the method, compressing the volume of the cleaned machining chips comprises processing the volume of chips by at least one of continuous rotary extrusion, conform extrusion, equal channel angular processing, equal channel angular extrusion, high pressure torsion, and shear assisted processing and extrusion. In certain non-limiting embodiments of the method, the aluminum-lithium alloy comprises 0.1% to 5% lithium by weight, aluminum, and impurities.
A further non-limiting aspect according to the present disclosure is directed to a method for processing aluminum-lithium alloy chips. The method includes obtaining machining chips produced during machining of an aluminum-lithium alloy. A volume of the machining chips is compressed to provide a compact comprising a density of at least 70%, at least 80%, at least 90%, or at least 95% of a full theoretical density of the aluminum-lithium alloy. In various non-limiting embodiments of the method, compressing the volume of the cleaned machining chips comprises processing the volume of chips by at least one of continuous rotary extrusion, conform extrusion, equal channel angular processing, equal channel angular extrusion, high pressure torsion, and shear assisted processing and extrusion. In certain non-limiting embodiments of the method, the aluminum-lithium alloy comprises 0.1% to 5% lithium by weight, aluminum, and impurities.
A further non-limiting aspect according to the present disclosure is directed to a cohesive compact comprising aluminum-lithium alloy machining chips and which has a density that is at least 70%, at least 80%, at least 90%, or at least 95% of a full theoretical density of the aluminum-lithium alloy. In certain non-limiting embodiments, the cohesive compact is made by a method according to the present disclosure. In certain non-limiting embodiments, the aluminum-lithium alloy comprising the aluminum-lithium alloy machining chips includes 0.1% to 5% lithium by weight, aluminum, and impurities.
A further non-limiting aspect according to the present disclosure is directed to a method for making an aluminum-lithium alloy. The method comprises introducing a cohesive compact comprising aluminum-lithium alloy machining chips and which has a density that is at least 70%, at least 80%, at least 90%, or at least 95% of a full theoretical density of the aluminum-lithium alloy into a molten bath of an aluminum-lithium alloy to form a molten alloy. In certain non-limiting embodiments, the cohesive compact is made by a method according to the present disclosure. Various non-limiting embodiments of the method further comprise solidifying at least a portion of the molten alloy to form an aluminum-lithium ingot or other solid form from the molten alloy.
It is understood that the inventions disclosed and described in this specification are not limited to the aspects summarized in this Summary. The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of various non-limiting and non-exhaustive aspects according to this specification.
The features and advantages of the examples, and the manner of attaining them, will become more apparent, and the examples will be better understood, by reference to the following description taken in conjunction with the accompanying drawing, wherein:
The FIGURE is a block diagram of a non-limiting embodiment of a method according to the present disclosure for recycling chips produced during machining of an aluminum-lithium alloy.
The exemplifications set out herein illustrate certain non-limiting embodiments, in one form, and such exemplifications are not to be construed as limiting the scope of the appended claims in any manner.
Aluminum-lithium alloys can have desirable properties, such as high strength to weight. In particular, aluminum-lithium alloys may have a lower density than conventional aluminum alloys and, therefore, are desirable for reducing the weight of aerospace components. Parts made from aluminum-lithium alloys may be substantially more costly than parts made of made from alloys that do not contain lithium. Lithium is a costly alloying additive due to the intrinsic cost of lithium, and aerospace and automotive parts produced from aluminum-lithium alloys may require extensive machining, which generates a high volume of machining chips. Machining chips produced during machining of aluminum-lithium alloys may be unsuitable for re-melting because of the large surface area of a volume of the chips and resulting high melt loss during re-melting. Additionally, due to the presence of lithium, the machining chips may require specialized processing and may need to be processed separately from, for example, other aluminum alloys. The present disclosure provides a method for processing machining chips comprising aluminum-lithium alloys that can improve the recyclability of the machining chips, thereby reducing material losses from machining operations and recovering a processing stream with a high material value.
The attached FIGURE includes a block diagram of a non-limiting embodiment of a method according to the present disclosure for recycling chips produced during machining of aluminum-lithium alloy. As shown, a volume of machining chips comprising an aluminum-lithium alloy may result, for example, from machining an aluminum-lithium alloy ingot or other solid form to produce a part such as, for example, an aerospace part or an automotive part at 102. In certain non-limiting embodiments of the method, a processing fluid may be used during the machining. The volume of loose machining chips can comprise a density no greater than 50% of the full theoretical density of the aluminum-lithium alloy. In certain non-limiting embodiments, the volume of loose machining chips can comprise a density no greater than 45%, no greater than 40%, or no greater than 35% of the full theoretical density of the aluminum-lithium alloy.
As used herein, an “aluminum-lithium alloy” is an alloy comprising 0.1% to 5% lithium by weight, aluminum, and impurities. In various forms, an aluminum-lithium alloy may comprise 0.2% to 2% lithium by weight and a balance of aluminum and impurities. In various non-limiting embodiments, the aluminum-lithium alloy can comprise at least 0.5% lithium by weight, such as, for example, at least 1% up to 5% lithium, at least 1.5% up to 5% lithium, at least 2% up to 5% lithium, or at least 2.5% up to 5% lithium, all by weight. As is known in the art, certain aluminum-lithium alloys may include additional intentional alloying additions such as, for example, copper, manganese, magnesium, zinc, titanium, zirconium, silicon, iron, chrome, and silver. Commercially available aluminum-lithium alloys presently include 2099, 2199, 2050, 2055, 2060, 2090, 8090, 2195, 2397, and 2070.
As used herein, “full theoretical density” means the density of the alloy corresponding to the limit attainable in a fully dense product without pores as calculated per the Aluminum and Aluminum Alloy Density Calculation Procedure on page 2-13 of “Aluminum standards and data 2017”, published by The Aluminum Association, Inc.
Aluminum and aluminum alloy machining may utilize a processing fluid for lubricating (e.g., lubricant) and/or cooling and/or to facilitate removal of machining chips produced by the machining operation. Again referring to the accompanying FIGURE, the illustrated method further comprises cleaning the machining chips to remove at least a portion of processing fluid from surfaces of the machining chips, thereby providing cleaned machining chips, 104. The processing fluid can comprise, for example, a conventional cutting fluid or another substance employed to facilitate machining of an ingot or other solid form comprising aluminum-lithium alloy. The processing fluid may inhibit compression of the machining chips into a compact, and the processing fluid also may be an undesirable contaminant if incorporated into an alloy produced from starting materials including the machining chips.
Cleaning the machining chips to remove at least a portion of processing fluid from surfaces of the machining chips can comprise, for example, one or both of contacting the machining chips with an aqueous solution to dissolve processing fluid on surfaces of the machining chips, and heating the machining chips in an inert atmosphere to pyrolize processing fluid on the machining chips (e.g., a pyrolysis process). Contacting the machining chips with an aqueous solution to dissolve processing fluid on surfaces of the machining chips can result in at least a portion of the processing fluid dissolving in the aqueous solution. In various non-limiting embodiments, the aqueous solution can have a pH of 1 to 14, such as, for example, 1 to 5, 6 to 7, 7 to 8, 6 to 8, or a pH of 8 to 14. In certain non-limiting embodiments, the aqueous solution can comprise water and one or more cleaning or solvating agents such as, for example, a detergent compound, a solvent, and/or a surfactant. In certain non-limiting embodiments, cleaning the machining chips reduces a carbon content on surfaces of the machining chips.
In various non-limiting embodiments, aluminum machining does not use a processing fluid and the machining chips may not comprise processing fluid. Therefore, cleaning the machining chips, step 104, can be optional.
Optionally, prior to compaction, machining chips are granulated (i.e., reduced in size by mechanical processing) to reduce an average size of the chips and/or to provide a substantially uniform size distribution of the machining chips, 106. For example, prior to compaction, the machining chips can be reduced in size by grinding the chips using a grinding apparatus. In certain non-limiting embodiments of the method in which the machining chips are cleaned to remove at least a portion of processing fluid from surfaces of the machining chips, the machining chips are granulated prior to the cleaning the machining chips at 104. In other non-limiting embodiments, the machining chips are granulated after cleaning the machining chips at 104. Providing the machining chips with a substantially uniform size distribution can facilitate compression of the machining chips into a compact. As used herein, a “substantially uniform size distribution” means that at least 90% of the smallest machining chips comprise a longest dimension that is at least 50% of the longest dimension of the largest machining chips. In certain embodiments, for example, the granulated machining chips can have a size distribution in which at least 90% of the machining chips have a longest dimension ranging no more than 5 mm from each other, such as, for example, no more than 2 mm from each other, or no more than 1 mm from each other.
In various non-limiting embodiments, the machining chips are granulated to comprise a longest size dimension no greater than 10 mm, such as, for example, no greater than 8 mm, no greater than 6 mm, or no greater than 4 mm. In certain non-limiting embodiments, the machining chips are granulated to comprise a longest size dimension of at least 0.1 mm, at least 1 mm, at least 2 mm, or at least 3 mm. For example, in certain non-limiting embodiments, the machining chips can be granulated to comprise a longest size dimension a size of 0.1 mm to 10 mm, such as, for example, 1 mm to 10 mm, 1 mm to 8 mm, or 3 mm to 4 mm.
As further shown in the FIGURE, non-limiting embodiments of a method according to the present disclosure further comprise compressing a volume of the cleaned machining chips (which, optionally, have been cleaned and/or granulated) to provide a cohesive compact comprising a density that is at least 70% of the full theoretical density of the aluminum-lithium alloy comprising the chips, 108. As used herein, “cohesive” means the object stays together when it is not handled, and that it can be handled without falling apart readily. The density of the compact produced by compacting a mass of the machining chips will be greater than the density of the mass of machining chips prior to compaction. Compressing the machining chips to form the compact can involve any suitable forming technique whereby a compressive force is applied to a mass of the machining chips to form a cohesive compact having a density greater than a density of the mass of machining chips prior to compaction. Such forming techniques may include one or more of continuous rotary extrusion, conform extrusion, equal channel angular processing, equal channel angular extrusion, high pressure torsion, and shear assisted processing and extrusion. One having ordinary skill will recognize or can determine additional forming techniques by which a cohesive compact of increased density can be formed by applying compressive force to a mass of machining chips.
In various non-limiting embodiments, compressing a volume of the machining chips comprises continuous rotary extrusion. In certain non-limiting embodiments, the a density of the compact is at least 80% of a full theoretical density of the aluminum-lithium alloy, such as, for example, at least 85% of a full theoretical density, at least 90% of a full theoretical density, at least 95% of a full theoretical density, at least 99% of a full theoretical density, or at least 99.9% of a full theoretical density of the aluminum-lithium alloy. Increasing the density can reduce the volume of air present in the compact, thereby increasing the processability of the compact and reducing potential reactivity concerns between atmospheric oxygen and lithium present in the machining chips. Additionally, increasing density of the compact can reduce material losses during melting of the compact.
Accordingly, a non-limiting aspect of the present disclosure also is directed to a cohesive compact comprising aluminum-lithium alloy machining chips (which, optionally, have been cleaned and/or granulated) and which has a density that is at least 70%, at least 80%, at least 90%, or at least 95% of a full theoretical density of the aluminum-lithium alloy. The compact may be used as a feed material in producing aluminum-lithium alloys in the form of ingots or other solid forms. In various non-limiting embodiments, the compact is made by a method according to the present disclosure.
A further aspect according to the present disclosure is directed to a method of making an alloy. Again referring to the FIGURE, in non-limiting embodiments of the method, a compact comprising aluminum-lithium alloy machining chips (which, optionally, have been cleaned and/or granulated) and having a density that is at least 70% of a full theoretical density of the aluminum-lithium alloy is introduced into a molten bath of an aluminum-lithium alloy to form a molten alloy, 110. The compact can comprise a shape with a reduced surface area compared to chips, such as, for example, a rod, a triangle, a semi-continuous coil, or a combination thereof. In various non-limiting embodiments of the method, the compact is made by a method according to the present disclosure. At least a portion of the molten alloy can be solidified to form an aluminum-lithium ingot or another solid form, 112. Thereafter, in certain non-limiting embodiments, the aluminum-lithium ingot (or other solid form) can be machined to form a part, 102. In certain non-limiting embodiments, the part can be an aerospace part or an automotive part.
The present disclosure will be more fully understood by reference to the following examples, which provide illustrative non-limiting aspects of the disclosure. It is understood that the disclosure described in this specification is not necessarily limited to the examples described in this section.
Milling machining chips that contained 16% coolant by weight were processed through a vertical axis crusher (VAC II available from PRAB Kalamazoo, Michigan) followed by centrifuging in a diagonal shaft wringer (available from PRAB Kalamazoo, Michigan) to form processed machining chips. The coolant in the processed machining chips was reduced to less than 2% by weight. The vertical axis crusher broke up long, stringy, portions of the machining chips and the wringer removed coolant from the machining chips. The processed machining chips were then screened through a classifying sieve to achieve a uniform size less than 3 mm by 3 mm of the processed machining chips. The uniform machining chips were then fed into a continuous rotary extrusion machine (available from CONFEX, Dorset, United Kingdom) to form a compact of a rod 10 mm in diameter that was 98% dense. The rod density was calculated by weighing a 36″ section of 10 mm diameter rod and comparing the result to the calculated weight of a 10 mm diameter rod 36″ long that was 100% dense.
Milling machining chips that contained 16% coolant by weight were washed in a multi-step process. The multi-step process removed the free coolant by gravity drying the milled machine chips on 100 mesh screens. The dried machining chips were then washed twice using mineral spirits (Exxsol) in a ribbon mixer. The mineral spirits were removed from the machining chips using a 100-mesh basket centrifuge after each wash. The machining chips were then placed in steel drums and processed through a vacuum furnace for 8 hours, operating at 400° F. and 2-5 torr. This multi-step process reduced the coolant on the machining chips to less than 0.05%. The machining chips were then ground to a uniform size of less than 3 mm using a Hippo hammer mill. The uniform machining chips were then fed into a continuous rotary extrusion machine to form a compact of a rod 10 mm in diameter that was greater than 98% dense. The rod density was calculated by weighing a 36″ section of 10 mm diameter rod and comparing the result to the calculated weight of a 10 mm diameter rod 36″ long that was 100% dense.
Sections of rods of Example 1 and Example 2 that were 36 inches in length were melted down in a non-inerted, 25 lb. capacity induction melter, containing a bath of prime aluminum plus 1% Lithium. The rods from Example 1 and Example 2 sunk below the surface oxide layer and readily melted.
A typical drawback of feeding machining chips into a melting furnace is their tendency to float on the top oxide layer. Due to the high surface area of untreated machining chips, they tend to oxidize and convert to dross instead of melting if not submerged quickly. This phenomenon can be even more pronounced as the oxide layer on an aluminum melt is thicker with aluminum-lithium alloys, making machining chip scrap more likely to float on the surface and oxidize instead of melting. Reducing the surface area of the machining chips by forming a compact increasing the ability of the compact to be submerged in the molten bath compared to untreated machining chips. The ability to sink the molten bath can be achieved by using large diameter (e.g., at least 5 mm, at least 10 mm, at least 25 mm) rods or bars. A smaller diameter rod or bar that is continuously extruded into a long length (e.g., at least 100 feet, at least 1000 feet) and coiled, can have enough mass to sink when added to the molten bath.
The residual level of contaminants on the rods can dictate the amount of extruded machining chips that can be added to a furnace charge. For example, the rod fabricated from Example 1 contained 15 ppm of sodium contamination and 10% of the melt furnace charge could be added as a compact of machining chips assuming a nominal 3 ppm sodium content from the prime aluminum and lithium of the furnace charge. If the rod contained 10 ppm of sodium contamination, 20% of the melt furnace charge could be added as a compact of machining chips. If the rod contained 5 ppm of sodium contamination, 58% of the melt furnace charge could be added as a compact of machining chips.
The following numbered clauses are directed to various non-limiting embodiments and aspects according to the present disclosure.
1. A method for processing aluminum-lithium chips, the method comprising:
16. A method for processing aluminum-lithium chips, the method comprising:
Various non-limiting embodiments are described and illustrated herein to provide an overall understanding of the structure, function, and use of the disclosed methods and articles. The various non-limiting embodiments described and illustrated herein are non-limiting and non-exhaustive. Thus, an invention is not limited by the description of the various non-limiting and non-exhaustive embodiments disclosed herein. Rather, the invention is defined solely by the claims. The features and characteristics illustrated and/or described in connection with various non-limiting embodiments may be combined with the features and characteristics of other non-limiting embodiments. Such modifications and variations are intended to be included within the scope of this specification. As such, the claims may be amended to recite any features or characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Further, Applicant reserves the right to amend the claims to affirmatively disclaim features or characteristics that may be present in the prior art. The various embodiments disclosed and described in this specification can comprise, consist of, or consist essentially of the features and characteristics as variously described herein.
Any references herein to “various embodiments,” “some embodiments,” “one embodiment,” “an embodiment,” or like phrases mean that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” “in an embodiment,” or like phrases in the specification do not necessarily refer to the same embodiment. Furthermore, the particular described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation. Such modifications and variations are intended to be included within the scope of the present embodiments.
In this specification, unless otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term “about,” in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described herein should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Also, any numerical range recited herein includes all sub-ranges subsumed within the recited range. For example, a range of “1 to 10” includes all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Also, all ranges recited herein are inclusive of the end points of the recited ranges. For example, a range of “1 to 10” includes the end points 1 and 10. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited. All such ranges are inherently described in this specification.
The grammatical articles “a,” “an,” and “the,” as used herein, are intended to include “at least one” or “one or more,” unless otherwise indicated, even if “at least one” or “one or more” is expressly used in certain instances. Thus, the foregoing grammatical articles are used herein to refer to one or more than one (i.e., to “at least one”) of the particular identified elements. Further, the use of a singular noun includes the plural and the use of a plural noun includes the singular, unless the context of the usage requires otherwise.
One skilled in the art will recognize that the herein described articles and methods, and the discussion accompanying them, are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific examples/embodiments set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components, devices, operations/actions, and objects should not be taken to be limiting. While the present disclosure provides descriptions of various specific aspects for the purpose of illustrating various aspects of the present disclosure and/or its potential applications, it is understood that variations and modifications will occur to those skilled in the art. Accordingly, the invention or inventions described herein should be understood to be at least as broad as they are claimed and not as more narrowly defined by particular illustrative aspects provided herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/012740 | 1/18/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63139007 | Jan 2021 | US |
