Method for producing regenerated metal

Abstract

To provide a method for producing a regenerated metal that is safe and excellent in energy efficiency.SOLUTION: A method for producing a regenerated metal is characterized in that microwaves are applied to a metal containing metal scrap at least partially adhered with oil.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Some aspects of the present invention relate to methods for producing recycled metals. [Background technology]

[0002] Metal scrap (metal chips) generated during the manufacturing process of metal products usually contains oil (organic matter) such as cutting oil (coolant) or hydraulic oil. When remelting metal with oil attached, the work environment can be affected by gas generated from the oil or other remaining organic matter, and the yield can be reduced due to burn damage. Furthermore, when metal is compressed and briquetted with residual water in the oil, an event similar to a steam explosion can occur due to the expansion of water in the briquettes added to the molten metal.

[0003] Patent Document 1 discloses a method for melting aluminum chips, which involves a preheating step in which oil and water in a water-containing cutting oil that has adhered to the aluminum chips is evaporated or decomposed and removed before the aluminum chips are melted to obtain molten aluminum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-183712 Summary of the Invention [Problem to be solved by the invention]

[0005] When oils such as hydraulic oil and cutting oil and other organic substances adhering to metal scrap are removed by heating to volatilize them in advance, there is a possibility that toxic gases may be generated from the oil and other remaining organic substances, which can pose safety issues. Here, Patent Document 1 describes the use of a preheating device that preheats aluminum chips while isolating them from the atmosphere in order to evaporate or decompose and remove the oil and water in the water-containing cutting oil. In this way, in order to remove the cutting oil that has adhered to the chips before melting them, it is necessary to newly install a large device such as a heating furnace, and it is also expected that the device will need to be preheated and operated continuously, leaving room for improvement in terms of cost and energy efficiency.

[0006] Some aspects of the present invention have been made in view of these problems, and have an object to provide a method for producing recycled metals that is safe and has excellent energy efficiency. [Means for solving the problem]

[0007] A method for producing recycled metals according to some embodiments of the present invention is characterized by irradiating microwaves to metals including metal scrap having oil attached to at least a portion thereof. In the above-described method for producing recycled metal, it is preferable to irradiate the metal with microwaves while applying pressure. In the above-mentioned method for producing recycled metals, it is preferable that microwave irradiation is used to perform at least one of vaporization, removal, and conversion of at least a portion of the oil into a substance different from the oil. Furthermore, at least a portion of the metal may be sintered or melted by the microwave irradiation. The recycled metal may be obtained as an alloy. In the method for producing recycled metals described above, the metal scrap may be aluminum scrap. The oil may be cutting oil.

[0008] In some embodiments of the present invention, a method for producing recycled metals involves irradiating metal, including metal scrap having oil adhering to at least a portion thereof, with microwaves to vaporize, remove, or convert at least a portion of the oil into a substance other than the oil. In this process, the oil and / or one of the substances converted from at least a portion of the oil increase the microwave absorption efficiency, thereby more effectively heating the metal to be heated. As a result, for example, simple equipment can be used to suppress the release of toxic gases outside the system without the need for a new large-scale device such as a heating furnace. Furthermore, the removal of organic matter such as water and oil, vaporization, or conversion to other substances, and the production of recycled metals can be achieved with high energy efficiency. [Effects of the Invention]

[0009] According to some aspects of the present invention, it is possible to provide a method for producing recycled metals that is safe and energy efficient. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing an example of the relationship between microwave irradiation time and the temperature of an object to be heated (aluminum metal) in this embodiment. [Figure 2] FIG. 1 is a schematic diagram for explaining the effect of microwave irradiation on other remaining organic matter when oil is not attached (a) and when oil is attached ((b-1) to (b-3)). [Figure 3] FIG. 1 is a schematic diagram of scanning electron microscope (SEM) images illustrating the difference in remaining organic matter between the case where oil is attached (I) and the case where oil is not attached (II). DETAILED DESCRIPTION OF THE INVENTION

[0011] When metal (e.g., aluminum metal) with residual (adhered) moisture, oil, or other organic matter other than oil is redissolved as is, toxic gases such as benzene and toluene may be generated, and the quality of the regenerated metal may be reduced. Furthermore, it was anticipated that costs would increase if new heating equipment, centrifugal equipment, etc. were to be installed to remove oil, etc.

[0012] On the other hand, in some embodiments of the present invention, a method for producing recycled metals (hereinafter referred to as the present production method) involves irradiating microwaves to heat metal (e.g., aluminum metal) containing metal scrap with oil adhering to at least a portion of it. Therefore, compared with heating furnaces, centrifugal devices, and the like, smaller equipment is required, achieving low costs. Furthermore, the oil (or oil-derived conversion products) adhering to the metal can increase the microwave absorption efficiency, allowing for more efficient heating. Furthermore, as described below, when the oil is volatilized (evaporated and removed) by microwaves, any remaining organic matter (such as surfactants and silicone oil-derived organic matter) is also decomposed and removed, thereby suppressing the generation of harmful gases, etc.

[0013] Therefore, this manufacturing method does not require the installation of new large-scale equipment, and can regenerate metals such as aluminum metal safely and with excellent energy efficiency.

[0014] In this production method, "metal scrap having oil adhering to at least a portion thereof" typically includes, for example, cutting oil generated when cutting a casting, a mold release agent used to facilitate release from a forging die when producing a forged product, or metal chips having at least a portion thereof adhering to a mold release agent used to facilitate release from a casting die when producing a casting. Examples of cutting oils include mineral oil, animal and vegetable oils, artificially synthesized oils (hereinafter referred to as "synthetic oils"), mixtures of at least two of mineral oil, synthetic oil, and animal and vegetable oils, and mixtures containing at least two of mineral oil, synthetic oil, and animal and vegetable oils and at least one additive such as a surfactant, a rust inhibitor, or a preservative. The above mixtures can also be used as emulsions by diluting them with a solvent such as water during cutting. Furthermore, "metal scrap having oil adhering to at least a portion thereof" also includes metal chips generated when cutting metal products obtained by rolling, extruding, drawing, pressing, forging, etc. In this case, examples of the "oil" adhering to the metal chips include, in addition to or instead of the above-mentioned cutting oil, rolling oil used during rolling, extrusion oil used during extrusion, drawing oil used during drawing, press oil used during press processing, forging oil used during forging, and oils derived from machines or devices such as hydraulic oil, cooling oil, rust preventative oil or lubricating oil that leaks from a processing machine or processing device during metal processing or cutting and adheres to the metal chips. Examples of "metal scrap having oil attached to at least a portion thereof" include metal scrap, metal scrap, or metal powder generated without undergoing a cutting process. In this case, examples of "metal scrap having oil attached to at least a portion thereof" include rolling oil used in rolling, extrusion oil used in extrusion, drawing oil used in drawing, press oil used in pressing, forging oil used in forging, oils derived from machines or devices such as hydraulic oil, cooling oil, rust preventative oil, or lubricating oil leaked from processing machines or processing equipment when crushing metal products or processing metal, and metal scrap, metal scrap, or metal powder that have oil attached due to storage or preservation of metal products, metal scrap, metal scrap, or metal powder.

[0015] In this way, the "oil" adhering to the scrap metal may be any oil that can be adhering during the manufacturing process of metal products and recycled metals, and may contain additives such as surfactants, rust inhibitors, and preservatives. Furthermore, the "oil" adhering to the scrap metal may be at least partially converted into other substances during the manufacturing process, and these converted substances may adhere to the scrap metal.

[0016] Hereinafter, specific embodiments to which the methods for producing recycled metals according to some aspects of the present invention are applied will be described in detail with reference to the drawings. In the present manufacturing method, examples of metal scrap having oil attached to at least a portion thereof include those containing aluminum, iron, copper, brass, zinc, stainless steel, and lead. In this specification, the metal containing metal scrap will be described, focusing in particular on aluminum metal or alloys, including aluminum scrap. However, aspects of the present invention are not limited to the following embodiments. As described above, the metal scrap may contain, instead of aluminum, iron, copper, brass, zinc, stainless steel, lead, etc. Therefore, the following description of the method for producing recycled aluminum using aluminum metal, including aluminum scrap, can be directly applied to the method for producing recycled metal using other metals, including scrap of other metals, as described above. Furthermore, in this specification, "organic matter" includes all organic matter used or generated in the process of producing metal products and recycled metals, etc. Therefore, the organic matter includes organic matter derived from oil, surfactants, silicone oil, etc. Furthermore, for clarity of explanation, the following description and drawings have been simplified as appropriate.

[0017] This manufacturing method is a method for producing recycled metal from metal containing metal scrap, i.e., using the metal as a raw material. More specifically, the manufacturing method according to this embodiment is a method for producing recycled aluminum from aluminum metal containing aluminum scrap, i.e., using the aluminum metal as a raw material. Furthermore, oil such as cutting oil is adhered to at least a portion of the metal scrap. Metal scrap (e.g., aluminum scrap) refers to shavings (metal chips) generated during the manufacturing process of metal products, and contains metal or alloy. Metal scrap can contain a specific metal (e.g., aluminum) as its main component. Here, the term "main component" refers to the component that is contained in the largest amount among all components contained in the target (here, metal scrap). The content of the specific metal in metal scrap (e.g., aluminum in aluminum scrap) can be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more. Furthermore, the metal may contain other components in addition to the specific metal scrap, as long as the effects of some aspects of the present invention can be obtained. For example, the metal may be composed of metal scrap, (moisture,) oil such as cutting oil, and other residual organic matter. The content of metal scrap in the metal may be, for example, 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more. As described above, examples of residual organic matter other than oil include organic matter derived from surfactants and organic matter derived from silicone oil. However, the residual organic matter other than oil is not limited to these and may be any organic matter that is mixed in during the manufacturing process of metal products and the manufacturing process of recycled metals.

[0018] As described above, the oil adhering to the metal scrap can be any conventional oil used in the manufacturing process of metal products, such as cutting, and in the manufacturing process of recycled metals. For example, if the oil is cutting oil, it may be water-soluble or water-insoluble, and the type is not particularly limited. In addition, the effects of the manufacturing method according to this embodiment can be more pronounced in the case of aqueous cutting oil.

[0019] The amount of oil attached to the metal (content) can be set as appropriate within a range that achieves the effects of several aspects of the present invention, but is preferably 1 mass % or more, and more preferably 2 mass % or more, relative to the mass of the metal (100 mass %) (including the content of attached substances such as oil). If the amount of attached oil is 1 mass % or more, the microwave absorption efficiency can be further improved, and oil, moisture, and other remaining organic matter can be more efficiently removed. The amount of oil attached is preferably 5% by mass or less, more preferably 4% by mass or less, relative to the mass of the metal (including the content of oil and other attached substances). If the amount of oil attached is 5% by mass or less, it is easy to prevent oil and other organic substances from remaining on the metal.

[0020] The amount of organic matter other than oil and moisture adhering to the metal can be appropriately set within a range that achieves the effects of several aspects of the present invention. However, the total amount of these other organic matter and moisture adhering materials other than oil (including the content of the adhering materials) is preferably 1% by mass or more, and more preferably 2% by mass or more, relative to the mass (100% by mass) of the metal (including the content of the adhering materials). If the amount of these other organic matter adhering materials other than oil is 1% by mass or more, the microwave absorption efficiency can be further improved, and oil, moisture, and other remaining organic matter can be more efficiently removed. The total amount of these non-oil deposits (including the content of the deposits) is preferably 5% by mass or less, more preferably 4% by mass or less, relative to the mass of the metal. If the amount of non-oil deposits is 5% by mass or less, it is easy to prevent oil and other organic substances from remaining on the metal.

[0021] In this manufacturing method, microwaves are irradiated onto metal having oil adhering to at least a portion thereof. FIG. 1 shows a graph illustrating an example of the relationship between microwave irradiation time and the temperature of the object (aluminum metal) to be heated in this embodiment. Specifically, FIG. 1 is a graph illustrating the relationship between the irradiation time (seconds) when 700 W of microwaves (MW: Microwave) are irradiated onto the object (object to be heated) and the temperature (°C) of the base with which the underside of the object comes into contact. Here, the base temperature of the underside of the object to be heated can be considered the temperature of the object (object to be heated). Also, symbol I is a graph for the case where aluminum metal having oil adhering thereto is used as the object to be heated. Furthermore, symbol II is a graph for the case where aluminum metal having no oil adhering thereto is used as the object to be heated. In the embodiment shown in FIG. 1, cutting oil is used as the oil.

[0022] As shown in Figure 1, when aluminum metal with oil attached is used, the temperature of the heated object rises more in Case I than when aluminum metal without oil attached is used, even with the same irradiation time. In other words, Figure 1 shows that when oil is attached to aluminum metal, aluminum metal can be heated to high temperatures efficiently using microwaves.

[0023] Next, Fig. 2 shows a schematic diagram for explaining the effect of microwave irradiation on the remaining organic matter when there is no oil (a) and when there is oil ((b-1) to (b-3)). Here, in the embodiment shown in Fig. 2, cutting oil 3 containing water is used as the oil. As shown in Figure 2(a), when microwaves are applied to aluminum metal 1 that does not have cutting oil 3 containing water attached, water (H2O) volatilizes (evaporates) at approximately 100°C. However, residual organic matter 2 derived from the silicone oil remains on the aluminum metal 1 even after microwave irradiation. On the other hand, when microwaves are applied to aluminum metal 1 with cutting oil 3 attached, as shown in Figure 2(b-1), the microwaves act preferentially on moisture (e.g., contained in the cutting oil attached to the aluminum metal), causing the moisture to evaporate at around 100°C. At the same time, as shown in Figure 2(b-2), the interaction between the polar groups 3a of the cutting oil 3, which includes polar groups 3a, lipophilic groups 3b, and an oil film 3c, and the aluminum metal surface is strengthened, promoting the heating effect and vaporizing or decomposing and removing part of the remaining organic matter 2. Furthermore, when the heating temperature reaches around 300°C due to microwave irradiation, the remaining organic matter (e.g., organic matter derived from silicone oil) is decomposed and removed (vaporized), yielding aluminum metal 1, as shown in Figure 2(b-3). As described above, the cutting oil in this embodiment may have a structure such as a polar group, a lipophilic group, and an oil film, but in some aspects of the present invention, in addition to the above-mentioned cutting oil, it may also be a mixture containing polar molecules and hydrophobic molecules, or a mixture of these may further contain a solvent such as water, a surfactant, an antiseptic, or a rust inhibitor, or it may be various oils used in metal processing such as rolling, pressing, extrusion, or drawing. In this embodiment, the term "polar group" refers to a portion of a molecule or a molecular aggregate that contains an element that is more electronegative than carbon, such as oxygen or nitrogen, and the term "lipophilic group" refers to a portion of a molecule or a molecular aggregate that is mainly composed of carbon and hydrogen and that is relatively less polar than the portion containing an element that is more electronegative than carbon.

[0024] In this way, in this manufacturing method, the oil adhering to the metal increases the microwave absorption efficiency and also has the effect of promoting the decomposition and removal of residual organic matter. In the above-described embodiment and related explanations, it has been described that a heating effect can be obtained by irradiating microwaves to a metal with oil containing polar groups attached thereto, but a heating effect can also be obtained by irradiating microwaves to a metal with oil or organic matter that does not contain polar groups or has low polarity. For example, when a metal contains metal particles and the metal particles are in contact with adjacent metal particles, localized heating by microwaves occurs at the contact points between the metal particles, and the oil or organic matter present near the contact points is converted into a substance with high microwave absorption efficiency by carbonization or the like, which may secondarily improve the efficiency of microwave absorption.

[0025] FIG. 3 shows schematic diagrams of scanning electron microscope (SEM) images illustrating the difference in remaining organic matter between the case where oil is attached (I) and the case where oil is not attached (II). In the embodiment shown in FIG. 3, cutting oil is used as the oil. As shown in FIG. 3(a), in case I where oil-attached aluminum metal was used, no white layer 4, which is presumed to be organic matter such as a mold release agent that was attached during casting, was observed. On the other hand, in case II where oil-free aluminum metal was used, as shown in an enlarged view in FIG. 3(b), more of the white layer 4 was observed than in case I. This also shows that by using microwave heating and drying to heat aluminum metal (briquette form in Figure 3) with oil adhering to at least some of its surfaces, it is possible to efficiently remove other residual organic matter adhering to the aluminum chips inside. Furthermore, microwave heating and molding of loosely packed oil-adhered aluminum metal results in the chip interface becoming homogeneous with the chips themselves, which is expected to improve yield when used as a briquette for melting. Furthermore, aluminum metal briquettes with oil adhering can prevent chip loss and achieve higher density compared to briquettes without oil.

[0026] In this manufacturing method, the frequency, power, and irradiation time of the microwave are not particularly limited and can be appropriately set within a range that achieves the effects of several aspects of the present invention. For example, the microwave frequency can be 2.45 GHz and the power can be 1.2 kW.

[0027] In addition, in this manufacturing method, it is preferable to irradiate microwaves to the metal having oil attached thereto while applying pressure. Note that in this manufacturing method, the metal having oil attached thereto may be irradiated with microwaves in a compressed state by applying pressure before being irradiated with microwaves. Furthermore, pressure may be applied to the metal in parallel with the microwave irradiation. Furthermore, the metal may be compressed by applying pressure after being irradiated with microwaves. By applying microwaves while applying pressure, oil such as cutting oil, moisture, other residual organic matter, etc. that has been attached are efficiently volatilized and removed. Therefore, it is preferable to apply pressure (compress) the metal having oil attached thereto before or in parallel (simultaneously) with the microwave irradiation.

[0028] By irradiating microwaves, at least a portion of oil, such as cutting oil, adhering to metal can be vaporized or removed. Furthermore, the oil may be converted into a different substance, and may be vaporized or removed after the conversion. Examples of reaction modes for converting at least a portion of oil into a different substance include carbonization, ceramicization, and metallization. Furthermore, with regard to organic substances other than oil, at least a portion of them can also be vaporized or removed by irradiating microwaves. Furthermore, the organic substances other than oil may be converted into a different substance, and may be vaporized or removed after the conversion. Furthermore, the metal (at least a part of it) can be sintered or melted by the microwave irradiation.

[0029] The recycled metal (for example, recycled aluminum) obtained by this production method may be in the form of, for example, recycled metal ingots or recycled metal melt, and the form is not particularly limited.

[0030] The manufacturing method may include the following steps. A step of preparing metal including metal scrap (e.g., aluminum scrap) and having oil attached to at least a portion thereof (preparation step). A step of irradiating the metal with microwaves (irradiation step). A process of compressing the metal by applying pressure (compression process). Here, the compression step may be performed between the preparation step and the irradiation step, may be performed in parallel with the irradiation step, or may be performed after the irradiation step. However, from the viewpoint of further exerting the effects according to some aspects of the present invention, it is preferable that the compression step be performed between the preparation step and the irradiation step or in parallel with the irradiation step.

[0031] The present manufacturing method may also include the following steps. A step of adjusting the amount of oil adhering to the metal prior to the irradiation step (adjustment step). The adjusting step can be, for example, any of the following steps. A process of removing a portion of the oil adhering to the metal prior to the irradiation process (oil pre-removal process). A step of further applying oil to the metal prior to the irradiation step (oil application step). As described above, the amount of oil attached to the metal, including the content of oil and other adhering substances, is preferably 1 to 5 mass %. Therefore, in order to keep the amount of oil attached within this range, the amount of oil attached may be removed using a conventionally known method before microwave irradiation, or new oil may be attached.

[0032] In the irradiation step, for example, the oil may absorb the microwaves and be heated, thereby vaporizing or removing at least a portion of the oil or organic matter other than oil. Furthermore, the oil or organic matter other than oil may be converted into a different substance by the heating, and may be vaporized or removed after the conversion. Furthermore, in the irradiation step, at least a portion of the metal may be sintered or melted.

[0033] In this way, in this manufacturing method, by irradiating microwaves (for example, under pressure) to oil-adhered metal chips discharged during the manufacturing process of metal products (e.g., aluminum products) or the manufacturing process of recycled metals, the oil and moisture adhering to the chips can be efficiently volatilized and removed. Furthermore, when microwaves are irradiated, the oil adhering to the metal increases the microwave absorption efficiency, allowing for effective heating. As described above, this manufacturing method can suppress the release of toxic gases outside the system even when oil is attached to the metal chips, and can provide highly energy-efficient recycled metal ingots. This effect is not limited to aluminum, but can also be applied to other metals. [Example]

[0034] Some aspects of the present invention will be explained in more detail below using experimental examples, but the scope of the present invention is not limited to these examples.

[0035] [Example 1] A pressure of 139 MPa was applied to aluminum chips (ADC12 alloy chips) with cutting oil adhering to them, and a cylindrical green compact with a diameter of 30 mm and a height of 30 mm was formed. This green compact was irradiated with microwaves (frequency: 2.45 GHz, output: 1.2 kW) and heated until the temperature inside the aluminum chips reached 500°C. The experiment was conducted in a position where a SiC plate was in contact with the green compact during microwave irradiation.

[0036] [Comparative Example 1] An experiment was carried out in the same manner as in Example 1, except that a hot plate (output: 1.2 kW) was used instead of microwaves to heat the aluminum chips until the internal temperature reached 500°C. Table 1 shows the time (minutes) until the volatilization of organic components such as benzene and toluene was completed, whether or not oily smoke was generated by the aluminum briquette, and the amount of carbon monoxide and carbon dioxide generated (during heating) in Example 1 and Comparative Example 1. Here, since gases such as carbon monoxide and carbon dioxide, as well as benzene and toluene, are considered to be environmentally harmful gases, it is desirable to reduce the amount of each gas generated and remove them in a short time. In this experimental example, a suction pump was used to recover generated gases using a gas recovery pack when the temperatures of the bottom of the microwave-absorbing material were 100°C and 300°C. As a result, in Example 1, recovery of surfactant-derived organic matter was confirmed at 100°C, and recovery of surfactant-derived organic matter and silicone oil-derived organic matter was confirmed at 300°C. Although not described in this experimental example, when aluminum chips (ADC12 alloy chips) with no cutting oil attached were used to similarly check the generated gases at 100°C and 300°C, recovery of surfactant-derived or silicone oil-derived organic matter was not confirmed at either temperature.

[0037] [Table 1]

[0038] As shown in Table 1, in Example 1 using microwaves, the time to complete evaporation of organic components was shorter, no oily smoke was generated, and the amount of environmentally harmful gases such as CO and CO2 generated was kept low compared to Comparative Example 1 using a hot plate.

[0039] For CO and CO2 detection, a gas analyzer equipped with a laser detection inline type or various gas sensors capable of measuring gas concentrations in real time was used. The point at which the internal temperature of the aluminum chips reached 450°C and no visible smoke or other generation of the above was observed was taken as the point at which the volatile components of the cutting oil had disappeared.

[0040] The invention according to the present embodiment described above makes it possible to provide a method for producing recycled metals, including recycled aluminum, that is safe and has excellent energy efficiency, without the need to install new large-scale equipment.

[0041] The aspects of the present invention are not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0042] 1. Aluminum metal 2 Residual organic matter 3 Cutting oil 3a polar group 3b Lipophilic group 3c oil slick 4 White layer I. When using aluminum metal with oil on it II. When using aluminum metal with no oil attached

Claims

1. A method for producing recycled metals, comprising irradiating microwaves onto metals including metal scrap having oil attached to at least a portion thereof.

2. The method for producing recycled metal according to claim 1, wherein the metal is irradiated with microwaves while being subjected to pressure.

3. The method for producing recycled metals according to claim 1 or 2, wherein the microwave irradiation causes at least a portion of the oil to be vaporized, removed, or converted into a substance different from the oil.

4. The method for producing recycled metal according to claim 1 or 2, wherein at least a portion of the metal is sintered or melted by the microwave irradiation.

5. The method for producing recycled metals according to claim 1 or 2, wherein the recycled metals are obtained as alloys.

6. The method for producing recycled metals according to claim 1 or 2, wherein the metal scrap is aluminum scrap.

7. The method for producing recycled metals according to claim 1 or 2, wherein the oil is cutting oil.

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