Method for producing regenerated metal

Abstract

A method for producing a regenerated metal according to the present disclosure is characterized in that a metal containing metal scrap at least partially adhered with oil is irradiated with microwaves. The method for producing a regenerated metal according to the present disclosure makes it possible to provide a method for producing a regenerated metal that is safe and excellent in energy efficiency.

Description

Recycled metal manufacturing method

[0001] The present disclosure relates to a method for producing recycled metals.

[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, gases generated from the oil or other remaining organic matter can affect the working environment and can reduce yields due to burnout. Furthermore, when metal is compressed and briquetted with residual water in the oil, the water in the briquettes can suddenly expand when added to the molten metal.

[0003] Patent Document 1 discloses a method for melting aluminum chips, which involves a preheating step of evaporating or decomposing and removing oil and water in a water-containing cutting oil that has adhered to the aluminum chips beforehand, before melting the aluminum chips to obtain molten aluminum.

[0004] Japanese Patent Application Laid-Open No. 2021-183712

[0005] When oils, such as hydraulic oils and cutting oils, and other organic matter adhering to scrap metal are removed by heating to volatilize them in advance, toxic gases may be generated from the oils and other remaining organic matter, posing safety issues. 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 the oil and water in aqueous cutting oil. Thus, removing the cutting oil adhering to the chips before melting them requires the installation of a large device, such as a heating furnace. Furthermore, it is anticipated that the device will require preheating and continuous operation, leaving room for improvement in terms of cost and energy efficiency.

[0006] The present disclosure has been made in consideration of these problems, and aims to provide a method for producing recycled metals that is safe and has excellent energy efficiency.

[0007] The method for producing recycled metals according to the present disclosure is characterized in that microwaves are irradiated onto metals including metal scrap having oil adhering to at least a portion thereof. Furthermore, in the above-described method for producing recycled metals, it is preferable that microwaves are irradiated onto the metal under pressure. In the above-described method for producing recycled metals, it is preferable that microwave irradiation be used to vaporize, remove, or convert at least a portion of the oil into a substance different from the oil. Furthermore, the microwave irradiation may sinter or melt at least a portion of the metal. The recycled metal may be obtained as an alloy. In the above-described method for producing recycled metals, the metal scrap may be aluminum scrap. Furthermore, the oil may be cutting oil.

[0008] In the method for producing recycled metals according to the present disclosure, microwaves are applied to metals, including metal scraps having oil adhering to at least a portion thereof, 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, organic substances such as water and oil can be removed, vaporized, or converted into other substances, and recycled metals can be produced with high energy efficiency.

[0009] According to aspects of the present disclosure, a method for producing recycled metals that is safe and highly energy efficient can be provided.

[0010] 1 is a graph showing an example of the relationship between microwave irradiation time and the temperature of the heated body (aluminum metal) in this embodiment. It is a schematic diagram for explaining the influence of microwave irradiation on other remaining organic matter in the case where oil is not attached (a) and the case where oil is attached ((b-1) to (b-3)). It is a schematic diagram of a scanning electron microscope (SEM) image for explaining the difference in remaining other organic matter in the case where oil is attached (I) and the case where oil is not attached (II). It is a schematic enlarged view of the SEM image in the case where oil is not attached (II).

[0011] If metal (e.g., aluminum metal) with residual (adhered) moisture, oil, or other organic matter other than oil is remelted as is, toxic gases such as benzene and toluene may be generated, and the quality of the reclaimed metal may be reduced. Also, if new heating equipment or centrifugal equipment needs to be installed to remove the oil, etc., it is expected that the cost will be high.

[0012] On the other hand, in the method for producing recycled metals according to the present disclosure (hereinafter referred to as the present production method), microwave irradiation is used to heat metal (e.g., aluminum metal) including metal scrap with oil adhering to at least a portion of it. Therefore, compared to heating furnaces, centrifugal devices, etc., 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, extrusion, 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 working, forging oil used during forging, and oils derived from machines or devices, such as hydraulic oil, cooling oil, rust preventative oil, or lubricating oil, which leaks from a processing machine or processing device during metal processing or cutting and adheres to the metal chips. Note that "metal scrap having oil adhering to at least a portion thereof" also includes, for example, metal offcuts, 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 during rolling, extrusion oil used during extrusion, drawing oil used during drawing, press oil used during press processing, forging oil used during 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, metal scrap, metal scrap or metal powder that has oil attached to it 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] Specific embodiments of the recycled metal manufacturing method according to the present disclosure will be described in detail below with reference to the drawings. In this manufacturing method, examples of metal scrap having oil at least partially attached thereto include aluminum, iron, copper, brass, zinc, stainless steel, and lead. This specification focuses on aluminum metal or alloys, including aluminum scrap, as the metal containing metal scrap. However, the aspects of the present disclosure are not limited to the following embodiments. As described above, the metal scrap may contain iron, copper, brass, zinc, stainless steel, and lead instead of aluminum. Therefore, the following description of the recycled aluminum manufacturing method using aluminum metal including aluminum scrap can be directly applied to the method of manufacturing recycled metal using other metals, including scrap of other metals. Furthermore, in this specification, the term "organic matter" includes all organic matter used or generated in the process of manufacturing metal products and the process of manufacturing recycled metal. Therefore, the organic matter includes oil, surfactants, silicone oil-derived organic matter, and the like. For clarity, the following description and drawings have been simplified as appropriate.

[0017] This manufacturing method is a method for producing recycled metal from metals containing scrap metal, 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 adheres to at least a portion of the scrap metal. Metal scrap (e.g., aluminum scrap) refers to cutting chips (metal chips) generated during the production of metal products, and contains metal or alloys. Metal scrap can contain a specific metal (e.g., aluminum) as a primary component. Here, the term "primary component" refers to the component that is most abundant among all components contained in the target (here, scrap metal). The content of the specific metal in the scrap metal (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 the present disclosure are achieved. 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 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 (content) of oil attached to the metal can be appropriately set within a range that achieves the effects of the present disclosure, but is preferably 1% by mass or more, more preferably 2% by mass or more, relative to the mass (100% by mass) of the metal (including the content of oil and other adhering substances). If the amount of oil attached 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. Furthermore, 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 adhering substances). If the amount of oil attached is 5% by mass or less, it is easy to prevent oil and other organic matter 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 in which the effects of the present disclosure can be obtained. However, the total amount of these other organic matter and moisture adhering to the metal (100% by mass) (including the content of the adhering matter) is preferably 1% by mass or more, more preferably 2% by mass or more. If the amount of these non-oil adhering matters 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. Furthermore, the total amount of these non-oil adhering matters 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 the adhering matter). If the amount of non-oil adhering matters is 5% by mass or less, it is possible to easily prevent oil and other organic matter 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 heated object (aluminum metal) in this embodiment. Specifically, FIG. 1 is a graph illustrating the relationship between the irradiation time (seconds) of 700W microwaves (MW: Microwave) irradiated onto the object (heated object) and the temperature (°C) of the base contacting the underside of the object. Here, the base temperature of the underside of the heated object can be considered the temperature of the object (heated object). Furthermore, symbol I is a graph for the case where aluminum metal having oil adhering thereto is used as the heated object. Furthermore, symbol II is a graph for the case where aluminum metal having no oil adhering thereto is used as the heated object. 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 was used, the temperature of the heated object rose more than when aluminum metal without oil attached was used, even for the same irradiation time, as shown in Figure 1. 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 influence of microwave irradiation on the remaining organic matter in the case where there is no oil (a) and the case where 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 FIG. 2(a), when microwaves are irradiated to aluminum metal 1 to which cutting oil 3 containing water is not attached, water (H ２0) volatilizes (evaporates) at approximately 100°C. However, residual organic matter 2 derived from silicone oil remains on the aluminum metal 1 even after microwave irradiation. On the other hand, when microwaves are irradiated onto aluminum metal 1 with cutting oil 3 attached, as shown in FIG. 2(b-1), the microwaves act preferentially on moisture (e.g., contained in cutting oil attached to the aluminum metal), causing the moisture to evaporate at around 100°C. At the same time, as shown in FIG. 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 causing a portion of the residual organic matter 2 to evaporate or be decomposed and removed. Furthermore, when the heating temperature reaches around 300°C by microwave irradiation, the remaining residual organic matter (e.g., organic matter derived from silicone oil) is decomposed and removed (vaporized), yielding aluminum metal 1, as shown in FIG. 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 disclosure, 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 is relatively less polar than the portion containing an element that is more electronegative than carbon.

[0024] Thus, in this manufacturing method, the oil adhering to the metal can increase the microwave absorption efficiency and promote 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 on a metal with oil containing polar groups attached thereto. However, a heating effect can also be obtained by irradiating microwaves on 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. Therefore, the oil or organic matter present near the contact points may be converted into a substance with high microwave absorption efficiency by carbonization or the like, which may secondarily improve the microwave absorption efficiency.

[0025] FIG. 3A shows schematic diagrams of scanning electron microscope (SEM) images illustrating the difference in remaining organic matter between the cases with oil (I) and without oil (II). In the embodiment shown in FIG. 3, cutting oil was used as the oil. As shown in FIG. 3A, when oiled aluminum metal was used (I), no white layer 4, presumably organic matter such as a mold release agent deposited during casting, was observed. On the other hand, when oil-free aluminum metal (II), shown in an enlarged view in FIG. 3B, was used, the white layer 4 was observed in greater amounts than in the case of I. This also demonstrates that microwave heating and drying of aluminum metal (briquettes in FIG. 3) with oil at least partially adhered thereto can efficiently remove other residual organic matter adhering to the aluminum chips inside. Furthermore, microwave heating and molding of loosely packed oiled aluminum metal results in the chip interface becoming homogeneous with the chips themselves, which is expected to improve yield when used as a melting briquette. Furthermore, aluminum metal briquettes with oil on them can prevent chipping and have a higher density than briquettes without oil on them.

[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 the present disclosure. 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 to which the oil is attached while applying pressure. Note that in this manufacturing method, the metal to which the oil is attached 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 to which the oil is attached before or in parallel (simultaneously) with the microwave irradiation.

[0028] By irradiating the microwaves, at least a portion of oil, such as cutting oil, adhering to the 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 forms for converting at least a portion of the 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 be vaporized or removed by irradiating the 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, by irradiating the microwaves, the metal (at least a portion of it) can be sintered or melted.

[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] This manufacturing method can include the following steps: - A step of preparing a 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 step of compressing the metal by applying pressure (compression step). 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 of the present disclosure, 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 adjustment step may be, for example, any of the following steps: A step of removing a portion of the oil adhering to the metal prior to the irradiation step (oil pre-removal step). A step of further adhering oil to the metal prior to the irradiation step (oil adhering step). As described above, the amount of oil adhering to the metal, including the content of adhering substances such as oil, is preferably 1 to 5 mass%. Therefore, in order to keep the amount of oil adhering within this range, the amount of oil adhering may be removed using a conventionally known method before microwave irradiation, or new oil may be adhered.

[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] Thus, in this manufacturing method, oil-adhered metal chips discharged during the manufacturing process of metal products (e.g., aluminum products) or the manufacturing process of recycled metals are irradiated with microwaves (e.g., under pressure), thereby efficiently volatilizing and removing the adhering oil and moisture. Furthermore, during microwave irradiation, the oil adhering to the metal increases the microwave absorption efficiency, allowing for effective heating. From the above, this manufacturing method can provide a highly energy-efficient recycled metal ingot that suppresses the release of toxic gases outside the system, even when oil is adhering to the metal chips. This effect is not limited to aluminum, but can also be applied to other metals.

[0034] Some aspects of the present disclosure will be described in more detail below using experimental examples, but the scope of the present disclosure 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 attached, 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 performed in a position where a SiC plate was in contact with the green compact during microwave irradiation.

[0036] Comparative Example 1: An experiment was conducted 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 their internal temperature reached 500°C. Table 1 shows the time (minutes) until volatilization of organic components such as benzene and toluene was completed, the presence or absence of oily smoke from the aluminum briquettes, and the amounts 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, along with benzene and toluene, are considered environmentally harmful, it is desirable to reduce the amount of both gases generated and remove them quickly. In this experimental example, a suction pump was used to recover generated gases using a gas recovery pack when the temperatures below 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 check the gas generated at 100°C and 300°C, recovery of organic matter derived from surfactants or silicone oil was not confirmed at either temperature.

[0037]

[0038] As shown in Table 1, in Example 1 using microwaves, the time to complete volatilization of organic components was shorter, no oily smoke was generated, and CO and CO were not generated, compared to Comparative Example 1 using a hot plate. ２ It can be seen that the amount of gases generated that are harmful to the environment is kept to a minimum.

[0039] In addition, CO and CO ２ The detection was performed using a gas analyzer equipped with a laser detection in-line type or various gas sensors that can measure gas concentrations in real time. The time when the temperature inside the aluminum chips reached 450°C and no smoke or other visible generation of the above was determined to be the time when 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 disclosure are not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present disclosure.

[0042] This application claims priority based on Japanese Patent Application No. 2024-026577, filed February 26, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0043] 1 Aluminum metal 2 Residual organic matter 3 Cutting oil 3a Polar group 3b Lipophilic group 3c Oil film 4 White layer I When aluminum metal with oil attached is used II When aluminum metal without oil attached is used

Claims

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

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

3. A method for producing recycled metals as described in 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. A method for producing recycled metals according to claim 1 or 2, wherein at least a portion of the metal is sintered or melted by the microwave irradiation.

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

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