JP2000273555A - Method for regenerating coated magnesium scrap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a regenerating method excellent in environmental properties in which the scrap of parts and products made of coated magnesium material is decomposed without using flux and also without generating harmful organic gas caused by the oxidation of a coating material, the coating material is decomposed, the decomposed products are removed, and it is regenerated. SOLUTION: Coated magnesium scrap is dissolved under the ordinary temp. or reduced pressure in a gaseous atmosphere of Ar, He, Ne, SF6, CO2, SO2 or N2, the molten metal is held under the pressure in the atmosphere, the coating material is decomposed into an inorganic matter, and the molten metal is then held under the reduced pressure in the atmosphere, by which the decomposed products in the coating material are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reclaiming painted magnesium and magnesium alloy (herein collectively referred to as magnesium-based or magnesium-based materials) waste, and more particularly to a method for refining painted magnesium and magnesium alloy. Dissolves scraps of parts and products made of system materials without using flux and without generating harmful organic gases due to oxidation of paint, decomposes paint, removes decomposition products, and further melts The present invention relates to a method for floating and separating and regenerating foreign substances such as oxides in an amount that adversely affects the properties of a magnesium-based material.

[0002]

2. Description of the Related Art In recent years, the need for lightweight materials has increased, and resin materials and lightweight metal materials have been used. However, resin materials are generally difficult to recycle, and therefore have environmental problems. On the other hand, metal materials are generally easy to recycle, and practical lightweight metals such as magnesium-based materials and aluminum-based materials are used. Of these, lightweight magnesium-based materials having the smallest density have attracted attention, and in particular, have been attracting attention as materials for automobiles or portable home electric appliances.

[0003] Parts and products made of a magnesium-based material are often used after being subjected to a chemical conversion treatment (oxidation treatment) such as chromate and then coated. At present, such painted parts and products made of a magnesium-based material are melted in the air at around 700 ° C. as they are, and the paint is burned by the high temperature. Organic C ₄ H ₉ O ₄ N,
C ₉ H ₁₃ N, C ₈ H ₉ ON, C ₉ H ₉ N, C ₅ H ₁₅ O ₂
N, C ₇ H ₇ ON and the like, and in many cases, dioxin is also generated. The higher the recycling temperature, the lower the unit number (carbon polymerization degree) of the organic gas component,
Although the toxicity is reduced, it is difficult to dissolve at a higher temperature than before because of the danger of magnesium ignition. Also, recycling of magnesium, not limited to painted magnesium waste, involves a large amount of flux, so there is a concern about environmental impact.

[0004]

As described above, the fact that a magnesium-based material has an advantage in terms of environmental friendliness and recyclability as compared with a resin material is a great driving force particularly in recent applications of magnesium. And the demand for magnesium is rapidly expanding worldwide, so parts and parts made of painted magnesium-based materials will be used in the future.
Since it is expected that a large amount of product scrap will be generated, it is required to establish a recycling technology for painted magnesium-based parts and products.

Accordingly, the present invention provides a method for dissolving scraps of painted parts and products made of a magnesium-based material without using a flux and without generating harmful organic gases accompanying the oxidation of the paint. It is an object of the present invention to provide an environmentally-friendly regeneration method for decomposing and removing decomposition products for regeneration. Further, the present invention relates to a method of floating, separating, and regenerating foreign substances such as oxides in a molten metal in an amount that adversely affects the properties of the magnesium-based material.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above object, and as a result, it has been found that scraps of painted magnesium-based materials and parts have extremely low oxygen partial pressure, It has been found that it is possible to dissolve the coating in an atmosphere that does not have an adverse effect on the coating and to decompose the coating material into inorganic substances without oxidizing the coating by holding the molten metal in the atmosphere, and to remove the decomposition products by holding the coating under reduced pressure. Reached the present invention.

[0007] Further, as described above,
Injection of a specific gas into the removed molten metal to float foreign matters such as oxides, sludge, and decomposition residues of paint contained in the molten metal, and to separate and separate the molten metal more sufficiently to clean and regenerate the molten metal. And arrived at the present invention.

That is, in the method for regenerating a coated magnesium waste material according to the present invention, the coated magnesium waste material is treated as A
r, He, Ne, SF ₆ , CO ₂ , SO _2, or N ₂ gas atmosphere is dissolved under normal pressure or reduced pressure, and the molten metal is held in the atmosphere under the pressure to decompose the coating material into inorganic substances. Then, the decomposition product of the paint is removed by maintaining the molten metal under reduced pressure in the atmosphere.

Further, in the method for regenerating the coated magnesium waste material of the present invention, the coating material is decomposed into inorganic substances and removed by the above-mentioned method, and subsequently, Ar, He, Ne, SF and SF are contained in the molten metal as a cleaning gas. ₆ , CO ₂ , SO ₂ or N
_The method is characterized in that foreign substances such as oxides in the molten metal are floated and separated by blowing the _two gases or a mixed gas of these gases and dry air while finely bubbling them.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A coated magnesium waste material to be regenerated by the regenerating method of the present invention is magnesium or a magnesium alloy (for example, AZ91, AM60, AM50, A50, which is a magnesium alloy for die casting).
S41) Includes used and collected products, such as cast products, die-cast products, processed products (plates, wires), etc., whose surfaces are coated with paint, and defective products generated in the manufacturing process. .

In the present invention, the paint includes all paints generally used for painting parts and products made of magnesium-based materials, such as phenolic resin-based paints, urea resin-based paints, and melamine resin-based paints. Paints, vinyl resin paints, epoxy resin paints, polyester resin paints, silicon resin paints, furan resin paints, cellulose paints, clear lacquers and the like.

One of the concerns when regenerating the coated magnesium waste material is that when the coated magnesium waste material is dissolved, the paint burns to generate harmful organic gases. is there. Further, when metal oxides are used as pigments in paints, there is a problem that they are mixed in the molten metal. In addition, contamination of foreign matters such as oxides and release agents, which is a problem even in the case of recycling magnesium-based waste materials in which no paint is used, also poses a problem.

In the regenerating method of the present invention, the coated magnesium waste material is treated with Ar, He, Ne, SF ₆ , CO
₂ , in an SO ₂ or N ₂ gas atmosphere, that is, in an atmosphere in which the oxygen partial pressure is extremely low and does not adversely affect the molten metal, at normal pressure or reduced pressure, and the molten metal is held in the atmosphere. The paint can be decomposed into inorganic substances without being oxidized, and the decomposition products can be removed by keeping the paint under reduced pressure.

As for the atmosphere as described above, the inside of the chamber in which the painted magnesium waste material is charged is 50 T
orr or less, and the atmosphere in the chamber is Ar, H
e, Ne, SF ₆ , CO ₂ , SO _2, or N ₂ gas is preferable to be formed by replacing the gas. Since the reason for this is to exclude oxygen in the chamber, better results are obtained as the degree of decompression is higher (the pressure after depressurization is lower). When the pressure after depressurization is higher than 50 Torr, Since the oxygen partial pressure remains to some extent, the paint is partially oxidized. However, the pressure after decompression is 50
Even if it is higher than Torr, an appropriate atmosphere can be obtained by repeating this atmosphere replacement two or three times.

The pressure of the above atmosphere when dissolving the coated magnesium waste material is not particularly limited, but there is no need to pressurize at all. Normal pressure may be used if only the decomposition of the paint is considered, but it is preferable to reduce the pressure in order to speed up the removal after the decomposition, that is, to increase the regeneration efficiency. The molten metal obtained by melting under such conditions is held in the above atmosphere until the paint is completely decomposed into inorganic substances. The holding time varies depending on the type of the paint and the relative amount of the paint to the magnesium-based material. Completion of the decomposition of the paint can be confirmed by a change in the pressure in the chamber caused by stopping the generation of the decomposition gas.

The temperature at which the coated magnesium waste material is melted and the temperature at which the molten metal is held may be the same as the temperature of the molten metal at the time of ordinary casting, and is from 600 to 700 ° C.
It is desirable to be between. The main component of the paint is an organic substance, and if necessary, a pigment such as a metal oxide is contained. Therefore, under conditions where the temperature of the molten metal is 600 to 700 ° C. and oxygen is excluded, the organic substance is completely decomposed. Mainly remains in the molten metal as carbon. When the temperature of the molten metal is lower than 600 ° C., the decomposition rate of the organic matter tends to be slow or insufficiently decomposed.
When the temperature exceeds the limit, there is a problem that the fuel is easily burned when returning to the atmosphere. Therefore, from the viewpoint of safety, the molten metal temperature is 60
More preferably, it is between 0 and 650 ° C.

Further, metal oxides which are added to the paint as required also remain in the molten metal. Furthermore, since parts and products made of a magnesium-based material are generally subjected to a chemical conversion treatment (oxidation treatment) such as chromate as a base treatment, and then a coating is applied, oxides accompanying this also remain in the molten metal. I do.

In the casting of a magnesium-based material, it is known that if the material is repeatedly melted and recycled, the fluidity of the molten metal and the corrosion resistance of the casting deteriorate even though the metal component is not changed. . This is due to the inclusion of foreign substances such as oxides and release agents. If such foreign matter remains in the molten metal, it is desirable to remove such foreign matter, and in some cases, it is essential to remove it.

Then, after the paint is decomposed and removed, a gas which does not adversely affect the molten metal is continuously blown into the molten metal, and the gas floats in the molten metal in a process of floating as bubbles in the molten metal. Foreign substances such as oxides and mold release agents are attached to the bubbles, floated together, and separated.

The temperature of the molten metal at the time of blowing gas into the molten metal may be the same as the temperature of the molten metal at the time of ordinary casting. However, when the temperature of the molten metal is 600 ° C. or less, the temperature of the molten metal decreases due to gas injection. This has an adverse effect on the castability of the molten metal, and when the temperature of the molten metal is 700 ° C. or higher, SF ₆ or S
The use of a gas containing O ₂ was insufficient. Therefore, the temperature of the molten metal is preferably between 600 and 700 ° C., more preferably between 600 and 650 ° C.

The test was repeated under the above-mentioned molten metal temperature conditions using various gases as the gas blown into the molten metal. In the process in which the gas blown into the molten metal floats in the molten metal, foreign substances such as oxides and release agents floating in the molten metal need to adhere to the air bubbles and float together. It is necessary that the gas blown into the melt does not adversely affect the molten metal (for example, does not significantly react with the molten metal). Ar, He, Ne, SF ₆ , CO ₂ , SO ₂ or N ₂ gas, or these gases and dry air (moisture Gas containing no air) was found. When a mixed gas of the above-mentioned gas and dry air, or SF ₆ and N ₂ gas is used, a reaction product with the molten Mg is slightly generated. Therefore, the gas blown into the molten metal is Ar, H
e, Ne, SF ₆ and CO ₂ are preferable, and SO ₂ or N ₂
Gas or a mixture of the above gases and dry air can also be used.

In the present invention, the cleaning gas is blown into the melt while finely bubbling in order to make the contact between the cleaning gas and the melt more efficient. At this time, the molten gas is effectively cleaned at a flow rate sufficient to cause convection in the molten metal by the cleaning gas blown into the molten metal and to cause effective contact between all the molten metal and the cleaning gas. It is desirable to blow the cleaning gas into the melt for a sufficient time to do so.

At least a part of foreign matters such as oxides in the molten metal floats by blowing the cleaning gas while finely bubbling the bubbles. Separation and removal can be performed effectively using a filter made of aluminum. This separation and removal technique using a filter can also be applied to the molten metal immediately after removing the decomposition products of the paint. By performing such treatment, the fluidity of the molten metal is generally improved, and the occluded gas in the molten metal is reduced, and as a result, the casting defects caused by the occluded gas are also reduced.

The cleaning method of the present invention can be applied not only to a molten metal obtained by dissolving only a painted magnesium waste material, but also to a case where a new ingot and a magnesium waste material are used in combination. When such a combination is used, the ratio of the magnesium-based waste material can be appropriately set within a range of 0 to 100%, but is generally desirably set to 50% or less. Thus, when used together with new metal, the amount of dross floating on the surface of the molten metal is small.

Example 1 As a coated magnesium waste material, the surface of a cast product made of an AZ91 alloy (Mg-9% Al-0.7% Zn-0.2% Mn) is subjected to a chemical conversion treatment by the DOW1 method, followed by intermediate coating. Cyclone 999 as a paint (Tokyo Paint Co., Ltd.)
And a used recovered product of a product coated using MGR-481 Gold (manufactured by Tokyo Paint Co., Ltd.) as a top coat.

The crushed material 2 of the recovered product is charged into a melting furnace 1 shown schematically in FIG. 1, and the pressure in the melting furnace is reduced to 50 Torr via a vacuum suction pipe 3. Ar was sealed to 1 atm (ie, the inside of the melting furnace was substantially replaced with Ar). The contents were heated to dissolve. The melt was kept at 650 ° C. for 10 minutes.

After the treatment, the gas in the melting furnace was analyzed, and it was found that most of the gas was Ar, and that H ₂ O, N ₂ , O
_2. CO ₂ was detected, and gases of other molecular weights were extremely weak. C and A are contained in the obtained molten metal.
Oxides such as l, Fe, Pb, Ba, and Cr were detected.

Embodiments 2 to 3 The melting furnace shown schematically in FIG.
0 liter), a molten metal having a surface area of about 500 cm ² and 15 cm below the surface of the molten metal, and a melting furnace equipped with a blowing device for finely bubbling a cleaning gas into the molten metal was used.
Using the recovered product used in the above, the crushed product 2 of this recovered product is charged into the melting furnace 1, and the inside of the melting furnace is evacuated through the vacuum suction pipe 3 to 50T.
orr, and then through a purifying gas introducing pipe 4 and a blowing device 5 for finely bubbling the purifying gas into the molten metal.
To 1 atm (that is, substantially A
r). The contents were heated to dissolve. The melt was kept at 650 ° C. for 10 minutes.

Thereafter, Ar is supplied at a flow rate of 0.1 liter per minute for 20 minutes (Example 2) or 40 minutes (Example 2) through the gas introducing pipe 4 and the blowing device 5 for finely bubbling the cleaning gas into the molten metal. 3) I blew it. A pinhole test and a salt spray test were performed to evaluate the cleanliness of the molten metal after the treatment.

<Pinhole Test> About 50 cc of the molten metal was poured into a crucible in a desiccator, and the desiccator was solidified while being suctioned under vacuum. The pinhole amount was measured from the specific gravity of the obtained casting material. Table 1 shows the results. It is well known that if oxides are present in the molten metal, the gas generated during solidification is trapped by the oxides and pinholes are generated. Can be.

<Salt Spray Test> A salt spray test was conducted according to JIS Z2371. Using 5% saline, 2
The occurrence of white rust after holding for 0 hour was visually observed. When no white rust was found, the results were evaluated as ○,
The results are shown in Table 1 as Δ when slight generation of white rust was observed, and as × when white rust was clearly observed.

Comparative Example 1 An AZ91 alloy (Mg-9% Al-0.7% Zn-) generated in a foundry was used instead of the recovered product used in Examples 2-3.
Processing was performed in the same manner as in Examples 2 to 3, except that Ar as a cleaning gas was blown at a flow rate of 0.1 liter per minute for 10 minutes using 0.2% Mn) unpainted scrap. The cleanliness of the molten metal after the treatment was as shown in Table 1.

[0033]

[0034]

As described above, the recycling method of the present invention is capable of scrapping painted parts and products made of a magnesium-based material with a simple apparatus without using flux and harmful to the oxidation of paint. It is possible to provide an environmentally friendly recycling method of dissolving without generating any organic gas, decomposing the coating material, and removing and regenerating the decomposition products.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus that can be used for carrying out a reproduction method of the present invention.

FIG. 2 is a schematic view of another apparatus that can be used for performing the reproducing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Crushed material 3 Vacuum suction pipe 4 Purification gas introduction pipe 5 Blowing device for fine bubbling

Claims (5)

[Claims] 1. The coated magnesium waste material is Ar, H
e, Ne, SF ₆ , CO ₂ , SO ₂ or N ₂ gas atmosphere is dissolved under normal pressure or reduced pressure, the molten metal is kept under the pressure in the atmosphere to decompose the coating material into inorganic substances, A method for regenerating a coated magnesium waste material, comprising removing decomposition products of a paint by maintaining the molten metal under reduced pressure in the atmosphere. 2. The pressure in the chamber containing the coated magnesium waste material is reduced to 50 Torr or less, and the atmosphere in the chamber is Ar, He, Ne, SF ₆ , CO ₂ , SO ₂ .
₂ or N ₂ gas, the waste material is dissolved in the atmosphere under normal pressure or reduced pressure, and the molten metal is maintained at 600 to 700 ° C. in the atmosphere under the pressure to decompose the coating material into inorganic substances. 2. A method according to claim 1, wherein the decomposition product of the paint is removed by maintaining the molten metal under reduced pressure in the atmosphere. 3. The method according to claim 1 or 2, wherein the paint is decomposed into inorganic substances and removed, and subsequently, Ar, He, Ne, SF ₆ , CO ₂ , SO _{2 are} added as a cleaning gas in the molten metal.
₂ or N ₂ gas, or a mixed gas of these gases and dry air, is blown while finely bubbling, so that foreign substances such as oxides in the molten metal are floated and separated. How to recycle waste materials. 4. The recycling method according to claim 1, wherein 50% by weight or more of the new metal and 50% by weight or less of the coated magnesium waste material are used in combination. 5. The coated magnesium waste material according to claim 1.
5. A method for regenerating a coated magnesium waste material, comprising regenerating by the method described in any one of (4) to (4), and subsequently filtering the molten metal through a metal or ceramic filter.