JPH0747785B2 - Dissolution method of flame retardant magnesium return material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a molten metal by melting a magnesium return material used for parts such as transportation machines and home electric appliances and various cases.

[0002]

2. Description of the Related Art Aluminum alloys are often used in cases such as vehicle oil pans and transmission cases, but magnesium or magnesium alloys having a smaller specific gravity than aluminum alloys can be made lighter. Attention has been paid. Generally, magnesium and magnesium alloy melts easily burn when exposed to air,
SF ₆ gas or S for die casting and squeeze casting
Maximum consideration has been given to ensuring safety, such as sealing with a mixed gas of F ₆ and CO ₂ and with sulfur powder in gravity. However, since the sealing gas such as SF ₆ is expensive, there is a problem that the manufacturing cost becomes high, and in gravity, SO ₂ gas is generated due to the sulfur powder, which causes a problem that the working environment is deteriorated.

Therefore, Shigeru Akiyama and Tadayoshi Nakamura, who are the inventors of the present invention, have made the molten metal flame-retardant by adding an alkaline earth metal such as calcium to magnesium or an existing magnesium alloy, and the purpose of flame retardance. It has been proposed to further add a rust preventive metal such as zinc in order to restore the corrosion resistance lowered by the alkaline earth metal added in (Japanese Patent Application No. 54394/1992). The flame-retardant magnesium material to which an alkaline earth metal is added or to which a rust preventive metal such as zinc is further added is a SF ₆ / CO ₂ gas seal or sulfur which is used in a normal magnesium alloy when melted. Even if the molten metal is brought into contact with the atmosphere without using the powdery powder, it does not burn, and even if it burns, it is possible to achieve an effect that the spread of burning is slow.

Burrs, runners, biscuits, and other return materials (return materials) are generated during casting such as die casting. The return material is about 40 for large parts such as wheels.
%, It is said that more will occur in small parts. Therefore, it is important to efficiently reuse the return material in order to reduce the cost of the magnesium material. As the return material, a mold release agent or lubricant during casting or a substance generated by partially thermally decomposing them is attached, or the return material itself chemically reacts with moisture or oxygen in the air, or by machining. Cutting oil may adhere, or dissimilar materials may adhere during transportation. Therefore, if the return material is directly charged into a melting crucible (hereinafter simply referred to as a crucible) or a crucible / holding furnace, there is a risk of explosive combustion due to deposits and chemical reactants. It is refined in to form a recycled ingot, which is remelted and used for casting.

[0005]

[Problems to be Solved by the Invention] It is difficult to completely remove the flux used for the refurbishment and refining of the return material, and the flux remains in the magnesium material of the product, leading to a decrease in corrosion resistance. Occurs.
Further, a large increase in cost cannot be avoided due to the regeneration process. Further, when using the flux, there is a problem that heat and flux fumes are generated to deteriorate the working environment. One of the reasons why the magnesium material is not widely used despite its high light weight effect is that the return material must be recycled through a recycling process using flux. Therefore, the present invention eliminates the need to recycle the return material using flux and allows the return material to be directly put into the crucible for casting to prevent cost reduction and work environment deterioration, and The purpose is to prevent the deterioration of the quality of the magnesium material using the material.

[0006]

In the present invention, a molten metal which is flame-retarded by adding at least an alkaline earth metal to magnesium or a magnesium alloy or those obtained by adding a reinforcing material to the molten metal is prepared. The return material is directly added and melted under the condition of the molten metal. The term "return material" is used in the sense that it includes burrs, runners, biscuits other than the desired shape generated during die casting, and cutting chips generated by machining.

In the present invention, an alkaline earth metal is added in order to make the molten metal of magnesium or magnesium alloy or a reinforcing alloy added thereto flame-retardant. The main component magnesium or magnesium alloy is preferably as low as possible in the content of corrosion-promoting elements iron, nickel, copper, for example, aluminum is 9% (hereinafter, all% are weight% unless otherwise specified). , About 1% zinc
The magnesium alloy containing AZ91 has a low impurity concentration A
Z91D and AZ91E are preferred. As a target type of magnesium or magnesium alloy, all of the alloys which do not contain a large amount of alkaline earth metal or the below-described rust preventive metal are targeted. That is, the content of the alkaline earth metal or the rust preventive metal may be magnesium or a magnesium alloy that is equal to or less than the addition amount targeted by the present invention. There are no restrictions on other components. AZ91 and A are typical alloys
There is M60.

The alkaline earth metal to be added is Ca, Ba or Sr, but Ca is the most desirable from the viewpoint of low vapor toxicity and availability. The content of the alkaline earth metal is less than 5%, preferably 3 when the flame retardancy of the molten metal is simply expected in applications where the anticorrosion requirement is not so strong.
% Or less. For applications where strong corrosion resistance is required, a rust preventive metal is added together with the alkaline earth metal for achieving the flame retardancy of the molten metal. The addition of the rust preventive metal reduces the influence of the deterioration of the corrosion resistance even if the content of the alkaline earth metal increases. In this case, alkaline earth metal is 10%
Less, preferably 8% or less, particularly preferably 5% or less. It does not have to be 10% or more. The amount of alkaline earth metal added is preferably as small as possible in order to keep the properties as low as possible from the cost and original magnesium and magnesium alloys. However, if the amount of the alkaline earth metal added is too small, flame retardancy cannot be expected, so the lower limit of the amount of the alkaline earth metal added is 0 regardless of whether or not the rust preventive metal is added. It is 0.1%, preferably 0.5% or more.

The rust preventive metal is Zn, which is experimentally evaluated.
Cd, Pb, Sn, Si, Mn, Zr and Be were selected. One or more of these metals are added to magnesium or a magnesium alloy together with an alkaline earth metal. Of these, Zn is most desirable because it has low toxicity to the human body. The amount of the rust preventive power improving element added varies depending on the element used and cannot be unequivocally determined because there is also a difference depending on the content rate of the corrosion accelerating element of the magnesium or magnesium alloy used.
It is preferably 8% or less. On the contrary, if the rust preventive power improving element is added too much, the corrosion resistance may be deteriorated, and it is preferably 10% or less in order to avoid a large difference from the characteristics of the original magnesium or magnesium alloy. The addition amount of the rust preventive power improving element may be appropriately determined based on, for example, the result of a salt spray test.

It is desirable that the alkaline earth metal material and the rust preventive metal material contain iron, nickel and copper as impurities as low as possible. The alkaline earth metal and the rust preventive metal are added in a predetermined amount in the state of a simple substance, an alloy or an intermetallic compound. Since these additional elements can also be added by dissolving in a commercially available pure magnesium or a commercially available magnesium alloy, there is a great advantage that the desired flame retardancy can be achieved even by a caster even if not an ingot manufacturer. is there. In particular, if the addition amount of the additional element is in the range of 1 to 2%, the characteristics are not significantly changed, which is convenient. It is most common to add such an additional element in a state in which magnesium or a magnesium alloy is dissolved, but it may be heated and dissolved together with a solid ingot. However, it is necessary to consider Zn, which easily vaporizes. In the case of pure magnesium or a composition that is close to pure magnesium in composition, an alloy such as Mg-Ca, Al-Ca, or an intermetallic compound may be used as the additional element in addition to a simple substance. For example, AZ
In No. 21, it is also possible to use Ca-containing AZ91 alloy by using Al-Ca.

After adding a required amount of Ca, or a rust preventive metal such as Ca and Zn to a molten metal of magnesium or a magnesium alloy, immediately or for a while, the additives are dissolved and then stirred with a stirring rod. However, it is desirable to dissolve it uniformly. The stirring time varies depending on the size of the crucible and the stirring ability, but it dissolves almost uniformly in 5 to 60 minutes. Until the additives are uniformly dissolved, SF ₆ , CO ₂ , N ₂ , A
It is desirable to seal with r gas or the like. Even if it is not sealed with such a gas in the latter stage of stirring for uniform dissolution, that is, even if the mixture is opened to the atmosphere and stirred, the molten metal is flame-retarded and does not ignite.

Ceramic particles can be added to magnesium or a magnesium alloy to form a reinforced composite material. When a reinforcing material such as ceramics is added, the reinforcing material is added in a state where the reinforcing material is uniformly dispersed or partially unevenly distributed. The alkaline earth metal, or the alkaline earth metal and the rust preventive metal is added to magnesium or a magnesium alloy and dissolved, and then the reinforcing material is added while stirring the molten metal. The addition amount per unit time varies depending on the structure of the stirring blade, the number of revolutions, the form of the reinforcing material, etc., so it cannot be determined unconditionally, but the criterion for judgment is that the added reinforcing material gradually dissolves in the molten metal. Therefore, the amount added per hour may be determined while confirming the melting state. Short fibers or granular powder can be used as the reinforcing material. As the fibers, inorganic fibers such as alumina, alumina silica, SiC and carbon fibers can be used. Besides, whiskers can also be used.
The size is preferably 1-2 mm or less in length. If the length is long, dispersion is possible, but the viscosity increase due to entanglement is large, and the fluidity at the time of casting deteriorates, making it practically impossible to contain a large amount of reinforcing material. When it is desired to contain a large amount of fibrous reinforcing material, a preform is first formed and then impregnated with a squeeze. Similarly, long fibers can be contained. On the other hand, as the granular powder, alumina, SiC, alumina silica, spinel or the like is used. The size is 0.1 μm to 2 mm, and when it becomes fine powder, the viscosity increases and the castability becomes poor. The content rate of these different materials is 35% by volume
Is the maximum, and filling is more difficult than this.

Further, once the ceramics are immersed in a solvent such as alcohol, the bulkiness decreases and
Wetting with molten metal and dispersibility tend to improve. As a method of improving the wettability between these different materials and the molten metal, for example, JP-A-57-169033 and JP-A-57-16.
The methods described in JP-A-9034, JP-A-60-159137 and JP-A-60-194039 can be used. The type and size of dissimilar materials to be dispersed, the amount, the type of wetting improver, etc. and the degree of effect can be easily judged by visually observing the state of the molten metal, so preliminary evaluation is possible. The applicable range may be determined.

Even if the melt contains 0.1% or more of alkaline earth metal, it cannot be said that there is no possibility of combustion when the ultrathin film return material is heated. It is safer to submerge below the surface of the melt. For thick return materials, it may be slowly submerged below the surface of the molten metal, but in actual castings, especially die-cast products, thin or extremely thin films such as burrs are often integrated. It is safer to sink the material immediately below the surface of the melt. The molten metal is held and the return material is put into the molten metal while the molten metal is in contact with air. However, for the sake of safety, SF ₆ , CO ₂ , N ₂ , A
It may be sealed with a known non-combustible gas such as r gas.

The molten metal needs to contain an alkaline earth metal and be made flame-retardant, but the return material does not necessarily have to be a magnesium material having the same composition as the molten metal. If the return material has the same composition as the molten metal, or if it does not have the same composition as the molten metal but contains an alkaline earth metal for flame retardation or further contains a reinforcing material The content of the earth metal may be 0, as long as the content of the alkaline earth metal in the melt after the return material is charged and melted is 0.1% or more, and the mixture is uniformly mixed. Good.

[0016]

The inventors of the present invention have found that the molten metal of magnesium or magnesium alloy containing 0.1% or more, preferably 0.5% or more of alkaline earth metal exhibits flame retardancy and does not burn even when contacted with air. Have been found by. If the return material is put into such a molten metal and sunk below the surface of the molten metal, even if the return material itself burns when it is heated in the solid state, it does not react with oxygen in the molten metal. No contact and no combustion.

[0017]

According to the present invention, since the return material is directly charged into the flame-retarded molten metal to be melted, there is no need to go through the re-refining process by the flux of the return material, which has been indispensable in the past, so that the cost of regeneration can be reduced. Is unnecessary, and the cost can be reduced. Since no recycling flux is used, it is possible to prevent deterioration of the corrosion resistance of the magnesium material product and improve the quality of the magnesium material product using the return material. The molten metal of the present invention can be safely carried out without the risk of explosion or combustion. In the past, the caster and the reclaimer were often different, and therefore the physical distribution cost for reclaiming was incurred, but according to the present invention, the reclaiming process is not required, so the caster alone can reuse the return material. As a result, distribution costs can be reduced and reuse becomes easier.

[0018]

【Example】

(Example 1) AZ91D (product of Dow Chemical Company) 40
A molten metal of 0 kg was prepared, and calcium and zinc were added thereto in an amount corresponding to 1%, respectively, and dissolved, and mixed to prepare an ingot. Atmosphere temperature 775
It was melted at ˜875 ° C. and held so that the temperature of the molten metal was 705 to 715 ° C., and 272 pieces of 0.75 Kg per shot were cast by a die casting machine in a cold chamber. This amount corresponds to about 50% of the total weight of the molten metal.
Next, burr the above die cast casting on the remaining molten metal,
With the runner and biscuit still attached, 50 shots worth of them were sequentially charged, and were sunk under the surface of the molten metal to dissolve them. At this time, an incombustible gas such as SF ₆ / CO ₂ is not introduced, and the atmospheric temperature is set to 775 to 8 while being brought into contact with air.
Melted at 75 ° C. During the melting of these 50 shots,
No flammable combustion occurred.

Thereafter, the remaining 222 shots worth of shots were divided into several times to be submerged and melted, but in that case, no ignition and combustion from the melt occurred at all. When the die-cast casting was submerged in the molten metal, a slight release agent on the biscuit raised the soot and burned, but it did not serve as an ignition source for the molten metal. This molten metal was cast using the same die casting machine, but there was no problem in castability. On the other hand, in the same manner as in Example 1, except that calcium and zinc were added, a cast product similarly cast using AZ91D was put into the molten metal of AZ91D to be melted.
Ignition and combustion occurred at the same time when the casting melted.

(Example 2) AZ91D (a product of Dow Chemical Co., Ltd.) 200 kg of molten metal was added with amounts of calcium and zinc corresponding to 0.6% respectively and dissolved, and mixed to prepare an ingot. 7 in the same manner as in Example 1
One die cast casting was created. 5 for the remaining melt
One cast product (corresponding to about 38 kg) was sequentially charged and melted in a state of being submerged below the surface of the molten metal. Also in this case, the release agent oil burned by raising the soot, but the molten metal and the return material did not burn, and there was no problem in casting using the molten metal.

Claims (1)

[Claims] 1. A molten metal is prepared by adding at least one alkaline earth metal to magnesium or a magnesium alloy or those obtained by adding a reinforcing material to the molten metal. A dissolution method that dissolves in a submerged state.