JP3709450B2 - Filter material for molten aluminum - Google Patents

Description

【００２６】
表１のデータからも明かなように、本発明に係る実施例１〜５においては、アルミニウム溶湯用濾材の室温曲げ強さ、熱間曲げ強さ（８００℃）、アルミニウム溶湯に対する耐食性（成分溶出量）、及びアルミニウムの通湯性（アルミニウム浸透性）の点で優れており、実用性の高いものである。
【００２７】
【発明の効果】
本発明のアルミニウム溶湯用濾材は、アルミニウム溶湯中に浸漬して使用しても不純物が溶出しないのでアルミニウム溶湯を二次汚染することがなく、極めて安定な結晶組織を有しており、室温曲げ強さ、熱間曲げ強さ（８００℃）、アルミニウム溶湯に対する耐食性（成分溶出量）、及びアルミニウムの通湯性（アルミニウム浸透性）に優れたものである。
【図面の簡単な説明】
【図１】 アルミニウム浸透性の評価法を説明する概略図である。[0001]
BACKGROUND OF THE INVENTION
The present invention is used to filter out solid impurities (non-metallic inclusions, etc.) mixed in molten aluminum or aluminum alloy (in the present specification, these are collectively referred to simply as molten aluminum). The present invention relates to a molten aluminum filter medium.
[0002]
[Prior art]
Normally, solid impurities, particularly non-metallic inclusions are mixed in the molten aluminum, so that the molten metal containing these inclusions is cast as it is, rolled, and commercialized as, for example, a disk material, The mixed non-metallic inclusions cause defects such as pinholes. In order to prevent the occurrence of such defects, it is common practice to remove non-metallic inclusions by filtering the molten aluminum prior to casting. Various apparatuses are known for use in filtration of the molten metal. As described in, for example, Japanese Patent Publication No. 52-22327, an aggregate such as fused alumina is made of SiO ₂ , B ₂ O _3. A tube-type filter medium bonded with an inorganic binder such as is used.
[0003]
However, such a conventional filter medium is used to filter a high-purity molten aluminum used for manufacturing a hard disk material of a computer, or Al-- used for manufacturing a can material such as a soft drink can and a beer can. When filtering the Mg alloy-based molten metal, SiO ₂ and CaO contained in the inorganic binder are reduced in the molten aluminum to produce free Si and free Ca, which are eluted into the molten aluminum to form the molten aluminum. There was a problem of contamination. In addition, since the Al-Mg alloy melt is an active property, it may erode the inorganic binder, reduce the bond strength between the aggregates, and reduce the durability of the filter media. Such a filter medium will collapse.
[0004]
From these facts, filter media produced using an inorganic binder containing no SiO ₂ are disclosed in, for example, Japanese Patent Publication No. 5-86459, Japanese Patent Publication No. 5-86460 and Japanese Patent Application Laid-Open No. 2-33472. Yes. When these filter media are used, there is no problem of secondary contamination of molten aluminum due to elution of free Si. However, a filter medium using such an inorganic binder has a problem that the strength of the filter medium is low and clogging is likely to occur because the bonding state between the aggregate particles is poor, and the amount of hot water passing through varies. It was.
[0005]
Therefore, a filter medium that solves the problems of free Si elution and bending strength has been demanded. In order to satisfy these requirements, a predetermined amount of SiO ₂ is included to improve the wettability with molten aluminum. with inorganic binding material which is also acicular filter medium obtained by precipitating a crystal of _{9Al 2 O 3 · 2B 2 O} 3 in the inorganic binding material is disclosed in Japanese Patent Laid-Open No. 5-138339.
[0006]
However, in the embodiment of the invention described in JP-A-5-138339 discloses the above after once melted inorganic binding material in order to obtain a needle-like crystals of _{9Al 2 O 3 · 2B 2 O} 3, a special not cooling means additional to it is necessary to suppress the crystal length to a particular range only, because in the inorganic binding material of SiO ₂ is contained 15 to 25 wt%, and is intended to contain CaO or the like, and the The point of preventing the elution of free Si or free Ca is not always satisfactory.
[0007]
[Problems to be solved by the invention]
In order to obtain molten aluminum used in various applications, such as disc materials in recent times, even if there are slight surface defects, the smallest possible non-metallic inclusions are removed from the molten aluminum. In addition, it is required to reduce as much as possible the impurities eluted in the aluminum melt after filtration. Accordingly, the SiO ₂ and CaO components contained in the inorganic binder are reduced as much as possible, and the strength and the like are considered. Therefore, it is desired to provide a filter medium that can be sufficiently satisfied.
[0008]
The object of the present invention is to provide a filter material for molten aluminum that has overcome the above-mentioned problems, that is, it can be used even if it is used in contact with molten aluminum or immersed in molten aluminum. Does not elute, so there is no secondary contamination of the molten aluminum, and the strength of the filter media is high due to the high bonding strength between the aggregates, and it can be used stably over a long period of time. Is to provide a filter material for molten aluminum having an almost constant crystal structure and an excellent hot and room temperature bending strength.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present invention and the like have used as an inorganic binder a crystal powder having a spinel crystal structure composed of Al ₂ O ₃ and MgO and a relatively small amount of an amorphous glass component. The crystallinity of the spinel crystals in the sintered body obtained by firing the mixture of the inorganic binder and the alumina aggregate particles is limited to a specific value, and the space between the spinel crystal particles in the sintered body is partially It has been found that good results can be obtained by limiting the composition and the molar ratio of the components of the amorphous glass phase bonded to the present invention, thereby completing the present invention.
[0010]
That is, the filter material for molten aluminum according to the present invention is an inorganic binder 5 composed of 85 to 98% by weight of crystal powder having a spinel crystal structure made of Al ₂ O ₃ and MgO and 15 to 2% by weight of an amorphous glass component. A sintered body of a mixture of ˜25 parts by weight and 100 parts by weight of alumina aggregate particles, and the crystallinity of the spinel crystals in the sintered body is 10% or more and / or in the sintered body The amorphous glass phase that partially bonds between the spinel crystal grains contains B ₂ O ₃ and SiO ₂ , and the molar ratio of B ₂ O ₃ / SiO ₂ is 0.3 or more.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The crystal powder having a spinel crystal structure composed of Al ₂ O ₃ and MgO used for producing the filter material for molten aluminum of the present invention is composed of Al ₂ O ₃ and MgO, and the molar ratio of Al ₂ O ₃ : MgO is 1. 1 and the weight ratio of Al ₂ O ₃ : MgO is 7: 3, forming a spinel crystal structure. Such crystal powder is extremely stable, has excellent wettability with molten aluminum, and is also excellent in aluminum erosion resistance, etc., so it is suitable as an inorganic binder for use in the production of aluminum melt filter media. is there.
[0012]
However, when the average particle diameter of the crystal powder having a spinel crystal structure composed of Al ₂ O ₃ and MgO is several tens μm to several mm as in many commercially available products, the sinterability is generally poor. As a means for achieving good sinterability, it is conceivable to add a large amount of sintering aid (bonding aid). However, when a large amount of aid is added in this way, resistance to molten aluminum is considered. The erodibility deteriorates.
[0013]
On the other hand, the smaller the average particle size of the crystal powder having a spinel crystal structure made of Al ₂ O ₃ and MgO, the better the sinterability, preferably 50 μm or less, more preferably 10 μm or less. When pulverized in this manner, it becomes more suitable as an inorganic binder used for producing a filter material for molten aluminum. The pulverization method may be any method, for example, dry pulverization such as a ball mill, or wet pulverization such as a bead mill, and the same effect can be achieved by using any method. Is done. However, the smaller the average particle size of the crystal powder, the higher the cost. As a means for suppressing this high cost, it is conceivable to use a crystal powder that has been appropriately pulverized and use a binding aid powder together.
[0014]
In the production of the filter material for molten aluminum of the present invention, when alumina aggregate particles and an inorganic binder are mixed and baked to form a filter medium, the filter medium is passed due to the fluidity and appropriate viscosity of the inorganic binder during calcination. It is necessary to ensure pores, and for this purpose, it is necessary to add a small amount of an amorphous glass component in the inorganic binder.
The amorphous glass component used as an inorganic binder together with crystal powder having a spinel crystal structure composed of Al ₂ O ₃ and MgO in the production of the molten aluminum filter medium of the present invention contains B ₂ O ₃ and SiO ₂ . Regarding the blending ratio of B ₂ O ₃ and SiO ₂ , the amorphous glass that partially bonds the spinel crystal particles in the sintered body obtained by firing the mixture of the inorganic binder and the alumina aggregate particles. It is necessary that the phase contains B ₂ O ₃ and SiO _{2 so} that the B ₂ O ₃ / SiO ₂ molar ratio is 0.3 or more. When this ratio is 0.3 or more, the substitution reaction between Al atoms and Si atoms in the molten metal is suppressed, and the filter medium is excellent in corrosion resistance. On the other hand, when this ratio is less than 0.3, that is, when the amount of SiO ₂ increases compared to the amount of B ₂ O ₃ , the corrosion resistance against molten aluminum tends to decrease, and elution of SiO ₂ tends to become a problem. is there.
[0015]
The blending ratio of the crystal powder to the amorphous glass component is 85 to 98 wt%, preferably 90 to 97 wt%, and 15 to 2 wt%, preferably 10 to 3 wt%, of the amorphous glass component. To be made up of. At a blending ratio within this range, the amorphous glass component effectively acts as a bonding aid, and the sinterability of the crystal powder having a spinel crystal structure can be enhanced. However, when the blending amount of the binding aid powder exceeds 15% by weight, the added binding aid is locally vitrified and unevenly distributed, and the aluminum erosion resistance is deteriorated.
In the present invention, the inorganic binder may contain other various substances such as ZrO ₂ when pulverizing spinel crystals, a sintering aid during sintering, dextrin as an organic solvent, and the like. Of course.
[0016]
As alumina aggregate particles used for producing the filter material for molten aluminum of the present invention, electrofused alumina, sintered alumina or the like can be used.
The filter material for molten aluminum according to the present invention comprises a sintered body obtained by firing a mixture of the above-described inorganic binder and alumina aggregate particles. As the manufacturing method, the inorganic binder powder and the aggregate particles may be mixed, formed into a predetermined shape and then fired, or the inorganic binder powder may be slurried and coated on the surface of the aggregate particles. May then be molded and fired. About the compounding ratio of said inorganic binder and alumina aggregate particle, it is made to consist of 5-25 weight part of said inorganic binder, Preferably 10-20 weight part, and 100 weight part of alumina aggregate particle | grains. . When the amount of the inorganic binder is less than 5 parts by weight, the aggregate particles may not be sufficiently bonded, and the aggregate particles may be detached from the filter medium. It tends to become narrower and more likely to clog.
[0017]
In the filter material for molten aluminum of the present invention, the crystallinity of the spinel crystal in the sintered body is 10% or more.
In this specification, the term “crystallinity of the spinel crystal in the sintered body” means an Al ₂ O ₃ .MgO spinel crystal appearing at 2θ = 36.8 ° obtained by powder X-ray diffraction of the sintered body. The peak height (assumed to be a numerator) is expressed as a percentage in comparison with the peak height of α-Al ₂ O ₃ (assumed to be the denominator) that appears at 2θ = 43.4 °.
[0018]
In the filter material for molten aluminum as described above, the crystallinity of the spinel crystal in the sintered body being less than 10% means that the amount of the amorphous glass component in the binder is relatively large. In addition, since these amorphous glass components are present between the spinel crystal particles and soften at a high temperature, the hot strength of the filter medium is lowered. Further, since the amorphous glass component is inferior in corrosion resistance to the molten aluminum as compared with the spinel crystal, it must be avoided that the amorphous glass component is present in a large amount in the binder. Therefore, as described above, the crystal powder is 85 to 98% by weight, preferably 90 to 97% by weight, and the amorphous glass component is 15 to 2% by weight, preferably 10 to 3% by weight.
[0019]
In the filter material for molten aluminum according to the present invention, since the crystallinity of the spinel crystal in the sintered body is 10% or more, the proportion of the spinel crystal particles bonded together without an amorphous glass phase is extremely high. It exhibits strong corrosion resistance against molten aluminum. That is, the ratio of the amorphous glass phase having poor corrosion resistance to the molten aluminum existing between the spinel crystal particles in the sintered body is reduced, and the molten aluminum is less likely to be eroded.
[0020]
【Example】
Hereinafter, the present invention will be described in detail based on examples and comparative examples.
Examples 1-5 and Comparative Examples 1-2
Fused alumina (average particle size 850 μm) is used as aggregate particles in the amount (parts by weight) shown in Table 1, and crystal powder having a spinel crystal structure composed of Al ₂ O ₃ and MgO as an inorganic binder (molar ratio 1). : 1, weight ratio 7: 3, average particle size 4.5 μm), B ₂ O ₃ and SiO ₂ were used in amounts (parts by weight) shown in Table 1, respectively, and these compounds were kneaded and pressure-molded. And dried in an electric furnace at 1430 ° C. for 12 hours to obtain pipe-shaped molded bodies each having an outer diameter of 100 mm, an inner diameter of 60 mm, and a height of 850 mm. About each pipe-shaped molded object of Examples 1-5 and Comparative Examples 1-2, the peak height and 2θ = 43.4 of Al ₂ O ₃ .MgO spinel crystals appearing at 2θ = 36.8 ° by powder X-ray diffraction. The peak height of α-Al ₂ O ₃ appearing at ° was obtained, and the crystallinity was calculated. Further, when the molar ratio of B ₂ O ₃ / SiO ₂ was measured, it was as shown in Table 1. Furthermore, the characteristics of each pipe-shaped molded body were examined by the following test method.
[0021]
《Bending strength》
A 100 mm × 20 mm × 18 mm rectangular parallelepiped test body was cut out from each of the pipe-shaped molded bodies. This rectangular parallelepiped test body was subjected to a room temperature bending strength test with a support span of 80 mm by a two-point support and one-point load method. In the hot bending test, each rectangular parallelepiped specimen was held at 800 ° C. for 20 minutes in an electric furnace for setting the atmospheric temperature, and then supported in an electric furnace for setting the atmospheric temperature, with a support span of 80 mm by a one-point load method. It carried out in. The test results were as shown in Table 1.
[0022]
<Elution amount of ingredients>
1 part by weight of each of the above-mentioned pipe-shaped compacts is immersed in 10 parts by weight of a high-purity (99.99% or higher) aluminum melt at 740 ° C., and the pipe is maintained for 72 hours while maintaining the temperature of the melt at 740 ° C. While repeating the pressure reduction and pressurization inside the shaped molded body, the molten aluminum is alternately passed from the outside to the inside of the pipe-shaped shaped body and from the inside to the outside, and then the molten aluminum is sampled and Si in the molten aluminum is sampled. , B and Mg amounts were measured and compared with the amounts of Si, B and Mg in the molten aluminum before immersion. The difference (that is, the increment) was used as the component elution amount for Si, B, and Mg. The measurement results were as shown in Table 1.
[0023]
《Aluminum permeability》
The permeability of the molten aluminum to each of the above pipe-shaped molded bodies was evaluated as follows. Outer diameter 100mm from the pipe-shaped molded body of the respective inner diameter 60 mm, to prepare a pipe-shaped test specimens height 65 c m (both ends are sealed), furnaces molten aluminum holding the pipe-shaped test specimens It was preheated inside, and a high-purity (99.99% or more) molten aluminum at 740 ° C. was poured to a height of about 70 cm and held at 740 ° C. for 24 hours. Thereafter, each specimen was taken out and cooled, and then cut in the longitudinal direction (vertical direction in a standing state in a furnace), and the height (A) at which aluminum penetrated was measured. The difference (R−A) between the molten metal surface height (R) and the aluminum penetration height (A) was defined as the required aluminum impregnation height (H). The outline of this evaluation method is as shown in FIG. That is, the lower the required aluminum impregnation height (H), the better the aluminum permeability. The measurement results were as shown in Table 1.
[0024]
"Comprehensive evaluation"
The case where all of the above bending strength test results, component elution amount measurement results, and aluminum permeability measurement results show preferable values is marked with ◎, and any of those results shows borderline values, others Indicates a case where a preferable value is shown, and a case where one of the results shows an unfavorable value is indicated as x.
[0025]
[Table 1]

[0026]
As is clear from the data in Table 1, in Examples 1 to 5 according to the present invention, room temperature bending strength, hot bending strength (800 ° C.), and corrosion resistance to molten aluminum (component elution) Amount) and aluminum hot water permeability (aluminum permeability), and is highly practical.
[0027]
【The invention's effect】
The filter medium for molten aluminum of the present invention does not elute impurities even if it is used immersed in the molten aluminum, so it does not cause secondary contamination of the molten aluminum, has an extremely stable crystal structure, and has a room temperature bending strength. In addition, it is excellent in hot bending strength (800 ° C.), corrosion resistance against molten aluminum (component elution amount), and aluminum hot water permeability (aluminum permeability).
[Brief description of the drawings]
FIG. 1 is a schematic view for explaining an aluminum permeability evaluation method.

Claims (4)

5 to 25 parts by weight of an inorganic binder composed of 85 to 98% by weight of crystal powder having a spinel type crystal structure composed of Al ₂ O ₃ and MgO and 15 to 2% by weight of an amorphous glass component, and alumina aggregate particles 100 A filter medium for molten aluminum, comprising a sintered body of a mixture with parts by weight, wherein the spinel crystal in the sintered body has a crystallinity of 10% or more. 5 to 25 parts by weight of an inorganic binder composed of 85 to 98% by weight of crystal powder having a spinel type crystal structure composed of Al ₂ O ₃ and MgO and 15 to 2% by weight of an amorphous glass component, and alumina aggregate particles 100 And an amorphous glass phase partially bonded between the spinel crystal grains in the sintered body contains B ₂ O ₃ and SiO _2, and contains B ₂ O ₃ / SiO _{2. A} filter medium for molten aluminum, wherein the molar ratio of ₂ is 0.3 or more. 5 to 25 parts by weight of an inorganic binder composed of 85 to 98% by weight of crystal powder having a spinel type crystal structure composed of Al ₂ O ₃ and MgO and 15 to 2% by weight of an amorphous glass component, and alumina aggregate particles 100 Amorphous glass comprising a sintered body of a mixture with parts by weight, wherein the spinel crystal in the sintered body has a crystallinity of 10% or more, and partially bonds between the spinel crystal grains in the sintered body A filter medium for molten aluminum, wherein the phase contains B ₂ O ₃ and SiO ₂ , and the molar ratio of B ₂ O ₃ / SiO ₂ is 0.3 or more. The filter material for molten aluminum according to claim 1, 2 or 3, which is obtained using a crystal powder having an average particle size of 50 µm or less.

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