JPH03285027A - Filter material for metallic molten metal - Google Patents

Abstract

PURPOSE:To obtain a filter material for metallic molten metal having high collecting capacity for impurities and long service life by binding ceramic aggregate particles with an inorganic binder of a frit having a specified compsn. constituted of B2O3, Al2O3, CaO and MgO and having specified particle size. CONSTITUTION:Ceramic aggregate particles are binded with an inorganic binder to obtain a porous filter material. At this time, as the above binder, a frit constituted of, by weight, 15 to 80% B2O3, 2 to 60% Al2O3, 0 to 30% CaO and 5 to 50% MgO and having <=35mum 50% average particle size is used. Furthermore, as the above aggregate, ceramic particles of alumina or the like having about 0.3 to 3.0mm average particle size and about 100 to 130 shape index are suitably used. This aggregate, 100 pts.wt., is blended with the above binder by about 4 to 20 pts.wt., which is heated to about 1200 to 1400 deg.C to melt the binder, and after that, gradual cooling is executed to form a porous filter material. In this way, the filter material for metallic molten metal having high bending strength and high collecting capacity for impurities by formed aluminum boride crystals can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a filter medium for molten metal suitable for filtering impurities (inclusions) contained in molten metal, particularly molten aluminum.

[Prior Art] Metal thin plates and foils are manufactured by casting a molten metal ingot and rolling it. However, if solid impurities such as metal oxides and minute fragments of refractories contained in molten metal are mixed into the ingot, pinholes and surface defects will occur during the process of rolling the ingot into thin sheets, foils, etc. Sometimes. To prevent this, it is necessary to remove solid impurities from the molten metal, and for this purpose, glass cloth, alumina balls, ceramic foam, etc. have conventionally been used as filters for molten metal applications.

However, glass cloth is cheap and tends to clog quickly, alumina balls have poor filtration accuracy because impurities once captured tend to flow out, and ceramic foam has large pores, making it difficult to filter fine impurities effectively. The drawback is that it cannot be done.

Therefore, as shown in Japanese Patent Publication No. 52-22327, Japanese Patent Application Laid-Open No. 64-21019, etc., aggregate particles such as silicon carbide or alumina are bonded with an inorganic binder, and there are countless numbers of particles between the aggregate particles. Tubular filter media with a structure in which fine continuous pores are formed are being used. This filter material has superior filtration performance compared to the other filters mentioned above, prevents clogging for a long time, prevents captured impurities from flowing out, and allows for precise pore size. This has the advantage of allowing for more efficient filtration.

[Problems to be Solved by the Invention] However, in Japanese Patent Publication No. 52-22327, SiO2 in the binder used is 10 to 50% by weight, B2
Since O3 is 5-20% by weight, borosilicate glass is formed. In this way, since there is a large amount of S102 in the binder,
It is reduced to molten aluminum, and there are problems with corrosion resistance and Si leakage.

On the other hand, when aggregate particles are bonded with an inorganic binder as described above, the inorganic binder is aluminum borate (9Af
LzO:+・2B20. ) It is preferable to produce needle-shaped crystals such as the following, since these crystals have poor wettability with, for example, molten aluminum and are a material that is difficult to react with (excellent in corrosion resistance). In the above-mentioned Japanese Patent Application Laid-Open No. 64-21019, B20315-80%, A-2032-60%,
If a binder with a composition of 3 to 30% CaO and 5 to 20% MgO is used, or even if raw raw materials are used, the composition will change no matter how uniformly mixed. There were variations in the strength of the fired body and in the binder composition, and it was not possible to obtain a uniform molten state.
3.2 B203) production amount is small. In addition, even if the cooling rate is 130 to 70°C/hr, the molten state is not uniform, so aluminum borate (9ARz
The amount of O:+2B20:l) produced was small, and variations within the fired body were also observed.

Thus, aluminum borate (9A l 203
If the amount of 2B203) produced is small, there will be problems in corrosion resistance, especially against molten aluminum, and in the worst case, there is a risk that the filter medium will collapse.

[Means for Solving the Problems] Therefore, the present inventor conducted various studies to solve the above-mentioned problems, and found that by using a frit of a specific composition and particle size as an inorganic binder, aluminum borate The present invention was completed based on the discovery that increasing the production amount can extend the life of the filter medium.

That is, according to the present invention, there is provided a porous filter medium in which ceramic aggregate particles are bound together by an inorganic binder, and the binder contains 15 to 80% by weight of B2O3, 2 to 60% by weight of A2, 30 to 30% by weight of CaOO, and MgO5-50% by weight
Provided is a filter medium for molten metal, characterized in that the frit has a composition of 50% average particle size of 35g1 or less.

[Function] The present invention is characterized in that a frit made of a boric acid composition and whose particle size is below a predetermined value is used as a binder.

By using such a frit as a binding material,
More aluminum borate (9A 20ff)
2B20. ) is generated, and the life of the filter medium can be extended.

The aggregate used in the present invention must be one that does not react with the molten metal and has an appropriate particle size, or is made of ceramic materials such as alumina, silicon carbide, silicon nitride, and zirconia. aggregate particles or meet these conditions.

In addition, the average particle diameter of the ceramic aggregate particles used is usually 0.
．． Approximately 3 to 3.01 ul is used.

In addition, as aggregate particles, the shape index defined below or 1
It is preferable to use a number in the range of 00 to 130.

That is, in the projected view of the aggregate shown in Figure 1, its maximum diameter is M, the diameter perpendicular to the maximum diameter M is B, and the projected area is A.
, circle J, and the length of the circle is P, the shape index (SF) is expressed by the following formula.

SF= (SFI +SF2 +5F3)/3 Here, SF, = (π/4)X (M2 /A)X
100SF2 = (1/4π)
/A) X l 00S F ++ = (
M/B) x l OO.

Incidentally, the shape index of a pearl is 100.

When aggregate particles having a shape index in this range are used, a porous body having a uniform pore diameter can be obtained, which improves the accuracy of collecting impurities in the filter medium, which is preferable.

As described above, the composition of the inorganic binder is B, 0315 to 80% by weight, and A.

032-60% by weight, CaOO-30% by weight, and M
It is necessary that the frit has a gO range of 5 to 50% by weight. Aluminum borate (9A sentence 203・
In order to produce 2B203), the above-mentioned composition is necessary, and since it is a frit, uniform meltability can be sufficiently ensured.

Furthermore, the frit has a 50% average particle diameter of 35 mm
Below, it is preferably 10 to 35 micropus. If the 50% average particle diameter exceeds 35 wells, the particle size distribution will vary,
This is not preferable because the strength of the resulting porous filter medium will be poor.

Further, the blending ratio of the inorganic binder having the above-mentioned specific composition and particle size to the ceramic aggregate particles is preferably 4 to 20 parts by weight based on 100 parts by weight of the aggregate particles.

When bonding an inorganic binder with such a specific composition and particle size to aggregate particles, the inorganic binder is heated to 1200 to 1400°C to melt the inorganic binder, and then cooled to 800°C at a cooling rate of 30 to 70°C per hour. When fired and slowly cooled under conditions such as slow cooling, aluminum borate (9AJLzO
:s 2B203) is suitably crystallized, which is preferable.

Note that the shape of the filter medium is not limited to a tube shape, but may be a plate shape. Further, the thickness of the filter medium should normally be about 15 to 35 as.

Next, an example of a method for manufacturing a filter medium according to the present invention will be explained.

For example, for 100 parts by weight of ceramic aggregate particles such as alumina, silicon carbide, and silicon nitride, the composition of B, O 15-80% by weight, A-2032-60% by weight, CaO 0-30% by weight, and MgO 5-50% by weight is used. Add 4 to 20 parts by weight of an inorganic binder consisting of a frit with a 50% average particle size of 35% or less, and add an appropriate amount of an organic binder such as carboxymethyl cellulose (CMC), calcium lignin sulfonate, or dextrin. After adding water and kneading, the mixture is molded into a molded article of a predetermined shape. Next, the filter medium of the present invention can be obtained by drying the obtained molded body and then firing it at a temperature of usually 1100° C. or higher.

[Examples] The present invention will be explained in more detail based on Examples below, but the present invention is not limited to these Examples.

(Example 1) Using sintered alumina with a particle size of 14 to 28 mesh as aggregate particles, the composition, shape, and particle size of the inorganic binder were varied, and various weights of the binder were added to 100 parts by weight of the aggregate as organic binder. , was added with water and kneaded. Next, using the obtained mixture, an outer diameter of 100 mmφ and an inner f1
Molding a pipe-shaped product with a diameter of 60 mm and a length of 900 m.
After drying at 105°C, the binder is sufficiently melted at 1300°C.
The temperature was then raised, and after being maintained for 3 hours, the temperature was increased to 800° C. and slowly cooled at a cooling rate of 50° C. per hour, thereby producing a fired filter medium.

Regarding the obtained filter medium, the crystallinity of aluminum borate (9AMzO:+ 2B203) (=9A of 16.5°, peak height of 12032B20:l/α-A of 43.4") was determined by powder X-ray diffraction method. The peak height of l 203) was determined.Furthermore, the bending strength by three-point bending at room temperature was also measured.

The results are shown in Table 1.

In Table 1, No. 6.8 to 12 indicate cases outside the scope of the present invention.

As is clear from Table 1, when a frit made of a boric acid composition and whose particle size is below a predetermined value is used as a binder, compared to other cases (No. 6.8 to 12), the filter material becomes It can be seen that the bending strength or the crystallinity of aluminum borate decreases.

(Example 2) Among the filter media produced in Example 1, No. 1, 9.1
3.17 were selected, and the boron (B) removal rates of these filter media were determined and shown in Table 2.

Table 2 This has the advantage of improving the ability to collect impurities from molten metal.

[Brief explanation of the drawing]

FIG. 1 is a projected explanatory diagram of aggregate used when calculating the shape index of aggregate.

Claims (1)

[Claims] (1) A porous filter medium in which ceramic aggregate particles are bound by an inorganic binder, the binder being B_2O_315 to 80% by weight, Al_2O
_32-60% by weight, CaO0-30% by weight and Mg
A filter medium for molten metal, characterized in that the frit has a composition of 5 to 50% by weight of O, and the 50% average particle diameter of the frit is 35 μm or less.