JPH0768341A - Filter for molten metal - Google Patents

Abstract

PURPOSE:To provide the filter having heat resistance and thermal impact resistance in combination and is made well usable over a long period of time by using a porous sintered compact which consists essentially of mullite and into which a specific ratio of zircon is incorporated as the filter for molten metal. CONSTITUTION:This filter 1 is composed of the porous sintered compact consisting essentially of the mullite and contg. 10 to 50wt.% zircon. The powder of the zircon (ZrSiO4) is added at 10 to 50wt.% into the powder of 90 to 95wt.% mullite (3Al2O3.2SiO2) and a dispersant, binder, etc., are added to this mixture and the mixture is mixed. The mixture is molded to a honeycomb shape by extrusion molding and is thereafter held for >=2 hours at >=1550 deg.C, by which the mixture is calcined and 5 to 40wt.% monoclinic zirconia crystals are preferably precipitated. Since the monoclinic zirconia crystals existing among the mullite particles relieve stresses, the thermal impact resistance is improved. The mullite has sufficient heat resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal filter for removing impurities such as slag and other non-metallic inclusions in molten metal such as cast iron.

[0002]

2. Description of the Related Art Conventionally, when a molten metal such as cast iron is cast into a mold, it is generally poured into the mold through a gutter-shaped runner. In this case, the molten metal is filtered by the filter 1 arranged in the middle of the runner 2 as shown in FIG.
The slag (oxide) and non-metallic inclusions in the original hot water are removed to make a clean molten metal. Such Motoyu cordierite as a filter 1 to be used for filtering _{(2MgO · 2Al 2 O 3 ·} 5SiO 2), consists of a ceramic material such as mullite _{(3Al 2 O 3 · 2SiO 2} ), parallel to the axial direction A honeycomb structure having a large number of through cells arranged in a line is often used (see, for example, Japanese Patent Publication No. 3-28986).

[0003]

[Problems to be Solved] However, although conventional cordierite forming a filter for molten metal has excellent thermal shock resistance, it has a problem that it melts and loses heat resistance at 1450 ° C or higher. Had sufficient heat resistance, but had a problem of low thermal shock resistance.
Thus, since there is no filter having both excellent heat resistance and thermal shock resistance, there has been a strong demand for a filter having both of these characteristics.

[0004]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a porous sintered body containing mullite (3Al ₂ O ₃ .2SiO ₂ ) as a main component and zircon (ZrSiO ₄ ) in an amount of 10 to 50% by weight. The body is a filter for molten metal.

In the filter of the present invention, it is essential to add 10 to 50% by weight of zircon to 90 to 50% by weight of mullite. If the amount of addition is less than 10% by weight, sufficient thermal shock resistance can be obtained. On the contrary, if the addition amount is more than 50% by weight, the heat resistance becomes low.

The zircon added is precipitated as zirconia (ZrO ₂ ) containing a monoclinic phase in the sintered body,
Since the monoclinic zirconia crystals existing between the mullite particles relax the stress, the thermal shock resistance can be improved. And in order to achieve such an effect,
It is preferable to precipitate 5 to 40% by weight of monoclinic zirconia crystals in the final sintered body. Also, since monoclinic zirconia crystals are not generated unless the temperature is 1550 ° C. or higher,
The firing for producing the molten metal filter of the present invention is 1
It is preferable to carry out at 550 ° C. or higher.

In the method for producing a filter for molten metal of the present invention, zircon powder having an average particle size of 5 μm or less is added to mullite powder at a rate of 10 to 50% by weight, and a dispersant, a binder and the like are added, and a ball mill or The slurry obtained by mixing with a vibrating mill is granulated to obtain a raw material, which is formed into a honeycomb shape by, for example, extrusion molding, and then at a temperature of 1550 ° C. or higher.
It can be obtained by holding for at least time and firing.

Further, the porous sintered body of the present invention may be of any shape such as a honeycomb body or a three-dimensional mesh, which has a filter function. And in the case of a honeycomb-shaped body, the number of cells is 5
0 to 800 cells / inch ² , in the case of a three-dimensional mesh, the average pore diameter is in the range of 0.9 μm to 3.5 mm, and the aperture ratio is preferably in the range of 35 to 80%.

Furthermore, if the molten metal filter is formed of a honeycomb-like body, the molten metal can be rectified at the same time as the filter function, and the flow of the molten metal can be made smooth.

[0010]

EXAMPLE As an example of the present invention, zircon powder was added to mullite powder in an addition amount shown in Table 1 and mixed, and then organic additives such as a binder and a solvent were added. After uniformly kneading the obtained raw material, it was formed into a honeycomb shape by an extruder, dried and cut, and then fired at a predetermined temperature of 1600 to 1700 ° C. to obtain various filters having different compositions. .

A cordierite filter was also prepared for comparison. Each filter had a square shape with a thickness of 15 mm and a cross section of 50 × 50 mm, the number of cells was 170 cells / inch ² , and the rib thickness was 0.45 mm.

With respect to the obtained filter, the characteristics of thermal expansion coefficient (normal temperature to 900 ° C.) and heat resistance and thermal shock resistance required for the molten metal filter were investigated. Heat resistance is 1
A certain amount of molten iron at 600 ° C. was passed through each filter, and the filter after passing was visually checked and judged. Regarding the thermal shock resistance, each filter was put in an electric furnace maintained at 1000 ° C., held for about 10 minutes, dropped in water and rapidly cooled to perform an underwater drop test, and the presence or absence of cracks was visually checked. The results are shown in Table 1.

As is clear from Table 1, those made of cordierite or mullite (Nos. 1 and 2) did not satisfy both the melting resistance and the thermal shock resistance. Among the mullites containing zircon, those containing less than 10% by weight of zircon (No. 3) have poor thermal shock resistance, while those containing more than 50% by weight of zircon (No. 3).
9 and 10) had poor melting resistance.

In comparison with these, the amount of zircon added is 10 to 5
Within the range of the present invention with 0% by weight (No. 4 to 8)
It can be seen that can be suitably used as a filter for molten metal without any problems in melting resistance and thermal shock resistance.

Even if the same experiment is performed by changing the number of cells and the rib thickness of the honeycomb body used in the above experimental example,
The result was similar. The same applies to a three-dimensional mesh body as well as the honeycomb body.

[0016]

[Table 1]

Next, in Table 1, No. For the sample of No. 6, the monoclinic zirconia crystal was set to 15 at a firing temperature of 1650 ° C.
A thermal shock resistance test was carried out on a mullite-based ceramic contained in an amount of 1 wt% and a mullite-based ceramic containing no monoclinic zirconia crystals which was fired at 1550 ° C. as a comparative example. Each of them had a test piece shape and a porosity of 40%.

The test was carried out by heating each test piece to a predetermined temperature and dropping it in water to measure the three-point bending strength for each temperature difference (ΔT). As shown in FIG. 2, it was found that the comparative example in which monoclinic zirconia did not exist had a low initial bending strength, and therefore the bending strength after heating and dropping in water was also low. On the other hand, it can be seen that both the bending strength and the thermal shock resistance are excellent in the examples of the present invention in which monoclinic zirconia crystals are present.

[0019]

As described above, according to the present invention, since the metal melt filter is constituted by the porous sintered body containing mullite as a main component and containing 10 to 50% by weight of zircon, excellent heat resistance is obtained. It is possible to obtain a filter for molten metal that has both excellent properties and thermal shock resistance and can be used satisfactorily for a long period of time.

[Brief description of drawings]

FIG. 1 is a perspective view of a molten metal filter according to an embodiment of the present invention.

FIG. 2 is a graph showing the thermal shock resistance of the mullite ceramics that forms the filter for molten metal of the present invention.

[Explanation of symbols]

 1: Filter 2: Runway

Claims (1)

[Claims] 1. A filter for a molten metal, which is installed in a runway through which a molten metal passes, and which comprises a porous sintered body containing mullite as a main component and 10 to 50% by weight of zircon.