Molten metal filtration unit

Abstract

The present invention provides a molten metal filtration unit (1), comprising: a plurality of cylindrical ceramic filter tubes (3) arranged substantially in parallel, each having a substantially circular cross-sectional shape perpendicular to the longitudinal direction on its outer and inner surfaces; and a pair of side plates (2A, 2B) arranged at both longitudinal ends of the plurality of ceramic filter tubes, wherein the plurality of ceramic filter tubes have a first end on the side from which the molten metal is discharged and a second end on the other side, and at least a portion of the plurality of ceramic filter tubes satisfy both of the following two relational expressions: (i) L1 / D1 ≧ 8.5 (ii) L2 / D2 ≧ 22, where L1 is the longitudinal length of a portion (3d) of the outer surface of the filter tube exposed to the molten metal, D1 is the outer diameter of the filter tube, L2 is the longitudinal length of a portion (3c) of the inner surface of the filter tube exposed to the molten metal, and D2 is the inner diameter of the filter tube.

Description

[Technical Field]

[0001] The present invention relates to a molten metal filtration unit for filtering molten metal such as aluminum. [Background technology]

[0002] Molten metals such as aluminum used in the production of castings typically contain impurities such as hydrogen and non-metallic inclusions, such as oxides. For example, dissolved hydrogen in the molten metal can form cavities called porosity in the casting, and oxides and other impurities can become inclusions in the casting. These cavities and inclusions are undesirable because they can be the starting point for fracture in the casting. Therefore, filtration devices have been developed to filter the molten metal and remove inclusions and other impurities contained in the molten metal.

[0003] To achieve this goal, a molten metal filtering device is typically used in which a molten metal filtering unit having a plurality of ceramic filter tubes for filtering impurities from the molten metal is mounted in a filtering chamber provided with an inlet and an outlet (see, for example, Patent Document 1). Such a molten metal filtering unit generally comprises a plurality of ceramic filter tubes and a pair of side plates disposed approximately parallel to each other at both ends of the longitudinal direction of the plurality of filter tubes. The molten metal introduced into the filtering chamber through the inlet of the filtering chamber enters the peripheral wall surface of the filter tube provided with one side plate, where impurities are filtered out, and then the molten metal is discharged from the opposite end of the filter tube provided with the other side plate and then flows out of the outlet of the filtering chamber.

[0004] In order to improve the processing capacity and efficiency of molten metal filtration units, attempts have been made to increase the amount of molten metal passing through and extend the service life of the filter tubes. One example of such an attempt is a molten metal filtration unit in which the ratio of the depth of the recesses formed in one of a pair of side plates into which multiple filter tubes are inserted and held to the spacing between adjacent recesses is adjusted within a predetermined range, and the spacing between adjacent recesses is also adjusted within a predetermined range (see Patent Document 2). This document considers that by configuring the multiple filter tubes and the corresponding recesses in this way, it is possible to achieve the effect of improving filtration efficiency while maintaining the strength of the side plates. Also, a filtration filter (filter tube) for molten metal has been reported in which the average particle size of the filter aggregate is within a predetermined range, the ratio of the average particle sizes on the inner and outer peripheral surfaces of the filter is within a predetermined range, and the porosity gradually increases from the inner peripheral surface side to the outer peripheral surface side (see Patent Document 3). This document considers that by appropriately adjusting the average particle sizes on the inner and outer peripheral surfaces of the aggregate that constitutes the filtration filter for molten metal, as well as the change in porosity between them, it is possible to obtain the effects of improving the performance of capturing inclusions contained in molten metal and the life of the filter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-4868 [Patent Document 2] Patent No. 6295108 [Patent Document 3] Patent No. 6423726 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a technology for arranging multiple tubes inserted into recesses in a side plate as densely as possible while taking into consideration maintaining the strength of the side plate, such as the molten metal filtration unit reported in Patent Document 2, it is desirable to further increase the number of filter tubes in order to further increase the amount of molten metal passing through and further extend the service life of the filter tubes. However, if the number of filter tubes is increased excessively, it becomes necessary to form a large number of recesses and outlet-side through holes in the side plate corresponding to the filter tubes, which can be inconvenient as it can make it difficult to maintain sufficient strength of the side plate. Furthermore, the molten metal filter (filter tube) reported in Patent Document 3 aims to improve the inclusion collection performance and filter life by focusing mainly on the aggregate of the filter. However, there is room for further improvement in the inclusion removal performance and further extension of the filter life by adding innovations to the structure of the molten metal filter and the entire filtration unit including the same.

[0007] Therefore, one of the problems to be solved by the present invention is to provide a novel molten metal filtering unit that is not available in the prior art. Furthermore, a further problem to be solved by the present invention is to provide a novel molten metal filtration unit that eliminates the above-mentioned disadvantages, i.e., that can simultaneously further increase the amount of molten metal passing through, further extend the service life of the filtration tubes, and further improve the performance of removing inclusions contained in the molten metal, while maintaining a high level of strength of the side plates. [Means for solving the problem]

[0008] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved in a molten metal filtration unit including a plurality of cylindrical ceramic filter tubes and a pair of side plates arranged at both ends of the filter tubes in the longitudinal direction by adjusting the ratio L1 / D1 of at least some of the filter tubes, where L1 is the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal to the outer diameter D1 of the filter tube, to a specific lower limit or more, and by adjusting L2 / D2 of the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal to the inner diameter D2 of the filter tube, to a specific lower limit or more. That is, the inventors have discovered that with a molten metal filtration unit having such a configuration, the amount of molten metal passing through (flow rate) can be further increased by increasing the area of ​​the portion of the outer surface of the filter tube that is exposed to the molten metal and by reducing (thinning) the inner diameter of the filter tube to a certain extent, and that the service life of the filter tube can be further extended by reducing the amount of molten metal passing through per unit area of ​​the filter tube, and in addition, by reducing the flow rate of the molten metal, the residence time within the filter tube can be extended and inclusions in the molten metal can be efficiently removed, thereby completing the present invention.

[0009] A typical embodiment of the present invention is as follows. A molten metal filtration unit, comprising: The filter includes a plurality of cylindrical ceramic filter tubes arranged substantially parallel to one another, each having a substantially circular cross section perpendicular to the longitudinal direction on its outer surface and inner surface, and a pair of side plates disposed at both ends in the longitudinal direction of the plurality of ceramic filter tubes, The plurality of ceramic filter tubes have a first end on a side from which the molten metal is dispensed and a second end on the other side, At least some of the ceramic filtration tubes When the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal is L1, the outer diameter of the filter tube is D1, the longitudinal length of the portion of the inner surface of the filter tube exposed to the molten metal is L2, and the inner diameter of the filter tube is D2, the following two relational expressions are satisfied: (1) L1 / D1≧8.5 (2) L2 / D2≧22 A molten metal filtration unit that meets all of the above requirements. [Effects of the Invention]

[0010] According to the present invention, a novel molten metal filtering unit not found in the prior art is provided. Furthermore, according to a preferred embodiment of the molten metal filtration unit of the present invention, by appropriately adjusting the relationship between the structural elements of the ceramic filter tube, it is possible to obtain the advantages of further increasing the flow rate of molten metal, further extending the service life of the filter tube, and further improving the performance of removing inclusions contained in the molten metal, all while maintaining a high level of strength of the side plates. (Here, "further improving removal performance" can also be rephrased as "further improving removal efficiency.") [Brief explanation of the drawings]

[0011] [Figure 1(a)] FIG. 1(a) is a schematic diagram of a molten metal filtration unit according to one embodiment of the present invention. [Figure 1(b)] FIG. 1(b) is a cross-sectional schematic diagram showing a mechanism by which molten metal is subjected to a filtering operation in a molten metal filtering unit according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a portion of a molten metal filtration unit according to one embodiment of the present invention, including a ceramic filter tube having a first end on the side from which molten metal is dispensed and a second end on the other side, and a pair of side plates arranged at both ends of the ceramic filter tube in the longitudinal direction. [Figure 3] FIG. 3 is a cross-sectional view of a ceramic filter tube of a molten metal filtering unit according to a modified embodiment of the present invention. [Figure 4]4(a) and 4(b) are diagrams illustrating the relationship between an opening at a first end of a ceramic filter tube on the side from which molten metal is discharged and a substantially circular through-hole provided in a side plate on the discharge side in a molten metal filtration unit according to one embodiment of the present invention. Fig. 4(a) is a cross-sectional view as viewed in the longitudinal direction, and Fig. 4(b) is a cross-sectional view as viewed in the horizontal direction perpendicular to the longitudinal direction. [Figure 5] FIG. 5 is a cross-sectional view illustrating the relationship between the inner diameter on the filter tube arrangement side and the inner diameter of the end on the discharge side in a substantially circular through hole provided in a side plate on the discharge side of a molten metal filtration unit according to one embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view illustrating head heights T0 and T1 of molten metal for evaluating the filtration performance of a molten metal filtration unit according to one embodiment of the present invention in the examples described later. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, the structure of a molten metal filtration unit according to one embodiment of the present invention and an outline of filtration of molten metal will be described with reference to Figures 1(a) and 1(b). The configuration shown in the figures is a simplified example for the purpose of explanation, and the molten metal filtration unit of the present invention is not limited to this.

[0013] In Figures 1(a) and 1(b), 1 denotes a molten metal filtration unit, 2A and 2B denote a pair of side plates (the side plate on the side where the molten metal is dispensed and the side plate on the opposite side) disposed at both ends of the filtration unit, 3 denotes multiple ceramic filter tubes (hereinafter simply referred to as "filter tubes") for filtering impurities from the molten metal, and 2e denotes through-holes in the side plate on the dispensing side. Although not shown in the figure, gaskets having a shape that can fit between each end of the filter tube and the corresponding side plate may be disposed. While providing such gaskets is not essential, providing gaskets is preferable from the viewpoints of stably fixing the filter tubes to the side plate and reliably preventing leakage of the molten metal. The multiple ceramic filter tubes 3 are arranged approximately parallel to each other and are cylindrical, with the outer and inner cross sections perpendicular to the longitudinal direction each being approximately circular. The filter tubes 3 are typically formed from a porous ceramic material. As shown by the arrows in Figure 1(b), foreign matter contained in the molten metal can be filtered and removed by the molten metal flowing between the inner and outer surfaces of the filter tube 3. The refined molten metal that has been filtered of foreign matter is then discharged from the through hole 2e in the side plate on the outlet side.

[0014] For ease of explanation, the molten metal filtration unit 1 in FIGS. 1(a) and 1(b) shows a structure in which only four ceramic filter tubes 3 are arranged, but this is not limiting. The number of ceramic filter tubes 3 is not particularly limited as long as there are a plurality of them, and may be, for example, 2 to 50, 3 to 40, 4 to 30, or 5 to 20. The cross-sectional shape of the ceramic filter tubes 3 is typically approximately circular as shown, but may be a mixed shape including some non-circular cross-sectional shapes such as flattened approximately oval or approximately rectangular. In such a mixed shape, the proportion of filter tubes with cross-sectional shapes other than approximately circular may be less than half of the total filter tubes, for example, less than one-third. The multiple ceramic filter tubes 3 are typically arranged horizontally and at approximately equal intervals, but adjacent ceramic filter tubes may be in direct contact in some areas. When the ceramic filter tubes 3 are arranged substantially horizontally at substantially equal intervals to form a plurality of rows, it is preferable that the rows are also arranged at substantially equal intervals.

[0015] Fig. 2 shows a cross-sectional view of a molten metal filtration unit according to one embodiment of the present invention, viewed perpendicular to the longitudinal direction of a filter tube. In the molten metal filtration unit according to the embodiment of Fig. 2, a portion of the ceramic filter tube is omitted for convenience of illustration, but the molten metal filtration unit has a configuration in which the ceramic filter tube is further extended in the longitudinal direction. In Figure 2, 1 denotes a molten metal filtration unit, 2A denotes a side plate on the side where the molten metal is discharged, 2B denotes a side plate on the opposite side from the discharge side (which is closed and has no through-holes), 2e denotes a substantially circular through-hole provided in the side plate on the discharge side, 3 denotes a cylindrical ceramic filter tube whose outer and inner cross-sections perpendicular to the longitudinal direction are both substantially circular, 3a denotes a substantially circular outer end face at the second end of the filter tube, 3b denotes a substantially circular inner end face at the second end of the filter tube, 3c denotes a portion of the inner surface of the filter tube exposed to the molten metal, 3d denotes a portion of the outer surface of the filter tube exposed to the molten metal, 3e denotes a substantially circular opening at the first end of the filter tube, 3w denotes an annular end face excluding the opening at the first end of the filter tube, 4A denotes a gasket for securing the first end of the filter tube, and 4B denotes a gasket for securing the second end of the filter tube. For the sake of explanation, only one of the multiple ceramic filter tubes 3 is shown in Figure 2. The ceramic filter tube 3 is fixed by fitting, via gasket 4A or 4B, to recesses (which typically have peripheral walls with a substantially circular outline) formed in the side plate 2A on the side from which the molten metal is dispensed and the side plate 2B on the opposite side to the dispense side, at each of an end face 3w and its peripheral edge excluding the opening at the first end of the filter tube 3 on the side from which the molten metal is dispensed and an outer end face 3a and its peripheral edge at the second end opposite the first end. Here, the recesses and gasket 4A formed in the side plate 2A or the recesses and gasket 4B formed in the side plate 2B are formed to fit the shapes of the first end of the ceramic filter tube 3 on the side from which the molten metal is dispensed and the second end on the opposite side, respectively, and have openings on the first end side that correspond to the openings of the filter tube.

[0016] The packings 4A and 4B may be composed only of a contact portion that is a flat plate-like body that contacts the end face of the filter tube 3. In such a configuration, the peripheral wall portion of the recessed portion formed in the side plate has a substantially circular cross-sectional shape that fits the shapes of the first end and second end of the filter tube 3, and the outer diameter of the filter tube 3 at the first end and second end is substantially equal to the diameter of the peripheral wall portion of the corresponding recessed portion formed in the side plate. Alternatively, the packings 4A and 4B may each comprise a flat contact portion that contacts the end face of the filter tube 3, and a ring-shaped sealing portion that contacts the outer edge of the filter tube 3 and the peripheral wall of the recess formed in the side plate. These two portions of the packing may be integrally formed, or may be two separate components connected and joined together. In this configuration, the contact portion of the packing absorbs longitudinal dimensional changes in the filter tube due to expansion and contraction caused by environmental conditions such as the set temperature of the molten metal, thereby maintaining the tightness of the contact between the filter tube and the side plate. Meanwhile, the sealing portion of the packing seals and joins the filter tube and the side plate, thereby maintaining the proper shape of the entire molten metal filtration unit. The contact portions of packing 4A and / or packing 4B may be fixed in a compressed state in recesses formed in side plate 2A and / or side plate 2B between the end of filtration tube 3 and side plate 2A and / or side plate 2B. The thickness of the contact portions of packing 4A and / or packing 4B in the longitudinal direction of the filtration tube in an uncompressed state may be, for example, 5% to 80% of the depth of the recesses formed in side plate 2A and / or side plate 2B in the longitudinal direction of the filtration tube, and may preferably be 10% to 70%, 15% to 60%, 18% to 50%, or 20% to 40%. The compression ratio (the ratio of the compressed thickness to the uncompressed thickness) of the intimately contacting portions of packing 4A and / or packing 4B when compressed into the recesses formed in side plate 2A and / or side plate 2B may be, for example, more than 0% and 80% or less, 10% to 70%, 20% to 60%, or 30% to 50%. The thickness of the compressed packing may be, for example, 2% to 50%, 4% to 40%, 5% to 30%, 6% to 20%, or 7% to 15% of the depth of the recesses formed in side plate 2A and / or side plate 2B in the longitudinal direction of the filtration tube.

[0017] In the molten metal filtration unit 1 illustrated in FIG. 2 , the side plate 2A on the side from which the molten metal is dispensed and the side plate 2B on the opposite side from the dispensed side are not particularly limited in shape, as long as they have recesses formed therein so that a first end of the ceramic filter tube 3 on the side from which the molten metal is dispensed and a second end on the opposite side can be fitted and fixed thereto via packings 4A and 4B, respectively. Each of the side plates 2A and 2B may typically be a flat plate. The bottoms of the side plates 2A and 2B may each be flat. Alternatively, when the longitudinal direction of the filter tube 3 is approximately horizontal, at least one of the side plates 2A and 2B may have a bottom formed so that the bottom edge of one is positioned vertically higher than the bottom edge of the other. When the molten metal filtering unit 1 is placed on the hearth (not shown in FIG. 2) of the molten metal filtering apparatus, the side end face of the side plate 2A on the discharge side is pressed against the inner wall surface of the filtering apparatus by the weight of the filtering unit, so that the filtering unit can be stably placed so that the through holes 2e (plural) in the side plate 2A on the discharge side and the outlet provided on the inner wall surface of the filtering apparatus can be reliably and continuously communicated at accurate positions. Details of the embodiment relating to the structure of the side plates will be described later in a separate section.

[0018] In FIG. 2, the ceramic filter tube 3 is illustrated as being cylindrical with a substantially circular cross section on the outer and inner surfaces that is the same from the second end to the first end. In Figure 2, [i]. The longitudinal length of the portion 3d of the outer surface of the filter tube 3 exposed to the molten metal, that is, the longitudinal length from the end point of the portion not covered by the side plate 2B and packing 4B on the opposite side to the outlet side of the filter tube 3 on the outer surface of the second end portion on the opposite side to the outlet side of the filter tube 3 to the end point of the portion not covered by the side plate 2A and packing 4A on the outlet side on the outer surface of the first end portion on the outlet side, is defined as L1; [ii]. The longitudinal length of the portion 3c of the inner surface of the filter tube 3 exposed to the molten metal, i.e., the longitudinal length from the inner end surface 3b at the second end opposite to the discharge side of the filter tube 3 to the end surface 3w at the first end on the discharge side, is defined as L2; [iii]. The outer diameter of the filtration tube 3 (which is the same from the second end to the first end in this figure) is D1, [iv]. When the inner diameter of the filtration tube 3 (which is the same from the second end to the first end in this figure) is D2, Usually, the following relationship is satisfied: (1) L1 / D1≧8.5 (2) L2 / D2≧22 Here, the "longitudinal direction" of the filtration tube 3 refers to the direction connecting the center of the outer circumferential circle of the end face 3w at the first end on the discharge side and the center of the outer circumferential circle of the outer end face 3a at the second end on the opposite side from the discharge side. Furthermore, when the "substantially circular" cross-sectional shape perpendicular to the longitudinal direction of the outer and / or inner surface of the filtration tube 3 is not a perfect circle, the outer and / or inner diameter is determined by the circumscribing circle of the cross-sectional shape.

[0019] When the ceramic filter tube 3 satisfies the above relational expression (1), the longitudinal length of the portion of the outer surface of the filter tube that is exposed to the molten metal can be adjusted to extend to a high ratio equal to or greater than a predetermined value relative to the outer diameter of the filter tube. This increases the area of ​​the outer exposed portion, making it possible to further increase the amount of molten metal that can pass through. At the same time, the amount of molten metal that can pass through per unit area of ​​the filter tube is reduced, making it possible to further extend the service life of the filter tube and ultimately significantly improve the filtration performance of the molten metal. Furthermore, by having the ceramic filter tube 3 satisfy the above-mentioned relational expression (2) in addition to the above-mentioned relational expression (1), the longitudinal length of the portion of the inner surface of the filter tube exposed to the molten metal can be adjusted to have a ratio of a predetermined value or more to the inner diameter of the filter tube (in other words, the inner diameter of the filter tube can be adjusted to have a ratio of a predetermined value or less to the longitudinal length of the portion of the inner surface of the filter tube exposed to the molten metal), thereby reducing the flow rate of the molten metal and lengthening the residence time of the molten metal within the filter tube, making it possible to efficiently remove inclusions from the molten metal.This offers the advantages of further increasing the flow rate of the molten metal and further extending the service life of the filter tube, as well as further improving the performance of removing inclusions from the molten metal. Furthermore, by making the ceramic filter tubes 3 satisfy the above-mentioned relational expressions (1) and (2), it becomes possible to increase the number of filter tubes to be installed on the side plates 2A and 2B of the molten metal filtration unit 1, thereby further improving the filtration performance.

[0020] In the above-mentioned relational expression (1) L1 / D1≧8.5, from the above-mentioned viewpoint, it is preferable that L1 / D1≧8.6, L1 / D1≧8.7, L1 / D1≧8.8, or L1 / D1≧8.9, and more preferably, L1 / D1≧9.0, L1 / D1≧9.1, L1 / D1≧9.2, L1 / D1≧9.3, L1 / D1≧9.4, L1 / D1≧9.5, L1 / D1≧9.6, L1 / D1≧9.7, L1 / D1≧9.8, L1 / D1≧9.9, L1 / D1≧10, L1 / D1≧10.5, L1 / D1≧11, L1 / D1≧11.5, L1 / D1≧12, L1 / D1≧12.5, L1 / D1≧13, L1 / D1≧13.5, or L1 / D1≧14. Alternatively, L1 / D1≧14.5, L1 / D1≧15, L1 / D1≧15.5, L1 / D1≧16, L1 / D1≧16.5, or L1 / D1≧17. In the above relationship (2) L2 / D2≧22, from the above-mentioned viewpoint, it may be preferable that L2 / D2≧22.5, L2 / D2≧23, L2 / D2≧23.5, L2 / D2≧24, L2 / D2≧24.5, L2 / D2≧25, L2 / D2≧25.5, or L2 / D2≧26. Alternatively, L2 / D2≧26.5, L2 / D2≧27, L2 / D2≧27.5, L2 / D2≧28, L2 / D2≧28.5, L2 / D2≧29, L2 / D2≧29.5, L2 / D2≧30, L2 / D2≧30.5, L2 / D2≧31, L2 / D2≧31.5, L2 / D2≧32, L2 / D2≧32.5, L2 / D2≧33, L2 / D2≧33.5, L2 / D2≧34, L2 / D2≧34.5, or L2 / D2≧35.

[0021] When each of the plurality of ceramic filter tubes 3 is cylindrical and has the same outer and inner circular cross section from the second end to the first end (i.e., when the outer diameter is the same from the second end to the first end and the inner diameter is the same from the second end to the first end), the plurality of filter tubes 3 usually have the same outer and inner diameters, but at least some of the filter tubes may have different outer and / or inner diameters. In such a case, the outer diameter D1 and / or inner diameter D2 of the filter tube 3 refers to the average value of the outer and / or inner diameters of all the plurality of filter tubes.

[0022] In a modified embodiment, at least some of the ceramic filter tubes 3 may have a circular cross section on the outer and / or inner surface that differs from that at the second end, i.e., the outer and / or inner diameter varies from that at the second end, over a portion or substantially the entire length from the second end opposite the molten metal outlet side to the first end. The change in the outer and / or inner diameter of the filter tube from that at the second end may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 15% or less, 10% or less, or 5% or less. In this way, when the ceramic filter tube 3 has an outer diameter and / or an inner diameter that change from those at the second end, the outer diameter D1 and / or the inner diameter D2 refer to the outer diameter of the outer end surface 3a at the second end of the filter tube and / or the inner diameter of the inner end surface 3b at the second end of the filter tube. The definition based on the average value of the outer diameter D1 and / or the inner diameter D2 of the plurality of filter tubes 3 as described above also applies to the case where at least some of the plurality of filter tubes have circular cross sections on the outer and inner surfaces that differ from those at the second end over part or substantially the entire length from the second end to the first end.

[0023] In a configuration in which at least some of the ceramic filter tubes 3 have an outer diameter and / or an inner diameter that change from that at the second end in part or almost the entire length from the second end to the first end on the side opposite to the outlet side of the molten metal, it is preferable that the inner diameter of the filter tube in this portion increases along the longitudinal direction from the second end to the first end, from the viewpoint of promoting the flow of the molten metal (refined molten metal) that has been filtered to remove impurities toward the outlet side. In other words, from the viewpoint of promoting the flow of the molten metal (refined molten metal) that has been filtered to remove impurities toward the outlet side, it is preferable that at least some of the ceramic filter tubes 3 have an inner diameter at the end face 3w of the first end on the outlet side of the molten metal that is larger than the inner diameter at the inner end face 3b of the second end on the opposite side. This configuration promotes smooth flow of the refined molten metal toward the outlet side, and ultimately promotes the filtering of the molten metal. pastThis can further improve performance. Furthermore, when the inner diameter at the end face 3w of the first end on the molten metal outlet side of at least some of the plurality of ceramic filter tubes 3 is larger than the inner diameter at the inner end face 3b of the second end on the opposite side, it is more preferable that the outer diameter at the end face 3w of the first end on the molten metal outlet side be substantially the same as the outer diameter at the outer end face 3a of the second end on the opposite side. This configuration maintains good structural strength of the entire filtration unit, facilitates the design of the recesses formed in the side plates, and optimizes the spacing and arrangement of the plurality of filter tubes to further improve filtration performance.

[0024] In at least some of the ceramic filter tubes 3, the inner diameter at the end face 3w of the first end on the molten metal outlet side is larger than the inner diameter at the inner end face 3b of the second end on the opposite side. For example, the inner diameter may be increased continuously in a so-called reverse tapered manner along the longitudinal direction from the second end to the first end in part or substantially the entire filter tube, or may be increased in a stepped manner including multiple portions where the inner diameter of the filter tube is constant along the longitudinal direction from the second end to the first end. From the viewpoint of further promoting the flow of the molten metal (refined molten metal) that has been filtered to remove impurities to the outlet side, a configuration in which the inner diameter is increased continuously in a so-called reverse tapered manner along the longitudinal direction from the second end to the first end in part or substantially the entire filter tube is preferred, and a configuration in which the inner diameter is increased continuously in a so-called reverse tapered manner along the longitudinal direction from the second end to the first end in the entire filter tube is more preferred.

[0025] In various embodiments of the present invention, including the above-described modified embodiments, the longitudinal length L1 of the portion of the outer surface of the ceramic filter tube 3 exposed to the molten metal, the outer diameter D1 of the filter tube 3, the longitudinal length L2 of the portion of the inner surface of the filter tube 3 exposed to the molten metal, and the inner diameter D2 of the filter tube 3 are not particularly limited as long as they satisfy the above-described relational expressions (1) and (2), but may be, for example, within the following ranges: The longitudinal length L1 of the portion of the outer surface of the filter tube 3 exposed to the molten metal may be, for example, typically 300 mm or more and 6000 mm or less, and preferably 400 mm or more and 5000 mm or less, 500 mm or more and 4000 mm or less, 600 mm or more and 3000 mm or less, 700 mm or more and 2500 mm or less, 800 mm or more and 2000 mm or less, or 850 mm or more and 1500 mm or less. The outer diameter D1 of the filtration tube 3 may be, for example, usually 30 mm or more and 300 mm or less, preferably 40 mm or more and 250 mm or less, 50 mm or more and 200 mm or less, 60 mm or more and 150 mm or less, or 70 mm or more and 120 mm or less. The longitudinal length L2 of the portion of the inner surface of the filtration tube 3 exposed to the molten metal may be, for example, usually 400 mm or more and 6000 mm or less, and preferably 500 mm or more and 5000 mm or less, 600 mm or more and 4000 mm or less, 700 mm or more and 3000 mm or less, 800 mm or more and 2000 mm or less, or 850 mm or more and 1600 mm or less. The inner diameter D2 of the filtration tube 3 may be, for example, usually 10 mm or more and 150 mm or less, preferably 15 mm or more and 120 mm or less, 20 mm or more and 100 mm or less, 25 mm or more and 80 mm or less, or 30 mm or more and 70 mm or less.

[0026] 3 shows a preferred example of a modified embodiment in which the inner diameter of the entire ceramic filter tube 3 at the end face 3w of the first end on the molten metal outlet side is larger than the inner diameter at the inner end face 3b of the second end on the opposite side, and the outer diameter at the end face 3w of the first end on the molten metal outlet side is the same as the outer diameter at the outer end face 3a of the second end on the opposite side. In the filter tube 3 shown in this figure, the inner diameter continuously increases along the longitudinal direction from the second end to the first end, with a constant inclination in a so-called reverse tapered shape. This structure of the ceramic filter tube 3 further promotes smooth flow of the molten metal (refined molten metal) that has been filtered to remove impurities to the outlet side.

[0027] In order to sufficiently filter the molten metal while promoting smooth flow of the molten metal (refined molten metal) that has been filtered of foreign matter to the outlet side, in at least some of the multiple ceramic filter tubes 3, the inner diameter at the end face 3w of the first end on the outlet side of the molten metal is larger than the inner diameter at the inner end face 3b of the second end on the opposite side, and typically the inner diameter at the first end of the filter tube may be 100.5% to 150% of the inner diameter at the second end. From the viewpoint of further promoting smooth flow of the refined molten metal to the outlet side while sufficiently filtering the molten metal, and thus further improving filtering performance, the inner diameter at the first end of the filtration tube may preferably be 100.6% to 145%, 100.7% to 140%, 100.8% to 135%, 100.9% to 130%, 101% to 125%, 101.5% to 120%, 102% to 115%, 102.5% to 110%, or 103% to 110% of the inner diameter at the second end.

[0028] 4(a) and (b) illustrate the relationship between a substantially circular opening 3e at a first end of a cylindrical ceramic filter tube 3 on the side from which molten metal is dispensed and a substantially circular through-hole 2e provided in a side plate 2A on the dispensing side in a molten metal filtration unit according to one embodiment. Fig. 4(a) is a cross-sectional view as viewed in the longitudinal direction, and Fig. 4(b) is a cross-sectional view as viewed in the horizontal direction perpendicular to the longitudinal direction. 4(b), a portion 3c of the cylindrical ceramic filter tube 3's inner surface extending in the longitudinal direction, which is exposed to the molten metal, forms a substantially circular opening 3e at the edge of a first end on the side from which the molten metal is dispensed. Meanwhile, the side plate 2A on the dispenser side forms a substantially circular through hole 2e, and a recess shaped to encompass the first end of the filter tube 3 is drilled around the periphery of the through hole 2e on the filter tube placement side. The first end of the filter tube 3 and the side plate 2A on the dispenser side are fitted and fixed together via a packing 4A so as to encompass the annular end face 3w of the first end of the filter tube 3 on the molten metal dispensing side and the annular periphery of the end of the portion 3d of the filter tube 3's outer surface extending in the longitudinal direction, which is exposed to the molten metal. In the embodiment shown in Fig. 4, the opening shape of the filter tube-side end of the substantially circular through-hole 2e provided in the side plate 2A on the melt discharge side is the same as the opening shape on the opposite side of the through-hole 2e from the filter tube-side end, i.e., the melt discharge side. Thus, in the embodiment shown in Fig. 4, the inner diameter of the melt discharge-side end of the substantially circular through-hole 2e in the side plate 2A on the melt discharge side is equal to the inner diameter S of the filter tube-side end of the through-hole 2e in the side plate 2A. i is equal to

[0029] In this embodiment, as shown in Fig. 4(a) together with Fig. 4(b), the shape of the opening 3e at the first end of the ceramic filter tube 3 on the side from which the molten metal is dispensed encompasses (encloses) the shape of the opening at the filter tube-mounted end of the substantially circular through-hole 2e provided in the side plate 2A on the dispense side, as viewed in the longitudinal direction. That is, the diameter D of the opening 3e at the first end of the ceramic filter tube 3 on the side from which the molten metal is dispensed (the inner diameter at the first end of the filter tube 3) 2y is the inner diameter S of the end of the through hole 2e of the side plate 2A on the side where the filtration tube is disposed. i In other words, the inner diameter S of the through-hole 2e of the side plate 2A at the end on the side where the filtration tube is disposed is larger than i is the diameter D of the substantially circular opening 3e provided at the first end of the filter tube 3 on the side from which the molten metal is poured. 2y In this embodiment, S i <D 2yThere is no particular limitation as long as it is within the range of S i D 2y Ratio to ([S i / D 2y ] × 100(%)) may usually be 80% or more and less than 100%, preferably 85% or more and less than 100%, 90% or more and less than 100%, 95% or more and less than 100%, 98% or more and less than 100%, 99% or more and less than 100%, 99.5% or more and less than 100%, or 99.9% or more and less than 100%. In this way, the inner diameter S of the through hole 2e of the side plate 2A at the end on the side where the filtration tube is disposed is i The diameter D of the opening 3e at the first end of the filtration tube 3 on the side where the molten metal is poured is 2y By making the structure smaller than this, the inner edge portion at the first end of the filter tube 3 is not exposed to the molten metal, which effectively suppresses deterioration and particle shedding of the filter tube 3 at that location and further extends the life of the filter tube. In the embodiment of FIG. 4, when the cross-sectional shape of the opening 3e at the first end of the filtration tube 3 and / or the through-hole 2e of the side plate 2A is not a perfect circle, the circumscribed circle of the cross-sectional shape is D 2y and / or S i The following shall be determined.

[0030] The cross-sectional view of FIG. 5 shows the inner diameter S of the end of a substantially circular through-hole 2e provided in a side plate 2A on the side from which the molten metal of the molten metal filtration unit according to one embodiment is provided on the side where the ceramic filter tube 3 is disposed (i.e., the side where the packing 4A is disposed in this drawing). i and the inner diameter S of the end of the tapping side ii As shown in the figure, in this embodiment, in the substantially circular through-hole 2e provided in the side plate 2A on the side from which the molten metal is to be poured, the inner diameter S ii is the inner diameter S of the end where the filtration tube 3 is disposed. i The inner diameter S of the end of the through hole 2e on the melt outlet side is smaller than ii The inner diameter S of the end where the filtration tube 3 is disposed is iThe means for making the height smaller than this may be a tapered shape with a constant angle or a varying angle as shown, or may be one or more stepped steps.

[0031] In the embodiment of FIG. i >S ii There is no particular limitation as long as it is within the range of S ii S i Ratio to ([S ii / S i ] × 100(%)) may typically be 70% or more and 99.5% or less, preferably 75% or more and 99.4% or less, 80% or more and 99.3% or less, 85% or more and 99.2% or less, 87% or more and 99.1% or less, 88% or more and 99% or less, 89% or more and 99% or less, 90% or more and 99% or less, 91% or more and 99% or less, or 92% or more and 99% or less. In this way, in the substantially circular through-hole 2e provided in the side plate 2A on the side from which the molten metal is to be poured, the inner diameter S ii The inner diameter S of the end where the filtration tube 3 is disposed is i By making the structure smaller than this, it is possible to prevent the molten metal from being discharged from the filtration unit without sufficient filtering of foreign matter, and to further reduce the possibility of foreign matter being contained in the filtered refined molten metal.

[0032] In this specification, any two or more of the embodiments described so far can be combined with each other, and further, if desired, can be combined with any of the embodiments described below. For example, the embodiment illustrated in FIG. 3 (an embodiment in which, in at least some of the plurality of ceramic filter tubes 3, the inner diameter at the end face 3w of the first end on the side from which the molten metal is discharged is larger than the inner diameter at the inner end face 3b of the second end on the opposite side) can be combined with the embodiment illustrated in FIG. 4 (an embodiment in which the shape of the opening 3e at the first end on the side from which the molten metal is discharged of the ceramic filter tube 3 encompasses or contains, when viewed in the longitudinal direction, the opening shape of the filter tube-mounted end of the substantially circular through hole 2e provided in the side plate 2A on the discharge side). 3 and the embodiment illustrated in FIG. 5 (in which the inner diameter S of the end on the molten metal side of the substantially circular through-hole 2e provided in the side plate 2A on the side from which the molten metal is to be poured is ii The inner diameter S of the end where the filtration tube 3 is disposed is i (embodiment in which the size is smaller than the size of the first embodiment) can be combined. Alternatively, the embodiment illustrated in FIG. 4 and the embodiment illustrated in FIG. 5 can be combined. Alternatively, the three embodiments illustrated in Figures 3, 4 and 5 can be combined. The advantages obtained by each of these embodiments are similarly additive when these embodiments are combined, and are not diminished or canceled out.

[0033] Particularly preferred examples are the three embodiments illustrated in Figures 3, 4 and 5, namely: <1> an embodiment in which, in at least some of the plurality of ceramic filter tubes 3, the inner diameter at an end face 3w at a first end on the outlet side of the molten metal is larger than the inner diameter at an inner end face 3b at a second end on the opposite side; <2> an embodiment in which the shape of the opening 3e at the first end of the ceramic filter tube 3 on the side from which the molten metal is to be dispensed encompasses or includes, as viewed in the longitudinal direction, the opening shape of the filter tube-mounted end of the substantially circular through-hole 2e provided in the side plate 2A on the dispenser side; <3> In the substantially circular through-hole 2e provided in the side plate 2A on the side from which the molten metal is to be poured, the inner diameter S of the end on the pouring side is ii The inner diameter S of the end where the filtration tube 3 is disposed is i This embodiment is modified to combine an embodiment that is smaller than the embodiment described above. This provides all of the advantages described above for each embodiment, namely, this embodiment can further promote smooth flow of the molten metal (refined molten metal) that has been filtered to remove impurities toward the outlet side, and in addition, it can effectively suppress deterioration and particle shedding of the filter tube at the inner edge of the first end of the filter tube, further extending the life of the filter tube, and also suppressing the molten metal from being discharged from the filtration unit with impurities not being sufficiently filtered, thereby further reducing the possibility of impurities being contained in the filtered refined molten metal.

[0034] In a preferred embodiment, at least some of the ceramic filter tubes 3 of the molten metal filtration unit 1 may be formed of a porous material having a porosity of typically 25% to 50%. Forming the filter tubes 3 from a porous material having a porosity within this range optimizes the balance between the filter tube's ability to remove and filter foreign matter from the molten metal and extending the filter tube's lifespan (suppressing a decline in filtration performance over a short period of time), thereby improving filtration performance. From the above perspective, the porosity of the porous material forming the filter tubes may preferably be 25% to 45%, 28% to 42%, or 30% to 40%.

[0035] In an embodiment in which the ceramic filter tube 3 is formed of a porous material having a porosity within the above range, examples of the aggregate constituting the porous material include, but are not limited to, one or more of silicon carbide, fused alumina, sintered alumina, and other aluminas. The aggregate constituting the porous material may preferably be one or more of aluminas such as fused alumina and sintered alumina.

[0036] The average particle size of the aggregate constituting the porous material of the ceramic filter tube 3 is not particularly limited, but from the viewpoint of adjusting the porosity within the above range, it may usually be 200 μm or more and 2500 μm or less. The average particle size of the aggregate of the ceramic filter tube 3 may be preferably 250 μm or more and 2000 μm or less, and more preferably 500 μm or more and 1700 μm or less. The "average particle size" of the aggregate constituting the porous material of the filter tube here is a value obtained by taking a scanning electron microscope (SEM) image of a cross section perpendicular to the longitudinal direction of the filter tube, measuring the particle diameters of the aggregate from the SEM image using the intercept method, and calculating the average value. Specifically, an arbitrary line is drawn on the SEM image of the cross section of the filter tube, and the long and short diameters of the aggregate particles that intersect with the line are measured. Next, the particle shape is defined as an ellipse, and the average value of the long and short diameters is defined as the particle diameter of the aggregate. Then, multiple SEM images are taken from different fields of view, and the above measurement is repeated using the multiple SEM images. The particle diameters of 500 or more aggregates are measured, and the average particle size of the aggregate in the cross-sectional structure of the filter tube is calculated by statistically processing the results. Furthermore, the "porosity" of the above-mentioned filter tube can be calculated by calculating the actual density based on the dimensions and mass of the filter tube, and then calculating the ratio of this density to the theoretical density of the filter tube (e.g., comprising ceramic materials such as silicon carbide and alumina as main raw materials and a small amount of inorganic binder).

[0037] Examples of materials constituting the parts of the molten metal filtration unit 1 other than the ceramic filtration tube 3 will be described below. The contact portions of the packings 4A and 4B of the molten metal filtration unit 1, which are flat bodies that contact the end faces of the filter tubes 3, may be made of, for example, alumina fiber, ceramic fiber, or other ceramic fiber material, specifically, a reaction product of basic aluminum chloride and silica. The sealing portions of the packings 4A and 4B, which are ring-shaped bodies that contact the edges of the outer surfaces of the filter tubes 3, may be made of, for example, a fiber-based material, typically, alumina-silica ceramic fiber containing an inorganic binder. In an embodiment in which the contact portions and sealing portions are integrally configured, they may be made of any of the materials described above.

[0038] Next, a non-limiting example of a method for manufacturing the ceramic filter tube 3 that constitutes the molten metal filtration unit 1 will be outlined. The method for manufacturing the ceramic filter tube 3 may include the steps of kneading, molding, drying, degreasing, and firing.

[0039] The kneading step is a step of kneading a mixture containing, for example, the raw aggregate particles and the inorganic binder to prepare a clay. Specifically, the clay can be obtained by kneading a mixture containing aggregate particles, an inorganic binder, an organic binder, and water, which constitutes the raw materials of the ceramic filter tube 3, using a kneading device such as a mixer / agitator.

[0040] The aggregate particles may be made of any of the materials described above. The inorganic binder may be one or more of boron trioxide, alumina, magnesium oxide, and silica. When boron trioxide and alumina are used as the inorganic binder, some of them may react during firing, producing needle-like crystals of 9Al2O3·2B2O3.

[0041] As the organic binder, for example, one or more of starch-based, cellulose-based, and polysaccharide-based binders can be used. Deionized water or distilled water containing few impurities can be preferably used as the water. To properly sinter the aggregate particles, a sintering aid may be added and kneaded. Furthermore, various optional additives such as organic pore-forming agents, lubricants, plasticizers, and mold release agents may be added and kneaded as needed.

[0042] The molding process is a process in which the clay obtained in the kneading process is filled into a mold prepared in advance and molded. The drying process that follows this is a process in which the molded body obtained in the molding process is dried. This drying process removes moisture from the molded body.

[0043] The degreasing process is a process for removing organic components such as organic binders from the compact from which moisture has been removed in the drying process. By exposing the compact to predetermined conditions such as temperature and time, the organic components contained in the compact can be decomposed and removed. Furthermore, when the organic pore-forming agent is removed, pores corresponding to the shape of the organic pore-forming agent can be generated.

[0044] The firing step is a step of firing the molded body from which the organic components have been removed in the degreasing step in a firing apparatus. The fired body obtained by firing may be subjected to processing of the ends, etc., as necessary, to obtain the ceramic filter tube 3.

[0045] <Additional Embodiments Regarding Side Plate Structure> The structure of the pair of side plates of the molten metal filtration unit according to the present invention is not particularly limited except as defined in the appended claims. These two side plates may have substantially the same external shape, being roughly rectangular parallelepiped plates, and may also satisfy specific relationships regarding their inventive shapes or dimensions, as exemplified in the following items (1) to (3). (1) Additional embodiment 1 of the molten metal filtration unit An additional example of a molten metal filtration unit includes a pair of side plates specified as follows: A pair of side panels a substantially cylindrical filtration tube connected substantially perpendicularly to the pair of side plates; A molten metal filtration unit comprising: The pair of side plates are a first side plate having a through hole at a location connected to the filtration tube; a second side plate whose portion connected to the filtration tube is closed, When the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, At least one of the pair of side plates has a bottom portion formed so that either the left side bottom edge or the right side bottom edge is positioned vertically higher than the other bottom edge. The molten metal filtration unit.

[0046] The molten metal filtering unit according to this additional embodiment may further include the following non-limiting configuration. (i) When the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, the first side plate has a bottom portion formed so that one of the left and right bottom sides is positioned higher in the vertical direction than the other bottom side, When the first side plate has a bottom portion formed so that the left bottom edge is positioned vertically higher than the right bottom edge, the second side plate has a bottom portion formed so that the left bottom edge is positioned vertically higher than the right bottom edge, or When the first side panel has a bottom portion formed so that the right bottom edge is positioned vertically higher than the left bottom edge, the second side panel has a bottom portion formed so that the right bottom edge is positioned vertically higher than the left bottom edge. (ii) When the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, At least one of the pair of side plates has a step portion formed so that either the left or right base edge is positioned vertically higher than the other base edge. (iii) In the above (ii), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, The pair of side plates have a step portion formed so that the left bottom edge is positioned vertically higher than the right bottom edge. (iv) In the above (ii), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, the step portion comprises a first bottom portion which is the lowest portion and a second bottom portion which is formed so as to be positioned vertically higher than the first bottom portion, The ratio (W1 / W2) of the horizontal length W1 of the first bottom portion to the horizontal length W2 of the second bottom portion is 0.1 or more and 6.0 or less, where W1 and W2 are lengths parallel to the longitudinal direction of the filtration tube. (v) In the above (ii), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, the step portion comprises a first bottom portion which is the lowest portion and a second bottom portion which is formed so as to be positioned vertically higher than the first bottom portion, The ratio (W1 / H2) of the horizontal length W1 of the first bottom to the vertical length H2 from the first bottom to the second bottom is 0.1 or more and 11 or less, where W1 is the length in a direction parallel to the longitudinal direction of the filtration tube. (vi) When the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, At least one of the pair of side panels is formed so that either the left or right bottom edge is positioned vertically higher than the other bottom edge, and is provided with a bottom portion having a first bottom portion which is the lowest part and a sloping portion connecting the first bottom portion to the bottom edge which is positioned vertically higher. (vii) In the above (vi), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, The ratio (W1' / W2') of the horizontal length W1' of the first bottom portion to the horizontal length W2' of the inclined portion is 0 or more and 6.0 or less, where W1' and W2' are lengths parallel to the longitudinal direction of the filtration tube. (viii) In the above (vi), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, The ratio (W1' / H2') of the horizontal length W1' of the first bottom to the vertical length H2' from the end of the inclined portion that contacts the first bottom to the other end of the inclined portion is 0 or more and 320 or less, where W1' is the length in a direction parallel to the longitudinal direction of the filtration tube. (ix) In the above (viii), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, The angle θ1 between the inclined portion and the vertical direction is equal to or greater than 60° and equal to or less than 89°. (x) In the above (vi), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, The pair of side plates are formed so that the left bottom edge is positioned vertically higher than the right bottom edge, and each has a bottom edge having a first bottom edge which is the lowest part and a sloped part connecting the first bottom edge to the left bottom edge. (xi) In the above (vi), when the longitudinal direction of the filtration tube is approximately horizontal, the first side plate is located on the left side of the filtration tube, and the second side plate is located on the right side of the filtration tube, The pair of side plates are formed so that the right bottom edge is positioned vertically higher than the left bottom edge, and each has a bottom edge having a first bottom edge which is the lowest part and a sloped part connecting the first bottom edge to the right bottom edge. (xii) A molten metal filtering device having a molten metal outlet, The molten metal filtering unit according to (ix) above, wherein the pair of side plates have an inclined portion formed so that when the longitudinal direction of the filter tube is approximately horizontal, the first side plate is located on the left side of the filter tube, and the second side plate is located on the right side of the filter tube, the right side bottom edge is positioned higher in the vertical direction than the left side bottom edge, is arranged so that the first side plate is in contact with the tapping port, The filtration device is provided with a wedge-shaped protrusion on the hearth, the protrusion having an angle θ2 between a surface in contact with the molten metal filtration unit and a horizontal plane, and the sum of θ1 and θ2 satisfies 61° or more and 114° or less. The filtration device.

[0047] (2) Additional embodiment 2 of the molten metal filtration unit An additional example of a molten metal filtration unit includes a pair of side plates specified as follows: A pair of side panels; a substantially cylindrical filtration tube connected substantially perpendicularly to each of the pair of side plates; A molten metal filtration unit comprising: The pair of side plates are a first side plate having a through hole at a location connected to the filtration tube; a second side plate whose portion connected to the filtration tube is closed, Each side panel has at least one leg depending from the bottom surface of the side panel; When the longitudinal direction of the filtration tube is approximately horizontal, the lowest position of the leg portion of the second side plate in the vertical direction is lower than the lowest position of the leg portion of the first side plate in the vertical direction. The molten metal filtration unit.

[0048] The molten metal filtering unit according to this additional embodiment may further include the following non-limiting configuration. (i) When the longitudinal direction of the filtration tube is approximately horizontal, the ratio of the vertical length of the leg portion of the first side plate to the vertical length of the leg portion of the second side plate is 0.20 or more and less than 1.0. (ii) The total ground contact area of ​​all the legs in the molten metal filtration unit is 0.015 or more and 0.075 or less relative to the total bottom area of ​​the pair of side plates. (iii) In the above (ii), the total ground contact area of ​​all the legs in the molten metal filtration unit is 0.020 or more and 0.060 or less relative to the total bottom area of ​​the pair of side plates. (iv) At least two legs are provided on the first side plate and one leg is provided on the second side plate. (v) In the above (iv), at least two legs are provided near both longitudinal ends of the bottom surface of the first side plate, and one leg is provided approximately at the longitudinal center of the bottom surface of the second side plate.

[0049] (3) Additional embodiment 3 of the molten metal filtration unit An additional example of a molten metal filtration unit includes a pair of side plates specified as follows: A pair of side panels; a substantially cylindrical filtration tube connected substantially perpendicularly to each of the pair of side plates; A molten metal filtration unit comprising: The pair of side plates are a first side plate having a through hole at a location connected to the filtration tube; a second side plate whose portion connected to the filtration tube is closed, Each side panel has a leg portion hanging down from the bottom surface of the side panel, The number of legs provided on the first side panel is at least one more than the number of legs provided on the second side panel. The molten metal filtration unit.

[0050] The molten metal filtering unit according to this additional embodiment may further include the following non-limiting configuration. (i) The first side panel has two legs and the second side panel has one leg. (ii) The first side plate has two legs near both longitudinal ends of the bottom surface, and the second side plate has one leg at approximately the center of the bottom surface in the longitudinal direction. (iii) When the molten metal filtration unit is placed on a horizontal surface and observed from above, the area of ​​the molten metal filtration unit is represented by the product of the length of the molten metal filtration unit in the longitudinal direction of the filtration tube and the longitudinal length of the side plate, and S1 is the area of ​​the molten metal filtration unit. The total area of ​​the contact area of ​​all legs of the molten metal filtration unit is S2. The area ratio S2 / S1 is equal to or greater than 0.0020 and equal to or less than 0.015. [Example]

[0051] The present invention will be described in more detail below with reference to examples. These examples should not be construed as limiting the present invention in any way, but are merely illustrative.

[0052] Ceramic filtration tube manufacturing example 1 100 parts by mass of fused alumina ("aggregate particles") with an average particle size of 600 μm was mixed with 10 parts by mass of an inorganic binder. The inorganic binder contained the following compounds: 45% by mass of boric acid trioxide, 20% by mass of alumina, 20% by mass of magnesium oxide, 10% by mass of silica, 0.01% by mass of Na2O, 0.01% by mass of K2O3, and 0.2% by mass of CaO. Next, using the clay containing the fused alumina and inorganic binder, a cylindrical molded body was fabricated. The outer and inner surfaces had circular cross sections perpendicular to the longitudinal direction, one end (first end) was open, and the other end (second end) was closed. This molded body was dried at 80°C for 8 hours and then degreased at 900°C for 6 hours. The dried and degreased molded body was then fired in a firing furnace at 1250°C for 7 hours to produce a ceramic filter tube. In preparing the cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal was 1400 mm, the outer diameter D1 of the filter tube was 100 mm, the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal was 1430 mm, and the inner diameter D2 of the filter tube was 60 mm. The outer diameter D1 and inner diameter D2 of the filter tube were constant throughout the longitudinal direction. The average particle size of the aggregate in the filter tube was 600 μm, and the porosity was 38% (this was also the case in the subsequent manufacturing examples). The average particle size and porosity were measured according to the methods described above.

[0053] Ceramic filtration tube manufacturing example 2 In producing the cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal was 1000 mm, the outer diameter D1 of the filter tube was 100 mm, the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal was 1030 mm, and the inner diameter D2 of the filter tube was 30 mm. A ceramic filter tube was produced in the same manner as in Production Example 1.

[0054] Ceramic filtration tube manufacturing example 3 In producing the cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal was 900 mm, the outer diameter D1 of the filter tube was 83 mm, the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal was 930 mm, and the inner diameter D2 of the filter tube was 41.5 mm. A ceramic filter tube was produced in the same manner as in Production Example 1.

[0055] Ceramic filtration tube manufacturing example 4 In producing the above cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the part of the outer surface of the filter tube exposed to the molten metal was 1000 mm, the outer diameter D1 of the filter tube was 83 mm, the longitudinal length L2 of the part of the inner surface of the filter tube exposed to the molten metal was 1030 mm, and the inner diameter D2 of the filter tube was 41.5 mm. A ceramic filter tube was produced in the same manner as in Production Example 1 above.

[0056] Ceramic filtration tube manufacturing example 5 In producing the above cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the part of the outer surface of the filter tube exposed to the molten metal was 1400 mm, the outer diameter D1 of the filter tube was 83 mm, the longitudinal length L2 of the part of the inner surface of the filter tube exposed to the molten metal was 1430 mm, and the inner diameter D2 of the filter tube was 41.5 mm. A ceramic filter tube was produced in the same manner as in Production Example 1 above.

[0057] Ceramic filtration tube manufacturing example 1C In producing the cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal was 800 mm, the outer diameter D1 of the filter tube was 100 mm, the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal was 830 mm, and the inner diameter D2 of the filter tube was 60 mm. A ceramic filter tube was produced in the same manner as in Production Example 1.

[0058] Ceramic filtration tube manufacturing example 2C In producing the cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal was 820 mm, the outer diameter D1 of the filter tube was 80 mm, the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal was 850 mm, and the inner diameter D2 of the filter tube was 40 mm. A ceramic filter tube was produced in the same manner as in Production Example 1.

[0059] Ceramic filtration tube manufacturing example 3C In producing the cylindrical molded body, the size of the molded body was adjusted so that the longitudinal length L1 of the portion of the outer surface of the filter tube exposed to the molten metal was 820 mm, the outer diameter D1 of the filter tube was 100 mm, the longitudinal length L2 of the portion of the inner surface of the filter tube exposed to the molten metal was 850 mm, and the inner diameter D2 of the filter tube was 60 mm. A ceramic filter tube was produced in the same manner as in Production Example 1.

[0060] Manufacturing of molten metal filtration units Example 1 Two side plates were prepared, each made of a material containing silicon carbide as the primary raw material. Each side plate was a flat plate measuring 60 mm thick, 700 mm long, and 720 mm wide. One side plate, on the side from which the molten metal was dispensed, had three sets of six 60 mm circular through-holes (holes with equal inner diameters on the filter tube side and the opposite side from which the molten metal was dispensed) arranged horizontally, and two sets of five 60 mm circular through-holes arranged horizontally, alternately spaced 55 mm apart. A total of 28 through-holes were provided. The side plate opposite the side from which the molten metal was dispensed had no such through-holes. Each side plate also had a recess with a peripheral wall having a circular cross-section that matched the shape (outer diameter) of each end of the filter tube and a flat bottom. The depth of the recess relative to the vertical and horizontal planes of the side plate (the depth in the direction corresponding to the longitudinal direction of the filter tube) was 31.3 mm. In one of the side plates on the side from which the molten metal is to be poured, each of the through holes was arranged at the center of each recess. A 6 mm-thick alumina fiber packing with a 60 mm diameter circular opening and a shape that fit the bottom of the recess was prepared, along with a packing with the same configuration except without the circular opening. The packing with the circular opening was placed in each recess of the side plate on the molten metal outlet side with the through holes, and the packing without the circular opening was placed in each recess of the side plate without the through holes. The first end of the ceramic filter tube from Production Example 1, which had an opening on the molten metal outlet side, was fitted and fixed to each recess of the side plate on the molten metal outlet side with the through holes and the corresponding packing with the circular opening. The closed second end of the filter tube was fitted and fixed to each recess of the side plate without the through holes and the corresponding packing without the circular opening. To prevent leakage of the molten metal, the packing was compressed from both sides of each side plate to a thickness of 3 mm, which is 50% of its original thickness, to obtain the molten metal filtration unit of Example 1.

[0061] Examples 2-5 and Examples 1C-3C Molten metal filtration units of Examples 2 to 5 and 1C to 3C were obtained in the same manner as Example 1, except that the ceramic filtration tube of Production Example 1 was replaced with the ceramic filtration tube of Production Examples 2 to 5 and Production Examples 1C to 3C, side plates with through holes of a size corresponding to the inner diameter of each filtration tube (in Examples 3 to 5, the side plates had a total of 39 through holes), and gaskets with openings of a size corresponding to these were used.

[0062] Filtration performance evaluation The molten metal filtration units of Examples 1 to 5 and 1C to 3C obtained above were subjected to the following measurements and evaluations (1) to (3). The results are shown in Table 1 below, along with the structural factors of the ceramic filtration tubes of these units. (1) Measurement of head height change of molten metal in the filtration chamber The molten metal filtration unit was placed on the hearth of a filtration chamber having an inlet and outlet for the molten metal. A predetermined amount of molten aluminum (720°C) was supplied through the inlet into the filtration tube of the molten metal filtration unit, and the change in the liquid level of the molten aluminum (hereinafter also referred to as "head height") in the filtration chamber was measured. Specifically, the molten metal head height T0 in the filtration chamber at the start of filtration was measured, and the molten metal head height T1 after 1,000 tons of molten metal had been passed through was measured (see Figure 6 for reference). In this measurement test, the flow rate of the molten metal into the molten metal filtration unit was set to 25 tons / hour. In Figure 6, which is provided for reference, 1 denotes the molten metal filtration unit, 2A is the side plate on the discharge side, 2B is the side plate on the inlet side, 2e is a through hole provided in the side plate on the discharge side, 3 is a ceramic filtration tube, 5 is the filtration chamber, 6 is the filter bed, 6A and 6B are each bases provided on the hearth, 7 is the filtration chamber housing, I is the inlet for molten metal into the filtration chamber, O is the outlet for molten metal from the filtration chamber, T0 is the head height of the molten metal in the filtration chamber when filtration begins, and T1 is the head height of the molten metal after 1,000 tons of molten metal have been passed through the molten metal filtration unit. The lower the change in head height of the molten metal in the filtration chamber (T1-T0 value), the lower the filtration resistance when the molten metal was continuously passed through, meaning that the device could be used stably. Therefore, the stability of filtration was evaluated using the following three-level score based on the change in head height of the molten metal in the filtration chamber. Table 1 shows the change in head height (mm) for each example and the score in parentheses. 3 points: The change in the height of the molten metal head was less than 50 mm. 2 points: The change in the height of the molten metal head was between 50 mm and 100 mm. 1 point: The change in the height of the molten metal head was >100 mm. (2) Measurement of the amount of molten metal passing through until a specified head height change is reached (evaluation of the lifespan of ceramic filter tubes) When inclusions are trapped in a ceramic filter tube, reducing the flow path for the molten metal, the head height of the molten metal in the filter chamber increases over time. Generally, molten metal is filtered by gravity. When filtering molten metal through a clogged filter tube, a head height is required to generate sufficient pressure for the molten metal to flow. However, a high head height poses the risk of the molten metal overflowing the filter chamber and a decrease in filtration rate. In this test, the lifespan of the filter tube was evaluated by measuring the amount of molten metal (tons) passed until the change in head height of the molten metal before and after filtration reached 120 mm. This test was performed by continuously measuring the head height of the molten metal (as described above in (1)) and calculating the amount of molten metal (tons) passed when the final change in head height of the molten metal (T1 - T0 value) reached 120 mm. In this test, the lifespan of the filter tube was evaluated using the following three-point scale based on the amount of molten metal passed. In Table 1, the amount of molten metal (tons) passed through each example is shown, along with the score in parentheses. 3 points: The amount of molten metal passed until the change in the molten metal head height reached 120 mm was greater than 2,500 tons (more than 2,500 tons of molten metal passed). 2 points: The amount of molten metal passed until the change in the height of the molten metal head reached 120 mm was between 1,500 and 2,500 tons (the amount of molten metal passed until the change in the height of the molten metal head reached 120 mm was between 1,500 and 2,500 tons). 1 point: The amount of molten metal passed until the change in the height of the molten metal head reached 120 mm was less than 1,500 tons (less than 1,500 tons of molten metal passed). (3) Comprehensive evaluation of the filtration performance of ceramic filter tubes The overall filtration performance of the ceramic filter tubes was evaluated based on the total score of the test results in (1) and (2) above. In the examples rated A and B, even when the amount of molten metal filtered increased, the head height was low during the passage of the molten metal, allowing for stable filtration and a long filter life, which was satisfactory. On the other hand, in the example rated C, the head height increased as the amount of molten metal filtered increased, raising concerns about overflow of the molten metal from the filtration chamber tank and an overall low filtration volume, making it unsuitable for operation. Table 1 shows the evaluation of each example and the total score in parentheses. A rating: 6 points B rating: 4 to 5 points C rating: 3 points or less

[0063] [Table 1]

[0064] As is clear from the results shown in Table 1, it has been demonstrated that by using a molten metal filtration unit according to the present invention that includes a ceramic filter tube that satisfies the relationship formulas (1) L1 / D1 ≧ 8.5 and (2) L2 / D2 ≧ 22, the life of the filter tube can be significantly improved while still ensuring a sufficient flow rate of molten metal, compared to a case where one of these relationship formulas is not satisfied. [Industrial Applicability]

[0065] The molten metal filtration unit of the present invention can further increase the amount of molten metal passing through, further extend the service life of the filtration tube, and further improve the performance of removing inclusions contained in the molten metal while maintaining a high level of strength of the side plates, and therefore can be suitably used in the form of a molten metal filtration device placed in a filtration chamber to remove inclusions from molten metal such as aluminum. [Explanation of symbols]

[0066] 1: Molten metal filtration unit 2A: Side plate on the tapping side 2B: Side panel opposite to the tapping side 2e: Through hole provided in the side plate on the molten metal side 3: Ceramic filtration tube 3a: outer end surface at the second end of the filtration tube 3b: inner end surface at the second end of the filtration tube 3c: The inner surface of the filter tube exposed to the molten metal 3d: The outer surface of the filter tube exposed to the molten metal 3e: opening at first end of filtration tube 3w: end surface at the first end of the filtration tube 4A: Packing for fixing the first end of the filtration tube 4B: Packing for fixing the second end of the filtration tube L1: The longitudinal length of the outer surface of the filter tube exposed to the molten metal L2: The longitudinal length of the inner surface of the filter tube exposed to the molten metal D1: outer diameter of the filtration tube D2: Inner diameter of the filtration tube D 2x : inner diameter at the second end of the filtration tube D 2y : inner diameter at the first end of the filtration tube S i : Inner diameter of the through hole in the side plate on the outlet side at the end where the filter tube is installed S ii : Inner diameter of the through hole in the side plate on the molten metal side at the end on the molten metal side 5:Filtration chamber 6: Filter bed 6A, 6B: Pedestal installed on the hearth 7: Filtration chamber housing I: Inlet for molten metal into the filtering chamber O: Tap hole for molten metal from the filtering chamber T0: Height of the molten metal head in the filtration chamber when filtration begins T1: The height of the molten metal head after 1,000 tons of molten metal is passed through the molten metal filtering unit.

Claims

1. A molten metal filtration unit, comprising: The filter includes a plurality of cylindrical ceramic filter tubes arranged substantially in parallel, each having a substantially circular cross section perpendicular to the longitudinal direction on its outer surface and inner surface, and a pair of side plates disposed at both ends in the longitudinal direction of the plurality of ceramic filter tubes, The plurality of ceramic filter tubes each have a first end on a side from which the molten metal is dispensed and a second end on the other side, At least a portion of the plurality of ceramic filtration tubes are The longitudinal length of the part of the outer surface of the filtration tube exposed to the molten metal is L. １ The outer diameter of the filtration tube is D １ The longitudinal length of the part of the inner surface of the filtration tube exposed to the molten metal is L ２ The inner diameter of the filtration tube is D ２ Then, the following two relations: (1) L １ / D １ ≧8.5 (2) L ２ / D ２ ≧22 Both of the above are satisfied. a first end of at least a portion of the plurality of ceramic filter tubes having an inner diameter greater than an inner diameter at the second end of the at least a portion of the plurality of ceramic filter tubes;

2. A molten metal filtration unit comprising: The filter includes a plurality of cylindrical ceramic filter tubes arranged substantially in parallel, each having a substantially circular cross section perpendicular to the longitudinal direction on its outer surface and inner surface, and a pair of side plates disposed at both ends in the longitudinal direction of the plurality of ceramic filter tubes, The plurality of ceramic filter tubes each have a first end on a side from which the molten metal is dispensed and a second end on the other side, At least a portion of the plurality of ceramic filtration tubes are When the longitudinal length of the portion of the outer surface of the filtration tube exposed to the molten metal is L 1 , the outer diameter of the filtration tube is D 1 , the longitudinal length of the portion of the inner surface of the filtration tube exposed to the molten metal is L 2 , and the inner diameter of the filtration tube is D 2 , the following two relational expressions are satisfied: (1) L 1 / D 1 ≧8.5 (2) L 2 / D 2 ≧22 Both of the above are satisfied. a molten metal filtration unit, in which the opening shape of the first end of at least some of the plurality of ceramic filtration tubes, when viewed in the longitudinal direction, includes the opening shape of an end of a substantially circular through hole provided in the side plate on the molten metal discharge side of the pair of side plates, on which the filtration tube is disposed.

3. A molten metal filtration unit comprising: The filter includes a plurality of cylindrical ceramic filter tubes arranged substantially in parallel, each having a substantially circular cross section perpendicular to the longitudinal direction on its outer surface and inner surface, and a pair of side plates disposed at both ends in the longitudinal direction of the plurality of ceramic filter tubes, The plurality of ceramic filter tubes each have a first end on a side from which the molten metal is dispensed and a second end on the other side, At least a portion of the plurality of ceramic filtration tubes are When the longitudinal length of the portion of the outer surface of the filtration tube exposed to the molten metal is L 1 , the outer diameter of the filtration tube is D 1 , the longitudinal length of the portion of the inner surface of the filtration tube exposed to the molten metal is L 2 , and the inner diameter of the filtration tube is D 2 , the following two relational expressions are satisfied: (1) L 1 / D 1 ≧8.5 (2) L 2 / D 2 ≧22 Both of the above are satisfied. At least some of the ceramic filtration tubes have an inner diameter at the first end greater than an inner diameter at the second end; a molten metal filtration unit, in which the opening shape of the first end of at least some of the plurality of ceramic filtration tubes, when viewed in the longitudinal direction, includes the opening shape of an end of a substantially circular through hole provided in the side plate on the molten metal discharge side of the pair of side plates, on which the filtration tube is disposed.

4. 4. The molten metal filtration unit according to claim 1, wherein in at least some of the plurality of ceramic filtration tubes, the inner diameter at the first end is 100.5% or more and 150% or less of the inner diameter at the second end.

5. 4. The molten metal filtration unit according to claim 2, wherein the inner diameter of the through hole in the side plate on the discharge side is smaller than the inner diameter of the end on the discharge side of the through hole on the side where the filtration tube is disposed.

6. The molten metal filtration unit according to claim 5, wherein the inner diameter of the outlet end of the through hole in the side plate on the outlet side is 70% or more and 99.5% or less of the inner diameter of the filter tube installation end.

7. The molten metal filtration unit according to any one of claims 1 to 3, wherein at least some of the plurality of ceramic filtration tubes are fitted and fixed at each end in a longitudinal direction into a recess formed in the side plate via a packing having a shape that fits the recess.

8. The molten metal filtration unit according to any one of claims 1 to 3, wherein at least a portion of the plurality of ceramic filtration tubes is formed of a porous material having a porosity of 25% or more and 50% or less.