Molten metal filtration unit

Abstract

The present invention is a molten metal filtration unit (1) comprising: a plurality of cylindrical ceramic filtration tubes (3), wherein the ceramic filtration tubes are disposed substantially in parallel and each have a substantially circular cross-sectional shape in the plane perpendicular to the longitudinal direction on an outer surface and an inner surface; and a pair of side plates (2A, 2B) disposed at the respective ends in the longitudinal direction of the ceramic filtration tubes. The ceramic filtration tubes each have a first end portion on the side where molten metal is discharged and a second end portion on the other side. At least some of the ceramic filtration tubes satisfy both relational expressions (i) and (ii), wherein the length in the longitudinal direction of a portion (3d) exposed to the molten metal on the outer surface of a filtration tube is denoted by L1, the outer diameter of the filtration tube is denoted by D1, the length in the longitudinal direction of a portion (3c) exposed to the molten metal on the inner surface of the filtration tube is denoted by L2, and the inner diameter of the filtration tube is denoted by D2: (i): L1 / D1 ≥ 8.5; and (ii): L2 / D2 ≤ 21.

Description

Molten metal filtration unit

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

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

[0005] JP-A-7-4868 Patent No. 6295108

[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 in that it may become difficult to maintain sufficient strength of the side plate.

[0007] Therefore, one of the problems to be solved by the present invention is to provide a novel molten metal filtration unit not found in the prior art. Another 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 further increase the flow rate of molten metal, achieve stable filtration even under the increased flow rate, and further extend the service life of the filtration tubes, all while maintaining a high level of strength of the side plates.

[0008] As a result of intensive research, the inventors have found that in a molten metal filtration unit including a plurality of cylindrical ceramic filter tubes and a pair of side plates disposed at both ends in the longitudinal direction of the filter tubes, at least a portion of the plurality of filter tubes has a longitudinal length L of a portion of the outer surface of the filter tube exposed to the molten metal. １ Outer diameter D of the filtration tube １ Ratio to L １ / D １ is adjusted to a specific lower limit or more, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ Inner diameter D of the filtration tube ２ Ratio to L ２ / D ２The inventors have found that the above-mentioned problems can be solved by adjusting the surface area of ​​the outer surface of the filter tube exposed to the molten metal to be equal to or less than a specific upper limit. That is, the inventors have found 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 filter tube's outer surface exposed to the molten metal and ensuring a certain degree of inner diameter for the filter tube, 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 have completed the present invention.

[0009] A typical embodiment of the present invention is as follows: A molten metal filtration unit, comprising: a plurality of cylindrical ceramic filter tubes arranged substantially parallel to each other, 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 arranged at both longitudinal ends of the plurality of ceramic filter tubes, the plurality of ceramic filter tubes having a first end on the side from which the molten metal is discharged and a second end on the other side, and at least some of the plurality of ceramic filter tubes having a longitudinal length L of a portion of the outer surface of the filter tube exposed to the molten metal. １ The outer diameter of the filtration tube is D １ The longitudinal length of the part of the inner surface of the filter tube exposed to the molten metal is L ２ The inner diameter of the filtration tube is D ２ Then, the following two relations are satisfied: (1) L １ / D １ ≧8.5 (2) L ２ / D ２ A molten metal filtration unit that satisfies all of the following requirements:

[0010] The present invention provides a novel molten metal filtration unit not found in the prior art. Furthermore, a preferred embodiment of the molten metal filtration unit of the present invention can further increase the flow rate of molten metal, achieve stable filtration even under the increased flow rate, and further extend the service life of the filtration tubes, while maintaining a high level of strength of the side plates. This ultimately provides the advantages of increasing the throughput and improving the processing efficiency of the molten metal filtration unit.

[0011] FIG. 1( a) is a schematic diagram of a molten metal filtration unit according to one embodiment of the present invention. FIG. 1( b) is a cross-sectional schematic diagram showing a mechanism by which molten metal is subjected to a filtration operation in a molten metal filtration unit according to one embodiment of the present invention. 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 discharged and a second end on the other side, and a pair of side plates disposed at both longitudinal ends of the ceramic filter tube. FIG. 3 is a cross-sectional view of a ceramic filter tube in a molten metal filtration unit according to a modified embodiment of the present invention. FIGS. 4( a) and 4( b) are views illustrating the relationship between the opening at the first end of the ceramic filter tube on the side from which molten metal is discharged and a substantially circular through-hole provided in the 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 viewed in the longitudinal direction, and FIG. 4( b) is a cross-sectional view viewed in the horizontal direction perpendicular to the longitudinal direction. 5 is a cross-sectional view illustrating the relationship between the inner diameter of the filtration tube on the side plate on the outlet side of a molten metal filtration unit according to one embodiment of the present invention and the inner diameter of the end of the filtration tube on the outlet side of the approximately circular through-hole provided in the side plate on the outlet side of the molten metal filtration unit according to one embodiment of the present invention. ０ and T １ FIG.

[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 (respectively, the side plate on the side where the molten metal is discharged and the side plate on the opposite side) arranged at both ends of the filtration unit, 3 denotes a plurality of ceramic filter tubes (hereinafter also referred to simply as "filter tubes") for filtering impurities from the molten metal, and 2e denotes a through-hole in the side plate on the discharge side. Although not shown in this figure, gaskets having a shape that can fit into each end of the filter tube and the corresponding side plate may be arranged between them. While providing such gaskets is not essential, providing gaskets is preferable from the viewpoints of stably fixing the filter tubes to the side plates and reliably preventing leakage of the molten metal. The plurality of 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 generally formed of a porous ceramic material. 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 to remove 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 as an example, but this is not limiting. The number of ceramic filter tubes 3 is not particularly limited as long as there are multiple ceramic filter tubes 3, 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 of the embodiment of Fig. 2, although a portion of the ceramic filter tube is omitted for convenience of illustration, the molten metal filtration unit has a configuration in which the filter tube is further extended in the longitudinal direction. 2, 1 denotes a molten metal filtration unit, 2A denotes a side plate on the side from which the molten metal is discharged, 2B denotes a side plate on the opposite side from the discharge side (which has no through-hole and is closed), 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 each 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 fixing the first end of the filter tube, and 4B denotes a gasket for fixing the second end of the filter tube. For the sake of explanation, only one of the multiple ceramic filter tubes 3 is shown in FIG. 2. The ceramic filter tube 3 is fixed by fitting, via gaskets 4A and 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 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 at an outer end face 3a and its peripheral edge at the second end opposite the first end. Here, the recesses and gaskets 4A formed in the side plate 2A and the recesses and gaskets 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 each be composed of a flat, plate-like contact portion that contacts the end face of the filter tube 3. In this configuration, the peripheral wall of the recess formed in the side plate has a substantially circular cross-sectional shape that fits the shape of the first and second ends of the filter tube 3, and the outer diameter of the filter tube 3 at the first and second ends is substantially equal to the diameter of the corresponding peripheral wall of the recess formed in the side plate. Alternatively, the packings 4A and 4B may each be composed of a flat, plate-like contact portion that contacts the end face of the filter tube 3, and a ring-shaped sealing portion that contacts the edge of the outer surface 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 independent members that are connected or joined together. In this configuration, the contacting portions of the packings absorb longitudinal dimensional changes of the filter tubes due to expansion and contraction caused by environmental conditions such as the set temperature of the molten metal, thereby maintaining the contact between the filter tubes and the side plates. Meanwhile, the sealing portions of the packings seal and join the filter tubes and the side plates, thereby maintaining the appropriate shape of the entire molten metal filtration unit. The contacting portions of the packings 4A and / or 4B may be fixed in a compressed state in recesses formed in the side plates 2A and / or 2B between the ends of the filter tubes 3 and the side plates 2A and / or 2B. The thickness of the tightly contacting portions of the 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 the side plates 2A and / or 2B in the longitudinal direction of the filtration tube, and preferably 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) when the tightly contacting portions of the packing 4A and / or packing 4B are compressed into the recesses formed in the side plates 2A and / or 2B may be, for example, greater than 0% and 80% or less, 10% to 70%, 20% to 60%, or 30% to 50%.The thickness of the packing when compressed may be, for example, 2% to 50% of the depth in the longitudinal direction of the filtration tube of the recess formed in the side plate 2A and / or the side plate 2B.

[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 of the side plates is positioned vertically higher than the bottom edge of the other side plate. When the molten metal filtration unit 1 is placed on the hearth (not shown in FIG. 2 ) of the molten metal filtration apparatus, the configuration of the bottom of the side plate 2A and / or the side plate 2B in this manner means that the weight of the filtration unit presses the side end face of the side plate 2A on the discharge side against the inner wall surface of the filtration apparatus, making it possible to stably place the filtration unit so that the through holes 2e (plural) in the side plate 2A on the discharge side and the tap openings provided on the inner wall surface of the filtration apparatus are reliably and continuously connected at accurate positions. Details of the embodiment relating to the structure of the side plates will be described in a separate section below.

[0018] 2, the ceramic filter tube 3 is illustrated as a cylinder having the same outer and inner substantially circular cross sections from the second end to the first end. In FIG. 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 opposite 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 of the filter tube 3, is defined as L.１ [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 L ２ [iii]. The outer diameter of the filtration tube 3 (in this figure, the same size from the second end to the first end) is D １ [iv] The inner diameter of the filtration tube 3 (in this figure, the same size from the second end to the first end) is D ２ When L is set, the following relation is usually satisfied: (1) L １ / D １ ≧8.5 (2) L ２ / D ２ ≦21 Here, the "longitudinal direction" of the filter 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, if the "substantially circular" cross-sectional shape perpendicular to the longitudinal direction on the outer and / or inner surface of the filter tube 3 is not a perfect circle, the outer diameter and / or inner diameter are 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, thereby increasing the area of ​​the outer exposed portion and further increasing the amount of molten metal that can pass through, allowing for more stable filtration even with an increased 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, thereby further extending the service life of the filter tube and ultimately significantly improving the filtration efficiency 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 that is exposed to the molten metal can be adjusted so that its ratio to the inner diameter of the filter tube is kept to a predetermined value or less. This ensures a sufficient flow path for the molten metal (refined molten metal) that has been filtered to remove foreign matter, thereby promoting the flow of the refined molten metal to the outlet side, i.e., enabling the increased amount of molten metal to flow smoothly and pass through, and providing the great advantage of being able to achieve both this and the above-mentioned effect of improving the filtration efficiency of the molten metal.

[0020] The above relational expression (1) L １ / D １ ≧8.5, from the above viewpoint, preferably, L １ / D １ ≧8.6, L １ / D １ ≧8.7, L １ / D １ ≧8.8, or L １ / D １ ≧8.9, and more preferably, L １ / D １ ≧9.0, L １ / D １ ≧9.1, L １ / D １ ≧9.2, L １ / D １ ≧9.3, L １ / D １ ≧9.4, L １ / D １ ≧9.5, L １ / D １≧9.6, L １ / D １ ≧9.7, L １ / D １ ≧9.8, L １ / D １ ≧9.9, or L １ / D １ ≧10. Alternatively, L １ / D １ ≧10.5, L １ / D １ ≧11, L １ / D １ ≧11.5, or L １ / D １ ≧12. ２ / D ２ In the case where L≦21, from the above viewpoint, preferably, L ２ / D ２ ≦20.5, L ２ / D ２ ≦20, L ２ / D ２ ≦19.5, L ２ / D ２ ≦19, L ２ / D ２ ≦18.5, L ２ / D ２ ≦18, L ２ / D ２ ≦17.5, or L ２ / D ２ ≦17. Alternatively, L ２ / D ２ ≦16.5, L ２ / D ２ ≦16, L ２ / D ２ ≦15.5, L ２ / D ２ ≦15, L ２ / D ２ ≦14.5, L ２ / D ２ ≦14, L ２ / D ２ ≦13.5, L ２ / D ２ ≦13, L ２ / D ２ ≦12.5, or L ２ / D ２ It may be ≦12.

[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 diameter and inner diameter, but at least some of the filter tubes may have different outer diameters and / or inner diameters. In such a case, the outer diameter D of the filter tube 3 １ and / or inner diameter D ２ refers to the average value of the outer diameter and / or inner diameter of all of the filtration tubes.

[0022] In a modified embodiment, at least some of the ceramic filter tubes 3 may have a circular cross section on the outer surface and / or inner surface that is different from that at the second end, i.e., the outer diameter and / or inner diameter may be different from that at the second end, over a portion or substantially the entire length from the second end opposite the outlet side of the molten metal to the first end. The percentage change in the outer diameter and / or inner diameter of the filter tube from that at the second end may be, for example, 20% or less, 15% or less, 10% or less, or 5% or less. When the ceramic filter tube 3 has an outer diameter and / or inner diameter that is different from that at the second end, the outer diameter D １ and / or inner diameter D ２ refers to the outer diameter of the outer end surface 3 a at the second end of the filtration tube and / or the inner diameter of the inner end surface 3 b at the second end of the filtration tube. １ and / or inner diameter D ２ The definition of the average value of also applies when at least some of the multiple filtration tubes have circular cross sections on the outer and inner surfaces that are different 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 along a portion or substantially the entire length from the second end to the first end on the side opposite the outlet side of the molten metal, it is preferable that the inner diameter of the filter tube in this portion increase along the longitudinal direction from the second end to the first end, from the viewpoint of facilitating 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 facilitating 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, thereby further improving the filtering efficiency of the molten metal. Furthermore, in at least some of the plurality of ceramic filter tubes 3, when 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, 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 perforated in the side plates, and enables the spacing and arrangement of the plurality of filter tubes to be optimized, thereby further improving filtration efficiency.

[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 discharge 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. 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 discharge 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 the various embodiments of the present invention, including the above-described modified embodiments, the longitudinal length L of the portion of the outer surface of the ceramic filter tube 3 exposed to the molten metal is １ , the outer diameter D of the filtration tube 3 １ , the longitudinal length L of the part of the inner surface of the filter tube 3 exposed to the molten metal ２ , and the inner diameter D of the filtration tube 3 ２ The longitudinal length L of the portion of the outer surface of the filter tube 3 exposed to the molten metal is not particularly limited as long as it satisfies the above-mentioned relational expressions (1) and (2), but may be within the following ranges, for example. １ The outer diameter D of the filtration tube 3 may be, for example, typically 300 mm or more and 5000 mm or less, and preferably 400 mm or more and 4000 mm or less, 500 mm or more and 3000 mm or less, 600 mm or more and 2500 mm or less, 700 mm or more and 2000 mm or less, or 800 mm or more and 1500 mm or less. １The longitudinal length L of the part of the inner surface of the filter tube 3 exposed to the molten metal 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. ２ The inner diameter D of the filtration tube 3 may be, for example, usually 400 mm or more and 5000 mm or less, preferably 500 mm or more and 4000 mm or less, 600 mm or more and 3000 mm or less, 700 mm or more and 2000 mm or less, or 800 mm or more and 1500 mm or less. ２ For example, it may be usually 15 mm or more and 200 mm or less, preferably 20 mm or more and 150 mm or less, 25 mm or more and 100 mm or less, 30 mm or more and 90 mm or less, or 35 mm or more and 85 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, forming 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 of 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% or more and 120% or less 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 efficiency, the inner diameter at the first end of the filter tube may preferably be 100.6% to 118%, 100.7% to 116%, 100.8% to 114%, 100.9% to 112%, 101% to 110%, 101.5% to 110%, 102% to 110%, 102.5% to 110%, or 103% to 110% of the inner diameter at the second end.

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

[0029] 4(a) together with FIG. 4(b), in this embodiment, 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. ｉIn 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 ２ｙ There is no particular limitation as long as it is in the range of S ｉ D ２ｙ Ratio to ([S ｉ / D ２ｙ ] × 100(%)) may be usually 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%. ｉ The diameter D of the opening 3e at the first end of the filter tube 3 from which the molten metal is poured is ２ｙ 4, when the cross-sectional shape of the opening 3e at the first end of the filter tube 3 and / or the through-hole 2e in the side plate 2A is not a perfect circle, the circumscribed circle of the cross-sectional shape is not a perfect circle, and ... 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 filtering 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 ｉｉis the inner diameter S of the end on the side where the filtration tube 3 is disposed. ｉ The inner diameter S of the through hole 2e at the end on the molten metal outlet side is smaller than ｉｉ The inner diameter S of the end on the side where the filtration tube 3 is disposed is ｉ The means for making the height smaller than 1 / 2 may be a tapered shape with a constant or varying angle as shown, or may be one or more stepped portions.

[0031] In the embodiment of FIG. ｉ >S ｉｉ There is no particular limitation as long as it is in the range of S ｉｉ S ｉ Ratio to ([S ｉｉ / S ｉ ]×100(%)) may be usually 80% or more and 99.5% or less, preferably 83% or more and 99.4% or less, 85% or more and 99.3% or less, 87% or more and 99.2% or less, 89% or more and 99.1% or less, 90% or more and 99% or less, 91% or more and 99% or less, or 92% or more and 99% or less. ｉｉ The inner diameter S of the end on the side 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 if desired, they can also 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 ceramic filter tubes 3, the inner diameter at the end face 3w of the first end on the molten metal discharge side 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 of the ceramic filter tube 3 is discharged encompasses or contains, 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 discharge side). Alternatively, the embodiment illustrated in Fig. 3 can be combined with the embodiment illustrated in Fig. 5 (an embodiment in which the inner diameter S at the end on the discharge side of the substantially circular through hole 2e provided in the side plate 2A on the side from which the molten metal is discharged is larger than the inner diameter S at the end on the discharge side). ｉｉ The inner diameter S of the end where the filtration tube 3 is disposed is ｉ 4 and the embodiment illustrated in FIG. 5 can be combined. Alternatively, the embodiment illustrated in FIG. 3, FIG. 4, and FIG. 5 can be combined. The above-described 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 FIGS. 3, 4, and 5, namely, <1> an embodiment in which, in at least some of the 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; <2> an embodiment in which the shape of the opening 3e of the first end of the ceramic filter tube 3 on the side from which the molten metal is discharged encompasses or contains, 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 side from which the molten metal is discharged; <3> an embodiment in which the inner diameter S of the end on the discharge side of the substantially circular through hole 2e provided in the side plate 2A on the side from which the molten metal is discharged is larger than the inner diameter S of the end on the discharge side of the ceramic filter tube 3 ｉｉThe inner diameter S of the end where the filtration tube 3 is disposed is ｉ This embodiment is a modified version that combines embodiments in which the filter tube 100 is smaller than the embodiment 100. This provides all of the advantages described above for each embodiment. That is, 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 can effectively suppress deterioration and particle shedding of the filter tube at the inner edge portion of the first end of the filter tube, thereby further extending the life of the filter tube. It also prevents 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 in 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 filtering performance over a short period of time), thereby improving filtering efficiency. 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 may typically be 200 μm or more and 2500 μm or less in order to adjust the porosity within the above range. The average particle size of the aggregate constituting the ceramic filter tube 3 may preferably be 250 μm or more and 2000 μm or less, 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 determined 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 major and minor axes of the aggregate particles intersecting the line are measured. The particle shape is then determined to be elliptical, and the average of the major and minor axes is defined as the particle size of the aggregate. Then, multiple SEM images of different fields of view are taken, and the above-mentioned measurement is repeated using the multiple SEM images taken to measure the particle diameters of 500 or more aggregates, and then statistically processed to determine the average particle diameter of the aggregates in the cross-sectional structure of the filter tube. 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 to the theoretical density of the filter tube (which contains, for example, 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 various parts of the molten metal filtration unit 1 other than the ceramic filter tube 3 are described below. The flat contact portions of the packings 4A and 4B of the molten metal filtration unit 1 that contact the end surfaces of the filter tube 3 may be formed, for example, from a ceramic fiber material such as alumina fiber or ceramic fiber, specifically, a reaction product of basic aluminum chloride and silica. The annular sealing portions of the packings 4A and 4B that contact the outer edge of the filter tube 3 may be formed, for example, from 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 formed from any of the materials described above.

[0038] Next, a description will be given of an outline of a non-limiting example of a method for manufacturing the ceramic filter tube 3 that constitutes the molten metal filtration unit 1. 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 preparing a clay by kneading a mixture containing, for example, the raw aggregate particles and the inorganic binder. Specifically, the clay can be obtained by kneading a mixture containing aggregate particles, the inorganic binder, the 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 the materials described above. The inorganic binder may be made of one or more of boron trioxide, alumina, magnesium oxide, and silica. When boron trioxide and alumina are used as the inorganic binder, a portion of them reacts upon firing to form 9Al ２ O ３ ・2B ２ O ３ Needle-shaped crystals may form.

[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 Related to Side Plate Structure> The structure of the pair of side plates included in 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 related to inventive shapes or dimensions, as exemplified in the following items (1) to (3). (1) Additional Embodiment 1 of the Molten Metal Filtration Unit One additional example of a molten metal filtration unit includes a pair of side plates specified as follows: 1. A molten metal filtering unit comprising: a pair of side plates; and a substantially cylindrical filter tube connected substantially perpendicularly to the pair of side plates, wherein the pair of side plates comprise: a first side plate having a through hole at a location connected to the filter tube; and a second side plate the location connected to the filter tube is closed, and when the longitudinal direction of the filter tube is substantially horizontal and the first side plate is located to the left of the filter tube and the second side plate is located to the right of the filter tube, at least one of the pair of side plates has a bottom formed so that either a left-side bottom edge or a right-side bottom edge is positioned vertically higher than the other bottom edge.

[0046] The molten metal filtration unit according to this additional embodiment may further include the following non-limiting configurations: (i) When the longitudinal direction of the filter tube is approximately horizontal and 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 first side plate has a bottom portion formed so that either the left side or the right side bottom edge is positioned vertically higher than the other bottom edge, when the first side plate has a bottom portion formed so that the left side bottom edge is positioned vertically higher than the right side bottom edge, the second side plate has a bottom portion formed so that the left side bottom edge is positioned vertically higher than the right side bottom edge, or when the first side plate has a bottom portion formed so that the right side bottom edge is positioned vertically higher than the left side bottom edge, the second side plate has a bottom portion formed so that the right side bottom edge is positioned vertically higher than the left side bottom edge. (ii) When the longitudinal direction of the filtration tube is approximately horizontal, and 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 side bottom edge or the right side bottom edge is positioned vertically higher than the other bottom edge. (iii) In (ii) above, when the longitudinal direction of the filtration tube is approximately horizontal, and 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 side bottom edge is positioned vertically higher than the right side bottom edge. (iv) In (ii) above, 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 consists of a first bottom portion which is the lowest part, and a second bottom portion which is formed to be located vertically higher than the first bottom portion, and 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 in a direction parallel to the longitudinal direction of the filtration tube.(v) In (ii) above, 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 part, and a second bottom portion which is formed to be located vertically higher than the first bottom portion, and the ratio (W1 / H2) of the horizontal length W1 of the first bottom portion to the vertical length H2 from the first bottom portion to the second bottom portion 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, and 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 is formed so that either the left side bottom edge or the right side bottom edge is located vertically higher than the other bottom edge, and is provided with a bottom edge having a first bottom edge that is the lowest part and a sloped portion that connects the first bottom edge to the bottom edge that is located vertically higher. (vii) In (vi) above, when the longitudinal direction of the filtration tube is approximately horizontal, and 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 edge to the horizontal length W2' of the sloped portion is equal to or greater than 0 and equal to or less than 6.0, where W1' and W2' are lengths parallel to the longitudinal direction of the filtration tube. (viii) In (vi) above, 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 not less than 0 and not more than 320, where W1' is the length in a direction parallel to the longitudinal direction of the filtration tube. (ix) In (viii) above, 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 not less than 60° and not more than 89°.(x) In (vi) above, when the longitudinal direction of the filtration tube is approximately horizontal and 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 located higher in the vertical direction than the right bottom edge, and are provided with a first bottom edge that is the lowest portion and a bottom edge that has a slope connecting the first bottom edge to the left bottom edge. (xi) In (vi) above, when the longitudinal direction of the filtration tube is approximately horizontal and 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 located higher in the vertical direction than the left bottom edge, and are provided with a first bottom edge that is the lowest portion and a bottom edge that has a slope connecting the first bottom edge to the right bottom edge. (xii) A molten metal filtering device having an outlet for molten metal, wherein the molten metal filtering unit described in (ix) above has an inclined portion formed so that when the longitudinal direction of the filter tube is approximately horizontal and 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 base is positioned vertically higher than the left side base, and the first side plate is arranged so that the first side plate is in contact with the outlet, and the filtering device has a wedge-shaped protrusion on the hearth, the protrusion having an angle θ2 between a surface in contact with the molten metal filtering unit and a horizontal plane, and the sum of θ1 and θ2 satisfies 61° or more and 114° or less.

[0047] (2) Additional embodiment 2 of molten metal filtration unit An additional example of a molten metal filtration unit includes one that includes a pair of side plates specified as follows: A molten metal filtration unit including a pair of side plates and a substantially cylindrical filtration tube connected substantially perpendicularly to each of the pair of side plates, wherein the pair of side plates include a first side plate having a through hole at a location connected to the filtration tube and a second side plate the location connected to the filtration tube is closed, each side plate has at least one leg hanging down from a bottom surface of the side plate, and when the longitudinal direction of the filtration tube is substantially horizontal, the lowest vertical position of the leg of the second side plate is lower than the lowest vertical position of the leg of the first side plate.

[0048] The molten metal filtration unit according to this additional embodiment may further include the following non-limiting configurations: (i) When the longitudinal direction of the filtration tube is approximately horizontal, the ratio of the vertical length of the legs of the first side plate to the vertical length of the legs of the second side plate is 0.20 or more and less than 1.0. (ii) The total ground contact area of ​​all 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 (ii) above, the total ground contact area of ​​all 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 at approximately 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 one that includes a pair of side plates specified as follows: A molten metal filtration unit that includes a pair of side plates and a substantially cylindrical filtration tube connected substantially perpendicularly to each of the pair of side plates, wherein the pair of side plates includes: a first side plate that has a through hole at a location connected to the filtration tube, and a second side plate that has a closed location connected to the filtration tube, each side plate having a leg that hangs down from a bottom surface of the side plate, and the number of legs provided on the first side plate is at least one more than the number of legs provided on the second side plate.

[0050] The molten metal filtration unit according to this additional embodiment may further include the following non-limiting configurations: (i) the first side plate includes two legs and the second side plate includes one leg; (ii) two legs are provided near both longitudinal ends of the bottom surface of the first side plate and one leg is provided approximately in the longitudinal center of the bottom surface of the second side plate; (iii) when the molten metal filtration unit is placed on a horizontal surface and observed vertically from above, the area of ​​the molten metal filtration unit is expressed as 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, S1 is the area of ​​the molten metal filtration unit, and S2 is the total area of ​​the contact areas of all the legs of the molten metal filtration unit, and the area ratio S2 / S1 is 0.0020 or more and 0.015 or less.

[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, but should be understood as merely illustrative.

[0052] Ceramic Filter Tube Manufacturing Example 1 10 parts by mass of an inorganic binder was mixed with 100 parts by mass of electrofused alumina ("aggregate particles") having an average particle size of 600 μm. The inorganic binder used was a material containing 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, and Na. ２ O 0.01 mass%, K ２ O ３0.01 mass% of fused alumina and 0.2 mass% of CaO. Next, using the clay containing the electrofused alumina and inorganic binder, a cylindrical molded body was produced, the outer and inner surfaces of which each had a circular cross section perpendicular to the longitudinal direction, one end (first end) open, and the other end (second end) closed. This molded body was dried at 80°C for 8 hours and then degreased at 900°C for 6 hours. Thereafter, the dried and degreased molded body was fired in a firing furnace at 1250°C for 7 hours to produce a ceramic filter tube. In producing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was determined as L. １ is 900 mm, the outer diameter of the filtration tube D １ is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ is 930 mm, the inner diameter of the filtration tube D ２ The size of the molded body was adjusted so that the outer diameter D of the filtration tube was 60 mm. １ and inner diameter D ２ was kept constant throughout the entire length. The average particle size of the aggregate of the filtration 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 Filter Tube Manufacturing Example 2 When producing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 1000 mm, the outer diameter of the filtration tube D １ is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ is 1030 mm, the inner diameter of the filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1 above, except that the size of the molded body was adjusted so that the diameter was 60 mm.

[0054] Ceramic Filter Tube Manufacturing Example 3 In manufacturing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 1200 mm, the outer diameter of the filtration tube D １is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ 1230 mm, inner diameter of filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1 above, except that the size of the molded body was adjusted so that the diameter was 60 mm.

[0055] Ceramic Filter Tube Manufacturing Example 4 In manufacturing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 1000 mm, the outer diameter of the filtration tube D １ is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ 1030 mm, inner diameter of filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1, except that the size of the molded body was adjusted so that the diameter was 50 mm.

[0056] Ceramic Filter Tube Manufacturing Example 5 In manufacturing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 1000 mm, the outer diameter of the filtration tube D １ is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ 1030 mm, inner diameter of filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1 above, except that the size of the molded body was adjusted so that the diameter was 70 mm.

[0057] Ceramic Filter Tube Manufacturing Example 1C In manufacturing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 800 mm, the outer diameter of the filtration tube D １ is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ 830 mm, inner diameter of the filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1 above, except that the size of the molded body was adjusted so that the diameter was 60 mm.

[0058] Ceramic Filter Tube Manufacturing Example 2C In manufacturing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 820 mm, the outer diameter of the filtration tube D １ is 80 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ 850 mm, inner diameter of the filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1 above, except that the size of the molded body was adjusted so that the diameter was 40 mm.

[0059] Ceramic Filter Tube Manufacturing Example 3C In manufacturing the cylindrical molded body, the longitudinal length of the portion of the outer surface of the filter tube exposed to the molten metal was set to L １ is 820 mm, the outer diameter of the filtration tube D １ is 100 mm, and the longitudinal length L of the part of the inner surface of the filtration tube exposed to the molten metal ２ 850 mm, inner diameter of the filtration tube D ２ A ceramic filter tube was produced in the same manner as in Production Example 1 above, except that the size of the molded body was adjusted so that the diameter was 60 mm.

[0060] Molten Metal Filtration Unit Manufacturing 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 being dispensed, had three sets of six 60 mm circular through holes (holes with equal inner diameters on the filter tube side and the opposite molten metal dispensing side of the side plate) arranged horizontally along the side plate, and two sets of five 60 mm circular through holes arranged horizontally along the side plate, alternately spaced 55 mm apart from each other. A total of 28 through holes were provided. The side plate opposite the side from which the molten metal was being dispensed had no such through holes. Each side plate also had a peripheral wall surface with a circular cross-section conforming to the shape (outer diameter) of each end of the filter tube, and a recess with a flat bottom surface. The depth of the recesses relative to the longitudinal and lateral planes of the side plate (depth in the direction corresponding to the longitudinal direction of the filtration tube) was 31.3 mm. In one of the side plates on the side from which the molten metal was discharged, each of the through holes was located 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 surface of the recess, and a packing with a similar configuration except without the circular opening, were prepared. The packing with the circular opening was placed in each recess of the side plate on the molten metal discharge side where the through hole was provided, and the packing without the circular opening was placed in each recess of the side plate without the through hole. The first end of the ceramic filter tube of 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 that had the through holes and the corresponding packing that had the circular openings, and the closed second end of the filter tube was fitted and fixed to each recess of the side plate that did not have the through holes and the corresponding packing that did not have the circular openings. To prevent leakage of the molten metal, pressure was applied from both sides of the side plates to compress the packing to a thickness of 3 mm, which was 50% of its original thickness, thereby obtaining the molten metal filtration unit of Example 1.

[0061] Examples 2 to 5 and Examples 1C to 3C Molten metal filtration units of Examples 2 to 5 and Examples 1C to 3C were obtained in the same manner as Example 1, except that the ceramic filter tube of Production Example 1 was replaced with the ceramic filter tube of Production Examples 2 to 5 and Production Examples 1C to 3C, and a side plate having a through hole of a size corresponding to the inner diameter of each filter tube and a packing having an opening of a size corresponding to the hole were used.

[0062] Evaluation of filtration performance The molten metal filtration units of Examples 1 to 5 and Examples 1C to 3C obtained above were subjected to the following measurements and evaluations (1) and (2). The results are shown in Table 1 below, along with the structural factors of the ceramic filtration tubes of these units. (1) Measurement of change in head height of molten metal within 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, and a predetermined amount of molten aluminum (720°C) was supplied through this inlet to the filtration tube of the molten metal filtration unit, and the change in the liquid surface height of the molten aluminum within the filtration chamber (hereinafter also referred to as "head height") was measured. Specifically, the head height T ０ The molten metal head height T after passing 40 tons (t) of molten metal through one filter tube was measured. １ was measured (see FIG. 6 for reference). In this measurement test, the flow rate of the molten metal per filter tube was set to 16 kg / min (approximately 950 kg / hr). In FIG. 6 for reference, 1 denotes a molten metal filtration unit, 2A denotes a side plate on the discharge side, 2B denotes a side plate on the inlet side, 2e denotes a through hole provided in the side plate on the discharge side, 3 denotes a ceramic filter tube, 5 denotes a filtration chamber, 6 denotes a filter bed, 6A and 6B each denote a base provided on the hearth, 7 denotes a housing of the filtration chamber, I denotes an inlet for the molten metal into the filtration chamber, O denotes an outlet for the molten metal from the filtration chamber, T ０ is the height of the molten metal head in the filtration chamber at the start of filtration, T １ indicates the head height of the molten metal after 40 tons of molten metal is passed through one filter tube. １ -T ０The lower the value of ( ), the lower the filtration resistance during continuous flow, indicating stable use. Therefore, the filtration stability was evaluated using the following three-level score system based on the change in head height of the molten metal in the filtration chamber. Table 1 shows the head height change (mm) for each example, along with the score in parentheses. 3 points: The change in head height of the molten metal was less than 50 mm. 2 points: The change in head height of the molten metal was 50 mm or more and 100 mm or less. 1 point: The change in head height of the molten metal was greater than 100 mm. (2) Measurement of the amount of molten metal flowing until a predetermined head height change was reached (evaluation of the lifespan of the ceramic filter tube). When inclusions are captured in the ceramic filter tube, the number of flow paths for the molten metal decreases, and the head height of the molten metal in the filtration chamber increases over time. Generally, molten metal is filtered by gravity flow. When filtering molten metal through a clogged filter tube, a head height is required to generate sufficient pressure for the metal to pass through. However, if the head height becomes too high, there is a risk that the molten metal will overflow from the inside of the filter chamber, and the filtration speed may decrease. In this test, the life of the filter tube was evaluated by measuring the amount of molten metal (tons / tube) that passed until the change in the head height of the molten metal before and after filtration reached 120 mm. Note that this test was conducted by continuing the measurement test for the head height of the molten metal described in (1) above, and measuring the final change in the head height of the molten metal (T １ -T ０The amount of molten metal passed (tons / tube) when the change in head height of the molten metal reached 120 mm was calculated. In this test, the lifespan of the filter tube was evaluated using the following three-level score system according to the amount of molten metal passed. Table 1 shows the amount of molten metal passed (tons / tube) for each example and the score in parentheses. 3 points: The amount of molten metal passed until the change in head height of the molten metal reached 120 mm was greater than 60 tons / tube (more than 60 tons per filter tube). 2 points: The amount of molten metal passed until the change in head height of the molten metal reached 120 mm was between 50 to 60 tons / tube (the amount of molten metal passed per filter tube until the change in head height of the molten metal reached 120 mm was between 50 to 60 tons). 1 point: The amount of molten metal passed until the change in head height of the molten metal reached 120 mm was less than 50 tons / tube (less than 50 tons per filter tube). (3) Comprehensive evaluation of the filtration performance of ceramic filter tubes The filtration performance of ceramic filter tubes was evaluated comprehensively 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 when passing the molten metal was low, allowing for stable filtration and a long filter life, which was good. On the other hand, in the example rated C, as the amount of molten metal filtered increased, the head height increased, raising concerns about the overflow of molten metal from the tank in the filtration chamber and the overall low amount of filtration, making it unsuitable for operation. Table 1 shows the evaluation of each example and the total score in parentheses. A: 6 points B: 4 to 5 points C: 3 points or less

[0063]

[0064] As is clear from the results shown in Table 1, the relationship (1) L １ / D １ ≧8.5 and (2) L ２ / D ２ It has been demonstrated that by using a molten metal filtration unit including a ceramic filter tube that satisfies the relationship ≦21, stable filtration is possible while ensuring a sufficient flow rate of the molten metal, and the life of the filter tube is significantly improved, compared to a case where one of these relationship formulas is not satisfied.

[0065] The molten metal filtration unit of the present invention can further increase the amount of molten metal passing through, achieve stable filtration even under the increased amount of molten metal passing through, and further extend the service life of the filtration tubes, while maintaining a high level of strength in the side plates.As a result, the processing volume of the molten metal filtration unit can be increased and the processing efficiency can be improved, and therefore the molten metal filtration unit 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.

[0066] 1: Molten metal filtration unit 2A: Side plate on the outlet side 2B: Side plate on the opposite side to the outlet side 2e: Through hole provided in the side plate on the outlet side 3: Ceramic filter tube 3a: Outer end surface at the second end of the filter tube 3b: Inner end surface at the second end of the filter tube 3c: Portion of the inner surface of the filter tube exposed to the molten metal 3d: Portion of the outer surface of the filter tube exposed to the molten metal 3e: Opening at the first end of the filter tube 3w: End surface at the first end of the filter tube 4A: Gasket for fixing the first end of the filter tube 4B: Gasket for fixing the second end of the filter tube L １ : longitudinal length of the part of the outer surface of the filter tube exposed to the molten metal L ２ D: longitudinal length of the part of the inner surface of the filter tube exposed to the molten metal １ :Outer diameter of filtration tube D ２ :Inner diameter of 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 S of the through hole in the side plate on the outlet side at the end where the filtration tube is arranged ｉｉ : Inner diameter at the end of the through hole in the side plate on the discharge side 5: Filter chamber 6: Filter bed 6A, 6B: Pedestal provided on the hearth 7: Housing of the filter chamber I: Inlet port for molten metal into the filter chamber O: Outlet port for molten metal from the filter chamber T ０ : Height of molten metal head in the filtration chamber at the start of filtration T １ : Height of molten metal head after passing 40 tons of molten metal through one filter tube

Claims

1. A molten metal filtration unit, comprising: a plurality of cylindrical ceramic filtration tubes arranged substantially in parallel, each having a cross-sectional shape perpendicular to the longitudinal direction on the outer and inner surfaces that is substantially circular; and a pair of side plates disposed at both ends in the longitudinal direction of the plurality of ceramic filtration tubes. The plurality of ceramic filtration tubes have a first end on the side where the molten metal flows out and a second end on the other side. At least a part of the plurality of ceramic filtration tubes has a longitudinal length L of the portion exposed to the molten metal on the outer surface of the filtration tube. １ Let it be, and let the outer diameter of the filtration tube be D １ Let it be, and let the longitudinal length of the portion exposed to the molten metal on the inner surface of the filtration tube be L ２ Let it be, and let the inner diameter of the filtration tube be D ２ When this is the case, the following two relational expressions: (1) L １ / D １ ≥8.5 (2) L ２ / D ２ ≤21, a molten metal filtration unit that satisfies any of them.

2. The molten metal filtration unit according to claim 1, wherein in at least a part of the plurality of ceramic filtration tubes, the inner diameter at the first end is larger than the inner diameter at the second end.

3. The molten metal filtration unit according to claim 2, wherein in at least a part of the plurality of ceramic filtration tubes, the inner diameter at the first end is 100.5% or more and 120% or less of the inner diameter at the second end.

4. The molten metal filtration unit according to claim 1, wherein in at least a part of the plurality of ceramic filtration tubes, the opening shape at the first end includes the opening shape of the end on the filtration tube arrangement side of a substantially circular through-hole provided in the side plate on the outlet side among the pair of side plates when viewed in the longitudinal direction.

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

6. The molten metal filtration unit according to claim 5, wherein in the through-hole in the side plate on the outlet side, the inner diameter of the end on the outlet side is 80% or more and 99.5% or less of the inner diameter of the end on the filtration tube arrangement side.

7. The molten metal filtration unit according to claim 1, wherein at least a part of the plurality of ceramic filtration tubes is fitted and fixed to the recesses formed in the side plates through packings having a shape adapted to the recesses at each end in the longitudinal direction thereof.

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

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