WO2022234109A1

WO2022234109A1 - Tundish with filter module

Info

Publication number: WO2022234109A1
Application number: PCT/EP2022/062319
Authority: WO
Inventors: Johan Richaud; Martin Kreierhoff; John ROGLER; Abhishek Chakraborty
Original assignee: Vesuvius U S A Corporation; Vesuvius Group, S.A.
Priority date: 2021-05-07
Filing date: 2022-05-06
Publication date: 2022-11-10
Also published as: JP2024519531A; BR112023023191A2; CN218693828U; AU2022268640A1; CL2023003269A1; MX2023012604A; CA3216140A1; CN115301935A; EP4334051A1; KR20240004469A; TW202308769A

Abstract

Filter module (1) of a filtering system for a tundish (10) comprises a filter unit (1f) provided with channels (1c) extending from a channel inlet to a channel outlet, and a wall module (2) comprising a wall defining an opening (2o) extending over an opening height (h2) from the floor (10f). A bypass passage (2b) is defined between the wall module (2) and the filter module (1) of largest width (t12) such that the metal melt can only flow from the inlet portion to the outlet portion by flowing either through the channels of the filter unit (1f) or through the bypass passage (2b). The wall module comprises a wall ledge (2L) having a width (t2L). The filter module (1) further comprises a filter ledge (1L) having a width (t1L) and being offset vertically relative to the wall ledge (2L) to form therewith a baffle.

Description

TUNDISH WITH FILTER MODULE

FIELD OF THE DISCLOSURE

[0001] Embodiments of the present invention relates to a tundish for continuous metal melt casting provided with a filter unit for removing solid impurities prior to casting the metal melt into a mould or tool. In particular it concerns a tundish comprising a filter module imposing two possible passages for the metal melt to flow from an inlet portion of the tundish to an outlet portion comprising a tundish outlet for casting the metal melt into the mould or tool. The metal melt must either flow through the filter unit or through a bypass passage designed such as to favor the flow through the filter unit. In case of clogging of the filter unit, however, flow can continue through the bypass passage.

BACKGROUND

[0002] In continuous metal forming processes, metal melt is transferred from one metallurgical vessel to another, to a mould or to a tool. For example, a ladle is filled with metal melt out of a furnace and driven over a tundish to discharge the molten metal from the ladle, generally through a ladle shroud into the tundish. The metal melt can then be cast through a pouring nozzle from a tundish outlet to a mould or tool for continuously forming slabs, billets, beams, thin slabs, and the like. Flow of metal melt out of the ladle into the tundish and out of the tundish into the mould or tool is driven by gravity.

[0003] The presence of defects such as inclusions and impurities in the cast metal parts is a cause of concern. They come mostly from debris and impurities which were present in the ladle or are caused by wear of the refractory materials in the pouring region of the tundish due to impacts and frictions between the metal melt and the refractory materials. It is important to prevent such debris and impurities from reaching the tundish outlet, to reduce the number of defects in the cast metal parts.

[0004] In order to decrease the amounts of debris and impurities to reach the tundish outlet, it has been proposed in EP3470149 to include a baffle module extending over a whole width of the tundish cavity, separating the tundish cavity into an inlet portion defined as the portion of the tundish receiving metal melt from a ladle, from an outlet portion defined as the portion of the tundish cavity comprising the tundish outlet. The baffle module is composed of two parallel walls vertically offset relative to one another, a first wall adjacent to the inlet portion defining an opening between a floor of the cavity and a free edge of the first wall, and a second wall extending from the floor to a height higher than the opening defined by the first wall. The metal melt flowing from the inlet portion to the outlet portion is deviated by the baffle module, letting most debris and other solids stranded at the foot of the second wall. A baffle module as described in EP3470149, however, retains mostly the heaviest debris and other solids which fail to follow a tortuous flow imposed by the baffles. The lighter solids, on the other hand, remain in suspension and pass through the baffle module to reach the tundish outlet. Considering that metal melts have high densities, the solids remain easily in suspension, and the removal efficacy of this baffle module is not satisfactory for many applications.

[0005] It has also been proposed to include a filter module extending over a whole width of the tundish cavity, separating the tundish cavity between the inlet portion and the outlet portion. For example, KR200303465 describes a tundish comprising a filter module extending over a whole cross-section of the tundish cavity, the filter module comprising a filter unit defining channels, through which metal melt in the inlet portion of the cavity must necessarily flow to reach the outlet portion, thus removing most debris and impurities from the metal melt reaching the outlet portion. The use of a filter module allows substantially decreasing the amounts of debris and impurities flowing out of the tundish into the tool, but also represents a substantial danger. Indeed, with time, debris and other solids will accumulate on an inlet side of the filter unit, thus decreasing substantially the permeability of the filter unit and increasing the pressure difference (DR) required for driving the flow of metal melt through the filter unit. The level of metal melt in the inlet portion of the cavity can thus rise relative to the level in the outlet portion until it reaches a top of the filter module to flow over the filter module rather than through the filter unit. If the filter module has a height close to the tundish height, there is a serious danger of metal melt spilling out of the tundish with dire consequences.

[0006] To solve the problem of overflow in case of clogging of the filter unit, KR101853768 describes a filter system comprising a combination of the solutions proposed in EP3470149 and KR200303465 discussed supra, by including a filter module between the first and second walls of the baffle module of EP3470149. The filter module is lower than the one described in KR200303465 and has a height similar to the height of the opening defined by the first wall. The first wall has the function of deflecting a fraction of the metal melt flowing over the filter module and of defining a bypass passage between the filter module and the first wall. This way, in case of clogging of the filter unit, the metal melt can flow through the bypass passage, over the filter module and second wall, and thus reach the tundish outlet with some of the heaviest debris and other solids left against the filter module and the second wall. The problem with this solution is that even when the filter unit is not clogged, a substantial fraction of the metal melt flows through the bypass passage and not through the filter unit, thus decreasing the efficacy of the filter system described in KR101853768.

[0007] Accordingly, there is a need for an improved filtering system that overcomes the limitations in the art. SUMMARY

[0008] Embodiments of the present invention are directed to a filtering system for efficiently removing most debris and other solids irrespective of their densities present in a metal melt flowing through a tundish from an inlet portion to an outlet portion and, at the same time ensuring a high level of safety with no risk of spilling metal melt over the tundish edges because of a dysfunction of the filtering system. These and other advantages of the present invention are explained more in detail in the following sections.

[0009] Embodiments of the present invention provide for a tundish for continuous metal casting. In various embodiments, tundish (10) defines a cavity, wherein the cavity has a cavity height (hlO) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X) and a cavity width measured along a transverse axis (Y), with X 1 Y 1 Z. The cavity comprises: an inlet portion (lOi) configured for receiving a flow of metal melt (20m) discharged by gravity from an outside of the tundish into the cavity of the tundish; an outlet portion (10o) comprising an outlet (llo) configured for discharging the metal melt out of the cavity into a mould; and a filtering system separating over the whole cavity width the inlet portion (lOi) from the outlet portion (10o). The filtering system comprises a filter module (1) extending over the whole cavity width and extending inside said cavity, wherein the filter module comprises an inlet side facing the inlet portion (lOi) of the tundish and extending from a floor (lOf) of the cavity to a top surface whose shortest distance from the floor measured along the vertical axis (Z) is equal to a minimum filter module height (hi), and wherein the filter module (1) comprises a filter unit (If) extending over a filter height (hf) along the vertical axis (Z) and provided with channels (lc) extending, from a channel inlet, opening at an inlet side facing the inlet portion (lOi) of the tundish, to a channel outlet, opening at an outlet side of the filter module (1) facing the outlet portion and separated from the inlet side by a filter depth (tf). The filtering system further comprises a wall module (2) comprising a wall extending over the whole cavity width and extending inside said cavity and defining one or more openings (2o) distributed over a width of the wall and over an opening height (h2) measured along the vertical axis (Z) from the floor (lOf). The filter module (1) is arranged closer to the outlet (1 lo) than the wall module (2), and a bypass passage (2b) is defined between the wall module (2) and the filter module (1) of largest width (tl2) measured along the longitudinal axis (X), such that the metal melt can only flow from the inlet portion to the inlet side of the filter module (1) through the one or more openings, and from the one or more openings to the outlet portion by flowing either through the channels of the filter unit (If) or through the bypass passage (2b). A wall ledge (2L) protrudes from the wall of the wall module (2) at a wall ledge distance (d2L) from the floor (lOf) not larger than the minimum filter module height (hi) (i.e., d2L < hi), and extends towards the inlet side of the filter module (1) without contacting the filter module (1), the wall ledge (2L) having a width (t2L) measured along the longitudinal axis (X), wherein 20 mm < t2L < tl2. Further, a filter ledge (1L) protrudes from the inlet side of the filter module (1) at a filter ledge distance (dlL) from the floor (lOf) greater than the opening height (h2) (i.e., dlL > h2), and is offset relative to the wall ledge (2L) (i.e., dlL ¹ d2L), the filter ledge extending towards the wall module (2) without contacting either the wall module or the wall ledge, the filter ledge (1L) having a width (tlL) measured along the longitudinal axis (X), wherein 20 mm < tlL < tl2.

[0010] In various embodiments, a ratio (h2 / hi) of the opening height (h2) to the filter module height (hi) is comprised between 20% and 95% (0.2 < h2 / hi < 0.95), preferably between 40% and 80%.

[0011] In various embodiments, a ratio ((tlL + t2L) / tl2), of the sum of the widths (tlL, t2L) of the filter and wall ledges to the largest width (tl2) of the bypass passage, is comprised between 20% and 150% (i.e., 0.2 < (tlL + t2L) / tl2 < 1.5), preferably between 30% and 120%, more preferably between 50% and 100%.

[0012] In various embodiments, the wall module comprises a single opening extending from a lower boundary separated from the floor by a distance of 0 to 5% of the cavity height (hlO) to a lower edge of the wall, defining the opening height (h2) as the distance separating the floor from the most remote point of the lower edge. Alternatively, in a second embodiment, the wall module comprises more than one opening, wherein a top opening is defined as the opening having a boundary most remote from the floor, separated from the floor by the opening height (h2).

[0013] In various embodiments, the opening height (h2) can be related to the cavity height (hlO) by a ratio (h2 / hlO) of the opening height (h2) to the cavity height (hlO) comprised between 10% and 60% (0.1< h2 / hlO < 0.6), preferably between 40 and 60%.

[0014] In various embodiments, a tortuosity of the bypass passage can be characterized very simply by defining a straight line extending between the floor in the inlet portion and the outlet portion passing through the bypass passage either, does not exist because a straight line cannot reach the floor or go through the bypass passage without abutting with a refractory element, or forms an angle ( Q ) with the vertical axis (Z) of not more than 70°, preferably, not more than 60°, more preferably not more than 45°.

[0015] In various embodiments, the filter ledge (1L) is ‘above’ the wall ledge (2L). In other words, the filter ledge distance (dlL) can be larger than the wall ledge distance (d2L) (i.e., dlL > d2L). Alternatively, the filter ledge (1L) can be ‘below the wall ledge (2L). In other words, the filter ledge distance (dlL) can be lower than the wall ledge distance (d2L) (i.e., dlL < d2L). But the filter ledge is not flush with the wall ledge, i.e., the filter ledge distance (dlL) is not equal to the wall ledge distance (d2L) (i.e., dlL ¹ d2L).

[0016] In various embodiments, the wall module (2) can comprise more than one wall ledge (2F), parallel to one another, never contacting each other and distributed over a height of the wall module (2). Similarly, the filter module (1) can comprise more than one filter ledge (IF), parallel to one another, never contacting each other and distributed over a height of the filter module (1). The one or more wall ledges and/or filter ledges define in combination additional baffles in the bypass passage.

[0017] In various embodiments, each baffle is defined by at least a wall ledge and a filter ledge, wherein the bypass passage imposes an inversion of the flow direction component along the longitudinal axis (X) of the metal melt to flow from the inlet portion to the outlet portion of the cavity.

[0018] In at least one embodiment, a lower boundary of the filter unit can be separated from the floor of the cavity by a lower distance (hd) comprised between 0 and 10 cm (i.e., 0 < hd < 10 cm), preferably between 2 and 5 cm. A higher boundary of the filter unit can be separated from the floor by a distance (hf + hd), such that a ratio ((hf + hd) / h2) of said distance ((hf + hd)) to the opening height (h2) is comprised between 0.7 and 1.2 (i.e., 70% < (hf + hd) / h2 < 120%), preferably between 80% and 100%.

[0019] In at least one embodiment, the wall ledge (2F) protrudes from a portion of a width of the wall; in some embodiments, wall ledge (2F) protrudes from a whole width of the wall.

[0020] In at least one embodiment, the filter ledge (IF) protrudes from a portion of a width of the inlet side of the filter module (1); in some embodiments, filter ledge (IF) protrudes from a whole width of the inlet side of the filter module (1).

DESCRIPTION OF THE DRAWINGS

[0021] The following detailed description of the various disclosed methods, processes, compositions, and articles refers to the accompanying drawings in which:

[0022] Fig. 1 shows a side cut view of a metallurgic installation comprising a tundish, according to at least one embodiment of the the presently disclosed subject matter.

[0023] Fig. 2 shows a top perspective view of the cavity of a tundish according to the present invention.

[0024] Figs. 3(a) - 3(d) show various embodiments of wall portions according to the present invention.

[0025] Figs. 4(a) - 4(f) show side cut views of various embodiments of filtering systems according to the present invention.

[0026] Figs. 5(a) and 5(b) show side cut views illustrating various dimensions in filtering systems according to the present invention. [0027] Figs. 6(a) and 6(b) show side perspective views illustrating how the cavity height (hlO) is measured.

[0028] Figs. 7(a) and 7(b) show top perspective views of two alternative embodiments of tundishes comprising more than one tundish outlet.

DETAILED DESCRIPTION

[0029] In continuous metal forming processes, metal melt is transferred from one metallurgical vessel to another, to a mould or to a tool. For example, as shown in Figure 1 a ladle (5L) is filled with metal melt out of a furnace (not shown) and driven over a tundish (10) to discharge the molten metal from the ladle, generally through a ladle shroud (5s) into the tundish. The metal melt can then be cast through a pouring nozzle (15) from a tundish outlet (llo) to a mould or tool (25) for continuously forming slabs, billets, beams, thin slabs, and the like. Flow of metal melt out of the ladle into the tundish and out of the tundish into the mould or tool is driven by gravity. The flow rates can be controlled by sliding gates in fluid communication with an outlet of the ladle and tundish. A ladle sliding gate (5g) can be used to control the flow rate off the ladle and even interrupt the flow at a sealed position. Similarly, a tundish sliding gate (not shown) can be used to control the flow rate off the tundish and interrupt the flow in a sealed position. Often, the flowrate out of the tundish is controlled by a stopper (7) instead of a sliding gate.

[0030] Since casting of metal into a mould or tool is to run continuously, the tundish plays the role of a buffer and the level (h20) of molten metal in the tundish must remain substantially constant during the whole casting operation. The level (h20) of molten metal in the tundish, however, drops during the replacement of an old ladle after it has been emptied by a new ladle filled with molten metal. The flow out of the tundish is maintained substantially constant by (1) reducing the time of ladle replacement and (2) controlling the aperture of the tundish outlet (llo) by means of the stopper (7) or a slide gate.

[0031] The presence of defects such as inclusions and impurities in the cast metal parts is a cause of concern. One source of such defects is the presence of foreign bodies in the metal melt (20m) present in the tundish. Slag (20s) too can contribute to these defects. They come mostly from debris and impurities which were present in the ladle or are caused by wear of the refractory materials in the pouring region of the tundish due to impacts and frictions between the metal melt and the refractory materials. It is important to prevent such debris and impurities from reaching the tundish outlet, to reduce the number of defects in the cast metal parts.

[0032] According to various embodiments of the presently disclosed subject matter, as illustrated in Figure 1, a tundish (10) for continuous metal casting according to at least one embodiment of the present invention defines a cavity having a cavity height (hlO) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X) and a cavity width measured along a transverse axis (Y), with X 1 Y 1 Z. The cavity comprises an inlet portion (lOi) configured for receiving a flow of metal melt (20m) discharged by gravity from an outside of the tundish into the cavity of the tundish. It comprises an outlet portion (10o) comprising a tundish outlet (llo) configured for discharging the metal melt out of the cavity into a mould or tool (25). The cavity comprises a filtering system separating over the whole width of the tundish the inlet portion (lOi) from the outlet portion (10o) and comprising, a filter module (1) extending over the whole cavity width and extending along the vertical axis (Z) from the floor (lOf) of the cavity over a minimum filter module height (hi) to a top surface, the filter module comprises an inlet side, facing the inlet portion (lOi) of the tundish. The filter module (1) comprises a filter unit (If) extending over a filter height (hf) along the vertical axis (Z) and provided with channels (lc) extending from a channel inlet opening at the inlet side to a channel outlet opening at an outlet side of the filter module (1) facing the outlet portion and separated from the inlet side by a filter depth (tf), and a wall module (2) comprising a wall extending over the whole cavity width and extending along the vertical axis (Z) and defining one or more openings (2o) distributed over a width of the wall and over an opening height (h2) measured along the vertical axis (Z) from the floor (lOf).

[0033] The filter module (1) is arranged closer to the outlet (1 lo) than the wall module (2), and a bypass passage (2b) is defined between the wall module (2) and the filter module (1) of largest width (tl2) measured along the longitudinal axis (X), such that the metal melt can only flow, from the inlet portion to the inlet side of the filter module (1) through the one or more openings (2o), and from the one or more openings (2o) to the outlet portion by flowing either through the channels of the filter unit (If) or through the bypass passage (2b),

[0034] The cavity: The cavity has a cavity height (hlO) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X) and a cavity width measured along a transverse axis (Y), with X 1 Y 1 Z. The cavity is defined by a floor (lOf), surrounded by peripheral walls. As illustrated in Figures 6(a) and 6(b), the cavity height (hlO) corresponds to the level of liquid filling the cavity measured from the floor (lOf) of the cavity, over which the liquid flows out of the cavity, over an edge thereof (without a lid closing the cavity). In other words, it is the smallest height of the peripheral walls measured from the floor to a top of the peripheral walls. If the tundish is provided with a spill-out spout (10s), the cavity height (hlO) is the distance separating the floor (lOf) from the bottom of the spout (cf. Figure 6(b)).

[0035] The tundish is fed in metal melt by pouring by gravity the metal melt from a ladle (5L) into a receiving portion of the tundish cavity. In order to shield the teeming stream from atmospheric contamination, the ladle is often provided with a ladle shroud (5s). To prevent the teeming stream from piercing the floor of the cavity upon hitting it, an impact pad (9) (or impact box) is often positioned within the impact area where the teeming stream hits the floor. One tundish is generally served by a single ladle (5L) at a time. Although the present disclosure could apply to multi-ladle feeding systems.

[0036] As illustrated in Figures 7(a) and 7(b), the cavity can comprise more than one tundish outlet (llo) served by a ladle (5L). In any event, there is always at least one metal feeding region associated with one or more tundish outlets (llo), each defining a metal flow path extending between the receiving portion (illustrated in the Figures as the position of a box or impact pad (9)) and the tundish outlet (1 lo). According to the invention, it suffices that all flow paths must be intercepted by at least one filtering system as defined more in detail below. In case of more than one tundish outlet (1 lo) more than one filtering system could be required to meet this requirement.

[0037] As shown in Figures 1, 4(a) to 4(f), and 5(a) and 5(b), in a stationary mode, i.e., when a ladle is currently discharging fresh metal melt into the tundish, the cavity is filled at a substantially constant level (h20) of metal melt (20m). It is only during the period an empty ladle (5L) is replaced by a new one, that the tundish is not fed in fresh metal melt, and the level (h20) of metal melt in the tundish drops with time, since casting proceeds continuously. A constant flow rate out of the tundish outlet is controlled as a function of decreasing pressure by a stopper (7) or a sliding gate (not shown) at the tundish outlet (llo).

[0038] The level (h20) of metal melt (20m) cannot exceed the cavity height (hlO) (i.e., h20 < hlO) lest metal melt would flow out of the tundish over the edges or through a spill-out spout (10s). The level (h20) of metal melt in a stationary mode can be comprised between 75% and 90% of the cavity height (hlO). A higher level would unduly increase the risk of overflow, and a lower level would increase the cost of an over dimensioned tundish.

[0039] The filtering system: The filtering system separates the cavity into an inlet portion (lOi) and an outlet portion (10o). The inlet portion (lOi) includes the region where fresh metal is poured into the tundish cavity from a ladle (5L). The outlet portion (10o) comprises a tundish outlet (1 lo). The metal melt is poured into the inlet portion and must flow through the filtering system to flow out of the tundish outlet (llo) into a mould or tool (25). The filtering system comprises a wall module (2) and a filter module (1) comprising a filter unit (If) provided with channels (lc) extending from a channel inlet opening at an inlet side of the filter module (1) facing the inlet portion (lOi) to a channel outlet opening at an outlet side facing the outlet portion (10o).

[0040] The metal melt (20m) has two options only for flowing through the filtering unit, through the channels (lc) of the filtering unit (If) or through a bypass passage (2b) defined between the filter module (1) and the wall module (2).

[0041] Various embodiments of the presently disclosed subject matter are directed to designing of a filtering system such that in a stationary mode, more than 50% of the metal melt flowing through the filtering system flows through the channels of the filter unit (If). Like any filtering system, the filter units (If) used in tundishes (10) become clogged with debris and solids retained upstream of the filter unit. One way to measure the degree of clogging of a filter unit is to monitor the pressure drop (DR = (Pu - Pd)) evolution with time, upstream (Pu) relative to downstream (Pd) of the filter unit. The pressure drop increases relative to a nominal pressure drop (DR0) with increasing degree of clogging. In the present invention, it is preferred that for pressure drops up to twice the nominal pressure drop (i.e., for DR / DR0 < 2), more than 50%, preferably more than 60%, more preferably more than 75% of the metal melt flows through the filter unit (If). Conversely, it is preferred that less than 50%, preferably less than 40%, more preferably less than 25% flows through the bypass passage (2b).

[0042] The filtering system of the present disclosure allows to retain substantial amounts of debris and other solids present in the metal melt prior to discharging the metal melt into the mould or tool (25). At the same time, in case of excessive clogging of the filtering unit (If) leading to high pressure drops across the filter unit, the metal melt can flow into the outlet portion (10o) through the bypass passage (2b). This way, the metal melt is not stuck in the inlet portion ( lOi) raising the level of metal melt dangerously close to or higher than the cavity height (hlO) in the inlet portion, with dire consequences of metal melt spilling out of the tundish.

[0043] Contrary to the system described in KR101853768 discussed supra, the filtering system of the present disclosure does not require a weir located downstream of the filter module (1), between the filter module (1) and the tundish outlet (llo). The design of the filtering system of the present disclosure is detailed in continuation.

[0044] The wall module (2): The wall module (2) is one of two essential components of the filtering system of the present invention, which divides the cavity into the inlet portion (lOi) and the outlet portion (10o). The wall module (2) is adjacent to the inlet portion (lOi) and is separated from the tundish outlet by the filter module (1). The wall module (2) comprises a wall extending over the whole cavity width and extending along the vertical axis (Z) up to an upper edge. It defines one or more openings (2o) distributed over a width of the wall and over an opening height (h2) measured along the vertical axis (Z) from the floor (lOf). The upper edge of the wall is located higher than the stationary level (h20) of metal melt. The upper edge is generally located at a distance from the floor (lOf) comprised between 90% and 100% of the cavity height (hlO), preferably between 95% and 100% of hlO. In case the tundish is provided with a spill-out spout (10s), the upper edge could extend higher than hlO, preferably flush with the free edge of the tundish excluding the spill-out spout. This is particularly true in case the spill-out spout (10s) is located in the outlet portion (10o).

[0045] As illustrated in Figures 3(a) to 3(d), the one or more openings (2o) can have various geometries. In the embodiment illustrated in Figures 3(a) and 3(b), a single opening (2o) extends from the floor (lOf) to a lower edge of the wall, which can be straight and parallel to the floor (cf. Figure 3(a)) or curved (cf. Figure 3(b)). The opening height (h2) is the distance from the floor to the most remote point of the lower edge. In a variation of this embodiment, the opening extends from a lower boundary separated from the floor (1 Of) by a distance of up to 5% of the cavity height (hlO) (forming a step) to the lower edge of the wall. The opening height (h2) is defined as the distance separating the floor from the most remote point of the lower edge (i.e., ignoring the presence of a step). The presence of a step over a whole width of the cavity impedes emptying the tundish of the whole metal melt left in it, filling the inlet portion (lOi) to the level of the step. The step can be provided with draining channels to obviate this problem. In an alternative embodiment, illustrated in Figure 3(c), the wall can comprise more than one opening (2o). A top opening is defined as the opening having a boundary most remote from the floor (lOf). The opening height (h2) is defined as the distance separating said boundary from the floor. Figure 3(c) illustrates identical round openings. It is clear that the more than one opening can have any geometry and dimension as desired.

[0046] To flow from the inlet portion to the outlet portion, metal melt must pass through the one or more openings of the wall. There is no alternative, unless the level of metal melt in the inlet portion increases beyond the upper edge of the wall. A ratio (h2 / hlO) of the opening height (h2) to the cavity height (hlO) is preferably comprised between 10% and 60% (i.e., 0.1 < h2 / hlO < 0.6), preferably between 15% and 50%, more preferably between 20 and 40%. The opening height (h2) is important because, as illustrated in Figure 1 (dashed line) it forces downwards the flow path of the metal melt after bouncing upwards against the impact pad (9) towards the surface of the metal melt. The presence of a step protruding out of the floor can serve to retain the heaviest solids, but its presence is not essential.

[0047] The wall module (2) also comprises a wall ledge (2L) protruding from a whole width of the wall at a wall ledge distance (d2L) from the floor (lOf) and extends towards the inlet side of the filter module (1) without contacting the latter, the wall ledge (2L) having a width (t2L) measured along the longitudinal axis (X). For walls comprising a single opening with a straight upper edge, the wall ledge can be flush with the upper edge, so that the wall ledge distance (d2L) is equal to the opening height (h2) (i.e., h2L = h2), as illustrated, e.g., in Figures 1, 3(a), 4(a), 4(b), 4(e), and 5(a). Alternatively, the wall ledge (2L) can be at any distance (d2L) from the floor, such that h2 < d2L < 80% hlO, preferably d2L is smaller than 70% hlO. This embodiment of a wall ledge which is not flush with the lower edge of the top opening is illustrated in Figures 3(d), 4(c), 4(d), 4(f), and 5(b). In some embodiments, wall ledge (2L) protrudes from a portion of a width of the wall.; in some embodiments, wall ledge (2L) protrudes from a whole width of the wall.

[0048] The wall module (2) can comprise more than one wall ledge (2L) distributed over a height of the wall module (2) as illustrated in Figure 4(e). In various embodiments, the more than one wall ledges are straight and extend parallel to one another and to the floor (lOf). If not parallel to one another, the more than one wall ledges (2L) preferably do not contact each other. The wall ledge distance (d2L) is the distance to the floor of the wall ledge located closest to the floor (lOf). In various embodiments, the wall and wall ledge (2L) are made of a refractory material, preferably the same refractory material lining the peripheral walls and floor of the cavity.

[0049] The filter module: The filter module (1) extends over the whole cavity width and extends along the vertical axis (Z) from the floor (lOf) of the cavity over a minimum filter module height (hi) to a top surface. The filter module is located adjacent to the outlet portion (lOo) and comprises an inlet side, facing the inlet portion (lOi) of the tundish. The filter module (1) comprises a filter unit (If) provided with channels (lc) extending from a channel inlet, opening at the inlet side to a channel outlet, opening at an outlet side of the filter module (1) facing the outlet portion and separated from the inlet side by a filter depth (tf). The filter unit (If) extends vertically preferably below the top surface, such that the top surface is not part of the filter unit (If). The filter unit (If) can extend over any fraction of the tundish width as desired. The larger the area in a plane (Y, Z), the higher the volumetric throughput through a filter unit of given permeability.

[0050] In at least one embodiment, a filter ledge (1L) protrudes from a whole width of the inlet side of the filter module (1) at a filter ledge distance (dlL) from the floor (lOf) greater than the opening height (h2) (i.e., dlL > h2). The filter ledge (1L) is offset relative to the wall ledge (2L) (i.e., dlL ¹ d2L) such that they do not face each other at a same level. The filter ledge (1L) extends towards the wall module (2) without contacting either the wall module or the wall ledge, the filter ledge (1L) having a width (tlL) measured along the longitudinal axis (X). In some embodiments, filter ledge (1L) protrudes from a portion of a width of the inlet side of the filter module (1); in some embodiments, filter ledge (1L) protrudes from a whole width of the inlet side of the filter module (1).

[0051] The filter module (1) can comprise more than one filter ledge (1L) distributed over a height of the filter module (1) as illustrated in Figure 4(f). In at least one embodiment, the more than one filter ledges are straight and extend parallel to one another and to the floor (lOf). If not parallel to one another, the more than one filter ledges (1L) preferably do not contact each other and do not contact a wall ledge (2L). The filter ledge distance (dlL) is the distance to the floor of the filter ledge located closest to the floor (lOf).

[0052] In one embodiment, the filter ledge distance (dlL) to the floor is larger than the wall ledge distance (d2L) (i.e., dlL > d2L). This embodiment is illustrated in Figures 1, 4(a)-4(c), 4(e), 5(a), and 5(b). In an alternative embodiment, illustrated in Figures 4(d) and 4(f), the filter ledge distance (dlL) to the floor is smaller than the wall ledge distance (d2L) (i.e., dlL < d2L).

[0053] The filter unit (If) can be any type of filter unit known in the art of continuous metal casting. The function of the filter unit (If) is to retain all debris and solids upstream of the filter unit (= retentate) while allowing the metal melt to flow through the filter unit through the channels (lc) (= filtrate) and thence to the tundish outlet (1 lo). The channels can be straight or have a tortuosity which, with their dimensions (cross-section and length) contribute to the definition of the permeability of the filter unit. The permeability of the filter unit depends on the requirements of a particular application and a skilled person knows how to optimize the properties of the filter unit (If) accordingly.

[0054] A lower boundary of the filter unit (If) can be separated from the floor (lOf) of the cavity by a lower distance (hd) comprised between 0 and 10 cm (i.e., 0 < hd < 10 cm), preferably between 2 and 5 cm. Similarly, a higher boundary of the filter unit (If) can be separated from the floor (lOf) by a distance (hf + hd), such that a ratio ((hf + hd) / h2) of said distance ((hf + hd)) to the opening height (h2) is comprised between 0.7 and 1.2 (i.e., 70% < (hf + hd) / h2 < 120%), preferably between 80% and 100%.

[0055] The bypass passage: The bypass passage (2b) defined in the filtering system is the gist of the present invention. It must ensure that casting can continue without incident even in case the filter unit (If) is clogged, and, at the same time, it cannot offer an easier flow path than through the filter unit (If), such that at stationary conditions, at least 50% of the metal flows through the filter unit to reach the outlet portion (10o) of the tundish. To this end, the bypass passage of the present disclosure is designed such as to impose to the metal melt flow first and second inversions of directions of the velocity vector along the longitudinal axis (X). This is achieved by the combination of the wall ledge (2L) and the filter ledge (1L) which impose a baffle to the passage defined between the wall and the filter module (1).

[0056] As discussed supra with respect to Figures 1, 4(a)-4(c), 4(e), 5(a), and 5(b), the wall ledge (2L) can be lower (i.e., closer to the floor (10f)) than the filter ledge (1L). This way, the fraction of metal melt above the opening height (h2) from the floor (lOf) is blocked by the wall and is deviated downwards (i.e., towards the opening (2o) whence it can change direction towards the filter module (1) upon approaching the floor (lOf). The metal melt can flow upwards directly behind the wall only until it reaches a lower surface of the wall ledge (2L). If the wall ledge (2L) is flush with the opening (i.e., d2L = h2), the metal melt cannot flow upwards at all directly behind the wall. Similarly, the fraction of metal melt below the opening height (h2) from the floor (lOf) cannot flow upwards directly behind the wall and is forced to flow towards the filter module (1). As the metal melt hits the lower surface of the wall ledge (2L), the flow is deviated towards the filter module (1). A filter fraction flows straight (parallel to the longitudinal axis (X)) or downwards against the filter unit (If). A bypass fraction flows upwards against the inlet side of the filter module (1), until it hits a lower surface of the filter ledge (1L). This deviates the flow with an inversion of the velocity vector component parallel to the longitudinal axis (X) (= X-component), such that the X-component of the flow turns back in the direction of the inlet portion (lOi). The flow hits the wall and the X-component of the velocity vector is inverted again, such that the flow turns back in the direction of the inlet portion (lOi). As shown in Figure 4(c), the wall module (2) can comprise a second wall ledge above the wall ledge (2L) to force the velocity vector to a direction more parallel to the longitudinal axis (X). The filter unit can comprise additional filter ledges to act in combination with corresponding additional wall ledges as additional baffles to change the X-component of the velocity vector.

[0057] As discussed supra with respect to Figures 4(d) and 4(f), the filter ledge (1L) can alternatively be lower (i.e., closer to the floor (10f)) than the wall ledge (2L). This way, upon feeling a resistance to flow through the filter unit (If) a fraction of the metal melt deviates upwards and hits the lower surface of the filter ledge (1L). This deviates the flow with an inversion of the X-component of the velocity vector, such that the X-component of the flow turns back in the direction of the inlet portion (lOi). The flow then hits the wall and is deviated upwards again until it hits the lower surface of the wall ledge (2L) forcing it to change again the direction of the X-component of the velocity vector in the direction of the outlet portion (lOo). The metal melt can thus continue to flow towards the outlet portion (10o) over the filter module (1) and down to the tundish outlet (llo). The filter unit can comprise additional filter ledges to act in combination with corresponding additional wall ledges as additional baffles to change the X-component of the velocity vector.

[0058] The skilled person can adapt the required fraction of metal melt forced through a given filter unit (If) by varying the dimensions of the bypass passage (2b) to render it more or less tortuous, and hence more or less easy to follow compared with the passage through the filter unit. Relevant dimensions are for example, the largest width (tl2) (with tl2 > 0), the filter ledge width (tlL), the wall ledge width (t2L), the filter ledge distance (dlL), the wall ledge distance (d2L), the distance (|dlL - d2L|) measured along the vertical axis (Z) separating the wall ledge and filter ledge, and the like.

[0059] According to at least one embodiment, a ratio ((tlL + t2L) / tl2), of the sum of the widths (tlL, t2L) of the filter and wall ledges (1L, 2L) to the largest width (tl2) of the bypass passage (2b), is comprised between 20% and 150% (i.e., 0.2 < (tlL + t2L) / tl2 < 1.5), preferably between 30% and 120%, more preferably between 50% and 100%.

[0060] The fraction flowing through the filtering unit also depends on the opening height (h2) and the minimum filter module height (hi). According to at least one embodiment, a ratio (h2 / hi) of the opening height (h2) to the filter module height (hi) is comprised between 20% and 95% (i.e., 0.2 < h2 / hi < 0.95), preferably between 40% and 80%.

[0061] A simple way of characterizing the tortuosity of the bypass passage is by drawing a straight line extending from the floor (lOf) in the inlet portion to the outlet portion passing through the bypass passage (2b). According to at least one embodiment, such straight line either, does not exist as the line does not reach the floor as illustrated in Figures 4(b) and 4(d), or forms an angle ( Q ) with the vertical axis (Z) of not more than 70°, preferably, not more than 60°, more preferably not more than 45°, most preferably not more than 35°. This is illustrated in Figures 4(a) and 4(c).

[0062] The foregoing conditions prevent the metal melt from finding a straight flow path from the floor where it bounces as it is discharged from a ladle (5L) through the bypass passage (2b). If such flow path were available, a substantial fraction of the molten metal would shunt the filter unit (If) and flow through the bypass passage instead, which is clearly not satisfactory.

[0063] For example, for a tundish of cavity height (hlO) comprised between 800 and 1800 mm, preferably between 1000 and 1300 mm, the opening height (h2) can be comprised between 80 and 600 mm, preferably between 100 and 500 mm. The largest width (tl2) separating the wall from the filter module in the bypass passage (2b) can be comprised between 60 and 800 mm; preferably between 80 and 600 mm. The filter ledge distance (dlL) to the floor can be comprised between 80 and 650 mm, preferably between 100 and 620 mm, and the wall ledge distance (d2L) to the floor can be comprised between 80 and 600 mm.

[0064] In various embodiments, the wall ledge width (t2L) and filter ledge width (tlL) can be comprised between 20 and 200 mm; in some embodiments, the wall ledge width (t2L) and filter ledge width (tlL) can be comprised between 50 and 150 mm. In at least one embodiment, each of the wall ledge width (t2L) and filter ledge width (tlL) has a minimum value of 20 mm. In at least one embodiment, each of the wall ledge width (t2L) and filter ledge width (tlL) has a maximum value of 200 mm. However, in some embodiments, the wall ledge width (t2L) and filter ledge width (tlL) may be adjusted or customized based on the size and dimensions of tundish (10). Nonetheless, in various embodiments, each of the wall ledge width (t2L) and filter ledge width (tlL) is a non-zero value; stated differently, various embodiments of the presently disclosed subject matter will include the presence of a wall ledge as well as a filter ledge - irrespective of their respective widths.

[0065] The tundish of the present disclosure has the advantages of removing most debris and other solids from the metal melt (20m) prior to casting it into a tool (25). When a filter unit (If) is new or its channels are clean and free of any solid debris, the filter unit is characterized by a pressure drop (DR) equal to the nominal pressure drop (DR0) between the inlet side and an outlet side of the filter unit. Upon use, debris and other solids, retained by the channels, accumulate and partially and eventually totally obstruct some or all the channels. The pressure drop (DR) increases, making it more difficult for the metal melt to flow through the filter unit (If). As the pressure drop (DR) increases, the metal melt will find it easier to flow through the bypass passage (2b) rather than through the filter unit.

[0066] For example, when the filter unit (If) is fully operational (e.g., DR / DR0 < 2), more than 50%, preferably more than 60%, more preferably more than 75%, most preferably more than 85% of the metal melt flows through the filter unit (If) of the metal melt flowing through the filtering system from the inlet portion (lOi) to the outlet portion (10o) flows through the filter unit (If), the rest flowing through the bypass passage (2b). In case of substantial clogging of the filter unit, however, (i.e., the pressure drop reaches high values e.g., DR / DR0 > 10), the metal melt finds it too difficult to flow through the filter unit (If) and finds an easier way out by flowing through the bypass passage (2b). This reduces the risk of seeing the level (h20) of metal melt rising in the inlet portion to dangerous levels close to the cavity height (hlO).

[0067] Besides being efficient and easily modulable to meet the requirements of specific applications, this solution is also very simple to implement, requiring only two modules of simple design each, the wall module (2) and the filter module (1). This solution is therefore also quite economical and ensures continuity of a metal casting session.

[0068] A tundish (10) for continuous metal casting, defining a cavity, wherein the cavity has a cavity height (hlO) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X) and a cavity width measured along a transverse axis (Y), with X 1 Y 1 Z, and wherein the cavity comprises an inlet portion (lOi) configured for receiving a flow of metal melt (20m) discharged by gravity from an outside of the tundish into the cavity of the tundish, an outlet portion (10o) comprising an outlet (llo) configured for discharging the metal melt out of the cavity into a mould, and a filtering system separating over the whole cavity width the inlet portion (lOi) from the outlet portion (10o). The filtering system comprises a filter module (1) extending over the whole cavity width and extending inside said cavity, wherein the filter module comprises an inlet side facing the inlet portion (lOi) of the tundish and extending from a floor (lOf) of the cavity to a top surface whose shortest distance from the floor measured along the vertical axis (Z) is equal to a minimum filter module height (hi), and wherein the filter module (1) comprises a filter unit (If) extending over a filter height (hf) along the vertical axis (Z) and provided with channels (lc) extending, from a channel inlet, opening at an inlet side facing the inlet portion (lOi) of the tundish, to a channel outlet, opening at an outlet side of the filter module (1) facing the outlet portion and separated from the inlet side by a filter depth (tf). The filter system further comprises a wall module (2) comprising a wall extending over the whole cavity width and extending inside said cavity and defining one or more openings (2o) distributed over a width of the wall and over an opening height (h2) measured along the vertical axis (Z) from the floor (lOf). The filter module (1) is arranged closer to the outlet (1 lo) than the wall module (2), and a bypass passage (2b) is defined between the wall module (2) and the filter module (1) of largest width (tl2) measured along the longitudinal axis (X), such that the metal melt can only flow from the inlet portion to the inlet side of the filter module (1) through the one or more openings, and from the one or more openings to the outlet portion by flowing either through the channels of the filter unit (If) or through the bypass passage (2b), characterized in that, a. a ratio (h2 /hl) of the opening height (h2) to the filter module height (hi) is comprised between 20% and 95% (0.2 < h2 / hi < 0.95), preferably between 40% and 80%, b. a wall ledge (2L) protrudes from a whole width of the wall at a wall ledge distance (d2L) from the floor (lOf) not larger than the minimum filter module height (hi) (i.e., d2L < hi), and extends towards the inlet side of the filter module (1) without contacting the filter module, the wall ledge (2L) having a width (t2L) measured along the longitudinal axis (X), wherein 0 < t2L < tl2, in that c. a filter ledge (1L) protrudes from a whole width of the inlet side of the filter module (1) at a filter ledge distance (dlL) from the floor (lOf) greater than the opening height (h2) (i.e., dlL > h2), and is offset relative to the wall ledge (2L) (i.e., dlL ¹ d2L); and extending towards the wall module (2) without contacting either the wall module or the wall ledge, the filter ledge (1L) having a width (tlL) measured along the longitudinal axis (X), wherein 0 < tlL < tl2, and in that d. a ratio ((tlL + t2L) / tl2), of the sum of the widths (tlL, t2L) of the filter and wall ledges (1L, 2L) to the largest width (tl2) of the bypass passage (2b), is comprised between 20% and 150% (i.e., 0.2 < (tlL + t2L) / tl2 < 1.5), preferably between 30% and 120%, more preferably between 50% and 100%.

[0069] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the invention may be apparent to those having ordinary skill in the art.

Claims

CLAIMS What is claimed:

1. Tundish (10) for continuous metal casting, defining a cavity, wherein the cavity has a cavity height (hlO) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X) and a cavity width measured along a transverse axis (Y), with X 1 Y 1 Z, and wherein the cavity comprises: an inlet portion (lOi) configured for receiving a flow of metal melt (20m) discharged by gravity from an outside of the tundish into the cavity of the tundish; an outlet portion (10o) comprising an outlet (1 lo) configured for discharging the metal melt out of the cavity into a mould; a filtering system separating over the whole cavity width the inlet portion (lOi) from the outlet portion (10o), the filtering system comprising a filter module (1) extending over the whole cavity width and extending inside said cavity, wherein the filter module comprises an inlet side facing the inlet portion (lOi) of the tundish and extending from a floor (lOf) of the cavity to a top surface whose shortest distance from the floor measured along the vertical axis (Z) is equal to a minimum filter module height (hi), and wherein the filter module (1) comprises a filter unit (If) extending over a filter height (hf) along the vertical axis (Z) and provided with channels (lc) extending, from a channel inlet, opening at an inlet side facing the inlet portion (lOi) of the tundish, to a channel outlet, opening at an outlet side of the filter module (1) facing the outlet portion and separated from the inlet side by a filter depth (tf), and a wall module (2) comprising a wall extending over the whole cavity width and extending inside said cavity, and defining one or more openings (2o) distributed over a width of the wall and over an opening height (h2) measured along the vertical axis (Z) from the floor (lOf), wherein the filter module (1) is arranged closer to the outlet (llo) than the wall module (2), and a bypass passage (2b) is defined between the wall module (2) and the filter module (1) of largest width (tl2) measured along the longitudinal axis (X), such that the metal melt can only flow from the inlet portion to the inlet side of the filter module (1) through the one or more openings, and from the one or more openings to the outlet portion by flowing either through the channels of the filter unit (If) or through the bypass passage (2b), characterized in that, a wall ledge (2L) protrudes from the wall of the wall module (2) at a wall ledge distance (d2L) from the floor (lOf) not larger than the minimum filter module height (hi) (i.e., d2L < hi), and extends towards the inlet side of the filter module (1) without contacting the filter module (1), the wall ledge (2L) having a width (t2L) measured along the longitudinal axis (X), wherein 20 mm < t2L < tl2, a filter ledge (1L) protrudes from the inlet side of the filter module (1) at a filter ledge distance (dlL) from the floor (lOf) greater than the opening height (h2) (i.e., dlL > h2), and is offset relative to the wall ledge (2L) (i.e., dlL ¹ d2L), the filter ledge extending towards the wall module (2) without contacting either the wall module or the wall ledge, the filter ledge (1L) having a width (tlL) measured along the longitudinal axis (X), wherein 20 mm < tlL < tl2.

2. The tundish according to claim 1, wherein a ratio (h2 / hi) of the opening height (h2) to the filter module height (hi) is comprised between 20% and 95% (0.2 < h2 / hi < 0.95), preferably between 40% and 80%.

3. The tundish according to claim 1, wherein a ratio ((tlL + t2L) / tl2), of the sum of the widths (tlL, t2L) of the filter and wall ledges (1L, 2L) to the largest width (tl2) of the bypass passage (2b), is comprised between 20% and 150% (i.e., 0.2 < (tlL + t2L) / tl2 < 1.5), preferably between 30% and 120%, more preferably between 50% and 100%.

4. The tundish according to claim 1, wherein the wall module (2) comprises a single opening (2o) extending from a lower boundary separated from the floor (lOf) by a distance of 0% to 5% of the cavity height (hlO) to a lower edge of the wall, defining the opening height (h2) as the distance separating the floor from the most remote point of the lower edge.

5. The tundish according to claim 1, wherein the wall module (2) comprises more than one opening (2o), wherein a top opening is defined as the opening having a boundary most remote from the floor (2f), separated from the floor by the opening height (h2).

6. The tundish according to anyone of the preceding claims, wherein a ratio (h2 / hlO) of the opening height (h2) to the cavity height (hlO) is comprised between 10% and 60% (0.1< h2 / hlO < 0.6), preferably between 40 and 60%.

7. The tundish according to anyone of the preceding claims, wherein a straight line extending between the floor (lOf) in the inlet portion and the outlet portion passing through the bypass passage (2b) either, does not exist, or forms an angle ( Q ) with the vertical axis (Z) of not more than 70°, preferably, not more than 60°, more preferably not more than 45°.

8. The tundish according to anyone of the preceding claims, wherein the filter ledge distance (dlL) is larger than the wall ledge distance (d2L) (i.e., dlL > d2L).

9. The tundish according to anyone of the preceding claims, wherein the wall module (2) comprises more than one wall ledge (2L), parallel to one another, never contacting each other and distributed over a height of the wall module (2).

10. The tundish according to anyone of the preceding claims, wherein the filter module (1) comprises more than one filter ledge (1L), parallel to one another, never contacting each other and distributed over a height of the filter module (1).

11. The tundish according to anyone of the preceding claims, wherein the bypass passage (2b) imposes an inversion of a flow direction component along the longitudinal axis (X) of the metal melt to flow from the inlet portion (lOi) to the outlet portion (10o) of the cavity.

12. The tundish according anyone of the preceding claims, wherein, a lower boundary of the filter unit (If) is separated from the floor (lOf) of the cavity by a lower distance (hd) comprised between 0 and 10 cm (i.e., 0 < hd < 10 cm), preferably between 2 and 5 cm, and / or wherein a higher boundary of the filter unit (If) is separated from the floor (lOf) by a distance (hf + hd), such that a ratio ((hf + hd) / h2) of the distance ((hf + hd)) to the opening height (h2) is comprised between 0.7 and 1.2 (i.e.,

70% < (hf + hd) / h2 < 120%), preferably between 80% and 100%.

13. The tundish according to anyone of the preceding claims, wherein a wall ledge (2L) protrudes from a portion of a width of the wall, or a whole width of the wall.

14. The tundish according to anyone of the preceding claims, wherein the filter ledge (1L) protrudes from a portion of a width of the inlet side of the filter module (1), or a whole width of the inlet side of the filter module (1).