Tundish with filter module

Abstract

The filter module (1) of the filtering system for the tundish (10) comprises a filter unit (1f) with a channel (1c) extending from a channel inlet to a channel outlet, and a wall module (2) with a wall defining an opening (2o) extending from the floor (10f) over an opening height (h2). A bypass passage (2b) is defined between the wall module (2) and the filter module (1) with a maximum width (t12), whereby the molten metal can only flow from the inlet portion to the outlet portion by either passing through the channel of the filter unit (1f) or by flowing through the bypass passage (2b). The wall module comprises a wall ledge (2L) with a width (t2L). The filter module (1) further comprises a filter ledge (1L) with a width (t1L) and offset vertically with respect to the wall ledge (2L) to form a baffle.

Description

[Technical field]

[0001] An embodiment of the present invention relates to a tundish for continuous molten metal casting with a filter unit for removing solid impurities before casting the molten metal into a mold or die. In particular, it relates to a tundish with a filter module that imposes two possible paths for the molten metal to flow from an inlet portion of the tundish to a discharge portion that includes a tundish discharge port for casting the molten metal into a mold or die. The molten metal must either flow through the filter unit or through a bypass passage designed to favor the flow through the filter unit. However, if the filter unit becomes clogged, the flow may still go through the bypass passage. [Background technology]

[0002] In a continuous metal forming process, molten metal is transferred from one metallurgical vessel to another, mold, or die. For example, a ladle is filled with molten metal from a furnace and driven over a tundish to discharge the molten metal from the ladle, typically through a ladle shroud and into the tundish. The molten metal can then be cast from the tundish discharge through an injection nozzle into a mold or die for continuously forming slabs, billets, beams, thin slabs, and the like. The flow of molten metal from the ladle to the tundish and from the tundish to the mold or die is driven by gravity.

[0003] There is concern about the presence of defects such as inclusions and impurities in cast metal parts. These defects arise primarily from debris and impurities present in the ladle or caused by wear of the refractory material in the pouring area of ​​the tundish due to collisions and friction between the molten metal and the refractory material. To reduce the number of defects in cast metal parts, it is important to prevent such debris and impurities from reaching the tundish discharge.

[0004] In order to reduce the amount of debris and impurities reaching the tundish discharge, it is proposed in EP 3470149 to include a baffle module extending across the width of the tundish cavity, separating the tundish cavity into an inlet section defined as the part of the tundish that receives molten metal from the ladle, and an outlet section defined as the part of the tundish cavity that includes the tundish discharge. The baffle module consists of two parallel walls vertically offset with respect to each other, a first wall adjacent to the inlet section defining an opening between the floor of the cavity and the 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 molten metal flowing from the inlet section to the outlet section is diverted by the baffle module, causing most of the debris and other solids to remain at the bottom of the second wall. However, the baffle module described in EP 3470149 retains most of the heaviest debris and other solids that do not follow the tortuous flow imposed by the baffles, while the lighter solids become suspended and pass through the baffle module to the tundish discharge. Given the high density of the molten metal, the solids become suspended easily, and the removal effectiveness of the baffle module is not satisfactory in many applications.

[0005] It has also been proposed to include a filter module that extends over the entire width of the tundish cavity and separates it between the inlet and outlet portions. For example, KR200303465 describes a tundish with a filter module that extends over the entire cross section of the tundish cavity, the filter module comprising a filter unit that defines a channel, so that the molten metal in the inlet portion of the cavity must necessarily flow to reach the outlet portion, and thus most of the debris and impurities are removed from the molten metal that reaches the outlet portion. The use of a filter module makes it possible to substantially reduce the amount of debris and impurities that flow out of the tundish into the mold, but also creates substantial dangers. Indeed, over time, debris and other solids accumulate on the inlet side of the filter unit, thus substantially reducing the permeability of the filter unit and increasing the pressure difference (ΔP) required to drive the flow of molten metal through the filter unit. Thus, the level of the molten metal at the inlet portion of the cavity can rise relative to the level at the outlet portion until the molten metal reaches the top of the filter module and flows over the filter module rather than through the filter unit. If the height of the filter module is close to the tundish height, there is a serious risk that the molten metal will overflow the tundish with disastrous consequences.

[0006] To solve the problem of overflow in case of clogging of the filter unit, KR101853768 describes a filter system that includes a combination of the solutions proposed in EP3470149 and KR200303465 discussed above, by including a filter module between the first and second walls of the baffle module of EP3470149. This filter module has a height that is lower than that described in KR200303465 and similar to the height of the opening defined by the first wall. The first wall has the function of deflecting a portion of the molten metal flowing above the filter module and of defining a bypass passage between the filter module and the first wall. This allows the molten metal to flow above the filter module and the second wall through the bypass passage in case of clogging of the filter unit, thus reaching the tundish discharge outlet with some of the heaviest debris and other solids remaining in contact with the filter module and the second wall. The problem with this solution is that even if the filter unit is not clogged, a substantial proportion of the molten metal will flow through the bypass passage and not through the filter unit, reducing the effectiveness of the filter system described in KR101853768.

[0007] Therefore, there is a need for an improved filtering system that overcomes limitations in the art. Summary of the Invention

[0008]

[0010] An embodiment of the present invention is directed to a filtering system for efficiently removing most debris and other solids, regardless of the density of the debris and other solids present in the molten metal flowing through the tundish from the inlet section to the outlet section, while at the same time ensuring a high level of safety without the risk of molten metal spilling over the edge of the tundish due to a malfunction of the filtering system. These and other advantages of the present invention are described in more detail in the following sections.

[0009] Embodiments of the present invention provide a tundish for continuous metal casting. In various embodiments, the tundish (10) defines a cavity having a cavity height (h10) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X), and a cavity width measured along a horizontal axis (Y), where X⊥Y⊥Z. The cavity comprises an inlet portion (10i) configured to receive a flow of molten metal (20m) discharged by gravity from the exterior of the tundish into the cavity of the tundish, an outlet portion (10o) having an outlet (11o) configured to discharge the molten metal from the cavity into a mold, and a filtering system separating the inlet portion (10i) from the outlet portion (10o) across the cavity width. The filtering system comprises a filter module (1) extending across the entire cavity width and extending inside said cavity, the filter module including an inlet side facing the inlet portion (10i) of the tundish and extending from the floor (10f) of the cavity to an upper surface whose shortest distance from the floor measured along the vertical axis (Z) is equal to the minimum filter module height (h1), the filter module (1) including a filter unit (1f) extending along the vertical axis (Z) over a filter height (hf) and comprising a channel (1c), the channel (1c) extending from a channel inlet opening at the inlet side facing the inlet portion (10i) of the tundish to a channel outlet opening at the 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) extending across the entire cavity width and having a wall extending inside said cavity and defining one or more openings (2o) distributed across the width of the wall and across an opening height (h2) measured along a vertical axis (Z) from the floor (10f).The filter module (1) is arranged closer to the discharge port (11o) than the wall module (2), and the bypass passage (2b) is defined between the wall module (2) and the filter module (1) with a maximum width (t12) measured along the longitudinal axis (X). Thereby, the molten metal can flow only from the inlet portion through one or more openings to the inlet side of the filter module (1) and from the one or more openings to the discharge port portion, either through the channels of the filter unit (1f) or through the bypass passage (2b). The wall ledge (2L) protrudes from the wall of the wall module (2) at a wall ledge distance (d2L) of not more than the minimum filter module height (h1) from the floor (10f) (i.e., d2L≤h1) and extends towards the inlet side of the filter module (1) without contacting the filter module (1). The wall ledge (2L) has a width (t2L) measured along the longitudinal axis (X), and 20 mm < t2L < t12. Further, the filter ledge (1L) protrudes from the inlet side of the filter ledge (1) at a filter ledge distance (d1L) greater than the opening height (h2) from the floor (10f) (i.e., d1L>h2), is offset with respect to the wall ledge (2L) (i.e., d1L≠d2L), and the filter ledge extends towards the wall module (2) without contacting either the wall module or the wall ledge. The filter ledge (1L) has a width (t1L) measured along the longitudinal axis (X), and 20 mm < t1L < t12.

[0010] In various embodiments, the ratio (h2 / h1) of the opening height (h2) to the filter module height (h1) is from 20% to 95% (0.2≤h2 / h1≤0.95), preferably from 40% to 80%.

[0011] In various embodiments, the ratio ((t1L + t2L) / t12) of the sum of the widths (t1L, t2L) of the filter ledge and the wall ledge to the maximum width (t12) of the bypass passage is from 20% to 150% (i.e., 0.2≤(t1L + t2L) / t12≤1.5), preferably from 30% to 120%, more preferably from 50% to 100%.

[0012] In various embodiments, the wall module includes a single opening that extends from a lower boundary separated from the floor to the lower edge of the wall by a distance of 0 to 5% of the cavity height (h10), and defines the opening height (h2) as the distance separating the floor from the farthest point of the lower edge. Alternatively, in a second embodiment, the wall module comprises a plurality of openings, and the upper opening is defined as an opening that is farthest from the floor and has a boundary separated from the floor by the opening height (h2) from the floor.

[0013] In various embodiments, the opening height (h2) can be related to the cavity height (h10) by a ratio (h2 / h10) of the opening height (h2) to the cavity height (h10) that is 10% to 60% (0.1 ≦ h2 / h10 ≦ 0.6), preferably 40 to 60%.

[0014] In various embodiments, the meandering of the bypass passage can be very simply characterized by defining a straight line that extends between the floor of the inlet portion and the outlet portion passing through the bypass passage, and does not exist because it cannot reach the floor without contacting the refractory element or pass through the bypass passage, or forms an angle (θ) with the vertical axis (Z) that is 70° or less, preferably 60° or less, more preferably 45° or less.

[0015] In various embodiments, the filter ledge (1L) is "above" the wall ledge (2L). In other words, the filter ledge distance (d1L) can be made greater than the wall ledge distance (d2L) (i.e., d1L > d2L). Alternatively, the filter ledge (1L) can be below the wall ledge (2L). In other words, the filter ledge distance (d1L) can be made lower than the wall ledge distance (d2L) (i.e., d1L < d2L). However, the filter ledge does not form the same plane as the ledge of the wall, i.e., the filter ledge distance (d1L) is not equal to the wall ledge distance (d2L) (i.e., d1L ≠ d2L).

[0016] In various embodiments, the wall module (2) may comprise two or more wall ledges (2L) that are parallel to one another, do not contact one another, and are distributed over the height of the wall module (2). Similarly, the filter module (1) may include two or more filter ledges (1L) that are parallel to one another, do not contact one another, and are distributed over the height of the filter module (1). One or more wall ledges and / or filter ledges combine to define additional baffles in the bypass passage.

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

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

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

[0020] In at least one embodiment, the filter ledge (1L) protrudes from a portion of the width of the inlet side of the filter module (1), and in some embodiments, the filter ledge (1L) protrudes from the entire width of the inlet side of the filter module (1). [Brief description of the drawings]

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

[0022] [Figure 1] FIG. 1 illustrates a cutaway side view of a metallurgical facility including a tundish in accordance with at least one embodiment of the subject matter of this disclosure. [Diagram 2] 1 shows a top surface perspective view of a cavity of a tundish according to the present invention. [Diagram 3] Figures 3(a) to 3(d) show various embodiments of wall sections according to the invention. [Figure 4] 4(a)-4(f) show cutaway side views of various embodiments of filtering systems according to the present invention. [Diagram 5] 5(a) and 5(b) show side cutaway views illustrating various dimensions of a filtering system according to the present invention. [Figure 6] Figures 6(a) and 6(b) show side perspective views showing how the cavity height (h10) is measured. [Figure 7] 7(a) and 7(b) show top surface perspective views of two alternative embodiments of a tundish with two or more tundish discharge ports. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In a continuous metal forming process, molten metal is transferred from one metallurgical vessel to another, mold, or die. For example, as shown in FIG. 1, a ladle (5L) is filled with molten metal from a furnace (not shown) and driven over a tundish (10) to discharge the molten metal from the ladle, typically through a ladle shroud (5s) and into the tundish. The molten metal can then be cast through an injection nozzle (15) from the tundish outlet (11o) into a mold or die (25) to continuously form slabs, billets, beams, thin slabs, and the like. The flow of molten metal from the ladle to the tundish and from the tundish to the mold or die is driven by gravity. The flow rate can be controlled by slide gates in fluid communication with the ladle and tundish outlets. A ladle slide gate (5g) can be used to control the flow rate from the ladle and, in some cases, to interrupt the flow at a sealed location. Similarly, a tundish slide gate (not shown) can be used to control the flow rate from the tundish and interrupt the flow at the sealing location. Often the flow rate from the tundish is controlled by a stopper (7) instead of a slide gate.

[0024] Since the casting of metal into the mold or die is carried out continuously, the tundish acts as a buffer and the level of molten metal in the tundish (h20) must be substantially constant throughout the entire casting operation. However, the level of molten metal in the tundish (h20) falls while the old ladle is being emptied and then replaced by a new ladle filled with molten metal. The outflow from the tundish is kept substantially constant by (1) reducing the time for ladle replacement and (2) controlling the hole of the tundish outlet (11o) by a stopper (7) or a slide gate.

[0025] There is concern about the presence of defects such as inclusions and impurities in cast metal parts. One cause of such defects is the presence of foreign bodies in the molten metal (20m) exiting the tundish. Slag (20s) can also contribute to these defects. The defects arise primarily from debris and impurities that were present in the ladle or caused by wear of the refractory material in the pouring area of ​​the tundish due to collisions and friction between the molten metal and the refractory material. It is important to prevent such debris and impurities from reaching the tundish discharge in order to reduce the number of defects in cast metal parts.

[0026] According to various embodiments of the subject matter of the present disclosure, as shown in FIG. 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 (h10) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X), and a cavity width measured along a horizontal axis (Y), where X⊥Y⊥Z. The cavity includes an inlet portion (10i) configured to receive a flow of molten metal (20m) discharged by gravity from outside the tundish into the cavity of the tundish. The tundish (10) includes a discharge portion (10o) including a tundish discharge port (11o) configured to discharge the molten metal from the cavity into a mold or die (25). The cavity separates an inlet portion (10i) from an outlet portion (10o) across the width of the tundish and comprises a filtering system comprising a filter module (1) extending across the entire cavity width and extending along a vertical axis (Z) from the floor (10f) of the cavity to an upper surface across a minimum filter module height (h1), the filter module having an inlet side facing the inlet portion (10i) of the tundish. The filter module (1) comprises a filter unit (1f) extending along a vertical axis (Z) over a filter height (hf) and comprising a channel (1c) extending from a channel inlet opening at the inlet side to a channel outlet opening at the 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) extending over the entire cavity width and comprising walls extending along the vertical axis (Z) and defining one or more openings (2o) distributed over the width of the wall and distributed over an opening height (h2) measured from the floor (10f) along the vertical axis (Z).

[0027] The filter module (1) is positioned closer to the discharge port (11o) than the wall module (2), and a bypass passage (2b) is defined between the wall module (2) and the filter module (1) of a maximum width (t12) measured along the longitudinal axis (X), whereby the molten metal can only flow from the inlet portion through the one or more openings (2o) to the inlet side of the filter module (1) and from the one or more openings (2o) to the discharge portion by either passing through the channels of the filter unit (1f) or by flowing through the bypass passage (2b).

[0028] Cavity: The cavity has a cavity height (h10) measured along the vertical axis (Z), a cavity length measured along the longitudinal axis (X), and a cavity width measured along the horizontal axis (Y), where X⊥Y⊥Z. The cavity is defined by a floor (10f) surrounded by a perimeter wall. As shown in Figures 6(a) and 6(b), the cavity height (h10) corresponds to the level of the liquid filling the cavity measured from the cavity floor (10f), beyond which the liquid will flow out of the cavity over the edge of the cavity (in the absence of a lid closing the cavity). That is, the cavity height (h10) is the minimum height of the perimeter wall measured from the floor to the top of the perimeter wall. If the tundish is provided with a spout (10s), the cavity height (h10) is the distance separating the floor (10f) from the bottom of the spout (Figure 6(b)).

[0029] The tundish is fed into the molten metal by pouring the molten metal from the ladle (5L) into the receiving portion of the tundish cavity by gravity. To protect the overflow stream from atmospheric contamination, the ladle is often provided with a ladle shroud (5s). To prevent the overflow stream from penetrating the cavity floor when it hits the floor, an impact pad (9) (or impact box) is often placed in the impact area where the overflow stream hits the floor. One tundish is usually served by one ladle (5L) at a time. Although the present disclosure may be applied to a multi-ladle feeding system.

[0030] As illustrated in FIGS. 7(a) and 7(b), the cavity may include two or more tundish discharge ports (11o) used by the ladle (5L). In any case, there is always at least one metal supply region associated with one or more tundish discharge ports (11o), and each metal supply region defines a metal flow path extending between a receiving portion (shown in the figure as the position of the box or shock pad (9)) and the tundish discharge port (11o). According to the present invention, it is sufficient that all flow paths must be blocked by at least one filtering system as more specifically defined below. In the case of multiple tundish discharge ports (11o), multiple filtering systems may be required to meet this requirement.

[0031] As shown in FIGS. 1, 4(a) - 4(f), and 5(a) and 5(b), in the stationary mode, i.e., when the ladle is currently discharging fresh molten metal into the tundish, the cavity is filled with molten metal (20m) at a substantially constant liquid level (h20). The tundish is not fed with fresh molten metal only during the period when the empty ladle (5L) is replaced with a new ladle, and since casting is carried out continuously, the liquid level (h20) of the molten metal in the tundish decreases over time. The constant flow rate from the tundish discharge port is controlled as a function of the pressure reduction by the stopper (7) or slide gate (not shown) of the tundish discharge port (11o).

[0032] So that the molten metal does not overflow over the edge or flow out of the tundish through the discharge port (10s), the liquid level (h20) of the molten metal (20m) cannot exceed the cavity height (h10) (i.e., h20 < h10). The liquid level (h20) of the molten metal in the stationary mode can be 75% - 90% of the cavity height (h10). The higher the liquid level, the excessively increased risk of overflow, and the lower the liquid level, the increased cost of an oversized tundish.

[0033] Filtering system: The filtering system separates the cavity into an inlet section (10i) and an outlet section (10o). The inlet section (10i) contains the area where fresh metal is poured from the ladle (5L) into the tundish cavity. The outlet section (10o) comprises the tundish outlet (11o). Molten metal is poured into the inlet section and must flow through the filtering system from the tundish outlet (11o) into the mould or die (25). The filtering system comprises a wall module (2) and a filter module (1) comprising a filter unit (1f) with a channel (1c) extending from a channel inlet opening at the inlet side of the filter module (1) facing the inlet section (10i) to a channel outlet opening at the outlet side facing the outlet section (10o).

[0034] The molten metal (20m) has only two options: to flow through the filtering unit, through the channel (1c) of the filtering unit (1f) or through the bypass passage (2b) defined between the filter module (1) and the wall module (2).

[0035] Various embodiments of the subject matter of the present disclosure are directed to a design of the filtering system such that in a stationary mode, more than 50% of the molten metal flowing through the filtering system flows through the channels of the filter unit (1f). As with other filtering systems, the filter unit (1f) used in the tundish (10) becomes clogged with debris and solids that are retained upstream of the filter unit. One way to measure the degree of clogging of the filter unit is to monitor the progression of the pressure drop (ΔP=(Pu-Pd)) over time upstream (Pu) of the filter unit relative to downstream (Pd). The pressure drop increases relative to the nominal pressure drop (ΔP0) as the degree of clogging increases. In the present invention, it is preferred that more than 50%, preferably more than 60%, and more preferably more than 75% of the molten metal flows through the filter unit (1f) for a pressure drop of up to twice the nominal pressure drop (i.e., ΔP / ΔP0≦2). Conversely, it is preferred that less than 50%, preferably less than 40%, and more preferably less than 25% flows through the bypass passage (2b).

[0036] The filtering system of the present disclosure allows for the retention of a substantial amount of debris and other solids present in the molten metal prior to discharging the molten metal into the mold or die (25). At the same time, if excessive clogging of the filter unit (1f) results in a high pressure drop across the filter unit, the molten metal can flow into the outlet section (10o) via the bypass passage (2b). In this manner, the molten metal does not stop at the inlet section (10i) and can raise the molten metal level dangerously close to or above the cavity height (h10) in the inlet section, with disastrous consequences such as molten metal overflowing the tundish.

[0037] In contrast to the system described in KR101853768 discussed above, 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 discharge (11o). The design of the filtering system of the present disclosure will be described in detail subsequently.

[0038] Wall module (2): The wall module (2) is one of the two essential components of the filtering system of the invention and divides the cavity into an inlet portion (10i) and an outlet portion (10o). The wall module (2) is adjacent to the inlet portion (10i) and is separated from the tundish outlet by the filter module (1). The wall module (2) comprises a wall extending across the entire cavity width and extending along a vertical axis (Z) to an upper edge. The wall module (2) defines one or more openings (2o) distributed across the width of the wall and across an opening height (h2) measured along the vertical axis (Z) from the floor (10f). The upper edge of the wall is located above the static level (h20) of the molten metal. The upper edge is generally located at a distance from the floor (10f) that is between 90% and 100% of the cavity height (h10), preferably between 95% and 100% of h10. If the tundish is provided with a spout (10s), the upper edge can extend higher than h10 and is preferably flush with the free edge of the tundish excluding the spout, this is especially true if the spout (10s) is located in the spout portion (10o).

[0039] As shown in Figures 3(a)-3(d), the one or more openings (2o) can have various shapes. In the embodiment shown in Figures 3(a) and 3(b), a single opening (2o) extends from the floor (10f) to the lower edge of the wall, and the single opening (2o) may be linear and parallel to the floor (see Figure 3(a)) or curved (see Figure 3(b)). The opening height (h2) is the distance from the floor to the furthest point of the lower edge. In a variation of this embodiment, the opening extends from the lower boundary separated from the floor (10f) by a distance of up to 5% of the cavity height (h10) (forming a step) to the lower edge of the wall. The opening height (h2) is defined as the distance separating the floor from the furthest point of the lower edge (i.e. ignoring the presence of a step). The presence of a step across the entire width of the cavity would prevent the tundish from emptying out the entire molten metal remaining therein, filling the inlet portion (10i) up to the level of the step. The step can be provided with drainage channels to avoid this problem. In an alternative embodiment shown in FIG. 3(c), the wall can include two or more openings (2o). The top opening is defined as the opening with the boundary furthest from the floor (10f). The opening height (h2) is defined as the distance separating said boundary from the floor. FIG. 3(c) shows identical round openings. It is clear that the multiple openings can have any shape and size as desired.

[0040] For the molten metal to flow from the inlet portion to the outlet portion, it must pass through one or more openings in the wall. There is no other option unless the liquid level of the molten metal in the inlet portion increases beyond the upper edge of the wall. The ratio (h2 / h10) of the opening height (h2) to the cavity height (h10) is preferably 10% to 60% (i.e., 0.1 ≤ h2 / h10 ≤ 0.6), preferably 15% to 50%, more preferably 20 to 40%. The opening height (h2) is important as it forces the molten metal to flow downward in the flow path of the molten metal after it hits the impact pad (9) and bounces upward towards the surface of the molten metal, as shown in Figure 1 (dashed line). The presence of a step protruding from the floor can help hold the heaviest solids, but its presence is not essential.

[0041] The wall module (2) also includes a wall ledge (2L) that protrudes from the entire width of the wall at the wall ledge distance (d2L) from the floor (10f) and extends towards the inlet side of the filter module (1) without contacting the filter module (1). The wall ledge (2L) has a width (t2L) measured along the longitudinal axis (X). In the case of a wall with a single opening having a straight upper edge, the wall ledge can be at the same height as the upper edge, such that the wall ledge distance (d2L) is equal to the opening height (h2), as shown, for example, in Figures 1, 3(a), 4(a), 4(b), 4(e), and 5(a) (i.e., h2L = h2). Alternatively, the wall ledge (2L) can be present at any distance (d2L) from the floor such that h2 < d2L < 80% of h10, preferably with d2L less than 70% of h10. This embodiment of the wall ledge that does not form the same plane as the lower edge of the upper opening is shown in Figures 3(d), 4(c), 4(d), 4(f), and 5(b). In some embodiments, the wall ledge (2L) protrudes from a part of the width of the wall, and in some embodiments, the wall ledge (2L) protrudes from the entire width of the wall.

[0042] The wall module (2) may include two or more wall ledges (2L) distributed over the height of the wall module (2), as shown in FIG. 4(e). In various embodiments, the two or more wall ledges are straight and extend parallel to each other and to the floor (10f). If the two or more wall ledges (2L) are not parallel to each other, they preferably do not touch each other. The wall ledge distance (d2L) is the distance to the floor of the wall ledge closest to the floor (10f). In various embodiments, the walls and wall ledges (2L) are made of a fire-resistant material, preferably the same fire-resistant material that lines the peripheral walls and floor of the cavity.

[0043] Filter module: The filter module (1) extends across the entire cavity width and extends along the vertical axis (Z) from the cavity floor (10f) over a minimum filter module height (h1) to a top surface. The filter module is located adjacent to the outlet portion (10o) and includes an inlet side facing the inlet portion (10i) of the tundish. The filter module (1) comprises a filter unit (1f) with a channel (1c) that extends from a channel inlet opening at the inlet side to a channel outlet opening at the 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 (1f) extends vertically, preferably below the top surface, whereby the top surface is not part of the filter unit (1f). The filter unit (1f) may extend across any portion of the tundish width as desired. The larger the area in the plane (Y,Z), the higher the volumetric throughput through the filter unit for a given transmittance.

[0044] In at least one embodiment, the filter ledge (1L) protrudes from the entire width of the inlet side of the filter module (1) at a filter ledge distance (d1L) from the floor (10f) that is greater than the opening height (h2) (i.e., d1L>h2). The filter ledge (1L) is offset relative to the wall ledge (2L) (i.e., d1L≠d2L) and does not face the wall ledge at the same liquid level. The filter ledge (1L) extends toward the wall module (2) without contacting either the wall module or the wall ledge, and the filter ledge (1L) has a width (t1L) measured along the longitudinal axis (X). In some embodiments, the filter ledge (1L) protrudes from a portion of the width of the inlet side of the filter module (1), and in some embodiments, the filter ledge (1L) protrudes from the entire width of the inlet side of the filter module (1).

[0045] The filter module (1) may comprise a number of filter ledges (1L) distributed over the height of the filter module (1), as shown in FIG. 4(f). In at least one embodiment, the two or more filter ledges are linear and extend parallel to each other and parallel to the floor (10f). If the two or more filter ledges (1L) are not parallel to each other, they preferably do not contact each other and do not contact the wall ledges (2L). The filter ledge distance (d1L) is the distance to the floor of the filter ledge closest to the floor (10f).

[0046] In one embodiment, the filter ledge distance (d1L) to the floor is greater than the wall ledge distance (d2L) (i.e., d1L>d2L). This embodiment is shown in Figures 1, 4(a)-4(c), 4(e), 5(a) and 5(b). In an alternative embodiment, the filter ledge distance (d1L) to the floor is less than the wall ledge distance (d2L) (i.e., d1L>d2L), as shown in Figures 4(d) and 4(f). <d2L)。

[0047] The filter unit (1f) can be any type of filter unit known in the art of continuous metal casting. The function of the filter unit (1f) is to retain (=retain) all debris and solids upstream of the filter unit while allowing the molten metal to flow (=filter) through the filter unit via the channel (1c) and from there to the tundish outlet (11o). The channel can be straight or serpentine, the dimensions of the channel (cross section and length) contributing to define the permeability of the filter unit. The permeability of the filter unit depends on the requirements of the particular application and the skilled person knows how to optimize the properties of the filter unit (1f) accordingly.

[0048] The lower boundary of the filter unit (1f) can be separated from the floor (10f) of the cavity by a distance (hd) that is 0 to 10 cm (i.e., 0≦hd≦10 cm), preferably 2 to 5 cm. Similarly, the upper boundary of the filter unit (1f) can be separated from the floor (10f) by a distance (hf+hd), whereby the ratio ((hf+hd) / h2) of said distance ((hf+hd)) to the opening height (h2) is 0.7 to 1.2 (i.e., 70%≦(hf+hd) / h2≦120%), preferably 80% to 100%.

[0049] Bypass passage: the bypass passage (2b) defined in the filtering system is the subject of the present invention. The bypass passage (2b) must allow the casting to continue without problems even if the filter unit (1f) is clogged, and at the same time cannot provide an easier flow path than through the filter unit (1f), so that in a quiescent state, at least 50% of the metal flows through the filter unit to reach the outlet part (10o) of the tundish. For this purpose, the bypass passage of the present disclosure is designed to impose a first and a second reversal of the direction of the velocity vector along the longitudinal axis (X) on the metal melt flow. This is achieved by a combination of the wall ledge (2L) and the filter ledge (1L) that impose a baffle on the passage defined between the wall and the filter module (1).

[0050] As explained above with respect to Figures 1, 4(a)-4(c), 4(e), 5(a) and 5(b), the wall ledge (2L) may be lower (i.e., closer to the floor (10f)) than the filter ledge (1L). In this way, the portion of the molten metal above the opening height (h2) from the floor (10f) is blocked by the wall and deflected downward (i.e., toward the opening (2o)) and can redirect toward the filter module (1) as it approaches the floor (10f). The molten metal can only flow upwards behind the wall until it reaches the lower surface of the wall ledge (2L). If the wall ledge (2L) were the same height as the opening (i.e., d2L=h2), the molten metal would not be able to flow upwards behind the wall at all. Similarly, the portion of the molten metal below the opening height (h2) from the floor (10f) cannot flow upwards just behind the wall and is forced to flow towards the filter module (1). When the molten metal hits the lower surface of the wall ledge (2L), the flow is deflected towards the filter module (1). The filter portion flows straight (parallel to the longitudinal axis (X)) or downwards towards the filter unit (1f). The bypass portion flows upwards towards the inlet side of the filter module (1) until it hits the lower surface of the filter ledge (1L). This deflects the flow by reversing the component of the velocity vector parallel to the longitudinal axis (X) (=X component), so that the X component of the flow returns towards the inlet section (10i). The flow hits the wall and the X component of the velocity vector is reversed again, so that the flow returns towards the inlet section (10i). As shown in Figure 4(c), the wall module (2) may include a second wall ledge above the wall ledge (2L) that forces the velocity vector to be more nearly parallel to the longitudinal axis (X). The filter unit may include additional filter ledges that act as additional baffles that, in combination with the corresponding additional wall ledges, change the X-component of the velocity vector.

[0051] As explained above with respect to Figures 4(d) and 4(f), the filter ledge (1L) may alternatively be lower (i.e. closer to the floor (10f)) than the wall ledge (2L). In this way, when it encounters resistance to flow through the filter unit (1f), a portion of the molten metal is deflected upwards and hits the lower surface of the filter ledge (1L). This deflects the flow by reversing the X component of the velocity vector, thereby causing the X component of the flow to return to the direction of the inlet section (10i). The flow then hits the wall and is deflected upwards again until it hits the lower surface of the wall ledge (2L), which forces the flow to change the direction of the X component of the velocity vector back to the direction of the outlet section (10o). Thus, the molten metal can continue to flow over the filter module (1) towards the outlet section (10o) and up to the tundish outlet (11o). The filter unit may comprise additional filter ledges which in combination with corresponding additional wall ledges act as additional baffles to change the X-component of the velocity vector.

[0052] A person skilled in the art can adapt the necessary portion of the molten metal forced through a given filter unit (1f) by changing the dimensions of the bypass passage (2b) to make this portion somewhat tortuous and therefore somewhat easier to follow compared to the passage through the filter unit. Relevant dimensions are, for example, maximum width (t12) (t12>0), filter ledge width (t1L), wall ledge width (t2L), filter ledge distance (d1L), wall ledge distance (d2L), distance measured along the vertical axis (Z) separating the wall ledge and the filter ledge (|d1L-d2L|), etc.

[0053] According to at least one embodiment, the ratio ((t1L+t2L) / t12) of the sum of the widths (t1L, t2L) of the filter ledge and the wall ledge (1L, 2L) to the maximum width (t12) of the bypass passage (2b) is 20% to 150% (i.e., 0.2≦(t1L+t2L) / t12≦1.5), preferably 30% to 120%, and more preferably 50% to 100%.

[0054] The fraction flowing through the filter unit also depends on the opening height (h2) and the minimum filter module height (h1). According to at least one embodiment, the ratio (h2 / h1) of the opening height (h2) to the filter module height (h1) is between 20% and 95% (i.e., 0.2≦h2 / h1≦0.95), preferably between 40% and 80%.

[0055] A simple way to characterize the tortuosity of the bypass passage is to draw a straight line extending from the floor (10f) of the inlet section through the bypass passage (2b) to the outlet section. According to at least one embodiment, such a line does not exist as it does not reach the floor as shown in Figures 4(b) and 4(d), or it forms an angle (θ) with the vertical axis (Z) of 70° or less, preferably 60° or less, more preferably 45° or less, and most preferably 35° or less. This is shown in Figures 4(a) and 4(c).

[0056] The above condition prevents the molten metal from following a straight flow path from the floor, which it would bounce back through as it is discharged from the ladle (5L) through the bypass passage (2b). If such a flow path were available, a substantial portion of the molten metal would be diverted from the filter unit (1f) and flow instead through the bypass passage, which is clearly insufficient.

[0057] For example, for a tundish with a cavity height (h10) of 800-1800 mm, preferably 1000-1300 mm, the opening height (h2) can be 80-600 mm, preferably 100-500 mm. The maximum width (t12) separating the wall from the filter module in the bypass passage (2b) can be 60-800 mm, preferably 80-600 mm. The filter ledge distance to the floor (d1L) can be 80-650 mm, preferably 100-620 mm, and the wall ledge distance to the floor (d2L) can be 80-600 mm.

[0058] In various embodiments, the wall ledge width (t2L) and the filter ledge width (t1L) can be between 20 and 200 mm, and in some embodiments, the wall ledge width (t2L) and the filter ledge width (t1L) can be between 50 and 150 mm. In at least one embodiment, the wall ledge width (t2L) and the filter ledge width (t1L) each have a minimum value of 20 mm. In at least one embodiment, the wall ledge width (t2L) and the filter ledge width (t1L) each have a maximum value of 200 mm. However, in some embodiments, the wall ledge width (t2L) and the filter ledge width (t1L) may be adjusted or customized based on the size and dimensions of the tundish (10). Nevertheless, in various embodiments, the wall ledge width (t2L) and the filter ledge width (t1L) each have a non-zero value, in other words, various embodiments of the presently disclosed subject matter include the presence of a wall ledge and a filter ledge regardless of their respective widths.

[0059] The tundish of the present disclosure has the advantage that most debris and other solids are removed from the molten metal (20m) before it is cast into the mold (25). When the filter unit (1f) is new, or its channels are clean and free of solid debris, the filter unit is characterized by a pressure drop (ΔP) equal to the nominal pressure drop (ΔP0) between the inlet and outlet sides of the filter unit. In use, debris and other solids retained by the channels build up, causing partial and eventually complete blockage of some or all of the channels. The pressure drop (ΔP) increases, making it more difficult for the molten metal to flow through the filter unit (1f). As the pressure drop (ΔP) increases, it becomes easier for the molten metal to flow through the bypass passage (2b) than through the filter unit.

[0060] For example, when the filter unit (1f) is fully operable (e.g., ΔP / ΔP0<2), more than 50%, preferably more than 60%, more preferably more than 75%, and most preferably more than 85% of the molten metal flows through the filter unit (1f). The molten metal flowing through the filtering system from the inlet section (10i) to the outlet section (10o) flows through the filter unit (1f) and the rest flows through the bypass passage (2b). However, when the filter unit is substantially clogged (i.e., the pressure drop reaches a high value, e.g., ΔP / ΔP0>10), the molten metal has difficulty flowing through the filter unit (1f) and finds it easier to flow through the bypass passage (2b). This reduces the risk that the molten metal level (h20) will rise to a dangerous level at the inlet section close to the cavity height (h10).

[0061] In addition to being efficient and easily modulatable to meet the requirements of a particular application, this solution is also very simple to implement, requiring only two modules, each of simple design: the wall module (2) and the filter module (1). This solution is therefore very economical and ensures the continuity of the metal casting session.

[0062] A tundish (10) for continuous metal casting defining a cavity, the cavity having a cavity height (h10) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X), and a cavity width measured along a horizontal axis (Y), where X⊥Y⊥Z, the cavity comprising an inlet portion (10i) configured to receive a flow of molten metal (20m) discharged by gravity from outside the tundish into the cavity of the tundish, an outlet portion (10o) having an outlet (11o) configured to discharge the molten metal from the cavity into a mold, and a filtering system separating the inlet portion (10i) from the outlet portion (10o) across the width of the cavity. The filtering system comprises a filter module (1) extending across the entire cavity width and extending inside said cavity, the filter module including an inlet side facing the inlet portion (10i) of the tundish and extending from the floor (10f) of the cavity to an upper surface whose shortest distance from the floor measured along the vertical axis (Z) is equal to the minimum filter module height (h1), the filter module (1) including a filter unit (1f) extending along the vertical axis (Z) over a filter height (hf) and comprising a channel (1c), the channel (1c) extending from a channel inlet opening at the inlet side facing the inlet portion (10i) of the tundish to a channel outlet opening at the 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) having a wall extending across the entire cavity width and extending into said cavity and defining one or more openings (2o) distributed across the width of the wall and across an opening height (h2) measured along a vertical axis (Z) from the floor (10f).The filter module (1) is arranged closer to the discharge port (11o) than the wall module (2), and a bypass passage (2b) is defined between the wall module (2) and the filter module (1) of a maximum width (t12) measured along the longitudinal axis (X), whereby the molten metal 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 discharge portion by passing through the channels of the filter unit (1f) or through the bypass passage (2b). a. The ratio (h2 / h1) of the opening height (h2) to the filter module height (h1) is 20% to 95% (0.2≦h2 / h1≦0.95), preferably 40% to 80%; b. The wall ledge (2L) protrudes from the entire width of the wall at a wall ledge distance (d2L) from the floor (10f) equal to or less than the minimum filter module height (h1) (i.e., d2L≦h1) and extends toward 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) and having a length of 0. <t2L<t12であり、 c. The filter ledge (1L) protrudes from the floor (10f) across the entire width of the inlet side of the filter module (1) at a filter ledge distance (d1L) greater than the opening height (h2) (i.e., d1L>h2) and is offset relative to the wall ledge (2L) (i.e., d1L≠d2L) and extends toward the wall module (2) without contacting either the wall module or the wall ledge, the filter ledge (1L) having a width (t1L) measured along the longitudinal axis (X) and a length (t1L) of 0. <t1L<t12であり、 d. The ratio ((t1L+t2L) / t12) of the sum of the widths (t1L, t2L) of the filter ledge and wall ledge (1L, 2L) to the maximum width (t12) of the bypass passage (2b) is 20% to 150% (i.e., 0.2≦(t1L+t2L) / t12≦1.5), preferably 30% to 120%, and more preferably 50% to 100%.

[0063] The foregoing description has been given for clarity of understanding only, and no unnecessary limitations should be understood therefrom, since modifications within the scope of the invention may be apparent to those skilled in the art. [Table 1]

Claims

1. A tundish (10) for continuous metal casting defining a cavity, said cavity having a cavity height (h10) measured along a vertical axis (Z), a cavity length measured along a longitudinal axis (X), and a cavity width measured along a horizontal axis (Y), where X⊥Y⊥Z; The cavity is an inlet portion (10i) configured to receive a flow of molten metal (20m) discharged by gravity from outside the tundish into the cavity of the tundish; a discharge port portion (10o) having a discharge port (11o) configured to discharge the molten metal from the cavity into a mold; a filtering system separating the inlet portion (10i) from the outlet portion (10o) across the entire cavity width, The filtering system a filter module (1) extending over the entire cavity width and extending inside the cavity, said filter module having an inlet side facing the inlet portion (10i) of the tundish and extending from the floor (10f) 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 (h1), said filter module (1) comprising a filter unit (1f) extending along the vertical axis (Z) over a filter height (hf) and comprising a channel (1c); The channel (1c) a filter module (1) extending from a channel inlet opening at an inlet side facing the inlet portion (10i) of the tundish to a channel outlet opening at an outlet side of the filter module (1) facing the outlet portion and spaced a filter depth (tf) from the inlet side; a wall module (2) comprising a wall extending across the entire cavity width and extending into the cavity and defining one or more openings (2o) distributed across the width of the wall and across an opening height (h2) measured along the vertical axis (Z) from the floor (10f), the filter module (1) is arranged closer to the outlet (11o) than the wall module (2), and a maximum width (t12) of a bypass passage (2b) measured along the longitudinal axis (X) is defined between the wall module (2) and the filter module (1), whereby the molten metal 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 either passing through the channel of the filter unit (1f) or by flowing 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 (10f) not greater than the minimum filter module height (h1) (i.e., d2L≦h1) 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), 20 mm<t2L<t12; a filter ledge (1L) protrudes from the inlet side of the filter module (1) at a filter ledge distance (d1L) from the floor (10f) that is greater than the opening height (h2) (i.e., d1L>h2) and is offset with respect to the wall ledge (2L) (i.e., d1L≠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 (t1L) measured along the longitudinal axis (X), where 20 mm<t1L<t12; The tundish (10) is characterized in that the ratio ((t1L+t2L) / t12) of the sum of the widths (t1L, t2L) of the filter ledge and the wall ledge (1L, 2L) to the maximum width (t12) of the bypass passage (2b) is greater than 20% (i.e., 0.2≦(t1L+t2L) / t12).

2. The tundish according to claim 1, wherein the ratio (h2 / h1) of the opening height (h2) to the filter module height (h1) is 20% to 95% (0.2≦h2 / h1≦0.95), preferably 40% to 80%.

3. 2. The tundish according to claim 1, wherein a ratio ((t1L+t2L) / t12) of the sum of the widths (t1L, t2L) of the filter ledge and the wall ledge (1L, 2L) to a maximum width (t12) of the bypass passage (2b) is smaller than 150% (i.e., (t1L+t2L) / t12≦1.5), preferably between 30% and 120%, more preferably between 50% and 100%.

4. 2. The tundish according to claim 1, wherein the wall module (2) comprises a single opening (2o), the single opening (2o) extending from a lower boundary separated from the floor (10f) by a distance of 0% to 5% of the cavity height (h10) to a lower edge of the wall, the opening height (h2) being defined as the distance separating the floor from the furthest point of the lower edge.

5. 2. The tundish according to claim 1, wherein the wall module (2) comprises two or more openings (2o), an upper opening being defined as the opening furthest from the floor (2f) and having a boundary separated from the floor by the opening height (h2).

6. The tundish according to any one of claims 1 to 5, wherein the ratio (h2 / h10) of the opening height (h2) to the cavity height (h10) is 10% to 60% (0.1≦h2 / h10≦0.6), preferably 40 to 60%.

7. A straight line extending between the floor (10f) at the inlet portion and the outlet portion passing through the bypass passage (2b) is Does not exist, or The tundish according to any one of the preceding claims, which forms an angle (θ) with the vertical axis (Z) of less than or equal to 70°, preferably less than or equal to 60°, more preferably less than or equal to 45°.

8. The tundish according to any one of claims 1 to 5, wherein the filter ledge distance (d1L) is greater than the wall ledge distance (d2L) (i.e. d1L>d2L).

9. The tundish according to any one of claims 1 to 5, wherein the wall module (2) comprises two or more wall ledges (2L) parallel to each other, not in contact with each other and distributed over the height of the wall module (2).

10. The tundish according to any one of claims 1 to 5, wherein the filter module (1) comprises two or more filter ledges (1L) parallel to each other, not in contact with each other and distributed over the height of the filter module (1).

11. 6. The tundish according to claim 1, wherein the bypass passage (2b) reverses a flow direction component of the molten metal along the longitudinal axis (X) to flow from the inlet portion (10i) to the outlet portion (10o) of the cavity.

12. the lower boundary of the filter unit (1f) is separated from the floor (10f) of the cavity by a distance (hd) between 0 and 10 cm (i.e. 0≦hd≦10 cm), preferably between 2 and 5 cm; and / or 6. The tundish according to any one of claims 1 to 5, wherein an upper boundary of the filter unit (1f) is separated from the floor (10f) by a distance (hf+hd), whereby the ratio ((hf+hd) / h2) of the distance ((hf+hd)) to the opening height (h2) is between 0.7 and 1.2 (i.e. 70%≦(hf+hd) / h2≦120%), preferably between 80% and 100%.

13. The tundish according to any one of claims 1 to 5, wherein a wall ledge (2L) protrudes from a portion of the width of the wall or from the entire width of the wall.

14. The tundish according to any one of claims 1 to 5, wherein the filter ledge (1L) protrudes from a portion of the width of the inlet side of the filter module (1) or from the entire width of the inlet side of the filter module (1).

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