DEVICE FOR REMOVING MATTES FROM THE SURFACE OF A LIQUID METAL BATH WITHIN A DUCT OF A LINE FOR CONTINUOUSLY COATING A METAL STRIP.

Abstract

A device is described for removing mattes from the surface of a liquid metal bath (2) within a conduit (3) of a line for continuously coating a metal strip (1) having first and second faces, the first face being designed to contact an inner roller (11), comprising a compartment (50) through which the liquid metal within the conduit is replenished by being drawn out by a pump (17) to which the compartment is connected, characterized in that the compartment is capable of being removed by a disassembly means without the need to cut the metal strip.

Description

DEVICE FOR REMOVING MATTES FROM THE SURFACE OF A LIQUID METAL BATH WITHIN A DUCT OF A LINE FOR CONTINUOUSLY COATING A METAL STRIP FIELD OF INVENTION The invention relates to continuous hot-dip coating installations for a metal strip. It occurs in continuous sheet processing lines, particularly annealing and galvanizing lines. BACKGROUND OF THE INVENTION A dip coating line is schematically composed, from its entrance, of a heating section, a cooling section, a coating section in which the strip is immersed in a bath of molten metal contained in a container, for example, zinc or an alloy based on zinc, aluminum, silicon or magnesium, and a cooling tower that allows the metal to solidify on the strip and cool it to room temperature. Therefore, after undergoing heat treatment and cooling in an annealing furnace under a controlled reducing atmosphere—a mixture of nitrogen and hydrogen—the strip is protected against external attack by immersion in a molten metal bath in a continuous process. Upon exiting the bath, the coating adheres to the strip, which can then be exposed to air without risk of oxidation. For galvanizing, the bath temperature is approximately 460°C. The strip is practically at this temperature when immersed in the bath. The connection between the furnace and the coating bath is made via a conduit, a tunnel submerged within the molten metal vessel, thus ensuring a sealed connection between the furnace and the bath. The end of this conduit submerged in the bath is a consumable part due to corrosion from the molten metal. It is characterized by its thick sheet metal thickness to extend its service life and resist corrosion. This consumable part will be referred to as the "shoe" throughout the rest of this description. A roller submerged in the molten metal, called the bottom roller, allows the belt to be deflected so that it comes vertically out of the vessel and through the cooling tower. Many chutes are equipped with a pivoting movement that allows the use of lower rollers of different diameters. They are also equipped with a retraction movement that allows the shoe to be removed from the molten metal for maintenance operations. The conveyor belt passing through the vessel carries the molten metal with it, causing the level to drop. The level is maintained by an external supply of solid blocks inserted into the vessel. Surface mattification, which consists of metal oxides, particularly zinc oxides, intermetallic compounds, or complex agglomerates, creates a film of solid matter on the surface of the zinc tank. This mattification can terminate on the shoe; it then spreads lengthwise through the molten metal and becomes lodged between the lower roll and the belt. As the belt passes over the lower roll, the mattification perforates the belt and creates a backing on the other side. These surface defects make the belt unsuitable for applications requiring high surface quality, such as exposed automotive sheet metal. BRIEF DESCRIPTION OF THE INVENTION In order to solve the problem of surface mats that spread along the belt, several surface cleaning solutions have been invented within the shoe. For example, Japanese patent JP04120258 describes a shoe containing, at its lower end and within it, a reservoir around the circumference of the shoe, which is thus wrapped around the belt. Molten metal is drawn into the belt by a recirculation pump before being released into the reservoir. The recirculation of molten metal within the shoe allows the removal of the ore from the mine. The reservoir is formed by an extension of the outer walls of the shoe into the interior of the shoe. Figure 1 illustrates, schematically and from the side, a coating section according to the prior art. A belt 1 is immersed in the molten metal bath 2 within a conduit 3 comprising a shoe 4 at its lower end. The lower end of the shoe comprises two reservoirs 5a, 5b, each positioned on either side of the belt and connected at their ends. These reservoirs are formed by two extensions 4a, 4b of the outer walls of the shoe. A recirculation pump 6 draws molten metal from the reservoirs 5a, 5b through an orifice 7 and returns it to the vessel 8 via a pipe 9. Arrows 10 illustrate the flow of molten metal in the vicinity of and within the shoe. Inside the vessel, the belt is wrapped around a lower roller 11, which returns it to a vertical plane for exit from the bath.A device, not shown in this figure, allows the capture and removal of the clumps present in the container, outside the shoe, these being found mainly on the surface of the bath. A primary disadvantage of these state-of-the-art solutions is that the reservoir is integrated into the shoe, with the shoe and reservoir located in the same place. Therefore, it is imperative to cut the belt for cleaning the reservoir, resulting in significant line downtime. A second disadvantage of these solutions is that no adjustment is possible between the inner tank and the shoe to achieve a precise geometric fit of the tank relative to the bath surface in the shoe. This is particularly problematic when the shoe comprises two inner tanks, one on each side of the belt. In fact, when the duct's adjustment is modified by rotating it around its axis, this has the effect of raising one of the tanks and lowering the other. This creates a difference in the immersion depths of the two tanks in the bath. Therefore, leveling the system requires adjusting the entire duct, which is complicated by its weight and its rotating and folding mechanisms. According to a first aspect of the invention, a device is proposed for removing mattes from the surface of a liquid metal bath within a conduit of a line for continuously coating a metal strip having first and second faces, the first face being designed to contact a lower roller, comprising a compartment that forms a reservoir by means of which the liquid metal within the conduit is replenished by being extracted by a pump to which the compartment is connected, characterized in that the compartment is fixed to a support by a joining and adjusting means and is capable of being extracted by a disassembly means without the need to cut the metal strip. Advantageously, the compartment is placed, in relation to the metal band, on the first side. According to one possibility, the device comprises a second compartment positioned, with respect to the metal band, on the side of the second face. The position of the two compartments, in particular their horizontality, can be adjusted independently of each other. Preferably, the compartment is separable from the duct. According to one modality, the compartment can be held by two arms connected to the duct by a means of joining and adjusting. According to one variant, the compartment can be held by two arms connected to the container holding the liquid metal bath by a means of joining and adjusting. According to another possibility, the compartment can be held by two arms connected to a support structure external to the container holding the liquid metal bath by means of joining and adjusting. Advantageously, the device according to the first aspect of the invention may comprise means for adjusting the position of the compartment independent of means for adjusting the duct. According to one modality, each lateral end of the compartment is connected to a position indicator flush with the bath surface outside the duct when the position of the compartment, in particular its horizontality, is correctly adjusted. The device can also be equipped with a camera positioned in the duct, allowing visualization of a bath surface within it. The compartment may include at least one position indicator for a front face of the compartment relative to the metal strip protruding from the bath surface visible to the camera. This position indicator is connected to a position indicator flush with the bath surface outside the duct when the compartment's position, particularly its horizontal alignment, is correctly adjusted. According to a second aspect of the invention, a continuous coating line is proposed comprising a conduit and a container positioned to receive a liquid metal bath, and further comprising a device for removing mattes according to the first aspect of the invention, or one or more of its improvements. According to a third aspect of the invention, a dematting method is provided for removing mattes from the surface of a liquid metal bath within a conduit of a line for continuously coating a metal strip, comprising a compartment forming a reservoir through which the liquid metal present within the conduit is replenished by extraction by a pump to which it is connected, comprising a step for extracting said compartment that does not comprise a step for cutting the metal strip. BRIEF DESCRIPTION OF THE FIGURES The other features and advantages of the invention will become apparent from the following detailed description, for the understanding of which reference is made to the attached drawings, in which: Figure 1 is a schematic side cut view of a coating section according to the state of the art. Figure 2 is a schematic side view of a coating section according to one embodiment of the invention. Figure 3 is a schematic front-section view of a coating section according to the embodiment of the invention in Figure 2. Figure 4 is a schematic front-section view of a coating section according to a second embodiment of the invention. Since the embodiments described below are not limiting in nature, it is possible, in particular, to consider variants of the invention that comprise only a selection of the features described, provided that this selection of features is sufficient to confer a technical advantage and differentiate the invention from the prior art. This selection comprises at least one feature, preferably functional, without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage and differentiate the invention from the prior art. In the rest of the description, elements that have an identical structure or similar functions will be designated by the same references. DETAILED DESCRIPTION OF THE INVENTION Figure 2 illustrates, schematically and in side section, a coating section according to a first embodiment of the invention. In this example, an independent compartment 50 forms a separate reservoir from a shoe 40. It is partially positioned within the shoe. It is located on the portion of the belt face that contacts the lower roller 11. In fact, it is on this face that it is necessary to prevent the mats from being removed from the belt before wedging between the belt and the lower roller. A discharge pump, not shown in this figure, draws the molten metal into the compartment 50 and returns it to the vessel 8. The arrows 10 illustrate the flow of molten metal in the vicinity of the compartment. In a variant not shown, a second independent compartment is placed on the opposite side of the belt, to enhance the replenishment of the molten metal within the shoe. The two compartments are independent of each other and are supported separately so they can be removed without cutting the belt. Therefore, one compartment can be extracted while the second remains in place. They are also independently adjustable to allow for adjusting the position of one relative to the surface of the molten metal and the belt without affecting the other. Thus, for example, the distance between the compartment and the belt can be different on the two sides of the belt. Advantageously, the two compartments are connected by at least one hydraulic connection so that a single pump is sufficient to draw the molten metal from both compartments.This hydraulic connection comprises a flexible section that allows relative movement between the two compartments. It also comprises an easily disconnectable connection means to facilitate the removal of the independent compartments and their associated equipment. Figure 3 schematically illustrates the embodiment of the invention again according to Figure 2, but this time with a front cross-sectional view passing through the independent tank. To simplify this view, belt 1 is schematically represented by a band, and the lower roller is not shown. The independent compartment 50 extends over the width of the shoe 40 such that its length is at least equal to the width of the belt. It is mechanically connected to two lateral arms 13 positioned laterally on either side of the duct 3 and is secured to the duct 3, or to the shoe 40, by a fastening and adjustment means 14. The fastening and adjustment means 14 is a means for removing the independent compartment 50. The connecting and adjusting means 14 allow independent adjustment of the relative lateral, upper, and lower positions of each arm with respect to the conduit. They allow the compartment 50 to be level independently of the shoe's horizontality and regardless of the distance between the independent compartment and the belt. The connecting and adjusting means 14 allow adjustment of the immersion depth in the bath of compartment 50, with a fine adjustment that allows precise adjustment of this depth at each of the compartment's lateral ends. They also allow precise adjustment of a distance L between an upper edge 25 (Figure 2), also called the blade, on the front face of the compartment, which is located near belt 1, and the belt. Each of the lateral arms 13 includes a position indicator 15 (Figure 3).These position indicators 15 are placed on the side arms 13 at the height at which the arms must be immersed in the bath 2. They allow for the adjustment of the horizontality of the independent compartment 50, as they are flush with the surface of the bath. Therefore, using the joining and adjusting means 14, it is easy to adjust the position of the arms, and consequently that of the independent compartment 50, without needing to see it. As shown in Figure 2, the adjustment is made such that the upper edge 25 (the blade) of the front face of the independent compartment 50 is located at a height P of between 0 and 20 millimeters below the surface of the molten metal bath 2 in the conduit 3, when the conduit is in the operating position in the vessel 8. The rear face of the independent compartment is higher than the blade on the front face by a height h of at least 20 millimeters. The bottom of the independent compartment is deeper than the bottom of the shoe by a height H of at least 20 millimeters. The distance L between the upper edge 25 of the compartment 50 and the band is, for example, between 10 and 50 mm. The distance between the outer wall of the compartment and the band may vary depending on its height.Therefore, it has a distance L at the top edge of the compartment and a distance greater than L at the bottom of the compartment, thus forming a clearance angle that limits the risk of contact between the belt and the compartment. At least one pump 17 (Figure 3), whose suction is connected within compartment 50 by a pipe 18 and whose discharge opens to vessel 8 by a discharge pipe 19, allows the replenishment of the molten metal bath within compartment 50 and, consequently, the shoe 40. In Figure 3, the suction pipe 18 is connected to the independent compartment 50 at its end near the pump. It can be connected at any other point, for example, midway along the length of the compartment. Alternatively, the suction pipe 18 can be connected at least at two different points, for example, one point near each end of the independent compartment. The pump can operate at a constant flow rate, for example, between 100 and 300 l / min.The pump's flow rate can also be adjusted according to the belt's width and speed, as well as the weight of the metal carried by the belt. A camera 30 (Figure 2) is placed inside duct 3. This camera transmits a video feed of the bath surface in the duct to the line's control room. The operator can then assess the amount of metal present in the duct and, consequently, the flow efficiency to the separate compartment. If necessary, the operator can modify at least one operating parameter of the system, such as the pump's flow rate, to achieve the desired efficiency. Using the camera, the operator can also check the belt's path and profile, for example, for the presence of a cross-chain, as it is immersed in the bath.If necessary, the operator can thus adjust the distance L between the upper edge 25 of compartment 50 and the belt 1. To help visualize the position of compartment 50 relative to the belt, the belt comprises at least one position indicator 24 emerging from the bath surface, for example, corresponding to an extension of the front face of the compartment, as shown schematically in Figure 2. Advantageously, compartment 50 comprises three position indicators 24, one at each end of the compartment and one in the center, as shown in Figure 3. Therefore, the operator can adjust the position of compartment 50 when the belt is not perfectly parallel to the duct in order to maintain a constant distance L between the upper edge 25 of the compartment and the belt over the width of the belt.In the case where the device according to the invention comprises two compartments, one on each side of the band, these can be adjusted independently of each other. The pump is designed for tool-free disassembly in production. It is mechanically secured by one of the side arms 13, either directly or indirectly, for example, via pipe 18. The independent compartment 50 can also be mechanically connected to this first arm 13 by the same pipe 18. It can be connected to the second arm 13 by a mechanical connection 20 similar to that provided by pipe 18. As a result, the independent compartment, the pump, and the suction 18 and discharge 19 pipes form an assembly that can be assembled, disassembled, and adjusted using the joining and adjusting device 14, regardless of the position of the conduit 3 and the shoe 40. Assembling and disassembling this assembly does not require cutting the belt. The compartment has a lifespan of a few weeks, while a shoe, due in particular to its thickness, has a lifespan of a few months. According to the prior art, the compartment is attached to the shoe. Therefore, this solution is costly in terms of maintenance, since it requires scraping the shoe more frequently than necessary. According to the invention, it is possible to replace the independent compartment, or any other component associated with it, at a different interval than the shoe. Alternatively, the system includes a second pump, for example, positioned at the other end of the separate compartment. It is then mechanically supported by the other side arm 13, either directly or indirectly. This second pump has its own suction 18 and discharge 19 pipes, independent of those of the first pump. Having two pumps can be advantageous, for example, for better mass balance within the conduit. Furthermore, smaller pumps are more readily available and come from a wider range of potential suppliers. Having two pumps also allows for operation in a degraded mode in the event of a failure of one of the two pumps. The flow of molten metal within the shoe, caused by the suction of the pump, or the two pumps, allows the removal of scum into the separate compartment before it is removed from the separate compartment, in vessel 8, by pump 17. Therefore, the horizontality of the separate compartment is important to ensure a homogeneous flow of molten metal along the entire length of the belt; this is made possible by the joining and adjusting system 14. The external position indicator 15, on each side of the compartment, allows the plant operator to see its position and correct it if necessary. Since the belt consumes molten metal, it reduces the molten metal level in vessel 8. To compensate for this, metal is added by dipping ingots into the bath. A means 21 for measuring the bath height allows the bath height to be controlled.For example, measuring means 21 is a measuring laser that points from above onto the molten metal level in vessel 8. When measuring means 21 detects a low level, the molten metal ingot loading equipment performs an ingot lowering step into the molten metal vessel, which causes the level in the vessel to rise. The independent compartment, as well as the other elements in contact with the liquid bath, in particular pump 17 and its suction and discharge pipes, are made of 316L type stainless steel. Figure 4 illustrates a second embodiment of the invention with a schematic representation similar to that of Figure 3. In this example, with two pumps 17, the independent compartment 50 and all elements attached to it, such as the pumps and their intake pipes 18 and discharge pipe 19, are mechanically connected to the vessel 8 by arms 23 and a connecting and adjusting means 22. Therefore, there is no longer any mechanical connection between the compartment 50 and the elements attached to it and to the conduit 3. On the one hand, the position of the compartment 50 and that of the conduit can be adjusted independently of each other without interfering with one another. When the conduit is retracted, the system linked to the compartment 50 is then visible, facilitating horizontal adjustment via the adjusting means 23. According to an unshown variant embodiment, the independent compartment 50, and the elements attached to it, are mechanically connected to a support structure external to the container 8. Solutions in which the independent compartment, and the elements attached to it, are mechanically connected to the vessel 8 or to an external structure are particularly advantageous for adding a mulch removal device to an installation that did not previously have one. Therefore, the duct can be secured without adding any extra weight. As will be readily understood, the invention is not limited to the examples just described, and numerous modifications can be made to these examples without departing from the scope of the invention. Furthermore, the various features, forms, variants, and embodiments of the invention may be combined in various ways, provided they are not incompatible or mutually exclusive.

Claims

CLAIMS 1. A device for removing mattes from the surface of a liquid metal bath (2) within a conduit (3) of a line for continuously coating a metal strip (1) having first and second faces, the first face being designed to contact a lower roller (11), comprising a compartment (50) forming a reservoir by means of which the liquid metal within the conduit is replenished by being drawn out by a pump (17) to which the compartment is connected, characterized in that the compartment is fixed to a support (3, 8) by a joining and adjusting means (14, 22) and is capable of being removed by a disassembly means without the need to cut the metal strip.

2. The device according to the preceding claim, further characterized in that the compartment (50) is placed, with respect to the metal band, on the first face.

3. The device according to one of the two preceding claims, further characterized in that it comprises a second compartment (51) positioned, with respect to the metal band, on the side of the second face, the position of the two compartments (50, 51), in particular their horizontality, being adjustable independently of each other.

4. The device according to one of the preceding claims, further characterized in that the compartment (50, 51) is separable from the conduit (3).

5. The device according to one of the preceding claims, further characterized in that the compartment (50, 51) is held by two arms (13) connected to the conduit (3) by the joining and adjusting means (14).

6. The device according to any one of claims 1 to 4, further characterized in that the compartment (50, 51) is held by two arms (23) connected to the container (8) containing the liquid metal bath by a joining and adjusting means (22).

7. The device according to any one of claims 1 to 4, further characterized in that the compartment (50, 51) is held by two arms (23) connected to a support structure external to the container (8) containing the liquid metal bath by a joining and adjusting means (22).

8. The device according to one of the preceding claims, further characterized in that it comprises a means for adjusting the position of the compartment (50, 51) independent of the means for adjusting the conduit (3).

9. The device according to one of the preceding claims, further characterized in that each lateral end of the compartment (50, 51) is connected to a position indicator (15) flush with the bath surface outside the conduit (3) when the position of the compartment, in particular its horizontality, is correctly adjusted.

10. The device according to any one of the preceding claims, further characterized in that it comprises a camera (30) positioned in the duct and enabling a surface of the bath to be viewed within the duct, wherein the compartment (50, 51) comprises at least one indicator (24) for the position of a front face of the compartment relative to the metal strip (1) emerging from the bath surface visible to the camera, said position indicator (24) being connected to a position indicator (15) flush with the bath surface outside the duct (3) when the position of the compartment, in particular its horizontality, is correctly adjusted.

11. A continuous coating line comprising a conduit (3) and a container positioned to receive a liquid metal bath (2), characterized in that it comprises a device for removing mattes in accordance with one of the preceding claims.

12. A method of removing matte for removing matte from the surface of a liquid metal bath (2) within a conduit (3) of a line for continuously coating a metal strip (1), comprising a compartment (50) forming a reservoir through which the liquid metal present within the conduit is replenished by extraction by a pump (17) to which it is connected, characterized in that it comprises a step for extracting said compartment which does not comprise a step for cutting the metal strip.

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