MXPA98007408A - Magnetic container of the immersion coating bath in calie - Google Patents

Abstract

The present invention relates to: A hot dip coating system comprises a molten coating metal bath contained in a container having a passage opening of the strip positioned below the upper surface of the bath. A strip of metal is directed along a path extending through the passage opening of the strip and through the bath of the molten coating metal to coat the strip. An electromagnet is employed to prevent the escape of the volume of the molten coating metal from the bath through the strip passage opening, while allowing the strip to move along its path. Records are provided to reduce the escape of the molten coating metal through the passage opening

Description

"MAGNETIC CONTAINER OF THE HOT DIVE COATING BATH" RELATED REQUEST This is a continuation in part of the request Number 08 / 964,428 called "Immersion Coating in Hot Using a Metal Coating Plug Refrigerated ", and the disclosure therein is incorporated herein by reference.

BACKGROUND OF THE INVENTION The present invention relates generally to a hot dip coating of a metal strip, such as a steel strip, with a coating metal such as zinc or aluminum, and more particularly with a hot dip coating process that dispenses with the need for one or more submerged strip guide rollers below the surface of a molten metal coating bath. The steel strip is coated with a coating metal, such as zinc or aluminum, to improve the strength of the steel strip to corrosion or oxidation. One method for coating the steel strip is to immerse the steel strip in a molten metal coating bath. The conventional hot dip process is continuous and usually requires, as a preliminary processing step, the pre-treatment of the metal strip before the strip is coated with the coating material. The pre-treatment improves the adhesion of the coating to the steel strip, and the pre-treatment step can be either (a) a preliminary heating operation and a controlled atmosphere or (b) a melt adhesion operation where The surface of the strip is conditioned with an inorganic flux. Regardless of the pre-treatment, the conventional hot dip coating process employs a coating step which is carried out in a molten metal coating bath containing one or more submerged guide rolls to change the direction of the coating. strip metal or otherwise guide the strip as you experience the hot dip coating step. More particularly, the steel strip normally enters the bath of the molten coating metal from above and moves in a direction that has an essentially downward component and then passes around one or more submerged guide rolls that change the direction of the strip steel from essentially downward to essentially upward, after which the strip is removed from the molten metal coating bath as the strip moves in the upward direction. A number of problems of the use of the submerged guide rollers in the bath of the molten coating metal are raised. These problems are described in detail in the application Number 08 / 822,782 entitled "Hot Dip Method and Apparatus", and the description herein is incorporated by reference. Certain attempts have been made to eliminate the use of submerged guide rolls in a hot dip coating process. In these attempts, the steel strip is introduced into the molten coating metal through a passage opening of the elongated strip in the container containing the bath; and the opening is typically placed below the surface of the bath, and the strip is directed through the opening and through the bath along an essentially vertical straight line path. Driving a strip through the bath along a straight line path eliminates the need for the submerged guide rollers to change the direction of the strip as it passes through the bath.

The passage opening of the elongate strip is typically placed at the bottom of the container containing the bath, and records are employed to prevent molten metal in the bath from escaping through the passage opening of the strip. Some records employ mechanical seals in the opening. These mechanical seals mesh the side surfaces of the edges of the strip as the strip moves up through the opening, causing the seal to wear or break which in turn causes the escape of the molten coating metal through the opening. Other problems associated with mechanical seals include freezing and large thermal gradients in the coating metal bath, and more quality problems with the strip coating including irregularities in the thickness of coating on the strip. Other records employ electromagnetic devices that are located adjacent to the opening of the strip passage and that develop electromagnetic forces that push the molten metal in the bath away from the opening. These devices can prevent the escape, from the molten metal bath, of the volume of the molten metal in the bath (volume container), but still allow some leakage or dripping of the molten metal from the bath through the opening of the passage of the molten metal. strip, particularly on the lateral edges and ends of the opening of the elongated container. Escape of this type can be a major problem.

COMPENDIUM OF THE INVENTION The present invention is directed to a hot dip coating system that provides all the benefits that accompany the removal of the submerged guide rolls and furthermore, they not only obtain a container from the volume of the molten coating metal in the bath but also reduce The escape or dripping of the molten coating metal through the opening of the strip passage is considerably reduced. The reduced exhaust of the present system is the exhaust that is allowed by the electromagnetic devices described in the previous paragraph. A system in accordance with the present invention includes one or more of the files that will be described below. The container containing the molten metal coating bath is in the form of a tundish with side walls converging downwards to the opening of the passage of the strip at the bottom of the container. The associated electromagnet has a pair of mutually opposite facing faces, each adjacent to a respective side wall of the container and each essentially following the contour of the adjacent side wall. This increases the density of the magnetic flux generated by the electromagnet through the bottom of the container, in turn increasing the upwardly directed magnetic force which pushes the bottom of the bath of the molten coating metal away from the lower opening of the container. The operation of the electromagnet shakes the bath, and that agitation contributes to the escape problem. In accordance with the present invention, a device is provided for mechanically dampening the agitation of the bath produced by operating the electromagnet. This cushioning device is in the form of a plurality of horizontally spaced, vertically separated flat pairs of members defining a central slot through which the steel strip passes. The planar members described in the preceding paragraph are composed of ferromagnetic material and define a low reluctance path for the magnetic flux in the free space between the opposite mutually oriented pole faces. As such, the flat members reduce the effective space between the mutually oriented pole faces of the electromagnet, thereby increasing the density of the magnetic flux in space by in turn increasing the magnetic force directed upwardly in the lower opening of the container. By reducing the space, the ferromagnetic planar members can be used independently of the damping device described in the previous paragraph. There are guiding elements that keep the steel strip centered inside the container. The guide elements counteract the tendency of the electromagnet to draw the strip towards one of the two polar faces facing each other and restrict the side-to-side movement of the steel strip that would otherwise be experienced as it moves through the container. , a movement which is undesirable. There is an electric current conductor having a pair of terminals each for direct contact with the molten coating bath in the lower part of the bath, and each placed in a drain at a respective end of the passage opening of the strip. The current conductor conducts either (a) the direct current from an external source (when the electromagnet is energized by direct current), or (b) the parasitic current generated by the magnetic flux from the electromagnet (when the electromagnet is energized by the current that varies in time). The electric currents described above flow between the terminals of the current conductor, in the lower part of the bath of the molten coating metal. The electric current cooperates with the magnetic flux from the electromagnet in the lower part of the bath to produce a magnetic force that pushes the lower part of the bath upwards away from the lower opening in the container. By using a current conductor the electric current is concentrated in the desired places at the bottom of the bath, and the efficiency of the magnetic force directed upwardly and in comparison with the magnetic force produced in the absence of a current conductor is considerably improved. In one embodiment, the electromagnet coils are part of a so-called LCR series electric circuit. This circuit is operated so as to automatically increase the current to generate the magnetic flux when there is a drop in the level of the bottom of the molten metal bath adjacent to a lower opening in the container. This increases the magnetic force by pushing the bottom of the bath up. Other features and advantages are inherent in the method and apparatus claimed and disclosed or will be apparent to those skilled in the art from the following detailed description along with the accompanying diagrammatic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram, partially in section, of a hot dip coating system in accordance with one embodiment of the present invention; Figure 2 is a perspective showing a container and an electromagnet used in the system; Figure 3 is an enlarged vertical sectional view of a system portion; Figure 4 is a perspective of a modality of a container employed in the system; Figure 5 is a perspective view of the container of Figure 4, in an inverted position; Figure 6 is a side elevation of a removable half of the container of Figures 4-5, showing the interior of the container; Figure 7 is a fragmentary vertical sectional view of the container taken along the line 7--7 in Figure 6, but showing the two halves from the container joined together; Figure 8 is a vertical sectional view similar to Figure 7 and taken along line 8--8 in Figure 6; Figure 9 is a vertical sectional view, similar to Figure 8, taken along line 9-9 in Figure 6. Figure 10 is a perspective view of one embodiment of an electromagnet used in the system; Figure 11 is an end view, partially in section, showing the portion of the electromagnet of Figure 10; Figure 12 is a horizontal sectional view taken along line 12--12 in Figure 10; Figure 13 is an inside view of a half of the container showing the modalities of certain interior fittings used in the system to reduce the exhaust; Figure 14 is a vertical sectional view amplified from the interior of the container and showing one embodiment of a device for damping the agitation of the molten target in the container; Figure 15 is a perspective of the agitation dampening device; Figure 16 is a perspective of the container and a mode of the current conductor employed in the system; Figure 17 is an enlarged fragmentary sectional view showing a terminal portion of a current conductor; Figure 18 is an enlarged fragmentary sectional view taken crosswise to the section shown in Figure 17, and showing other portions of the current conductor; Figure 19 is a fragmentary internal view of one half of the container showing another embodiment of a current conductor; Figure 20 is a circuit diagram showing a current conductor used in the direct current; Figure 21 is a fragmentary vertical sectional view illustrating an attachment within the container to reduce the effective space between the mutually opposite oriented pole faces of an electromagnet placed on the outside of the container; Figure 22 is a bottom view showing one of the pair of notched strip guide elements each positioned at a respective opposite end of the bottom of the container; Figure 23 is a circuit diagram of an electrical circuit in series for the electromagnet. Figure 24 is a circuit diagram of a parallel electrical circuit for the electromagnet; and Figure 25 is a graph plotting current (I) versus inductance (L) for the series circuit of Figure 23.

DETAILED DESCRIPTION Referring initially to Figure 1, which are generally illustrated at 30 there is one embodiment of the hot dip coating system in accordance with the present invention. The system 30 in Figure 1 is intended for use in the coating of a continuous metal strip, such as steel - with a coating metal composed of zinc or zinc alloy. Other embodiments of the hot dip coating systems according to the present invention may be employed in order to coat a strip of continuous metal with other coating metals such as aluminum, aluminum alloys and the like. Tin, lead and alloys of each are typical examples of still other coating metals that can be applied in hot dip coating systems in accordance with the other embodiments of the present invention. Referring now to Figures 1 and 3, a strip 32 of continuous steel is unwound from a roll (not shown) and subjected to a conventional pre-treatment operation (not shown). After pre-treatment, the strip 32 is directed by the guide rollers 36, 37 along a path extending through an elongated opening 43 similar to a slot in the bottom of the container 38 in the form of an elongated trough. containing a bath 40 is molten metal coating in this case zinc. The bath 40 has an upper surface 41, and a lower opening 43 of the container is placed below the upper surface 41 of the bath 40. The opening 43 allows the introduction of the strip 32 into the bath 40, and the strip is then moved to along a path extending through the bath 40. The movement of the strip 32 through the bath 40 coats the strip 32 with a coating metal layer of which the bath 40 is composed, and a coated strip 31 it comes out of the bath 40 downstream of the upper surface 41 of the bath. The container 38 has an open upper end 42 through which the coated metal strip 31 moves up after passing through the bath 40.

Placed above the container 38 is a pair of blades 44, 44 called air blades (Figure 1) of a type that is conventionally used to control the thickness of the coating on the strip 31, e.g. directing jets of heated or unheated air or nitrogen against the strip 31. Placed downstream of the air blades 44, 44 there is a winding reel (not shown) in which the strip 31 coated on a roll is re-rolled. or coil that can be removed from the winding reel. The container 38 will now be described in greater detail with reference to Figures 3-8. As seen in Figure 3, the container 38 has an essentially funnel-shaped vertical cross section that is taken along a vertical plane perpendicular to the plane of the strip 32. Also as shown in Figure 3, the container 38 has (i) a relatively narrow part 58 extending downstream from the opening 43 and (ii) a relatively wide portion 59 positioned downstream of the narrow part. Referring now to Figures 4 to 8, the container 38 is composed of two container means 52, 52 joined together at the opposite ends along the vertical flanges 53, 53. When the two halves of the container are joined together, they define the container 38 in the form of an elongate trough. The container 38 has a pair of longitudinal side walls 55, 55 and a pair of end walls 56, 56 each extending between the ends of the side walls 55, 55. The side walls 55, 55 define the vertical cross section in shape of funnel shown in Figures 3 and 8-9. The container 38 and its funnel-shaped cross-section includes the relatively narrow lower portion 58 mentioned above and the relatively wide upper portion 59. An intermediate part 60 of the container is positioned between the broad upper portion 59 and the narrow lower portion 58 and comprises a pair of side wall portions 61, 61 converging in an upstream direction from the wide upper portion 59 to the part 58 narrow bottom. The materials from which the container 38 can be constructed include non-magnetic stainless steel and refractory materials. Referring now to Figure 6 illustrating the interior of the container 38, the narrow part 58 of the container includes a passage 62 that extends downstream from the lower opening 43 of the container. The passage 62 is defined by a pair of opposite longitudinal sides 63, 63 (only one of which is shown in Figure 6) and a pair of opposite ends 64, 64, each extending between the sides of the passageway 63, 63. The electromagnet 50 will now be described in greater detail with reference to Figures 2 and 10-12. The electromagnet 50 comprises a rectangular external member 100 composed of magnetic material comprising a pair of opposite side longitudinal walls 101, 101 each having a pair of opposite ends and a pair of end walls 102, 102 each extending between the two ends. corresponding ends of the side walls 101, 101. The side walls 101, 101 together with the end walls 102, 102 define a vertically disposed internal space 104 having open upper and lower ends 105, 106, respectively. The electromagnet 50 also comprises a pair of pole members 108, 108 each composed of magnetic material and each mounted on a respective side wall 101 of the outer member 100, within the space 104 positioned vertically. Each pole member 108 extends inwardly into the space 104 toward the other pole member and terminates at a pole face 109 that faces opposite and faces the pole face 109 at the other pole member 108 (Figures 10 and 12). ). The pole faces 109, 109 define a space 110 therebetween to accommodate the container 38. As shown in Figure 11, each pole member 108 encompassing a coil 112 for conducting the electric current. In accordance with one embodiment of the present invention, a current that varies in time from a current source 113 is flowed through each coil 112 to generate a magnetic field within the pole member 108 encompassed by that coil 112. The current source 113 is typically adjustable to vary the amperage of the current that varies with the time that is introduced in the coil 112 thus allowing the resistance of the magnetic field generated by the electromagnet 50 to be controlled. In another embodiment, a direct current that does not change with time is flowed through coil 112 to generate the magnetic field. An adjustable current source can also be used in this mode. The coil 112 is composed of a multiplicity of coil turns or coils 115 each extending around the pole member 108 and each composed of an appropriate conductive material such as copper. The turns or turns 115 of the coil are insulated from each other and from the pole member 108 with an insulation material illustrated in Figure 11, the coil 112 is shown composed of solid wire; in the other embodiments, the coil may be composed of copper tubing, for example, through which a cooling fluid may be circulated. Pole members 108, 108 and outer member 100 provide a path 116 for the magnetic field generated by the flow of current through coil 112. Path 116 is shown in dashed lines with arrows in Figure 12. More particularly, the magnetic field extends from a pole face 109 in a pole member 108 through the space 110 to the pole face 109 in the other pole member 108. The magnetic field then extends in sequence through the other pole member 108 and then in opposite directions through the longitudinal side wall 101 where the other pole member 108 is mounted then through both end walls 102, 102. of the external member 100, and then through the longitudinal side wall 101 where the pole member 108 is mounted and then through a pole member 108 back to the pole face 109 in the pole member. The flow direction of the current through each coil 112 in each of the pole members 108 is controlled so that the magnetic field generated by each of the coils in each of the pole members extends through the space 110, in the same direction. The electromagnet 50 is composed of a conventional magnetic material such as ferrite or electric steel laminations. As can be seen in Figures 10 and 12, the electromagnet 50 is composed of two half magnets 114, 114 each having a horizontal cross-section in the shape of "E". Referring to Figure 3, each pole face 109 of the pole member 108 is positioned adjacent a respective side wall 55 of the container 38 in substantially narrow abutting relationship with that side wall of the narrow bottom portion 58 of the container, and in FIG. the portion 61 of the convergent side wall. Each pole face 109 has a contour essentially following the contour of the adjacent side wall 55, particularly along the converging side wall portion 61 and along the bottom portion 58 of the container, in this embodiment. The distance between the mutually opposite oriented pole faces 109, 109 (space 110) is smaller in the part 58 of the narrow container adjacent to the lower opening 43 of the container. Because the width of the space 110 of the pole face is smaller at that site, the magnetic field strength (flux density) is higher at that site, compared to other sites downstream of part 58 of the container where space 110 is wider. Further, because the resistance to the passage of the magnetic flux (i.e., reluctance) is less in the free space than in the molten metal of bath 40, there is a tendency for the flow The magnetic passage passes between the pole faces 109, 109 to be concentrated just below the bottom of the bath 40 in the passage 62, adjacent to the bottom opening 43 of the container. Accordingly, for a current that varies in determined time flowing through the coils 112, 112, the magnetic force exerted against the bath 40 by the electromagnet 50 is higher in the lower part 58 of the container, adjacent to the opening 43 lower of the container, than anywhere else in the bath 40 of molten metal. In general, the magnet's power (and magnetic flux) can be adjusted by adjusting the amperage of the current that varies in time that is used to energize the magnet. The magnetic flux generated by a current that varies in time extends through space 110 in Figure 3 and induces eddy currents within bath 40. Referring to Figure 6, path 45 of eddy currents includes a portion 46 that it extends along the bottom of the bath 40, horizontally in the longitudinal direction of the container 38 adjacent the opening 43. The direction of the eddy currents there is a right angle with respect to the magnetic flux direction at that site. As a result the flux and parasitic currents intersect in a horizontal plane producing magnetic forces directed in an upward direction as seen in Figures 3 and 6. These forces push that part of the bath 40 that is adjacent to the lower opening 43 (ie, the bottom of the bath 40) in an upward direction away from the opening 43 (ie, downstream as seen in Figure 3), an effect known as magnetic levitation. The magnetic levitation resulting from the upward force exerted against that part of the molten metal bath adjacent to the lower opening 43, is a factor in the volume container of the molten metal bath. The magnetic levitation described above could produce a bath volume container 40 of about 98 percent or more when the other files (which will be described below), which enhance the effect of the magnet 50, are associated with the magnet. The volume container due to magnetic levitation of the type described in the preceding paragraphs can be satisfactory to prevent leakage through the opening 43 of the strip passage of most of the molten coating metal from the bath 40, and can reduce Some of the descending or dripping leak tends to occur along the sides 63, 63 and the ends 64, 64 of the passage 62 (Figure 6). The operation of the electromagnet 50 agitates the bath 40, producing, for example, circulatory or oscillatory agitation currents having a vertical component; this agitation contributes to dripping or leakage through the lower opening 43 of the container 38. A device for damping this agitation is generally indicated at 70 in Figures 13 to 15. The device 70 comprises a plurality of pairs of flat members 71, 72 essentially parallel. Preferably, each flat member 71, 72 is composed of a material such as stainless steel, which is resistant to the thermal conditions in the molten metal bath 40. Alternatively, the flat members 71, 72 can be coated with a thermal coating material (not shown). Each pair of flat members 71, 72 separate vertically along the path of the strip 32, and each pair of flat members 71, 72 extends through the bath 40 in a direction transverse to the direction of the path of the strip. Each pair of flat members 71, 72 defines a slot 73 therebetween. Each groove 73 is aligned with a groove defined by each of the other pairs of the flat member 71, 72 to allow the passage of the strip 32 through the vertically aligned grooves 73 as the strip 32 moves along the length of the groove. his career. The flat members 71, 72 extend through the path of the stirring currents produced by the electromagnet 50 and thus function to dampen the agitation. As shown in Figure 14, some of the flat members 71, 72 are placed inside the container 38 between the side wall portions 61, 61 of the container converging downwardly. These flat members have respective lateral dimensions in a direction extending between the side wall portions 61, 61 progressively decreasing in a downward direction. The vertically aligned, flat members 71, 71 and the vertically aligned members 72, 72 are maintained in vertically separated relationship by the spacers 75, 75 each placed between the adjacent flat members 71, 71 and between the adjacent flat members 72, 72 . In one embodiment, all of the flat members 71, 71 in the damper device 70 are held together in one unit by their spacers 75, each of which is rigidly secured to the flat members above and below that spacer; and all the flat members 72, 72 in the damper device 70 are similarly held together in one unit by their spacers 75. In another embodiment, all flat members in a unit are held together by vertical rods (not shown) each from which it passes through the aligned openings in the flat and separating members. A group of vertically separated transverse members placed horizontally 76, 77, 78, 79, placed at each end of the shock absorbing device 70, is connected to the unit of the members 71, 71 vertically separated planes with the unit of the members 72, 72 vertically separated planes in the cushioning device 70 to provide pairs of members 72, 72 planes horizontally aligned. The shock absorbing device 70 has a vertical dimension which corresponds preferably to the depth of the bath 40 of the molten coating metal to be contained in the container 38. In the embodiment of Figures 13-15, the shock absorbing device 70 is suspended by on top by the end brackets 80, 80 each placed at the opposite end of the shock absorbing device 70 and extending vertically upwards therefrom. Each end bracket 80 includes a slot 82 for receiving a threaded member 81 to fix the bracket 80 to an arm 84 of a device 83 which, inter alia, functions as a mounting frame for the shock absorbing device 70 in the embodiment of Figure 13. The device 83 also has another function that will be described later in greater detail. The above described files for connecting together the flat members in the shock absorbing device 70 and for mounting the shock absorbing device 70 within the container 38 are only illustrative; Other records may be used to do this. In some embodiments, each pair of the flat members 71, 72 can be replaced by a single flat member having a lateral dimension corresponding to the combined side dimensions of the flat members 71, 72 and having an elongated slot centrally integral, in instead of the groove 73. As mentioned above, with reference to Figure 3, there is a space 110 between the two mutually opposite oriented pole faces 109, 109 of the magnet 50. As can be seen by comparing FIGS. 3 and FIG. Figure 14, the pairs of flat members 71, 72 extend horizontally between the pole faces 109, 109 oriented mutually opposite in that part of the space 110 above the narrow lower part 58 of the container 38. That part of the space 110 described in FIG. the previous paragraph is wider than that part of the space in the narrow lower part 58. The wider the space between the pole faces 109, 109, the lower the magnetic flux density will be through that part of the space. The increased magnetic flux density is desirable, and the flux density can be increased by decreasing the effective space between the pole faces 109, 109. A record to do this is described in the next paragraph. In a preferred embodiment, the flat members 71, 72 are composed of the ferromagnetic material, e.g. carbon steel or magnetic stainless steel. In comparison with the metal of the molten bath (eg zinc), both materials described in the previous paragraph are more permeable to the magnetic flux and provide a relatively low reluctance flow path for the magnetic flux extending between the faces 109, 109 of polo. By composing the plane members 71, 72 of these materials, the effective space between the pole faces 109, 109 is reduced. More particularly, the effective space is reduced to (a) the width of the groove 73 plus (b) the distance between the outer edge 74a of the flat member 71 and the adjacent pole face 109 plus (c) the distance between the edge ( 74b) and the flat member 72 and the adjacent pole face 109. Figure 21 illustrates an alternative modality of a file to reduce the effective space between the pole faces 109, 109. In this embodiment, the vertically aligned pairs of the horizontally separated, flat, separate elements 171, 172 define a space 173 therebetween through which the path for the strip 32 extends. Each pair of flat elements 171, 172 is placed in the space 110 between the pole faces 109, 109 in that part of the space 110 above the narrow bottom part 58 of the container 38 (Figures 3 and 21 are taken together.) Both planar elements in a pair remain therein. horizontal plane Each flat element extends from a respective internal side wall surface 174, 175 of the converging side wall portions 61, 61 through the bath 40 towards the other flat element, in a direction transverse to the direction of the path of the strip The flat elements 171, 172 are composed of ferromagnetic material, eg magnetic stainless steel thereby reducing the effective space between the faces 109, 109 of mutually oriented poles in the same manner as the flat members 71, 72 (see previous paragraph).

In the embodiment illustrated in Figure 21, the flat elements 171, 172 are partially embedded in the side wall portions 61, 61 of the container 38.

Other records may be employed to secure the planar elements 171, 172 to these side wall portions. Referring now to Figures 6 to 8 and 13, the passage 62, as mentioned above, has a pair of opposite ends 64, 64 each spaced apart from an adjacent end wall 56 of the container 38. There is a space 67 therebetween. end wall 56 of the container and end 64 of the passage. A dam or dam 65 extending upwardly from the end 64 of the passage extends laterally through the interior of the container between the opposite converging side wall portions 61, 61 of the intermediate portion 60 of the container (Figures 7-8). Each dam or dam 65 occupies part of the space between the end wall 56 of the container and the end 64 of the passage. Placed at each end of a container 38, between an end wall 56 of the container and a dam or dike 65 there is a sump 66. Each sump 66 comprises a structure for restricting a puddle of molten metal. The sump 66 is positioned on top of a portion 68 of the bottom wall of the container extending between the end 64 of the passage 62 and the adjacent end wall 56 of the container 38.

In the embodiment shown in Figures 3 and 13, each pole member 108 (and its pole face 109) extends (a) down to the bottom of the passage 62 (corresponding to the bottom opening 43 of the container) and (b) longitudinally to a site adjacent to each space 67 of the end of the container 38. Accordingly, when the flow or flux passes between the pore faces 109, 109 there is a flow or flux in the lower portion of passage 62 and the spaces 67, 67 of end. Referring now to Figures 13 to 16 a 18, another expedient is illustrated therein for reducing leakage or dripping of the molten metal through the lower opening 43. This file is in the form of an electric current conductor, a mode of which is generally indicated at 83 in Figure 13. As mentioned above, when the electromagnet 50 is operated together with an electric current that varies in time ( alternating current or pulsed direct current), the magnetic flux developed by the electromagnet generates eddy currents in the bath 40 of molten metal. These eddy currents typically follow a path that is diagrammatically indicated at 45 in Figure 6 and that includes a portion 46 that flows along the bottom of the bath 40 in the longitudinal direction of the container 38. The current conductor 83 defines a low resistance conducting path that will be followed by that part of the parasitic current other than the portion 46 that flows along the bottom of the bath 40. Referring to Figure 13, the driver Current 83 is a generally "U" shaped element composed of electrically conductive material eg copper. The conductor 83 comprises (i) a pair of arms 84, 84 each placed adjacent to a respective end wall 56 of the container 38 and (ii) a transverse member 86. Each arm 84 has an upper end portion 85 connected by the cross member 86 to the upper end portion 85 of the other arm. The current conductor 83 also comprises a pair of bottom end portions 87, 87 each connected to a respective arm 84 and each placed within a respective end space 67 of the container 38 above the wall portion 68 of the container. container, and in electrical contact with that part of the bath 40 placed in the sump 66. Although not shown in Figure 13, the conductor 83 is electrically insulated against the electrically conductive contact with each shock absorber device and bath 40 (except in what refers to that part of the bath 40 in the sump 66).

In the embodiment of Figure 13, the parasitic current flows through the current conductor 83, instead of flowing through the bath 40 along the path 45 (Figure 6), and the parasitic current is routed through the conductor 83 to the end space of the container 38, that is, to that bath part 40 of molten metal placed in the sump 66. As mentioned above, the magnetic force produced by the co-operation between the magnetic field generated by the electromagnet 50 and eddy currents developed in the bath 40, pushes the molten metal bath 40 away from the lower opening 43 of the container and keeps the lower part of the bath 40 above the lower opening 43 of the container. The magnetic force directed upwardly exerted against the bottom of the bath 40 at any location along the length of the vessel 38 is a function of both (a) the amount of magnetic flux therein and (b) the amount of current parasite in it. The pole faces 109, 109 are each oriented through the end spaces 67, 67 thereby providing the magnetic flux at this site. As mentioned above, the current conductor 83 directs the parasitic current generated by the electromagnet 50 towards the end spaces 67, 67 adjacent the bottom of the container 38. The current conductor 83 is absent at least a certain amount of current parasitic would follow a path 45 that deviates from the end spaces 67, 67 (see Figure 6). Employing the current conductor 83 having end portions 87, 87 not insulated in the end spaces 67, 67 in the sumps 66, 66, the parasitic current is more concentrated in the end spaces 67, 67 than the would do in the driver 83 of current absent. This increases the magnetic force directed upwards in the end spaces 67, 67 which in turn contributes to a reduction in leakage or dripping through the lower opening 43 of the container, particularly along the ends 64, 64 of the passageway. 63. The current conductor 83 also functions to considerably reduce the flow of the parasitic current flowing along the upper part of the bath 40. This is desirable because the parasitic current flowing along the upper part of the Bath 40 would cooperate with any magnetic field that is generated at that site by electromagnet 50 to produce a magnetic force that pushes bath 40 down there. Because the current conductor 83 considerably reduces the flow of the parasitic current flowing along the top of the bath, there is also a considerable reduction in the magnetic force that pushes down the bath at this site. This in turn increases the effectiveness of the magnetic force that pushes the bath up into the lower part of the bath which in turn contributes to the reduction in the drip or leakage of the bath through the lower opening 43 of the container. As mentioned above, the magnetic flux density generated by the electromagnet 50 is highest at these sites where the space 110 between the opposite pole faces 109, 109 of the electromagnet 50 is smaller. Similarly, the parasitic currents generated in the bath 40 are relatively high at those sites where the space 110 is relatively small, ie, adjacent to the bottom of the bath 40. In addition, the current conductor 83 concentrates the parasitic current along the bottom of the bath 40 adjacent to the upper part of the passage 63. As mentioned above, the current conductor 83 has vertically positioned arms 84, 84 most of which are placed inside the bath 40. illustrates an alternative embodiment in Figure 16 where the U-shaped current conductor indicated generally at 183, has arms 184, 184 positioned vertically, are centrally located outside the bath 40 and has a transverse member 186 and connects the arms 184, 184. Only the portions 187, 187 of the terminal end of the current conductor 183 are placed in the bath 40, in the end spaces 67, 67 in the sumps 66, 66. A connecting portion 188 extends from each end portion 187 through a longitudinal side wall 55 of the container 38 to a respective arm 184. The foregoing discussion was in the context of the electromagnet 50 which is operated with an electric current that varies in time either from alternating current or from direct pulsing current. In this case, the resulting magnetic flux produces eddy currents in the bath 40, and these eddy currents flow through the low resistance path that is provided by the current conductor 83 or 183. In another embodiment of the present invention, the electromagnet 50 can be operated with a current that does not vary with time, e.g., a direct current without pulsation. In this arrangement, each coil 112 in a pole member 108 of the magnet 50 (Figure 11) is connected to a direct current source that flows uninterrupted through the coil 112 to generate a magnetic field flowing through the bath 40 between facing faces 109, 109 (Figure 3). The magnetic field generated in this way does not produce eddy currents in the bath 40. Instead, an external source is used to introduce the direct current into the bath 40 at a site between the pole faces 109, 109. An embodiment of this arrangement (on the last sheet of the drawing) is illustrated in Figure 20. In the embodiment of Figure 20, a direct current source 119 is connected via a line 117 with a pair of terminal end portions 118, 118 each placed within a respective end space 67 of the container 38, above the portion 68 of the bottom wall and in electrical contact with the bath in the sump 66 at that site (Figure 6). The direct current flows from a terminal end portion 118 along the bottom of the bath 40, in the longitudinal direction of the container 38. This direct current cooperates with the magnetic field generated by the uninterrupted flow of direct current through of the coils in the pole members 108 of the electromagnet 50 (Figure 11). The cooperation described in the preceding paragraph produces a magnetic force that pushes the molten metal bath 40 upward away from the lower opening 43 in the container 38. In all embodiments of the present invention, the terminal end portion (87, 187 , or 118) is composed of a conductor having a lower electrical resistance than the bath 40 of molten metal. Typically, the terminal end portion is composed of copper while the molten coating metal bath is composed of zinc. The copper in the terminal end portion will be metallurgically combined with the molten zinc in the bath to form a copper-zinc alloy (brass) that is absorbed in the bath. The net result is the erosion of the terminal end portion. From the point of view of the present invention, the phenomenon described in the two preceding paragraphs is undesirable; therefore, records are provided to prevent erosion of the terminal copper end portions in the molten zinc of bath 40. Referring to Figures 17 and 18, each end portion 187 is provided with a channel 189 internally communicates with an internal channel 190 in connection portion 188. The internal channel 190 is connected to an inlet duct 191 communicating with a cooling fluid source 192, e.g. refrigerated water. The cooling fluid flows from the source 192 through the inlet duct 191 and the channel 190 to the channel 189 to cool the lower end portion portion 187, thereby solidifying a certain amount of the zinc coating metal in the sump 66 as a crust or layer 194 around the end portion portion 187 (Figure 17) . The crust 194 protects a terminal end portion 187 of the copper against erosion in the molten zinc of the bath 40. The spent cooling fluid is removed from the channel 189 through an outlet conduit 193 (Figure 18). (In Figure 17, the dam or dam 65 and the lower wall portion 68 of the container are shown with dimensions of thickness that are relatively small compared to the thickness dimensions of the corresponding elements in Figures 6 and 13. It can be used any variation). In the embodiment of Figure 20, employing non-pulsed direct current, the terminal end portion 118 has an internal channel 289 connected to an inlet duct 291 and an outlet duct 293. The inlet duct 291 is connected by a line 294 to a source of cooling fluid (not shown). The outlet duct 293 is connected via a line 295 with a drain duct for the spent cooling fluid (not shown). Circulation of the cooling fluid through the channel 289 produces a protective coating or layer of zinc coating metal solidified around the copper end portion 118 to protect the end portion portion 118 against erosion in the molten zinc of the bath 40. As mentioned above, the current conductor 183 has arms 184, 184 and a transverse member 186 which are placed outside the bath 40 of molten metal coating (Figure 16). A variation of the embodiment described in the preceding paragraph is illustrated in Figure 19 wherein at least a portion of each arm 184 is immersed in a bath 40 of molten metal facing. Protecting that portion of the arm 184 that is immersed in the bath 40, there is an insulating layer 196 for electrically and thermally insulating the submerged arm portion of the molten metal coating bath 40. That part of the arm 184 that is adjacent to the joint of the arm 184 with the lower end portion portion 187 is protected from the molten coating bath by a crust 194 of solidified coating metal (discussed above in connection with Figure 17). A layer of electrical and thermal insulation similar to layer 196 in Figure 19 would be employed in the embodiment of Figure 13 to protect that portion of each arm 84 that is immersed in the bath 40. The end portion portion 87 in the The current conductor 83 is not cooled in the manner shown in Figure 13, but is exposed to the bath of the molten coating metal. A non-protected end-end portion such as 87 may be employed in situations where the molten coating metal does not form an alloy with the conductive metal (e.g. copper) of which the end-end portion 87 is composed. As a less desirable alternative, the end-end portion 87 can be protected with an insulation layer (such as a layer 196 in Figure 19), except for the tip 89 of the end-end portion 87. Referring now to Figures 21-22, there is a guide element 120 placed at each end 64 of the passage 62 which, as mentioned above, is placed in the narrow lower part 58 of the container 38 (See Figures 6). and 13). Each guide element 120 has a notch 121 positioned horizontally having an open end 123 facing the corresponding open end of the corresponding notch in the guide member 120 at the other end 64 of the passage 62. Each notch 121, constitutes a structure for engagement with a respective edge portion 122 of the steel strip 32 as the strip moves through the passage 62. The notches 121, 121 keep the strip 32 essentially centered between the faces 109, 109 of mutually oriented poles of the magnet 50, and a side restricting the lateral movement of the steel strip 32 as it moves through the container 38. This counteracts the tendency of the electromagnet 50 to attract the strip 32 towards one of the two mutually opposite facing faces 109, 109 which in turn tends to cause side-to-side movement to the strip 32, as it moves through the container, a movement which is undesirable. Referring now to Figures 23-24, Figure 23 illustrates a LCR series circuit for the electromagnet 50 and Figure 24 illustrates a parallel LCR circuit for the electromagnet 50. Each LCR circuit includes a current source 113 which varies in time, a capacitor 125, a coil 112 for each pole member 108 of the magnet 50, and a resistor 127. In both Figures, C represents the capacitance of the circuit, L represents the inductance of the circuit (which includes a coil 112 for each member 108 of pole) and RL represents the resistance of the coils. The inductance varies directly with the flow generated by the coil and the number of turns in the coil and varies inversely with the level of the current (amperage). The inductance produces a delay in the frequency compared to the frequency of the power source; the capacitance produces a forward frequency.

The series LCR circuit illustrated in Figure 23 is operated in such a way that the current in the circuit increases automatically when there is a drop in the level of the lower part of the molten metal bath 40, thereby increasing the ascending magnetic force. exerted in the lower part of the bathroom. This particularity is discussed in the following four paragraphs. Referring to Figure 25, this figure plots the current as an inductance function for a system using the LCR series circuit of Figure 23. The vertical line in Figure 25 marked "Resonance" refers to a condition of the circuit in series LCR of Figure 25 to which the frequency advance due to the capacitance of the circuit coincides or is balanced with the frequency delay due to the inductance of the circuit, so that the natural frequency of the circuit is equal to the frequency of the power supply. For a given power supply, a resonance condition provides more energy for the magnet energized by the circuit to a non-resonance condition. When the series LCR circuit of Figure 25 is operated close to its resonance, the level of the circuit current is a function of how close the resonance is operating. If the capacitance (C) and the resistance (R) are set, the current (I) can be plotted as a function of the inductance (L) (see Figure 25); the variations in the inductance (L) therefore affect the current (I). The system 30 and the magnet 50 are operated normally so that the lower part of the bath 40 is maintained above the lower opening 43 in the container 38 (see Figure 3). Anywhere, between the pole faces 109, 109, the density of the magnetic flux through the free space (air) is greater than the magnetic flux density could be through the molten metal of the bath 40 at the same site. If there is an increase in bath mass 40, e.g. by adding more molten coating metal to the bath, the increased mass initially causes the lower part of the bath to descend to the lower part 43 of the container. When this occurs, a part of the space 110 formerly occupied by air (free space) is filled with the molten coating metal; consequently, the inductance (L) in the system decreases because the molten metal that has descended acts as a magnetic shield that reduces the passage of the magnetic flux in that part of the space 110 where the bath has descended. The decrease in flow protection at that site, and the total flow through space 110 and a decrease in the total flow produces a decrease in inductance. If the series LCR circuit of Figure 23 is operated so that the inductance (L) in the graph of Figure 25 is to the right of the vertical line marked "Resonance", a decrease in inductance (L) will produce an increase in current (I). This, in turn, will increase the total flow through the space 110, thereby increasing the magnetic force acting to push up the bottom of the bath 40. As a result, a system employing an LCR circuit in series of Figure 23, and which is operated in a manner described above, is self-adjusting to compensate for a drop in the bath bottom 40. The continuous strip 32 is typically a flat thin planar element, eg, a steel sheet. However, a strip having the configuration described in the preceding paragraph is only illustrative of a type of continuous strip with which the present invention can be put into practice. Other strip configurations such as rods, rods, wires, tubes and configurations can be employed as long as the escape of the molten coating metal from the hot dip coating bath can be minimized in accordance with the present invention.

The present invention has been illustrated in the context of the opening of the passage of the strip that lies below the container containing the molten metal coating bath. However, the present invention can also be employed in a system wherein (i) the passage opening of the strip is placed on the side wall of the container and (ii) the container contains a coating bath of molten metal having a surface top placed above the level of the opening of the strip passage. The foregoing detailed description has been provided for reasons of clarity of understanding only and unnecessary limitations should not be understood as the modifications will be apparent to those skilled in the art.

Claims (32)

CLAIMS:

1. A system for hot dip coating a steel strip, the system comprises: an elongate trough vessel for retaining a molten metal coating bath; the container has a pair of opposite side walls extending in the longitudinal direction of the container and a pair of opposite end walls; the container has a relatively broad top and a relatively narrow bottom; the side walls converge in a downward direction towards the bottom; the container has an elongated opening in the bottom of the lower part; means for moving a steel strip along a path extending in a downstream direction through the lower opening and through the bath; and an electromagnet positioned along the container comprising a means for preventing leakage through the opening of the volume of the molten metal from the bath; - - the electromagnet comprises a pair of opposed pole members each composed of magnetic material and each positioned along a respective side wall of the container; the pole members have polar faces facing each other; and each of the pole faces is positioned adjacent a respective side wall of the container in an essentially narrow abutting relationship with that side wall in the bottom of the container and that part of the side wall converging towards another side wall; each of the pole faces has a contour essentially following the contour of the adjacent side wall along that part of the side wall converging towards the other side wall and along the bottom of the container.

A system according to claim 1, wherein the electromagnet provides a volume container of the molten metal but allows another escape of the molten metal from the bath through the lower opening, the system further comprising: a means for reducing the escape of the molten metal that is allowed by the electromagnet.

3. A system according to claim 1, wherein the electromagnet comprises a means for stirring the bath and the system comprises; a means to dampen the agitation produced by the electromagnet.

4. A system according to claim 3, wherein the damper means comprises: a plurality of essentially parallel pairs of planar members; the pairs of flat members are vertically spaced along the path of the strip and extend through the bath, in a direction transverse to the direction of the path of the strip; each of the pairs of planar members defines a slot therebetween; the slot is aligned with the slot defined by each of the other pairs of flat members, to allow the passage of the strip through the slots as the strip moves along its path.

A system according to claim 4, wherein: at least some of the flat members are placed within the container between the side walls of the container that converge downward and have respective lateral dimensions, in a direction extending between the side walls that decrease progressively in a downward direction.

A system according to claim 4, wherein there is a space between two polar faces facing each other and wherein: the pairs of flat members are placed in the space and between the converging side walls of the container; and at least one pair of flat members are composed of ferromagnetic material to reduce the effective space between the pole faces.

7. A system according to claim 6, wherein: the pair of ferromagnetic planar members is positioned adjacent to the narrow bottom of the container.

8. A system according to claim 1, wherein there is a space between two polar faces facing each other and wherein the system comprises: means for reducing the effective space between the mutually oriented pole faces.

9. The system according to claim 8, wherein the container comprises an internal surface in each of the side walls of the container and a space reducing means comprises: a pair of separate flat elements arranged horizontally each remaining in the same plane and each extending from a respective internal side wall surface through the container to the other flat element, in a direction transverse to the direction of the strip path; the flat elements define a space between them; the trajectory of the strip extends through the space between the flat elements; and the pair of planar elements is placed in the space and between the converging side walls of the container; the flat elements of ferromagnetic material being composed.

A system according to claim 1, wherein: the narrow bottom of the container includes a passage extending downstream from the lower opening; the passage is defined by a pair of opposite longitudinal sides and a pair of opposite ends each extending between the sides of the passage; each end of the passage is separated from the adjacent end wall of the container; and the container comprises a dam or dam at each passage end; each dam extends upwardly from the end of the passage and laterally through the interior of the container between the opposite side walls of the container.

A system according to claim 10, wherein the container comprises: a sump at each end of the container between an end wall of the container and the adjacent dam or dam.

12. A system according to claim 11, wherein: each of the sinks comprises a means for restraining a puddle of molten metal.

13. A system according to claim 1, wherein: the electromagnet comprises a means for generating a magnetic field extending between the polar faces facing each other; the system comprises a means for providing an electric current having a portion of (i) flowing along the bottom of the bath, in the longitudinal direction of the container, and (ii) cooperating with the magnetic field generated by electromagnet to produce a magnetic force that pushes the bath of molten metal away from the lower opening; the system comprises an electrical current conductor that defines a low resistance conductive path that is to be followed by that part of the electric current other than the portion thereof that flows along the bottom of the bath,

14. A system of confounding with claim 13, wherein the narrow bottom of the container includes a passage extending downstream of the lower opening; the passage is defined by a pair of opposite sides and a pair of opposite ends each extending between the sides of the passage; each end of the passage is separated from an adjacent end wall of the container; the container comprises a lower wall portion extending between one end of the passage and the adjacent end wall of the container; and the current conductor further comprises a means for directing the electric current to the end space between (a) a passage end and (b) the adjacent end wall of the container.

15. A system according to claim 14, wherein: the electromagnet comprises a coil means, the system comprises a means for flowing an electric current that varies with time through the coil means to generate the magnetic field; and the electromagnet comprises a means, which responds to the flow of the current that varies in time through the coil means, to generate a magnetic field that flows through the bath of molten metal between the oriented pole faces and in turn generates currents parasites in the bathroom that include the portion of current that flows along the bottom of the bathroom.

16. A system according to claim 15 wherein: the current conductor comprises a means for substantially reducing the flow of eddy currents along the top of the bath. - -

17. A system according to claim 15 wherein: the current conductor is composed of an electrically conductive material; the current conductor comprises a pair of arms each placed adjacent to a respective end wall of the container; each arm connects conductively with the other arm; and the current conductor comprises a pair of terminal end portions each connected to a respective arm and each located within a respective end space of the container, above the lower wall portion of the container, and in electrical contact in the bathroom in that place.

18. A system according to claim 17, wherein: each of the arms includes a portion that is placed inside the container; and the system comprises a means for isolating electrically and thermally in the arm portion from the molten metal bath.

19. A system according to claim 17, wherein: both of the arms are placed outside the container; and the current conductor comprises a connection portion extending from each terminal end portion through a wall of the container, to a respective arm.

20. A system according to claim 17, wherein the terminal end portion is composed of copper, the coating metal is zinc, and the system comprises: a means to prevent the copper in the terminal end portion from being metallurgically combined with the zinc in the molten metal coating bath.

A system according to claim 20, wherein the prevention means comprises: means for cooling the terminal end portion to solidify the coating metal around the terminal end portion to protect the terminal end portion against erosion by the molten coating metal in the bathroom.

22. A system according to claim 21, wherein the cooling medium comprises: - 5 - an internal channel within the terminal end portion; and a means for flowing a cooling fluid through the internal channel.

23. A system according to claim 14, wherein: the electromagnet comprises a coil means; the system comprises a means for flowing the direct current uninterruptedly through the coil means to generate a magnetic field flowing through the bath between the facing pole faces; the current conductor comprises a pair of terminal end portions each placed within a respective end space of the container, above the lower wall portion of the container and in electrical contact with the bath therein; and the system comprises means for connecting each of the terminal end portions with a direct current source.

24. A system according to claim 14, wherein: the container comprises a dam at each end of the passage; - each dam extends towards the end of the passage and laterally through the interior of the container between the opposite side walls of the container; the container comprises a sump at each end of the container between an end wall of the container and the adjacent dam; the sump comprises a means for restricting a puddle of molten coating metal; and the current conductor comprises a pair of terminal end portions each placed within a respective container sump, above the portion of the bottom wall of the container, and in electrical contact with the puddle of molten metal in the sump. .

25. A system according to claim 1, wherein the mutually oriented pole faces push the steel strip to undergo a side-to-side movement as the strip moves along its path through the container, and the system comprises: a means for maintaining the steel strip moving along the trajectory, essentially - - centered between the mutually oriented pole faces and for restricting the side-to-side movement of the steel strip as it moves through the container.

26. A system according to claim 25 wherein the steel strip has a pair of opposite edges and wherein: the narrow bottom of the container includes a passage extending downstream from the lower opening, the passage being defined by a pair of opposed longitudinal sides and a pair of opposite ends each extending between the sides of the passage; each end of the passage is separated from an adjacent end wall of the container; and the means for maintaining the essentially centered steel strip comprises a pair of horizontally oriented mutually oriented notches each placed at a respective end of the passageway; each notch comprises means for engaging a respective edge portion of the steel strip moving along the path.

27. A system according to claim 1, and comprising: a means, including the electromagnet, to exert an ascending magnetic force in the lower part of the bath; a coil for each of the pole members of the electromagnet, an electric circuit in series that includes the coils; the series circuit comprises a source of electrical energy and a capacitor means connected in series with the coils; the circuit has a fixed capacitance, a fixed resistance and an inductance; the circuit comprises a means that enables the circuit to be operated close to its resonance; the circuit comprises a means, which responds to the operation of the inductance slightly greater than the inductance produced by the resonance in the circuit, to increase the current to the coils when there is a drop in the level of the lower part of the molten metal bath, to thereby increase the ascending magnetic force in the lower part of the bath. - -

28. A system according to claim 1, wherein the electromagnet surrounds the container and comprises: an outer member composed of magnetic material comprising a pair of opposite oriented longitudinal side walls each having a pair of opposite ends, and a pair of end walls each extending between the corresponding ends of the side walls; the side walls and the end walls define a vertically placed space having upper and lower open ends for receiving the container; each of the pole members of the electromagnet is mounted on a respective side wall of the outer member within the vertically placed space; each of the pole members extends inwardly, into the space towards the other pole member and terminates on a respective face of the mutually opposite oriented pole faces; the pole faces define a space therebetween to accommodate the container; and a pair of coils for conducting the electric current, each of the coils comprises a respective member of the pole members; each coil comprises a means that responds to the flow of electric current through the coil, to generate a magnetic field within the pole member encompassed by the coil.

29. A system according to claim 28, wherein the electromagnet comprises: a means, including the pole members and the outer member, to provide a path along which the magnetic field extends from the face of pole in one pole member through the space towards the pole face and in the other pole member, then in sequence through the other pole member through the longitudinal side wall where the other pole member is mounted to through the end walls in the outer member, through the longitudinal side wall where a pole member is mounted, and then through a pole member again towards a pole face.

30. A system according to claim 28, wherein: the electromagnet is composed of two halves each elongated in the direction of elongation of the container; Each half has a horizontal cross-section in the shape of an "E". 1 - . 1 -

31. A system according to claim 1, wherein: the container is composed of refractory material.

32. A system according to claim 1 wherein: the container is composed of non-magnetic stainless steel.