MXPA98007412A

MXPA98007412A - Hot immersion coating using a cooling metal cover refriger

Info

Publication number: MXPA98007412A
Application number: MXPA/A/1998/007412A
Authority: MX
Inventors: A Carter William; L Gerber Howard; Kolesnichenko Anatoly; G Saucedo Ismael; G Martin Philip; J Deegan James; W Sliwa Joseph
Original assignee: Inland Steel Company
Priority date: 1997-11-04
Filing date: 1998-09-11
Publication date: 1999-06-01

Abstract

A hot dip coating system comprises a molten coating metal bath contained in the container having an opening of the strip passage positioned below the upper surface of the bath. A metal strip is directed along the path extending through the passage opening of the strip and through the bath of the molten coating metal to coat the strip. A plug composed of solidified coating metal surrounds the strip downstream of the passage opening of the strip and is essentially stationary relative to the movable strip. The stopper prevents the escape of the molten coating metal from the bath through the opening of the bead passage while allowing the strip to move along its path. Records are provided for cooling the coating material downstream of the passage opening of the strip to form and hold the plug and to heat that part of the molten metal coating bath that is immediately downstream of the tap.

Description

"HOT DIP COATING USING A REFRIGERATED COVER METAL PLUG" BACKGROUND OF THE INVENTION The present invention relates generally to the hot dip coating of a? metal strip, such as a steel strip, with a coating metal such as zinc or aluminum, or alloys of each, and more particularly, with a hot dip coating process that dispenses with the need for one or more Submerged strip guide rollers beneath 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 resistance of the metal strip to corrosion or oxidation. One method for coating a 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 pretreatment of the steel strip before the strip is coated with a coating metal. The pre-treatment improves the adhesion of the coating of the steel strip, and the pre-treatment step can be either (a) a preliminary heating operation in a controlled atmosphere, or (b) an addition operation wherein the The surface of the strip is conditioned with an inorganic flux. When the steel strip has been subjected to preliminary heating in a controlled atmosphere, the strip can enter the hot dip coating bath at an elevated temperature which, in the case of a molten coating bath composed of zinc or copper alloy zinc, for example, can be at the same temperature as the molten metal coating bath (e.g., 450 ° C). When the pre-treatment step is a flux addition operation, the steel strip can enter the bath of the molten coating metal at a temperature ranging from room temperature to about 232 ° C, for example. Regardless of the pre-treatment step, the conventional hot-dip coating process employs a coating step carried out in a molten metal coating bath containing one or more submerged guide rolls to change the direction of the strip steel or otherwise guide the strip as you experience the hot dip coating step. More particularly, the steel strip normally enters the molten coating metal bath from a and moves in a direction having an essentially downward component, then passes around one or more of the submerged guide rollers which change the direction of the strip of 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 molten coating metal bath are raised. These problems are described in detail in Application Number 08 / 822,782 entitled "Hot Immersion Coating Method and Apparatus" and the description therein is incorporated therein by reference. Certain attempts have been made to eliminate the use of submerged guide rolls in the hot dip coating process. In these attempts, the steel strip is introduced into the molten coating metal through a passage opening of the strip in the container containing the bath; the opening is positioned below the surface of the bath, and the strip is directed through the opening through the bath along the straight line path, which may be either essentially vertical or essentially horizontal.

Driving a strip through the bath along the straight line path eliminates the need for submerged guide rollers to change the strip direction as it passes through the bath. The opening of the strip passage is typically placed in the lower part of the container containing the bath, or in a side wall of the container below the bath surface, and means or records are employed to prevent the 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 strip as it moves downstream through the opening, causing the seal to wear or break, which in turn causes the molten metal to escape through the seal. opening. Other problems associated with mechanical seals include large thermal gradients in the coating metal bath between seal location and downstream locations, freezing bath, quality problems with strip coating and irregularities in the thickness of the seal. coating on the strip. Other records employ electromagnetic devices which are placed adjacent to the passage opening of the strip and which develop electromagnetic forces that push the molten metal in the bath away from the opening. When electromagnetic devices are used to contain the molten metal in the opening, discarding is not a problem (as it is with mechanical seals). Some electromagnetic devices prevent the escape from the molten metal bath of the overwhelming majority of the molten metal in the bath (bulk container, but there is still some escape or dripping of the molten metal from the bath through the opening of the strip passage , particularly along the edges of the opening.In some cases, the bulk container may be approximately 98 percent or more, but in all cases, the exhaust is the least of a significant nuisance if not a major problem. .

COMPENDIUM OF THE INVENTION The present invention is directed to a hot dip coating process that (1) provides all the benefits that accompany the removal of submerged guide rolls, (2) eliminates the need for mechanical seals and (3) not only obtains a container bulk of the molten coating metal in the bath but also prevents the leakage or dripping of the molten coating metal through the passage opening of the strip. This is achieved by forming a bath plug, composed of a solidified coating metal from the bath. The plug extends downstream from the passage opening of the strip, surrounds the strip at a location immediately downstream of the opening, and is practically stationary relative to the strip. The plug prevents the escape of molten metal from the bath through the opening while allowing the strip to move through the bath. The related process comprises cooling the metal of the container, immediately downstream of the passage opening of the strip, to form the plug and to hold the plug as the strip undergoes the coating. The process further comprises heating the molten metal bath at a site downstream of the plug. One function of the heating step is to control the size (length) of the stopper and maintain a relatively stable bath temperature, among other things. The container employed in the present invention has (i) a relatively narrow part extending downstream from the passage opening of the strip and (ii) a relatively wide portion placed downstream of the narrow part. The plug extends from the strip passage opening to the narrow part, and the heating step is carried out immediately downstream of the plug. The controls are exerted to control the cooling effect produced by the cooling passage and to control the heating effect produced by the heating step so that the amount of heat introduced into the bath by the heating step compensates for the amount of heat It is removed from the bath by the cooling passage. The cooling effect of the cooling passage and the heating effect of the heating step are balanced to keep the bath temperature relatively stable, which is important. The heating step also compensates for various heat losses due to factors other than the cooling effect of the cooling passage. The various heat losses include heat losses from the molten metal bath towards the walls of the vessel containing the bath to the atmosphere. When the container is composed of refractory material, the various heat losses may be so minor that they can be ignored. In one embodiment, the cooling passage uses, as the cooling medium, the strip and the movement of the strip through the bath. The effect of coolant is influenced by the speed at which the strip moves through the bath, and by the temperature of the strip. The desired refrigerant effect is achieved by providing the strip with a temperature considerably below the melting temperature of the coating metal as the strip enters the passage opening of the strip. Preferably, the cooling effect is controlled by controlling the temperature of the strip as it enters the passage opening of the strip, while maintaining the velocity of the strip essentially unchanged. In another embodiment, the cooling passage uses, as the cooling medium, a cooling element placed immediately downstream of the passage opening of the strip. In this embodiment, the strip moves through a passage in the cooling element, which is in fact an extension upstream of the container containing the molten coating bath, and the passage opening of the strip towards the bath is at the end upstream of the passage in the cooling element. The cooling element is provided with a plurality of cooling channels through which a cooling fluid can be circulated. A cooling fluid is circulated through the cooling element, and the cooling effect produced by the cooling element is controlled, by controlling the number of cooling channels through which the cooling fluid is circulated. There are a number of embodiments of the heating step that are employed in the present invention. One of these embodiments employs an electromagnet to generate a magnetic field that extends through the coating bath immediately downstream of the plug; this mode not only heats the bath, but also, (a) provides a magnetic levitation effect that aids the bulk container of the bath and (b) shakes the bath, which can be beneficial. Another embodiment of the heating step employs induction heating at a site immediately downstream of the plug. A third embodiment employs resistance heating elements to provide conduction of heating at a site immediately downstream of the plug. Other features and advantages are inherent in the method and equipment claimed and disclosed or will become 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 of a hot dip coating system in accordance with one embodiment of the present invention; Figure la is a functional diagram illustrating the speed and tension controls of the strip coated by the system; Figure 2 is an enlarged vertical sectional view of a portion of the system of Figure 1; Figure 3 is a fragmentary cross-sectionally representative view of a hot dip coating system according to another embodiment of the present invention; Figure 4 is a fragmentary end view, partially in section, and partially recessed of a portion of the system of Figure 3; Figure 5 is a fragmentary vertical sectional view of a portion of the system of Figure 3; Figure 6 is a fragmentary horizontal sectional view taken along line 6-6 of Figure 2; Figure 7 is a fragmentary horizontal sectional view taken along line 7-7 in Figure 5; Figure 8 is a perspective view of a container for retaining a molten metal coating bath for use in a system in accordance with the present invention; Figure 9 is a perspective view of the container of Figure 8, in an inverted position; Figure 10 is a side elevational view of the separable half of the container of Figures 8-9, showing the interior of the container; Figure 11 is a vertical section of the container taken along line 11--11 in Figure 10, but showing the two halves of the container joined together; Figure 12 is a vertical sectional view similar to Figure 11 and taken along line 12-12 of Figure 10; Figure 13 is a perspective view of an electromagnet for use in the hot dip coating system according to the present invention; Figure 14 is an end view, partially in section, of a portion of the electromagnet of Figure 13; Figure 15 is an end view similar to Figure 14, showing a modified version of the electromagnet portion illustrated in Figure 14; Figure 16 is a horizontal sectional view taken along line 16-16 in Figure 13; Figure 17 is a perspective of a refrigerated element used in the embodiment of the system illustrated in Figures 3-5; Figure 18 is a vertical sectional view illustrating a variation of the equipment shown in Figures 4-5; Figure 19 is a vertical sectional view similar to Figure 18, showing yet another variation of the equipment shown in Figures 4-5; Figure 20 is an enlarged fragmentary vertical sectional view, showing a further variation of the equipment shown in Figures 4-5; Figures 20a and 20b are fragmentary vertical sectional views showing the alternative arrangements for a part of the variation of the equipment shown in Figure 20; Figure 21 is a flow diagram illustrating a fluid cooling arrangement for the cooling element used in the embodiment of Figures 3-5; Figure 22 is a fragmentary elevation view, partly in section, showing a mechanical gate or lower seal for use with a system of the present section; Figure 23 is a fragmentary end view, oriented in a direction opposite to that of Figure 22, and showing the gate of Figure 22; Figure 24 is an enlarged fragmentary vertical sectional view showing a part of the gate; Figure 25 is an enlarged fragmentary horizontal sectional view of a part of the gate; Figure 26 is an enlarged fragmentary vertical sectional view of another part of the gate; Figure 27 (sheet 14) is a fragmentary, vertical sectional view similar to Figure 5; and Figures 28 and 29 are longitudinal sectional views of the container illustrating diagrammatically the different types of stirring streams in the coating bath.

DETAILED DESCRIPTION Referring initially to Figure 1, which is generally illustrated at 30 and one embodiment of a 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 to coat a strip of continuous metal with other coating metals such as aluminum, aluminum alloys or the like. The 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 2, a continuous steel strip 32 is unwound from a coil 33 and subjected to a pre-treatment operation in a pre-treatment apparatus indicated generally at 34. The pre-treatment in this case includes the application to the strip 32 of a flux to facilitate the hot dip coating of the zinc towards the steel strip 32. This pre-treatment will be discussed in greater detail later. After the pre-treatment, the strip 32 is guided by the guide rollers 36, 37 along a path extending through an opening 43 of the strip towards the bottom of a container 38 containing a bath 40 of molten metal coating, in this case, zinc. The bath 40 has an upper surface 41, and the passage opening 43 of the strip 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 then moves along a path extending through the bath 40. The movement of the strip 32 through the bath 40 covers strip 32 with a layer of the coating metal of which the bath 40 is composed, and a strip 31 of coating leaves 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 upwardly after passing through the bath 40. Placed above the container 38 is a pair of so-called air blades 44, 44 ( Figure 1) of a tube of the type conventionally used to control the thickness of the coating on the strip 31, eg, directing jets of heated or unheated air or nitrogen against the strip 3L. Positioned downstream from the air blades 44, 44 is a winding reel 39 in which the coated strip 31 is rewrapped in a reel 35 which is capable of being removed from the reel 39. An important part of the coating system 30 Hot Dipper is a stopper 46 (Figure 2), composed of coating metal solidified from bath 40 and surrounding strip 32 at a site immediately downstream of container opening 43 (Figures 2 and 6). The cap 46 fills the space between the strip 32 and an upstream portion 58 similar to a vertically placed, narrow neck of the container 38. The plug 46 is essentially stationary relative to the movable strip 32. The plug 46 comprises the structure for preventing the escape of the molten metal from the bath 40 through the opening 43 while allowing the strip 32 to move through the bath 40. An additional file in the form of a mechanical gate or seal , is employed at the beginning of the hot dip coating operation to prevent the escape of the molten metal from the bath 40; this will be described later. The system 30 includes records for cooling the metal within the container 38 downstream of the opening 43 to form the stopper 46 and for maintaining the stopper as the strip 32 experiences the coating. The system 30 also includes a file for heating the molten metal bath 40 at location 47 immediately downstream of the plug 46. The object of the heating step will be described below. In the modality illustrated in Figure 2, the molten metal bath is heated in the room 47 of the bath by an electromagnet 50 which uses a current that varies in time (alternating current or direct pulsing current) to generate a magnetic field that extends through the bath 40 in the site 47, which is immediately in the water below the stopper 46. The flow density of the magnetic field generated by the magnet 50 is at a maximum at the site 47 of the bath because the clearance 110 between the faces 109, 109 of pole of magnet 50, it is narrower there. The magnetic field also extends through the free space between the pole faces 109, 109 at the sites above (ie, downstream of) the bath site 47, but the density of the flow is lower at the sites in downstream because the space is wider there; as the width of the space increases, the density of the flow decreases. The magnetic field also extends below (i.e., upstream of) the bottom 49 of the magnet 50, to heat at least the top portion of the plug 46. In addition, the heating record that is illustrated in Figure 2, there are other forms of records for heating the molten metal bath at site 47, in system 30; these other records will be described later in connection with the system illustrated in Figures 3-5. As mentioned above, in a hot-dip coating system, such as that illustrated in Figure 1, the strip is subjected to a pre-treatment operation at 34 where a flux is applied to the strip . When subjected to that kind of pretreatment, the strip 32 enters the bath 40 at a relatively cold temperature essentially below the temperature of the molten metal coating bath. Under those circumstances, the coolant passage forming a plug 46 employs a relatively cold strip 32 and the movement of the cold strip 32 through the bath 40 to provide the cooling effect. The cooling effect produced by the movement of the strip 32 through the bath 40 is influenced by the speed at which the strip 32 moves through the bath 40, and by the temperature of the strip. The desired refrigerant effect is achieved by providing the strip 32 at a temperature substantially below the melting temperature of the coating metal in the bath 40, at the time when the strip 32 enters the opening 43 of the passage of the strip in the container 38. Due to reasons to be discussed later, the cooling effect is preferably controlled by controlling the temperature of the strip 32 as it enters the passage opening 43 of the strip, while maintaining the speed of the strip essentially unchanged . The effect of coolant produced by the strip 32 not only forms and maintains the plug 46, but also, cools the bath 40. It is desirable to keep the bath 40 within a pre-selected temperature range above the melting temperature of a metal coating. When the bath 40 is composed of zinc (melting temperature of 420 °), the bath is maintained at a temperature up to about 500 ° C, e.g. a temperature within the range of 425 ° C to 470 ° C. The heat loss in the bath 40 produced by the strip 32 can be counteracted completely or in part by using different heating records downstream of the plug 46. In one embodiment of the present invention, the heat loss in the bath 40, due to the The effect of the coolant of the strip 32 is reduced by heating the strip 32 after the flux has been applied to the strip and before the strip enters the opening 43 of the passage of the strip. When this is done, care must be taken not to overheat the strip 32. The strip must still be at a temperature cold enough to form and maintain the plug 46; in addition, the strip must be at a temperature that does not interfere with the function that the flux will perform when the strip coated with the flux enters the bath 40. More particularly, the function of the flux is to remove the iron oxide from the surface of the steel strip when the strip enters the molten metal bath leaving a clean surface on the strip, to which the coating metal will adhere better. A mechanism involved in the cleaning operation is the dissociation of the flux at a temperature of the molten coating bath to produce a compound that performs the cleaning function. At the temperature of the molten coating bath, the dissociation of the flux is complete during the relatively short time in which the movable strip remains in the bath. At lower temperatures, dissociation requires a longer period of time at that temperature. When the dissociation occurs outside the bathroom, the flux is completely or partially ineffective. Therefore, if the strip is heated, before entering the bath to reduce the heat loss through the bath due to the effect of the strip coolant, a temperature of the strip to which the flux will dissociate must be avoided. through the period of time preceding the entrance of the strip into the bathroom. For a given flux, the time during which the flux will remain stable at a certain temperature (that is, the time before the flux is dissociated) that information that can be obtained from commercial flux suppliers.

Heating the strip to reduce heat loss through the bath is easier than heating the bath to compensate for the heat loss caused by the unheated strip (or to a lesser extent heating). In summary, it is desirable to heat the strip after the flux has been applied at a rapidly elevated temperature as long as that temperature (a) allows the refrigerant effect required to form and maintain the plug, and (b) prevent the dissociation of the flux during the time preceding the entrance of the strip in the bathroom. The file used to adjust the temperature of the strip 32 when it undergoes a pretreatment involving the application of the flux, in accordance with the modality of Figure 1, will be discussed later. As mentioned above, the cooling effect can also be influenced by the speed with which the strip 32 moves through the bath 40. Increasing the speed of the strip increases its cooling effect at a given strip temperature and the Decreasing the speed of the strip decreases its cooling effect. The mechanism for controlling the speed of strip 32 will now be described with reference to Figure la.

The strip 32 is unwound from the coil 33 by a flange 67 placed between the pretreatment apparatus 34 and the container 38. The coil 33 is mounted on an unwinding reel 68 which can be associated with a brake or with a driving motor which acts as an impeller or brake for the reel. The flange 67 is rotated by a rotor 68, the speed of which is controlled by a speed control device 69. The flange 67 tightens the strip 32. The speed of the strip 32 is controlled by the flange 67 as the motor 68 and the speed control device 69. Placed downstream of container 38 there is a so-called oscillating roller 71 and a second flange 72 which is rotated by a motor 73, the speed of which is adjusted by a speed control device 74. The oscillating roller 71 and the second flange 72 cooperate to maintain attention in the strip 32 downstream of the container 38. As mentioned above, the coil 35 composed of the coated strip is rotatably mounted on a winding reel 39. The reel 39 is driven by a motor 75 and the motor 75 and the reel 39 pull through the middle of the strip 32, against the second flange 72. The oscillating roller 71 rests against the strip 32 from above and is provided with a counterweight to form a cavity in the strip. The vertical position of the oscillating roller 71 is detected and used to control the speed of the second flange 72 in order to maintain the proper tension in the strip 32, downstream of the container 38. The equipment described above for controlling the speed and tension of strip 32, is conventional and is known to those skilled in the art of operating continuous hot dip coating systems (or other continuous strip treatment systems). As mentioned above, the speed of the strip 32 is determined by the speed of the flange 67 and the motor 68, and the speed of these is controlled by the speed control device 67. The device 67 can be operated manually or automatically in response to the temperature detected in the bath 40, e.g. at site 47 (Figure 2) or in response to a combination of (a) the temperature detected in bath 40, and (b) the temperature of strip 32 as it enters vessel 38 through opening 43 step of the strip. Related temperatures can be detected using conventional temperature sensing devices to measure the temperature at the bath site 47 (and / or elsewhere in the bath 40) and to measure the temperature of the strip 32 below the opening 43 bottom of the container 38, for example. Even when adjusting the speed of the strip 32 can change the cooling effect produced by the strip, changes in the speed of the strip can have undesirable side effects.; these include subjecting strip 32 to uneven heat treatment upstream of bath 40 (when the system of Figure 3 is employed) and producing uneven coating weights along the length of the strip. The preferred method for controlling the cooling effect of the strip 32 is to select a desired strip speed due to reasons other than the cooling effect of the strip and then adjust the cooling effect by adjusting the temperature of the strip, while maintaining the strip speed 32 essentially unchanged. The temperature of the strip is adjusted upstream of the container 38, using the conventional strip heating and / or cooling apparatuses. As mentioned above, the bath site 47 is placed immediately downstream of the plug 46, and a heating effect there is produced by the electromagnet 50, or by some other heating file to be described later. In accordance with the present invention, the heating effect produced at the bath site 47 is controlled so that the amount of heat introduced into the bath by the heating step compensates for the amount of heat that is removed from the bath by the cooling step which, in the specific embodiment that is now being described, is controlled by controlling the temperature of the strip 32 while maintaining the velocity of the strip essentially unchanged. To the extent necessary, the heating step also compensates for various heat losses from the bath. In all the embodiments of the present invention, the various heat losses are relatively insubstantial (if not insignificant) compared to the amount of heat removed from the bath by the cooling effect. The cooling effect of the cooling passage and the heating effect of the heating step are balanced to keep the bath temperature 40 relatively stable. When the molten metal coating bath is composed of zinc, it is desirable to maintain the bath at a temperature of above 420 ° C (the melting temperature of zinc) up to about 500 ° C (eg a temperature within the range of 435 ° C to 470 ° C). Maintaining the bath at a relatively stable temperature, such as a temperature within the scales described in the previous paragraph (when the bath is zinc) - maintains plug 46 in a solid state and allows the plug size to be controlled and excessive plug growth prevented; This will be discussed in more detail below. The heating effect produced on the site 47 of the bath, which is immediately downstream of the plug 46, can be controlled by adjusting the resistance of the magnetic field generated there by the electromagnet 50. The magnetic field resistance can in turn be controlled by adjusting the current flowing through the coils associated with the electromagnet 50, these coils will be described in greater detail later in connection with a detailed description of the electromagnet 50. In the embodiment of Figures 1-2, the bath 40 may be composed of an alloy consisting essentially of zinc with an amount small (eg 0.2 percent) aluminum. A bath composed of this alloy has a melting temperature slightly lower than 420 ° C. The plug 46 has a temperature that is below the melting temperature of the bath 40 and above the temperature (eg 40 ° C) at which the strip 32 enters the container 38 through the opening 43 of the passage of strip. The plug 46 prevents escape of the molten coating metal from the container 38 through the opening 43 in the passage of the strip. With the embodiment of Figures 1-2, if the strip 32 enters the passage opening 43 of the strip at a temperature of about 120 ° C or higher, it may be difficult to keep the plug 46 in a condition in which the plug prevents the escape from the bath 40. Unless otherwise indicated, the bath and strip temperatures discussed herein are in the context of the bath 40 which is composed of an unalloyed zinc or the zinc alloy which is described in the previous paragraph. The cap 46 exerts a drag or friction on the strip 32 as the strip moves through the plug, and the frictional drag exerted by the plug 46 can be reduced by decreasing the length of the plug 46 (i.e., decreasing the vertical dimension of plug 46 in Figure 2). The length of the stopper can be determined by measuring the temperature of the stopper at a site near the end downstream of the stopper. The colder the temperature of the plug at a determined downstream plug site, the longer the plug will be. This will be discussed in greater detail subsequently. The length of the plug, and the drag or friction exerted by the plug, can be decreased by reducing the cooling effect produced by the strip 32 which in turn requires either reducing the speed of the strip 32 or increasing the temperature of the strip. strip 32 as it enters the passage opening 43 of the strip, or a combination of the two. The length of the plug 46 can also be decreased by increasing the heating effect produced by the electromagnet 50 with the room 47 of the bath which in turn is increased by increasing the electric current used to energize the electromagnet 50. The appropriate combinations of (a) speed of the strip, (b) the temperature of the strip, and (c) the heating effect produced by the electromagnet 50, in order to decrease the length of the plug 46 or to increase its length, can be determined empirically; preferably, the speed of the strip is essentially unchanged and adjustments are made to (b) or (c) or both. The container 38 will now be described in greater detail with reference to Figures 2 and 8 to 12. As seen in Figure 2, the container 38 has a vertical cross-section in essentially a funnel shape, which is taken along a vertical plane perpendicular to the plane of the strip 32. Also, as shown in Figure 2, the container 38 has (i) a relatively narrow part 58 that extends downstream from the opening 43 and (ii) a relatively large part 59. wide placed downstream of the narrow part. The plug 46 extends from the opening 43 to the narrow part 58. Referring now to Figures 8 to 12, 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 a container 38 in the form of an elongated trough having an open upper end 42 and a passage opening 43 of the strip, similar to a slot placed in the lower part of the container (Figure 9). ). The container 38 has a pair of longitudinal side walls 55, 55 and a pair of end walls 56, 56 each of which extending between the ends of the side walls 55, 55. The side walls 55, 55 define the cross section Vertical funnel shape shown in Figures 2 and 11-12. The container 38 and its funnel-shaped cross-section include the relatively narrow lower portion 58 mentioned above and the relatively wide upper portion 59. A portion 60 of the intermediate 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 portion 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 10 illustrating the interior of the container 38, the passage opening 43 of the strip is defined by a pair of sides 63, 63 (only one of which is shown in Figure 10) and an end pair 64, 64. Referring again to the pre-treatment apparatus 34 (Figure 1), this apparatus can be of the type conventionally used to apply the flux to a strip 32 of continuous steel, before hot-dip coating the strip with zinc. More particularly, the apparatus 34 comprises an alkali cleaning section 85 followed by a rinse section 86 in turn followed by an acid stripping section 87, followed by a rinse section 88, followed by a section 89 where it is applied the flux, after which the strip is passed through a drying section 90 which employs induction heating or hot forced air heating, for example. The strip is directed through the apparatus 34 by the upper and lower guide rolls 91, 92, respectively.

The heating in section 90 is used to dry the flux on the strip and optionally to heat the strip. The heating in section 90 is controlled in a series of examples so that the temperature of the strip 32 as it enters the opening 43 of the passage of the strip in the container 38 is substantially lower than the melting temperature of the metal of the strip. melted coating in the bath 40. In one example, the strip 32 enters the opening 43 of the passage of the strip at a temperature of about 38 ° C even though higher temperatures may be employed. As mentioned above, in the embodiment illustrated in Figures 1-2, the strip 32 must be maintained at a temperature of less than about 120 ° C in order to maintain the plug 46 in a state in which the plug prevents escape of the metal of cast coating from the bath 40, through the opening 43. When a strip temperature of less than about 120 ° C is employed, there are no problems of dissociation with the fluxes conventionally employed to coat the steel strip with zinc when employed the coating method of Figure 1. If necessary, a cooling step employing conventional cooling records can be placed upstream of the opening 43 of the strip passage and downstream of the apparatus 34, to ensure that the strip 32 enters the opening 43 at a temperature low enough to provide the desired cooling effect. In one embodiment, there is associated with the system 30, downstream of the opening 43 of the strip passage both a heating step and a cooling step each employed as necessary to ensure that the strip 32 enters the opening 43 from the passage of the strip to the desired temperature. The heating step employs the heat produced to the drying section 90 of the pre-treatment apparatus 34, and if necessary also employs a supplementary heating section (e.g., an induction heater) downstream of the drying section 90. The electromagnet 50 will now be described in greater detail with reference to Figures 2 and 13 to 16. The electromagnet 50 comprises an outer rectangular member 100 composed of magnetic material comprising a pair of longitudinal side walls 101, 101 facing each other having an pair of opposite ends and a pair of end walls 102, 102 each extending between the corresponding sections of the side walls 101, 101. The side walls 101, 101 together with the end walls 102, 102 define an internal space 104 placed vertically having open upper and lower ends 105, 106, respectively. The electromagnet 50 also comprises a pair of pole member 108, 108, each composed of a 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 is opposite and faces the pole face 109 at the other pole member 108 (FIGS. 16). The faces 109, 109 of pole define a space 110 therebetween, to accommodate the container 38. As shown in Figure 14, each pole member 108 encompassing a coil 112 for conducting the electric current. In accordance with the present invention, a current that varies with time is flowed through each coil 112 to generate a magnetic field within the pole member 108, encompassed by the spool 112. The pole members 108, 108 and the external member 100 provide a path 116 for the magnetic field described in the previous paragraph. The flow path 116 is shown in dashed lines with arrows in Figure 16. More specifically, the magnetic field extends from a 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 and then through both the walls 102, 102 of end of the outer 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 that pole member. The direction of flow 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. As seen in Figures 3 and 16, the electromagnet 50 is composed of two and a half magnets 114, 114 each having a horizontal cross-section in the shape of an E. With reference to Figure 2, each pole face 109 of the member 108 The pole has a generally convex contour that follows the concave contour of the adjacent side wall portion 61 of the container 38. The distance between the mutually opposite oriented pole faces 109, 109 is smaller in that portion of the part. 58 of narrow vessel that is immediately downstream of the plug 46 and which corresponds to the site 47 in the bath 40. Because the space 110 of the pole face is shorter at that site, the magnetic field strength (density flow rate) is higher at that site compared to other bath sites downstream of plug 46. Therefore, for a given current flowing through coils 112, 112, the magnetic force exerted by the against the bath 40 by the electromagnet 50 is higher at the site 47 (immediately downstream of the plug 46) than at any other location in the bath 40 of molten metal. The horizontal magnetic field that is generated at the bath site 47 has a relatively high magnetic flux density. The magnetic flux induces parasitic currents that march in a path 117 of loops within the bath 40 (Figure 10). The path of the parasitic currents includes a portion 118 (Figure 10) extending horizontally in the longitudinal direction of the container 38 at the site 47 of the bath. The direction of the parasitic currents there is 90 ° C with respect to the direction of the magnetic flux there. As a result, the flow and parasitic currents intersect in the horizontal plane resulting in magnetic forces directed in an upward direction as seen in Figures 2 and 10. These forces push that part of the bath 40 which is immediately placed in water. down the plug 46 (at site 47) in an upward direction away from the plug 46 and away from the opening 43, that is, downstream as seen in Figure 2. The magnetic flux and eddy currents that produce the forces above-mentioned magnetics in the bath 40 (Figure 10) also cause agitation in the bath 40 in the form of stirring streams having portions that can flow through the top of the plug 46 and thatBy doing so, they can cause plug erosion, which is undesirable. More specifically, referring to Figures 28 and 29, these figures diagrammatically illustrate two types of different agitation currents that may occur in the bath 40, depending on the power at which the electromagnet 50 is operating and the flow it produces. in bath 40. At a relatively low flow magnet power, agitation in bath 40 may manifest as rolling agitation currents, which is representatively shown at 66 and Figure 29. Magnet energy and flow higher, the agitation in the bath 40 may manifest itself as - - sharp back-and-forth movements shown representatively in 65 of Figure 28. Still the highest magnet and flux energy (eg greater than 75 percent of the maximum energy in one embodiment) the agitation in the bath 40 again it manifests as rolling (66 in Figure 29). When rolling occurs (Figure 29) the erosion of plug 46 is relatively small; when sudden backward and forward movement occurs (Figure 28), the erosion of plug 46 increases considerably. If rolling occurs by operation at relatively low magnet energy and flow, the erosion of plug 46 can be reduced; however, the resulting magnetic field may be so weak as not to provide the required heating in that part of the molten metal bath at site 47 immediately downstream of plug 46, which is undesirable. Accordingly, a preferred way to control the erosion of plug 46 is to operate the magnet energy and flow above that which causes the action of sudden back and forth movements illustrated in Figure 28, and instead this results in the rolling action illustrated in Figure 29. Furthermore, the higher the magnet energy and the flow, the greater the levitation effect produced at the bath site 47 by the interaction of the magnet flux and parasitic currents there . Generally, the magnet energy (and flux) can be adjusted, adjusting the amperage of the current that varies with the time it takes to energize the magnet. The magnetic levitation in accordance with the present invention produces a force directed upwardly against the bath 40 at the bath site 47 to considerably relieve the downward pressure in the bath 40 in the plug 46, but still the contact between the bath 40 and the Upper of the plug 46. When the container 38 is composed of stainless steel, the molten coating metal retained at the site 47 has a cooling effect on the walls of the container 38 at site 47, absorbing a large amount of the heat generated by the magnetic field in that site. In the absence of molten coating metal there, the heat generated there by the magnet 50, could burn a hole in the wall of the stainless steel. The magnetic levitation (rising force) exerted against the molten metal bath part at site 47 is a factor in the bulk container of the molten metal bath. Without plug 46, the magnetic levitation described above could produce bulk container of bath 40 of about 98 percent or more when other expedients, which enhance the effect of magnet 50, are associated with the magnet. The bulk container due to magnetic levitation of the type described in the preceding paragraph may be satisfactory to prevent leakage through the opening 43 of the strip passage of most of the molten coating metal from the bath 40, but not it can prevent dripping or leakage down along the sides 63, 63 and the ends 64, 64 of the opening 43 (Figure 10). That function, however, is carried out by the plug 46. Referring now to Figure 14, the coil 112 in the pole member 108 is connected to a device 113 to vary the amperage of the current that varies with time introduced into the coil 112, thereby allowing the resistance of the magnetic field generated by the electromagnet 50 to be controlled. The coil 112 is composed of a multiplicity of coil turns 115 each extending around the pole member 108 and each composite of an appropriate conductive material such as copper. The turns 115 of the coil are insulated from one another and from pole member 108 with conventional electrical insulation material (not shown). In the embodiment illustrated in Figure 14, coil 112 is shown composed of solid wire; in the other embodiments, the coil may be composed of - copper tubing, for example through which the cooling fluid can be circulated. The electromagnet 50 is composed of a conventional magnetic material such as ferrite or electric steel laminations. Referring now to Figures 3 to 5, which are generally indicated at 130 in Figure 3. There is a hot dip coating system constructed in accordance with another embodiment of the present invention. Positioned upstream of system 130 (to the left of Figure 3) is the downstream portion 134 of the apparatus for subjecting uncoated strip 32 to a pre-treatment operation. The pretreatment to which the strip 32 of the embodiment of Figure 3 is subjected, subjects the strip to a reducing atmosphere (e.g. hydrogen) in the downstream part of the apparatus 134. This reducing atmosphere is maintained between the part 134 of the apparatus and the hot dip coating system 130 by a shell 135 extending from the part of the apparatus 134 to the hot dip coating system 130, in the manner shown in FIG. Figure 3. Placed inside the housing 135 are the guide cylinders 36, 37 for directing the strip 32 from the part 134 of the pre-treatment apparatus to the hot-dip coating system 130.

The pretreatment operation to which strip 32 is subjected at 134 and upstream there is a conventional treatment familiar to those skilled in the hot dip coating industry, and is used instead of applying a flux to strip 32 before entry of the strip into the hot dip coating bath. Referring now to Figures 4 and 5, the hot dip coating system 130 comprises a container 138 having a lower opening 149 upstream. Immediately positioned upstream of the container 138, in the lower opening 149, there is a cooling element 139 which constitutes an upstream extension of the container 138. The cooling element 139 contains an opening 143 of the passage of the lower upstream strip corresponding to the opening 43 of the passage of the strip in the container 38 of the system 30 (Figure 2). Extending downstream from the opening 143 of the strip passage is a strip passage 148 (in the partial recess in Figure 4) corresponding to the narrow part 58 of the container 38 in the system 30 (Figure 2). The passage 148 has a downstream end communicating with the lower opening 149 in the container 138.

In the system 130, the cooling passage is carried out by the cooling element 139 to produce a plug 146 that surrounds the strip 32 in the passage 148 of the strip (Figure 5). The plug 146 extends from the opening 143 of the strip passage downstream in the passage 148 of the strip to the lower opening 149 of the container 138. The plug 146 fills the space in the passage 148 not occupied by the strip 32, and the plug 146 is essentially stationary relative to the movable strip 32. The cooling element 139 forms and maintains the plug 146 while the strip 32 undergoes the coating in the bath 40 of molten metal, in order to produce the coated strip 31. The plug 146 prevents escape of the molten coating metal from the bath 40 through the passage opening 143 of the strip. An additional expedient, in the form of a gate or mechanical seal, is employed at the beginning of a hot dip coating operation to prevent the escape of the molten metal from the bath 40; this will be described later. The cooling element 139 is mounted to the bottom of the container 138 by an arrangement illustrated in Figure 4. Associated with the container 138 is an electromagnet 150 having a pair of pole members 208, 208 each mounting on the lower portion thereof, a bracket 140 carrying a connector 141 threaded in a "U" shape engaging within a circumferential groove 133 in a pin 142 extending outward from one end of the cooling element 139. The container 138 comprises a upper part 159 and a lower part 160 having side walls 161, 161 converging terminating in the lower part of the container 138. Unlike the container 38 in the system 30 (Figures 1-2), the container 138 does not have a lower portion similar to a narrow neck corresponding to the narrow part 58 in FIG. the container 38 (Figure 2). As mentioned above, the passage 148 in the cooling element 139 replaces the narrow part 58 in the container 38. Another difference between the apparatus of the system 130 and the apparatus of the system 30 is as follows: each pole member 208 of the electromagnet 150 in the system 130 is cut along its lower part at 162 to accommodate the cooling element 139 (Figures 4 and 15). In this regard, compare the first lower portion 49 of the pole member 108 of the electromagnet 50 (Figures 2 and 14) with the lower portion 162 at a cut-away angle of the pole member 208 of the electromagnet 150 (Figures 4 and 15).

In the embodiment employing the system 130, the strip 32 enters the passage opening 143 of the strip (Figure 5) at a temperature that corresponds essentially to the temperature of the molten metal coating bath 40 (eg 435 ° C to 470 ° C). Typically, strip 32 enters aperture 143 of the strip passage at a temperature of about 450 ° C. In the system 30 of Figures 1-2, the effect of coolant occurred as the strip 32 entered the passage opening 43 of the strip at a temperature considerably lower than the temperature of the molten metal coating bath 40. However, in system 130, strip 32 enters aperture 143 of the strip passage essentially at the same temperature as the molten metal coating bath; therefore, the strip 32 can not perform a cooling function in the system 130. Therefore, the cooling element 139 is employed to carry out that function. The discussion in the preceding paragraph assumes that the strip 32 has been heated in an upstream pre-treatment apparatus using a hydrogen reducing atmosphere, and that the strip has not undergone a significant cooling step after the pre-treatment. -training In another embodiment of the present invention, where strip 32 is pre-treated using a hydrogen reducing atmosphere, strip 32 is then cooled upstream of vessel 138 from a relatively high temperature at or above the bath temperature 40, to a relatively low temperature essentially lower than the bath temperature (eg, the temperature less than 120 ° C. At that low temperature, the strip 32 can act as a cooling medium (as does the strip in the embodiment of Figure 2), and the cooling element 139 need not be used The following discussion is directed to that embodiment of the present invention which does not employ the cooling element 139 to carry out the cooling function. wherein the cooling element 139 performs the cooling function, and some of the structural details of the cooling element 139, will be described now referring to Figures 4, 5 and 17. The cooling element 139 comprises two units 144, 144 of the cooling element each composed of a material, such as stainless steel, non-magnetic, which is a relatively good thermal conductor and which has a melting temperature considerably higher than the temperature of the molten metal coating bath 40. The cooling element can also be composed of a ceramic material that is sufficiently thermally conductive to carry out the cooling function. When assembled together, the half 144 of the cooling element is the mirror image of the other. The halves 144, 144 of the cooling element are maintained in separate relation by means of spacers 145, 145 (Figure 17) composed of refractory material and placed at opposite ends of the cooling element 139; the passage 148 of the cooling element is defined in the space between the two halves of the cooling element, intermediate to the end separators. Each half 144 of the cooling element has a first lower channel 151 through which a cooling fluid and a second upper channel 152 can circulate through which a cooling fluid can circulate. The first channel 151 _ is positioned relatively close to the opening 143 of the passage of the strip, and the second channel 152 is placed downstream of the first channel 151. The cooling effect produced by the cooling element 139 results from the circulation of the fluid cooling through channels 151 and 152. The cooling effect can be controlled by controlling the number of cooling channels through which the cooling fluid is circulated, and this will be described in more detail later. In the embodiment illustrated in the drawings, the cooling element 139 is shown as having two cooling channels, 151 and 152. One or more additional cooling channels can be provided if desired. In the embodiment of the system 130 illustrated in Figures 3 to 5, the bath is heated immediately downstream of the plug 146 by the electromagnet 150 which is essentially identical to the magnet 50 of the system 30, except for the part 162 recess at the bottom of the pole members 208, 208 as described above. The structure and function of the magnet 150 is essentially otherwise identical to the structure and function of the magnet 50, unless otherwise indicated. The mass of the plug 146 is determined by the length of the plug. The plug 146 must be of sufficient length to support the weight of the molten metal bath above the plug 146. If the plug is too short, it could be forced downwardly and outwardly of the lower opening 143 in the cooling element 139 by the weight of the molten metal bath that rests down against the plug 146. Also, if the plug is too short, the plug could be susceptible to melting - localized mainly due to the heat of the molten metal bath placed above the plug. On the other hand, if the plug 146 is too long, the plug friction against the surface of the strip 32 could create too much drag on the strip 32 as the strip moves downstream through the plug 146, and this is undesirable. This resistance to the advance increases considerably as the length of the plug 146 increases. It is desirable to maintain the drag at a relatively low level. In general, the length of the plug should be just long enough to ensure mechanical support of the weight of the molten metal coating bath above the plug to prevent localized melting. Any length greater than this is unnecessary and creates a resistance to further advancement which is undesirable. The length of plug 146 in a downstream direction from the opening 143 can be controlled by controlling the cooling effect produced by the cooling element 139 and controlling the heating effect produced by the electromagnet 150. By circulating a cooling fluid through from the bottom, the first cooling channel 151 of the cooling element 139 can be used to form the plug 146, and by circulating the fluid through the cooling. of the upper one, the second cooling channel 152 can be used to increase the length of the plug 146. Restricting the circulation of the cooling fluid through the second channel 152 will decrease the length of the plug 146. The heating effect produced by the electromagnet 150 in the site 147 of the bath immediately downstream of the plug 146, can also be used to decrease the length of the plug 146 thereby decreasing the drag resistance exerted against the strip 32 by the plug 146. In other words, the heating effect produced by the electromagnet 150 and the restriction of the circulation of the cooling fluid through the second channel 152, they cooperate to decrease the length of the plug 146. By controlling the heating effect produced by the electromagnet 150 of can also be used as a record to maintain the bath 40 at a stable temperature in system 130, just as an elec is used troimán 50 to do this in the system 30. In summary, the system 130 is controlled in order to provide the plug 146 with a sufficient length (a) to resist being pushed in an upstream direction by the pressure of the bath 40 placed in downstream of plug 146, and (b) to resist localized melting due to bath heat. In addition, the system is controlled to provide the plug 146 with a length short enough to avoid resistance to excessive advancement in the strip 32 as the strip moves downstream through the plug 146. Figure 21 is a diagram of flow illustrating an arrangement for circulating the cooling fluid through the cooling element 139 and for controlling the circulation of the cooling fluid. A tank 164 contains a cooling fluid, typically water at an ambient temperature. Connected to the tank 164, there is an output line 165 connected to the branch lines 167a, 167b, each of which leads to a half 144 of the cooling element. Each branch line 167a, 167b in turn communicates with a line 153 leading to a first lower fluid cooling channel 151 in a half 144 of the cooling element. The volume of fluid flowing through line 153 and channel 151 is controlled by valve 155 on line 153 and measured by a flow meter 154 on line 153. Also communicating with branch line 167a or 167b there is a line 156 leading to the upper second fluid cooling channel 152 in a half 144 of the cooling element. The flow of fluid through line 156 and second channel 152 is controlled by half 158 in line 156 and measured by the flow meter 157 on line 156. Connected with the first fluid cooling channel 151 is an output line 169 and connected to the second fluid cooling channel 152 there is an output line 170. The output lines 169, 170 join in downstream with withdrawal line 171. The temperature of the cooling fluid in the supply line 165 from the tank 164 is measured by a thermoelectric cell 166 in the line 165. The temperature of the fluid leaving the cooling element 139 is measured by a thermoelectric cell 172 in the line of Withdrawal 171. The plug 146 can be formed by opening the valves 155, 155, while the halves 158, 158 remain closed. The length of the plug 146 can be increased by opening the valves 158, 158 preferably to a fully open position. Valves 158, 158 partially open has a minor effect on the degree to which the length of the plug 146 increases. The length of the plug 146 may decrease to a degree by completely closing the valves 158, 158 to decrease the flow of the fluid through the cooling element; however, the effect of this expedient on decreasing the plug length is not as considerable as a considerable increase in the heating effect produced by the electromagnet 50 at the bath site 47. Generally, during operation of system 130, valves 155, 155 are fully open while valves 158, 158 may be closed, partially open, or fully open, depending on the length of plug 146 in channel 148, and of the need to increase or decrease the length of the plug 146. Also, as mentioned above, the length of the plug 146 can be decreased by increasing the heating effect produced by the electromagnet 150 at the site X47 of the bath immediately downstream of the plug 146 (Figure 5). In summary, various combinations of (i) increase or decrease of the heating effect from the electromagnet 150 and (ii) increase or decrease of the cooling effect from the cooling element 139 can be used to control the length of the plug 146. < The appropriate combination for a given set of operating conditions and parameters for system 130 can be determined empirically. The heating effect at the site 147 of the bath immediately downstream of the plug 146 can also be produced by other heating records illustrated in Figures 18 to 20, and these files will now be described.

In Figure 18, the heating file comprises resistance heating elements in the form of rods 175, 176, placed in the bath 40 at the site 147 of the bath, and adjacent thereto, to subject the bath to heating by conduction at site 147. Resistance heating elements are a commercially available expedient conventionally employed by those skilled in the art for heating molten metal baths. The heating file used in the Figure 19 is an induction heating element 177, positioned around that part of the container 138 that contains the room 147 of the bath. The induction heating element 177 comprises a coil 178 composed of a plurality of turns or loops 179 and a member 180 composed of magnetic material for concentrating, at the site 147 of the bath, the magnetic field developed by the coil 178. The member 180 Magnetic is composed of conventional magnetic material, eg, ferrite or electric steel laminations. The coil 178 is composed of copper. The turns of the spool 179 may be solid as shown in FIG. 19 or may be tubular to allow a cooling fluid to circulate through the turns of the tubular spool. The coil 178 and its coil turns 179 completely surround that part of the container 138 that contains the site 147 of the bath. A variation of the induction heating element 177 of Figure 19 is shown at 187 in Figure 20. The induction heating element 187 comprises a coil 188 composed of a plurality of turns 189 each composed of a plurality of wires 191, 191 connected together, for example by brazing to form a turn 189 of the coil having an elongated vertical cross section as shown in Figure 20. The heating element 187 also comprises a magnetic member 190 similar to the magnetic member 180 in Figure 19, and performs a similar function. Instead of the solid wires 191, 191 of which the turns 89 of the coil are composed, tubular elements (192 in Figure 20a) may be used, for example, made of copper, and brazed together in the manner that it is shown in Figure 20a. When the tubular elements 192 are used (Figure 20a) instead of the solid wires 191 (Figure 20) it is possible to be able to circulate a cooling fluid through the turns of the coil. Another variation of the turns or coils of the coil is shown at 193 in Figure 20b, where the coil turn 193 of the coil is composed of a single tube having an elongated rectangular vertical cross section. A configuration like that shown at 193 in Figure 20b facilitates circulation of the cooling fluid through the coil. The induction heating elements illustrated in Figures 19, 20, 20a and 20b produce a magnetic field at the site 147 of the bath which is sufficient to provide the desired heating effect but which is insufficient to produce a magnetic levitation effect in the room 147 of the bathroom. As mentioned above, the electromagnet 150 (Figures 4 and 5) can produce a magnetic levitation effect at the site 147 of the bath. Even though the induction heating records (Figures 19 and 20-20b) can not produce a magnetic levitation effect, they have an advantage in relation to the file of Figures 4-5, which employs the 150 electromagnet. Figures 4-5 can create an attractive force between the steel strip 32 and the magnetic pole members 208, 208 (Figure 5). If the strip 32 moves away from the exact center line between the pole members 208, 208, the attraction of the closest pole member increases, and this can make it difficult to keep the strip 32 centered. When the heating records are used for induction of Figures 19 and 20-20b, however, the displacement of strip 32 out of the exact center line is not a problem; in fact, the use of these induction heating records to provide the heating effect tends to keep the strip 32 centered between the two opposite sides of the heating element (e.g., 181, 182, in Figure 19). The heating records of Figures 18-20, 20a and 20b are illustrated in these figures together with the system 130 which uses the cooling element 139 to carry out the cooling effect and produce the plug. However, these same heating records can also be used with the system 30 where the desired cooling effect is carried out by the strip 32, and wherein the cooling effect is controlled by controlling the temperature and speed of the strip 32 as it enters the passage opening 43 of the strip. Figures 22 to 25 illustrate a mechanical gate or lower seal arrangement for use to prevent escape of the molten coating metal from the bath 40 through the passage opening of the strip in the absence of a solidified coating metal plug. That situation (absence of a plug) typically occurs at the beginning of a hot dip coating operation before the plug has been formed. The mechanical gate is also used when changing the width of the strip that is being coated. In this situation, the gate closes before the width of the strip is changed, and the plug then melts, e.g., discontinuing the cooling effect while continuing the heating effect; then a strip having a different width than the previously coated strip is pulled through the gate and the bath, the plug is refrozen and the gate then opens. The mechanical gate or lower seal arrangement will be discussed below in the context of container 38 and electromagnet 50, but a mechanical gate arrangement is not limited to that embodiment. Below the container 38 and the pole members 108, 108 of the electromagnet 50 is a frame 200 having a dependent flange 202 that is spaced apart from and parallel to the plane of the end wall 56 of the container 38.

(Figure 8). Associated with the narrow part 58 of the container 38, at the lower end of the narrow part 58, there is an elongated seal ring 202 that surrounds the lower end of the narrow part 58. Placed below the seal ring 202 there is a pair of gate members 204, 205 each in the form of an elongated seal bar having a triangular cross section. Referring to Figure 22, each gate member 204, 205 is mounted to move between (i) a closed position to prevent escape of the molten metal from the bath 40 through the opening 43 (solid lines) and (ii) an open position displaced from the closed position (dot and dash lines). Each gate member 204, 205 is connected to a respective carrier bar 207, 208 connecting the structure that will be described below. Each carrier bar 207, 208 is fixed to a respective link member 209, 210, each of which is carried by and mounted for pivoting movement with a respective pivot arrow 211, 212, each rotatably mounted on the frame 200. With reference to Figure 23, the link member 209 is pivotally connected at 216 to an intermediate link member 214 in turn pivotally connected to the link member 210 at 215. As a result of the link described in the previous paragraph, each link member in the pair 209, 210 will pivot in response to the pivoting movement of the other link member in that pair. A handle (not shown) is connected with either the arrow 211 or the arrow 212 to initiate the pivotal movement of the link members which in turn causes the arched movement of the stamp gate members 204, 205 between their positions closed and open. The manner in which the gate members 204, 205 are mounted on their respective bars 207, 208 will now be described with reference to Figures 22 and 26. This description is in the connection of the gate member 204 and its bar 207 carrier, it being understood that the same description is applicable to the gate member 205 and its carrier bar 208. The carrier bar 207 contains a recess 218 for receiving the head 219 of a shoulder bolt 220 that slidably extends through an opening 224 in the carrier bar 207 and toward a bore 221 in the gate member 204. The shoulder bolt 220 has a terminal end 222 that is fixed to the gate member 204 to fix the shoulder bolt to the gate member. A coil spring 223 is received in the bore 221 in the gate member 204, and abuts against the adjacent surface 228 of the carrier bar 207. The carrier bar 207 is fixed to its link member 209, but the only connection of the gate member 204 with link member 209 is by shoulder bolt 220 which is axially movable relative to carrier bar 207.

The spring 223 spirally piercing member 221 of gate 204 drives the gate member 204 and the pin 220 fixed shoulder in a direction along the axis of the bolt 220 away from shoulder 207 bar carrier. The recess 218 in the carrier bar 207 is deep enough to allow axial movement therein of the head 219 in the bolt 220 of the shoulder. The action of the spring 223 spirally pushing the gate member 204 away from the bar 207 carrier, also pushes the member 204 gate in engagement with the ring 202 seal on the 58 narrowest part of the container and into engagement with the strip 32 (Figure 24). The combination of drilling 221 and the coil spring 223, to push the member 224 gate away from the bar 207 carrier and meshing sealing with the seal ring 202 and the strip 32, is provided in a plurality of sites along the length of the gate member 204 (and the gate member 205). In a commercial scale hot dip coating system, the gate member 204 can be up to 2.44 meters long, for example. In a gate member of that length, the combination of the coil spring 223 and the bore 221 would be placed (i) at sites adjacent to each end of the gate member 204 and (ii) at a plurality of intermediate sites placed between the two end and spaced sites along the length of the gate member 204. The arrangement described in the preceding paragraph distributes the sealing pressure exerted by the gate member 204 almost equally along the length of the gate member. The same arrangement also helps to correct errors in the positioning of the carrier bar 207 relative to the seal ring 202, when the carrier bar 207 is in the closed position illustrated in full lines in Figure 22. When the gate member 204 is in its second closed position (full lines in Figure 22 and Figure 24), the gate member 204 has a horizontal surface 225 for engaging the seal ring 202 and a vertical surface 226 for engaging the strip 32 (FIG. 24). ). The gear between the gate member 204 and the seal ring 202 described in the preceding paragraph occurs when the gate member 204 and its associated structure are used with the system 30 (Figures 2 and 22), a system that does not employs a separate refrigeration element below container 38. When the gate member 204 and its associated structure are used with the system 130, which employs the cooling element 139 (Figures 4-5), there is no seal ring, such 202 in Figure 22, to engage the gate member 204; instead, the horizontal surface 225 in the gate member 204 engages the bottom surface 137 of the cooling element 139. The surfaces 225, 226 in the gate member 204 are covered with a layer 227 of soft flexible refractory sealing material. . As shown in Figure 24, the layer 227 of the sealing material (i) sealingly meshes the seal ring 202 at the lower end of the narrow part 58 of the container, (ii) sealingly engages the adjacent surface of the strip 32 and (iii) sealingly closes the opening 43 of the passage of the strip. As the strip 32 moves in a downstream direction at the beginning of the hot dip coating operation, the layer 227 of sealing material functions as a cleaner for sealingly engaging the adjacent side surface of the strip 32, so as to help prevent the escape of molten metal. The gate member 204 and the sealing material layer 227 each have a dimension, in the direction of the width of the strip 32, which is greater than the width of the strip 32 (FIG. 25). Accordingly, layer 227 extends laterally beyond the vertical edge 48 of strip 32. There is the same dimensional relationship between strip 32 and layer 227 in the other gate member 205. As a result, layer 227 on vertical surface 226 of gate member 204 is sealingly engaged with layer 227 on vertical surface 226 of opposite gate member 205, on edge 48 of strip 32 and beyond (Figure 25) . This prevents the escape of the molten coating metal from the bath 40 along the edge 48 of the strip 32. A starting procedure for the hot dip coating operation, using the gate members 204, 205 and the structure associated with them, will now be described. The container 38 is initially provided in an empty condition, without the hot dip coating bath. The strip 32 is placed upstream and downstream of the container 38 and occupies that part of the path of the strip extending through the passage opening 43 of the strip and the container 38. The gates 204, 205 are they move to the closed position shown in full lines in Figure 22. The molten coating metal is then introduced into the container 38. The gates 204, 205 and their associated structure prevent the molten coating metal from escaping through the opening. 43 of the passage of the strip. The strip 32 moves downstream along its path as the molten coating metal is introduced into the container 38. As described above the movement of the strip 32 through the bath 40 cools the metal of molten coating at a site downstream of the opening 43 of the strip passage to form the plug 46 there. Once the stopper 46 has been formed and grown to a size large enough to hold the bath 40, the gate members 204, 205 can pivot to the open positions shown in dotted lines in the Figure 22. The length of the minimum plug required to hold the bath 40 can vary from bath to bath and can be determined empirically. Initially during the start-up procedure, that part of the bath 40 downstream of the site where the plug 46 is formed (site 47 in Figure 2) is not heated. Once the plug 46 has been formed and has the desired size, the bath 40 is immediately heated downstream of the plug 46 (site 47 in Figure 2), due to the reasons described above. In one embodiment of the start-up procedure, it is proposed that cold metal pellet pieces composed of the facing metal be placed immediately downstream of the opening 43 of the strip passage, at the top of the members 204, 205 of gate before introducing the molten coating metal into container 38. It is proposed that the placement of the cold metal pellets on the upper part of the members 204205, can improve the cooling of the initial molten coating metal that arrives there. Typically, a cold pellet layer having a depth of about 25.4 to 50.8 millimeters can be placed on top of the gate members 204, 205. It is proposed that this amount of shot can produce relatively rapid cooling of the molten metal initially introduced into the container 38, and be capable of relatively rapid formation of the plug 46 compared to smaller amounts of shot or no shot. The starting procedure described above was in the context of the container 38 and a plug 46 formed as a result of the cooling effect produced by the movement of the strip 32 through the opening of the strip passage towards the end in water above the narrow part 58 of the container. The same starting procedure can be carried out when the container 138 and the cooling element 139 are employed. As indicated above, it is desirable to maintain the temperature of the bath 40 above the melting temperature of the coating metal (420 ° C. ) in the case of zinc) up to approximately 500 ° C, eg a temperature within the range of 435 ° C to 470 ° C, and keep the bath at a relatively stable temperature within these scales. This can be achieved, in one embodiment, by placing the thermoelectric cells in the positions indicated in Figure 27 (Figure 27 is on sheet 14). A series of thermoelectric cells 230-232 are placed in the cooling element 139. The series of thermoelectric cells 230-232 preferably should be placed at the intermediate point 229 of the longitudinal dimension of the cooling element 139 (see Figure 17), along the vertical internal surface 136 of the half 144 of the cooling element (Figure 27). For example, assuming that the cooling element has a longitudinal dimension of 406 millimeters, the series of thermoelectric cells 230-232 could be placed 203 millimeters from one end of the cooling element (e.g., end 131 in Figure 17). Referring to Figure 27, a thermoelectric cell 230 is placed at or near the bottom of the vertical inner surface 136, another thermoelectric cell 231 is positioned approximately at the midpoint of the vertical dimension of the vertical surface 136, and a third thermoelectric cell 232 is placed near the top of the vertical surface 136.

Assuming that the cooling element described two previous paragraphs has the vertical dimension of 76 millimeters, an intermediate-level thermoelectric cell 231 would be placed at a distance of about 38 millimeters from the bottom of the vertical surface 136, and the thermoelectric cell Upper 232 would be placed approximately 12 millimeters below the top of the vertical surface 136. A group of similar thermoelectric cells having vertical spacings essentially identical to those of the thermoelectric cells 230-232 can be placed on the vertical surface 136 about halfway between the end 131 and the intermediate point 229 of the element 139 of refrigeration (Figure 17). In addition to the group of thermoelectric batteries 230-232, another thermoelectric cell 233 (Figure 27) is placed on the inner surface of the convergent side wall 161 of the container 138, at the lower end of the side wall, and the thermoelectric cell 233 is aligned in a vertical plane with the thermoelectric batteries 230-232. An additional thermoelectric battery can be placed on the internal surface of the side wall 161 converging at the same vertical level as the thermoelectric cell 233 and is aligned in a vertical plane with the group of thermoelectric cells described in the previous paragraph. The thermoelectric cell 233 measures the temperature of the bath at site 147 of the bath (Figure 19). The thermoelectric cells 230-233 are used to help control the temperature of the bath 40 and the size (length) of the plug 146, in the manner that will be described below, with reference to Figures 4-5, 18-20 and 27 The temperature inside the bath 40 is monitored in the thermoelectric cell 233 in the room 147 of the bath (Figures 19 and 27). As mentioned above, it may be desirable to maintain the temperature of the bath 40 within the temperature range of 435 ° C to 470 ° C, for example; and the bath temperature controls will be discussed in that context. It can be assumed that, in this example, the molten coating metal is introduced into the container 138 at a temperature of about 480 ° C. When the temperature of the bath 40 decreases to 435 ° C, as measured in the thermoelectric cell 233, the heating element associated with the vessel 138 is activated. As mentioned above, the heating element can be an electromagnet 150 (FIGS. 4-5), an induction heating element 177 or 187 (Figures 19 and 20-20b) or a resistance heating element (rods 175, 176) (Figure 18). Each heating element is capable of acting between (a) an active heating condition in which heat is imparted to the bath 40 and (b) an inactive heating condition in which no heat is imparted to the bath 40. As long as the Bath temperature is within the range of 435 ° to 470 ° C, the heating element is kept in its inactive condition. When the temperature of the bath 40 decreases to a level that requires the actuation of the heating element (eg, 435 ° C, the heating element is connected and kept connected until the temperature of the bath 40, as determined by the thermoelectric pair 233, reaches the upper level of the selected temperature scale (eg 470 ° C), at which time the heating element is switched off.As discussed above, the thermoelectric cell 233 (Figure 27) monitors the bath temperature 40 at site 147 of the bath, a site that is immediately downstream of plug 146. It is important to monitor the temperature at room 147 of the bath to ensure that the temperature at that site does not decrease less than the melting temperature of the metal of the bath. Molten coating (in the case of zinc 420 ° C) The lower level of the temperature scale within which the bath 40 is kept must be high enough to prevent the temperature of the bath from becoming too high. At room 147, decrease to a temperature that approximates the melting temperature of the molten coating metal.

As described above, the cooling fluid is normally circulated through the lower cooling channels 151, 151 in the cooling element 139, continuously through the hot dip coating operation while the channels 152, 152 Higher cooling normally are in a wait state. Assuming that the required height (length) for the plug 146 is 76 millimeters, if the height of the plug 146 is not maintained at that level or above, the cooling fluid is circulated through the cooling channels 152, 152 to increase the height of the plug 146. The height of the plug 146 can be determined by monitoring the thermoelectric cells 230-232. The temperature detected in the lower thermo battery 230 is always lower than that detected in the thermoelectric cell 231 at the intermediate level, and the temperature detected in the upper thermoelectric cell 232 is always above the temperature detected in the thermoelectric cell 231 at the intermediate level. . For example, when the temperature detected in the thermoelectric cell 231 at the intermediate level is 250 ° C, the temperature detected in the lower thermo battery 230 may be 200 ° C, and the temperature detected in the upper thermo cell 232 may be 340 ° C. Similarly, when the temperature detected in the thermoelectric cell 231 at the intermediate level is 300 ° C, the temperature detected in the lower thermoelectric cell 230 can be 250 ° C, and the temperature detected in the upper thermo cell 232 can be of 390 ° C. The following discussion assumes that it is desirable to maintain the temperature in the thermoelectric cell 231 at the intermediate level within the range of 250 ° C to 300 ° C, and the manner in which the circulation of the cooling fluid through the element is controlled. 139 refrigeration will be discussed in that context. When the temperature in the thermoelectric cell 231 increases to the upper level of this temperature scale (300 ° C), the cooling fluid is circulated through the upper channels 152, 152 in the cooling element 139. This will produce a rapid drop to the temperature detected in the thermoelectric cell 231. When the temperature detected in the thermoelectric cell 231 at the intermediate level decreases to a level less than the desired temperature scale at 250 ° C, the circulation of the cooling fluid to through the upper channels 152, 152 stops. However, if the temperature detected in the upper thermoelectric cell 232 approaches the melting temperature of the coating metal (420 ° C) for the zinc, that is, a signal that the cooling fluid must be circulated through the the upper channels 152, 152, independently of the temperature detected in the thermoelectric cell 231 at the intermediate level. Circulating the cooling fluid through the upper channels 152, 152 produces a rapid cooling along the upper part of the vertical surface 136 in the cooling element 139, in turn producing a rapid increase in the height of the plug 146 When the circulation of the cooling fluid through the upper channels 152, 152 is finished, the height of the plug 146 gradually decreases. The discussion above is related to the use of temperatures detected in the plug of the thermoelectric cells 231 and 232 as indications for determining when the cooling fluid should be circulated through the upper channels 152, 152; that discussion also relates to the use of temperatures detected in the thermoelectric cell 233 of the bath as an indication to determine when the heating element for the bath 40 must be activated. That discussion applies to normal steady state operating conditions for the system. In spite of any of the aforementioned, if the plug 146 holds the strip 32, this action can be used as a cue (a) to increase the heat supplied to the bath 40 by the heating element of the bath (use, the magnet 150) and (b) to stop the circulation of the cooling fluid through the upper channels 152, 152, thereby reducing the length of the plug 146 which in turn reduces the resistance to the advance exerted on the strip 31 by the plug 146. In general, the circulation of the Cooling fluid through the lower channels 151, 151 is continuous and unrestricted. Under certain circumstances, the length of plug 146 can become excessive and can not be decreased quickly enough by the combination of (i) activation of the heating element and (ii) cessation of cooling fluid circulation through the channels 152, 152 upper cooling. Under those circumstances, the circulation of the cooling fluid through the lower channels 151, 151 can be restricted or stopped entirely; this should help to decrease the plug length 146 more quickly. The arrangement of thermoelectric cells described above has been described in the context of container 138 and cooling element 139 where thermoelectric cells 230-233 are used to measure the temperature of bath 40 and plug 146 in the passage 148. A similar arrangement can be employed with container 38 and its upstream portion 58 similar to a narrow neck (Figure 2). In this embodiment, (Figure 2), a thermoelectric cell similar to 233 would be used to measure the temperature of bath 40 in vessel 38, at site 47 of the bath, and thermoelectric cells similar to 230-232 would be used to measure the temperature of the plug 46 in part 58 of the narrow upstream container. Strip 32 is typically a planar thin planar element, e.g. a sheet or sheet of steel. However, a strip having the configuration described in the previous paragraph is only illustrative of a type of continuous strip with which the present invention may be put into practice. Other configurations of strips such as rods, rods, wires, tubes and configurations can be employed as long as leakage of the molten coating metal from the hot dip coating bath can be prevented in a manner in accordance with the present invention. , i.e., using a plug composed of solidified coating metal together with the above-described expedients for cooling the coating metal downstream of the strip passage opening and for heating the molten coating metal in waters down the plug.

The present invention has been illustrated in the context of an 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 opening of the strip passage is placed in the side wall of a container and (ii) the container contains a coating bath of molten metal having the upper surface placed above the level of the passage opening of the strip. The foregoing discussion has been directed primarily to one use of the present invention when the molten metal coating bath is zinc or zinc alloy. When the present invention is used with other coating metals (v. Gr, aluminum), some of the operating parameters may differ from those employed when the coating metal is zinc (eg, bath temperature, strip velocity and / or temperature, and plug temperature). However, the proper operating parameters for these other coating metals can be determined empirically, and these determinations should be within the skill level in the hot dip coating industry, given the foregoing discussion.

The detailed description given above has been provided for clarity of understanding only and unnecessary limitations should not be understood as the modifications will be apparent to those skilled in the art.

Claims

CLAIMS:

1. A hot dip coating system comprising: a continuous metal strip; a container for containing a molten metal coating bath; a molten metal coating bath contained in the container, the bath has a top surface; a passage opening of the strip associated with the container, the opening is positioned below the upper surface of the bath; the opening comprises a means for allowing the introduction of the continuous metal strip into the bath; a means for moving the metal strip continuous along a path extending through the passage opening of the strip and through the bath in order to coat the strip with a layer of the coating metal; a plug, composed of a coating metal solidified from the bath, surrounding the strip at a site downstream of the opening, the plug being essentially stationary relative to the strip; the plug comprises a means for preventing the escape of the molten metal from the bath through the opening while allowing the strip to move through the bath; means for cooling the coating metal within the container downstream of the opening to form the cap and maintaining the cap as the strip undergoes the coating; and means for heating the molten metal bath at a site downstream of the plug.

The system of claim 1, wherein: the cooling means comprises means for cooling the metal immediately downstream of the opening to form the plug at that site.

The system of claim 1, wherein the cooling means includes the strip and the means for moving the strip through the bath, and further comprises: a means for controlling the cooling effect produced by the movement of the strip through of the bathroon.

The system of claim 3, wherein the system comprises a means for controlling the speed at which the strip moves through the bath and the means for cooling the coating metal comprises: means for providing the strip to a temperature essentially lower than the melting temperature of the coating metal as the strip enters the opening of the passage of the strip in the container.

5. The system of claim 4, wherein: the means for controlling the cooling effect comprises a means for controlling the temperature of the strip to which the strip enters the passage opening of the strip.

The system of claim 5 wherein: the means for controlling the speed of the strip comprises a means for maintaining the speed of the strip essentially unchanged.

The system of claim 3 and comprising: means for controlling the heating effect produced by the heating means so that the amount of heat introduced into the bath by the heating means compensates for the amount of heat removed from the bath through the cooling medium.

The system of claim 7, wherein the cooling medium, the heating means and the means for controlling the heating effect comprise: a means cooperating to balance the cooling effect in the cooling medium the heating effect of the heating means to maintain the temperature of the bath relatively stable.

9. The system of claim 8, wherein the balancing means comprises: means for maintaining the plug in a solid state and for controlling the length of the plug.

The system of claim 7, wherein: the means for controlling the heating effect comprises a means for controlling the bath temperature, the bath temperature control means is immediately placed downstream of the plug.

The system of claim 1, wherein: the cooling means comprises a cooling element positioned downstream of the opening.

The system of claim 11, wherein: the cooling means comprises a means for controlling the cooling effect produced by the cooling element.

The system of claim 12, comprising: a plurality of cooling channels in the cooling element; and means for circulating a cooling fluid through each of the cooling channels in the cooling element; il - the means for controlling the cooling effect produced by the cooling element comprises a means for controlling the number of cooling channels in the cooling element through which the cooling fluid is circulated.

The system of claim 1 and comprising: a gate means placed immediately upstream of the opening to close the opening in order to prevent the escape of the molten metal from the bath through the opening, in the absence of the plug , while allowing the strip to move through the bathroom; and a means mounting the gate means to move between (i) a second position to prevent the escape of molten metal from the bath through the opening, and (ii) an open position displaced from the closed position.

The system of claim 14, wherein the gate means comprises: a pair of gates each placed on a respective opposite side of the strip in the opening; and a scouring cleaning means in each of the gates to sealingly engage a respective opposite side of the strip as the strip moves in a? 2 - downstream direction, to help prevent the escape of molten metal.

The system of claim 1, wherein the heating means comprises at least one of the following: (a) an induction heating means positioned around the bath immediately downstream of the plug; (b) an electromagnetic means that employs a current that varies with time to generate a magnetic field comprising a part extending through the bath immediately downstream of the plug; and (c) means for subjecting the bath to heating by conduction at a site immediately downstream of the stopper.

The system of claim 1 or claim 16, wherein: the container has (i) a relatively narrow part extending downstream from the opening and (ii) a relatively wide portion placed downstream of the part narrow The plug extends from the opening to the narrow part; and the heating means is associated with that portion of the container that is immediately downstream of the stopper.

The system of claim 17, wherein: the cooling means comprises a cooling element positioned downstream of the opening and upstream of the heating means.

The system of claim 1, wherein there is a preselected bath temperature scale for coating the strip and wherein: the heating means comprises a means capable of actuating between (a) an active heating condition wherein the heat it is imparted to the bathroom and (b) an inactive heating condition where the heat is not imparted to the bathroom; the system comprises a means for monitoring the temperature of the bath; the system further comprises means for actuating the heating means towards its active condition for heating the bath, when the bath temperature is at the lower end of the bath temperature scale, and for driving the heating means to its temperature. inactive condition when the ¡4 - Bath temperature is at the upper end of the bath temperature scale.

The system of claim 1, wherein: the movable means comprises means for moving the strip through the stopper; the plug exerts friction on the strip as the strip moves through the plug; and the heating means comprises means for reducing the length of the plug in order to reduce the friction exerted on the strip by the plug.

The system of claim 1, wherein: the container has (i) a relatively narrow part extending downstream from the opening and (ii) a relatively wide portion positioned downstream of the narrow part; and the plug extends from the opening in the narrow part.

The system of claim 21 and comprising: an electromagnetic means that employs a current that varies with time to generate a magnetic field comprising a portion extending through the bath immediately downstream of the plug.

23. The system of claim 21 or 22 wherein: the electromagnetic means is placed around that portion of the container that is immediately downstream of the plug; and the electromagnetic means comprises means for generating an electromagnetic field that induces a parasitic current in the bath that cooperates with the field to exert a force, immediately downstream of the plug, which pushes the molten metal bath in a direction having a component that extends away from the opening.

The system of claim 22, wherein: the electromagnetic means comprises a means for stirring the bath; the system comprises a means for adjusting the amperage of the current that varies with time in order to control the agitation produced by the electromagnetic medium and to avoid the agitation of the type of sudden movement backwards and forwards, in order to reduce the erosion Stopper by stirring.

The system of claim 1, wherein: means for moving the strip along the path comprising the means for moving the strip along an essentially vertical path extends through the opening and through the bath; and the container has an essentially funnel-shaped vertical cross section that is taken along a vertical plane perpendicular to the plane of the strip.

26. The system of claim 1 and comprising: means for controlling the length of the plug in a downstream direction from the opening.

The system of claim 26 wherein the means for controlling the length of the cap comprises: means for controlling the cooling effect of the cooling medium.

The system of claim 26 or 27 wherein: the heating means is placed immediately downstream of the plug; and the means for controlling the length of the plug comprises a means for controlling the heating effect of the heating means to maintain the bath at a relatively stable temperature. 7 -

29. The system of claim 26, wherein the cooling means comprises: a cooling element positioned downstream of the opening; and means for controlling the cooling effect produced by the cooling element.

The system of claim 29, wherein the cooling element comprises: a first channel means through which the cooling fluid can be circulated, the first channel means being placed relatively close to the opening of the passage of the strip; and a second channel means through which a cooling fluid can be circulated, the second channel means is positioned downstream of the first channel means.

The system of claim 30 wherein the cooling means comprises: a means for circulating a cooling fluid through the first channel means to form the plug; and means for circulating a cooling fluid through the second channel means to increase the length of the plug.

32. The system of claim 31 wherein the means for controlling the cooling effect comprises: means for restricting the circulation of cooling fluid through the second channel means to decrease the plug length.

The system of claim 30 wherein: the means for controlling the cooling effect of the cooling medium comprises means for restricting the circulation of the cooling fluid through the second channel means; the heating medium is placed immediately downstream of the plug; and the heating means and the circulation restriction means comprise a means cooperating to decrease the length of the plug.

34. The system of claim 33 and comprising: means for controlling the heating effect of the heating means to maintain the bath at a relatively stable temperature.

35. The system of claim 1 wherein: the container has an upstream opening for introducing the strip into the bath; the cooling means comprises a cooling element; the cooling element comprises a passage for the metal strip; the passage has (i) a downstream opening, communicating with the upstream container opening to receive the molten metal from the bath, and (ii) an upstream opening for receiving the strip, constituting the opening in upstream the opening of the passage of the strip; the cooling element comprises a pair of channel means, one on each side of the passage of the strip, for driving a cooling fluid through the cooling element to cool the passage.

36. A hot dip coating system comprising: a container for containing a molten metal coating bath; the container has an upstream opening for introducing a continuous metal strip into the bath; a cooling element associated with the upstream container opening; the cooling element comprises a passage for the metal strip; the passage has (i) a downstream opening communicating with the upstream facing opening to receive the molten metal from the bath, and (ii) an upstream opening for receiving the strip; the coolant element has a pair of channel means, one on each side of the passage of the strip to drive a cooling fluid through the cooling element to cool the passage.

37. The system of claim 36 wherein: each channel means comprises first and second channels; the first channel is positioned relatively close to the opening upstream of the passage; and the second channel is positioned downstream of the first channel.

38. The system of claim 36 or 37 and comprising: a first temperature sensing means for detecting the temperature in the passage at a site about halfway between the upstream and downstream openings.

39. The system of claim 38 and comprising: a second temperature sensing means for sensing the temperature in the passage at a location essentially downstream of the first temperature sensing means.

40. The system of claim 39 and comprising: means for detecting the temperature in the container immediately downstream of the upstream opening in the container.

41. The system of claim 37 and comprising: a cooling fluid control means (a) for circulating the cooling fluid through the first channel without circulating the cooling fluid through the second channel, and ( b) to circulate the cooling fluid through the first and second channels at the same time.

42. A method for coating a continuous metal strip with a coating metal layer, the method comprising the steps of: providing a container for containing a molten coating metal bath; containing a molten metal coating bath in the container, the bath having a top surface; providing a passage opening of the strip associated with the container, the opening being positioned below the upper surface of the bath; moving a continuous strip of metal along a path that extends through the opening of the strip passage through the bath; coating the strip with a layer of the coating metal as it moves along the path; forming, from the bath, a plug which is composed of solidified coating metal, which surrounds the strip at a site downstream of the opening and which is essentially stationary relative to the strip; employs the plug to prevent the escape of molten metal from the bath through the opening while allowing the strip to move through the bath; Cool the coating metal inside the container downstream of the opening to form and hold the plug; and heating the molten metal bath to a site downstream of the plug.

43. The method of claim 42, wherein: the cooling step is carried out immediately downstream of the opening to form a plug at that site.

44. The method of claim 42 wherein the cooling step employs the strip and the movement of the strip through the bath, and further comprising: controlling the cooling effect produced during the movement of the strip through the bath.

45. The method of claim 44 wherein the method comprises controlling the speed at which the strip moves through the bath and the step of controlling the cooling effect comprises: providing the strip at a temperature substantially below the temperature of melting of coating metal as the strip enters the passage opening of the container strip.

46. The method of claim 45 wherein: the step of controlling the cooling effect comprises controlling the temperature of the strip to which the strip enters the opening of the passage of the strip.

47. The method of claim 46, wherein: the step of controlling the speed of the strip comprises maintaining the speed of the strip essentially unchanged.

48. The method of claim 45, wherein: the method comprises applying a flux to the surface of the strip before the strip enters the opening of the strip passage; the strip is maintained at an elevated temperature lower than the temperature at which the flux will dissociate during the period between (a) the time when the flux is applied and (b) the time when the strip enters the bath; the strip enters the passage opening of the strip at a temperature sufficiently lower than the melting temperature of the coating material to allow the strip to carry out the cooling step to form and maintain the plug.

49. The method of claim 48, wherein: the coating metal consists essentially of zinc; the bath has a temperature higher than 420 ° C as the strip enters the opening of the passage of the strip; and the strip is provided with a temperature greater than 38 ° C and less than 120 ° C as the strip enters the opening of the strip passage.

50. The method of claim 44 and comprising: controlling the heating effect produced by the heating step so that the amount of heat that is introduced into the bath by the heating step compensates for the amount of heat removed from the bath through the cooling step.

51. The method of claim 50 and comprising: balancing the cooling effect of the cooling passage and the heating effect of the heating step to keep the bath temperature relatively stable.

52. The method of claim 51, wherein: the step of balancing holds the plug in a solid state and controls the length of the plug.

53. The method of claim 50 or 51 wherein: the step of controlling the heating effect comprises controlling the bath temperature and carrying out the bath temperature control step at a site immediately downstream of the plug.

54. The method of claim 42 wherein: the cooling passage employs a cooling element positioned downstream of the opening.

55. The method of claim 54 wherein: the cooling step comprises controlling the cooling effect produced by the cooling element. 9

56. The method of claim 55, and comprising: providing the cooling element with a plurality of cooling channels; and circulating a cooling fluid through the cooling element; The step of controlling the cooling effect produced by the cooling element comprises controlling the number of cooling channels in the cooling element through which the cooling fluid is circulated.

57. The method of claim 42 and comprising: employing a gate means placed immediately upstream of the opening, to close the opening in order to prevent the escape of the molten metal from the bath through the opening, in absence of the stopper while allowing the strip to move through the bath; and assemble the gate means to move between (i) a closed position to prevent the escape of the molten metal from the bath through the opening, and (ii) an open position displaced from the closed position.

58. The method of claim 57 and comprising: employing, as the gate means, a pair of gates each placed on a respective opposite side of the strip in an aperture; and employing a sliding cleaning means in each of the gates to sealingly engage a respective opposite side of the strip as the strip moves in a direction in water to help prevent the escape of the molten metal.

59. The method of claim 42, wherein the heating step comprises at least one of the following: (a) carrying out induction heating at a site immediately downstream of the plug; (b) generating a magnetic field that varies with time comprising a part extending through the bath immediately downstream of the plug; and (c) carrying out the heating by conduction in a site immediately downstream of the stopper.

60. The method of claim 59, wherein: the container has (i) a relatively narrow part that extends downstream from the opening (ii) a relatively wide portion placed downstream of the narrow part; the stopper extends from the opening to the narrow part; and the heating step is carried out to a site immediately downstream of the plug.

61. The method of claim 60, wherein: the cooling step employs a cooling element positioned downstream of the opening and upstream of the site where the heating step is carried out.

62. The method of claim 42, wherein (a) there is a pre-selected bath temperature scale for coating Xa strip, (b) the heating step has (i) an active stage in which the heat is imparted to the bath and (ii) an inactive stage in which the heat is not imparted to the bath, and (c) the method comprises: monitoring the bath temperature; employ the active heating stage to heat the bath, when the bath temperature is at the lower end of the bath temperature scale; and employing the inactive stage when the bath temperature is at the upper end of the bath temperature stage.

63. The method of claim 42 wherein: the movement step comprises moving the strip through the plug; the plug exerts friction on the strip as the strip moves through the plug; the method comprises employing the heating step to reduce the length of the stopper and thereby reduce the friction exerted on the strip by the stopper.

64. The method of claim 42, wherein: the method comprises providing the strip with a temperature, at the time the strip enters the opening of the strip passage, which is too high to allow the strip to perform the cooling passage, and the cooling passage employs a cooling element positioned downstream of the opening.

65. The method of claim 64 wherein: the coating metal consists essentially of zinc; the bath is maintained at a temperature higher than 420 ° C to 500 ° C; and the structure of the strip is within the temperature range maintained for the bath at the time when the strip enters the opening of the strip passage.

66. The method of claim 42 wherein: the container has (i) a relatively narrow part extending downstream from the opening and (ii) a relatively wide portion positioned downstream of the narrow part; the stopper extends from the opening to the narrow part; and the method comprises generating a magnetic field having a part extending through the bath at a site immediately downstream of the plug.

67. The method of claim 66 wherein: the step of generating the magnetic field comprises generating an electromagnetic field that induces a parasitic current in the bath that cooperates with the field to exert a force, immediately downstream of the plug, which pushes the molten metal bath in a direction having a component extending away from the opening.

68. The method of claim 66 and comprising: employing a current that varies in time to generate the magnetic field; use the magnetic field to shake the bath; and adjust the amperage of the current that varies in time to control the agitation produced by the magnetic field and avoid the agitation of the type of sudden movement backwards and forwards, in order to reduce the erosion of the plug by agitation.

69. The method of claim 42 wherein: the step of moving the strip along the path comprises moving the strip along an essentially vertical path that extends through the opening and through the bath.

70. The method of claim 42 and comprising: controlling the length of the plug in a downstream direction from the opening.

71. The method of claim 70 wherein the step of controlling the length comprises: providing a plug with a sufficient length (a) to resist being pushed in an upstream direction by the pressure of the bath placed downstream of the plug, and (b) to resist localized melting due to the bath heat; and providing the stopper with a length short enough to avoid resistance to excessive advancement in the strip as the strip moves downstream through the stopper.

72. The method of claim 70, wherein the step for controlling the length comprises: controlling the cooling effect of the cooling passage.

73. The method of claim 70 or 72 and comprising: carrying out the heating step immediately downstream of the plug; and controlling the heating effect of the heating step in order to maintain the bath at a relatively stable temperature.

74. The method of claim 70, wherein the step of controlling the length of the plug comprises at least one of the following sub-steps: (a) controlling the cooling effect of the cooling passage; (b) controlling the heating effect of the heating step; (c) employ a combination of sub-steps (a) and (b).

75. The method of claim 74 and comprising: maintaining the speed of the strip essentially unchanged.

76. The method of claim 70 wherein the cooling step comprises: employing a cooling element positioned downstream of the opening; and controlling the cooling effect produced by the cooling element.

77. The method of claim 76 wherein the cooling step comprises: providing the cooling element with a first channel means through which a cooling fluid can be circulated and placing the first channel means relatively close to the opening of the passage of the strip; providing the cooling element with a second channel means through which a cooling fluid can be circulated and placing the second channel means downstream of the first channel means; circulating a cooling fluid through the first channel means to form the plug; and circulating a cooling fluid through the second channel means to increase the length of the plug.

78. The method of claim 77 wherein the step of controlling the cooling effect comprises: restricting the circulation of the cooling fluid through the second channel means to decrease the length of the plug.

79. The method of claim 78 comprising: carrying out the heating step immediately downstream of the plug; the heating step cooperates with the flow restriction step to decrease the length of the plug.

80. The method of claim 79 and comprising: controlling the heating effect of the heating step to maintain the bath at a relatively stable temperature.

81. A start-up procedure for use with the method of claim 42, the start-up procedure comprises the steps of: providing the container initially in an empty condition, without the bath; placing the damper means capable of closing immediately upstream of the passage opening of the strip to close the opening in order to prevent escape of the coating metal from the bath through the opening in the absence of the plug, while allows the strip to move through the opening and through the bathroom; close the gate means; introduce molten coating metal into container; moving the continuous metal strip along its path as the molten coating metal is introduced into the container; cooling the molten coating metal introduced into the container, in a site downstream of the opening, to form the plug; and then open the gate.

82. A starting procedure according to claim 81 and comprising: not initially heating that part of the bath downstream of the site where the plug is formed; and then, once the stopper has been formed, heat that part of the bath that is immediately downstream of the stopper.

83. A starting procedure according to claim 81 or 82 and comprising: placing the chunks of the cold metal pellet, composed of facing metal immediately downstream of the opening, before introducing the molten coating metal into the container, to improve the cooling of the initial molten coating metal at that site.

84. A start-up procedure according to any of claims 81 to 83 and comprising: carrying out the cooling step at a site immediately in the waters below the opening to cool that part of the bath at that site and form the plug in that site.

85. A method according to claim 42, wherein the coating metal comprises one of the following: zinc, aluminum and alloys of each.