Patent Publication Number: US-2022213582-A1

Title: Method and Device for Rinsing an Overflow Chamber at the Bath-Side End of a Snout of a Hot-Dip Coating Device

Description:
TECHNICAL FIELD 
     The disclosure relates to a method for rinsing an overflow chamber at the bath-side end of a snout of a device for hot-dip coating a metal strip with a metal melt. Furthermore, the disclosure relates to said device for hot-dip coating with the necessary components for carrying out the method. 
     BACKGROUND 
     European patent specification EP 2 989 226 B1 discloses a device for the continuous hot-dip coating of metal strip. Such device comprises a container with a metal melt for passing the metal strip along with a snout for passing the metal strip in a protective gas atmosphere after its exit from the metal melt. The snout has at least one overflow chamber at its bath-side end for collecting impurities from the surface of the metal melt in the vicinity of the freshly coated metal strip. The device further comprises a lifting device for retracting the snout from the metal melt and/or for lowering the snout into the metal melt. Finally, the device has a suction pump for preferably continuous suction of the impurities from the overflow chamber. The overflow chamber also has at least one passage opening, also called a rinsing opening, through which fluid metal melt can flow from the molten bath into the drain chamber, which is then continuously sucked out of the overflow chamber with the aid of a suction pump. Maintaining the rinsing flow within the overflow chamber reliably ensures that slag or impurities, as the case may be, are continuously discharged from the snout, since the constant feed of fluid metal melt maintains a “soft” consistency of the slag and prevents deposits, so-called “caking,” in the snout to the greatest possible extent. Without a sufficient feed of fluid metal melt, slag particles floating in the snout on the surface of the molten bath would bond with each other in the manner of sintering. The snout disclosed in EP 2 989 226 B1 can be pivoted and telescoped without interfering with slag removal. Finally, the device disclosed in said patent specification has a control or regulating device for controlling the suction pump as a function of the difference in height between the bath level and an overflow edge of the overflow chamber. 
     The rinsing process as known from the said prior art has the disadvantage that it can only be operated when the snout with its overflow chamber is immersed in the metal melt. 
     SUMMARY 
     The disclosure provides an improved method for rinsing an overflow chamber and an improved device for hot-dip coating a metal strip for carrying out the method in such a way that the rinsing process can be continued even after the snout has been withdrawn from the melt. 
     This is achieved by the method as claimed. Accordingly, the method provides that the snout with the overflow chamber is retracted from the molten bath at least to such an extent that no more melt can flow over an overflow edge in the interior of the snout into the overflow chamber and that the rinsing cycle can be carried out even when the snout has been retracted from the melt by feeding the melt from the molten bath to the overflow chamber with the aid of a delivery pump. 
     Particularly at the end of a coating process, for example in the transition between two metal strips to be coated or for maintenance purposes, it is occasionally necessary for the snout to be retracted from the molten bath. In such situations, the method offers the advantage that the rinsing process of the overflow chambers does not have to be interrupted, but can be continuously maintained until the overflow snout is immersed in the melt again. The uninterrupted continuation of the rinsing process of the overflow chambers even outside the melt offers the advantage that the chambers can continue to be cleaned even in this situation, for example to prevent caking, and that the dry running of the suction pump is prevented. 
     In accordance with a first exemplary embodiment, the method further provides that the level of the melt in the overflow chamber is controlled to a predetermined target level even when the snout is retracted from the melt by suitably varying the power of the suction pump and/or the delivery pump. 
     An improvement is further achieved by a device for the hot-dip coating of a metal strip with a delivery pump for carrying out the method. The advantages of this device correspond to the advantages mentioned above with reference to the claimed method. 
     Further advantageous embodiments of the device are the subject of the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A single FIGURE showing the device for carrying out the method for rinsing an overflow chamber at the bath-side end of a snout of a device for hot-dip coating a metal strip with a metal melt is attached to the description. 
     
    
    
     DETAILED DESCRIPTION 
     The FIGURE shows the device  100  for hot-dip coating a metal strip  200  with a metal melt  120 . The metal melt  120  is contained in a container  110 . The metal strip  200  is deflected in the metal melt by a deflection roller  115  in the interior of the container. It is passed through a snout  130  prior to its entry into the metal melt  120 , wherein the snout ensures that the metal strip is guided under a protective gas atmosphere prior to its entry into the metal melt  120 . The snout  130  has at least one, preferably two or four, overflow chambers  132  fluidly connected to each other at its bath-side end. Such overflow chambers are used to collect slag residues or impurities from the surface from the metal melt in the vicinity of the metal strip. A suction pump  150  is provided for the preferably continuous suction of the impurities from the overflow chamber; in this manner, such slag residues or impurities are prevented from coming into contact with the freshly coated metal strip and caking there or on the inside of the snout. In addition, a lifting device  140  is provided in the snout  130  for retracting the snout  130  out of the metal melt and for lowering the snout into the metal melt; the directions of travel for the snout  130  are indicated by a double arrow in the FIGURE. 
     In addition to the suction pump  150 , the device  100  also has a delivery pump  160  for feeding metal melt, preferably from the container  110  into the at least one overflow chamber  132 , in particular even if the bath-side end of the snout is no longer immersed in the metal melt  120 . Through the preferably simultaneous operation of the delivery pump  160  and the suction pump  150 , it is possible to maintain a continuous rinsing in the form of a continuous melt flow in the overflow chamber  132 , even when the snout is retracted from the melt, and in this manner to ensure the continuous cleaning of the overflow chamber and to prevent the suction pump from running dry. 
     The snout is not only formed to be raised and lowered, but also to pivot. This applies in particular to the bath-side end piece of the snout with the overflow chamber  132 ; however, other elements of the snout may also be formed to pivot. 
     The metal melt is, for example, liquid zinc. Finally, the device  100  can also include a level control  170  for controlling the level of the melt  120  in the overflow chamber  132 , even when the snout  130  is retracted from the melt  120 . The control is designed to adjust the level of the melt in the overflow chamber  132  to a predetermined target level N Target  by suitably varying the power of the suction pump  150  and/or the delivery pump  160 . The target level of the melt in the overflow chamber is below an overflow edge  134  of the overflow chamber  132 . 
     LIST OF REFERENCE SIGNS 
       100  Device 
       110  Container 
       115  Deflection roller 
       120  Metal melt 
       130  Snout 
       132  Overflow chamber 
       134  Overflow edge 
       140  Lifting device 
       150  Suction pump 
       160  Delivery pump 
       170  Level control 
       200  Metal strip 
     N Target  Target level