Plant for coating flat metal products by means of continuous hot dipping and relative coating process

Abstract

A plant for coating a strip ( 5 ) by means of continuous hot dipping, comprising a containment tank ( 2 ) to contain molten zinc; a coating vessel ( 3 ) receiving the molten zinc, arranged above the containment tank and provided with an opening ( 4 ) on a bottom thereof for passing the strip; a chamber ( 6 ) arranged below the coating vessel and provided with guide rollers ( 7, 8 ) to guide the strip towards said opening; wherein the containment tank is arranged below the guide rollers so that chamber and containment tank form a single place, and wherein there is provided an intercepting and conveying system ( 9 ), arranged within the chamber, to intercept and convey the molten zinc leaking from said opening into the containment tank, said intercepting and conveying system being configured to bypass and wind the guide rollers and the strip being fed towards said opening.

1 . A plant for coating a flat metal product by means of continuous hot dipping, comprising
 a containment tank for containing molten coating material,   a coating vessel adapted to receive and contain molten coating material, arranged above said containment tank and provided with an opening on a bottom thereof for passing the flat metal product to be coated,   a chamber arranged below said coating vessel and provided with at least one first guide roller for diverting the flat metal product upon its entry into the chamber, and with at least one second guide roller, placed above said first guide roller, for further diverting and stabilizing the flat metal product being fed towards the opening,   wherein the containment tank is arranged within said chamber, chamber and containment tank defining a single place,   and wherein there is provided an intercepting and conveying system arranged within the chamber, between the coating vessel and the containment tank, and having a cavity facing the containment tank,   
       wherein
 the containment tank is arranged below said at least one first guide roller, the intercepting and conveying system is configured to intercept and convey into said containment tank, the molten coating material which leaks from said opening, 
 said at least one first guide roller is at least partially housed within the cavity of said intercepting and conveying system, 
 and said at least one second guide roller is completely housed within said cavity, 
 whereby the at least one first guide roller, the at least one second guide roller and the flat metal product, being fed by said first and second guide rollers towards the opening, are completely protected from the falling of drops of molten coating material during the steady state operation of the plant or from the falling of large quantities of molten coating material in both the start-up or shut-down step and in the maintenance or emergency phases. 
 
     
     
         2 . A plant according to  claim 1 , wherein said intercepting and conveying system defines channels which diverge from each other in the a direction from said coating vessel to said containment tank. 
     
     
         3 . A plant according to  claim 2 , wherein said channels are defined by a pair of deflectors, the upper ends of which define a passing gap for passing the flat metal product in a vertical direction, and by a structure which is external to said deflectors and independent of these latter. 
     
     
         4 . A plant according to  claim 3 , wherein each deflector is arranged at a respective side of a vertical feeding plane of the flat metal product and is connected to two opposite lateral walls of the chamber. 
     
     
         5 . A plant according to  claim 4 , wherein said structure is configured so as to define, at a respective upper end, a flared opening which extends transversally to the chamber and within which the upper ends of the deflectors are arranged. 
     
     
         6 . A plant according to  claim 3 , wherein there are provided adjustment means for adjusting said passing gap. 
     
     
         7 . A plant according to  claim 6 , wherein said passing gap adjustment means are configured to move two support shafts of the deflectors, arranged parallel to the vertical feeding plane, each support shaft being integrally fixed to a respective deflector and connected to two opposite walls of the chamber. 
     
     
         8 . A plant according to  claim 3 , wherein there are provided heating means arranged within said chamber. 
     
     
         9 . A plant according to  claim 8 , wherein there are provided first heating means on at least one of the guide rollers, said first heating means preferably being electrical resistors housed in a plurality of hollows provided in a hollow jacket of the first guide roller. 
     
     
         10 . A plant according to  claim 9 , wherein there are provided second heating means in proximity of the external walls of said structure, said second heating means preferably being heating plates. 
     
     
         11 . A plant according to  claim 1 , wherein the supports of the guide rollers have bearings on the outside of the chamber. 
     
     
         12 . A plant according to  claim 1 , wherein the coating vessel is part of an electromagnetic device suitable to keep a bath of molten coating material in semi-levitation. 
     
     
         13 . A plant according to  claim 1 , wherein there is provided a channel, communicating at a first end with the opening of the coating vessel and at a second end with the chamber, suitable for passing the flat metal product from said chamber to said coating vessel. 
     
     
         14 . A coating process for a flat metal product by means of continuous hot dipping, carried out by means of a plant according to  claim 1 , the process comprising the following steps:
 providing an inert atmosphere in said single place at a higher pressure than the pressure outside said single place;   feeding the flat metal product into the chamber, guiding it towards the coating vessel by means of said at least one first guide roller and said at least one second guide roller,   coating the flat metal product within said coating vessel;   wherein it is provided that the molten coating material which leaks from the opening of the bottom of the coating vessel is intercepted and conveyed into the containment tank, placed below said at least one first guide roller, by means of the intercepting and conveying system provided in the chamber so as to protect the at least one first guide roller, the at least one second guide roller, and the flat metal product, being fed towards said opening, which are found within the cavity of said intercepting and conveying system.   
     
     
         15 . A process according to  claim 14 , wherein it is provided that said single place is maintained at a temperature of around 450-490° C. to maintain the coating material in a molten state.