Method and installation for dip coating of a metal strip, in particular a steel strip

A plant for the continuous hot dip-coating of a metal strip (1), of the type comprising:

• a tank (11) containing a liquid metal bath (12),
• a duct (13) through which the metal strip (1) in a protective atmosphere runs and a lower part (13a) of which duct (13) is immersed in the liquid metal bath (12) in order to define with the surface of said bath, and inside this duct, a liquid seal (14),
• a roller (15), placed in the metal bath (12), for deflecting the metal strip (1), and
• means (16) for wiping the coated metal strip (1) on leaving the metal bath (12),
• characterised in that said plant further comprises,
• on the one hand, in a region (17) where the strip (1) leaves the liquid metal bath (12), an enclosure (20) for isolating the liquid metal in this region (17) with respect to the surface of the bath (12) and for recovering metal oxide particles and intermetallic compound particles by the liquid metal flowing from this region (17) into the enclosure (20), wherein the drop in height of the liquid metal (12) in the enclosure (20) is greater than 50 mm in order to prevent the metal oxide particles and intermetallic compound particles from rising as a countercurrent to the flow of liquid metal, and,
• on the other hand, means (30) for extracting the particles from this enclosure (20),
• said plant being further characterized:
• in that the enclosure (20) surrounds the metal strip (1) and has a bottom (21) and two concentric walls (22,23) making between them a compartment (24) and defining, in an upper part of the enclosure (20), an opening (25), and
• an upper edge (22a) of an external one of the concentric walls (22) being positioned above the surface of the liquid metal bath (12), and an upper edge (23a) of an internal one (23) of the concentric walls being positioned below said surface;
• and by
• means (35, 36) for positioning the metal strip (1) with respect to the upper edge (23a) of the internal wall (23) of the enclosure (20),
• wherein the upper edge (23a) of the internal wall (23) of the enclosure (20) comprises, in the longitudinal direction, a succession of hollows (26) and projections (27),
• wherein the difference in height between the hollows (26) and the projections (27) is between 5 and 10 mm.