Patent EA-004413-B1 (EA)
Title: Method and installation for dip coating of a metal strip, in particular a steel strip
Inventor: DAUCHELLE DIDIER
IPC: C23C2/26
Filed: 2001-11-06
Abstract: 1. Process for the continuous dip-coating of a metal strip (1) in a tank (11) containing a liquid metal bath (12), in which process the metal strip (1) is made to run continuously, in a protective atmosphere, through a duct (13), the lower part (13a) of which is immersed in the liquid metal bath (12) in order to define with the surface of the said bath, and inside this duct (13), a liquid seal (14), the metal strip (1) is deflected around a deflector roller (15) placed in the metal bath (12) and the coated metal strip (1) is wiped on leaving the metal bath (12), characterized in that, in the region (17) where the strip (1) leaves the liquid metal bath (12), the liquid metal is isolated from the surface of the said bath in an isolating enclosure (20) and the metal oxide particles and intermetallic compound particles are recovered by the liquid metal flowing from this region (17) into the said enclosure (20), the drop in height of the liquid metal (12) in this enclosure being determined in order to prevent metal oxide particles and intermetallic compound particles from rising as a countercurrent to the flow of liquid metal, and the said particles are extracted from this enclosure (20). 2. 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 the lower part (13a) of which duct (13) is immersed in the liquid metal bath (12) in order to define with the surface of the 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), - characterized in that it comprises, on the one hand, in the 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 said bath (12) and for recovering the metal oxide particles and intermetallic compound particles by the liquid metal flowing from this region (17) into the said enclosure (20), 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 said particles from this enclosure (20). 3. Plant according to claim 2, characterized in that the drop in height of the liquid metal in the enclosure (20) is greater than 100 mm. 4. Plant according to claim 2 or 3, 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 the upper part of the said enclosure (20), an opening (25), the upper edge (22a) of the external wall (22) being positioned above the surface of the liquid metal bath (12) and the upper edge (23a) of the internal wall (23) being positioned below the said surface. 5. Plant according to claim 4, characterized in that the internal wall (23) of the enclosure (20) has a lower part flared out towards the bottom of the tank (11) and an upper part parallel to the metal strip (1). 6. Plant according to claim 4, characterized in that the upper edge (23a) of the internal wall (23) of the enclosure (20) is straight. 7. Plant according to claim 4, characterized in that 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). 8. Plant according to claim 7, characterized in that the hollows (26) and the projections (27) are in the form of circular arcs. 9. Plant according to claim 7 or 8, characterized in that the difference in height between the hollows (26) and the projections (27) is between 5 and 10 mm. 10. Plant according to any one of claims 7 to 9, characterized in that the distance between the hollows (26) and the projections (27) is of the order of 150 mm. 11. Plant according to any one of claims 4 to 10, characterized in that the upper edge (23a) of the internal wall (23) of the enclosure (20) is tapered. 12. Plant according to any one of claims 2 to 4, characterized in that it includes means for adjusting the vertical position of the enclosure (20) with respect to the surface of the liquid metal bath (12). 13. Plant according to claim 2, characterized in that the means for extracting the particles are formed by a pump (30) connected, on the suction side, to the compartment (24) of the enclosure (20) via a connecting pipe (31) and provided, on the delivery side, with a pipe (32) for discharging the withdrawn liquid metal into the volume of the bath (12). 14. Plant according to any one of the preceding claims, characterized in that it includes 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). 15. Plant according to claim 14, characterized in that the positioning means are formed by two horizontal rollers (26, 27) placed on each side of the metal strip (1) and offset one with respect to the other.