Patent ID: 6106620
Filing Date: 2000-08-22
Classification: C23C

Abstract:
A hot dip coating apparatus comprising:a pot for containing a bath of molten metal,duct means defining an elongate strip inlet passage having a longitudinal direction extending downwardly from an opening in a floor surface of the pot, the passage and the opening being dimensioned so that a metal strip to be coated may move upwardly through the passage and the opening into the bath without contacting the apparatus or the duct means, andelectro-magnetic plugging means to prevent leakage of bath fluid from the pot through the passage, wherein:the plugging means comprise two magnetic field generators disposed one on each side of the duct means;each generator projects an oscillating magnetic field into the passage from at least two poles of opposite polarity that are adjacent the passage and spaced apart in said longitudinal direction;said at least two poles of each generator are respectively directed towards and in substantial alignment with the corresponding poles of the other generator in transverse directions substantially perpendicular to said longitudinal direction to form two pairs of mutually aligned poles;the magnetic fields projected by the generators extend along flux paths which are substantially mirror images about a longitudinal center plane of the passage;both generators operate at a frequency of more than three kiloHertz; andthe poles of each mutually aligned pair of poles are of opposite instantaneous polarity, whereby;in use in the absence of an intervening strip to be coated, the projected magnetic fields extend across the passage between the poles of each said mutually aligned pair of poles and,in use in the presence of an intervening strip to be coated, the projected magnetic fields extend longitudinally of the passage between the at least two poles of each generator without crossing said intervening strip.