The invention relates to a device and a method for hot-dip coating a metal strip with a metal covering, wherein the metal strip is directed continuously through a melt bath, wherein the thickness of the metal covering present on the metal strip when it leaves the melt bath is adjusted by means of a scraping device, and wherein slag which is present on the melt bath is driven away from the metal strip leaving the melt bath by means of a gas flow. To prevent slag from coming into contact with the metal strip leaving the melt bath, the invention drives away the slag from the metal strip by means of at least one nozzle which is arranged in close proximity to the metal strip, that a gas flow which extends over the width of the metal strip is directed onto the surface of the melt bath.

The present invention is provided with: a duct of which one end interconnects to a wiping nozzle (22, 23) and the other end is open; a first valve (17) that controls the actual gas pressure (P1) of the wiping nozzle (22, 23); a second valve (18) that controls the gas flow rate (Q2) dissipating to outside the system from another branched duct; a wiping pressure setting unit (11) that sets the set gas pressure (P1) of the wiping nozzle (22, 23); a first valve aperture setter (13) that sets the valve aperture of the first valve (17); a second valve aperture setter (14) that sets the valve aperture of the second valve (18); and a computation processing unit (12) that presents to the first valve aperture setter (13) the valve aperture at which the gas pressure (P1) matches a set gas pressure (P1), and presents to the second valve aperture setter (14) the valve aperture at which the total gas flow rate (QT) supplied from a gas supply device (15) becomes uniform.

A detection device includes a chamber for vacuum coating, a capacitance measurement device and a baffle mechanism located in the chamber. The baffle mechanism is a closed structure encompassed by a number of baffle walls, wherein at least one baffle wall includes a fixed baffle plate and a moveable baffle plate. The moveable baffle plate is pivotable about the fixed baffle plate. The moveable baffle plate, after pivoting, may get parallel with an adjacent baffle wall. The adjacent baffle wall and the moveable baffle plate are respectively connected to the capacitance measurement device, and the capacitance measurement device is used to measure the capacitance between the adjacent baffle wall and the moveable baffle plate. The detection device may accurately detect the service life of the baffle mechanism and achieve precise management of the apparatus.

Red rust staining of Al/Zn coated steel strip in acid rain or polluted environments can be minimised by forming the coating as an AlZnSiMg alloy coating with an OT:SDAS ratio greater than a value of 0.5:1, where OT is the overlay thickness on a surface of the strip and SDAS is the measure of the secondary dendrite arm spacing for the Al-rich alpha phase dendrites in the coating. Red rust staining in acid rain or polluted environments and corrosion at cut edges in marine environments can be minimised in AlZnSiMg alloy coatings on steel strip by selection of the composition (principally Mg and Si) and solidification control (principally by cooling rate) and forming Mg.sub.2Si phase particles of a particular morphology in interdendritic channels.

Red rust staining of Al/Zn coated steel strip in acid rain or polluted environments can be minimised by forming the coating as an AlZnSiMg alloy coating with an OT:SDAS ratio greater than a value of 0.5:1, where OT is the overlay thickness on a surface of the strip and SDAS is the measure of the secondary dendrite arm spacing for the Al-rich alpha phase dendrites in the coating. Red rust staining in acid rain or polluted environments and corrosion at cut edges in marine environments can be minimised in AlZnSiMg alloy coatings on steel strip by selection of the composition (principally Mg and Si) and solidification control (principally by cooling rate) and forming Mg.sub.2Si phase particles of a particular morphology in interdendritic channels.

An AlZnSiMg alloy coated strip that has Mg.sub.2Si particles in the coating microstructure is disclosed. The distribution of Mg.sub.2Si particles is such that the surface of the coating has only a small proportion of Mg.sub.2Si particles or is at least substantially free of any Mg.sub.2Si particles.

An AlZnSiMg alloy coated strip that has Mg.sub.2Si particles in the coating microstructure is disclosed. The distribution of Mg.sub.2Si particles is such that the surface of the coating has only a small proportion of Mg.sub.2Si particles or is at least substantially free of any Mg.sub.2Si particles.

A wiping device which blows a wiping gas toward a steel sheet from a pair of wiping nozzles disposed on both sides of the steel sheet so as to face sheet surfaces of the steel sheet, wherein the steel sheet is interposed between the pair of wiping nozzles and is pulled from a hot dip coating bath, the device includes a suctioning tube, wherein: the suctioning tube is disposed on both sides in a width direction of a section of the steel sheet, the section being positioned between the pair of wiping nozzles, so that the suctioning tube is in parallel to the steel sheet; the suctioning tube has a suctioning port that suctions an air; the suctioning port is disposed to face a side end surface of the steel sheet; a cross-sectional shape of the suctioning tube has the largest dimension thereof along a pulling direction of the steel sheet.

A wiping device which blows a wiping gas toward a steel sheet from a pair of wiping nozzles disposed on both sides of the steel sheet so as to face sheet surfaces of the steel sheet, wherein the steel sheet is interposed between the pair of wiping nozzles and is pulled from a hot dip coating bath, the device includes a suctioning tube, wherein: the suctioning tube is disposed on both sides in a width direction of a section of the steel sheet, the section being positioned between the pair of wiping nozzles, so that the suctioning tube is in parallel to the steel sheet; the suctioning tube has a suctioning port that suctions an air; the suctioning port is disposed to face a side end surface of the steel sheet; a cross-sectional shape of the suctioning tube has the largest dimension thereof along a pulling direction of the steel sheet.

There are provided an electromagnetic wiping device, a plated steel sheet wiping apparatus including the electromagnetic wiping device, and a method for manufacturing a plated steel sheet. A portion of a plating layer of a steel sheet having passed through a plating bath is preliminarily removed at least in an edge region of the steel sheet, and a gas wiping operation is performed. Therefore, overplating is prevented at least in the edge region of the steel sheet. In addition, since the load of gas wiping can be reduced while maintaining the line speed of the steel sheet, the quantity of scattered particles and the formation of dross can be reduced for improving the plating quality of the steel sheet and the productivity of a manufacturing process.