Verfahren zum Anbringen eines UEberzuges aus einem Metall,einer Metall-Legierung,einem Metalloxyd od.dgl.

摘要

Apparatus for depositing a coating of a powder on a moving metal strip comprises a rotatable metering roll having a length at least equal to the width of the strip to be coated and provided on its curved surface with depressions uniformly distributed, a container for powder having a powder outlet arranged to supply powder to said depressions, means for removing the powder from the curved surface of the roll surrounding the depressions, and means for removing the powder from the depressions in the roll and depositing it on the surface of the metal strip. In the arrangement shown metal strip 10 is passed round a deflector roller 11 and thence under a powder depositing station 12. The strip coated on one side is then passed round a further deflecting roller 13 and beneath a second powder depositing station 14. Each powder depositing assembly comprises a powder hopper 15, a metering roll 16 and a cylindrical brush 17. Powder 18 is introduced into hopper 15 and the metering roller 16 is rotated at a speed dependant on the quantity of powder to be deposited on the strip 10. The roll 16 preferably consists of a smooth surfaced roll the curved surface of which is covered with a closely conforming sheet of uniformly perforated metal, such as perforated zinc. The lower edge of the downstream side of the hopper 15 may serve as a wiper or a separate wiper 21 may be attached thereto and brush 17 which rotates in the opposite sense to roll 16 removes the powder from the perforations and propels it towards strip 10. Screens 19 and 20 provided with means for vibrating them in their own planes may be provided above the strip 10 and such screens may be electrically connected so that there is a potential difference between them and the strip. In other embodiments the metering roll consists of a hollow cylinder formed of a material which is permeable to gas, but not to the powder e.g. sintered bronze and having axially positioned therein an apertured pipe connected to a source of compressed air and stationary baffles extending from said pipe to the interior surface of the cylinder, which baffles define a sector of the cylinder such that compressed air in this sector perculates through to the cylinder surface and blows the powder from the surface of the cylinder on to the strip to be coated. Such a metering roll can be used for coating the strip from beneath. Again vibrating screens may be provided between the metering roll and the strip and the potential drop may be graduated in accordance with the spacing of the screens. A hood may also be provided between the metering roll and the strip to confine the powder therewithin. The apparatus may be used to deposit metal or plastics powder in particular metallic alloys and the coating step may be followed by compacting and sintering. Coatings of Al, Ni, Zn, Sn, Fe/Ni, Fe/Ni/Cr may be formed as single or as multilayers. Steel strip may be so coated.