GB1357214A - Method and apparatus for coating a metallic strip - Google Patents

Abstract

1357214 Powder coating metal strip BRITISH STEEL CORP 7 June 1972 [29 June 1971 30433/71 Heading C7D [Also in Division D1 In a method for coating a metallic strip (e.g. a ferrous strip) with a metallic powder (e.g. Al- or Cr - containing powder) the strip 13 is caused to travel via deflector rolls 14 to 17 past a first wetting means 22 and at a constant spacing across its width from a first electrostatic deposition device 23 which coats the first side 11 of the strip with the metallic powder, and then passes via deflector rolls 18 and 19 to a second wetting means 24 and at a constant spacing across its width from a second electrostatic deposition device 25, which coats the reverse side 12 of the strip, before passing through dryer 26 and compacting rolls 30, 31, the constant spacing of the strip 13 from the second electrostatic device 25 being maintained by passing the wetted and coated surface 11 over smooth surfaced support rolls 33 and 34 arranged respectively immediately upstream and downstream of the device 25. The wetting solution is preferably a solution of sodium or potassium silicate, carboxymethyl cellulose or a suspension of a gelatinous metal hydroxide (e.g. Ni(OH) 2 or Al(OH) 3 ). The electrostatic deposition devices are preferably electrostatically charged grids disposed parallel to and spaced from the surfaces of the strip by 1À0 to 1À5 inches. The strip is coiled and heat treated to diffuse the metal coating into the strip.