ES340096A1 - Electrodeposition of chromium upon a continuous metal strip - Google Patents

Abstract

In a process for electro-plating chromium on to continuous thin gauge metal strip, the strip is passed through a chromium plating bath comprising chromic acid and a catalyst comprising fluoride ion or complex fluoride ion with or without sulphate ion, at a velocity of at least 30 m/min. The strip may be of iron or an alloy thereof, e.g. stainless steel, and may be precoated, e.g. with copper or nickel. Sulphate ion may be present in the bath as H 2 SO 4 or as strontium fluoride the complex fluoride ion may be fluoaluminate, fluosilicate, fluozirconate, fluotitanate or fluoborate and fluoride ion and complex fluoride ion may be present in the bath as potassium salts thereof. Prior to electro-deposition oil or grease may be removed from the strip prior to plating by anodic or cathodic treatment in an alkaline bath which may contain sodium hydroxide or other inorganic hydroxide, or inorganic salt e.g. a silicate, borate or phosphate. The bath may also contain a surfactant, e.g. sodium alkylsulphate. Rust may be removed by treatment in a hydrochloric or sulphuric acid bath. The plated strip may receive a subsequent treatment with aqueous dichromate solution such as alkali metal, e.g. sodium, dichromate. The solution may also contain a phosphate, e.g. monosodium phosphate. The strip may be cathodic during this treatment. The plated strip may be given a further coating of polybutadiene-base pigment enamel a base coat of oleoresin varnish enamel followed by a top coat of vinyl base enamel or an enamel containing zinc oxide.