GB1096948A - Treatment of surfaces to produce level electrodeposits - Google Patents

Abstract

Smooth continuous electroplated metal (e.g. Ni, Cu or Cr) is produced on a basis metal (e.g. Fe, cast iron or steel) having surface cavities less than 0.15 mm in width by a) degassing the basis metal, e.g. by heating, b) grit blasting the surface to be plated thereby forming a saturated matte finish surface, the degassing step a) preceding or succeeding the grit blasting step b), c) applying a hardenable polyester resin, d) hardening the resin, e) grinding or otherwise abrading the hardened resin coating and the saturated matte finish surface to a smooth level surface in which substantially all of the remaining hardened polyester resin is present in cavities having a width of less than 0.15 mm, the remaining resin constituting less than 1% of the area of the smooth level surface, and f) electroplating a metal plate over the smooth level surface. Prior to blasting, the basis metal may be electroplated with a deposit of Cr 0.02 to 0.1 mm thick using a bath containing chromic acid and sulphate ions. A Cu-Ni undercoat beneath this Cr may be employed. After degassing, the metal may be degreased with CCl4, benzene, trichloroethylene or tetrachloroethylene. The polyester resin may be saturated or unsaturated and in the latter case may contain monomers which form cross-links. Many examples of resins are given. Typically the final electroplating may be of Cr from a bath containing 250 g/l chromic acid 2.5 g/l sulphate ion at 30-50 DEG C. and using a current density of 15-50 amps/sq.dm. for 3 hours to produce Cr 0.07 mm thick. A specific example is of electroplating a cast iron roll with Cr.