| 摘要 |
948,739. Chromium plating. METAL & THERMIT CORPORATION. May 24, 1960 [May 28, 1959], No. 18317/60. Heading C7B. Iron, steel or other basis metals with or without pre-coat platings of Cu or Ni, are given a double plating of Cr in which the first plating is effected with a chromic acid bath containing both fluoride and sulphate ions, containing 150 g. to 525 g. CrO3 per litre, and ratio by weight CrO 3 to F and SO 4 ions being 110:1 to 175:1, and at 32-60 ‹C., and in the second plating a similar bath is used in which ratio CrO3 to F and SO 4 ions is 50:1 to 100:1, whereby the top coating has fine cracks on the surface, at least 10 per cm. and preferably 40 per cm. The first coating is at least À25 Á thick and the second À5 Á, the total coating being preferably 1.5 to 3.8 Á thick. The fluoride ions are added in the form of fluo-silicate, -titanate, -aluminate, or -zirconate, as alkali metal or alkaline earth salts. Preferably the SO 4 ions comprise 25-65% of the combined SO 4 and F ions present. Specifications 697,786 and 711,468 are referred to. |
