ASTM-B630:88(R2021) pdf free download – Standard Practice for Preparation of Chromium for Electroplating with Chromium.
5.1.3 cathodic Alkaline Cleaning—Removal of final traces of dirt, grease, and oil is best accomplished by cathodic alkaline cleaning. Cathodic electrocleaning is necessary because anodic electrocleaning will strip chromium and may expose the basis metal. In cathodic cleaning, the parts are negatively charged and attract positively charged metallic ions, soaps, and other colloidal materials in the solution, causing them to “plate out” as loose smut on the surfaces being cleaned. Thus, do not allow the cleaning solution to become heavily contaminated with dirt, grease, or oil.
5.2 Masking—Rigid, nonconducti ye materials or stop-offs, which are especially compounded nonconductive tapes. waxes, lacquers, or polymeric materials, will protect areas that are to remain free of chromium. Due to the varying kinds of chromium electroplating solutions and interactions with these materials, vendor instructions should he followed.
5.3 Acth’ating:
5.3.1 The procedure used for etching or activating the chromium surface is most important and usually determines the soundness of the adhesion. Chromium exhibits a strong tendency to acquire surface oxides rapidly (air passivity) that reduce the adhesion of subsequent chromium deposits. Anodic etching in a chromic acid solution, 250 gIL, at room temperature is recommended. In some instances, this procedure may be performed in the chromium electroplating solution.
5.3.2 Give the part an anodic etch for 5 to 60 s at 6 V. For effective control, confirm etch action by visual observation of uniform gassing; increase etch time if necessary. When basis metal is exposed or high-speed chromium electroplating solutions are used, keep the lime as short as possible.
5.3.3 When the part to be electroplated has a large mass, allow it to reach the temperature of the electroplating bath before etching.
5.4 Ch roni iunz Elect roplating:
5.4.1 Make the part cathodic up to 3.0 V. Slowly increase the voltage in steps of 0.25 V so that gassing and electroplating start after 30 to 60 s and full current is reached in 5 mm.
5.4.2 The composition of the ordinary or ‘conventiona1” solution is 250 to 400 gIL of chromic acid (Cr03) and sulfate radical (SO4 ) to maintain a ratio by weight of Cr03 to SO4 = of 10010 I, although many electroplaters prefer ratios as low as 80 to 1, which facilitates electroplating chromium on chromium. The sulfate is generally added as sulfuric acid (94 to 96 mass % H2S04). Refer to Guide B 177 for more information on the operation of the electroplating solution.
5.4.3 Some proprietary baths contain a supplementary catalyst in the fonn of fluorides or other mixed catalysts. Some of these baths arc satisfactory, but some could be unsuitable. The supplier of any proprietary bath should be consulted for specific information.
6. Keywords
6.1 activation; chromium; cleaning; preparation; striking.