ASTM B630-88(R2021) pdf free download

ASTM B630-88(R2021) pdf free download.Standard Practice for Preparation of Chromium for Electroplating with Chromium
1. Scope
1.1 This practice is intended to serve as a process guide (not as a standard procedure) for producing adherent electrodeposits of chromium on chromium for engineering use. 1.2 Only well-known, generally practical methods using hexavalent chromium plating baths have been included. Some of the newer proprietary chromium plating processes produce chromium plating for which this process is unsuitable. Suppli- ers of the processes should be consulted. 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Preparation of Surface
4.1 Surface Finishing—The smoothness of the chromium coating before electroplating with chromium should closely approximate the requirements of the finished part. It is usually achieved by appropriate grinding with a diamond wheel. 4.2 Stripping and Basis Metal—With previously electro- plated parts where the chromium deposit has been worn through, or where grinding has exposed the basis metal, preferred results are obtained by stripping the remaining chromium completely. However, it is possible to obtain satis- factory deposits on such substrates by careful attention to details in the pretreatment and electroplating process steps. 4.3 Stripping may be done by several methods, including proprietary processes or inhibited hydrochloric acid solution (10 to 20 % by volume), or anodic treatment at 55 to 800 A/m 2 (5 to 75 A/ft 2 ) in a solution of 35 to 50 g/L (5 to 7 oz/gal) of sodium hydroxide or 60 to 75 g/L (8 to 10 oz/gal) of sodium carbonate at 20 to 25°C (70 to 80°F). 4.4 Process Outline: 4.4.1 Preclean (see 5.1.1 and 5.1.2), 4.4.2 Alkaline electrolytic clean (see 5.1.3), 4.4.3 Rinse (cold water), 4.4.3.1 Rinse (hot water), 4.4.3.2 Dry, 4.4.3.3 Mask (see 5.2), 4.4.4 Activate (see 5.3), 4.4.5 Chromium electroplate, 4.4.6 Rinse (cold water), 4.4.7 Rinse (hot water), and 4.4.8 Dry.
5. Procedure
5.1 Cleaning—The following cleaning treatments may be used for all conditions and types of electrodeposited chro- mium. The choice of the procedures will be governed largely by the condition of the surface. 5.1.1 Precleaning—When considerable amounts of grease and oil are present on the surface, precleaning (emulsion or alkaline spray or soak) is necessary to remove the bulk of the soil. 5.1.2 Abrasive Cleaning—Oxide and other films may be removed by mechanical techniques using such abrasives as fine emery on a cloth or a wheel, pumice slurry, or greaseless buffing compounds. Grit blasting, shot blasting, wet blasting, or vapor honing may also be used. Abrasive cleaning is generally not necessary when suitable mechanical finishing procedures have been used. 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 be- cause 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, nonconductive 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 be followed. 5.3 Activating: 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 ten- dency to acquire surface oxides rapidly (air passivity) that reduce the adhesion of subsequent chromium deposits. Anodic etching in a chromic acid solution, 250 g/L, at room tempera- ture is recommended. In some instances, this procedure may be performed in the chromium electroplating solution.