Reducing surface roughness of metallic objects and burnishing liquid used

Abstract

A physicochemical process for refining metal surfaces which includes the steps of introducing metallic objects to be refined and a solution capable of reacting with the metal to produce a softer phosphate or oxalate conversion coating on the metal surface into a finishing unit for agitation. Agitation is carried out to produce movement among the metallic objects for conversion of the metallic surface by the solution. The mechanical and chemical action achieves a reduction in the surface roughness of the metallic objects. A burnishing step is carried out by agitating the metallic objects with a burnishing liquid to remove the conversion coating and to achieve a specular finish. The burnishing liquid contains 0.01 to 1.5 weight percent of a phosphate compound and 0.002 to 0.2 weight percent of an organic slip agent and is used at a pH of 8.5 to 10.5. The low organic content of the burnishing liquid produces a waste stream having a low oxygen demand for waste treatment facilities. Optionally, high density, non abrasive particles may be used during the conversion and burnishing steps to help in reducing surface roughness and removal of the conversion coating.