Mechanism And Control Measures To Black Spot Defect On The Surface Of Electrolytic Chromium-Coated Steel

In recent years, coating quality is paid more and more attention because electrolytic chromium-coated steel has more and more extensive application at home and abroad. The black annular spot defect, commonly known as the burning point, on the coating found in the chrome plating unit seriously affects the quality of the coating surface. This paper is about the research of the mechanism to the black spot defect on the surface of electrolytic chromium-coated steel and control measures.Black spot defect seriously affects the downstream process and the quality of printing and coating to the products. It has a negative impact in the user’s reputation.The defect is studied by scanning electron microscope, energy spectrum analysis, Hull cell experiment and simulation plating experiment. It is found that the production factor of the black annular spot defect is coating burning caused by large current density at the place with solid impurity and not fully dissolved chromic anhydride. The defect is annular because of the solid impurity falling down from the surface of steel. Control measures to the defect are put forward according to its production factor.