Principles of Electrochemical Polishing

    Electrochemical polishing uses the polished workpiece as the anode and the insoluble metal as the cathode. The two electrodes are immersed in the electrochemical polishing tank at the same time. Direct current is applied to produce selective anode dissolution, and the brightness of the anode surface increases. This process is the same as the electroplating process. exactly the opposite.

    Electrochemical polishing mechanism-the theory of viscous film is as follows. Polishing is mainly the result of the combined effect of the anode electrode process and the surface phosphate film. The metal ions dissolved from the anode and the phosphoric acid in the polishing solution form low solubility, high viscosity, and diffusion Phosphate with a low rate, slowly accumulates near the anode, and adheres to the surface of the anode, forming an electrolyte layer with greater viscosity. The mucosa with high density and poor conductivity is unevenly distributed on the microscopic surface, which affects the distribution of current density on the anode. Obviously, the thickness of the mucosa at the microscopic protrusions is smaller than that of the depressions, so that the current density at the protrusions is higher and the dissolution rate is faster. With the flow of the mucous membrane, the position of the convex and concave changes continuously, and the rough surface is gradually leveled. The stainless steel surface is thus polished to achieve a highly smooth and glossy appearance.

    It can be seen that the concentration and viscosity of the solution are important factors, especially the viscosity of the solution, which is often reflected in the fact that although the component concentration of the newly prepared polishing solution meets the requirements, it is not polished because the viscosity has not yet reached the requirements. Polishing starts well after electrolysis. In particular, the concentration and viscosity of the interface between the solution and the part play an important role in polishing. This is why it is required that the water film on the surface of the parts be uniform before entering the polishing liquid, otherwise the unevenness of the water film on the surface of the parts will destroy the normal formation of mucous membranes and cause local over-corrosion. The parts after water washing are best to be drained quickly after being dried, so that the surface over-corrosion phenomenon can be avoided after electrification and polishing.

    Electrochemical polishing cannot completely replace mechanical polishing. Electrochemical polishing only has a microscopic leveling effect on the metal surface. Macro leveling depends on mechanical polishing. Electrochemical polishing is particularly sensitive to the inhomogeneity of the chemical composition of the material and the micro-segregation, so that the metal matrix and non-metallic inclusions are often violently etched, sometimes with poor metallurgical state, and the non-uniformity of the metal crystal grain size structure. , Rolling traces, salt or oxide contamination, excessive pickling and excessive quenching, etc. will all have an adverse effect on electrochemical polishing. These defects are often compensated by mechanical polishing in advance.

    Compared with manual mechanical polishing, electrochemical polishing can exert the following advantages:

    1 The product has the same color inside and outside, clean and bright, long-lasting luster, and clear outline;

    2 The burrs in the threads dissolve and fall off during the electrolysis process, and the threads are loosely matched to prevent the seizure phenomenon when the threads are occluded;

    3 Enhanced corrosion resistance of polished surface;

    4 Compared with mechanical polishing, it has high production efficiency and low production cost.

(Huiputech)