Knowledge of Electropolishing Processes

Electropolishing processes use polished workpieces as anodes and insoluble metals as cathodes, and anodes and cathodes are immersed in electrolytic tanks at the same time; selective anodic dissolution is generated by ionization reactions of direct currents so as to achieve the effects of removing tiny burrs on surfaces of workpieces and improving brightness of workpieces.

 

Principles of electropolishing processes

The main theory of the electropolishing process is that the metal ion of the workpiece and the phosphoric acid in the polishing solution form a layer of phosphate film, and the film adsorbs on the workpiece. This kind of film is thin on the protruding part of the workpiece and thick on the concave part of the workpiece. The film will quickly dissolve due to the high electric current density of the protruding part. With the flow of the film, the protruding surface and the concave surface vary, and the rough surface will be gradually leveled.

 

Workpieces as anodes are connected to positive poles of direct-current power supplies. Conducting materials such as lead and stainless steel which are electrolytic corrosion resistant as cathodes are connected to negative poles of direct-current power supplies. The workpiece and the conducting material between which there is a certain distance are immersed in the electrolyte which generally contains sulfuric acid and phosphoric acid as elementary composition. At a certain temperature, the tiny protruding part on the surface of the workpiece will be firstly dissolved, and the surface will gradually become smooth and bright after the power is on (usually from dozens of seconds to several minutes). 

 

Features of electropolishing processes

There are four features of electropolishing processes. 

① The surface which needs to be polished won’t form the deteriorative layer and have the subsidiary stress, and the original stress layer will be removed or reduced.

② Electropolishing processes can process hard materials and soft materials which are difficult to be processed as well as parts and metal products with thin walls, complicated shapes and small sizes.

③ Electropolishing processes have advantages of short time, high production efficiency and polishing several workpieces at the same time.

④ The best surface roughness which can be obtained by the electropolishing process is related to the original surface roughness. Application scopes of electropolishing processes are limited due to electrolytes’ shortcomings such as poor universality, short service lives and strong corrosion. Electropolishing processes are mainly used for metal products and parts such as mirrors, stainless steel tableware, ornaments, needles, springs, blades and stainless steel pipes which have small surface roughness, and they can also be applied to polishing some mold such as plastic bakelite molds and glass molds.