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Surface Treatment Secret: Electrolytic Polishing

Release time:

2016-05-18 09:27

Surface Treatment Secret: Electrolytic Polishing
Surface Treatment Secret: Electrolytic Polishing

I. Definition

Electropolishing involves using the workpiece to be polished as the anode and an insoluble metal as the cathode. Both electrodes are simultaneously immersed in an electrolytic cell, and a direct current is passed through the system, triggering an electrochemical reaction that selectively dissolves the anode material. As a result, fine burrs on the workpiece surface are removed, and the surface brightness is enhanced.

II. Principle

The theory primarily states that metal ions detached from the workpiece form a phosphate film by reacting with phosphoric acid in the polishing liquid, which then adsorbs onto the workpiece surface. This adhesive film is thinner at protruding areas and thicker at recessed areas. Since the current density is higher at the protrusions, these areas dissolve more rapidly. As the adhesive film flows, the surface continuously alternates between convex and concave regions, gradually smoothing out the rough surface.

The workpiece serves as the anode and is connected to the positive terminal of a DC power supply. A cathode made of conductive materials such as lead or stainless steel—materials that are resistant to corrosion by the electrolyte—is connected to the negative terminal of the DC power supply. The two electrodes are immersed in an electrolyte (typically composed mainly of sulfuric acid or phosphoric acid) at a certain distance from each other. Under specific conditions—such as a certain temperature, voltage, and current density (generally below 1 ampere per square centimeter)—the workpiece is subjected to an electric current for a specified duration (usually ranging from tens of seconds to several minutes). As a result, the tiny protruding areas on the workpiece surface dissolve first, gradually transforming the surface into a smooth and lustrous finish.

III. Usage

Use the original solution, with the lead plate serving as the cathode (negative electrode) and the workpiece serving as the anode (positive electrode). The temperature should be between 60 and 80 degrees Celsius, the current density between 15 and 50 amperes per square decimeter, the voltage around 10 volts, and the duration 5 minutes. Process flow: Chemical degreasing → Hot water rinse → Cold water rinse → Electrolytic polishing → Hot water rinse → Cold water rinse → Passivation → Cold water rinse → Hot water rinse → Hot pure water rinse.

Note: Some process steps can be adjusted according to actual conditions.

IV. Characteristics

Typical products: architectural structures, food processing and storage, and medical and pharmaceutical applications.

Suitable for production: From single-piece to large-batch products.

Quality: Highly glossy, smooth, and hygienic surface.

Speed: Moderate production speed, 5–30 minutes per cycle.

V. Advantages

1. The interior and exterior colors are consistent, the luster is long-lasting, and even recessed areas that cannot be polished by mechanical polishing can be smoothed out.

2. High production efficiency and low cost. Samples can be prepared in large quantities.

3. Enhances the corrosion resistance of the workpiece surface and is suitable for all types of stainless steel materials.

VI. Disadvantages

1. The quality of electrolytic polishing is influenced by the electrolyte as well as the specifications for current and voltage. It is necessary to explore various polishing parameters, but since there are many factors that affect electrolytic polishing, it can be difficult to identify the correct polishing parameters.

2. For samples such as cast iron and inclusions, it is relatively difficult to obtain good results.

3. Enhances the corrosion resistance of the workpiece surface and is suitable for all types of stainless steel materials.

7. Applicable Materials

1. Most metals can be electrolytically polished, with stainless steel being the most commonly used for surface polishing—particularly austenitic nuclear-grade stainless steel.

2. Different materials must not be electrolytically polished simultaneously, nor should they even be placed in the same electrolytic solution.

8. Process Cost

The entire electrochemical polishing process is largely automated, so labor costs are very low.

9. Environmental Impact

Electropolishing uses less harmful chemicals, requires only a small amount of water throughout the process, and is easy to operate. Additionally, it can enhance the properties of stainless steel and help slow down its corrosion.

X. Case Demonstrations

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