Detailed explanation of the principle and application of chromium-free electrolytic polishing

Compared with chemical polishing , electrolytic polishing is superior. Electrolytic polishing has the following advantages:

1. The equipment is simple, and the process parameters are easy to adjust. It can replace mechanical polishing, or under some special requirements, continue mechanical polishing and then perform chemical polishing or electrolytic polishing. The surface brightness is higher, and it is easier to use automated scale than mechanical polishing. produce;

2. The requirements for profile structure and size range are wide, and industrial profiles with high surface requirements for precision parts can be processed. Profiles with large or small external dimensions and complex shapes cannot be processed by mechanical polishing;

3. The surface of the aluminum profile after electrolytic polishing is clearer and cleaner, without residual mechanical polishing dust, and has better corrosion resistance;

4. The specular reflectivity of the electrolytically polished surface is higher, and the metallic feel will be better.

Electrolytic polishing, also known as electrochemical polishing, uses aluminum as the anode to immerse in the prepared electrolyte solution, and uses corrosion-resistant and tiny protrusions and good performance materials (such as stainless steel ) as the cathode. According to the principle of electrolytic tip discharge, The small protruding parts on the surface of the aluminum profile after being energized are preferentially dissolved. At the same time, the dissolved product and the electrolyte on the surface form a high-resistance viscous liquid film layer. Maintain preferential dissolution. At the same time, the liquid film layer of the concave part is thicker and the resistance increases. Its dissolution rate is relatively slow. After a short period of electrolytic treatment, the protruding part is dissolved and flattened to the position of the concave part, making the aluminum surface rough The degree of reduction is reduced to a smooth and bright process.

Selection and application of chromium-free electrolytic polishing

1. Typical electrolytic polishing process

Electrolytic polishing can make the bright effect of the aluminum surface show high specular reflection performance, which is suitable for aluminum materials with special bright surface quality requirements in the industrial and scientific fields. Typical electrolytic polishing processes include acidic electrolytic polishing and alkaline electrolytic polishing, mainly in the following categories:

â‘ Sodium carbonate-trisodium phosphate alkaline electrolytic polishing process (Brytal process), this process is especially suitable for polishing high- purity aluminum , commonly used for aluminum products that have been mechanically polished and still need to further improve brightness is low, the aluminum sheet was dissolved polishing rate is small, the disadvantage is the solution drains faster, more sensitive to impurities.

â‘¡ Phosphoric acid-chromic acid- sulfuric acid acidic electrolytic polishing method (Battle method), sulfuric acid can effectively reduce the polishing operation current density and voltage, and allow electrolytic polishing at a higher temperature within a certain range, while also suppressing the occurrence of pitting corrosion chromic provide specular reflectivity alumina aluminum polishing surface.

â‘¢ electropolishing process fluoroboric acid, fluoroboric acid as a main component in the electrolyte, this process is more suitable for high purity aluminum material, which can reach 85% reflectivity.

④ Sulfuric acid-chromic acid electrolytic polishing process (Aluflex method), the bath control is relatively simple, the dissolution rate of aluminum in the polishing solution is quite fast in the initial 2min, about 25μm. And when the content of aluminum ions in the bath is too high, defects such as insufficient brightness or attachments on the surface may occur.

2. Chromium-free electrolytic polishing process

Because the traditional aluminum and aluminum alloy electrolytic polishing solution contains highly toxic chromic acid, it seriously pollutes the environment and the wastewater is difficult to treat, which is not conducive to the normal implementation of cleaner production. For this reason, it is imperative to adopt a new type of polishing process that is not harmful to the environment to replace the original typical electrolytic polishing process.

Summarizing the process research done by the predecessors on chromium-free electrolytic polishing, most of these polishing liquids are mainly phosphoric acid, and alcohols are used to replace chromic acid as a corrosion inhibitor . The alcohol molecules can form hydrogen bonds to form associations. Cooperation uses this special property to achieve leveling. According to the theory of electrolytic polishing, an alcoholic electrolytic polishing solution with associated properties forms a mucosa layer on the surface of the aluminum material to be polished, so that its concave position is in a stable passivation state, and the protrusions are dissolved at a faster rate Smooth and shiny surface. Increasing the number of hydroxyl groups of alcohol molecules is beneficial to polishing, and the effect of using soluble polyol polymers containing more hydroxyl groups is more obvious.

The chromium-free electrolytic polishing process has the great advantages of no yellow smoke, no flow marks, high stability, high brightness and high efficiency.