Electropolishing Processes For Different Substrate Materials

1) Electropolishing process for steel materials

Due to the many types of steel materials, the composition varies greatly, different steel should be selected through the test polishing solution formula and operating conditions to obtain the best results. Production is widely used in phosphoric acid, sulfuric acid as the main component of the polishing solution, and then add a small amount of chromic anhydride can be used to polish most of the carbon steel and alloy steel.

Changes in the various components of the electropolishing solution have a certain degree of influence on the quality of electropolishing. When the sulphuric acid content in the electrolyte is high, the solution conductivity increases, the dispersion capacity is enhanced and the polished surface has a good lustre. However, the sulphuric acid should not be too much, otherwise it will make Cr03 in the form of Cr03-S03 partly precipitated out, thus reducing the surface lustre and shortening the service life of the polishing solution. The amount of water in the polishing solution should be kept certain, when the water is not enough, it may lead to the precipitation of Cr03. However, the maximum content of water should not exceed 30%, otherwise the lustre of the polished surface will be reduced.

Due to electropolishing, the anodic dissolution of steel parts occurs, and the dissolved iron remains in the solution, so the solution continues to accumulate iron ions. When the iron content of Fe203 to 7% to 8%, the solution lost polishing ability, need to be partly or fully replaced, or remove the solution of accumulated iron. There are two ways to remove iron: one is to make iron electrodeposition on the cathode; the second is to make iron precipitation in the form of insoluble salt.

2) Electropolishing process of aluminium and its alloys

Aluminum and its alloy electropolishing more than the use of phosphoric acid-based polishing solution. Such polishing solution is characterized by fast dissolution of the aluminum substrate, leveling performance, electropolishing the metal surface will generate a layer of corrosion-resistant oxide film layer, general products do not need to be anodized. Electro-polishing solution in phosphoric acid is mainly used to dissolve aluminium and its oxides, adding sulphuric acid can reduce the resistance of the polishing solution, thus reducing the operating voltage and promoting the stability of the electrolytic process.

The purity of the aluminium has a clear impact on the quality of the electropolishing. For example, in the three-acid mixture of polishing solution, polishing products containing 99.6% aluminium, its reflection capacity can be increased by 75% to 90%; and for products containing 99.2% aluminium, can only be increased by 68% to 80%, and the lower the purity, the more likely to appear speckle-like leaching. Therefore, in order to obtain high reflective capacity of aluminum products, should use high purity aluminum as raw materials.

Polishing solution in the chloride ion is a harmful impurity, when the content of chloride ion more than 1%, the surface of aluminum products are prone to pitting corrosion, the content of more than 5%, should be partially or fully replaced polishing solution. In addition, polishing solution should be regularly refilled with water and acid, so that the relative density of polishing solution to maintain at 1.67 ~ 1.70.

After polishing, the parts should be quickly removed from the polishing solution and immediately washed adequately, otherwise the polished surface will easily produce spots. After polishing, if you need to remove the oxide film on the surface of the product, available 10% NaOH solution, at 50 ℃ for a few seconds to dip.