Chrome-free electropolishing--The Aluservice alternative to chemical and electrolytic polishing

摘要

Traditionally, to obtain a mirrorlike finish on aluminium two different methods are used: chemical and electrochemical polishing. The first type is the most widely used and involves the use of a three-acid solution (phosphoric acid, sulphuric acid, nitric acid) at a temperature greater than 95 °C with an average density of 1.750. The two critical points of this method have an environmental origin: air and water. The nitrates in wastewater cannot be eliminated but only diluted (which is forbidden) or concentrated at very high costs. The electrochemical polishing process is likewise a three-acid mixture: phosphoric acid, sulphuric acid, chromic acid. The operating temperature ranges between 65 and 75 °C, with an average density of 1.730. As noted the mixture contains chromic acid and, despite being easily eliminated, its presence in the factory is discouraged by the authorities. Aluservice has provided an answer to these problems with the development a product called Chrome-Free Electrolytic Brightening AluBrill ALS - 94. As regards the operating conditions, the pieces to be polished go through a slightly alkaline degreasing solution to remove oils, greases and pastes which would contaminate the polishing solution. After a thorough rinsing, the pieces are finally polished and the patinate is removed before being anodized.