No yellow smoke polishing process on the surface of industrial aluminum profiles
- 2019-10-08-

No yellow smoke polishing is currently a hot topic, and there are many non-yellow-smoke polishing solutions on the market. According to the introduction, it can be compared with electrolytic polishing. No yellow smoke polishing can be understood from two aspects: First, no nitric acid and nitrate are added to the chemical polishing solution, in which case there is naturally no yellow smoke; second, a certain amount of nitric acid or nitrate is added to the chemical polishing solution. However, by adding other substances to suppress the generation of nitrogen oxides, it is also possible to achieve no yellow smoke during polishing, and this may also be referred to as yellow-free polishing. In the latter case, the consumption of various added substances during the polishing process is not equivalent, so when one of the added substances is consumed to a critical point, a small amount of yellow smoke may also be generated, which may also be called Polished for low yellow smoke. The former is achieved by adding certain organic substances in a polishing solution containing no nitric acid. Most of the formulations are commercial products; the latter is to add a clathrate compound to the polishing solution containing nitric acid to absorb nitrogen oxides to eliminate yellow smoke. The main compounds are hydroquinone, urea, thiourea, cyclodextrin, deoxycholic acid, perhydrotriphenylene and 4,4'-dinitrobenzene biphenyl. Not all of these clathrate compounds are suitable for chemical polishing with nitric acid, which requires experimentation to find suitable additives and additions.

The polishing effect without yellow smoke polishing cannot be generalized, depending on the type of polished aluminum. For example, a polishing system using ammonium nitrate monoammonium fluoride can obtain very good lightness for some industrial aluminum profiles , and there is no yellow smoke during the polishing process. The following is a description of the two types of yellow smoke (or low yellow smoke) polishing process that I have used in small batches.

  The basic composition of the polishing solution consists of phosphoric acid, sulfuric acid and a mixed additive having a volume ratio of phosphoric acid to sulfuric acid of 8:2. Adding components: copper sulfate (or copper nitrate), nickel sulfate (or nickel sulfate), silver nitrate, potassium permanganate. In this polishing system, the polishing quality is close to that of triacid polishing, and no yellow smoke is generated during polishing. If 40-50 g/L ammonium nitrate is added to the polishing solution, the polishing luminosity and flatness are obviously improved, the polishing quality is better than the ordinary triacid polishing, and the high-luminescence aluminum can obtain more than 90% of the bright reduction degree. At the same time, there is no yellow smoke in the polishing process after the addition of ammonium nitrate. This is mainly due to: the addition of an ammonium salt inhibits the generation of yellow smoke; and the formation of a metal replacement layer on the aluminum surface during the polishing process. , slowing down the corrosion rate during the polishing process, so that the workpiece is almost free of yellow smoke during the polishing process.