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In order to prevent the corrosion of steel parts, it is […]
In order to prevent the corrosion of steel parts, it is one of the common methods to plate a layer of zinc on the surface. Due to different processes, different names have been generated.
Galvanizing is mainly electroplated and fired. The former is the process of energizing the electrolyte containing zinc ions, and plating a layer of zinc on the surface of the steel parts; the latter is the process of melting the zinc and immersing the steel parts to make the surface adsorb a layer of zinc. Since the former is normal temperature and the latter requires high temperature, it is also referred to as cold galvanizing, and hot galvanizing is called hot galvanizing.
The quality of hot-dip galvanizing is better than cold galvanizing. 1, the general electrogalvanized layer thickness of 5 ~ 15μm, while the hot-dip galvanized layer is generally more than 35μm, even up to 200μm. 2, hot dip galvanizing coverage better than electroplating zinc.
Since zinc is easily corroded, after the galvanization, a passivation process is used to generate a thin film on the surface of the galvanized layer to reduce corrosion.
Because the passivation process is not the same, the passivation film has different colors respectively, so there is a non-standard name on the market: yellow zinc plating, blue and white zinc and so on.
???In the passivation process, there is a passivation process using chromic acid. Cr of chromic acid is +6. During the passivation, part of Cr+6 is reduced to Cr+3 by zinc and the compound of trivalent chromium and zinc is blue. Green, plays a role in the skeleton in the passive film, hexavalent chromium and zinc compounds are red or brown. As the passivation film is yellow, it is commonly called yellow zinc plating.
???Because hexavalent chromium compounds are highly toxic, are carcinogenic, are restricted by various countries and will be banned, trivalent chromium or chromium-free passivation processes have been researched.
???The galvanized layer using a non-hexavalent chromium passivation process is called environmental zinc. Environmental protection galvanizing does not necessarily mean the use of trivalent chromium (CR+3) for passivation, because this is only a relative concept. If galvanized, it must be inseparable from acid and alkali. These are all harmful substances. The so-called environmental protection can only be Try to minimize pollution and production hazards. Currently, because hexavalent chromium (CR+6) is a carcinogen, it is banned from use by RoHS. Therefore, a formal development company or an environmental protection company does not use this passivation solution. Currently, it is generally used as a trivalent product. Chrome instead of it. Moreover, trivalent chromium can also be passivated color zinc, black zinc, blue and white zinc, etc., but black zinc is the most expensive, because there is silver inside, Army Green is currently basically hexavalent chromium
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