A thin film-type oxide coating is formed on the surfaces of metals and metal products in contact with air. It performs a protective function by preventing metal molecules from entering into electrochemical bonds with the bodies with which the metal is in contact. However, it is difficult to expect significant protection of the metal in this case, so metallurgical industries use not only natural oxidation, but also the application of artificial coating. In the domestic sense, it will protect the metal surface from corrosion and rust. The specialists of the company that provides the service scrap machinery removal near me know about all this
Methods of blackening, or bluing metal
Depending on the characteristics of the steel or cast iron object, and the desire to obtain a specific result, blackening can be performed in different ways:
Thermal – exposure to high temperature in various working environments. Melted salts, ammonia-alcohol solution, heating of the atmosphere to 300-500⁰ with the preliminary application of the catalyst to the surface can be used.
Acidic – electrochemical or chemical-physical action on the metal in an acidic environment.
Alkaline – immersion of the product in an alkaline solution with the addition of oxidizing catalysts.
The key to quality blackening of metal is the correct choice of method, as well as the maximum purification of the surface to be treated.
The resulting film has a thickness of about 10 microns, a microporous structure and a fine crystal lattice. In order to increase the protective properties even further, blackening, or blistering, of metal can be carried out in an oil working environment. In this case the coating will be saturated with lipophilic substances.
Often the purpose of blackening is not only to “protect” the metal product from corrosion as much as possible, but also to give it a black color. It is important to understand the essential difference between dyeing, in which a change of shade is achieved by applying a layer of artificial dye, and nielloing – in which the metal becomes black due to the release of pigments contained in it, or in the oxides formed chemically. While the paint layer can rub off or be damaged by mechanical action, blistering provides the tightest bond between the metal substrate and the pigmented oxide film.