The surface blackening treatment of steel parts is also known as bluing. The commonly used methods for blackening include traditional alkaline heating blackening and later room temperature blackening.
Author: Marisa
The surface blackening treatment of steel parts is also known as blueing. The commonly used methods for blackening include traditional alkaline heating blackening and later room temperature blackening. But the room-temperature blackening process is not very effective for low-carbon steel. It is better to use alkaline blackening for A3 steel. Alkaline blackening is further subdivided, with a difference between once blackening and twice blackening.
The main components of black liquor are sodium hydroxide and sodium nitrite. The temperature tolerance required for blackening is relatively high, and a good surface can be obtained between 135 ° C and 155 ° C, but the required time is slightly longer. In practical operation, it is important to pay attention to the quality of rust and oil removal before blackening of the workpiece, as well as the passivation and oil immersion after blackening. The quality of blackening often varies due to these processes, and the metal "blueing" solution is treated using alkaline oxidation or acidic oxidation methods; The process of forming an oxide film on the metal surface to prevent corrosion is called "blueing". The oxide film formed on the surface of black metal after the blueing treatment is mainly composed of iron trioxide on the outer layer and ferrous oxide on the inner layer.
(1) The metal surface must be washed and dried before undergoing the blue treatment.
(2) The conditions for the blue treatment of metal devices are related to the carbon content in the metal.
(3) Analyze the content of sodium nitrate, sodium nitrite, and sodium hydroxide in the solution regularly every week or so, to supplement relevant components promptly. Generally, all solutions should be replaced after six months of use.
(4) After the metal turns blue, it is best to rinse with hot soapy water for a few minutes and then rinse with cold water. Then, rinse with hot water and blow dry.
Blue treatment on the surface of steel parts can greatly enhance their corrosion resistance and prolong their service life. This method is commonly used for weapons, springs, steel wires, etc. The basic principle is that iron reacts at a certain temperature and for a certain period in a mixed solution containing oxidants and caustic soda to form sodium ferrite (Na2FeO2) and sodium ferrite (Na2Fe2O4). Sodium ferrite and sodium ferrite then interact to form a ferric oxide film.
Blackening treatment is the formation of a protective film of ferric oxide (black) on the surface of a metal, with a layer thickness of less than 3um. It is commonly used in bolts, nuts, and measuring instruments. The material that can be treated is steel. Purpose and specialty: sprayed bottom layer, appearance (glossy), rust-proof, but easier to rust than phosphate rust-proof treatment
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