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Surface blackening treatment process
Surface blackening of steel parts processing, also known as barffing. Black treatment now commonly used methods have the traditional alkaline heating and blackening of the late appearance of two kinds of room temperature. But the blackening process at room temperature is not very good for low carbon steel. A3 steel is slightly better by alkaline blackening.
Alkaline black fractionize comes out, have again black and two black distinction. The main components of the black liquor are sodium hydroxide and sodium nitrite. When you are black, you need a good tolerance of temperature. You can get a nice surface between 135 and 155 degrees Celsius, but it takes only a little time. In the actual operation, the need to pay attention to is the work piece before blackening and rust removing oil quality, and blackening after passivation of immersion. Blackening quality is often due to these processes and change.
“Blue” liquid metal
Using alkaline oxidation or acid oxidation; to form a layer of oxide film on metal surface to prevent metal surface corrosion, this process is called “blue”.
The black metal surface by the “blue” treatment after the formation of the oxide film, the outer layer is mainly magnetite, the liner layer is feo.