How Does Hot Blackening Work?
- Hot blackening is a chemical process that creates a black oxide layer on the surface of ferrous metals (like steel or iron). This layer improves appearance and provides mild corrosion resistance without affecting the part’s dimensions.
* Cleaning (Degreasing & Descaling):
1. The part is cleaned thoroughly using alkaline degreasers and acid pickling to remove oil, dirt, rust, and mill scale.
2. Cleanliness is critical to ensure uniform blackening.
* Hot Blackening Bath (Black Oxide Formation):
- The part is immersed in a hot alkaline salt bath (typically sodium hydroxide with sodium nitrate/nitrite) at around 135–150°C (275–300°F).
- A chemical reaction occurs that converts the metal surface into magnetite (Fe₃O₄), a black oxide layer.
* Sealing (Usually in Oil):
- After rinsing, the part is dipped in a rust-inhibiting oil or wax, which penetrates the porous oxide layer and enhances corrosion resistance. #Hot Blackening Chemical Manufacturer.
