Black finishing

What is black finishing?

To create corrosion protection for iron-containing surfaces, during black finishing workpieces are immersed in baths containing acidic or alkaline solutions, with a distinction being made between hot and cold black finishing. This process causes an oxide layer with a distinctive deep-black color to form on the surface, with a thickness of around 1 µm. In contrast to phosphate conversion coating and chromating, during black finishing only oxygen, and no other chemical elements, is stored in the layer. Due to the low layer thickness, the dimensional accuracy of the workpieces remains virtually unchanged after treatment. Based on this property and its very low thermal loading (< 150°C), which prevents microstructural changes, black finishing is one of the most commonly used processes in mechanical engineering and toolmaking. Un- and low-alloyed steels as well as cast iron are suitable for black finishing. Hardened steels can also be black finished. The black finishing process is standardized in Germany according to DIN 50938 and internationally according to ISO 11408.

Blued gear
Screws blackened by bluing

Properties and benefits

The iron oxide layer, which is formed during the black finishing process is largely bending- and erosion-resistant and can withstand high temperatures of up to 300°C. It enhances the resistance of the workpieces to mechanical loading and produces a slight corrosion protection (e.g. against hand perspiration, solvents and varnishes), which is often sufficient for use within buildings. Via additional treatment with greases, oils or wax, which can be incorporated within the porous black finishing layer, the protective effect can be further enhanced. The surfaces resulting from black finishing have an increased erosion resistance and provide advantages in terms of running-in and emergency-running properties. Lubricants adhere better than with untreated components and the risk of cold-welding of sliding surfaces is reduced by black finishing. 

Application area

The method is most frequently used in mechanical engineering and toolmaking, where black finishing is a popular method for providing basic corrosion protection. Furthermore, black finishing is also often used as a pre-treatment prior to further surface finishing (e.g. such as varnishing), to produce a better surface for bonding. In addition to its protective properties, black finishing is also often applied for visual reasons. Iron workpieces can be given an antique look with this process, which is popular for example when creating rustic-looking furniture. The process is also often used for firearms (especially pistols), as well as bladed weapons. Since the low thermal loading does not give rise to microstructural changes, and the workpieces retain their dimensions due to the low layer thickness, the process can also be used for measuring tools.

Durch Brünieren geschwärzte Waffen

Why order black-finished CNC parts from FACTUREE?

  • Express delivery within 9-12 working days
  • Constant free capacities thanks to a large production network
  • Quotation within 48 hours
  •  Reliable punctual delivery

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