Blackening stainless steel

What is stainless steel blackening?

The coloring of stainless steel is an extension of classic burnishing, which is specially adapted to the alloy of the material.

Unlike burnishing, this does not involve the formation of an oxide layer, but rather a conversion layer consisting of the material’s own nickel and parts of the process solution. This complex forms a black appearance as well as improved corrosion protection, which is used in areas such as mechanical engineering and fastening technology (e.g. nails, nuts, screws, washers, etc.).

Advantages of blackening stainless steel

How does blackening stainless steel work?

Coarse impurities and corrosion products are removed from the workpieces by boil-off degreasing and pickling to create a basis for further finishing.

The stainless steel coloring process produces a deep black and dimensionally stable conversion layer on nickel-containing stainless steels, depending on the base material. The products are immersed in highly concentrated alkaline molten salts at temperatures of up to 130 °C.

After treatment, the components are rinsed several times to remove the molten salt from the workpiece. The blackened surface is then dewatered and lightly oiled using a dewatering fluid. This process is recommended, but not absolutely necessary.

Are you looking for a partner for stainless steel blackening?

Then contact us now.
We look forward to being able to process your request individually.

Why choose Techno Coat?

Everything from a single source

Blackening stainless steel is not our only area of expertise when it comes to surface finishing. We offer numerous other coatings, such as PVD or galvanic processes.

Speed

Are flexibility and prompt order processing important to you? We have the capacity to realize your ideas even at short notice.

Many years of experience

Our many years of experience from over 25 years of surface coating is one of our hallmarks.

High quality standards

Internal testing procedures and our certified QMS are used to ensure that you benefit from the high quality of our shift systems in the long term.

How we blacken stainless steel - the process

Mechanical cleaning

As a pre-treatment, it may be necessary to remove scale, oxides and other foreign contaminants such as wax crayon, adhesive residues or paint from the components using suitable processes.

Decoction degreasing

Oils, fats and other additives are dissolved in the decoction degreaser and thus removed from the surface.

Sinks

Chemical residues from the degreasing process are removed in the rinsing tank.
This step is repeated several times during the rest of the process.

Pickling

A pickling agent based on hydrochloric acid activates the surface and removes any oxides. This is followed by a further rinse cycle.

Coloring

The components are blackened in a 140 °C molten salt bath for 5 – 15 minutes. This is followed by intensive rinsing cycles and finally a hot rinse cycle.

Dewatering Fluid

Finally, there is a dip in a low-viscosity fluid that displaces the water from the surface.

Frequently asked questions

What are the advantages of blackening stainless steel?

The layer created by blackening stainless steel offers the following advantages:

non-slip and ductile
resistant to bending and abrasion
Retention of the conductivity and magnetic properties of stainless steel
Dimensional accuracy is not impaired
Comparatively inexpensive process
Very uniform layer structure
Surface structure corresponds to the unfinished surface

What are the disadvantages of blackening stainless steel?

The following disadvantages must be taken into account when blackening stainless steel:

Coating quality is highly dependent on the coated material (processing of the surface and alloy components)
Highly compacted surfaces often lead to an uneven coating
the surface produced has a slight soot formation
Oxidizing acids and hot sulphuric acid completely destroy the coating

What investment capacities are available?

Our system capacities are 600 x 300 x 400 mm. Please also contact us for oversizes.