Technical possibilities at Metoba
Metoba offers the following techniques for processing Blackening of stainless steel :Rack-finishingBulk-finishing
1. Characteristics and properties
The burnishing of stainless steel is equivalent to the black oxidation of stainless steel, the latter being the technically correct designation. In contrast to the burnishing of normal steels, in which the burnishing layer is composed of iron oxides of various valences, the black oxidation of stainless steel causes the nickel atoms contained on the surface to be chemically oxidised at a temperature of 130°C and turn deep black as a result of this process.
The resulting layers are usually glossy, although the degree of gloss depends on the surface texture of the base material. The dimensional accuracy of the workpieces remains virtually unchanged. The resulting layer is non-slip, ductile and less than 1µm thick.
The colouring is very uniform at all points of the workpiece, even in bores and recesses with a diameter greater than 1 mm. Workpiece properties are not changed by black oxidation. The gloss of the black layers produced can be further enhanced by greasing or oiling.
The black oxidized surfaces are resistant to alkaline media, and are briefly resistant to weak acids. Oxidizing acids and hot sulphuric acid completely destroy the layer.
2. Benefits and areas of application
Areas of application for this process include the optical industry, the manufacture of electrical appliances, high-quality screws and screw connectors, springs and medical and automotive technology.
Black oxidation is used for decorative applications, especially in stainless steels. It serves as a cost-effective replacement for the otherwise used black chrome plating. The advantages of black oxidation are the uniformity of the coating and the optimum spreading capacity by using a wet chemical process. A further, decisive advantage is the adherence to the dimensional accuracy of the workpieces, especially in the case of fits.
3. Basic material
Stainless steels in all specifications with a nickel content of at least 7% can be machined.
4. Required delivery condition
In order to create a technically and optically high-quality layer by black oxidizing stainless steel, it is necessary to carry out a material-specific pretreatment. The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with common aqueous alkaline degreases. Silicone-containing, alkali-/alkaline-earth-containing oils and high-pressure additives must be avoided at all costs.
Before burnishing, the workpieces must be thoroughly degreased and cleaned. There must be no oil or grease on the surface, as this would not allow burnishing in the areas wetted with oil and would therefore not achieve a perfect result.