Nickel coating of workpieces
Nickel plating is recommended for the corrosion protection of mainly steel, cast zinc, iron, brass and its alloys. Nickel plating gives not only an even gloss to the surface, but ensures good resistance in neutral, alkaline and acidic environment.
In electroplating technology, nickel coating is used for:
- protective and decorative purposes.
The appearance of glossy nickel used by us is suitable for decorative purposes. Usually it is used as a self-contained coating or as an intermediate layer. The most important feature of these coatings is their appearance.
For protective and decorative purposes, the nickel coating is used individually or as part of a copper – nickel – chromium coating system.
The essence of the copper-nickel-chrome coating system is that copper is used as a base layer, nickel is used as an intermediate layer and a chrome coating is applied to the workpiece as a last layer. This surface treatment gives objects excellent resistance to corrosion, condensation and temperature fluctuation, while they retain their shiny, glossy appearance. Apart from the external appearance of these coatings, the excellent corrosion resistance of the deposited coating is also important.
Depending on the goal to be achieved, reflection and corrosion resistance are the most important properties of the deposited coatings.
The galvanic nickel-plating on the surface of steel and zinc castings is called cathodic coating. This means that the corrosion of the base metal will always start on places of defect (scratches, holes, etc.).
A thin oxide film develops on the nickel coating, which results in the significant drop in glossiness, the surface becoming dull. To prevent this, a thin chromium layer is deposited on the nickel coatings and this can help keep the coating glossy. In the air, a passive film is rapidly formed on the chromium surface, which has a positive effect on the corrosion resistance of the nickel layer. This is because the deposited chromium layer becomes nobler than the (especially glossy) nickel layer underneath.
It should be noted, however, that working conditions are more sophisticated, at the same time the solutions and electrolytes are also more delicate. They require more care and are more expensive, and one has to consider at all times the way the additives applied modify the structure of the coating and its anticorrosion value (e.g. the sulphuric content of glossy nickel coating).
A sophisticated glossy technologies selected with due care and thoughtfulness can be used to achieve favourable technical and economic results.
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