Technical possibilities at Metoba
Metoba offers the following techniques for processing Chrome VI-free passivations :Bulk-finishingKorbtechnik
1. Characteristics and properties
Since July 2007, European legislation has restricted or prohibited the use of chromium(VI), lead, mercury and cadmium. Until 30 June 2008, an exception was made for bolts and nuts used to fasten the chassis. The chromium(VI)-free layers also contain chromates, though in trivalent form, which are significantly less toxic to the environment and facilitate the recycling of the coated components. The term “chromating” is generally only used for chromate layers containing chromium(VI), while RoHS-compliant after-treatments are referred to as “passivation”. The properties of the layers applied from chromium(VI)-free passivations differ from those applied from chromium(VI)-containing chromates, e.g. in terms of corrosion protection, environmental compatibility or self-healing effect.
2. Benefits and areas of application
Chromium(VI)-free passivations are excellently suited for mass-produced articles such as screws and fasteners, as well as for all workpieces which, in addition to excellent corrosion protection, are intended to achieve a decorative and attractive appearance and are used in particular in the automotive industry. The passivation of zinc coatings considerably improves corrosion protection. The test methods for corrosion protection of passivated zinc coatings and the general test methods are defined in DIN 50961 and DIN 50960. The corrosion protection can be further increased by subsequent sealing of the passivated layers in polymer-containing solutions.
3. Basic material
Passivations are applied to deposited zinc layers.
4. Required delivery condition
The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with conventional aqueous alkaline degreasers. Oils containing silicone, alkali/alkaline earth and high-pressure additives must be avoided at all costs.
The workpieces to be passivated are processed immediately after zinc coating.