Multifunctional coatings for metallic components | FASTENER EURASIA MAGAZINE
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GEOMET® - Multifunctional coatings for metallic components

The GEOMET® zinc flake anticorrosion technology is a leading player in the protection of metallic parts owing to its properties:

•    Highly resistant to corrosion
•    Thin thickness: to ensure no thread interference
•    Exempt of hydrogen embrittlement: a cost-effective coating that does not induce hydrogen embrittlement
•    Lubricated:  to secure joint and ease assembly and disassembly
•    Damage resistant: to resist “attack” by assembly tools, thermal shocks and chemicals
•    Compatible with paint after assembly
•    Environment-friendly: GEOMET® coating is water-based


The GEOMET® high resistance to corrosion relies on a combination of 3 different mechanisms:

•    Barrier protection – Overlapping zinc and aluminium flakes provide a barrier between the substrate and the corrosive atmosphere
•    Galvanic action – Zinc corrodes to protect a steel base material
•    Passivation – Metal oxides slow down the corrosion reaction of the zinc and steel to provide a greater corrosion protection than with pure zinc.


By its nature, chemical composition and curing conditions, GEOMET® water-based zinc and aluminium flakes coatings makes it possible to obtain a micro-layer of 8-10 μm (including the topcoat). The coating film grants to the base metal a high resistance to corrosion, passing the latest stringent automotive requirements. These ones are generally based on a Salt Spray Test resistance of 1000 hours without red rust (ISO 9227/ASTM B117), but also on specific cyclic corrosion tests (ACT, GMW 14872, SAE J2334, …) and resistance to dynamic corrosion test on vehicle. 

The entire coating process does not generate hydrogen and, consequently, no hydrogen-induced embrittlement risks are associated with it. This particularity and the extremely low coating thickness that is suitable even for fine screw’s threads, make GEOMET® the preferred coating for screws and fasteners in the automotive and other industries where high-strength steel of classes up to 12.9 are used. 


Particularly in the automotive industry and depending on where and how the coated parts are assembled, the high anticorrosion performance is nowadays only one of the requirements. Other associated performances, like dimensional tolerances, screw assembly at a specific torque, friction coefficient stability after multi-tightening, heat loosening, heat resistance, chemical resistance, appearance, have become over the time more and more important.

NOF Metal Coatings Group has developed a range of coating systems to satisfy all these additional requirements. The association of GEOMET® basecoat with a variety of topcoats provides a fine-tuned friction behaviour of fasteners on automatic assembly lines (PLUS®, DACROLUB®), gives strong resistance to chemicals (GEOKOTE®) and as well as aesthetical and functional properties (GEOBLACK®).


Higher coating thicknesses are required for conventional and solvent based coatings to achieve the same corrosion resistance as water-based zinc and aluminium flakes coatings. This has a direct effect on the fastener’s tolerances and, indirectly, on the global resources.
Since the beginning, NOF Metal Coatings Group chose to produce and commercialize only water-based coatings. The Group policy consists in developing innovative production processes allowing the already low VOC amount in chemicals to be considerably reduced. 


The process and equipment cannot be the same according to the kind of parts such as automotive screws, large assemby studs for wind towers, brake discs or chassis parts like control arms.   
For each of these parts, NOF Metal Coatings Group has studied specific coating processes and cooperate with approved line manufacturers who design the coating equipment according to the highest quality standards. GEOMET® coating systems are applied by specialized job coaters licenced applicators or directly by the part or car makers, all over the world. These companies work in strict cooperation with the NOF Metal Coatings Group’s technical team to achieve the best quality results.