Zinc Flake Coating on Fasteners: How It Works and How It Compares

Key things to remember

The essentials from this document in plain words. Check the full document before you rely on a figure.

• ✓Zinc flake is a mix of zinc and aluminium flakes in an inorganic binder, applied without electricity. It protects as a sacrificial coating and as a barrier; zinc plating and hot dip galvanising are sacrificial only.
• ✓No acid is used, so there is no risk of hydrogen embrittlement, which matters most for high strength fasteners. It is cured at a low 180 to 200°C, with little effect on the steel.
• ✓Typical thickness is 5 to 20 microns (zinc plating is around 5, hot dip galvanising around 45). The thickness can be set to suit thread tolerances, so do not compare coatings by thickness alone.
• ✓Four systems under ISO 10683: base coat only, base coat plus lubricant, base coat plus top coat, or all three. Top coats can add corrosion resistance, colour or a set torque/tension relationship.
• ✓Listed advantages include 450 to 1,200 hours of corrosion protection, resistance to temperatures up to 300°C, and resistance to acidic and alkaline chemicals.
• ✓Limits: screw sizes below M6 and nuts with a thread tolerance class lower than 6H are not suitable.
• ✓Hobson uses it on class 10.9 and 12.9 nuts, bolts, flange bolts and screws, on disc springs, washers and grub screws, and on concrete screws.

Who it helps: Engineers and buyers choosing a coating for high strength fasteners.