Hot-dip galvanised coating is achieved by dipping fasteners in a bath of molten zinc at a temperature of approximately 450°C.
Excess molten zinc is removed to prevent fowling of threads, usually by a spinning process. The protection offered to the carbon steel fastener by the zinc coating is a result of the same sacrificial corrosion process as for a zinc electroplated finish.
A hot-dip galvanised coating offers significantly more corrosion protection than zinc plating simply because the zinc coating thickness is typically 5 to 10 times as much.
Hence a galvanised fastener is generally preferable to a zinc plated one in applications exposed to the elements.
The high coating thickness on a galvanised fastener, typically in the order of 50 microns, brings with it some problems. Firstly, allowances must be made for thread fit.
This is achieved by tapping nuts oversize. Galvanising also appears as a rough finish, which may preclude it if appearance is important.
Exafast’s fasteners are galvanised according to the requirements set down in Australian Standards ASB193 and AS1214.