Steel Profile

Generally, the thicker the profile of steel to be galvanised, the heavier the final coating of zinc on the steel surface will be.  The reason for this is that the steel has to remain in the galvanising kettle for a longer time until the temperature of the steel reaches the temperature of the zinc.  This has the effect of building up the zinc-iron alloy layers of the zinc coating and thereby increasing the final coating thickness.

Generally, steel less than 4mm is aluminium-killed steel and this tends to produce bright and shiny zinc coatings.  Over 4mm, it is only by special order that customers will receive aluminium-killed steel.  When aluminium-killed steel is used, coating thickness will be restricted to about 100 µm even on heavy sections and will always be aesthetically attractive.

On sections over 4mm, silicon-killed steel is normally used to make the thicker profiles.  Silicon-killed steel is highly reactive with zinc and tends to produce heavier, darker grey coatings, which are less attractive but have a much higher corrosion resistance.  Customers should always specify on their orders to steel suppliers that the steel should be suitable for hot-dip galvanising and on large orders even specify the limits of the silicon and phosphorous contents, i.e. phosphorous to be ideally less than 0.03mm and silicon to be less than 0.03mm (aluminium-killed steel) or in the range 0.15 to 0.30mm, which would be considered to be a controlled silicon-killed steel suitable for the galvanising process.

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