EDITORIAL Infrastructure
“ Hot-dip galvanised coatings offer both barrier and sacrificial cathodic protection,” explains Simon Norton, Director, IZA Africa.“ The zinc forms a dense, adherent layer of iron-zinc alloys with the steel substrate, ensuring that zinc preferentially corrodes in aggressive environments, thereby prolonging the service life of the underlying steel.”
An overview of the hot-dip galvanising process
Continuous galvanising
In integrated continuous galvanising plants, steel strip and coil are galvanised immediately after annealing by immersion in a molten zinc bath at line speeds of up to 150 m / min. An air or nitrogen knife regulates zinc coating thickness to ensure even deposition, typically resulting in coatings of mostly pure zinc with minimal alloying elements.
Process throughput can exceed 600 000 tonnes annually. The resulting galvanised products exhibit high ductility, abrasion resistance, and suitability for further manufacturing into automotive panels, household appliances, corrugated roofing, and structural components. In South Africa, Arcelormittal Steel, Duferco Steel, and Safal all run continuous galvanising plants.
Batch( General) hotdip galvanising
In South Africa, there are 24 hot-dip galvanisers located near end-user markets in Cape Town, Johannesburg, Durban, and Port Elizabeth. Unlike continuous lines, batch galvanising fully immerses prefabricated components in molten zinc at 450 ° C, ensuring complete coating of steel items, including recessed geometries and internal cavities.
This process accommodates a wide variety of steel components, from small fasteners and fabricated profiles to large structural beams and lattice towers. In South Africa, we have hot-dip galvanising kettles up to 14 m long and sufficiently wide for large steel structures. Contact the IZA Africa to find out where to go.
Zinc electroplating
Zinc electroplating, which is not galvanising, deposits zinc through an electrolytic reduction process using soluble or insoluble anodes in zinc sulphate or other electrolyte systems. It produces thin, uniform coatings of up to 9μm per side, with high ductility and an excellent surface finish, making it suitable for automotive body sheet and precision forming applications.
Zinc electroplating applies the same principle to individual components( e. g., bolts, springs, crank handles), with coating thicknesses reaching up to 25 μm.
Although its service life in atmospheric conditions is considerably shorter than that of hot-dip galvanised coatings, electroplated finishes offer better appearance, dimensional accuracy, and formability. However, they are not suitable for outdoor exposure in South African coastal areas or in mines.
Zinc for infrastructure durability and sustainability
By significantly delaying corrosion, hot-dip galvanising prolongs service life, reduces maintenance needs, and improves the total cost of ownership for steel-based infrastructure. This not only conserves raw material resources but also supports global sustainability objectives.
“ Galvanising is more than just corrosion protection,” concludes Norton.“ It represents an engineering solution that enhances durability, improves the circular economy of steel use, and reduces the environmental footprint of critical infrastructure and manufacturing industries.”
IZA Africa continues to promote hot-dip galvanising across South Africa and the African continent to support the delivery of durable, cost-effective, and sustainable steel applications in the construction, automotive manufacturing, energy, and transport sectors. ■
www. sabuildingreview. co. za 89