galvanoimisen

Galvanization, or galvanising, is the process of applying a protective zinc coating to steel or iron to prevent corrosion. In Finnish, the process is called galvanoiminen. The coating protects by acting as a sacrificial anode to corrode in preference to the base metal and by forming a corrosion-resistant barrier.

The most common methods are hot-dip galvanizing and electrogalvanizing. Hot-dip galvanizing (HDG) involves cleaning the steel surface and immersing it in molten zinc, which forms a zinc–iron alloy layer bonded to the base metal and a outer pure zinc layer. This method yields thick, durable coatings suitable for complex shapes and long-term outdoor exposure. Electrogalvanizing deposits zinc onto the surface from an electrolytic bath, producing thinner, more uniform coatings with tighter tolerances, often used for smaller parts or where precise coating thickness is required. A less common method, sherardizing, coats surfaces by tumbling steel parts with zinc powder in a heated drum.

Coating performance depends on thickness, environment, and coating structure. HDG coatings typically range from roughly 30 to 200 micrometers, with thicker coatings for harsher environments. The protection comes from both the barrier effect of the zinc layer and the ongoing galvanic protection as zinc preferentially corrodes.

Advantages include extended service life, good durability, and suitability for heavy-duty outdoor applications. Limitations include possible coating damage from mechanical wear, roughness on HDG surfaces, and incompatibility with nonferrous substrates in some cases. Common applications are structural steel, pipelines, automotive components, agricultural equipment, and street furniture. Standards such as ISO 1461 and ASTM A123 govern coating quality and thickness.