Steel is afraid of rusting, so we need to find ways to protect it in order to extend its service life. Before the 18th century, this method was used, such as oiling and painting, but it was not durable and easy to peel off. For small items, copper-clad and tin plated methods are used, but this is too costly. With the development of modern industry, a large amount of steel is exposed to outdoor and humid environments, and there is an urgent need for a method that can protect steel on a large scale.
In 1742, French chemist Melouin conducted an experiment by immersing iron in molten zinc and removing it to form a silver white zinc layer on the surface, which could prevent rust. He published a paper at the Royal Academy of France on the formal birth of hot-dip galvanizing. In 1837 (industrial patent), Sorel of France applied for a patent for hot-dip galvanizing, officially proposing that zinc is more reactive than iron and can "sacrifice itself" to protect steel (cathodic protection principle).
In the same year, Crawford in the UK improved its process by using ammonium chloride as a flux, laying the foundation for modern hot-dip galvanizing technology. In the mid to late 19th century, hot-dip galvanizing became popular: railway tracks, streetlight poles, guardrails, and building components were all made of "black steel" and then hot-dip galvanized.This is galvanised square tubing.
With the explosive demand for urban construction, factories, greenhouses, and guardrails, cold galvanizing (electroplating) emerged at the same time, and electrolytic galvanizing was invented in the late 19th century.The zinc layer is thin, shiny, and inexpensive, giving birth to cold galvanized square steel. In 1931, Polish engineer Sendzimir invented the hydrogen reduction method, a continuous hot-dip galvanizing production line for strip steel. The cost significantly decreased and the quality remained stable. Later, the square tube was directly welded with galvanized steel strip (now the mainstream process).