Should solar street poles be cold-galvanized or hot-galvanized?

Nowadays, premium Q235 steel coils are the most popular material for solar street poles. Because solar street lights are subjected to wind, sun, and rain, their longevity depends on their ability to withstand corrosion. The steel is typically galvanized to improve this.

There are two types of zinc plating: hot-dip and cold-dip galvanizing. Because hot-dip galvanized steel poles are more resistant to corrosion, we usually advise buying them. What are the distinctions between hot-dip and cold-dip galvanizing, and why do hot-dip galvanized poles have superior corrosion resistance? Let’s take a look with Tianxiang, a famous Chinese street pole factory.

1) Cold Galvanizing (Also called electro-galvanizing): After degreasing and pickling, the steel is placed in a zinc salt solution. The solution is connected to the negative electrode of the electrolysis equipment, and a zinc plate is placed opposite, connected to the positive electrode. When the power is turned on, as the current moves directionally from the positive to the negative electrode, a uniform, dense, and well-bonded zinc deposit layer forms on the surface of the steel pipe.

2) Hot-dip galvanizing: The steel surface is submerged in molten zinc following cleaning and activation. A layer of metallic zinc develops on the steel surface as a result of a physicochemical reaction between the iron and zinc at the interface. Compared to cold galvanizing, this method produces a stronger bond between the coating and the substrate, improving coating density, durability, maintenance-free operation, and cost-effectiveness.

1) Processing Method: Their names make the difference clear. Zinc obtained at room temperature is used in cold-dip galvanized steel pipes, whereas zinc obtained at 450°C to 480°C is used in hot-dip galvanizing.

2) Coating Thickness: Although cold-dip galvanizing usually produces a coating thickness of only 3–5 μm, which makes processing much simpler, it has poor corrosion resistance. In contrast, hot-dip galvanizing typically offers a coating thickness of 10μm or more, which is several tens of times more corrosion resistant than cold-dip galvanized light poles.

3) Coating Structure: The coating and substrate are separated by a comparatively brittle compound layer in hot-dip galvanizing. However, because the coating is made entirely of zinc, which results in a uniform coating with few pores, making it less prone to corrosion, this has little effect on its resistance to corrosion. In contrast, cold-dip galvanizing uses a coating made of zinc atoms and a physical adhesion process with numerous pores, which makes it susceptible to environmental corrosion.

4) Price Difference: The production of hot-dip galvanizing is more difficult and complex. Therefore, smaller companies with older equipment typically use cold-dip galvanizing, resulting in significantly lower costs. Larger, more established hot-dip galvanizing manufacturers generally have better quality control, leading to higher costs.

Some people might say that even if they know the difference between cold-dip galvanizing and hot-dip galvanizing, they still can’t tell the difference. These are processing methods that are invisible to the naked eye. What if an unscrupulous merchant uses cold-dip galvanizing instead of hot-dip galvanizing? Actually, there’s no need to worry. Cold-dip galvanizing and hot-dip galvanizing are quite easy to distinguish.

Cold-dip galvanized surfaces are relatively smooth, mainly yellowish-green, but some may have iridescent, bluish-white, or white with a greenish sheen. They may appear somewhat dull or dirty. Hot-dip galvanized surfaces, in comparison, are somewhat rougher, and may have zinc bloom, but they look very bright and are generally silvery-white. Pay attention to these differences.