Hot dip galvanizing is the process of immersing metal in a molten zinc bath. To make galvanized steel using this method, we need to follow 4 steps: surface cleaning, fluxing, hot dip plating and cooling.
Pre-galvanizing is also called mill galvanizing. This process is very close to hot-dip galvanizing, but takes place in the first stage of production. It always occurs in steel mills with material that already has a specific shape or before being cut to size and processed.
Pre-galvanizing includes some of the steps of hot-dip galvanizing, such as cleaning the surface, immersing in a hot zinc bath, and the coiling process.
The hot-dip galvanizing process protects steel in three primary ways, but perhaps the most noteworthy way is by acting as a sacrificial coating for the steel. The zinc in the protective coating acts as an anode for the steel. After hot-dip galvanizing, the zinc has become an integral part of the steel, so its protective capabilities are enhanced.
At the same time, because pre-galvanized products have a thin coating and are subsequently cut to size and shape, their sacrificial protection can be as good as hot-dip galvanized steel.
| feature | hot dip galvanized | Pre-galvanized |
|---|---|---|
| coating thickness | BS EN ISO 1461 requires a minimum average thick coating of 45-85μm | Coating thickness can vary, but is typically about 20μm for sheets and 20-30μm for pipes and wires |
| continuous coating | Continuous coating of the entire object | Uncoated area of cut edge |
| coating bonding | Strong metallurgical bond with base steel | Strong metallurgical bond with base steel |
| Coating formability | Forming after hot dip galvanizing is not recommended as this may damage the coating | Thin coatings can form normally without causing any damage |
| Coating appearance | Usually bright, but can vary | Usually achieves uniform brightness |
| Wear resistance | Thicker hard zinc-iron alloy layer provides high wear resistance | The alloy layer is thin and the wear resistance is reduced |
| sacrifice protection | Provides the highest level of sacrificial protection | Reduced sacrificial protection due to thin layer coating and certain uncoated areas (cut edges) |
There are some differences between hot dip galvanizing and pre-galvanizing processes. Understanding these differences will allow us to choose the most appropriate methods and products for your project. In summary, it is always necessary to choose the best galvanized steel product among the various options available in the market.
United Steel Industry As the most important steel pipe manufacturer and exporter in China, in the past 20 years, we have completed more than 100 projects, with partners in more than 100 countries, and established relationships with oil and gas and EPC companies in many countries business relationship.
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