1. What Is Hot Dipped Galvanization?
Hot dipped galvanization is a process where the metal is dipped into a molten pool of zinc. To make galvanized steel using this method, we need to follow 4 steps: clean the surface, fluxing, hot-dipping & cooling down.
2. What Is Pre-Galvanizing?
Pre-galvanizing is also known as the mill galvanizing. This process is very close to the hot dipped galvanization but performed at the very first stage of production. It always occurred at the steel mill on the materials that already have a specific shape or before being cut into sizes and processed.
Pre-galvanizing involves some steps of hot dipped galvanization such as cleaning the surface, dipping into a hot zinc liquid bath combining with the recoiling process.
The hot-dip galvanizing process protects steel in three main ways, but perhaps the most notable way is by acting as a sacrificial coating for the steel. The zinc in the protective coating plays as an anode for the steel. After experiencing hot-dip galvanization, the protection ability is enhanced as the zinc now becomes an integral part of the steel.
Meanwhile, as the pre-galvanized products have thin coatings and will be cut later to sizes and shapes, the sacrificial protection can be as good as hot-dip galvanized steel.
| Feature | Hot dipped galvanization | Pre-galvanizing |
|---|---|---|
| Coating thickness | Thick coating with minimum average requirements of 45-85μm within BS EN ISO 1461 | The coating thickness may vary but is typically circa 20μm for sheets and 20-30μm for tubes and wires |
| Coating continually | Continuous coating over the whole object | Uncoated area at cut edges |
| Coating bond | Strong metallurgical bond with the base steel | Strong metallurgical bond with the base steel |
| Coating formability | Forming after hot dipped galvanizing is not advised as it may damage the coating | Thin coating may be normally formed without any damange |
| Coating apprearance | Typically bright but can be variable | Normally archieve an uniform bright |
| Abrasion resistance | Thicker layer of hard zinc-iron alloy gives a high resistance to abrasion | Thin alloy layer with reduced resistance to abrasion |
| Sacrificial protection | Offer the highest level of sacrificial protection | Reduced sacrificial protection due to thin layer coating and at some uncoated areas (cut edges) |
Galvanized Round Tube
