Hot Dipped Galvanization & Pre-Galvanizing

Differences between hot dipped galvanization & pre-galvanizing：

1. Application comparison

Hot dipped galvanization is an economical choice if you are finding a solution that can be executed on both simple and complex shapes. It is often used on objects that have been fabricated beforehand but yet to be galvanized and the hot-dipped galvanization plays as the last step.

Meanwhile, pre-galvanizing, as its name implies, is performed at the first stage of production. Hence, it mainly occurred at the mills, and the results of the process will be cut into size and fabricated later.

2. Coating comparison

As making a protective coating for the steel and metals in the main object of the galvanizing process, we can not miss out on comparing the coating finish of the 02 methods to make galvanized steel.

a. Coating thickness

Both methods result in a uniform thickness for the coating. However, the hot-dipped galvanization produces a thicker layer of protection than the pre-galvanization does. The minimum average thickness of hot-dip galvanized steel is of 45-85μm while it is between 20 and 30 μm for the pre-galvanized products’.

b. Coating continually

As hot dipped galvanization requires dipping the whole steel/metals into the molten vat of zinc, the galvanized steel coming out from this process has a continuous coating over the surface. Pre-galvanizing is performed at the first stage before the sheets are cut into sizes and pieces so the cut edges are not coated.

c. Coating bond

The first steps of these 02 processes of making galvanized steel are both cleaning the surface, either mechanically, chemically, or both. Hence, the bond between the base metal (steel) and the protective coating is metallurgical and strong.

d. Coating formability

Coating formability for these 02 processes is totally different. As pre-galvanizing is performed at the mills, any coating applied on its results can be done without damaging the layer. However, coating formability applied on hot-dip galvanized steel is not advised as it may damage the protective coating of the products.

e. Coating appearance

The hot dipped galvanization forms a typically bright finish for the galvanized steel, though it can be also variable. As for the pre-galvanizing process, it produces a uniform bright finish for the coating. 

3. Abrasion resistance comparison 

After the hot-dip galvanizing process, there are 03 alloy layers end up being produced on the base metal. These layers are metallurgically bonded to the steel and become an integral part of the steel itself, which forms a perfect protective coating.

The pre-galvanizing process produces galvanized steel with thinner coating, which makes it a bit prone to corrosion. 

4. Sacrificial protection

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.