How can you distinguish between cold galvanizing and hot-dip galvanizing?
The two have significant differences in their working methods.
The zinc used in hot-dip galvanizing is obtained at temperatures between 450°C and 480°C
while the zinc in cold-galvanized steel pipes is obtained through electroplating at room temperature.
Concept Analysis：
Hot-dip galvanizing: also called hot-dipping or hot-dip zinc coating, is an effective method of metal corrosion protection.
It involves melting zinc ingots at high temperatures, adding some auxiliary materials
and then immersing the metal structural components into a galvanizing bath
allowing a layer of zinc to adhere to the metal components, thereby achieving corrosion resistance.
The advantage of hot-dip galvanizing lies in its strong corrosion resistance
as well as the good adhesion and hardness of the galvanized layer, thereby achieving the purpose of corrosion prevention.
Cold galvanizing: This is electro-galvanizing with a small amount of zinc, only 10-50 g/m².
It is a process that uses the electrolytic effect to deposit a layer of metal film on the surface of metal or other material parts.
The process of forming a uniform, dense, and well-adhered metal layer can prevent corrosion
improve wear resistance, electrical conductivity, reflectivity, and enhance appearance.
Price difference：
There is also a significant price difference between cold galvanized pipes and hot galvanized pipes.
To ensure quality, manufacturers generally do not use electro-galvanizing for hot-dip galvanized steel pipes;
however, small-scale enterprises with relatively outdated equipment mostly adopt electro-galvanizing
which is why the price of cold galvanized steel pipes is lower than that of hot-dip galvanized steel pipes.
Purpose distinction：
Hot-dip galvanizing: Suitable for steel components used outdoors, such as highway fences, power towers, and large fasteners
for long-term rust prevention of relatively 'rough' workpieces. Older iron water pipes were also hot-dip galvanized.
Electro-galvanizing: Used for rust prevention of components for indoor use, such as the bottom and panels of machinery, and small fasteners.
Quick identification tips：
Scratch test: Lightly scratch the surface with a hard object (such as a key).
Hot-dip galvanized coating will only leave a scratch without exposing the base material
while cold galvanizing can easily have its zinc layer scratched off, revealing the black or gray base material underneath.
Magnet attraction: Both substrates are mostly iron-based and can be attracted by a magnet.
This method can only rule out non-iron-based pipes and cannot directly distinguish them
but it can help judge whether it is 'fake galvanization' (for example, pipes coated with zinc-colored paint on the surface may not be magnetic).
Summary：
The surface of hot-dip galvanized steel is not as delicate and shiny as that of cold-galvanized steel，and the coating is uniform.
However, in terms of zinc layer thickness, hot-dip galvanizing is dozens of times thicker than cold galvanizing.
Its corrosion resistance is also dozens of times higher than that of electro-galvanized steel.
Hot-dip galvanizing, also known as hot-dip zinc coating, is a method in which steel workpieces are degreased and derusted to reveal a clean
wettable surface, and then immediately immersed into a plating bath where zinc has been preheated and melted
forming a layer of zinc coating on the surface of the workpiece.
Cold galvanizing involves taking workpieces that have been degreased and derusted, ensuring they are clean and wettable
and hanging them as the cathode in a specialized electroplating tank, with zinc used as the anode.
When a direct current power supply is connected, zinc ions from the anode migrate to the cathode and discharge onto it
coating the workpiece with a layer of zinc.
The hot-dip galvanized coating is relatively thick and has a high corrosion resistance.
Electroplated zinc, the workpiece surface is smooth and even, the coating is relatively thin, and the corrosion resistance time is relatively short.