The Difference between Hot-dip Galvanizing and Cold-dip Galvanizing

Both hot-dip galvanizing and cold-dip galvanizing are zinc processing processes. Hot-dip galvanizing is to melt zinc, while cold-dip galvanizing uses electrolysis. They are very different in production, but they are similar in finished product performance. How to distinguish between hot-dip galvanizing and cold-dip galvanizing? In what ways are they different? Let's learn about it with carbon steel pipe suppliers.

 Hot-dip galvanizing vs. Cold-dip galvanizing

1. Different thickness

The hot-dip galvanized zinc layer itself is relatively thick, generally more than 10um in thickness, so it has good anti-corrosion ability. Although the surface is bright, it is slightly rough, and there may be spangles. The zinc layer of electro-galvanized is very thin, only about 3-5um in thickness. Although the surface is smooth, it will appear dark and dirty, with better processing performance and insufficient corrosion resistance.

2. Different output
Hot-dip galvanizing is mass-produced (such as galvanized seamless steel pipes), so it has a good output. However, electro-galvanizing cannot be produced in large quantities, so its output is relatively low.

3. Different prices
The effect, processing performance and bonding force of the electro-galvanized surface are not good, and the price will be more expensive than hot-dip galvanized, and the cost of electro-galvanized itself is higher, and its price is also high.

4. Different coating structure
The surface of hot-dip galvanizing is a pure zinc coating, which is uniform and non-porous, but there is a relatively brittle compound between the coating and the substrate. The electro-galvanized coating is only composed of zinc atoms. It is the zinc atoms deposited on the surface of the steel strip, which belongs to physical adhesion. There are many holes on the surface to dry, so it is relatively easy to be corroded.

5. Different in process

There are many processing techniques for hot-dip galvanizing. After the workpiece is degreasing, pickling, dipping, drying and other processes, it can be immersed in the molten zinc bath, and it can be taken out after a certain period of time. This is hot-dip galvanizing. Like some hot-dip pipe fittings are processed in this way. The cold-dip galvanizing is actually electro-galvanizing, which is processed by electrolytic equipment. After degreasing, pickling and other processes, it is immersed in a solution containing zinc salts, connected to the electrolytic equipment, and placed on the workpiece during the directional movement of the positive and negative electrodes. It comes from the deposition of zinc layer.

6. Different in appearance
The overall appearance of hot-dip galvanizing is slightly rougher, and it will produce process watermarks, dripping tumors, etc., especially at one end of the workpiece, which is silver-white as a whole. The surface layer of electro-galvanized is relatively smooth, mainly yellow-green, of course, there are also colorful, bluish-white, white with green light, etc. The whole workpiece basically does not appear zinc tumors, agglomerations, etc.

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