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The difference between hot dip galvanizing and cold dip galvanizing

Release time:

2023-12-01

Hot-dip galvanizing pipe reacts molten metal with an iron matrix to produce an alloy layer, thereby combining the matrix and the coating. Hot-dip galvanizing is to pickle the steel pipe first. In order to remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned in an aqueous solution of ammonium chloride or zinc chloride or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to in a hot dip plating tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion, and long service life.

There are many processes for cold galvanizing, that is, electroplating. Generally speaking, it is cleaning, electroplating, and passivation processes. Among them, color passivation is the color we see in cold-plated pipes, which belongs to zincate galvanizing. After passivation, the surface of the part will be red, green, slightly yellow (Cr+6 red, Cr+3 green), and purple cannot appear (the appearance indicates that the passivation film layer is loose). The simple method is to rub back and forth on the surface of the part with your fingers. After several times, there should be no color change (fading).

Commonly used process methods to form a "zinc protection" layer include spraying and coating with inorganic zinc-rich coatings or epoxy zinc-rich coatings. This is the type of silver paint mentioned above.

Among them, the fundamental difference is that the coating thickness varies greatly. The thickness of the electro-galvanized layer is generally only 20 to 30 μm, the thickness of the spray-coated zinc layer is generally only about 100 μm, and the thickness of the dip-galvanized layer is generally about 200 μm. However, in any process, the thickness of the coating is also different. Strict testing still uses numbers to speak.

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