Galvanizing amount and zinc layer characteristics

1. The amount of galvanizing is a commonly used and effective method to express the thickness of the zinc layer of galvanized sheets. The galvanizing amount of steel plates is generally 180-220g/㎡. In humid southern areas, the galvanizing amount can be increased to 275g/m2 to increase the service life of steel components.

The service life of galvanized products is generally 20-25 years. 2. Zinc layer characteristics of galvanized strip steel. The electro-galvanized layer cannot form zinc flowers, but the hot-dip galvanized layer has zinc flowers. The formation process is as follows: when the galvanized strip comes out of the zinc pot, a large amount of zinc liquid is blown back to the zinc pot by the air knife. At this time, there is still a pure zinc layer on the surface of the strip, which is attached to the surface of the steel plate in a liquid state, forming a large number of crystallization nuclei on the surface of the steel plate. As the steel plate rises and cools, the crystallization nuclei slowly grow into zinc flowers. The faster the cooling rate, the smaller the spangles, and the slower the cooling rate, the larger the splatters. ​

3. Flower-free galvanized sheet: In fact, zinc flowers only have ornamental value and have no actual use value. On the contrary, they are not good at anti-corrosion. In developed countries, small zinc flowers and zinc-free galvanized steel sheets are implemented. Japanese, American and German standards stipulate the zinc coating amount of galvanized thin steel sheets:
 

JISG3302
Code name	Z12	Z18	Z22	Z25	Z27	Z35	Z43	Z50	Z60
Galvanizing amount	120	180	220	250	270	350	430	500	600
ASTMA525
Code name	A40	A60	G60	G90	G115	G140	G165	G185	G210
Galvanizing amount	122	183	183	275	351	427	503	564	640
DIN1716
Code name	100	200	275	350	450	600
Galvanizing amount	100	200	275	350	450	600

Exterior

(1) Surface condition: Due to different treatment methods in the coating process, the surface conditions of galvanized sheets are also different, such as ordinary zinc flowers, fine zinc flowers, flat zinc flowers, no zinc flowers, and phosphated surfaces. German standards also specify surface grades.

(2) The galvanized sheet should have good appearance and should not have defects that are harmful to the use of the product, such as no plating, holes, cracks and scum, excessive plating thickness, scratches, chromic acid dirt, white rust, etc. Foreign standards are not very clear on specific appearance defects. Some specific defects should be listed in the contract when ordering.