How does the surface state of the original galvanized sheet in hot-dip galvanizing affect the quality of hot-dip galvanizing products?
(1) influence of surface roughness:
A. The strip steel with rough surface of the original plate has good adhesion of the coating layer (gear assembly principle).
B, steel plate surface roughness can lead to the increase of the weight, zinc coatings for steel surface of the base of a series of four bumps, districts produce different organization, four parts are dense 51 split phase (FeZn) and the convex part of 51 (FeZn), as well as a loose network of 5 phase (FeZns), thus the rough surface of the zinc layer, make out more zinc from the zinc liquid fluid.
(2) influence of rolling emulsion:
The increase of the oil in the rolling emulsion leads to the decrease of the zinc-adhesion.
(3) impact of original plate placement time: the length of original plate placement time has been verified and has no significant impact on galvanized products without rust.
A. Longer pickling time will increase surface roughness, resulting in thick coating, but good adhesion.
B. For thicker galvanized sheet, hot rolled sheet is generally used after pickling.
Why does the hot dip galvanization generally use the boiling steel as galvanizing original plate?
Because: if the steel base contains higher Si, it will bring the following difficulties to hot galvanizing:
(1) the steel base contains a relatively high proportion of sedation steel, and its galvanizing layer (feseized 3) is thicker.
(2) the steel base is composed of stainless steel with high Si, and its coating is in gray state, while its adhesion decreases.
(3) as the calcined steel contains other elements, such as excessive C, Si,Mn,P, etc., some of these elements prevent the preferential formation of Fe2Al, while some of them aggravate the diffusion of Zn to Fe2Als intermediate phase layer, resulting in defects such as plating shedding and cracks.
Conclusion: for a long time, the galvanized steel with Si content less than 0.07% is often used as the original plate.