company news about Production process of hot dip galyanized steel coil

What are the reasons for the missing plating?

Causes and solutions:

1. The surface of plated parts is not clean

(1) the surface of the plating part contains paint, grease and welding; It can be polished or scrubbed with relevant solvent.

(2) iron oxide; Under pickling; Continue pickling.

2. Pickling and operation:

(1) under pickling and over pickling. Under pickling, iron oxide (rust spot) is left on the surface of plated parts; The surface structure of the steel substrate is destroyed by over pickling, and the Si and a small amount of active metal refractory oxide are attached to the surface of the plated parts, which prevents the combination of iron and zinc. Or because of the over pickling, the plated parts absorb hydrogen, and when galvanizing, the hydrogen expands and escapes due to heat, and the plating is missed. Solution: strictly control pickling and grasp pickling time.

(2) during pickling, the plating parts are stacked and overstocked, resulting in missed washing, or due to the structural reasons of the plating parts, the vortex gas caused by careless turning during pickling causes missed washing. Solution: as far as possible to open pickling, frequently turn.

3. Auxiliary plating

(1) the concentration of auxiliary is low, and the effect of auxiliary plating is not ideal; Solution: adjust the appropriate concentration of additives.

(2) improper proportion of additives and high content of zinc salt make the salt film of additives easy to absorb water and deliquescence, the hydroxide decomposes into gas and explodes zinc, resulting in missed plating. Solution: adjust the proportion of additives.

4. Composition of liquid zinc and pot operation:

(1) aluminum content in liquid zinc is too high, resulting in missed plating; Solution: adding zinc or using ammonium chloride consumption to reduce aluminum content;

(2) the speed of the plating parts in the pot is too slow, and the auxiliary agent is decomposed and failed when heated, resulting in missed plating. Adjust the speed of cooking properly.

(3) the zinc dipping time is too short, so that the iron zinc reaction can be carried out in the future,

(4) the zinc ash on the zinc surface was not cleaned when the plating parts were put into the pot, which caused the overheated zinc ash to burn the auxiliary and missed plating.

(5) when the plating part is put into the pot, due to the process hole or structure, the high-temperature gas in the plating part is heated to escape, and the auxiliary agent is burned, resulting in missed plating. Solution: appropriate amount of ammonium chloride

5. Plating material

(1) the surface of steel contains refractory oxides of silicon, aluminum and other elements, which prevents the reaction between iron and zinc.

(2) the steel matrix contains too much carbon, or the steel produces too much iron carbide in the refining process, which makes it difficult to combine iron and zinc, resulting in missed plating.

(3) the defects of the material processing and forming of the plating parts cause the material to be rotten and cracked, and the acid, water and additives to enter, causing the leakage of plating. At present, there is no good solution except ammonium chloride.