After pretreatment of steel strip to the acid tank pickling.
The pickling method can be summarized as two classes;
It is the acid leaching method, 2 it is acid electrolytic process.
Is a widely used method, while the latter is an auxiliary method, in most cases are combinations of acid leaching.
Acid leaching method: single or mixed acid with nitric acid, hydrofluoric acid, sulfuric acid, etc.
Nitrate is antioxidant, can make the stainless steel passivation, descaling effect but used alone doesn't work.
Hydrofluoric acid corrosion, erosion of iron scale not only, also metal erosion matrix, and make the rough surface.
Therefore, these two kinds of acid cannot separate function, and use their best mixture effect, good surface can be obtained in a short period of time, have a lower risk of pitting corrosion, so no matter what grade of steel, mostly adopt the mixed acid.
Sulfuric acid pickling under high temperature effect is good, but at low temperature was very poor, so generally only used in the following two cases: one is to improve the descaling of hot-rolled coil, chrome steel, sometimes set hot sulphur acid trough, combined with the mixed acid tank of nitric acid, hydrofluoric acid is used;
Second, pickling line in cold rolled coil annealing, to neutralize after dealing with the alkali tank on the strip out of the base, between the salt bath and washing trough setting sulfur acid tank, in order to improve the efficiency of storage tank behind.
Using sulfuric acid pickling, the key is to master acid temperature.
Stainless steel pickling generally don't use hydrochloric acid.
Because hydrochloric acid erosion not only iron scales, and the erosion of metal substrate, even when using, also with nitric acid mixture, but this kind of mixed acid still has corrosive to metal substrate, lead to the metal surface is rough, so the general stainless steel factory is rarely used.
Pickling electrolytic process (
Also known as electrolytic pickling)
Electrolytic pickling is in only by acid leaching method is difficult to complete descaling speed adopted by the descaling methods, combined with acid leaching method, can improve the efficiency.
The characteristics of this method is: as a result of electrochemical action, uniform surface glossiness is good.
Electrolytic electrolytic pickling is usually used in nitric acid and sulfuric acid electrolytic, two methods to nitric acid electrolytic use most.
Nitrate used as acid dipping alone without descaling effect, but through the electrode (
Silicon cast iron)
When an electrical current flow, due to electrochemical action oxide film ionization, can for pickling, but due to the low corrosion, descaling capacity is small, generally not used alone.
Sulfuric acid descaling ability worse some of electrolysis.
This method in addition to the electrolytic device, also need to be recycled waste acid, waste gas sulphur oxide from the device, so the high cost of equipment.
Strip steel pickling is continuous, the pickling methods including pretreatment, combined use different ways.
Combinations according to steel, strip steel surface state and equipment condition decision.
