Hydrochloric acid pickling process control

In the Hydrochloric acid pickling process control, the most important thing is to control the pickling time and life of the pickling tank to ensure the maximum productivity and service life of the pickling tank.

To obtain the best pickling effect, first, control the concentration of hydrochloric acid, and secondly control the content of iron ions (iron salts) in the pickling solution. Because not only the concentration of acid will affect the pickling effect of the workpiece, the content of iron ions (iron salt) will reduce the mass fraction of the pickling solution, which will also affect the pickling effect and speed of the workpiece. It is worth noting that to obtain the best pickling efficiency, the pickling solution must also contain a certain amount of iron ions (iron salts).

Control of the hydrochloric acid washing tank

(1) Pickling time

The pickling time basically depends on the concentration of hydrochloric acid/iron ion (iron salt) and the temperature of the pickling solution.

(2) Best pickling

The best pickling effect of the workpiece should be when the concentration of hydrochloric acid and the concentration of precipitated iron ions (iron salts) reach a relative balance.

(3) Remedy for decreased acid effect

When the pickling solution decreases or loses its pickling effect due to the saturation of iron ions (iron salt), it can be diluted with water to restore the pickling function. Although the concentration of hydrochloric acid is reduced, it can still perform the pickling function, but at a slower rate. If new acid is added to the pickling solution with saturated iron content, the concentration of the new hydrochloric acid solution will fall above the saturation point, and the pickling of the workpiece will still be impossible.

(4) Treatment measures after acid solubility drops

After the pickling solution has been used for a period of time, its concentration decreases and even becomes waste acid. However, the manufacturer cannot recover the acid at this time and still retains a certain use-value. To use the reduced concentration of low acid, at this time, the workpiece that needs to be re-dipped due to partial leakage in the hot-dip galvanizing is generally put into Among them, pickling and reprocessing is also an effective use of waste acid.

Method of replacing old acid with hydrochloric acid pickling solution:

When the iron salt in the old acid exceeds the specified content, it should be replaced with a new acid. The method is that the new acid accounts for 50% and the old acid is added to the new acid after precipitation. The amount of the old acid is ~50%. A part of the old acid is used to maintain an appropriate amount of iron salt in the pickling solution because the hydrochloric acid Iron salts with a content of less than 16% can increase the activity of the pickling solution.

However, with the advancement of hot-dip galvanizing technology, the amount of old acid added must be carried out based on strictly controlling the iron salt content of the old acid, and the iron salt concentration of the newly prepared hydrochloric acid solution must be controlled within the range.

Workpiece steel material and pickling speed

The pickling speed varies with the composition of the steel workpiece to be pickled and the scale produced.

The carbon content in steel has a great influence on the dissolution rate of the steel matrix. When the carbon content increases, the dissolution rate of the steel matrix increases rapidly.

The dissolution rate of the steel workpiece matrix after cold and hot processing will increase, and the dissolution rate of the steel matrix after annealing the steel workpiece will decrease. In the iron oxide scale on the surface of steel workpieces, the dissolution rate of iron monoxide is higher than that of ferroferric oxide and ferric oxide. The rolled iron sheet has more iron monoxide content than the annealed iron sheet. Therefore, its pickling speed is also faster. The thicker the iron oxide layer, the longer the pickling time. If the thickness of the scale is uneven, it is easy to produce local defects of “under-pickling” or “over-pickling”. If you want to know more, please contact us.