Pickling of Steel
Pickling is a process used to clean and remove surface blemishes and corrosion from steel. The primary use of pickling is to prepare steel for galvanizing, but it is used by some manufacturers of high-strength steel components that are sensitive to environmental corrosion. Pickling involves various forms of acid and it is essential to use the correct type and concentration to ensure that the process does not cause damage to the steel. The pH level of the acid solution used for pickling must be monitored for best results.
The first step in pickling is to apply an dilute solution of hydrochloric acid (HCl) or other acid. This solution dissolves or softens any oxide or scale on the surface of the steel. The solution is then rinsed away and a strong solution of hydrochloric acid is applied. This solution eats away at the surface of the steel and removes any oxides and other imperfections. After this solution has had a chance to penetrate the surface of the steel, it is then rinsed away and a more dilute solution of hydrochloric acid is used to neutralize the surface.
Once the surface has been neutralized, it is important to rinse off any residual acid. This can be done with water or an alkaline solution. Once all the acidic residue has been washed away, the steel must be dried. This can be done with compressed air or a warm air blower.
The depth of pickling achieved on the surface of the steel will vary, depending on the strength of the acid solutions used and the length of time that the steel is in contact with them. If an extremely smooth finish is required, then a higher concentration of acid should be used, as well as more prolonged contact times. If a fairly coarse finish is acceptable, then a lower concentration of acid and shorter contact times should be used.
Pickling is a widely used process and it is essential to take into account the strength of the acid solutions and the length of time that the steel is in contact with them. It is also important to rinse off any residual acid and to thoroughly dry the steel to remove any moisture that could promote corrosion in the future.
