Pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper, precious metals and aluminum alloys. A solution called pickle liquor, which contains strong acids, is used to remove the surface impurities. It is commonly used to descale or clean steel in various steelmaking processes.
Once the hot-band coil leaves the hot mill it goes through a series of value-added processing steps. The first of which is pickling which involves unwinding the steel and running it through a series of hydrochloric acid tanks and rinse tanks.
The primary acid used is hydrochloric acid, although sulfuric acid was previously more common. Hydrochloric acid is more expensive than sulfuric acid, but it pickles much faster while minimizing base metal loss.
Carbon steels, with an alloy content less than or equal to 6%, are often pickled in hydrochloric or sulfuric acid. Steels with an alloy content greater than 6% must be pickled in two steps and other acids are used, such as phosphoric, nitric and hydrofluoric acid. Rust- and acid-resistant chromium-nickel steels are pickled in a bath of hydrochloric and nitric acid. Most copper alloys are pickled in dilute sulfuric acid, but brass is pickled in concentrated sulfuric and nitric acid mixed with sodium chloride and soot.
Sheet steel that undergoes acid pickling will oxidize (rust) when exposed to atmospheric conditions of moderately high humidity. For this reason, a thin film of oil or similar waterproof coating is applied to create a barrier to moisture in the air. This oil film must later be removed for many fabrication, plating or painting processes.
To achieve the highest strip cleanliness and high surface quality with a reliable and cost-efficient process Hertz controls (India )Pvt. Ltd. offers modular continuous and Push-Pull Pickling Lines. They are supplied with compact Scale Breakers and customers have the choice of different pickling concepts (i Box, turbulent shallow or flat tanks).
Push-Pull Pickling Lines
For the pickling of up to 1,000,000 tons of strip per year depending on the product mix, Push-Pull Pickling Lines offer significant advantages in terms of investment costs and operational flexibility (frequent change of strip dimensions and steel grades) with uniquely designed V-shape flat pickling tanks.