.055” – .500”
36” – 72”
10,000# to 60,000#
During cooling of the steel coil in the final processing at the finishing mill, scale develops and covers the entire strip surface. (scale is normal and is blue/grey in color). This scale forms when the iron in the steel reacts with oxygen in the air. Pickling is the processes used to remove this type of scale.
The pickling process is carried out in three deep acid-bath tanks with the first tank being the weakest strength. The steel, at room temperature, acts as a large heat sink thus reducing the effectiveness of the pickling reaction. The reaction between the hydrochloric acid and the scale is complex but the end result is that the scale is almost completely removed in the acid.
Following the pickling, the strip will have a residue of acid solution on the surface. The residue needs to be removed prior to cold rolling and this is carried out in the dip and rinse spray tanks. The pH is measured and controlled in these tanks for two basic reasons: First to reduce the activeness of the surface so that it will slow down the reformation of oxides (rust); Second, to prevent a low or high pH solution being carried into the mill – as this will wash off into the coolant and adversely affect its lubrication properties. The strip then passes through a set of squeegee rolls and a hot air drier.
To protect the coils from rusting, they are provided with a uniform coating of special rust preventive oil. This also guards against atmospheric corrosion and allows for a longer storage period. This oil can be easily removed in normal degreasing once your coils are delivered.