Steps to Making High-Quality Cold Rolled Steel Coils

[edit] Introduction

Cold rolled steel coils usually have a thickness ranging from 0.2 mm to 4 mm. They go through a complicated manufacturing process, involving heat treatment, cold rolling, and pickling.

[edit] Pickling

The hot rolled coils go through a pickling line consisting of hydrochloric acid solutions and scale breaker machines. These two systems remove any type of oxide film or surface scale on the rolls. Oxide films may cause surface flaws, thus reducing the overall quality of the rolls when they enter the cold rolling stage.

[edit] Cold rolling

Once the hydrochloric acid solutions and scale breaker machines remove the oxide films, the rolls go into the tandem mills one by one. The tandem mills are responsible for setting the thickness of the rolls. They can cut down the dimensions by up to 90%, depending on the requirement. Once the steel rolls pass through the tandem mills, there are no options to change their sizes.

[edit] Electrolyte cleaning

Cold rolled steel rolls contain a lot of contaminants and lubricant oil. Not cleaning them would lead to spots on the rolls. Electrolyte cleaning is essential to make sure that no roll contains even a speck of contaminant. Even a drop of oil may later look like a big spot.

[edit] Annealing or heat treatment

This is a crucial stage of producing high-quality cold rolled steel coils. In this stage, a two heat treatment method is used: continuous annealing and batch annealing. These two heat treatment methods are used simultaneously to provide high tensile strength to the rolls. The steel rolls also achieve better drawing qualities because of the multiple annealing methods.

[edit] Skin pass

The skin pass is a quality-check stage where the rolls go through a final rolling process. This rolling process can remove any sort of stretch marks or defects on the rolls. Once the rolls pass through this stage, you will see a smooth and lustrous surface. In addition to removing the stretch marks, the skin pass reduces the thickness of the coils by 1%.