Cold Rolled: How it is Made

We previously discussed the manufacturing method of hot rolled steel, and now it is fitting to delve into its cold rolled steel. Cold rolling is the subsequent stage in producing flat-rolled steel items. The process initiates with hot rolled pickled and oiled (P&O).

Hot rolled steel is transformed into a final thickness that is thicker than several sheet products. A cold-reducing process is consequently employed, resulting in a thinner thickness. The cold reduction process initiates by applying tension to the sheet, thus thinning the product while making it harder and more difficult to form.

As formability is crucial in fabricating sheet metal, the steel undergoes the process of annealing, which is achieved through heat treatment that alters the material's properties to enhance ductility. By doing so, the product becomes highly desirable for the customer.

Shall we delve deeper into this process?

The Cold Reduction Process

Are you in need of cold rolled coils? The process for achieving this involves sending hot rolled P&O material through a series of tandem rolling mill stands, which consist of either four-high or six-high vertically stacked rolls.

As the material exits each stand, it becomes progressively thinner than the original hot rolled P&O. When it exits the final stand, the material is recoiled. However, at this stage, the material is hard, causing it to be unsuitable for numerous applications.

How can we rectify this problem?

The Annealing Process

is utilized to soften steel. This process can be accomplished in two ways: batching or continuous annealing. Batch annealing includes stacking hard coils four or five high on fixed bases or stools, hence the name "batch". The material is covered to ensure the coils are concealed from the oxides in the atmosphere. These oxides have the potential to harm the surface finish.

A considerable furnace is lowered onto the stacks of coils. The area between the cover and the furnace is heated using gas, while the interior of the cover is fan-circulated to transfer heat to the coils.

The following annealing technique is known as "continuous." The material can be fed via a furnace in a continuous rolled strip. It is then cooled and re-coiled.

Heating the material results in a softer texture, making it more malleable and applicable in various scenarios. The newfound flexibility makes the material fit for use.

Cold Rolled Finishing

However, to ensure customer satisfaction, the material must undergo finishing.

After annealing, the material must be kept covered while still at a high temperature to prevent oxidization and allow for the breakdown of oils and vapours present after cold rolling.

The next step is temper rolling, which involves cold rolling the material with a very low reduction. This process enhances the surface finish and flatness of the final cold-rolled product.

The finished coil is then delivered to service centres for processing before being sent out to customers for the fabrication of metal furniture, commonly used in offices, motorcycle exhaust pipes, lighting fixtures, and more.

Additionally, the cold-rolled product can undergo further processing to create galvanised, galvannealed, electro-galvanised materials, which we will discuss later.

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