Steel hot rolling process
Forming of bars to reach the defined geometry
Hot rolling is a thermomechanical process. The steel (bars for diameters greater than 35-40 mm or coils for smaller diameters) is initially heated and is then passed through a number of rolling stands, each equipped with counter-rotating steel rollers. As the metal passes through each pair of rollers, the cross section of the bar changes shape and the rollers reduce the cross-sectional area and conversely increase the length of the bar.
The sum of the changes along the rolling line (called calibration) allow a hot pre-shaped product to be obtained with typical tolerances of +/- 0.3 mm.
Heating the steel to temperatures of roughly 1000-1100°C and then air cooling it means that the final mechanical properties are strictly related to the chemical composition of the steel: medium and high alloy steels have high hardness after rolling, while low alloy steels have low hardness. In all cases though, the process is accompanied by general grain refinement due to the hot forming process and subsequent recrystallization.
Calvi has two rolling mills
Induction rolling mill no. 1
This mill is equipped with a new generation 1000 kW induction furnace and five quick-change rolling stands, for rapid machine set-up times. The mill is also provided with automatic coiling reels which allow coil-to-coil or coil-to-bar rolling and ensure greater production flexibility and efficiency.
Induction rolling mill no. 2
This mill has six rolling stands for bar rolling and a 2500 kW induction furnace allowing it to deliver a more uniform rolled product and significantly increase production performance. The mill is provided with an in-line surface cleaning system that together with its rapid induction heating system guarantees low surface oxidation. Mechanical arms unload the material automatically and place the bars in two “cradles”.
A turning workshop completes the rolling department. Equipped with modern CNC lathing machines, the workshop builds specific equipment for new profiles or intervenes swiftly on the rollers whenever necessary.
