Levelling: New Techniques

During the sheet manufacturing process, it is subjected to hot and cold rolling, which provide it with certain mechanical properties. However, during this process the sheet adopts rolling defects and high residual stresses are generated in its interior, which cause the sheet not to meet required quality levels. Sheet defects arise due to stress differences between sheet longitudinal and transversal fibres. Such stresses can arise for different reasons, for example due to uneven cooling during the rolling process, uneven roll pressure, coiling process, material impurities, etc. Therefore the rolling process alone is not able to meet the flatness and material specifications required by the market. The correct use of such sheet defects and the release of residual stresses inside the material is required.

The analytical model has been implemented in custom software, with an easy and intuitive interface that enables different process variables to be calculated for a specific leveller configuration almost instantaneously.

Different levelling technologies exist to eliminate sheet defects and reduce residual stresses, such as simple straightening, stretch leveling , tension levelling or roll levelling. However, roll levelling provides certain advantages that make it one of the most attractive options. It is the most economic option, it is a fast and continuous process, and it can process a wide range of band thickness and widths. Final levelling quality is lower than with stretch levelling, but even so it offers an acceptable level of quality for the majority of processes. Many subsequent processes can be affected if sheets have not been properly levelled, due to the existence of internal stresses and shape defects, such as pressing and stamping processes, cutting processes, roll forming, etc.

At Fagor Arrasate , we have made a firm commitment to such advanced calculation tools with the aim of optimising the levelling process. These tools are particularly interesting, as conventional roll levellers are currently undergoing a process of adaptation and improvement. The tendency to use materials with ever greater yield strengths and/or lower Young’s modulus has obligated the need for further research into levellers and thereby ensure their correct operation with such advanced materials.