The reduction of production costs is in the focus of many developments by SMS group, with one of the aims being reduction of operating costs by saving energy, for example. The new Convection Roll Cooling (CRC) is such a development and offers an annual cost cutting potential in hot strip production of up to one million Euros.
Conventional work roll cooling systems operate to the spray cooling method. They operate with a pressure between 7 and 12 bars and a 7-stand finishing mill requires about 7,000 m³ of water per hour. The new work roll cooling system by SMS group, however, operates to the forced convection principle. Here, the cooling effect is generated by the formation of a water stream channel against the work roll rotation at the roll surface. For this purpose, the cooling water stream is rectified by means of an intelligent device and then led, in a defined manner, through a nozzle gap to the area between work roll surface and the cooling shell which has a curvature radius similar to that of the work roll. There is no metallic contact between cooling shell and roll.
Right from the beginning of the design development phase of the new work roll cooling system, advanced and efficient calculation methods were used. Compact roll cooling design, clearances and cooling water volumes, for example, were checked by means of Computational Fluid Dynamics (CFD) simulations and optimized in iterative processes. In a next step, SMS group manufactured a prototype in its Hilchenbach workshop, which served for checking the proper functioning and the swivel mechanism towards the roll. The development experts paid particular attention to reproducing the rolling mill surrounding to be able to assess the cooling water drain behavior in the mill stand. Cooling water supply remained as provided for in the original design.
Supported by the results from simulation and testing, SMS group succeeded in convincing Salzgitter Flachstahl GmbH to install the newly developed equipment in several hot mill finishing stands for testing under operating conditions. The existing spray cooling of the work rolls was replaced by the compact roll cooling system. Since it was possible to use the former fastenings and interfaces, the modification could be accomplished during a regular repair downtime. The only work to be done in addition to replacing the cooling unit itself was to adapt the media supply system. The automation system was not affected by the modification.
The trial runs several weeks. The system remained without failure over the entire period and confirmed that the new cooling system, operating at a pressure of around 1.5 bars and with a 30 percent lower water volume than before, is able to achieve the capacity required to cool the work roll barrels. This was accompanied by the positive side effect that due to the changes in water supply and process mode almost no cooling water hit the strip surface. Hence, strip temperature losses in the finishing mill reduced significantly.
The patented convection work roll cooling system offers a fast Return On Investment (ROI) thanks to savings in reduction of required pump energy of up to one million Euros per year. It is easy to integrate in existing hot strip mills and CSP® plants and will perceptibly cut operating costs there as well.
Another benefit with respect to new facilities is a considerable reduction of investment costs for the water management system due to the substantially lower consumption of energy and water. The savings potential here is around 1.5 million Euros.