Foil and coil - Siemens foil mills
Paul R Osborne, Product Manager – Aluminium at Siemens VAI, Christchurch,
UK, presents the Siroll ALU foil mill.
As the demands for aluminium foil applications in terms of quantity and quality have increased, so have the burdens on the equipment to produce it. Over the past two decades there have been significant changes in rolled width (+150%), rolling speed (+220%) and foil thickness (-25%). Today’s rolling mills are expected to produce foils that are less than six micrometres thick in widths of over two metres, and be capable of speeds in excess of 2,000m/min.
The unique properties of aluminium foil have led to its use in a diverse range of applications. Whether in a plain, coated or laminated form, the foil can be used in electronic devices, insulation, air conditioners, or to protect foods and pharmaceuticals. Approximately 75% of aluminium foil’s use is in packaging.
A good example of the imaginative development of aluminium foil products is household foil, which is now available in different varieties. Having extended the original product in terms of the range of widths (280-600mm) and thicknesses (10-18µm), we are now seeing ‘non-stick’, textured and ready-cut sheet versions. There is also a foil aimed at addressing the problem of baked-on food that keeps the foil clean and permits re-use, and another that features a black coating on one side to transfer radiant heat more efficiently and improve roasting performance.
A further example is the expanded use of push- through blister packs which, having become established for medicine tablets and capsules, are now growing in use for confectionery products such as chewing gum.
Foil use within Europe has more than doubled in the last 20 years, and while investment in the long established European plants has been limited, in recent times, there has been extensive development in Asia. In the last five years, China alone has added 27 new imported rolling mills and approximately 70 locally supplied ones. The increase in production capacity, created by these new mills, while primarily targeting the growing local Chinese market, also includes a significant portion for export.
Siemens VAI, based in Christchurch, UK, has developed solutions to meet the demands of high speed foil production, based on in-house foil rolling know-how. The integration of equipment, systems and solutions has resulted in the Siroll ALU product range.
Due to the high demands with respect to product quality, the Siroll ALU foil mill necessarily incorporates a range of Dynamic Actuators. This typically includes Double acting Roll load cylinders, giving excellent gauge control performance, including the rolling of low load passes; e-block work roll bending, providing a continuous transition between positive and negative bending; coolant and hot edge sprays, to address asymmetric or edge flatness issues and variable crown roll, with its dynamically inflatable sleeve to correct parabolic errors.
Siemens VAI can provide the appropriate sensors and control systems to take advantage of these actuators and reach the performance levels demanded. Technological mill control is provided by Siroll process control. This platform has increased its performance capabilities by adding new features and more effective control algorithms. In addition, the Siemens SIMATIC S7-400 PLC is capable of efficient configuring and programming.
Performance and production
Throughout the rolling mill, in combination with the mechanical equipment, a range of automation features have been specifically developed and implemented into the Siroll ALU solution to facilitate faster operation and minimise non-productive time. These include on-line banding and automated spool and scrap coil handling.
Minimising time between coil changes is key to maximising production. The fully automated coil handling system designs can cater for coils on steel or cardboard spools, and the coil loading and unloading sequences can be fully automatic. This is complemented with the key alignment system, which automatically positions the drive keys to match the spool slot, simplifying and speeding up the loading process.
Further solutions speed up other tasks – the on-line coil preparation system for thicker foil permits the efficient removal of the coil’s outer laps prior to rolling, while the foil feeding system allows simple threading of material from the coil into the mill, minimising downtime between coil loads.
The sideshifting work roll change car minimises the time required for this procedure. In the coil handling area, both the on-line banding station and automated spool and scrap coil handling prevent interlap and scratching, providing efficient and time saving solutions.
A compilation of these features came together in the form of the foil mills supplied to Shanghai Shenhuo Aluminium Foil Company as part of its foil plant development in Pudong, China. The three state-of-the-art, wide, high speed mills, commissioned by Siemens VAI in 2007, were designed to produce in excess of 25,000t of foil per year.
The first coil rolled on each mill was of saleable quality and the foil roughing mill achieved rolling speeds of >1,750mpm 20 days after start up. The foil intermediate mill attained a speed of 1,000mpm on the first coil and >1,800mpm within seven days, and reached a product thickness of 7.5µm at 16 days. The foil finishing mill achieved seven micrometres within the first week of rolling.
Aircraft and shipping will continue to drive changes in the width of cold rolled aluminium strip. With 2.6m being targetted, it will not be long before foil producers find ways to take advantage of this with a range of new applications.
Further information: Siemens VAI