Non-contact brakes and clutches from ZF Industrial are increasingly being used in a wide variety of applications where web tension must be controlled reliably, accurately and with a rapid response.
A combination of EBU brakes and EKU hysteresis clutches managed by ZF's ERM controllers has proven to have the accuracy and reliability to successfully replace DC drive-based tension control systems in three high-precision presses at Day International (UK) Ltd. The company manufactures rubber sheeting used for producing newspapers and banknotes in high-speed printing presses; a process that primarily involves attaching a layer of rubber to a fabric backing. After considering a manual clutch system to replace the increasingly high-maintenance inverters, the company's engineers rejected the idea due to risks of contamination from dust particles, a problem conveniently avoided by the magnetic non-contact operation of the hysteresis units from ZF Industrial.
After twelve months of faultless use, Day International fitted a similar system to accurately control a three-way web of materials as they were joined and fed through an adhesive curing oven. After continued success, the third main operation was also upgraded, which involved feeding the sheets extremely slowly through the equipment that grinds the surfaces of the cured rubber sheets flat to tolerances of 10microns. By using such a versatile system, engineers could reduce wastage and downtime, and also standardise spares, easily expand the systems to control new webs and integrate the complete set-up with their current PLC.
ZF's EBU series hysteresis brakes have also been used successfully to eliminate wastage and maintenance downtime on a large shrink-wrapping machine at Iggesund Paperboard. The old friction-based tension control system was overheating and, by replacing it with non-contact ZF brakes, Iggesund has been able to achieve the exact tension required for the plastic to adhere to 3-tonne rolls of paperboard being prepared for storage and delivery. Easily integrated and open-loop-controlled via a PLC and a ZF ERM controller, the new braking system is able to accurately control the tension at all stages of the wrapping process, despite widely varying levels of resistance required. The EBU series brakes use a magnetic flux to control the film tension in the machine, providing reliable control that results in over 35,000 tons of paperboard being wrapped in a year without any rejects or maintenance downtime.
3000 labels per minute
Skanem Labels at Cardiff also found that a friction-based control system did not have the accuracy or flexibility needed when upgrading their Gallus printing machines. After one of their customers asked for a custom peel-and-seal type label that required an extra web to be fed into a printing machine, the engineers retrofitted the complete ZF tension control system including EBU Brakes, EKU Clutches and the ZF ERM Controller. The speed of the printing machine was monitored by Honnigman sensors in the roller end shafts, which fed back to the ERM controller to provide the highly accurate operation required for a machine capable of producing over 3000 colour labels per minute from a 2000-metre roll of film.
ZF EBU Brakes are also being used by RTI Ltd, a specialist company that manufactures, maintains and upgrades 35mm movie film processing machines. Its latest equipment is designed to process a 1200m reel of film every 20 minutes (3500m/hr) and use larger reels than normal to allow for an increase in processing capacity. However, the previous friction-based braking system could not ensure a smooth transition when changing over reels; overheating occurring at the end of the on-wind process due to the higher reel speeds and greater stopping loads.
However, the ZF systems are easy to fit and commission, and ensure that the continuous process of the delicate film can be maintained without costly extended changeover times or threats of breakage. ZF EBU brakes are now the 'tension control system of choice' for new RTI machines and when upgrading existing equipment. The tension control parameters have been calculated by supplier DJ Automation and are now stored, enabling them to provide an off-the-shelf system for future RTI machines.
Long service life
The non-contact operation of the brakes allows for an extremely long service life and avoids the creation of dust particles, making them suitable for environments where medical or food products are produced. The ZF range of brakes includes a high-power series that offers (continuous) slip powers from 250 to 2000W and peak capabilities of twice these figures. Hysteresis clutches are also supplied, which are especially useful for winding-on applications in cable manufacturing or food packaging industries and the four different versions available cover most requirements with torque capacities ranging from 0.08Nm to 520Nm.
The range is backed-up by ZF, one of the most respected manufacturers of driveline technology in the world, with production centres, partners and representatives on every continent. In the industrial sector, ZF is at the forefront of developments, from individual units to complete systems for virtually all types of machinery and production units, including those used in robotic systems and the factory automation sector.
