Electromechanical Cylinders Find Niche Onboard

Electromechanical cylinders, the latest development of SKF's innovative roller screw technology, now provide an attractive and very cost-effective alternative to the use of bulky, inconvenient and potentially environmentally damaging hydraulic systems in ships' rudder and stabiliser control systems. By using electromechanical cylinders instead of hydraulic drives, ships can dispense with the need to carry the hundreds of litres of costly hydraulic fluid which takes up valuable space, is always a fire risk and which, if spilled, is harmful to the environment. Additional benefits of the electromechanical cylinders, which use long-life brushless DC motors as their power source, include greatly reduced maintenance, space savings, and improved dynamic characteristics which allow more responsive handling of the vessel. The electromechanical cylinders deliver efficiencies of up to 80%, compared with 50% or less for hydraulic actuators, and they are easy to specify, as they can be ordered as a complete assembly including actuator, motor and electronic control system. As no complicated pipework, oil tanks or hydraulic pumps are needed, they are also easier, faster and much less costly to install than their hydraulic counterparts. The key to the high load capacity and extended operating life of SKF's electromechanical cylinders is the novel design of the roller screws around which they are built. These use a thread arrangement for the screw and nut which eliminates rolling element recirculation, thereby suppressing the potential risk of recirculation failure. In addition, the profile of the screw shaft and nut thread has a 90-degree angle, giving optimised resistance to shear, and the profile of the thread shanks on the roller is shaped to give many more contact points than a conventional ball screw. This allows SKF roller screws to handle loads up to three times larger than similarly sised ball screws, making them ideally suited for demanding marine applications.