In a special application involving special challenges, a RINGFEDER® friction spring is used within a torque limiter with a ball latch. It is located in the drive line of the movable lift aids on the wing panels, in order to protect the motor and the gearbox from damage if there is a critical blocking of the flaps. The retraction force of the individually designed friction spring holds the ball in the arrester in the corresponding pockets, transmitting the torque from one side of the limiter to the other. If the torque exceeds the limit value defined, the balls emerge from their pockets and compress the spring, which may cause the torque limiter to slip through. In this way, safe and reliable overload protection is established.
For the use in the emergency exit doors of a passenger aircraft of the A321 type, the manufacturer AIRBUS confronted RINGFEDER® with the challenging task of designing a high-performance, innovative safety coupling. This coupling ensures that, in case of an emergency, the exit doors are in a defined torque range and can therefore be opened by any passenger irrespective of his/her physical constitution. For this purpose, a specially dimensioned design with an outer diameter of only 13 millimetres were used, which furthermore also complies with the strict specifications of the manufacturer with regard to corrosion and temperature resistance, closeness of the system without any adhesion or fittings, weight and maintenance friendliness.