The ROBA-capping-head uses ROBA-contitorque, a magnetic clutch which works according to the hysteresis principle. In normal operation, it transmits set torque synchronously from an input onto an output element. Torque is generated here through magnetic forces, which are produced by permanent magnets and which magnetise hysteresis material. The torque transmission takes place contactlessly. First the cap is screwed onto the mouth of the PET bottle. The magnetic clutch features synchronous running, i.e. no slipping through. Only at the end of the capping process, when the cap has been screwed onto the bottle up to the end position, does the clutch slip through precisely at the set limit torque.

This means that the input and output sides rotate towards each other with a relative speed, the so-called slip speed. During this process, the hysteresis material is constantly re-magnetised; the torque transmission takes place asynchronously. In this case, the torque of the ROBA-contitorque magnetic clutch is retained at a constant value independent of the slip speed. After completion of the capping process, the relative speed returns to zero and the torque is transmitted synchronously between the input and output sides. 

On the ROBA-capping-head, the hysteresis technology ensures contactless and thus wear-free torque transmission: no contamination is generated through friction – which is suitable for use in the food industry. In addition, the clutches are characterised by a high repetitive torque accuracy of ±2%. “The ROBA-capping-head achieve a high torque consistency and repetitive accuracy through a special contactless seal labyrinth", explains Oskar Fleischmann from Research and Development at mayr power transmission.