Analysis of the high-speed rotary motion of a superconducting magnetic bearing during ring spinning
Ring spinning is the leading textile technology for the production of short staple yarn, which runs commercially up to a maximum speed of 25 000 rpm. Higher speeds result in yarn damage mainly due to frictional heat. To eliminate this limitation, a friction-free superconducting magnetic bearing (SMB) was introduced as alternative high-speed yarn twist element consisting of a cryostat with an array of superconductors and a levitating permanent magnet ring with a yarn guide. Whereas stable spinning was possible until 30 000 rpm, it turned out that the new SMB twist element is more susceptible to external disturbances resulting in oscillating movements of the magnet. Therefore, a measurement system with an array of 5 synchronized optical laser triangulation sensors and one tachometer was implemented to analyse this motion in detail during spinning with high speeds. To test the system, the spinning speed was varied between 10 000 rpm and 21 000 rpm for different yarn qualities. In general, the magnetic ring oscillates around its centre position with the rotation frequency and a peak amplitude between 10 μm and 14 μm, which might be due to a small imbalance of the magnet. At the same time, the small tilt of the ring remained fixed with respect to the machine for all speeds. In addition, larger oscillation amplitudes of up to 300 μm are observed at 18 Hz for selected spinning parameters arising most probably from resonance effects with machine vibrations.