Superconducting Magnetic Bearing as Twist Element in Textile Machines

Superconducting magnetic bearings (SMBs) enable the levitation of a magnet in a stable position over a cooled superconductor without the need for an additional positioning system. These passive bearings are being investigated for applications wherever a stationary levitation or a contact-free rotary or linear motion is desired and cannot be realized by simpler means. Ring spinning is the most widely used technique for the production of short staple yarn in the textile industry. The productivity of the ring-spinning process depends on the rotational speed of the spindle. It is limited by friction in the so-called ring-traveler twist element. During the spinning process, the traveler is dragged along the ring by the yarn with up to 30000 r/min. The resulting friction causes wear of the twist element and melting of synthetic yarn at high spindle speeds due to strong heat generation. Recently, an SMB was implemented as a contact-free twist element in a ring-spinning machine up to 11000 r/min. This prototype SMB consists of a rotating permanent-magnetic (PM) NdFeB ring acting as a yarn-driven traveler and a stationary bulk YBCO ring at 77 K in an open LN₂ bath. In this paper, we investigate the bearing properties of this SMB with regard to the special requirements of the ring-spinning process. Dynamics of the spatially vibrating and rotating PM ring are analyzed including the forced vibration due to interaction with the yarn. For the expected yarn forces, the displacement amplitude at the resonance frequency remains below the field-cooling height. In addition, the possibility of realizing higher rotational speeds by mechanically reinforcing the NdFeB ring with a shrunk-on steel shell is discussed.