A superconducting magnetic bearing (SMB) is applied as high-speed yarn twist element for ring spinning, which is the leading technology for the production of short staple yarn in textile industry. The conventional ring spinning twist elements currently used commercially operate at a maximum speed of 25.000 rpm, as friction heat damages the yarn at higher velocities. Our new SMB eliminates this undesired friction in the twist element and is designed to increase the production speed up to 50.000 rpm. The bearing consists of a reinforced permanent magnet ring levitating freely above a superconductor ring made from YBCO bulk segments, which is placed inside a bath cryostat attached to the ring spinning machine [1,2]. The superconductors are cooled down to a temperature between 77 K and 65 K in a field-cooling mode. The magnet ring containing an additional eyelet for the yarn rotates during the spinning process due to the yarn winding onto the spindle.

The talk will give an overview on the current status of the device and will discuss challenges for the application. The focus is on different measurement techniques to characterize the static and dynamic behavior of the SMB in detail. This includes oscillation measurements of the non-rotating magnetic ring, when it was exited with an initial axial or lateral displacement and released afterwards [3, 4]. The dynamic mechanical stiffness and the damping coefficients in axial, radial and tilting direction were calculated from these measurements. These studies also allow to optimize the SMB by a modification of the magnet ring aspect ratio, which results in an improved stiffness verified by simulations of the magnetic flux density distribution [5].

Measurements of the ring position were carried out while spinning at high rotational speeds to validate the static measurements as well as the modeling assumptions for the ring movement itself [6]. The measurement system consists of 5 optical positioning sensors and a tachometer. In contrast to static measurements, the operating bearing is continuously exited with a revolving force via the yarn. In general, the magnetic ring oscillates around its center position with the rotation frequency and a peak amplitude of up to 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.

Finally, we studied the hysteretic losses in the SMB generated by a process-related tilt of the field-cooled permanent magnet using a caloric measurement setup with a resolution down to 5 mW [7]. The determined losses increase almost linear with speed, whereas an exponential increase was observed for the tilt angle. The results were confirmed by 2D simulations using a two-component model leading to similar dependencies for the hysteretic losses on speed and tilt.

[1] M. Sparing et al., IEEE Trans. Appl. Supercond. 25 (2015) 3600504.
[2] M. Hossain et al., Text. Res. J. 90 (2020) 951.
[3] M. Sparing et al., IEEE Trans. Appl. Supercond. 26 (2016) 3600804.
[4] T. Espenhahn et al., IEEE Trans. Appl. Supercond. 31 (2021) 5000105.
[5] T. Espenhahn et al., J. Phys. D: Appl. Phys. 53 (2020) 035002.
[5] M. Sparing et al., Eng. Res. Express 2 (2020) 035039.
[6] T. Espenhahn et al. Supercond. Sci. Technol. (2021) accepted.

This work was supported by the German Research Foundation (DFG).

Keywords: Superconducting magnetic bearings, YBCO bulk, in-situ measurements, hysteretic losses