Start-up and coast-down friction and temperature in an active gas foil journal bearing with adjustable sleeve diameter

Łukasz Breńkacz
Paweł Bagiński
Artur Andrearczyk
Małgorzata Bogulicz
Grzegorz Żywica

Abstract:

The tested active gas-foil bearing is representative of high-speed, high-precision rotor supports used in compact turbomachinery and precision spindles. We report diameter-resolved experiments on an active gas-foil bearing, in which the sleeve is set before each run to adjust the radial clearance. Fifteen set points (35.1554–35.5110 mm; 25.4 µm steps) were tested under repeatable transients: 30 s start-up to 24,000 rpm, a short steady segment, and 30 s coast-down. The friction torque (converted to power and energy loss) and journal temperature were measured using calibrated sensors. The results show a clear asymmetry: at comparable speeds, the coast-down torque exceeds the start-up torque. Increasing the sleeve diameter reduces transient losses, with friction-induced power dropping from 310 W (start- up) and 400 W (coast-down) at the smallest setting to 200–250 W at the largest. The maximum friction torque changes little beyond Ds ≈ 35.25–35.30 mm, indicating a practical window for start/stop mitigation. Temper- atures remain moderate (62 to 70 ◦C), while coast-down heating rates are typically two to four times higher than during start-up. By scheduling the clearance through sleeve-diameter adjustment, the bearing systematically reduces start/stop energy dissipation and the associated thermal loads—key factors affecting efficiency, durability, and mainte- nance in oil-free machines. The quantified start-up and coast-down losses, together with the measured tem- perature fields, provide benchmark data for precision rotor design and control.

Year:

2026

Type of Publication:

Article

Keywords: