Experimental investigation of airless minimum oil lubrication for high-speed spindle bearings

:Frictional heat generation and lubricant starvation are major challenges in high-speed spindle bearings, where maintaining a stable oil film with minimal churning losses is critical for performance and durability. Conventional oil-air lubrication systems address this through continuous compressed-air supply which may result in high energy demand, increased noise, and added system complexity. This study presents a systematic experimental investigation of an airless minimum oil lubrication concept. To eliminate the need for compressed air, the investigated bearing-oiler system employs an integrated oil channel in the outer ring and a precision injection oiler capable of delivering micro volumes of oil close to the bearing contact zone. Systematic tests are carried out to examine the influence of key parameters (oil delivery position, flow rate, viscosity, and bearing speed) on bearing temperature, frictional torque, and oil film thickness. Results demonstrate stable operation up to 2.7 × 106 n · dm (n denotes the rotational speed in rpm and dm the bearing pitch diameter in mm), with stable temperature evolution and adequate film formation. Relative to oil-air lubrication, the airless approach achieves comparable thermal and tribological performance. The findings provide insight into the thermal and tribological behavior of airless minimum oil lubrication under high-speed bearing operating conditions.