Experimental characterization of the tribological and acoustic performance of different stern-tube bearing materials

The present study focuses on the experimental characterization of different stern-tube bearing materials regarding their tribological and acoustic performance. Three materials, in particular, COMPAC elastomeric polymer, rubber polymer, and white metal (Babbitt), were evaluated under water and oil-lubricated conditions using a flat-on-disk setup. Surface topography analysis, stiffness coefficient measurement, and performance assessment were conducted in three phases. Performance assessment under water/oil-lubricated conditions was conducted measuring vertical force, friction force, and friction coefficient, along with the synchronous recording of sound pressure emissions using a microphone. Results showed significant differences in friction characteristics and acoustic performance of the specimens under varying loads and rotational speeds. COMPAC specimens with a shape factor of 1.0 exhibited lower friction coefficient, in comparison to Babbitt liners, while entering the hydrodynamic regime, for linear velocities exceeding 0.7 m/s. At 50 RPM and 0.2 MPa load, all specimens exhibited comparable acoustic performance in the low frequency range (16–500 Hz). COMPAC and SAE-30-lubricated Babbitt specimens maintained noise levels below 60 dB at frequencies above 1500 Hz, highlighting their suitability for noise-sensitive applications. Rubber and SAE-10-lubricated Babbitt liners exhibited increased noise levels at frequencies above 3000 Hz. Rubber specimens were characterized by higher friction coefficient and sound pressure levels across all conditions, especially at frequencies above 1000 Hz. Sound pressure levels increased with rotational speed for all specimen types, with the differences between them being less pronounced at higher speeds.