•A bidirectional wettability transition of impregnated graphite using laser treatment is reported.•Graphite became ordered and hydrophilic as laser energy increased.•Flocculent nanostructure and adsorbed hydrocarbon caused hydrophobic transition.•The increasing real contact area and oxygen content led to hydrophilic transition.Controlling the wettability of surfaces is imperative for the tribology behavior during the friction and wear, especially in aqueous environment. In this work, fiber laser treatment of impregnated graphite was used to achieve a bidirectional wettability transition. The treated surfaces were characterized using scanning electron microscopy, 3D confocal surface topography analysis, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The surface treated by a low–energy laser became hydrophobic (increase of contact angle from 73.6° to 131.6°) and the surface treated by a high–energy laser became more hydrophilic (decrease of contact angle to 6.7°). Examination of the morphology indicated that with increasing laser energy, the roughness increased and the surface changed from a flocculent to scaly structure. Analysis of the energy spectra revealed an increase of oxygen content on the hydrophilic surface. In addition, Raman spectra analysis indicated a positive correlation between graphite ordering and the contact angle. The FTIR results demonstrated the existence of hydrocarbon on the hydrophobic surface. After ultraviolet/O3 cleaning, the contact angle of the hydrophobic surface decreased to 37°; however, the contact angle of the surface which did not be treated by laser hardly changed. Based on these results, it was concluded that the wettability transition was caused by the changes in surface morphology and chemical composition.Download high-res image (439KB)Download full-size image

•A method is developed to study how aging in oil affects the lip seal performance.•There is good agreement between simulation and experimental results.•This method lays a solid foundation for the prediction of lip seal life.•This method can be also used for other forms of seal.The effect of aging in oil on the seal performance of a radial lip seal is investigated in the present study by conducting a constant temperature oil bath test to obtain aged rubber samples and seals, and measuring the changes of material properties and seal performance with the aging time. The change of lip surface micro-morphology with the aging time is also measured by using a 3D white light optical interferometer. The leakage and friction torque are computed in a numerical simulation, utilizing a mixed elastohydrodynamic lubrication (EHL) model, to determine how aging in oil affects the lip seal performance. Finally, the simulation results of the EHL model are verified by a bench test on aged lip seals.

•We study two-phase mechanical seal using a test rig with transparent seal runner.•We examine the relation between tribology performance and phase distribution.•The plain-face seal has a speed limit above which it becomes unstable.•LST seals with suitable parameters improve the performance of mechanical seals.•LST shows potential in two-phase mechanical seals.Two-phase mechanical face seals with laser surface texturing (LST) on their end faces were investigated using a test rig with a transparent rotating ring. Cavitation occurred in some of the dimples and annular vaporization regions attached to the dimples were observed. The speed limit of the LST seals with suitable parameters was obviously higher than that of a seal with a plain end face, while those with sub-optimal LST parameters exhibited a lower speed limit. These results reveal that LST shows potential in two-phase mechanical face seals, but the LST parameters should be carefully considered.

Since aging is an inevitable phenomenon during storage of a radial lip seal, this study aims to investigate the effect of aging on the seal performance. An air oven aging test is conducted to produce aged rubber samples and seal products. An aging life prediction model is constructed to predict the equivalent material properties at any storage temperature. The material property parameters of aged rubber samples are measured in a uniaxial compression experiment. The pumping rate and friction torque of the seal are calculated through numerical simulation by using a mixed elastohydrodynamic lubrication (EHL) model. A bench test is used to verify the aging life prediction model and the simulation results of the EHL model. Finally, the verified EHL model is used to study how aging during storage affects the lip seal performance, as characterized by the leakage and friction torque.

A mixed lubrication model of a rotary lip seal using flow factors has been developed. The model consists of coupled fluid mechanics, contact mechanics and deformation mechanics analyses. The fluid mechanics analysis is described by a Reynolds equation that takes into account the surface roughness effect using flow factors. The contact mechanics analysis uses the Greenwood and Williamson model to compute contact pressure. The deformation mechanics analysis utilizes the influence coefficient approach to compute deformation of the seal. Results for a typical seal show how the operation parameters and the surface roughness affect seal behavior.Highlights► Predicts performance: minimum film thickness, contact area, pumping rate, friction torque. ► Analyzes fluid mechanics, asperity contact, and elastic deformation of the lip. ► More computationally efficient than deterministic approach. ► Provides effective tool for designer to predict and optimize performance of a seal design.