In this study, the characteristics of an ultra-thin gas
squeeze film are analysed using the modified molecular gas film
lubrication (MMGL) equation with coupled roughness and rarefaction
effects taken into consideration. A modified squeeze number (Σ)
and modified plate aspect ratio (β) are proposed to estimate
molecular gas film lubrication characteristics. Using Σ,
β and a simple mapping method, the linearized MMGL problem can be
reduced to the continuum gas film problem and the MGL characteristics
can be exactly estimated if the pressure flow factors
(ϕXP,ϕYP) and the rarefaction coefficient (Q̄P(D)) are known. The present models are computationally compact,
and thus applicable to simulation of a microelectromechanical system.
Most previous studies have employed surface patterning to improve the performance of lubrication systems. However, few have experimentally analyzed improved effects on friction reduction in SiC mechanical seals by ultra-fast laser pulse texturing. This work applies surface texturing on a non-contact mechanical seal and analyzes the characteristics of the resultant surface morphology. A femtosecond laser system is employed to fabricate micro/nanostructures on the SiC mechanical seal, and generates microscale-depth stripes and induces nanostructures on the seal surface. This work examines the morphology and cross section of the SiC nanostructures that correspond to the different scanning speeds of the laser pulse. Results show that varying the scanning speed enables the application of nanostructures of different amplitudes and widths on the surface of the seal. The friction coefficient of the introduced SiC full-textured seal is about 20% smaller than that of a conventional SiC mechanical seal. Hence, femtosecond laser texturing is effective and enables direct fabrication of the surface micro/nanostructures of SiC seals. This
A two-dimensional, quasi-static, inverse heat conduction problem (IHCP) is implemented to investigate the absorption efficiency of surface coatings in laser surface hardening process. The analysis of IHCP includes the utilization of the method of direct sensitivity coefficient and the measurement of interior temperatures nearby the laser heating surface. The results shows that the estimation of surface absorptivity generally agrees with that observed by experimental works. It is realized that the different kinds of coating make influences on the surface absorptivity as well as surface temperature significantly. Furthermore, the power density and scanning speed of laser beam to control the quality of surface hardening may be determined based on the informations of heat flow in the workpiece.
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