| Summary: | 碩士 === 國立虎尾科技大學 === 機械與機電工程研究所 === 101 === Abstract
This study used the principle of optical interference to create an optical analyser for measuring lubricant performance. The effects thatthe fixed angle of inclination to the slider, varyingtangential speeds, different loads, and variouslubricant properties have on the lubricant film thickness wereexamined. Hydrodynamic lubrication theory was adopted to assess the feasibility of the proposed analyser.
Under a specific load, the main system generatedhydrodynamic lubricationbetween the surface of a static slider and a fused-silica (SiO2)plate, on whicha tangential speed was applied. The resulting minimum film thicknesswas then measured using the optical interference principle. The workingsurface of the sliderwas a high-reflectance polished surface. The surface of the fused-silica plate was coated with Cr and SiO2 films. A microstructure was used to installthe slider, which retained a fixed angle of inclination (although up-down movement was allowed) and underwent hydrodynamic lubrication with the fused-silica plate. The proposed system adopted halogen light sources and anoptical image extractor to capture clear interference images of the lubricant filmthickness at the nanoscale. The minimum lubricant filmthickness measurable using the proposed device was approximately 100 nm, and the minimum resolution necessitated relatively extensive examination. By employing a servo motor and programmable logic controller, the tangential speed of the fused-silica plate could be controlled, generating a regular luminous intensity curve. The lubricant film thickness was calculated using the capturedinterference images combined with equal thickness interference.
The proposed opticallubricant performance analyser was used to investigate the effectsthat three types of lubricants (two biolubricants and one mineral oil) had on the thickness of hydrodynamic lubricant film. Sliders of the same material formed alubricant film interface with the different lubricants. The results showed that when the load was increased, the lubricant film thickness decreased; the larger the angle of inclination, the thicker the lubricant film thickness. However, when the angle of inclination reached a specific degree, the lubricant film thickness declined in correlation to the angle of inclination. Such variations in film thickness may occurbecause of the cavitation phenomenon,which verifies the feasibilityof the proposed measurement system.
The three lubricants used for this experiment were R68 lubricant and biolubricants derived from coffee and rice straw. Under a pressure of 54 kPa at low (12 mm/s) and high (61 mm/s) rotational speeds, the thickness of rice straw biolubricant and R68 lubricant films was higher than that of the coffee biolubricant. The greater film thickness of R68 lubricant and rice straw biolubricant was attributed to the contact angle. The smallerthe contact angle, the higher the adhesion is, resulting in greater lubricant film thickness.
Under a pressure of 408 kPa at low (12 mm/s) and high (61 mm/s) rotational speeds, the thickness of the coffeebiolubricantfilm exceeded that of the R68 lubricant and rice straw biolubricantfilms. The three lubricants exhibited identical trends regarding lubricant filmthickness under high pressure. When the pressure was increased, the effect of the contact angle on the lubricant film thickness decreased in significance, and the reduction in film thickness was primarily attributed to high pressure.
The nanoparticle analyserresults showed that the average nanoparticle size of the coffee and rice straw biolubricants and R68 lubricant was 258 nm, 285 nm, and 92 nm, respectively. Thus, the size of the nanoparticles in lubricants has minimal influence on the thickness of lubricant film.
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