Conference Proceedings

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Browsing Conference Proceedings by Author "Jiang, S."

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    Analysis of electrochemical machining-textured surfaces under point contacts in rolling tribo-test.
    (Springer, Cham., 2021) Gyimah, G. K.; Oman, E. K.; Nyanor, P.; Acakpovi, A.; Jiang, S.; Guo, Z.; Barber, G. C.
    Purpose: The need for the right textured surface and selecting the right material in tribology is critical to friction reduction and energy savings in machine elements under full film lubrication rolling point contacts. This study provides a guide to proper material selection and the right surface texturing technique to enable machine elements to carry heavy loads at different speeds under the fully-flooded EHL regime. Design/Methodology/Approach: A lapped GCr15 ball bearing, cast iron (HT 500) plates, GCr15 tempered plates and GCr15 plates without tempering were used. The electrochemical machining (ECM) technique was used to manufacture Micro-texture surfaces on the plates. The ECM micro-textured surfaces and lapped plain surfaces of the same material were subjected to friction and wear behaviour between a ball and a plate test in a fully-flooded EHL point contact rolling condition. The tribological test was conducted under different rolling speeds and pressure. The topographical characteristics of the lapped plain surfaces and the Electrochemical Machining (ECM) textures surfaces were analysed by both optical and scanning electron microscopy. Findings: The outcome of the study showed that the geometry characteristics (micro-textured and lapped untextured) and the densities of the micro-texture impact was critical to the film formation in the tribological behaviour test against the lapped GCr 15 steel bearing balls. Significantly, low friction and wear were observed for the micro-textured surfaces as compared to the lapped untextured surfaces. Research Limitation/Implications: The research was on rolling point contact in fully-flooded EHL tribo-test using lapped untextured and micro-textured surfaces in contact with ball bearing. The study did not consider line contact and sliding force. The rolling point contact is the predominant phenomenon in gears, cams, tractions and balls in energy transmission. Practical Implication: The outcome of this research increase the knowledge base of this area, it informs technologies and tribologies to select and design machine elements with energy-saving criteria in mind. In addition, this work has opened other opportunities for research to harness the full potentials of the micro-texturing. Social Implication: This paper also guides to industrial and manufacturing sectors using machine elements as moving systems to generate and transmit energy in adopting energy-saving systems and policies that is based on the outcome of such studies. Originality/Value: The innovation of this research is centered on the tribological performance of GCr15 undergoing Micro-texturing by Electrochemical Machining which demonstrates better film thickness formation within EHL regime over HT 500 counterpart material. This outcome is a good starting point for further research and development.
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    Oil film characterization of PTFE during EHL point contact and pure rolling tribology tests.
    (IEEE, 2021) Gyimah, G. K.; Jiang, S.; Acakpovi, A.; Oman, E. K.; Nyanor, P.; Barber, G. C.
    A polymer additive blended with commercial engine oil to have enhanced film-forming ability has been developed and studied using optical interferometry. An experimental study was carried out on the impact of polymer additives (Polytetrafluoroethylene – PTFE) in an oil film between a steel ball and a flat glass surface in non-conformal contact. The contact region was studied by means of optical interferometry using monochromatic two-beam interferometry, a microscope and a high-speed video recording device. A new method of determining the interference grade of the central film thickness was developed and used in this study. The interference intensities of the central point of contact at various speeds were captured by the high-speed video recording device and the central interference gray values were determined. These values were then used in new method to obtain the film thickness of the modeled lubricants, and compared with the rectangular SLIM fit and the LINE fit methods film thickness determination. Hamrock and Dawson calculations for EHL film thickness formation was also used for comparative analysis. The film thickness stability was simulated under both steady state and rolling state conditions. The lubricant film thickness stability obtained confirmed the beneficial effect of PTFE on film thickness behavior under pure rolling conditions. The regime observed by the profile of the film thickness suggest the transition between the hydrodynamics and elastohydrodynamic lubrication.
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    PTFE and MoS2 Additives for Mineral Oil Film Formation in EHL Point Contacts.
    (ASME, 2016) Gyimah, G. K.; Guo, Z.; Huang, P.; Jiang, S.; Barber, G. C.
    Lubricant film-forming viscosity index improvers blended with commercial engine oil have been developed and studied by using optical interferometry. The influence of the viscosity index improvers (PTFE and MoS2) mixed with oil were experimentally studied and compared with engine oil without the index improvers as the baseline. The effect of the viscosity index improvers on lubricant film thickness, contact pressure and rolling speed for the case of a steel ball loaded on a flat glass surface in point contact condition was investigated. An optical interferometry technique which utilized a monochromatic two-beam interferometry light source, a microscope and a high-speed video recording device was used for the investigation. Hamrock and Dawson calculations for EHL film thickness were also used for comparative analysis. The lubricants used were commercial SAE #30 engine oil and PTFE and MoS2 mixed with commercial SAE #30 engine oil. The oil viscosities ranged from 0.0109 Pa.s to 0.255 Pa.s. The rolling speed and the loads were varied between 0.189 m/s to 0.641 m/s and 1 N to 2.6 N respectively. The lubricant film thickness stability at the point of contact between the steel ball and the glass disc was investigated for both steady and rolling state conditions. The viscosity index improvers were found to have a significant effect on the film thickness behavior under pure rolling point contact conditions.