Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
The film thickness of a ball-on-disc contact lubricated with four greases of different formulations\nwas measured under different operating conditions until starvation. Two polymer-thickened\ngreases and two lithium-thickened greases, formulated with base oils of different nature and/or\nviscosity, were tested. The central film thickness was measured under constant operating conditions\n(load, temperature, slide-to-roll ratio) varying only the entrainment speed. In a separate test, the film\nthickness was measured over time with all operating conditions set to constant. Pictures of the\nfilm thickness profile across the contact area were also registered. The results were compared with\nthe fully flooded results. The coefficient of friction (COF) was measured in a ball-on-disc contact\nunder equal operating conditions and the results were correlated with the film thickness findings.\nThe different grease formulations and the influence of the operating conditions on the film thickness\nand COF were discussed. The polymer thickened the greases, promoting lower COF and higher film\nthickness, especially when there is thickener material crossing the contact which happens quite often\nfor these greases....
This article describes experimental and theoretical studies on the cavitation phenomena in\nthe grease lubrication film under pure sliding elastohydrodynamic contact. In situ observation tests\nusing the optical interferometry technique were conducted, and the growth of cavitation was captured\nusing a high-speed camera. The results showed that the cavity grew in two stages, which was similar\nto the behavior in the base oil, and that the cavity growth rate in the initial stage was higher than\nthat in the second stage. In the initial stage, the cavity growth time in the grease was longer than\nthat in the base oil, and the cavity length after the growth depended on the base oil viscosity. It was\nalso found in the test using diurea grease that small cavities were formed by the lumps of thickener.\nThe cavity growth in the initial stage was discussed by numerical simulation of pressure distribution\nbased on a simple rheological model....
Hybrid polymer matrix composites (HPMC) are prominentmaterial for the formation of biomaterial and offer various advantages\nsuch as low cost, high strength, and the fact that they are easy to manufacture. However, they are associated with low mechanical\n(low hardness) and tribological properties (high wear rate). The average hip joint load fluctuates between three to five times of the\nbody weight during jumping and jogging and depends on various actions relating to body positions. Alternate bone and prosthesis\nmaterial plays a critical role in attaining strength as it determines the method of load transferred to the system.Thematerial property\ncalled modulus of elasticity is an important design variable during the selection of the geometry and design methodology. The\npresent work is demonstrated on how to improve the properties of high-density polyethylene (HDPE) substantially by the addition\nof bioceramic fillers such as titanium oxide (TiO2) and alumina (Al2O3). The volume fractions of Al2O3 and TiO2 are limited to\n20% and 10%, respectively. Samples were fabricated as per ASTM standards using an injection moulding machine and various\nproperties such as mechanical (tensile, flexural, and impact), tribological (hardness, wear), and corrosion including SEM, density,\nand fractography analysis studied. Experimental results revealed that an injectionmoulding process is suitable for producing defectfreemouldHPMC.\nHPMCcomprising 70%HDPE/20%Al2O3/10%TiO2 has proved biocompatible and a substitute for biomaterial.\nA substantial increase in the mechanical and tribological properties and full resistance to corrosion makes HPMC suitable for use\nin orthopaedic applications such as human bone replacement, bone fixation plates, hip joint replacement, bone cement, and bone\ngraft in bone surgery....
Fuel and water contents are inevitable in automotive engine oils. This study intends\nto investigate the impact of the addition of gasoline (3â??20%) and water (1%) on the lubricating\nperformance of synthetic base oil (PAO), with or without an anti-wear additive (ZDDP), for a\nsteel-cast iron contact. Fuel-added PAO showed an increase in the load carrying capacity. Oil electrical\nconductivity and total acid number (TAN) measurements showed slightly increased conductivity\nand marginally increased acidity at a higher fuel concentration. In contrast, an increased wear\nrate, proportional to the fuel concentration, was observed in a prolonged test with constant-loading.\nResults suggested that the fuel addition is a double-edged sword: reducing the scuffing risk by\nproviding stronger surface adsorption and increasing the sliding wear rate by bringing down the\noil viscosity. The PAO-water blend formed an emulsion and resulted in a significantly increased\nload-carrying capacity, again likely due to the higher polarity and possibly acidity. For the\nZDDP-containing PAO, the addition of 1% water and 3% fuel generated 24% and 52% higher wear.\nThe phosphate polymerization level was reduced on the worn surfaces by the introduction of water\nbut the thickness of ZDDP tribofilm was not significantly affected....
Jacking-oil pockets are applied in many journals and thrust bearing applications in order\nto provide a hydrostatic oil film force that ensures a wear free run-up following a successful lift-off\nprocedure. However, all components of the jacking-oil system have to be carefully designed in\norder to limit costs and prevent significant disturbance of hydrodynamic operation after deactivation\nof lift-oil. Experimental data and predictions for a four-pad tilting-pad journal bearing in load\nbetween pivot configuration are presented. Dynamic processes of the lift-off procedure as well as\ncharacteristic parameters of stationary conditions are studied. Moreover, hydrodynamic operation\nand hybrid lubrication providing a combined hydrodynamic and hydrostatic pressure distribution are\ninvestigated for sliding speeds up to 20 m/s. Analyzes of lift-off procedure prove that characteristic\nparameters such as lift-off pressures and vertical lift displacements are considerably influenced\nby manufacturing tolerances and misalignments. The comparison of hydrodynamic and hybrid\nlubrication provides a significant increase of load carrying capacity by additional jacking-oil supply\nat the maximum journal speed. In summary, results of measurements and predictions correlate well\nfor all three investigated lubrication conditions....
Loading....