Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
Oilââ?¬â??air lubrication supplies lubricants in the form of droplets to elastohydrodynamic lubrication (EHL)\ncontacts, such as those in high-speed spindle bearings. However, there is a paucity of information related\nto understanding the lubrication behaviors of oil droplets within EHL contacts. In this study, behaviors of\nlubricant droplets, in terms of spreading around a static contact as well as passing through a rolling contact,\nwere studied with an optical ball-on-disk EHL test rig. Influences of oil droplet size, viscosity, and surface\ntension on droplet spreading were examined. Lubricating film formation was also investigated when droplets\ntraveled through the EHL contact region. The results indicated that droplet size and running speed significantly\ninfluenced film profiles. With increasing entrainment speeds, a small droplet passed through the contact without\nspreading and generated films with a significant depression in the central contact region....
To reduce the friction of a piston ring while maintaining a large oil film load-carrying capacity,\nan approach comprising of the inverse method and the sequential quadratic programming algorithm was\nproposed. The approach considers the variation of mixed lubrication and variable lubricant viscosity with\ntemperature along the engine stroke, is developed to optimize the profile of a piston ring. A piston ring profile\nis represented by a polynomial function. A case study of the second piston ring shows that the proposed\nmethod can be applied for the optimization of a piston ring profile. In addition, this paper illustrates the effects\nof the degree of a polynomial function. The results show that the minimization of friction and maximization of\noil film load-carrying capacity can be balanced simultaneously when the degree of the polynomial is 2 and 5....
In this study, a sintering methodology is presented by using abnormal glow\ndischarge to metal matrix composites (MMC), consisting of 316 steel, reinforced with titanium\ncarbide (TiC). The wear behaviour of these compounds was evaluated according to the\nstandard ASTM G 99 in a tribometer pin-on-disk. The effect of the percentage of\nreinforcement (3, 6, and 9%), with 40 minutes of mixing in the planetary mill is analysed,\nusing compaction pressure of 700MPa and sintering temperature of 1,100�°C�±5�°C, gaseous\natmosphere of H2 - N2, and sintering time of 30 minutes. As a result of the research, it shows\nthat the best behaviour against wear is obtained when the MMC contains 6% TiC. Under this\nparameter the lowest percentage of pores and the lowest coefficient of friction are achieved,\nensuring that the incorporation of ceramic particles (TiC) in 316 austenitic steel matrix\nsignificantly improves the wear resistance. Also, it is shown that it is possible to sinter such\nmaterials using the abnormal glow discharge, being a novel and effective method in which the\nworking temperature is reached in a short time....
To further extend knowledge about fluid film friction in elastohydrodynamic contact, it is important\nto examine how lubricant flows. In this paper, several film thickness results obtained by interferometry technique\nfor different kinds of experiments were analyzed and discussed based on lubricant flow continuity. Results of\ntwo steady-state and two transient experiments are presented. Possible speed profiles that can explain observed\nfilm thickness distributions were suggested. It is shown that major part of present experiments can be explained\nby a single speed profile known as a plug flow. This finding is in contradiction to usual linear speed profile\npredicted by Reynolds equation....
The ability of the antifriction materials to withstand with no lubrication for a while\ncan be a solution for the catastrophic failure of automotive journal bearings from the internal\ncombustion engines in accidental breakdown of the oil pump. A thick layer of antifriction\nmaterial (babbit) was deposited by gravitational casting on a steel disk substrate. Four\ntribological disk samples coated with babbit are tested against a steel shoe on Amsler\ntribometer at different speeds and loads in dry friction. The values of the friction coefficient\nversus speed and load are presented, the obtained results indicating a mild wear regime,\nrecommending the new babbit as a possible coating for the bushes of the journal bearings in\nautomotive internal combustion engines. Further tests must be dedicated to the establishment\nof the wear intensity of the steel shoe - babbit disk tribological pair, both for motor oil\nlubricated and dry friction conditions....
The regularities of the wear of the steel 1045 during cutting off the feed of a lubricant under the nonââ?¬â??stationary friction conditions were established. The influence of the properties of the secondary structures, formed on the contact surfaces under conditions of rolling with a different degree of slippage, on the wear of advancing and lagging surfaces was determined. The influence of specific friction work, the degree of hardening ââ?¬â?? weakening of surface layers of metal and the intensity of saturation by active elements of nearââ?¬â??surface layers of metal on the wear resistance of friction pairs is examined. The change is established in localization of the depth of spreading the stressed and deformed state of material of the contact surfaces with an increase in the slip rate from 0.315 m/s to 1.14 m/s at rolling with the slippage....
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