Evaluation of Anti-Friction Properties of Solid Lubricant Coatings for a Piston Skirt of a High-Force Diesel
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uation of Anti-Friction Properties of Solid Lubricant Coatings for a Piston Skirt of a High-Force Diesel K. V. Gavrilova, A. V. Morozovb, *, M. V. Seleznevc, Yu. V. Rozhdestvenskiia, N. A. Khozeniuka, A. A. Doikina, and V. S. Hudyakova aSouth
Ural State University (national research university), Chelyabinsk, 454080 Russia Institute for Problems in Mechanics, Russian Academy of Sciences, Moscow, 119526 Russia c 25th State Research Institute of Chemmotology, Ministry of Defense of Russia, Moscow, 121351 Russia *e-mail: [email protected] b
Received February 19, 2020; revised July 7, 2020; accepted July 7, 2020
Abstract—Anti-friction properties of solid lubricating coatings dedicated for the decrease in friction and increase in seizure resistance in the piston skirt–cylinder liner couple of high-forced combustion engines have been compared. Various modifications of coatings based on a polymer binder with addition of highpurity molybdenum sulfide and graphite have been deposited onto the segment surface. The graphite-based coating (foreign manufacturer), which is now successfully employed for steel pistons in diesels of heavy vehicles, has been used as the reference specimen. The studies were carried out at the friction temperature of 110°С in the range of normal loads of 50–450 N at a constant reciprocating frequency of 20 Hz, which is comparable to operating conditions of tribocoupling in diesel engines. Analysis of the results has shown that deposition of all coatings significantly decreases the friction coefficient, which amounts to 0.12–0.14 in some coatings (containing simultaneously molybdenum disulfide and graphite), which corresponds to the condition of contact of friction surfaces in the presence of lubricating material and the absence of direct metal contact in the friction couple. Keywords: solid lubricating coatings, seizure, wear, piston skirt, graphite grease, molybdenum grease DOI: 10.3103/S1068366620050104
INTRODUCTION Evaluation of friction loss in an engine indicates that their main fraction (up to 66%) corresponds to the piston skirt, piston rings, and bearings, while the residual 34% correspond to the friction losses in the gas distribution mechanism and transmission [1]. It should be noted that friction losses in the piston–cylinder and piston ring–cylinder couples correspond to 45% to 50% out of the total friction losses in combustion engines according to the data from [2, 3]. Therefore, recently, there has been demand to provide a hydrodynamic friction mode and the application of coatings reducing friction, when this condition is violated. Along with the characteristics of coatings, which decrease friction coefficient and, consequently, decrease fuel consumption, their ability to avoid increased wear and seizure of friction surfaces [4] under particular operating conditions is of particular interest. More specifically, with insufficient oil injection as exemplified by a cold start, absence of a local gap caused by mechanical or heat strain of the liner, insufficient lubricating ability of m
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