Available online at ScienceDirect. Procedia Engineering 150 (2016 )

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1 Available online at ScienceDirect Procedia Engineering 150 (2016 ) International Conference on Industrial Engineering, ICIE 2016 The Influence of Anti-Wear Additives on the Bearings Hydro- Mechanical Characteristics I.V. Mukchortov a, K.A. Pochkaylo a, E.A. Zadorozhnaya a, * a South Ural State University, Lenin av., 76, Chelyabinsk , Russia Abstract The experimental dependencies of the friction coefficient and the wear rate for lubricants without additives and the oil containing an anti-wear additive are obtained. The received laws cannot be explained with the hydrodynamic theory of greasing, theories of boundary friction or their combination. To eliminate these contradictions we offer a rheological model of a lubricant including the dependence of viscosity on a thickness of the lubricant layer The Authors. Published by by Elsevier Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of ICIE Peer-review under responsibility of the organizing committee of ICIE 2016 Keywords:anti-wear additives; hydro-mechanical characteristics; bearings 1. Introduction One of the main tendencies in the design of internal combustion engines is an increase of the specific power. Decrease in the size of the engine as the capacity increases leads to an increase in loadings at certain engine details, in particular, on the bearings of a crankshaft. In designing the bearings of the crankshaft it is necessary to define the maximum size of contact pressure at which the hydrodynamic mode of friction occurs. When we perform the hydrodynamic calculations the bearings, we are faced with difficulties in determining the parameters of the transition from the liquid to the transitional mode and the boundary mode. These parameters are most important for a prediction of a speed of the wear process, preservation of the geometrical parameters of the bearings and engine characteristics. Models of transitive and boundary friction modes are usually developed in relation to the friction of the piston rings [1-20]. It is known that the friction of the piston rings about a cylinder liner can't be described by * Corresponding author. Tel.: ; fax: address: zadorozhnaiaea@susu.ru The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of ICIE 2016 doi: /j.proeng

2 608 I.V. Mukchortov et al. / Procedia Engineering 150 ( 2016 ) any of classical models. A distinctive feature in this case is the combination of high values of the friction coefficient with small speeds of the wear process. Combined friction models are used more often [4, 6]. The predominant approach to the construction of boundary friction models is the distribution of the hydrodynamic and dry friction at the contact area. The monotonic change of the friction coefficient and intensity of the wear process as the contact pressure changes corresponds to such a representation. However it does not correspond to the experimental dependencies. In this connection the detailed studying of the transitive friction mode in the engines bearings represents an important problem. Namely, we want to study the character of the dependence of the friction coefficient on contact pressure and the relationship of the friction coefficient with the speed of the wear process. Another important task is to identify the role of anti-wear additives such as ZDDP in transient modes. There is data on the influence of anti-wear additives on the hydro-mechanical characteristics of the bearings [21, 22]. 2. Experiment Method In order to ensure the required accuracy, all measurements were performed on a standard friction machine with a friction torque sensor. As a bearing model a steel roller and a part of the loose leaf of the diesel engine bearing were used. The roller was made of a crankshaft material and processed similarly to a crankshaft journal. The bearing loose leaf has a bronze anti-friction layer. For maintenance of uniform distribution of the contact pressure on the contact area, the part of the loose leaf, a longitudinal size of which is less than a length of the loaded area (a corner of coverage less than 10º) was used. The anti-friction layer of the loose leaf has been honed till a size 4 mm 12.5 mm (cross-section and longitudinal accordingly) to reach the contact pressure in a range of hydrodynamic and boundary friction modes at reliably measured values of the friction force (torque). To test the oil-20a was used as the base oil. This is industrial oil without additives, derived by the selective clearing: the class of viscosity is ISO 32. This oil contains a certain amount of oil surface-active substances (SAS). The torque sensor of the friction machine has been carefully calibrated to measure the friction moments in a wide range. Amperage directly from the sensor was used as an output signal. It has allowed us to solve the problem of nonlinearity for characteristics of sensors of this type. The measurements were made under the following conditions: the diameter of the roller was 95 mm; the frequency of rotation was 1000 min 1 ; the temperature in the friction contact was 100±3 º (having blown in hot air with adjustable temperature); the lubricant was introduced in a friction zone at atmospheric pressure; the range of pressing loads was ; the range of contact pressure was 0 20 P. The intensity of the wear was measured by weighing part of the bronze loose leaf before tests (after extra running) and after tests within 1 hour. The tests were repeated with the addition to the oil a concentrate of the antiwear additive ZDDP in an amount corresponding to 1.25% (recommended) and 2.5% (a maximum for engine oil). 3. Results Figure 1 shows the dependence of the friction coefficient on the reciprocal pressing load. A noteworthy feature is a shift value of the contact pressure corresponding to the minimum of the friction coefficient. The second feature of the diagram is abnormal dependence of the friction coefficient in some area more to the left of the minimum value. This feature is more clearly seen in the graphs of the dependence of the friction coefficient on the contact pressure. As can be seen from the data shown in Figure 2, the addition of ZDDP did not affect the friction coefficient in the hydrodynamic regime at P 5MPa. The effect of the anti-wear additive is that friction hydrodynamic regime realized at higher contact pressures. The second feature of the friction in the radial bearings is the existence of the field with approximately constant values of the friction coefficient. To elucidate the mechanism of friction in this area of contact pressure we measured the wear value. Figure 3 shows the wear values of the samples after the test. The values for the base oil are not shown because they are too large. Upon reaching the minimum friction coefficient and its subsequent increases, the wear rate is not changed. This is not unexpected, since in the region where the friction coefficient is minimum, the mode of the friction is hydrodynamic.

3 I.V. Mukchortov et al. / Procedia Engineering 150 ( 2016 ) Fig. 1.Diagrammes of Gersi. 1 is base oil; 2 is oils with 1,25 % ZDDP; 3 is oils with 2,5 % ZDDP; F is the pressing force of the sample to the roller Fig. 2. Dependence the friction coefficient on contact pressure; 1 is base oil; 2 is oil with 1,25 % ZDDP; 3 is oil with 2,5 % ZDDP; P is the contact pressure

4 610 I.V. Mukchortov et al. / Procedia Engineering 150 ( 2016 ) A more interesting fact is the almost constant rate of wear of contact in a wide pressure range from 8 to MPa for oil with 1,25% ZDDP and from 10 to MPa for oil with 2,5% ZDDP. When these contact pressure values are implemented the dependence of the wear rate, which is characteristic of hydrodynamic friction mode, is maintained. 4. Discussion The received friction laws in radial bearings and their models are reliably reproduced and have an objective character. From the data it follows that when using oils containing anti-wear additives, the friction hydrodynamic mode performed at much higher contact pressures than when using oils without additives. Fig. 3. The wear value of the sample at tests within 1 hour In the hydrodynamic lubrication theory for certain geometrical parameters of the bearing, a unique parameter that determines the limiting value of the contact pressure is the viscosity of the lubricant. The presented data are consistent with the theory of hydrodynamic lubrication in only one way: assuming that the viscosity of the lubricant in a small thickness of the lubricant layer depends on the presence of anti-wear additives and differs from the viscosity of oil in a free state. It follows that to improve the correctness of the hydrodynamic radial bearings calculations should be made using a rheological model comprising the dependence of the viscosity of the lubricant on the lubricating film thickness. The fluid mode of the friction can't be explained from the perspective of any of the theories of boundary friction, if this mode is implemented at pressures much greater than the contact pressure corresponding to the minimum friction coefficient. The most probable explanation of the presence of the dependence of the viscosity of the lubricant on the lubricant layer thickness and the influence of the anti-wear additives on this dependence, is the representation about the polymolecular adsorption, stated in [21-23]. Acknowledgements This work has been carried out with the financial support of the Russian Foundation for Basic Research (project \16, project \16).

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