Abstract
A method for evaluation of the lubricating and rheological properties of hydraulic oils in tribological contacts has been developed, which consists in online studying samples of commercial batches of oils on a software and hardware complex with visual evaluation of the kinetics of changes in the main tribological indicators of friction contact. Using a roller analogy, the operation of gears in the conditions of rolling with 30% sliding is simulated. Samples of AMG-10 oil from two producers are analyzed. It is established that with increasing temperature of lubricant for Sample 2 (“Kvalitet-Avia” AMG-10), a long-term restoration of protective boundary films of oil is observed and the period of their formation increases by 2.5 times, causing the implementation of a semidry mode of lubrication at start-up. The total thickness of the lubricating layer is 1.27 times less as compared with Sample 1 ("Bora B" AMG-10 oil), regardless of the lubricant temperature. Also, the rheological properties of the oils have been determined. Sample 1 exhibits low shear stresses at the level of 9.4 MPa and high effective viscosity, 4249 and 5039 Pa·s, at a volumetric oil temperature of 20 and 100 ºС, respectively. For Sample 2, with increasing oil temperature to 100 ºC shear stress increases by 1.15 times and the effective viscosity in contact decreases by 1.53 times. Additives present in Sample 1 are characterized by more effective antiwear properties and thus increase the wear resistance of contact surfaces in the conditions of rolling with sliding thanks to strengthening of the surface metal layers during operation, while Sample 2 undergoes strengthening-softening processes which reduce the wear resistance of friction pairs
Highlights
Routes to increase the wear resistance of triboconjuction elements are based on modification of contact surfaces via selecting lubricant сompositions and finding optimal operating modes for friction pairs
Despite the high shear rate gradients in the contact lubricating layer, from 5.63·103 to 5.73·105 s-1, which occur at a maximum sliding speed of 0.71 m/s in the conditions of rolling with sliding, the lubricant is characterized by effective viscosity, on average, 4249 and 5039 Pa·s at a volumetric oil temperature of 20 and 100 oС, respectively (Fig. 5)
With Sample 1, there was not fixed any failure of the lubricating layer during start-up and direct metal contact of the friction surfaces
Summary
Routes to increase the wear resistance of triboconjuction elements are based on modification of contact surfaces via selecting lubricant сompositions and finding optimal operating modes for friction pairs. An important factor in ensuring a high efficiency of friction units is a high-quality choice of lubricants with high lubricating, antifriction and antiwear characteristics. Among various producers of commercial oil batches, it is important to choose a lubricant that meets required physical and chemical characteristics, and has effective tribological properties. Tribological indicators have not yet been standardized for a wide range of lubricants. The development of methods for evaluating the quality of lubricants in tribological contact is an important area of research, the results of which can make it possible to provide valuable recommendations on oil workabiity in certain operation modes
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