Journal of Friction and Wear最新文献

Analytical and numerical modeling approaches for the contact-working system of turbo- and electric machines have been developed. The simulation allows determining some dynamic characteristics and loads in the rotor–stator system when there is a loss in clearance between them and there occurs subsequent motions with impacts or without separation from each other. In the system, the rotor and stator are deformable, the stiffness of rubbing surfaces is variable, and the working clearance between them is extremely small (50–500 times less than the rotor radius at the contact point). It is shown that the effect of the absolute elasticity for stator generates a significant change in natural oscillations of the coupled rotor–stator system, that is, a significant change in its eigenfrequencies and eigenmodes. It is noted that the elastic deformation of rubbing surfaces leads to a nonlinear increase in their contact stiffness, which consists of quasi-static and dynamic components. The consequences of an extremely small clearance are an elastic deformation of the contact surfaces commensurate with it (up to half the clearance size at the point of contact) during whirling with slipping of rotor over stator, as well as the disappearance of pure rolling, which is accompanied by the actual absence of rotary speeds even at low frequencies of contact whirling. The resulting diagrams of changes in the contact stiffness and whirling frequencies and the XY trajectories can serve as sources of initial information for identifying the operation of a real rotary machine on the threshold of a dangerous whirling with slipping and whipping and for further studies of contact oscillations of rotors.

The total resource of the assembly unit, as well as the post-repair resource of the unit, depend on the specified resource for critical joints. The main problem of calculating the joint accuracy is to determine the margin of accuracy or the margin of material for wear since an increase in the estimated fit tolerance will lead to a decrease in durability, and its decrease will entail an increase in costs due to an increase in rejects or the need to introduce a technological operation. In this regard, a method for calculating the joint fit tolerance depending on the specified or design wear characteristics was developed based on the analysis of the parametric failure model. When modeling various wear rates, it is recommended to use the relative wear resistance of the joint in the obtained dependences only if the wear function is approximated in a linear form. An expression for calculating the relative wear resistance of a joint is obtained depending on the wear resistance of the surfaces of the parts that form it. Using the example of calculating the fit tolerance of a rolling bearing operating under hydrodynamic friction conditions, the resulting fits are analyzed at a certain resource of no-failure operation of the joint for cases of increasing the wear resistance of the joint by 10 and 20%. The scientific novelty of the research lies in obtaining a theoretical relation between the fit tolerance and the probabilistic characteristics of the wear process at a specified probability of failure-free operation. The practical significance of research is expressed in the possibility of calculating the accuracy parameters of a particular joint at a specified resource.

Over five centuries, friction science used the friction coefficient as the main quantitative characteristic of the friction process. The concept of the friction coefficient as a characteristic of resistance to the movement of frictional surfaces in a latent form was formulated by Leonardo da Vinci. Two centuries later, already in an explicit form, as a formula, the friction coefficient appeared in the studies of Guillaume Amonton. Modern engineering believes that the friction coefficient has no physical meaning, it is merely a convenient friction parameter that can be easily determined in an experiment. What is the physical meaning of resistance to the movement of frictional surfaces? If we perform a thermodynamic analysis of the friction process, considering each deformable friction contact element as an independent transformer and dissipator of energy of the external relative displacement (motion) of surfaces, then it becomes possible to consider the friction coefficient in a new physical sense. The accumulation of the potential energy of a deformed structure (defects in the crystalline structure) by a friction contact is, in essence, a method of deceleration of frictional surfaces moving relative to each other. The static potential energy of the formed defects in the structure of the contact structure is a measure of the decrease in the kinetic energy of the relative motion of the frictional surfaces. The pragmatism of the energy (thermodynamic) approach of friction is organically embedded in the general problems of energy consumption and saving energy resources of modern tribology.

The effect of 2,2,6,6-tetramethylpiperidine (TMP), para-cumylphenol (PCP), 2,6-di-tert-butyl-4-methylphenol (DTBMP), dicumyl peroxide (DCP), 2,2,6,6-tetramethylpiperidine-1-oxyl (TMPO), dodecantiol (DdSH), dibutyl disulfide (Bu₂S₂), didodecyl disulfide (Dd₂S₂), and molecular oxygen on the wear index (W_i) of purified Vaseline oil (PVO), hexadecane (HD), polyethylsiloxane (PES-5), and a mixture of PES-5 containing 10 wt % PVO or HD was studied for the first time. The reason for the extremely high wear of steel surfaces in a solution of PES-5 containing 10 wt % of hydrocarbon lubricants, consists in the antagonism of polyorganosiloxanes with hydrocarbon lubricants and in the lack of molecular oxygen necessary for the formation of a servovite film. The prospect of studying mixtures of polyorganosiloxanes and hydrocarbons is to find a mixture that would have synergism in the anti-wear area. Studies of additives and gaseous media can also be promising. The results of the study of mixtures of polyorganosiloxanes containing about 10% by weight of hydrogen lubricants can be effectively used to reduce the wear of steel surfaces operating in an oxygen atmosphere.

A mathematical model of an oilless rotary vane compressor is presented. The model takes into account the mutual influence of tribological and operating parameters of the stage. To specify conditions for the mathematical model to be unambiguous, experiments were carried out to determine the values of the friction coefficient and the maximum allowable sliding speed of promising self-lubricating materials as functions of the load and speed parameters of the compressor stage. Mathematical modeling of the integral energy characteristics of the oilless stage of the rotary vane type has shown the conceptual option to expand the range of its operation modes based on the justified use of self-lubricating materials in friction units and account of the mutual influence of tribological and operational factors. Theoretical studies have confirmed that the speed of the stage and the degree of pressure can be increased by a factor no less than 2 compared with those of commercially produced machines. However, setting the friction coefficient in modeling stages of a rotary vane type as a constant can lead to incorrect conclusions in designing in what regards the best operating and structural parameters of the stage. Increasing the speed of the oilless stage of the rotary vane type will enable a reduction in the production requirements for end clearances and an increase in the specific weight and size characteristics and the degree of pressure increase in the stage by a factor of 1.5–2 for the effective efficiency values of 0.8 or more. The proposed mathematical model makes it possible to more accurately predict the energy losses related to mechanical friction in the stages and the integral energy characteristics of the stage in a wide range of operating and design parameters.

This paper discusses a method for determining the anti-wear properties of motor oils after temperature control in the temperature range from 160 to 280°C. Optical density, viscosity, and wear scar diameter are considered. The effect of degradation products on the anti-wear properties of the oils under study was evaluated. The degree of influence of degradation products on anti-wear properties is shown, which is determined by the dependence of the change of diameter of the wear spot of thermostated oils on the absorption coefficient of the light flux. It is noted that the decomposition products have an ambiguous effect on the anti-wear properties of motor oils, which vary from 0.32 to 0.26 mm, and significant changes occur at a coefficient of K_P = 0.05 of all studied oils, while the minimum diameter of the wear spot is characterized by mineral oil, partially synthetic and synthetic oils have values greater than 1.2 times and the reason for this is their heterogeneous composition, which depends on the quality of the additives used and their tendency to decomposition. As an assessment of anti-wear properties, a criterion is proposed that characterizes the concentration of degradation products and is recommended for classifying motor oils into groups of performance properties. The data obtained on the anti-wear properties of motor oils make it possible to compare oils of the same purpose and create a databank that will allow equipment designers to reasonably select oils depending on the temperature conditions of the tribocouples.

The influence of compositions based on 1H,1H,9H-trihydroperfluorononan-1-ol, montmorillonite, and polytetrafluoroethylene Fluralite on the structure and wear resistance of the polyurethane elastomer modified by them is considered. The introduction of polyelement modifiers leads to the reorganization of the amorphous structure of the polymer matrix and changes in the properties of the surface. There is an increase in the intensity of the amorphous halo and a decrease in its radial half-width. According to the methods of X-ray photoelectron spectroscopy and X-ray microanalysis, the surface (up to 3 nm) and deep layers (up to 5 μm) of the modified polyurethane elastomer are enriched with fluorine, which together leads to the formation of a hydrophobic boundary lubricant layer and provides increased wear resistance. The developed polyurethane composites may be of interest as monolithic sports, roofing, and waterproofing coatings.