Vol 40, No 4 (2019)

Results of studies of the surface and wear characteristics of roller—pad friction pairs in burn-in tests with motor oil treated with ultrasound at different frequencies are presented. It has been found that the treatment of oil with ultrasound at a frequency of 17 kHz leads to an increase in the pre-score load by 22.2% and a decrease in the friction coefficient by 13.1% with the optimal load increasing by 12.5%. The treatment of oil at a frequency of 12 kHz results in an increase in the score resistance by 6.5% and a decrease in the friction coefficient by 3.6%. The optimal load does not change in this case compared with the results of tests conducted using untreated oil. When the oil was treated at a frequency of 8 kHz, no significant differences between the values under study were observed. A decrease in the value of roughness parameter R_a for the samples treated with ultrasound at a frequency of 17 kHz by 50% and 78.2% was established for the roller and pad, respectively.

This paper focuses on the influence of diffusion and segregation processes on the strength and tribological characteristics of friction units. The application of the quantum chemical method made it possible to reveal that the appearance of segregated atoms at the grain boundaries is the main reason for hardening or destruction of metal surface layers. The proposed approach was also applied to assess the compatibility of various elements consisting of iron and to relate this compatibility to the tribological characteristics. Comparative tests on friction and wear were aimed at investigating initial 38Х2МЮА-Ш nitrated steel, 38Х2МЮА-Ш nitrated steel with a diamond-like coating, and Nb- and Hf-alloyed 38Х2МЮА-Ш nitrated steel with a diamond-like coating. The tribospectral identification method proposed by the authors was used to study the friction processes in heavily loaded friction units using the example of Mi-26 helicopter spline joints.

The compositions of antifriction biocompatible polyamide matrix composites filled with graphite nanocomponents obtained by modified industrial phytogenic waste—hydrolytic lignin—are developed. Paraffin oil and polysiloxane fluid were used as safe plasticizing agents and lubricating components. The oil absorption of the obtained materials and the tribological characteristics of the composites are studied. The composites are studied using thermogravimetric analysis, infrared spectroscopy, and microstructural analysis. It is shown that the composites filled with thermally expanded graphite from lignin and plasticized with a blend (paraffin oil + PES-5) in the amount of a 5–15% additive have average friction factors of 0.072 and 0.074 with a specific load of 2.33 and 0.33 MPa respectively. With an increase in the additive content, the friction factor grows slightly. Therefore, to increase composite durability, the recommended composite plasticizer content should be 28–30%.

The results of studying the improvement of tribological properties of polyethylene products by modification with Nd and Al chelate complexes containing bulky tert-butyl groups in the ligand surrounding are given. The effect of additives on the coefficient of friction and wear of friction parts under static load is studied. The influence of coordination compounds on thermomechanical characteristics of polymers is studied. It is shown the treatment of polyethylene with Nd and Al complexes gives rise to a 1.2- to 1.5-fold decrease in the coefficient of friction and a 1.5- to 2-fold increase in the wear resistance.

Using an analysis of the relationship between the elements that characterize the initial scattering of the fit clearances, the wear rate, and its scattering, a dependence for the calculation of the design fit tolerance was obtained by modeling the parametric failure of a joint. The dependence allows for an accurate determination of the requirements for the initial scattering of the clearances in the joint to ensure a specified lifetime at a fixed probability of failure-free operation. It is shown by using a real example that the reduction in the fit tolerance from 20 to 1 µm can result in an increase in the lifetime by only 5%. A further increase in the durability of the joint can be achieved by the creation of the parts’ surfaces with higher wear resistance maintaining the accuracy of the machining within the specified cost-effective design limits.

This study evaluates the computation method of the study of worm gears with Archimedean and involute worms when engagement correction is presented, based on the contact pressures and the wheel teeth wear, as well as the gear life and the sliding speed in the engagement. The regularities of influence of correction on the stated gears parameters are stated. When there are positive values of the correction coefficient of wheel teeth, the maximal contact pressures and the linear wear of wheel teeth decrease as compared with the noncorrected gear, and when the correction coefficient is negative they increase. The stated regularities are represented in a diagram form.