Journal of Friction and Wear最新文献

A theoretical model of the formation of the stress-strain state in elastomers under the action of a concentrated load is considered. Experimental studies were carried out using the polarization-optical method. As a sample, transparent L-83 polyurethane with physical and mechanical characteristics corresponding to typical rubbers was used. It is shown that the stress-strain state of the surface layer calculated as a result of the theoretical solution of the mathematical model coincides with the experimental data. When loading, zones of compressive and tensile stresses are created. The magnitude of the tensile stress determines the likelihood of surface destruction (tearing). Simulation of an oblique impact confirmed the qualitative picture of the stress-strain state in elastomers under the action of a concentrated load. A theoretical study made it possible to establish that the potential energy of deformation is distributed over the depth of the surface layer in inverse proportion to the square of the distance from the point of application of the force, i.e., the point of contact of the solid particle with the surface of the elastomer. This makes it possible to mathematically calculate the level and distribution of energy dissipation in the wear volume of the surface layer. Theoretical and practical studies have shown that in the practical use of elastomer linings, it is recommended to install them at an angle close to 90° to the direction of solids flow.

This article discusses the issues of maintaining operability of hinged friction joints operating at 500°C. The object of study is the hinged joint of a pipe dryer operating contact loads in the friction joint up to 100 kN and operation temperatures in the range from 200 to 500°C. The studies have been performed with WOLFRAKOTE TOP FLUID high temperature lubricant comprised of solid lubricants suspended in base mineral oil. The experimental results of the lubricating composition upon heating in mold have demonstrated that burn up of the liquid component is intensified at 450°C being accompanied by transfer of lubricating medium into powdered form. Assessment of changes in tribological properties of high temperature lubricant in various aggregate states has demonstrated that heating and transfer of lubricant from liquid to solid state at low contact loads and velocities does not impair its tribotechnical properties. However, the increase in load and velocity parameters causes sharp increase in friction forces with the use of lubricating medium in powdered form. Based on the performed studies recommendations are presented aimed at improving the operability of hinged joints operating at higher temperatures.

The tribological properties under extreme conditions, structure, and chemical composition of antifriction coatings based on molybdenum disulfide deposited by magnetron deposition and suspension spraying with various types of a film former onto the surface of samples made of 12Kh18N10T stainless steel are studied. Tribological reciprocating movement tests in accordance with the ASTM G133 standard are carried out under reciprocating movement of a ball made of ShKh15 steel with a diameter of 6.35 mm in vacuum at the temperature of the samples of 250°C. The coefficient of friction and lifetime of the coatings under extreme operating conditions are determined. Suspension deposited coatings show a coefficient of friction of 0.046–0.049, and the magnetron deposited coating of 0.061. The maximum service life of the suspension deposited coatings is 19.7–21.8 h, and of the magnetron deposited coating, 22.7 h.

The results of tribological studies of various asbestos-free brake friction materials from leading manufacturers are presented. Two main aspects of the effect of the thermal conditions on the friction and wear characteristics of the selected materials are established: a change in the physical and mechanical properties at a low thermal load of the friction contact and changes due to various structural transformations and mechanochemical processes of the surface layers at a high thermal load of the friction contact. It is shown that high-temperature friction of frictional asbestos-free polymeric materials proceeds in a multistage mode, accompanied by pyrolysis of volatile products, binder destruction, degradation of the reinforcing element, and carbonization of the friction surface, which are constant factors. The materials under study are capable of forming a frictional transfer film on the counterbody friction surface in the form of a monolithic layer or separate transferred fragments oriented along the sliding direction. The developed materials form a film on the counterbody surface at relatively high temperatures, in the region of maximum friction values. It is established that the mechanism of high-temperature destruction of the surface layers of asbestos-free brake friction materials is characterized by the accumulation of damage in the subsurface layer and the wear process is most fully explained by fatigue peeling.

The article studies the characteristics of mill knives of high-speed steel HS 18-0-2-5 with as well as without МоС and Мо₂С molybdenum carbide coating at plane milling of oak wood. The molybdenum carbide coating was deposited by arc vacuum physical vapor deposition (Arc-PVD). The knife edge wear was determined using a contour measuring system for determining the displacement of the cutting edge along the axis of the cutter wedge sharpness angle (WB_W). Compared to a milling cutter with knives without coating, the molybdenum carbide coating improves the wear resistance of the knife blades and increases the cutting power by almost 40% when milling oak wood samples. The mills with the knife edges coated with the molybdenum carbides exhibited an average reduction in oak wood surface roughness R_a by 1.5–3 µm as compared to the bare tool in the entire range of applied feed rates and milling length. The laboratory tests of the wood-cutting tool covered with MoC coating prove that their durability has increased by 30% against the durability of the bare tool used in milling oak wood.