Влияние адгезии на трение качения и скольжения: эксперимент

Normal and tangential contact between a cylindrical steel indenter (wheel) and an elastomer with high adhesive properties is investigated. In the case of indentation in the normal direction, a computer simulation of the process of indentation and detachment was carried out, which shows good coincidence with an experiment. For the rolling friction mode, when analyzing the measured dependences of the tangential component of the contact force on the wheel displacement, the adhesive component of the friction force was determined. The situation of sliding friction, in which the rotation of the wheel was impossible, is considered. In the presence of adhesion, the sliding friction force is proportional to the contact area. In the absence of adhesion (the elastomer is covered with a chalk dust), a stick-slip friction mode is realized. The frequency and amplitude of stick-slip transitions depend on the indentation depth of the indenter into the elastomer.

Functional composite electrochemical coating Ni-Co-Al2O3 -an alternative to chromium plating

The physico-mechanical properties of composite electrochemical coatings (CEC) nickel-cobalt-aluminum oxide were investigated depending on the electrolyte parameters and electrolysis conditions. The previously developed low-concentration chloride electrolyte for nickel plating was used as an electrolyte to replace environmentally hazardous chromium plating electrolytes containing hexavalent chromium, which is prohibited by the laws of many countries. The wear resistance of the obtained CEC was determined on a three-ball friction machine. This made it possible to establish that the wear resistance of the CEC exceeds the wear of chrome coatings in dry friction mode by 2-2,5 times and is comparable to chromium in the friction mode with lubrication. In the dry friction mode, the higher wear resistance of the nickel-cobalt-alumina coating is explained only by the higher hardness of the latter. Probably, upon destruction of the coating, the particles of the alloying addition act as a solid lubricant, which causes an increase in the resistance of the CEC during wear. The microhardness of the CEC was determined using a PMT-3 microhardness tester and amounted to 6-25 GPa. The microhardness value was influenced by the concentration and properties of the dispersed phase, as well as the electrolysis conditions - the temperature and pH of the electrolyte, and the cathode current density. “Corrodcote” test was used in the study of corrosion. According to its data, the corrosion resistance of CEC is 2-3 times higher than the corrosion resistance of chromium deposits. The results obtained make it possible to recommend the developed functional CEC of nickel-cobalt-alumina instead of chromium coatings as corrosion- and wear-resistant.

Evaluation of tribotechnical properties of modified surfaces after plasma electrolytic treatment

The article considers the study of the effect of plasma electrolytic processing on the tribotechnical characteristics of medium-carbon steel. Friction tests were carried out in dry friction mode. Electron microscope and profilometer were used to study the friction tracks. For a comprehensive assessment of the quality of the modified surface layer, the Kragelsky-Kombalov complex parameter was calculated. It was found that plasma electrolytic treatment leads to a decrease in the coefficient of friction and weight wear in comparison with hardened and untreated steel. It has been determined that the mechanism of wear of samples after plasma electrolytic treatment is fatigue wear at boundary friction and plastic contact.

Counter-rotating electric generator for wind power plants with liquid metal energy transfer

The problem of creating effective structures that ensure mutual rotation of the rotor and stator of an electric generator. The wide practical application of counter-rotor wind-electric generators, which provide a significant increase in specific power, is hindered by the disadvantages and low reliability of existing systems for removing electric energy from the windings of a rotating counter-rotor, due to the dry friction mode. It is possible to increase the reliability of the contact removal of electrical energy from the counter rotor (rotating stator) by replacing solid brushes with liquid metal contact groups, which will lead to a certain increase in the resistivity of the contact group, compensated by the contact area of the liquid metal with the contact ring. It is most advisable to use liquid metal contact groups based on gallium, which will raise the permissible temperature limit of operation by about 2 times compared to the achieved level to 275 °C and, thereby, additionally raise the specific power of the electric generator.

Liquid metal sliding contacts for electric machines

The electric sliding contact in the brush mechanism is one of the most unreliable components of electric machines of alternating and direct current and other electrical equipment in which the transmission of electric current is carried out using sliding contacts that require fairly frequent maintenance and can be a source of sparking. It is possible to increase the reliability and efficiency of electric machines with sliding electric contacts by replacing the dry friction mode with the liquid friction mode in the sliding electric contact. The most appropriate material for use in the construction of a liquid metal sliding contact is gallium. When replacing the sliding electrical contacts of asynchronous electric machines with a phase rotor from traditional solid to liquid metal gallium, it is possible to increase their power up to 1.4 times due to the availability of a higher thermal operating mode.

Study on Lubrication Characteristics of C4-Alkane and Nanoparticle during Boundary Friction by Molecular Dynamics Simulation

Lubricant has been widely applied to reduce wear and friction between the contact surfaces when they are in relative motion. In the current study, a nonequilibrium molecular dynamics (NEMD) simulation was specifically established to conduct a comprehensive investigation on the dynamic contact between two iron surfaces in a boundary friction system considering the mixed C4-alkane and nanoparticles as lubricant. The main research objective was to explore the effects of fluid and nanoparticles addition on the surface contact and friction force. It was found that nanoparticles acted like ball bearings between the contact surfaces, leading to a change of sliding friction mode to rolling friction mode. Under normal loads, plastic deformation occurred at the top surface because nanoparticles were mainly supporting the normal load. By increasing the number of C4-alkane molecules between two contact surfaces, the contact condition has been changed from partial to full lubrication. In addition, an attractive force from the solid–liquid LJ interaction between C4-alkane and surfaces was observed at the early stage of sliding, due to the large space formed by wall surfaces and nanoparticles. The findings in this paper would be beneficial for understanding the frictional behavior of a simple lubricant with or without nanoparticles addition in a small confinement.

The Influence of Friction Deformation on the Microstructure and Hardening of Beryllium Bronze

The peculiarities of the microstructure and properties of BrBNT1.7 beryllium bronze tape samples were studied: the samples were subjected to dispersion hardening as a result of quenching in a supersaturated solid solution and aging. Friction deformation in a dry friction mode provides additional effective hardening while maintaining increased plasticity (bending-and-unbending test).

Conformal Efficiency Factors of Friction Pairs in Construction Machinery

Formulae for the efficiency factor of moving friction pairs of construction equipment are investigated in terms of their mutual adaptation (conformism) during friction and wear. As a basis, the average coefficients of sliding friction and dimensions of the reference line curves, the half-sums of their products of the worn surfaces microrelief for mating parts are taken. Coefficients of sliding friction and dimensions of reference lines were determined from the partial values of microwear and micromaterial of the normalized system of relative reference lines and convergences. Calculated values of conformal efficiency factors were compared with efficiency factors obtained from the tested dependence, as well as from the wedge operator in the dry friction mode. The research was carried out on the example of model hinges of hydraulic excavator attachments.

The friction and wear behaviors of self-lubricating composites with two types of warp-knitted fabric structures

Replacing the traditional self-lubricating fabric composites with new type of wear-resistant composite reinforced by warp-knitted fabrics PTFE-Nomex and PTFE-Nomex/Nomex (self-lubricating fiber: PTFE, reinforcing fiber: Nomex), in which the hybrid graphite/graphene particle modified phenolic is used as the adhesive resin. The influence of the fabric structure on the friction and wear properties of self-lubricating fabric composites was evaluated by the ball-on-disk and bearing friction tests. And the wear mechanism of the composites was investigated through scanning electron microscopy (SEM) and mechanical tests. The ball-on-disk friction test shows that the friction and wear properties of two kinds of composites with different structures are different with the increase of friction distance. In addition, the self-lubricating warp-knitted composite materials were prepared as self-lubricating joint bearing liners to evaluate the bearing application. It is proposed that the wear resistance of the two kinds of warp-knitted composites is poor, and the single layer is slightly better. It is related to the friction mode, mechanical and bonding properties of the bearing liners.