Friction Pair Research Articles

Обоснование оптимальных наработок основных насосов карьерного гидравлического экскаватора

As the pump operates and wears out, the gap in the friction pairs increases and the volumetric efficiency decreases, the pump flow gets reduced, which leads to increasing duration of working and auxiliary operations, the operating cycle of the excavator, a decrease in its productivity and excessive fuel consumption. Infrequent pump replacement can lead to a significant increase in fuel consumption and reduced excavator performance. If the pump is replaced prematurely, its service life will not be used to the full extent. In order to develop a method for establishing optimal operating hours that allow minimizing fuel consumption and the cost of replacing a pump, taking into account operating conditions, a mathematical model of the pump operation is proposed, which makes it possible to obtain an expression for determining the differentiated optimal value of operating time between replacements. A calculation method and a software algorithm have been developed in the MatLab Simulink software suite to calculate the rate of decrease in the volumetric efficiency, as well as to establish the influence of volumetric efficiency on the fuel consumption and performance of a hydraulic excavator to be utilized in the model using the example of the HPV375 pump of the Komatsu PC2000-8 excavator, Based on the proposed mathematical model of the main pumps operation, a method has been developed for calculating the differentiated operating time between replacements of the main pumps of a mining hydraulic excavator, taking into account the rate of decrease in volumetric efficiency, replacement costs and damage due to changes in productivity and excessive fuel consumption. The dependence of the rate of changes in the volumetric efficiency of the pump is presented for the excavation, viscosity, contamination and temperature of the working fluid parameters. A coefficient of “reserve of partial engine power transferred to the pump” is proposed, determined by the ratio of the difference between the average maximum and initial partial power to the value of the initial partial power, which allows estimation of the operating time of the main pumps without affecting productivity of the excavator.

Friction, wear, and anti-scuffing behaviors of zinc phosphate film on cylinder liners

Zinc phosphate chemical conversion coating possesses excellent tribological properties, which has attracted increasing attention. In this work, the friction, wear and anti-scuffing performance of zinc phosphate film applied on the cylinder liners were studied using a self-designed friction and wear experimental apparatus, which can sufficiently simulate the working conditions of the piston ring and cylinder in a real engine. The experimental results indicate that comparing with the uncoated cylinder liner, the friction force and total wear losses of friction pairs for the zinc phosphate coating are reduced by 8% and 27.5%, respectively, which is attributed to the formation of the protective film containing metal oxides and iron phosphate. In the scuffing test, uncoated cylinder liner exhibits better anti-scuffing performance because of the spalling of the cast iron graphite. On the contrary, the zinc phosphate coating particles remaining on the worn surface after oil-cut off are peeled off and acted as the abrasive at the contact interface, which accelerates the plastic deformation of friction pairs and the cast iron graphite is covered by the plastic flow of the material.

Investigation of friction and vibration performance of lithium complex grease containing candle soot on aviation electrical machine

The prolonged operation of the motor in the all-electric aircraft can cause the fragmentation and shortening of grease thickener fibers, ultimately resulting in the lubricating grease becoming ineffective. In order to avoid grease failure causing motor winding burnout, this paper uses a four-ball friction testing machine to test the tribological properties of six composite greases containing candle soot with different concentrations, and analyzes the changes in friction coefficient and wear diameter. In addition, by building a test platform for motor vibration and noise, this paper studies the influence of lithium complex grease on vibration and noise characteristics of aviation electrical machine at different propeller speeds. The results show that the addition of 0.04 wt% candle soot lithium grease has the best tribological properties and vibration inhibition properties, because the candle soot in the oil film changes the sliding friction into rolling friction in the contact area of some friction pair. The temperature rise test of aviation electrical machine shows that the lithium complex grease plays an active role in the heat dissipation performance of the high-speed rotating motor.

ВЫБОР ПАРАМЕТРОВ ТЕХНИЧЕСКОГО СОСТОЯНИЯ ЭЛЕМЕНТОВ ПОГЛОЩАЮЩЕГО АППАРАТА, ОПРЕДЕЛЯЮЩИХ ЕГО БЕЗОТКАЗНОСТЬ

The problems to plan and ensure a given level of reliability of mechanical systems at all stages of their design and operation occupy an important place in the problem of ensuring the quality of machine-building products. With a significant number of scientific methods and approaches to solving theoretical and applied issues of reliability theory, one of the key directions is to determine the reliability indicators of technical systems and their elements, in particular a wide range of products including sliding friction pairs with periodic impacts. The study of failure origins, from the point of view of physical-mechanical processes occurring in surface layers of elements, under the influence of external factors, allows selecting parameters characterizing the functional state of the pair, and, as a result, its reliability. For example, for sliding friction pairs with periodic impacts, such a parameter is the geometric dimensions of the conjugate elements. The decrease in the geometric dimensions of conjugate elements, due to wear, characterizes the rate of change of the initial parameter values to the maximum permissible ones determining the failure, and can be approximated by linear, power, exponential and other dependencies obtained from actual measurements. According to the obtained functional dependencies of parameter changes over operating time, it makes possible to determine the norm for the parameter regulating their pre-failure state, beyond which failure prediction is possible with varying probability, and, as a result, the reliability of the system as a whole. The use of this method to reliability forecasting through the determination of the pre-failure state of the system can be projected onto technical objects, which performance indicators are geometric parameters that ensure the performance, first of all, of the functions of the elements themselves and the entire technical system, and worn out during operation.

Thermal fatigue life prediction of brake disks based on coupled thermal simulation

The thermal-mechanical performance of friction pairs of the foundation brake gear is an important guarantee for the safe operation of high-speed trains. The thermal stress of brake disks under high temperature is the primary cause of thermal fatigue damage. In this article, the brake bench tests were carried out under braking speed of 350km/h and a thermo-mechanical-wear coupled model was established to simulate tests. By analyzing the results of bench test and finite element simulation, it shows the top temperature of brake disk was over 600°Cand the friction surfaces of brake friction pair show obvious wear. Combining the FE simulation and test results of the thermal fatigue sample, the thermal fatigue characteristics of brake disk material were studied. Based on the residual stress results, the propagation life of brake disk thermal fatigue crack was estimated. It shows that when the crack length increases to 10mm, the crack propagation life of brake disk is halved, and continues to decrease as the crack grows.

Research on Prediction Methods for Eccentric Wear of the Slipper Pair in Axial Piston Pumps and Lubrication Performance Analysis

Abstract The axial piston pump (APP) is the core power component of hydraulic systems. Its friction pair wear can cause the degradation of piston pump performance until the function is completely lost or the service life is terminated. The slipper pair, prone to wear failure, is selected as the research object in this paper. The prediction method for the eccentric wear of the slipper pair is established, and the gradual change rules of the performance with wear accumulation are explored. The micro-surface rough peak contact and the stress state of the slipper pair are analyzed, and the mixed lubrication model of the slipper pair is established based on the elastohydrodynamic lubrication (EHL) model of the slipper pair. Grid discretization of a sealing belt of the slipper pair is carried out based on two-body abrasive wear and Archard adhesive wear models to improve the prediction method for eccentric wear of the slipper pair. The effectiveness of the proposed method is verified by a surface morphology analysis of the worn slipper. The results showed that the wear depth and wear width of the outer edge of the slipper bottom surface are positively correlated with the oil discharge pressure and the inclination angle of the swashplate, and negatively correlated with the rotational speed and the dynamic oil viscosity. The outer edge of the slipper is wedged after eccentric wear, and the hydrodynamic effect of the lubricating oil film of the slipper pair is enhanced. Hence, proper wear can improve the lubrication performance of the slipper pair.

STRUCTURE AND PROPERTIES OF SELF-LUBRICATING COPPER-NICKEL-GRAPHITE COATING FABRICATED USING COLD SPRAY

Application of self-lubricating Cu-matrix coatings is an attractive way to provide high electrical conductivity and wear performance in contact friction pairs in various areas of modern engineering. In the present work, the structure and properties of self-lubricating copper-nickel-graphite coating deposited on copper substrate using high-pressure cold spray were studied for the first time. The coating was fabricated by spraying dendritic copper and flaked nickel-coated graphite powders mixed in a ratio 70/30 wt.%, which ensured the formation of a lamellar structure. The obtained coating exhibited an attractive combination of hardness (108.8 HV1), coefficient of friction (0.34) and electrical conductivity (43.8 % IACS), which open prospects for its electrical applications.

Temperature Field Characteristics of Limited Slip Clutch under Various Condition Parameters

The temperature field of limited slip clutch (LSC) seriously interferes with torque transmission. In this paper, the attribute of dynamic partition of slip heat flux is considered. A calculation model of temperature field is also established by combining the proposed new method of fluid-solid equivalent convective heat transfer. The simulation and experiment of different relative speed, lubricant flow, and temperature are carried out. Furthermore, the comprehensive evaluation index of average temperature growth ratio and maximum radial temperature difference is proposed. The results show that the deviations of temperature rising rate and average temperature are not more than 0.2 °C/s and 6 °C, respectively. Heat flux partition value of separator plate increases approximately proportionally with relative speed. Changing relative speed from 40 r/min to 80 r/min, average temperature growth rate and maximum radial temperature difference of separator plate increase by 0.35 °C/s and 2.08 °C, respectively. On the contrary, increasing lubricant flow or reducing lubricant temperature weakens actual heat flux input of clutch. From 3 L/min to 10.5 L/min about lubricant flow, the average temperature growth rate and maximum radial temperature difference caused by higher relative speed are reduced by 0.32 and 2.71 °C, respectively. However, when lubricant temperature is adjusted from 65 °C to 30 °C, average temperature growth rate is reduced by 0.51 and the variation of maximum radial temperature difference does not exceed 0.32 °C. The research can accurately simulate actual energy flow at friction pair interface and assist in exploring the influence of condition parameters on temperature field.

Study on fretting friction properties based on GCr15 alloy and liquid epoxy resin protective coatings on GCr15 alloy

GCr15 alloy steel is a representative alloy steel of high carbon chromium bearing steel, with good comprehensive performance. However, the fretting wear and fatigue at the interface of the GCr15 friction pair greatly reduce its service life. In this study, the friction pair of GCr15 alloy was prepared by the surface treatment of epoxy resin coating. The tangential fretting wear experiments were conducted on the samples with the point contact mode in an SRV-IV multifunctional tester to investigate the evolution law of coefficient of fretting wear, dissipation energy and damage varying with the normal load and displacement amplitude. The results showed that the coefficients of the friction pairs treated with epoxy resin composite materials are lower than those of GCr15-GCr15 friction pairs under the same normal load and displacement amplitude, and the friction coefficients of both types of friction pairs gradually decreased with the increase of normal load and the decrease of displacement amplitude. At the same time, epoxy resin coating treatment reduced the dissipation energy of fretting wear. From the perspective of damage protection, GCr15-GCr15 exhibits severe scratch damage, micropores, and microcracks after friction experiments, while the epoxy resin coating mainly showed furrow. In addition, the decrease in hardness of polymer composite coating increased the wear rate of the samples to a certain extent.

Core-rim structured MXene@SiO2 composites as oil-based additives for enhanced tribological properties

Herein, we have prepared SiO2 particles uploaded MXene nanosheets via in-situ hydrolysis of tetraetholothosilicate. Due to the large number of groups at the edges of MXene, SiO2 grows at the edges first, forming MXene@SiO2 composites with a unique core-rim structure. The tribological properties of MXene@SiO2 as lubricating additive in 500 SN are evaluated by SRV-5. The results show that MXene@SiO2 can reduce the friction coefficient of 500 SN from 0.572 to 0.108, the wear volume is reduced by 73.7%, and the load capacity is increased to 800 N. The superior lubricity of MXene@SiO2 is attributed to the synergistic effect of MXene and SiO2. The rolling friction caused by SiO2 not only improves the bearing capacity but also increases the interlayer distance of MXene, avoiding accumulation and making it more prone to interlayer slip. MXene@SiO2 is adsorbed on the friction interface to form a physical adsorption film and isolate the friction pair. In addition, the high temperature and high load induce the tribochemical reaction and form a chemical protection film during in the friction process. Ultimately, the presence of these protective films results in MXene@SiO2 having good lubricating properties.

Omnidirectional simulation analysis of thermo-mechanical coupling mechanism in inertia friction welding of Ni-based superalloy

The coupling between heat and pressure is the kernel of inertia friction welding (IFW) and is still not fully understood. A novel 3D fully coupled finite element model based on a plastic friction pair was developed to simulate the IFW process of a Ni-based superalloy and reveal the omnidirectional thermo-mechanical coupling mechanism of the friction interface. The numerical model successfully simulated the deceleration, deformation processes, and peak torsional moments in IFW and captured the evolution of temperature, contact pressure, and stress. The simulated results were validated through measured thermal history, optical macrography, and axial shortening. The results indicated that interfacial friction heat was the primary heat source, and plastic deformation energy only accounted for 4% of the total. The increase in initial rotational speed and friction pressure elevated the peak temperature, reaching a maximum of 1525.5 K at an initial rotational speed of 2000 r/min and friction pressure of 400 MPa. The interface heat generation could form an axial temperature gradient exceeding 320 K/mm. The radial inhomogeneities of heat generation and temperature were manifested in a concentric ring distribution with maximum heat flux and temperature ranging from 2/5 to 2/3 radius. The radial inhomogeneities were caused by increasing linear velocity along the radius and an opposite distribution of contact pressure, which could reach 1.7 times the set pressure at the center. The circumferential inhomogeneity of thermo-mechanical distribution during rotary friction welding was revealed for the first time, benefiting from the 3D model. The deflection and transformation of distribution in contact pressure and Mises stress were indicators of plastic deformation and transition of quasi-steady state welding. The critical Mises stress was 0.5 times the friction pressure in this study. The presented modeling provides a reliable insight into the thermo-mechanical coupling mechanism of IFW and lays a solid foundation for predicting the microstructures and mechanical properties of inertia friction welded joints.

LUBRICATION BEHAVIOR OF THE POE/R452A MIXTUREAT DIFFERENT SLIDING VELOCITIES UNDER STARVED LUBRICATION CONDITIONS

There are no international standards guiding tribological testing in oil-refrigerant mixtures. The conditions fortribological tests, including sliding velocity, are chosen arbitrarily. The article presents an attempt to examinethe influence of the sliding velocity of friction pair elements on the coefficient of friction and lubricatingproperties of compressor polyester oil (POE) and its mixture with the R452A refrigerant (POE/R452A) understarved lubrication conditions. The R452A refrigerant is currently widely used in transportation refrigeration.The authors’ original test procedure with the use of a model block-on-ring type friction pair was applied toevaluate the lubricating properties of the oil-refrigerant mixture. Tests were conducted in three operationalsituations: no lubrication, starved lubrication with POE oil, and starved lubrication with the POE/R452Amixture. In each case, the tests were performed at different sliding velocities and the same sliding distance.A series of tests was also conducted where the load was increased in steps by 20 N to determine the relationshipbetween the coefficient of friction, sliding velocity, and load on the friction pair.The results support the potential use of higher sliding velocities and the reduction in test duration. For starvedlubrication with the POE oil and the POE/R452A mixture, the differences in wear at specific velocities forthe same sliding distance reached up to 30%, and the rankings of lubricating properties at different velocitiesremained unchanged.

STRUCTURE AND PROPERTIES OF THE NITRIDED LAYERWITH SULFIDES

This study contains a short overview of sulfur nitriding methods, i.e. a modified version of nitriding. Thisinformation is accompanied by the results of our own tests of nitrided and sulfur-nitrided coatings with theaddition of MoS2 in the scope of structure assessment by means of a scanning microscope – SEM/EDS andthe results of tribological tests performed under dry friction conditions on the T-05 apparatus for four variantsof thermo-chemical treatment. In tribological tests, the degree of wear was observed by measuring the weightloss of both samples and counter-samples, and the beneficial effect of sulfides on reducing wear was indicated,with the sulfur nitriding variant with MoS2 added being the most advantageous. In this case, the lowest degreeof wear was found for the friction pair with a sulfur-nitrogen coating reinforced with MoS2, which may leadto extending the operating time.

Improving the Abrasion Resistance of Nodular Cast Iron Castings by Remelting Their Surfaces by Laser Beam.

This paper presents the results of research conducted in the field of the technology of surface hardening of castings from unalloyed and low-alloy nodular cast iron using the laser remelting method. The range of studies included macro- and microhardness measurements using Rockwell and Vickers methods as well as metallographic microscopic examinations using a scanning electron microscope. Moreover, abrasive wear resistance tests were performed using the pin-on-disk method in the friction pair of nodular cast iron-SiC abrasive paper and the reciprocating method in the friction pair of nodular cast iron-unalloyed steel. Analysis of the test results shows that the casting surface layer remelting by laser for unalloyed nodular cast iron results in a greater improvement in its resistance to abrasive wear in the metal-mineral system, as compared to low-alloy cast iron. Additionally, carrying out the laser hardening treatment of the surface layer made of the tested grades of nodular cast iron is justified only if the tribological system of the cooperating working parts and allowable dimensional changes during their operation are known.

Ultra-low friction system using special wetting interfaces: Bridging across various wetting regimes

Friction was the main way of energy loss in society, and reducing friction has become a focal point in current research. Inspired by special wetting phenomena, an asymmetric multiphase composite (AMPC) friction system was constructed. Tribological behavior of the friction system was evaluated using hydrogel on anodized aluminum as friction pair and superhydrophobic alumina with micro/nano-composite as substrate. Ultra-low friction coefficients (∼10−3) were measured under both Cassie and Wenzel regimes. Especially in Wenzel state, increased contact stress or extended shear rate promoted the formation of transfer lubricant film, thus enabling the ultra-low friction coefficient. Moreover, the system showed mechanical stability during prolonged water lubrication. This novel lubrication approach may provide valuable scientific solutions for specific tribology applications.

Износостойкость теплостойких сталей ВКС-7 и ВКС-10 после ионно-плазменного азотирования, вакуумной цементации и вакуумной нитроцементации

Tribotechnical characteristics of martensitic grade steels HSM-7 (16Cr2Ni3MoVNbNAl) and HSM-10 (13Cr3Ni3Mo2VNbNAl) were analyzed. Steels underwent ion plasma nitriding, low-pressure carburizing and low-pressure carbonitriding. The concept of a two-stage hardening technology has been implemented: the creation of a thermally stable finely dispersed state of steel at the first stage and the use of such a state for accelerated and qualitative saturation of the surface layer with nitrogen or carbon at the second stage. To create an ultra-finely divided state in the samples of steels under investigation, the method of intensive plastic deformation (IPD) was used. The method is based on the grinding of the microstructure due to large shear deformations. IPD was performed by the method of warm precipitation in a die with a degree of deformation of 80 % at a temperature of 700 ℃. The wear resistance tests of the samples were carried out on a special stand with reciprocating motion in the medium of a plastic lubricant material of mating samples having flat friction surfaces at a pressure of 10 MPa and an average velocity of 0,19 m/s. It is shown that HSM-7 and HSM-10 steels after ion-plasma nitriding and vacuum cementation have high wear resistance (wear intensity I  10-10). After low-pressure carbonitriding, the values of the wear intensity of the friction pair samples are almost the same and amount to 0,3·10-10, which is ~3,0 times less than after low-pressure carburizing. As a result of ion-plasma nitriding and low-pressure carbonitriding, a nanostructured surface layer is formed on steel surfaces contributing to wear resistance increase. The ideas concerning nitrided steel score resistance increase are given.

Research Status of Wear Prediction of Spherical Friction Pair

Spherical friction pairs are widely used in mechanical equipment, and predicting the wear of spherical friction pairs can help evaluate and predict bearing life. At present, when using the finite element analysis method to calculate the wear of spherical friction pairs, it is still necessary to simulate under idealized conditions, and the limitations of calculation amount and time need to be considered. The accuracy of the prediction method is measured by experimental means to measure the wear amount, which can be characterized by measuring the mass, volume, or wear thickness of the material under grinding. Based on the wear test methods used and the characteristics of the tested materials, suitable wear characterization parameters and measurement methods can be selected. This article also analyzes the influence of friction pair materials and service conditions on the wear of spherical friction pairs. Finally, the article looks forward to the development trend of predicting the wear of spherical friction pairs.

Research on tribological performance of textured thrust bearing using gray relational degree and improved multi-objective water circulation algorithm

To enhance the loading capacity of the oil film, reduce the lubricating oil temperature, and minimize the deformation of the friction pairs, three types of concave textures were proposed. The tribological properties of the thrust bearing underwent multi-objective optimization analysis using the two different methods. By comparing the two methods, it was found that the improved algorithm (MOWCA) demonstrated better optimization performance. Under this algorithm, when the texture shape was triangular, the number of textures was 18n, the size was approximately 0.135 mm, and the spacing between textures was approximately 4.6 mm, the loading capacity of the oil film increased by approximately 26.8%, and the temperature decreased by approximately 0.46%.

Structural and Tribological Analysis of Brake Disc–Pad Pair Material for Cars

The study of the tribological behavior of the braking system in auto vehicles requires knowing the characteristics of the material in contact and, in the work process, the friction pair brake disc pads. Material structural analysis is necessary because the wear process depends both on the friction-pair chemical composition (brake disc pads) and on the work process parameters (pressing force, rotational speed, traffic conditions, etc.). The material of the brake discs is generally the same, gray cast iron, and the brake pads can be semimetallic (particles of steel, copper, brass, and graphite, all united with a special resin), organic materials (particles of rubber, glass, and Kevlar, all joined with the help of a resin), composite materials that contain different constituents, and ceramic materials (rarely have small copper particles). Therefore, the purpose of this paper is to analyze the crystalline structure, tribological behavior (at friction and wear), and the mechanical properties of the materials of the brake disc–pad friction pair specific to the field through study and analysis.

Preparation of Hydrophilic Hyper-Cross-Linked Polystyrene Nanospheres with Antibacterial for Improved Water Lubrication Performance.

The present study utilizes styrene as a raw material to prepare hyper-cross-linked polystyrene nanospheres (HPSs) through the Friedel-Crafts reaction, establishing stable covalent bond structures within the polymer chains. The hydrophilic polystyrene nanospheres─TMA@SHPSs were successfully synthesized via sulfonation and ion exchange reactions, demonstrating exceptional properties in reducing friction and wear. Compared with pure water, the addition of 4.0 wt % TMA@SHPSs results in a 62.2% reduction in the friction coefficient, accompanied by a significant decrease to 1.17 × 105 μm3 in wear volume. The results demonstrate that TMA@SHPSs, as water-based lubrication additives, generate composite protective films (tribo-chemical protective films and physical protective films) during the friction process, which effectively prevents direct contact between the friction pairs and achieves remarkable antifriction and antiwear effects. The results of the antimicrobial activity test indicate that TMA@SHPSs demonstrate exceptional antibacterial efficacy due to the bacteriostatic effect induced by hydration and the bactericidal properties of quaternary ammonium cations.