Conditions Of Boundary Friction Research Articles

On the effectiveness of using carbamide-based salt baths for low-temperature cyanidation of improved carbon and alloy steels

Purpose. A study of cyanidation of improved carbon and alloy steels of grades 30, 30HGT, 30H13 at a temperature of 550–580 °C was carried out in baths based on carbamide and sodium carbonate. Recommendations on the use of these baths for surface hardening of carbon and alloyed improved steels used for the manufacture of machine parts are formulated. Methods. The microstructure of the diffusion layer of steels on transverse sections was studied using a Quanta FEG – 650 electron scanning microscope with an EBCD focused ion beam microanalysis system. Cyanide wear tests were performed under friction conditions analogous to those of die tools. The wear resistance of the carbonitrided samples was investigated on a SMTs-2 friction machine. The tests were performed under both dry friction and boundary friction conditions. Results. The high efficiency of the proposed bath composition at a given temperature has been experimentally shown. As a result of cyanidation, modified layers saturated with solid inclusions (ε-phases) are formed on the surface of steels, characterized by high hardness, low coefficient of friction and high wear resistance. Conclusion. According to the results of the conducted research, it can be concluded that low-temperature cyanidation of improved steels of various grades can be carried out in cyanide-free salt baths. The optimal composition of the cyanide bath is 40% carbamide (NH2)2CO; 40 % soda ash Na2CO3 and 20 % NaCl table salt. The proposed bath does not contain toxic and scarce components, therefore it is environmentally safe and very cheap and can be used with great effect in machine-building, repair and tool industries.

Determining features in the wear resistance characteristics of tribocompounds with a textured hole surface under conditions of boundary friction

The influence of surface texture in the form of pits on the wear resistance of tribocompounds under conditions of limit friction was investigated. At the first stage of research, the mechanism of lubricant behavior between the contacting surfaces and inside the holes was modeled. The limiting condition of the rotation frequency of the sample (n>27) was established, under which a drop of lubricant "leaves" the hole in the upper position of the sample and remains in the space between the sample and the surface of the counterbody, ensuring the regeneration of the boundary lubricating film on the surface of the tribocontact when it is destroyed. When the rotation frequency of the sample is reduced (n<27), the lubricant droplet remains in the hole and does not affect the processes of the boundary lubricant film. At the second stage, experimental studies of tribocombinations with a textured hole surface under conditions of extreme friction were carried out. It was established that the high wear resistance of the textured hole surfaces is provided by the high protective effect of the texture, as well as the high efficiency of the marginal lubricating film. It has been proven that the strengthening of the surface texture by the method of ion-plasma thermocyclic nitriding additionally increases the wear resistance by 1.7 times due to the high protective effect of surface nitrided layers and their high hardness (up to 9500 MPa). This strengthens the effect of inhibiting the occurrence of defects in the surface layers of tribocontact, ensures a high rate of wetting of the places of actual contact of triboconnections, and speeds up the process of regeneration of the boundary lubricating film. Research results can be used to modify the surface layer of heavily loaded parts operating under extreme operating conditions with limited supply of lubricant under various types of friction and wear

Amide/Amino-Based Functional Additives for Lubricants: Structure, Antimicrobial Activity and Wear Resistance.

The lubricating properties of the lubricants were tested under boundary friction conditions; it was found that the surface-active additives had reduced the wear mark and thus the value of the Goz/40 parameter (limiting load of wear). The introduction of a surfactant containing amide compounds into the oils and greases was highly effective in slowing down the oxidation process. Lubricants containing mono-15 ([3-(N,N,N-dimethylbuthylamine)propyl]hexadecanamide chloride) and 15-4-15 (tetramethylene-bis [3-(N,N,N-dimethylamine)propyl]hexadecanamide) additives were characterised by higher oxidation stability compared to the unmodified lubricants. Both of the analysed substances showed bactericidal properties against Staphylococcus aureus and Salmonella enteritica. Tests of antibacterial activity in the lubricants with the addition of mono-15 and 15-4-15 confirmed that these lubricants can be considered bactericidal against Gram-positive and Gram-negative bacteria.

Tribotechnical Characteristics of Nickel-Based Composite Coatings Obtained by Hybrid Technologies

As an object of this study, the coatings were used, which are composed of self-fluxing nickel-based alloys or compositions containing them, formed in a hybrid technological process with two main stages: spraying by the plasma method and subsequent remelting – by the gas-flame method or laser heating. An experimental measurement of their resistance to abrasive wear under conditions of boundary friction with the introduction of lubricants has been carried out for the coatings obtained in this process. At the same time, the influence of the coating composition and the remelting method on the wear value measured by the artificial base method has been investigated. To evaluate the dynamics of structure formation in the surface layer subjected to mechanical loads during the friction, X-ray diffraction analysis, metallographic method, and scanning electron microscopy in the electron diffraction mode have been used. After the laser remelting stage, it is possible to obtain coatings with wear resistance that is twice or more superior to the level for sprayed coatings of the same composition processed by the gas flame method. Wear of the coating surface has been found to occur through the mechanism of fatigue failure of the least hard component of the coating, i. e., the nickel-containing intermetallic phase, with the formation of an island-type film of hard crystallites of the carbide-boron phase weakly bound to the coating base, which ultimately leads to cracking of particles of this phase and their crumbling from the surface. The durability of layers obtained after the laser remelting stage can be increased, according to experimental data, by reducing the grain size of the phases in the coating and its texturing, as well as increasing the concentration of alloying elements in the composition of the metal-containing binder phase of the coating. The use of alloying additives leads to an additional increase in wear resistance by 2–4 times. This is due, depending on the type of additives, with an increase in the amount of the hardening phase while maintaining the plasticity of the matrix (coatings with chromium carbide additives), the degree of alloying of the nickel matrix (by the tungsten carbide and boron carbide additives), as well as the presence of a finely dispersed carbide-boride component, which reduces the processes of deformation and scratching.

Determination of the properties of lubricant additives operating under boundary friction conditions

Sodium silicate and sodium hydroorthophosphate dissolved in glycerin are tested on an ИИ-5018 friction machine during sliding under boundary friction conditions. The dependences of the change in the friction force on normal loads and the coefficient of friction on the sliding speed are obtained. The optimal composition of the lubricant with a complex of additives is determined. Keywords: friction machine, laboratory tests, lubricant, coefficient of friction, additive. vkohan@yandex.ru, mia@rgups.ru, glazunovdm@yandex.ru

Variational and asymptotic analysis of a static electro-elastic problem with Coulomb’s law

The electro-elastic problem in a three-dimensional thin domain Ωɛ is considered. In modeling the contact the Coulomb free boundary friction condition is used. First, we show the variational formulation of the problem and give the existence and the uniqueness of the solution. Then, we study the asymptotic analysis when then the small parameter ɛ tends to zero. A limit problem, the uniqueness result of the limit displacement and electric potential are obtained.

The Influence of Biocarbon Powder Produced from a Pine Nutshell on Tribotechnical Properties of Copper Based Friction Material Running Under Conditions of Boundary Friction

The Influence of Biocarbon Powder Produced from a Pine Nutshell on Tribotechnical Properties of Copper Based Friction Material Running Under Conditions of Boundary Friction

Mechanical Properties of Arc Coatings Sprayed with Cored Wires with Different Charge Compositions

The mechanical properties (hardness, cohesion, and residual stresses) of arc coatings designed for operation under conditions of boundary friction and corrosive-abrasive wear are analyzed. The coatings were formed by arc spraying cored wires (CW) with different charge compositions (the content of carbon, aluminum, and boron in CW charge varied). It is shown that the hardness of the coatings increases with an increase in the carbon content in them up to 1 wt. %, and then decreased due to an increase in the content of residual austenite in their structure. The level of residual stresses of the first kind in such coatings increased by four times with an increase in the carbon content to 2 wt. %. The hardness of the coatings and the level of residual tensile stresses in them also increase with a decrease in the aluminum content in them. In this case, the cohesive strength of the coatings increased due to the implementation of aluminothermic reactions in the droplets of the CW melt during their flight and crystallization on the sprayed surfaces. However, then, with an increase in the aluminum content in the coatings of more than 2 wt. %, their cohesive strength decreased. The level of residual tensile stresses in coatings with a high content of retained austenite decreased after heat treatment (tempering) of the specimens. Sometimes, after tempering, these stresses even transformed into residual compressive stresses (in particular, under using CW C1.4Cr14Ni2). At the same time, the tempering of specimens with a predominance of ferrite in the coating structure increased the level of residual tensile stresses in them, which is due to the precipitation of finely dispersed carbides or borides. It has been shown that the addition of boron-containing components (ferrochromium-boron, chromium-boron) to the composition of the CW charge leads to a significant increase in the hardness of the coatings. Thus, an increase in the boron content in coatings from 0 to 4 wt. % leads to an increase in their hardness from 320 HV to 1060 HV. However, this is accompanied by an increase in tensile residual stresses in the coatings and a decrease in their cohesive strength.

Improving the lubrication effectiveness of turnout reducers

The main types of damage to the gear teeth of the turnout reducers are considered, as well as the disadvantages and advantages of the lubricants used in them. Based on the results of laboratory tests, the coefficient of friction of lubricants under boundary friction conditions was determined and an optimal composition adapted to the operating conditions of turnout reducers is proposed. Keywords:lubricant, automation, teleautomatics, railway transport, turnout, reducer, tooth gearing. glazunovdm@yandex.ru

Study of the Influence of Temperature on Contact Pressures and Resource of Metal-Polymer Plain Bearings with Filled Polyamide PA6 Bushing

It is known that the elastic characteristics of polyamides change with increasing temperature; in particular, the Young’s modulus decreases significantly. This fact is practically not taken into account in design calculations of metal-polymer plain (MP) bearings, operating under conditions of the boundary and dry friction. The purpose of the study was the analysis of the effect of temperature on the change of the Young’s modulus and, accordingly, the contact strength and triboresource according to the developed method of calculating MP bearings. MP bearings with a bushing made of polyamide PA6 reinforced with glass or carbon-dispersed fibers were investigated. Quantitative and qualitative regularities of change of the maximum contact pressures and resource of the bearings at temperature increase under conditions of boundary and dry friction are established. The pressures in the bearing bushing made of PA6 + 30GF will be lower than for the bushing made of PA6 + 30CF. The resource of the bushing made of PA6 + 30CF will be significantly greater than for PA6 + 30GF. For thermoplastic polymers, the increase in temperature will have a useful practical effect due to the decrease in the rigidity of the polymer composites of the bearing bushing.

МИТАЦИОННОЕ МОДЕЛИРОВАНИЕ ТЕМПЕРАТУРНОГО РЕЖИМА ПОДШИПНИКОВЫХ УЗЛОВ, ПРИСПОСОБЛЕННЫХ К ТЕРМОНАГРУЖЕННОСТИ

Modern transport and technological machines operate under the seasonality conditions of agricultural operations and significant energy loads. Universal joints of unequal velocity, being part of mechanical power transmissions, work under adverse conditions and limit equipment reliability. It was established that the temperature mode of the bearing assemblies of the universal joints affects the wear rate of their working surfaces. When the temperature in the friction zone increases due to mechanical operation and heating from the environment and adjacent heat sources, boundary friction and temperature conditions exceeding the level of material self-tempering occur. As a result of research, the universal joints (RU199508) were designed to ensure the intensification of cooling its bearing units directly in the maximum heat generation zone during the universal joint operation. Numerical simulation was performed according to the thechinque of calculating radiators for a universal joint with a cross K 040 GOST 13758-89 on needle bearings No. 804704 K5. The results showed the size of the outer surface area that is sufficient for its cooling. When the maximum values of the fracture angle of the universal joint, torque, angular velocity, and efficiency of 0.99 are combined, its bearing units are effectively cooled. It has been found that if the efficiency of the bearing assemblies is less than 0.952, their surface is no longer sufficient to provide efficient cooling and maintain thermal balance conditions in the friction zone. The use of the radiator can increase the heat transfer area by 19%. The radiator ribs fixed on the side surfaces of the yoke eyes with a thickness of 2 mm and a distance of 4 mm and a total area of 166.1 cm2 will ensure the operability of the bearing units. It will remain satisfactory even if their efficiency decreases to 0.943 as a result of mechanical wear.

Influence of Contamination of Gear Oils in Relation to Time of Operation on Their Lubricity

The quality and reliability of consumables, including gear oils, results in the failure-free operation of the transmission components in heavy trucks. It is known that oil viscosity is essential for all lubricated tribopairs for wear and friction reduction in all vehicles with a gearbox. Viscosity may be influenced by the contamination that wear products can impart on the oil. Oil contamination can also affect lubrication efficiency in the boundary friction conditions in gearboxes where slips occur (including bevel and hypoid gearboxes). The present research focused on this issue. An obvious hypothesis was adopted, where it was theorized that exploiting the contaminants that are present in gear oil may affect how the lubricating properties of gear oils deteriorate. Laboratory tests were performed on contaminants that are commonly found in gear oil using the Parker Laser CM20. The study was designed to identify a number of different solid particles that are present in oil. At the second stage, friction tests were conducted for a friction couple “ball-on-disc” in an oil bath at 90 °C on a CSM microtribometer. The quantitative contamination of the gear oils that contained solid particles and the curves representing the friction coefficients of fresh oils with a history of exploitation were compared. The test results were statistically analysed. Exploitation was shown to have a significant impact on the contamination of gear oils. It was revealed that the contamination and the mileage had no effect on the tested oils.

ИСПОЛЬЗОВАНИЕ МОНОМОЛЕКУЛЯРНОЙ ЗАЩИТНОЙ ПЛЕНКИ НА ПОВЕРХНОСТИ УЗЛОВ ТРЕНИЯ ДЛЯ ПОВЫШЕНИЯ НАДЕЖНОСТИ СЕЛЬСКОХОЗЯЙСТВЕННОЙ ТЕХНИКИ

One of the factors limiting the reliability of machines and mechanisms is the wear of the contacting surfaces of friction units, which affects their service life. To prevent it, the friction units are treated with lubricants. Surfactants containing fluorinated hydrocarbon radicals are of the greatest interest as an additive to lubricants. (Research purpose) The research purpose is in studying the effect of a protective monomolecular film of fluorinated surfactants on the processes of friction and wear occurring on the surfaces of friction units under conditions of boundary and hydrodynamic friction. (Materials and methods) The structure of the metal was studied before and after the application of a monomolecular protective film, the contact potential difference and the hardness of the samples were determined. The influence of surface energy on the oil absorption of materials was evaluated. (Results and discussion) It was revealed using the contact potential difference method, the process of applying a monomolecular protective film ends after 1.5-3.0 minutes and further exposure in the composition does not lead to a change in the contact potential difference. The values of the adhesion action and wetting energy for surfaces with this coating indicate that the surface energy does not depend on the material, but is determined by the coating of the monomolecular protective film of the test sample. The compositions of 0.05 percent of solutions of fluorinated surfactants form a more porous coating compared to the concentration of 0.5 percent. (Conclusions) Fluorinated surfactants have a high tribotechnical efficiency as antifriction and anti-wear nanomaterials. Their use makes it possible to protect the contact surfaces with a film 3-6 nm thick both under boundary and under hydrodynamic friction. The specified protective film performs the function of a "compensator" for various lubrication modes.

МЕХАНИЧЕСКИЕ И ТРИБОЛОГИЧЕСКИЕ СВОЙСТВА ЗАЩИТНО-ВОССТАНОВИТЕЛЬНЫХ ПОКРЫТИЙ РАБОЧЕЙ ФАСКИ КЛАПАНОВ ДВИГАТЕЛЕЙ ВНУТРЕННЕГО СГОРАНИЯ

Over the past 7-10 years, there has been a steady increase in the cost of gasoline and gas fuel. This circumstance forces the enterprises operating automotive equipment to switch to the use of gas-powered fuel. (Research purpose) The research purpose is in creating a protective and recovering coating that can withstand the wear of the working chamfer of the valve caused by high operating temperatures, dry friction in the valve–seat interface, as well as high flow rates of exhaust gas. (Materials and methods) The article presents an analysis of a priori information, which resulted in the following powder compositions: Ni- ZrO2-SiC; Ni–B4C–BN–ZrO2; Ni–B4C–ZrO2–MgO; Ni-B4C. The samples were subjected to tests on the SMT 2070 friction machine under boundary friction conditions to determine the tribological parameters of coatings made of these materials. The parameters of the friction moment and the coefficient of friction were taken during the tests, depending on the applied load on the tribo-coupling. (Results and discussion) At the first stage of the research, the microhardness of the coatings was analyzed. Tribological studies were performed depending on the microhardness of the coatings. Along with the economic effect, there are negative factors that affect the performance of the valve-seat coupling: increased temperatures up to 750-800 degrees Celsius, the transition to dry friction, high exhaust rates of combustion products (over 1000 meters per second). The best value of the coefficient of friction obtained during the tests belongs to the composition Ni–ZrO2–SiC, which takes values below 0.1. (Conclusions) The use of standard and well-known methods of protecting the working chamfer of the valve in this case is ineffective, since it does not provide the required operating conditions. The article recommens the use of Ni-ZrO2-SiC as the material of the protective and restorative coating of the working chamfer of the valve.

Shock Characteristics of the Opposed Disc Springs (ODS) Shock Isolator with Pretightening under Boundary Friction Condition

In this study, to solve the problems of shock environment and shock isolation, about which there is still a lack of reasonable description, an isokinetic shock distinguishing method (ISDM), which can quantitatively distinguish between shock and forced vibration state, is presented. And the shock isolation performance of an opposed disc springs (ODS) shock isolator with pretightening under boundary friction condition is investigated. The static and dynamic stiffness properties of the ODS shock isolator are discussed. Relying on ISDM, a shock dynamic model of the ODS shock isolator with pretightening under boundary friction condition is established. The average method is adopted to solve the model theoretically. The shock acceleration ratio (SAR), shock displacement ratio (SDR), and relative displacement ratio (RDR) of the model are calculated using the numerical method and verified by experiments. Both numerical and experimental results show that ISDM is effective. And the effects on isolation efficiency of the number of disc springs, additional supporting force, pretightening force, load, and the shock velocity constant of the ODS shock isolator are discussed, which provide guidelines for its further practical application.

Regularities of the influence of submicron ceramic powders TiO2, AlN, Cr2O3 on the tribological properties of a friction material

Friction units for automotive and special vehicles are designed to operate under boundary friction conditions. Modern vehicles contain friction assemblies that use friction materials. Currently, friction materials are actively used: based on thermosetting resins; pulp and paper-based materials; sintered powder materials; materials of carbon or carbon composition; materials with a ceramic matrix. The development of a unified understanding of the effect of the size and chemical nature of ceramic additives on the processes occurring in a friction material during friction is very important and can be obtained both on the basis of experimental and theoretical studies. The paper presents the results of a study of the effect of submicron TiO2, Cr2O3, AlN powders with a size of 0.2-0.5 microns on the tribotechnical properties of a frictional material based on copper intended for operation under boundary friction conditions. It was found that when using the addition of Cr2O3 powder, the greatest increase in the value of the friction coefficient is noted - from 0.042 to 0.082, a slightly smaller increase in the friction coefficient is shown by the use of AlN and TiO2 defects - 0.042-0.074 and 0.042-0.060, respectively. The least wear of the friction material was obtained when using 3.0 vol. % aluminum nitride additive - 2.1 microns / km. Increasing the addition of any of the submicron powders by more than 7 vol. % leads to a significant decrease in wear resistance. This is due to the formation on the surface of the friction material of a modified layer containing ceramic particles and the metallic phase of the friction material. For the friction material, an unstable value of the friction coefficient and increased wear were recorded

Tribotechnical Properties of a Copper-Based Powder Friction Material with the Addition of Iron-Chromium Alloy Powder

The results of studying the effect of the additive powder of the iron-chromium alloy PH-30 on the tribological properties of a composite friction material based on copper operating in the conditions of boundary friction are presented. It is shown that the introduction of 10 to 40 vol % PH-30 powder helps to increase the coefficient of friction from 0.042 to 0.075. It is found that at 10 vol % PH-30 the material’s wear is minimal and is 4 μm/km, while at 40 vol %, catastrophic wear is observed, exceeding 20 μm/km. The limit value of the material’s wear of 9 μm/km is noted with the powder content of PH-30 of less than 28 vol %. The increase in the tribotechnical properties of copper-based friction material with the addition of PH-30 powder is explained by the action of not only the PH-30 powder itself but also Fe4Cu3, FeSn intermetallide, and solid ceramic particles of chromium carbide Cr23C6 formed on the surface after sintering.

Analysis of the wear resistance of a hard anti-friction coating, applied to a plain bearing, under the conditions of boundary friction

Improving the reliability and efficiency of using components and assemblies in severe climatic conditions is a difficult task, the solution of which requires a special approach. The paper justifies the use of modern anti-friction materials, analyzes and discusses the possibility of using plain bearing assemblies of the truck walking beam suspension in their composition. Anti-friction properties of various types of coatings were analyzed. A theoretical calculation of the wear resistance in the plain bearings of a truck walking beam suspension made of BrOF 10-1 bronze was performed. The paper presents the experimental results of comparative measurements of the wear resistance in two types of anti-friction materials (BrOF 10-1 and a coating based on molybdenum disulfide). We also considered the nature and features of the wear of anti-friction coatings and give recommendations for their use.

Triboacoustic Characteristics of Copper-Based Powder Frictional Composites for Operation in Dry and Boundary Friction Conditions

The paper presents results of the tribotechnical and acoustic characteristics of copper-based frictional composite materials depending on the composite structure and content of metallic (tin, iron) and carbon (coke, graphite) additives in the composition. Changes in the studied characteristics are most pronounced under dry friction conditions. The introduction of the additives leads to reduced friction components of noise to 56 dB. In the boundary friction mode, the greatest effect of introduced target additives on the acoustic characteristics does not exceed 11 dB relative to the material without additives. For a composite based on 12% tin bronze, an increase in the graphite content from 10 to 30 vol % results in a 5 dB noise reduction.

Tribological properties of a plain bearing with a sleeve made of a nanostructured zirconia crystal

The article deals with the issues of the working capacity of a plain bearing with a sleeve made of nanostructured partially stabilized zirconium dioxide. The tribological properties of the shaft-sleeve interface under boundary friction conditions are investigated. An X-ray phase analysis of samples of zirconium dioxide crystals with various additives of yttrium oxide stabilizer has been performed. The optimal composition for the manufacture of bearing bushings has been selected. A procedure for tribological testing of a sliding bearing has been developed. Special attention is paid to the influence of the clearance between the shaft and the bushing on the tribotechnical characteristics of the interface. The calculation of the wear rate of the sliding bearing is carried out taking into account the clearance. A method for calculating the service life of a bearing is proposed. The prospect of using nanostructured crystals of zirconium dioxide for the manufacture of sleeve bearing bushings for precision mechanisms and devices has been experimentally confirmed