Lubricant Supply Research Articles

Molecular Dynamics Simulations of Lubricant Supply in Porous Polyimide Bearing Retainers

Space bearing retainers are widely made of a porous, oil-impregnated material due to the unmaintainability of spacecraft. Porous polyimide (PI) material with a certain micropore structure can be used as a lubricant storage and migration channel to realize the lubricant circulation supply in the bearing system. In this work, molecular dynamics simulations are adopted to model the lubricant outflow process from the pore of the PI material. Coarse-grained models are constructed to investigate the lubricant migration behaviors with different rotation speeds, rotation radii, and pore sizes. The results show that a lubricant within the pore fails to outflow due to the capillary effect in a static state. However, for the rotating pores, if the centrifugal forces resulting from rotation exceed the capillary forces, the lubricants will begin to flow out. Furthermore, the lubricant in the large pore is easier to outflow due to the smaller capillary force, which is the main mechanism of lubricant outflow from the pores.

Improved Operating Behavior of Self-Lubricating Rolling-Sliding Contacts under High Load with Oil-Impregnated Porous Sinter Material

Resource and energy efficiency are of high importance in gearbox applications. To reduce friction and wear, an external lubricant supply like dip or injection lubrication is used to lubricate tribosystems in machine elements. This leads to the need for large lubricant volumes and elaborate sealing requirements. One potential method of minimizing the amount of lubricant and simplifying sealing in gearboxes is the self-lubrication of tribosystems using oil-impregnation of porous materials. Although well established in low-loaded journal bearings, self-lubrication of rolling-sliding contacts in gears is poorly understood. This study presents the self-lubrication method using oil-impregnated porous sinter material variants. For this, the tribosystem of gear contacts is transferred to model contacts, which are analyzed for friction and temperature behavior using a twin-disk tribometer. High-resolution surface images are used to record the surface changes. The test results show a significant increase in self-lubrication functionality of tribosystems by oil-impregnated porous sinter material and a tribo-performance comparable to injection-lubricated tribosystems of a sinter material with additionally solid lubricant added to the sinter material powder before sintering. Furthermore, the analyses highlight a significant influence of the surface finish, and in particular the surface porosity, on the overall tribosystem behavior through significantly improved friction and wear behavior transferable to gear applications.

Self-replenishing lubrication mechanism of nano-silver-reinforced AISI 4140 steel composites under dry sliding for mechanical applications

Wear is one of the most important factors limiting mechanical components' lifespan and durability. In this study, a novel, AISI 4140-Ag steel-based, self-lubricating nanocomposite was manufactured by the spark plasma sintering (SPS) technique. The high-level aim of this investigation is to obtain a deeper understanding of how silver (Ag) at the nanoscale can enhance the self-lubricating layer's replenishment, which aids in maintaining a steady supply of solid lubricant under dry conditions. Tribological experiments were conducted under various loads (30–150 N) at 5 Hz frequency and 300 °C temperature using a Rtec Universal Tribometer (ball-on-disc setup). After that, advanced surface characterization techniques were utilized to illustrate predominant wear modes, lubrication mechanisms, and the chemical identity of the self-lubrication layer. Noticeably, the AISI 4140-Ag nanocomposite reduced the friction coefficient and wear rate by 36.16–51.14 % and 93.40–97.36 %, respectively, compared to the AISI 4140 composite. The excellent self-lubricating performance is mainly attributed to the replenishment of a self-lubricating layer on the substrate material and a transfer layer on the counterbody, composed of AgO and Fe2O3. The results of our study hold considerable promise for the advancement of self-lubricating composites and the enhancement of their durability in mechanical applications.

IMPACT OF LOADS ON LOCOMOTIVE MOTOR AXLE BEARINGS ON THE CONDITIONS OF FORMATION OF OIL FILM ON FRICTION SURFACES

During the active operation of locomotives, a significant portion of failures (up to 20 %) is attributed to the malfunction of motor-axial bearings. This is due to the imperfection of the lubrication system of the motor-axial bearings, the proper functioning of which largely depends on various factors such as climatic conditions, the level of wear of lubricating oil, and lubrication devices, among others. There is a need to improve the existing lubrication systems for motor-axial sliding bearings. One of the methods to address this issue involves examining the factors influencing the lubrication process of the friction surfaces of motor-axial bearings and the conditions of lubricant material supply. The article provides calculations of the loading forces on the motor-axial bearings, their action vectors, and analyzes the impact of these parameters on the ability to form an oil film on the friction surfaces of motor-axial bearings. To determine the magnitude of the load, technical specifications of the locomotive were used, and the relationship between power usage and locomotive speed was analyzed. The study involved an analysis of recent publications regarding the generation of contact pressure force between the contact surfaces of friction pairs, the magnitude of which exceeds permissible limits, considered one of the primary factors leading to bearing failure. Additionally, the existing bearing lubrication system used on the locomotive was analyzed, its shortcomings were identified, and methods for addressing these issues were discussed. The calculations were performed for the 2TE116 locomotive with traction electric motors ED-118B, based on the operational characteristics of the locomotive in the speed range of 0-80 km/h.

Tribological Properties of Aluminium Matrix Syntactic Foams Manufactured with Aluminium Smelter Waste

Aluminium smelter waste (ASW) is a big contributor to landfills, and its recycling has been of great interest. This study investigates the tribological properties of aluminium matrix syntactic foams manufactured using an Al 6082 alloy and ASW. Ball-on-disc tests were conducted under both dry and lubricated conditions. Under dry sliding conditions, the coefficient of friction (COF) had an initial sharp increase, followed by a gradual decrease and finally a steady state as the sliding distance increased. The wear surfaces showed the presence of adhesive, abrasive and oxidative wear, with some presence of delamination. Syntactic foams containing small ASW particles led to a decrease in surface roughness, decrease in the average COF and decrease in specific wear. Heating large ASW particles before manufacturing the syntactic foams enhanced overall wear properties because the particles are hardened due to a compositional change. The T6 treatment of the syntactic foams enhanced the wear properties due to the hardening of the Al matrix. The average COF of the ASW syntactic foams was higher than that of the E-sphere syntactic foam, which was predominantly abrasive wear. The specific wear of the ASW syntactic foams can be higher or lower than the E-sphere syntactic foam, depending on the ASW particle size. Under lubricated sliding test conditions, the wear was reduced significantly, and the type changed from predominantly adhesive to predominantly abrasive. The porous ASW particles acted as lubricant reservoirs and provided a constant supply of lubricant, further improving the lubrication effect.

Minimum Quantity Lubrication (MQL) Supply through Internal Cooling Channels in Drilling Processes

Minimum quantity lubrication (MQL) technologies possess great potential for improving the sustainability of manufacturing processes, which can reduce the absolute quantity of metalworking fluid (MWF) and also enable near-dry chips that are easier to recycle. During drilling in particular, the MWF is transported to the contact zone through internal cooling channels of the drilling tool. The MWF supply and its associated flow behaviour in the transfer from the outlet of the cooling channels to the contact zone have not been sufficiently investigated yet. Great potential is seen in the proper delivery of the MQL into the contact zone. This work aims to visualize and quantify the cooling lubricant supply into the cutting zone using the MQL technique. The visualization of the MQL application is made possible by high-speed shadowgraphic imaging. Detailed image processing is used to evaluate the resulting images. The developed evaluation routine allows for the assessment of the impact of the main process parameters such as the varying pressure of the aerosol generator and the cooling channel diameter. It is found that the oil leaves the cooling channels at the tip of the drill bit in the form of ligaments. An increase in pressure and cooling channel diameter leads to an increase in the frequency of oil ligament separation. Three main flow regimes are identified with different separation frequencies. Low inlet pressures result in intermittently dispersed droplets. The most upper pressure levels lead to an almost continuous dispersion of the oil. At the same time, the air and oil mass flow rates also increase.

Experimental Study of Lubricant Distribution and Lubrication Enhancement Induced by Ball Bearing Cage

Abstract The bearing cage played a pivotal role in affecting the lubricant redistribution and lubrication states. In this study, a cage unit is incorporated into an optical ball-on-disc apparatus for the purpose of a quantitative study of cage-induced lubrication phenomena. It is found that the presence of the lubricant layer on the ball surface, shaped by the cage, affects the inlet lubricant supply of contact between the ball and the glass disc. Thereafter, the oil reservoirs surrounding the contact area and the film thickness were measured. The results showed that the lubricant reservoirs and inlet lubricant supplement were significantly improved with the employment of the cages. In addition, the lubrication state transformed from starved to fully flooded, effectively enhancing the lubrication state. Moreover, the lubricant on the steel ball surface moved from the side bands to the central rolling track, indicating that the lubricant redistribution was the main reason for the lubricating enhancement. Notably, the groove modification on the inner surface of the cage pocket facilitated the directional lubricant migration and the migration effect depended on the groove angles. In conclusion, these results offer an in-depth understanding of the bearing lubrication mechanism, thereby inspiring advancements in cage design and lubricant flow regulation.

Effect of chevron-shaped wetting patterns on oil film thickness in cylinder-on-disc contact under starved lubrication or limited lubricant supply

This study addresses the oil starvation problem in roller bearing line contacts and proposes a novel Chevron-shaped wetting/oleophilic pattern on the bearing track to enhance oil replenishment. Validation through optical cylinder-on-disc lubrication film tests reveals the impact of the pattern on inlet oil supply and film thickness. Notably, a Chevron pattern oriented opposite to disc movement significantly increases film thickness. Wetting is more pronounced in oleophilic areas (Chevron pattern), forming an inverted V-shaped "virtual wall" that directs lubricant backflow toward the center and reduces side leakage. A pattern length equal to the bearing track width was found to be more effective compared to smaller sizes, as the oil side ridges are located on the oleophobic and oleophilic boundaries, which capitalizes the wettability step effect more effectively. This research provides a basis for designing oleophobic surfaces with improved anti-wear and anti-friction properties.

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

Elastohydrodynamic lubrication performance of PUMA-PSMA supramolecular polymer gel lubricant

In this study, free radical polymerization was employed to prepare a supramolecular polymer gelator called PUMA-PSMA, containing urea groups. The incorporation of this gelator is anticipated to enhance the heat resistance of the gel lubricant. The resulting PUMA-PSMA gels demonstrate favorable mechanical strength and the ability to recover from deformation. Additionally, the PUMA-PSMA gel has a greater film thickness compared to the base oil when the oil supply is abundant. In cases of limited lubricant supply, the PUMA-PSMA gel effectively undergoes shear thinning, reducing the duration of oil starvation. These gel lubricants help prevent the loss of lubricant to some extent and are poised to serve as an innovative type of lubricant.

Experimental Study on the Influence of Stearic Acid Additive on the Elastohydrodynamic Lubrication of Mineral Oil 2137

Using an optical elastohydrodynamic lubrication (EHL) test rig, oil film thickness and the coefficient of friction (COF) were measured, and the influence of stearic acid additive on the EHL performance of mineral oil 2137 was investigated. The results showed that 2137 with 0.3 wt% stearic acid (denoted to as 2137s) achieved the same film thickness as 2137, while the COF of 2137s was significantly lower than that of 2137 when the contact was under conditions of a fully lubricant supply. Under conditions of limited lubricant supply, 2137 base oil was prone to oil starvation with the increase of entrainment velocity. On the other hand, 2137s significantly mitigated the oil starvation. This was attributed to the fact that lower surface energy by the adsorption of stearic acid results in discontinuous oil-droplet distribution on the lubrication track and, therefore, early pressure generation. Moreover, it is interesting to find that less 2137s supply quantity can produce higher film thickness when the contact is at high speeds, which is attributed to the fact that a smaller quantity of 2137s gives smaller droplets on the lubrication track, and the resultant small surface area–volume ratio presents oil more resistance to the centrifugal force and results in less oil escaping from the lubrication track. The addition of stearic acid reduced the average COF of 2137 mineral oil by about 13.3%

Electronic-Control Friction Behavior of Porous Metal-Organic Framework@Ag Nanocrystals as Self-Repairing Lubricant Additive.

The low conductivity and poor antifriction performance of lubricants are the main causes of wear failure in mechanical equipment under electronic-control friction. Metal-organic framework (MOF) nanocomposites can be used to fabricate a new kind of lubricant additive. Herein, porous Cu-BTC@Ag MOF nanocrystals were successfully synthesized via an in situ generation method. Transmission electron microscopy results showed that the nano-Ag element was evenly dispersed throughout the Cu-BTC matrix. Cu-BTC@Ag nanocrystals can significantly improve the electrical conductivity of the EMI-BF4 ionic liquid, which increased by 38.8%. The average coefficients of friction (COF) and wear volume of EMI-BF4 ionic liquid with 0.5 wt % Cu-BTC@Ag decreased by 8.3 and 16% without applied voltage, respectively. This finding was due to the continuous extrusion of the EMI-BF4 stored in the Cu-BTC@Ag pores under external load. It entered the contact zone, thereby maintaining the continuous supply of lubricant. At 20 V applied voltage in the friction process, the COF of the EMI-BF4/2.0wt %Cu-BTC@Ag lubricant decreased by 18.8%, and its wear volume decreased by 32.7%. The Cu-BTC@ Ag nanocrystals adsorbed onto the metal surface to form a friction reaction film by the action of electric fields, which can repair the wear defects on the friction interface. Therefore, Cu-BTC@Ag nanocrystals acting as an additive in lubricant have remarkable prospects in the area of electronic-control friction.

Tribological Performance of Brass Journal Bearing Working Under Contaminated Conditions

Abstract: Bearings for sugar mills are known to withstand high load and low speed operations. A temperature rise was detected in the warehouse of a sugar factory, when working in the polluted or contaminated environment of the sugar industry. Therefore, an experiment was conducted on brass (CuZn) plain bearings when lubricated with water with different flow rates. In this study, the rise in temperature of a plain bearing in a sugar factory was analyzed. By simulating the operating conditions in a sugar mill the causes for rise in temperature in the bearing were identified and commissioning in a plain bearing test rig that takes into account the combination of operating conditions (self-load, speed, dirt, lubricants, etc). Insufficient supply of internal lubricant can lead to plain bearing failure. This affects the production costs of the industry and can also endanger human lives. The brass journal bearing gives the best performance under the Q3 flow of water and also have lesser rise in temperature.

Review Paper of Wear on Journal Bearing

Abstract: Journal Bearing is used to bear the load and confine the rotation of the shaft. A loaded rotating journal (Shaft) is supported by circular bushing (sleeve or bearing), the diameter of bearing is slightly more than diameter of journal, to provide the clearance so proper supply of lubrication oil is possible, which can enhance the performance characteristics of journal bearing. Journal bearing are mostly used to carry the radial loads of shafts working in dry and lubrication conditions. Journal bearing is used in various applications like sugar mill bearing, cement industry and turbine etc. The hole or groove is provided on bearing for the supply of lubricant. Journal bearings are most suitable for low temperature applications with slow speed. The common reasons for failure of journal bearing are the wear and temperature of journal bearing. The bearing is worn out and leading to wear particles in lubricants, heavy vibrations may be cause by rubbing oil whirl.

A textured surface with oil inflow and outflow function designed for starved lubrication

This study presents a surface, referred as ‘pocket-textured surface’, which combines traditional surface texture with the oil storage pocket that can improve the tribological performance of line contact under extremely starved lubrication conditions. The pocket-textured surface has up to 48% lower friction coefficient than the untextured surface with the same little lubricant supply. Tribological experiments were carried out to explore the tribological behavior of pocket-textured surfaces with different ratios of texture hole depth and oil pocket depth under different loads and sliding speeds. In addition, a high-speed camera observed the lubricant inflow and outflow, and Ansys simulation calculated the deformations and pressures of the pocket-textured surface.

Lubrication Film Generation with Limited Lubricant Supply and Its Tuned Oil Replenishment in a Cylinder-on-Disc Contact

Limited lubricant supply (LLS) with tuned dosage is an emerging approach to reduce friction and energy consumption. However, LLS can cause severe starvation when the oil supply is insufficient. Therefore, how to effectively replenish oil to the lubricated contact in LLS operation is very important. Using a custom-made optical slider bearing test rig, this work experimentally revealed some characteristics of LLS lubrication in a cylinder-on-disc contact, and proposed two wettability gradient patterns, namely stripe wettability and interlaced wettability, to regulate the lubricant supply to improve the lubricating properties of LLS. The effect of these two wettability patterns was evaluated experimentally according to the lubricating film thickness. The interferograms of the bearing contact under LLS show that the two patterns can augment the oil replenishment through unidirectional lubricant transport by the unbalanced interfacial force via the wettability gradient. Moreover, the interlaced wettability pattern is more effective due to the discontinuous distribution of lubricant from its hydrophilic/hydrophobic region intervals and the transfer of the hydrophobic film to the hydrophilic regions.

Tribological performance of ionic liquid impregnated porous aluminum borate ceramic

To achieve superior tribological performance without continuous lubricant supply, a novel ceramic - phosphonium based ionic liquids (P-ILs) system is developed via vacuum impregnation. The P-ILs with different viscosity and density impregnated in ceramic pellets were tested at different temperatures and sliding velocities. The results suggest that at a low temperature of 5 °C, the phosphonium benzoate and phosphonium salicylate IL exhibited a low coefficient of friction (COF) than the phosphonium saccharinate IL under a sliding velocity of 100 mm/s. Whereas this trend reversed at a higher temperature of 50 and 100 °C. Similar observations were also made for the wear rate of this unique system. It was found that the tribological performance of the P-IL+ceramic system depends on the thermal response of these ILs which is further correlated with the density and viscosity of P-ILs that control the supply of lubricants at the sliding interface.

ЗАБЕЗПЕЧЕННЯ АВТОНОМНОСТІ Й ЕНЕРГОНЕЗАЛЕЖНОСТІ ВІЙСЬКОВОЇ ЧАСТИНИ НГУ ЯК НЕОБХІДНІСТЬ ІСНУВАННЯ ШЛЯХОМ НАДАННЯ ПРАКТИЧНИХ РЕКОМЕНДАЦІЙ З ОРГАНІЗАЦІЇ ПРОЦЕСІВ ЕКСПЛУАТАЦІЇ ТА УТРИМАННЯ ТЕХНІЧНИХ ЗАСОБІВ РЕЗЕРВНОГО ЗАБЕЗПЕЧЕННЯ ЕЛЕКТРОЕНЕРГІЄЮ

The paper substantiates the relevance of using practical recommendations for the organisation of the processes of operation and maintenance of technical means of backup power supply, which is one of the most important areas of ensuring the autonomy and energy independence of a military unit. The analysis of the regulatory framework of Ukraine, scientific and technical literature, and existing practical problematic issues in military units of the National Guard of Ukraine made it possible to highlight the interdependence of the issues of operation and maintenance of technical means of backup power supply, petroleum, oil and lubricants supply, and material liability, and to outline recommendations for ensuring the autonomy and energy independence of a military unit. The issue of the organization of backup power supply of the military unit is one of the most important areas of work today and requires constant monitoring, analysis and resolution of existing problems. The purpose of the article is to ensure the autonomy and energy independence of the military unit of the NSU as a necessity for existence by providing practical recommendations for organizing the processes of operation and maintenance of technical means of backup power supply. The analysis of the processes of operation and maintenance of technical means of backup power supply in the military unit of the National Guard of Ukraine made it possible to highlight the interdependence of the issues of fuel and lubricant supply and material responsibility, to outline recommendations for the further operation and maintenance of technical means of backup power supply, among which the main ones are: the clear assignment of technical means of backup power supply to the nomenclature of the engineering service, the introduction of the position of the assistant chief of the engineering service for the provision of technical means of backup power supply and the provision of fuel and lubricants at all stages of operation. The proposed practical recommendations are aimed at ensuring the autonomy and energy independence of a military unit of the National Guard of Ukraine and can be used by human resources specialists to justify the expediency of introducing the necessary positions of those responsible for the electrical power sector in a military unit, as well as directly during the work of personnel responsible for the operation and maintenance of technical means of backup power supply.

The Effect of Stearic Acid Adsorption on Lubricating Oil Film in Slider-on-disc Contact under Limited Lubricant Supply

The Effect of Stearic Acid Adsorption on Lubricating Oil Film in Slider-on-disc Contact under Limited Lubricant Supply

НОРМАТИВНО-ПРАВОВЕ РЕГУЛЮВАННЯ ДІЯЛЬНОСТІ СЛУЖБИ ЗАБЕЗПЕЧЕННЯ ПАЛЬНО-МАСТИЛЬНИМИ МАТЕРІАЛАМИ: АНАЛІЗ ПРОБЛЕМНИХ ПИТАНЬ ТА ПРОПОЗИЦІЇ ЩОДО ЇХ ВИРІШЕННЯ

The article is devoted to the analysis of the state of regulatory and legal regulation of the activity of the fuel and lubricant supply service of the State Border Guard Service of Ukraine. The official duties of the officials of the fuel and lubricant supply service are determined by the Statutes of the Armed Forces of Ukraine, the order of the Administration of the State Border Guard Service of Ukraine dated June 24, 2008 No. 544 "On the approval of the Guidelines on the provision of fuel to the bodies of the State Border Guard Service of Ukraine", as well as the order of the Administration of the State Border Guard Service of Ukraine of the Border Service of Ukraine dated December 21, 2020 No. 134 "On the approval of the Advisor on military (ship) management of the State Border Service of Ukraine." The review of the regulatory legal support of the fuel and lubricant supply service of the State Border Guard Service of Ukraine made it possible to establish that the duties of the officials of the fuel and lubricant supply service include tasks related to: monitoring the quality and proper use of fuel, planning the necessary efficiency measures and feasibility of using and saving fuel; organization of maintenance, improvement and operation of fuel warehouses, filling stations and other subordinate fuel service facilities in accordance with current regulatory documents; ensuring proper use, maintenance and storage of technical means; organization and maintenance of accounting and reporting on fuel service; collection, delivery and proper use of spent oil products, etc. The procedure for performing these tasks must be regulated by relevant departmental acts. At the same time, the governing documents of the State Border Service of Ukraine and the Ministry of Internal Affairs of Ukraine do not define the procedure for performing the specified tasks. According to the authors, it is the task that regulates the order and conditions of storage of fuel and lubricant materials, special liquids at fuel warehouses and filling stations; tasks of fuel quality control; maintenance of technical means of the fuel and lubricant supply service are fundamentally important for the high-quality organization of the activities of state border protection units and must be regulated for the high-quality performance of official duties by officials of the State Border Service of Ukraine, who are assigned the tasks of organizing and managing the military (ship) economy.