Grease Lubrication Research Articles

WLI, XPS and SEM/FIB/EDS Surface Characterization of an Electrically Fluted Bearing Raceway

Electrical bearing currents may disturb the performance of the bearings via electro-corrosion if they surpass a limit of ca. 0.1 to 0.3 A/mm2. A continuous current flow, or, after a longer time span, an alternating current or a repeating impulse-like current, damages the raceway surface, leading in many cases to a fluting pattern on the raceway. Increased bearing vibration, audible noise, and decreased bearing lubrication as a result may demand a replacement of the bearings. Here, an electrically corroded axial ball bearing (type 51208) with fluting patterns is investigated. The bearing was lubricated with grease lubrication and was exposed to 4 A DC current flow. It is shown that the electric current flow causes higher concentrations of iron oxides and iron carbides on the bearing raceway surface together with increased surface roughness, leading to a mixed lubrication also at elevated bearing speeds up to 1500 rpm. The “electrically insulating” iron oxide layer and the “mechanically hard” iron carbide layer on the bearing steel are analysed by WLI, XPS, SEM, and EDS. White Light Interferometry (WLI) is used to provide an accurate measurement of the surface topography and roughness. X-ray Photoelectron Spectroscopy (XPS) measurements are conducted to analyze the chemical surface composition and oxidation states. Scanning Electron Microscopy (SEM) is applied for high-resolution imaging of the surface morphology, while the Focused Ion Beam (FIB) is used to cut a trench into the bearing surface to inspect the surface layers. With the Energy Dispersive X-ray spectrometry (EDS), the presence of composing elements is identified, determining their relative concentrations. The electrically-caused iron oxide and iron carbide may develop periodically along the raceway due to the perpendicular vibrations of the rolling ball on the raceway, leading gradually to the fluting pattern. Still, a simulation of this vibration-induced fluting-generation process from the start with the first surface craters—of the molten local contact spots—to the final fluting pattern is missing.

Effect of operating conditions and surface roughness on grease lubrication efficiency

The aim of this paper is to investigate the effect of operating parameters (load and rotational speed) and arithmetic mean deviation (Ra) roughness value on temperature rise and tribological behavior of greased point contact under heavy load. The 3-factor, 4-level orthogonal friction experiments are designed and carried out. The moving point heat source integration method is applied to calculate the transient temperature rise of interfaces. The results show that the case with load 1900 N, rotational speed 260 rpm and Ra 0.4 μm has the highest friction coefficient and temperature rise. The grease fails and layered spalling and oxidative wear occur on the wear scar. Four second-order regression models are established to predict friction coefficient and the maximum temperature rise under different load, rotational speed and surface roughness. And the determination coefficients R2 of them are higher than 97 %. The models are helpful to determine if the working conditions fall within effective lubrication range and avoid severe damage.

Effects of Lubricating Conditions on Wear Performance of U77MnCrH Rail

With the rapid development of railway towards being high speed and having heavy load capacity, the wheel–rail wear and rolling contact fatigue in the curve section with a small radius of freight have become the key problems in urban railways, which need to be solved urgently. The aims of this study were to compare the wear resistance with three different lubricating conditions on wheel–rail wear based on the wheel–rail rolling contact simulation tests. The wear loss, microhardness, and microstructure of the contacted surface of the rail were detected systematically. The results showed that the wear rates of rail were reduced by 71% for grease lubrication and 55% for solid lubrication, compared to those without lubrication. At the same time, the thickness of plastic deformation layer of rail samples were about 167 μm for the dry state, 138 μm for the solid lubrication state, and 128 μm for the oil lubrication state, respectively. It indicates that the thickness of the plastic deformation layer was significantly reduced under both grease and/or solid lubricating conditions. In addition, the microstructure of the deformation layer with two kinds of lubricated states was coarser and denser than that without lubricants. The average grain size of the deformation layer was approximately 0.22 μm under dry conditions and 0.32 μm under lubricated conditions. It also indicated that the changes in lubricants did not have a significant effect on the average grain size of the deformation layer. The results of the present study could provide theoretical reference for the development and design of lubricants used as rail materials.

Study on electric erosion in grease lubrication using optical interference method

Protecting bearings from electrical environments is crucial as modern industry evolves. With increasing exposure to electrical conditions, the risk of bearing failure due to electric erosion becomes a significant concern. To better understand how lubrication interacts with electric discharge in rolling bearings, an optical ball-on-disc tribometer was modified to measure film thickness under elastohydrodynamic lubrication (EHL) with electric discharge. The results of the study revealed that an electrical potential difference between the surfaces separated by the lubrication film leads to a reduction in film thickness, which can be attributed to the generation of Joule heating. As the electrical potential difference increases, the film thickness decreases even further, ultimately resulting in destructive electric discharge. Interestingly, sporadic discharge was observed in the region of minimum film thickness as the entrainment velocities increased prior to the occurrence of destructive discharge. In addition, the study also investigated the use of grease with a conductive additive, a double trifluoro-sulfonate ionic liquid. It was found that incorporating this ionic liquid into the grease can decrease the energy during discharge, thereby mitigating bearing electric erosion.

Experimental Study on In Situ Storage of Grease-Lubricated Ball Screws

Lubricating grease plays an important role in the rolling screw transmission of the actuation system and is particularly concerned with the performance stability of long-term storage in aerospace applications. In this article, a batch of ball screws that were lying flat in the warehouse for about eight years were selected to extract lubricating grease from the screw raceway after being stored in situ. The oxidation performance, friction performance and rheological properties of lubricating grease were tested and compared to those of fresh grease to analyze and summarize the performance changes in lubricating grease. The transmission efficiency, friction torque, and temperature rise of ball screws without removing the original grease and those filled with fresh grease after cleaning were tested and compared. The impact of grease degradation on the transmission performance of ball screws was analyzed to provide a reference for ball screw lubrication schemes and further accelerated storage experimental design.

Laboratory evaluation of a nanostructured lubricating grease for tram runflat tires

PurposeThis paper aims to develop a stable gel-type lubricant emulating commercial conditions. This encompassed rheological and tribological assessments, alongside field trials on the Medellín tram system.Design/methodology/approachThe gel-type lubricant with graphite and aluminum powder is synthesized. Rheological tests, viscosity measurements and linear viscoelastic regime assessments are conducted. Subsequently, tribological analyses encompassing four-ball and twin disc methods are executed. Finally, real-world testing is performed on the Medellín tram system.FindingsAn achieved lubricant met the stipulated criteria, yielding innovative insights into the interaction of graphite and aluminum powder additives under varying tests.Originality/valueNovel findings are unveiled regarding the interaction of graphite and aluminum powder additives in tribological, rheological and real-world trials. In addition, the wear behavior of polymers is observed, along with the potential utilization of such additives in tramway systems.

Design of a test rig for grease endurance tests

BackgroundThe performance and endurance of lubricating greases is often assessed through model tests (like four-ball tests or SRV tests). This approach has some limitations, especially when greases with special fillers are investigated, because simplified laboratory test conditions can never replicate real operating conditions. ObjectiveFor a more reliable assessment on the performance of a lubricating grease, lubricants must be tested in close-to-actual operational conditions, e.g. through component tests. This paper presents both the design and implementation of a dedicated test rig to test lubricating greases through middle-sized thrust ball bearings. MethodsThe test rig design is optimized to monitor the effectiveness of lubrication and determine the useful life of grease by recording representative parameters, namely bearing temperature at different location in the bearing, vibration level, and electric contact resistance (ECR) through the bearing. ResultsThe results of a couple of assessment tests are presented and confirm that the test rig is working as expected. ConclusionsThe chart of the parameters being monitored shows that the instant performance of grease lubrication can be tracked during the endurance tests, and grease failure identified. The special mechanical layout of the rig also allows the user to obtain additional information that is usually not available in other commercial greased bearing testers. This work is meant to be the first step of the development a new approach to evaluate the grease lubrication performance and a few experimental results are included as they are intended as a functional validation of the prototyped test rig.

Study on Grease Lubrication and Electric Erosion Characteristics in AC Electric Fields

Protecting motor bearings from electric erosion is crucial as electric vehicles evolve. To better understand how lubrication interacts with electric discharge within motor bearings during varying speeds of vehicle operation, an optical ball-on-disk tribometer was modified to investigate the influence of alternating current (AC) electric fields on film thickness, friction force under various lubrication regions, and discharge characteristics. The study revealed that in AC electric fields, as the lubrication state shifts from mixed lubrication to fluid lubrication region, the electrical characteristic of the lubricating oil film changes from resistive to capacitive, accompanied by an increase in discharge frequency. Under the elastohydrodynamic lubrication (EHL) region, an electrical potential difference between the surfaces separated by the lubrication film leads to a reduction in film thickness, which can be attributed to the generation of Joule heating. If the potential difference across the oil film increases to the threshold voltage, destructive discharge occurs with the emission of a significant amount of purple light. Joule heating generated by the AC electric fields also results in a reduction in the friction coefficient under the fluid lubrication region. However, due to the reduction in film thickness, the lubrication state eventually moves to mixed lubrication, leading to a substantial increase in the friction coefficient. In addition, the study also investigated the use of grease with a nanographite conductive additive. It was found that inappropriate additive amounts can lead to discharge phenomena occurring outside the contact region.

Environmentally friendly tailor-made oleo-dispersions of electrospun cellulose acetate propionate nanostructures in castor oil for lubricant applications

The aim of this work is to find an alternative lubricating grease formulation that can be produced from renewable and biodegradable sources with minimal risks to human health and the environment. We used a castor oil and electrospun cellulose acetate propionate (CAp) as raw materials. We hypothesized that the acetyl and propionyl groups could provide an adequate chemical compatibility with the castor oil and that the electrospun nanostructures could enable improved physical stability by creating a variety of morphologies allowing the tailoring of the rheological and tribological properties of the resulting greases. The experimental results show that the use of electrospun CAp nanostructures can indeed yield physically stable formulations, even when used at low concentrations (3 ​wt%). The resulting dispersions went through structural transitions due to changes in the thickener morphologies and/or concentration, as shown by oscillatory rheology, oil holding capacity, tackiness, and lubrication performance in metal–metal contact. We found that the formulations, containing smooth or porous CAp nanofibers, at 5 ​wt% as a thickener, possess suitable rheological and tribological properties with a performance comparable to that of traditional lithium lubricating greases.

Development of a Space Grease Lubricant with Long-Term-Storage Properties

Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finally, the manufacturing of prototype formulations and their broad characterization by means of LTS behaviour, outgassing, and tribological performance is presented.

Analysis of the thermal lubrication characteristics of cycloid pinwheel transmission mechanisms in RV reducers

In this paper, the cycloidal pin wheel drive mechanism of the secondary drive component of the rotary vector (RV) reducer is studied. Under the condition of grease lubrication, considering tooth profile modifications and machining errors, we established a three-dimensional load-bearing contact analysis model of a cycloid pinwheel transmission mechanism. We studied the time-varying contact characteristics of the gear teeth and dynamic joint surfaces of the inner and outer races of a crankshaft bearing. Considering the thermal effects, we proposed an analysis model of the lubrication characteristics of cycloid pinwheel transmission mechanisms. We also studied the thermal lubrication properties, such as load de-formation, lubrication film thickness, contact pressure and temperature increase at the lubrication contact area. The accuracy of the model was verified by temperature experiments on the inner raceway of an RV reducer bearing and the evolution law of the dynamic thermal lubrication characteristics of the inner and outer races of the crankshaft bearing, the meshing gear tooth pair and the whole process of single pin tooth meshing were revealed. This study provides an effective method for analyzing the temperature increases of the key joints of RV reducers.

Study on the fastening property of precision locknut under simulated dynamic impact loading with consideration of interference factors

Abstract Screw thread fastening system is the category of mechanical connection utilizing both wedge and friction actions to transfer clamping force and torque. This fastening system shows the advantages of simple in structure and ease in application. However, its shortcomings include the performance limitation by dimension and precision, stress concentration induced by the notch geometry, loosening in dynamical service, susceptible to atmospheric condition, etc. Therefore, the possible interference on the anti-loosening property of the locknut by noise factors of the ambient temperature, operator characteristics, and type of torque wrench used was investigated using Taguchi method in this study beside the main control factors of type of locknut, fit clearance, and type of lubrication grease. The goal was to evaluate the anti-loosening property of the locknut, i.e. the anti-loosening ratio and axial force ratio, in a more realistic manner. The connection joint of the locknut was subjected to cyclic transverse impact and the anti-loosening property was measured after a specified number of cycles. The loading effect on the surface roughness of thread surface was examined and discussed after the test. It was found that the factor of locknut type dominated the influence over the lubrication grease and fit clearance factors. Through the analysis, the design with optimal combination of the control factors improved the axial force ratio and anti-loosening ratio by 7.8% and 47.9%, respectively.

Analysis of Lubrication Characteristics and Friction Coefficient of Steel/Plastic Spur Gear Pair under Grease Lubrication

Analysis of Lubrication Characteristics and Friction Coefficient of Steel/Plastic Spur Gear Pair under Grease Lubrication

A novel numerical analysis method for predicting non-Newtonian lubricant (grease) distribution in ball bearings

Grease is a visco-elastic fluid and the most common lubricant for rolling bearings. During the churning phase (initial phase) of bearing operation, most of the grease is collected at various locations in the bearing, e.g. by the seal, at the bottom cage bar, in the cage pockets, which are then called grease reservoirs. These are formed based on bearing operating conditions, grease type, bearing geometry, bearing type. The grease reservoirs supply lubricant to the bearing contacts via bleeding: during operation the oil bleeds out of the reservoirs and lubricates the contacts. Since the distribution of grease is crucial to the bearing lubrication, the design of bearing components e.g., the cage, shall aim at an optimal grease reservoir creation during the churning phase. It is difficult to observe the effect of component design on the grease distribution through real life experiments, so CFD simulations with MPS (Moving Particle Semi-implicit) method are performed here. Flow Simulations with MPS method can help determine the factors influencing the grease distribution inside the bearing after churning, with the final aim of enhancing lubrication. For the current simulations, a CAE software based on MPS, namely Particleworks, was used. Grease consists of a base oil, a thickener, and additives. Since it is a non-Newtonian fluid, it has a nonlinear relation shear stress vs shear rate. It is a visco-elastic material, so it does not flow in the absence of a threshold force. For current simulations, the grease rheology has been modelled using the Herschel-Bulkley model. The model was fitted on in-house rheometer test data and was reduced to a single cage-ball segment. All critical kinematic properties were preserved, that is the speeds of both the inner ring and ball surfaces and the oscillation of the ball position within the pocket as it travels through the loaded and unloaded zones of the bearing. The location and the duration of grease injections resulted in different grease distributions in the model. For demonstration purposes, this document only focuses on the results obtained injecting a grease layer on the inner ring surface in front of the contact. This realistically predicted grease reservoirs to be located at the cage bottom, on the top of cage and in the cage pockets. Sensitivity study on particle size, time step, surface tension and the parametric variation of the bearing speed were also performed. This is an important milestone, as we are able for the first time to virtually simulate the onset of grease reservoirs at locations corresponding to evidence from real bearing operations. The distribution of grease observed at the cage pockets is very important for oil film replenishment. This outcome gives us confidence that the MPS method can be used to support the design of bearing components contributing to enhanced lubrication.

Review of Wind Power Bearing Wear Analysis and Intelligent Lubrication Method Research

With the significant penetration of wind generation, wind turbines require higher and higher lubrication performance for bearings. To improve the lubrication performance of wind power bearings, this study takes wind power bearings as the research object and comprehensively analyzes the wear forms of wind power bearings as well as intelligent lubrication methods. Firstly, the main roles and wear forms of wind turbine bearings are sorted out and analyzed. Secondly, the common lubrication problems of wind power bearings are analyzed from the bearing grease selection, lubrication mode, and lubrication status, highlighting the important influence of lubrication on bearings. Thirdly, the wind turbine bearing wisdom lubrication method research and organization, mainly including the wind power generation bearing lubrication materials, lubrication devices and monitoring methods, and other issues of research and analysis. Finally, current challenges and future development directions are summarized, which are designed to provide theoretical reference and technical support for the related research and engineering practice in the field of wind power engineering.

КОНСЕРВАЦИОННЫЕ И РАБОЧЕ-КОНСЕРВАЦИОННЫЕ СМАЗОЧНЫЕ МАТЕРИАЛЫ «РОСОЙЛ»

The paper contains an overview of Rosoil rust-preventive, protective and operating lubricants for metallurgy, mechanical engineering and other industries, including for military-industrial enterprises, as well as for the needs of the Ministry of Defense of the Russian Federation and the population. The main physicochemical and operational characteristics of rust-preventive, protective and operating lubricants are given such as rust-preventive greases for corrosion protection of ferrous and non-ferrous metal products during storage and transportation; protective grease lubricants for anticorrosive and mechanical processing of metals; protective antifriction greases for lubrication when manufacturing and operationing steel ropes made of uncoated wire and galvanized wire; universal lubricants for multi-purpose applications; corrosion-preventing oil for protection of military equipment; gun oils for cleaning, lubrication and corrosion protection of artillery and small arms during storage and operation; corrosion inhibitors to improve the protective properties of lubricating oils for various purposes and fuels. It is shown that the range of Rosoil rust-preventive, protective and operating lubricants contains 19 products, most of which are designed to replace imported materials and surpass them in protective properties and tribo-engineering characteristics.

Effect of Grease Filling on the Film Thickness in Deep-Groove Ball Bearings

Determining the film thickness during the bleeding phase of grease lubrication in a bearing is difficult due to the various replenishment and loss mechanisms involved. An additional factor that could influence the film thickness is the amount of grease in the bearing. In this study, film thickness is measured in deep-groove ball bearings using two different greases, each with initial grease filling percentages of 7.5%, 15%, and 30% of the bearing’s free volume. Film thickness is measured during the early stage of the bleeding phase at various loads and speeds using the electrical capacitance method. Results show that, after churning, values of temperature and film thickness are similar for the three different filling quantities. This indicates that bulk grease flow or oil bleed from the reservoirs formed in the unswept region does not impact the lubricant film thickness in the early stage of bearing operation.

Motion Analysis of Wire Rope Maintenance Device

This work outlines a design for a wire rope maintenance device that is based on commonly used, low-dropping point lubricating grease for wire rope lubrication and operates along the strand’s twist direction. Unlike similar existing devices, this device scrapes abrasives from the wire rope’s surface along the strand’s twist direction and applies lubricating grease in the same direction. It addresses issues related to the accumulation of old lubricating grease between strands, as well as the problems of a heavy weight, high traction force requirements, complex operation, unstable motion, potential surface damage to the wire rope, and the strong pollution found in existing products. The wheel system of this device was kinematically modeled and subjected to force analysis, and its accuracy was verified through simulations and experiments. Test results show that when this device is used for cleaning and lubricating wire ropes, it requires less than 150 N of traction force, maintains a stable speed of 0.6 m/s, and ensures coaxiality within ±0.1 mm, thus meeting the maintenance requirements of ropeway wire ropes. In future work, the effects of different factors, such as changes in scraper shape and size, lubricating grease application speed, and temperature and pressure inside the grease storage chamber can be studied to understand their influence on the application of grease to wire ropes.

Analysis of Influencing Factors on the Tribological Behavior of 42CrMo4/17NiCrMo6-4 under Grease Lubrication.

The tribological behavior of 42CrMo4/17NiCrMo6-4 under grease lubrication was explored in terms of load, speed, hardness matching, and lubrication quantity. Optical microscopy, scanning electron microscopy, and a surface profilometer were used to investigate the wear mechanism. The results show that hardness matching has the greatest impact on the wear resistance and friction reduction of the friction pair, followed by the load factor, with the impacts of speed and lubricant quantity being minor. Increasing the hardness of 42CrMo4 reduces the friction coefficient and wear volume of the friction pair substantially. When the maximum surface hardness of 42CrMo4 was compared with the lowest surface hardness, the friction coefficient was reduced by 21.5%, and the wear volume was reduced by 87.2%. Abrasive wear is the sort of wear failure that was seen, and as the hardness of 42CrMo4 increased, more severe fatigue wear appeared on 17NiCrMo6-4. While the wear volume initially increases and subsequently lowers with increasing load, the friction coefficient initially decreases and then stabilizes. A synergistic combination of abrasive and adhesive wear occurs under high load, changing the wear type from abrasive wear under low load. The wear volume is decreased by the sticky layer generated under high load conditions, which achieves superior wear prevention. This study is anticipated to offer recommendations for designing gears' required hardness under various operating circumstances.

Analyzing the Effects of Lubrication Techniques on CNC Spindle Bearing Heat: An Experimental Investigation

The machining ability and accuracy of a machine are determined by parameters such as the stiffness and load capacity of its spindle unit. In addition, the effectiveness and technique of lubrication and cooling can significantly affect the operational characteristics of the machine spindle. The current study investigated the effects of two different lubrication methods, grease and air-oil mixture, on the temperature which is generated at the spindle bearings of a Computer Numerical Control (CNC) machine. The temperature distribution and rise rate of the bearings were measured using a thermal imaging camera and thermocouples. The results indicated that the air-oil mixture method was more effective in dissipating heat and reducing the temperature of the bearings than the grease method, due to the direct cooling provided by the air-oil mixture to the bearing balls, resulting in improved lubrication efficiency and heat exchange with the environment. Compared to the grease lubrication method, the temperature of the bearings was lower by 7°C to 9°C depending on the position of the bearing on the CNC spindle. Therefore, it is recommended to use the air-oil mixture lubrication method, especially for high-speed processing on CNC machines. However, the discharge of oil particles from the ventilation system should be carefully controlled. Overall, the findings offer valuable insights into optimizing lubrication methods for CNC machines to enhance processing quality and reduce the impact of temperature on the bearing performance.