Self-lubricating Bearings Research Articles

Laser powder bed fusion of porous 304SS samples for use in developing oil impregnated ball bearings

The ball bearing market is mature where there is a massive range of products available with new ones being developed all the time due to technological advancements. Additive Manufacturing (AM) provides a promising approach for developing oil-impregnated ball bearings. Oil impregnated bearings are critical for applications requiring smooth and low-friction motion. This study explores the feasibility of utilizing laser powder bed fusion (LPBF) technology to fabricate 304 stainless steel (304SS) samples with open pores, which can then be impregnated with a lubricant. To achieve this, 304SS powder was used, and optimum selective laser melting (SLM) printing parameters were altered to induce intentional pores. Initial screening of samples involved Archimedes density measurements and computed tomography (CT) scanning was conducted on a selected samples to assess their porosity levels. CT scan foam analysis results indicated a correlation between hatch spacing and porosity. Results revealed trends in cell volume and solidified scanning tracks thickness, indicating greater connectedness with larger pores. Synthesis of these findings could help in the development of efficient and reliable open pores that may find use in oil-impregnated self-lubricating ball bearings.

An analytical approach to incomplete spherical conformal contact: application on self-lubricating spherical plain bearings

Purpose Contact pressure is a critical factor that significantly influences the wear of self-lubricating spherical plain bearings. The purpose of this paper is to address the issue of conformal contact in spherical plain bearings with a self-lubricating fabric liner, and then a universal theoretical analytical model for conformal contact between frictionless spheres is proposed. Design/methodology/approach This study establishes an analytical model to calculate the conformal contact in spherical plain bearings and verifies the new model by finite element analysis. Findings The new model proposed in this paper overcomes the limitations of elastic half-space and small-deformation assumptions. After conducting accuracy validation, it was observed that the computational error of the new model has significantly decreased in comparison to the Johnson model. For a conformal contact with a clearance of 0, the error is nearly 0. Practical implications The analytical model can calculate the contact pressure distribution of self-lubricating spherical plain bearings bonded with a self-lubricating layer and can be extended to the conformal contact problem of spherical contact surfaces in biomechanics and other fields. Originality/value The model presented here overcomes the limitations of the elastic half-space and small deformation assumptions. It accurately calculates the contact pressure distribution of self-lubricating spherical bearings. Moreover, the complex nonlinear relationship between variables such as normal force, clearance, maximum contact pressure and contact radius was investigated using this model. The model can also be extended and applied to the conformal contact problem of spherical contact surfaces in various fields, including biomechanics. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2024-0296/

Simulation and experimental verification of the orthogonal friction continuous wear of PTFE-Kevlar fabric liner

Woven fabric liners, which are customizable and maintenance-free, have extensive applications in self-lubricating spherical bearings. However, owing to the orthogonal anisotropy and non-homogeneous characteristics, their frictional and wear behaviors are complex. Currently, average performance testing is primarily based on long-term macroscopic wear experiments. However, unobservable parameters such as mesoscopic stress and pressure distribution in liners are bottlenecks in the experimental exploration of wear sources and mechanisms. Therefore, an innovative strategy for modeling orthogonal friction and continuous wear in non-homogeneous liners is presented. This approach has the potential to overcome experimental limitations and significantly expedite liner design and cost-effective validation. The initial step involves establishing a mesoscopic voxel-based planar model of the liner that maintains the topological relationship during wear processes. This is achieved by introducing a circular voxel mesh and spatial transformation methods. Based on orthogonal friction and wear assumptions, separate constitutive models for orthogonal friction and wear are developed. Using the CETR UMT-3 friction and wear testing machine, GCr15 is selected as the counterface material, the pin disc wear method is adopted to conduct sliding test on PTFE and Kevlar fibers, and the required wear constitutive parameters are fitted. Furthermore, incremental equations for the total wear are derived. An element wear fusion strategy is introduced. This approach leads to the development of a continuous wear algorithm for liners and subsequently to the establishment of a voxel-based finite element model with continuous wear capability in the form of a circular voxel grid. This method transcends experimental methods and allows for the determination of the mesoscopic contact pressure, stress distribution, and variations in the contact material composition patterns of liner. The accuracy of the average macroscopic wear prediction is validated experimentally. This method has the potential for practical applications in bearing design.

Tribological properties and related effects of compressed, thermally modified and wax-impregnated wood

This paper develops a process for the preparation of modified wood with low friction and low wear for tribological applications such as self-lubricating bearings. Two types of wood, beech (Fagus sylvatica) and robinia (Robinia pseudoacacia), have been studied and the results compared with naturally lubricated native lignum vitae. The process developed consists of plasticisation followed by compression in a mould, thermal modification and subsequent wax impregnation. Plasticisation was carried out by conditioning the samples to a low equilibrium moisture content of 10%, followed by heating to a sample core temperature of 80 °C. This process protects the internal wood structure from mechanical damage during densification. After plasticisation, the wood was compressed in a press mould. A low springback effect (SBE), resulting in compression of up to 40%, was achieved by unloading the mould without opening it. This step optimises compressive strength and hardness. Subsequent heat treatment reduces thickness swelling by up to 85%. Finally, a wax impregnation was applied to reduce friction. Sliding wear tests on modified beech wood have shown that the lowest wear occurs in the cross-sectional orientation (load perpendicular to the fibre ends; rxt orientation). Sliding friction studies using a steel ball on a ball-on-disc tribometer showed that compressed and thermally modified samples impregnated with rapeseed wax or beeswax exhibited coefficients of friction in a range of 0.08 to 0.09. These values are almost four times lower than those of plain compressed wood and even lower than those of lignum vitae, which was used for plain bearings decades ago. This study clearly demonstrates the high potential of compressed, thermally modified and wax-impregnated wood.

Characterization of influence of high spindle speeds on self-lubricating bearing system

Abstract This paper studies the influence of bearing speed under a self-lubricating system. In the early 20th century, specialized precision manufacturing companies were founded, further establishing ball bearings as a very valuable, high-quality, and easily accessible mechanical component. This study used a self-lubricating system to achieve constant temperature and precision control. The spindle speed was analysed and tested at three speeds under a fixed pre-loading of 13000 N and a fixed lubricating oil viscosity index of 15. The results showed the spindle speed increases, the heat generated increases, and internal component temperature changes also increase. When the spindle speed is 12,000 rpm, the temperature of the inner ring of the bearing increases and changes by 166.4 %, causing fatigue and scratch wear at the same time. Using a lubricating oil self-lubricating system can slow down the temperature rise rate of components. The operation system can quickly reach a stable state, reducing thermal deformation and temperature accuracy errors.

Friction and Wear Performance of a Hydraulic Motor Roller/Piston Pair Contact lined with the Self-Lubricating Bearing Bush Modified by PEEK

Poly Ether Ether Ketone (PEEK) is a kind of special engineering plastic with excellent properties such as high-temperature resistance, self-lubrication, wear resistance, and high mechanical strength. However, its blending or composite modification applications still face numerous challenges. The primary objective of this research was to evaluate the friction and wear performance of a three-layer self-lubricating bearing bush, which was made from a modified material containing short carbon fiber and Poly Ether Ether Ketone (SCF/PEEK). The bearing bush is used as a surface contact layer on the pistons of a hydraulic motor in the interface with the cam roller. The bearing bush was processed using a 15% SCF-modified PEEK material, and the friction and wear test was conducted using a self-built friction test machine. This study aimed to assess the frictional and wear characteristics of the SCF/PEEK-modified material in the bearing bush. The results show that as the experimental pressure rises from 15 MPa to 25 MPa, the friction coefficient of the SCF-modified bearing bush experiences a significant decrease from 0.420 to 0.296. Furthermore, the stability of the frictional morphology of carbon fibers indicates its effective adaptability to low speed and high load conditions.

The effect of lubrication on the tribological properties of polymer composites for high contact pressure hydropower bearings

Premature failure of polymeric self-lubricating bearings is a limiting factor in the sustainable and continued operation of hydropower plants. In this work, the tribological performance of two novel polymer composites was studied with respect to commercially available materials. The materials were evaluated under dry and lubricated conditions, using water and an environmentally adaptive lubricant (EAL). The two tested commercial materials yielded a low dry sliding friction and wear. Under water lubricated conditions, the in-house developed polyphenylene sulphide (PPS) based composite provided an exceptionally low friction and a wear rate of a factor of 3 lower than the best performing commercial material. Using the EAL wear was reduced for most materials by up to 85%.

Tribological Properties of Polytetrafluoroethylene (PTFE)/Aramid Fabric Composite Liner Modified by PAO40/Polysulfone/SiO2 Hybrid Shell Microcapsules

Hybrid shell microcapsules have been incorporated into polytetrafluoroethylene (PTFE)/aramid fabric composite liners to enhance the tribological behavior of self-lubricating spherical plain bearings. PAO40/polysulfone/SiO2 hybrid shell microcapsules were synthesized utilizing a combination of Pickering emulsification technology and solvent evaporation. The modified liner with 9 wt% microcapsules exhibited the highest reduction in the average friction coefficient and wear rate, which were 31.1% and 47.9% lower than the unmodified liner. Furthermore, the tribological behavior of modified liners was investigated under different loads and sliding speeds. The friction process of the modified liner and the formation process of the transfer film were analyzed. Investigations into the friction reduction mechanism revealed that the PAO-40# released from microcapsules transitioned the friction type from dry to mixed. SiO2 particles are conducive to forming a denser transfer film by the PTFE abrasive. The results of this study have important scientific significance.

Study on the tribological performance of self-lubricating thrust ball bearings with different embedded features

PurposeThe purpose of this paper is to develop a new type of embedded solid self-lubricating thrust ball bearing for conditions where grease lubrication cannot be used and to analyze its tribological performance under different lubrication characteristics (lubrication position, width and filling amount).Design/methodology/approachLubrication parameters such as position (a), width (W) and filling amount (Q) were considered. Grooves were made on the raceway with a fiber laser and solid self-lubricating materials were applied through scraping. The frictional behavior of the new bearing was analyzed using a vertical test rig and the bearing’s surface topography was examined with a noncontact profilometer to study wear mechanisms.FindingsThe new inlay thrust ball bearings exhibited excellent lubrication effects and effectively controlled the temperature rise of the bearings. When a is 0 degrees, W is 0.5 mm and Q is 16 mg, the bearing experiences the least wear, and the friction coefficient and temperature are the lowest, measuring 0.001 and 41.52 degrees, respectively. Under the same experimental conditions, compared to smooth bearings without solid lubrication, the friction coefficient decreased by 96.88% and the temperature decreased by 59.74%.Originality/valueThis study presents a self-lubricating thrust ball bearing designed for conditions where grease lubrication is not feasible. A comprehensive investigation was conducted on its surface morphology, wear mechanisms and tribological performance. This work provides valuable insights into the research of self-lubricating thrust ball bearings.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0073/

Preparation of inorganic oil-containing carbon nanocapsules and tribological properties of PA6 composites

Oil-containing polymer composites have garnered significant attention in the field of tribology due to their remarkable environmental stability and outstanding self-lubricating performance. It is important to develop an oil-containing polymer composite with excellent self-lubricating properties and mechanical properties. In this study, we successfully synthesized hollow mesoporous carbon nanospheres (HMCNs) with a particle size of about 200 nm and explored the key factors affecting their preparation. Subsequently, an impregnation technique was employed to create oil-containing nanocapsules (Oil@C) by using PAO40 lubricant as core material and HMCNs as wall material. Self-lubricating PAO40@HMCNs nanocapsules have an oil content of approximately 51.6 wt%. The unique mesoporous structure of HMCNs facilitates the controlled release of lubricants. During friction, the Oil@C in the polymer composites continuously provided lubricant to the worn surface, resulting in a remarkable 72.8 % reduction in the coefficient of friction and an 83.2 % decrease in wear rate. Analysis of the friction pair revealed that the PAO40 lubricant released from the nanocapsules played a crucial role in improving the tribological properties of the composites. The prepared PA6 composites exhibit outstanding tribological and self-lubricating properties, making them promising candidates for applications in mechanical parts, such as self-lubricating slide bearings.

Tribological properties of self-lubricating fabric linings prepared with GO-modified basalt fiber

The wear resistance and friction reduction of the fabric liner are important for the service life of self-lubricating spherical plain bearings. Basalt fiber was subjected to chemical modification by grafting graphene oxide onto its surface, resulting in the preparation of GO@BF. Polytetrafluoroethylene/basalt fiber and polytetrafluoroethylene/GO@BF fabric liners were prepared, and the tribological properties were investigated. The friction regions of fabric liners were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy, and the friction and wear mechanisms were analyzed. The results show that the addition of graphene oxide can effectively improve the friction reduction and abrasion resistance of the fabric liner. During the friction process, graphene oxide and polytetrafluoroethylene transfer film form a synergistic lubrication mechanism, which effectively reduces the formation of abrasive particles on the friction surface, and improves the tribological performance of the fabric liner.

Influence of housing hole accuracy on the starting torque of self-lubricating spherical plain bearings

The accuracy of the housing hole mainly refers to the dimensional tolerance, ovality and surface roughness of the hole, which directly affects the swing flexibility and service life of the self-lubricating spherical plain bearings (SSPBs) after the bearing is fitted in the housing hole. The dimension tolerance between the bearing and the housing has been ordained in the aviation standard. However, it is found that the ovality and surface roughness of the housing hole also have a great influence on the interference fit state, thus affecting the starting torque. In this paper, the effects of the three indexes of the housing hole accuracy (dimensional tolerance, ovality and surface roughness) on the starting torque were studied. Firstly, a theoretical analysis of the liner deformation inside the bearing was carried out based on the Lame equation. Then, the concept of equivalent interference was proposed considering the interference fit caused by the ovality and surface roughness, and the amount of the equivalent interference was determined. Furthermore, the influences of the three indexes on the starting torque were studied quantitatively with theoretical solution, numerical analysis and experimental verification. The results showed that the proposed concept of the equivalent interference can analyze the influence of the ovality and the surface roughness effectively, and the ovality has a greater effect on the starting torque than the surface roughness. The three precision indexes of the housing hole are reasonably designed to ensure that the starting torque after fitted meets standard requirements.

Ni-Cr Based Self Lubricating Composite Performance for High Speed Engineering Application

Developed High speed-rotating machinery is used in agriculture for various processes. This machinery runs using the tractor PTO operated at variable speed. Operating systems of machinery were depends on the skill of the driver. Due to jerks during operation and lack of maintenance such machinery gets fails. To increase the life of rotating components, Ni-Cr based self-lubricating composite bearings were developed and used for the actual application. Self-lubricating composite was tested under the different velocities of 3.14, 3.77, 4.71, and 6.28m/s up to a maximum of 8 Hours. The average wear rate of 7.2%MoS2 content composite is less than the other compositions of Ni-Cr-wt% of MoS2 self-lubricating composite. The result of the actual trial shows that the average wear rate of Ni-Cr- 7.2 wt%MoS2 at velocities 3.14m/s,3.77m/s,4.71m/s, and 6.28m/s is 5.74*10-9mm3/Nm, 6.09*10-9mm3/Nm, 6.30*10-9mm3/Nm, and 6.44*10-9mm3/Nm respectively.

Mapping Acoustic Frictional Properties of Self-Lubricating Epoxy-Coated Bearing Steel with Acoustic Emissions during Friction Test

This work investigates the stick–slip phenomenon during sliding motion between solid lubricant-impregnated epoxy polymer-coated steel bars and AISI 52,100 steel balls. An acoustic sensor detected the stick–slip phenomenon during the tribo-pair interaction. The wear characteristics of the workpiece coated with different epoxy coatings were observed and scrutinized. The RMS values of the acoustic sensor were correlated with the frictional coefficient to develop a standard based on the acoustic sensor, leading to the detection of the stick–slip phenomenon. As per the findings, the acoustic waveform remained relatively similar to the friction coefficient observed during the study and can be used effectively in detecting the stick–slip phenomenon between steel and polymer interaction. This work will be highly beneficial in industrial and automotive applications with a significant interaction of polymer and steel surfaces.

Finite Element Analysis of Self-Lubricating Spherical Bearings Based on Workbench

Finite Element Analysis of Self-Lubricating Spherical Bearings Based on Workbench

Vacuum tribological properties in Cr-doped H-DLC self-lubricating radial spherical plain bearings

To improve the vacuum tribological properties of the self-lubricating radial spherical plain bearings (SSPBs), the multi-layered Cr-doped hydrogenated diamond-like carbon films (Cr-H-DLC) and non-doped H-DLC films as the lubricating materials were prepared on the inner ring with an outer spherical surface and the outer ring with an inner spherical surface by unbalanced magnetron sputtering. The microstructure, phase composition, tribological properties, and failure mechanism of Cr-H-DLC SSPBs and H-DLC SSPBs were investigated. The results showed that the microstructure of the outer and inner spherical surfaces for the two kinds of SSPBs was dense. The microgram indicated that the self-lubricating film thickness of the outer spherical surface was greater than that of the inner spherical surface. What is more, the Raman spectra showed that the self-lubricating coating on the outer spherical surface contains more graphite characteristics of sp2 hybrid bonds based on the value of ID/IG. According to the vacuum tribological test, the oscillating life of H-DLC SSPBs was higher than that of Cr-H-DLC SSPBs. Moreover, the change law of friction torque and friction temperature rise showed that the testing process of coated SSPBs could be divided into running-in, stable, and failure periods. Compared with the ID/IG values before and after the vacuum test, it could be inferred that the graphitization of the sp3 hybrid bond in the self-lubricating film on both spherical occurred. Based on the microscopic wear morphology, the failure mechanism of H-DLC SSPBs and Cr-H-DLC SSPBs were abrasive wear and fatigue wear. When the lubricating layer of the friction interface was worn, the metal substrate of the inner and outer rings would contact, resulting in adhesive wear.

Tribological performances of polytetrafluoroethylene/Kevlar fabric liner reinforced by oil-containing microcapsules

The wear depth of polytetrafluoroethylene (PTFE)/Kevlar fabric liner is directly related to the service life of self-lubricating spherical plain bearings. Herein, two kinds of oil-containing microcapsules were applied to improve the wear properties of PTFE/Kevlar fabric liner at various temperatures. The addition of microcapsules successfully reduced the wear and COF simultaneously, which was owing to the synergistic effect of hard shell and liquid lubricants core. The hard shell enhanced the mechanical strength of PTFE, while the released lubricants made up the shortcoming due to the incomplete PTFE lubricating film, and inhibited the abrasive wear of SiO2 debris. The present work suggested that the addition of oil-containing microcapsules was an effective method to enhance the tribological performances of PTFE/Kevlar fabric liner.

A new coated self-lubricating spherical plain bearing with high performance and excellent security

The low service performance and sudden failure characteristics of coated self-lubricating spherical plain bearings (SPBs) limit their engineering application prospects. In the current study, two new self-lubricating coatings types were applied to the bearing contact surfaces. The bearings were compared and investigated using life tests. Furthermore, the wear failure mechanism was investigated. The results show that self-lubricating coatings improved the service performance of the traditional bearings with manganese phosphate coating. Among them, double-sided coated bearings had the best service performance and life. More interestingly, the torque and temperature rise signal curves will show a notable signal downstage before the signal mutation stage. The large-area and complete mixed friction transfer film on the contact surfaces was the main reason for the signal downstage. Moreover, the failure mechanism changed from abrasive wear to adhesive wear and fatigue wear with the increment of load. This study results preliminarily verify the performance improvement of high-performance coatings and provide a theoretical reference for further breaking through the engineering application bottleneck of coated self-lubricating SPBs.

Prediction of friction coefficient and torque in self-lubricating polymer radial bearings produced by additive manufacturing: A machine learning approach

Additive manufacturing is a rapidly developing technology that enables the production of complex parts with intricate geometries. Self-lubricating radial bearings are one of the machine elements that can be produced using additive manufacturing. In this research, we present a machine learning-based approach to model the friction coefficient and friction torque in self-lubricating radial bearings manufactured by additive manufacturing using polyether ether ketone (PEEK), polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and nylon. The proposed approach includes different machine learning models (artificial neural networks, support vector machines, regression trees, linear regression models) that utilize experimental data to predict the coefficient of friction and friction torque of different types of radial bearings. Experimental data were obtained by performing tribological tests on self-lubricating radial bearings under various operating conditions. The results reveal that the machine learning models are successful in predicting the friction coefficient and friction torque in self-lubricating radial bearings with high accuracy. The approach can be utilized to optimize the design and performance of self-lubricating radial bearings manufactured using additive manufacturing.

Wear Mechanism of TC4 Titanium Alloy with TiN Coating against Self-Lubricating Fabric

Vapor deposition technology can improve the surface wear resistance of titanium alloys, and prepare lightweight and corrosion-resistant self-lubricating spherical plain bearings made of titanium alloys. However, titanium alloys with hard films can be worn by soft self-lubricating fabrics. This paper focuses on the wear problem of TiN coating on the surfaces of self-lubricating spherical plain bearings based on titanium alloys. Ring-to-plate wear tests were carried out to study the tribological properties of TiN coating on TC4 titanium alloy against self-lubricating fabric under different working conditions (load: 500–2000 N and speed: 100–500 r/min), along with the investigation of the wear mechanism of TiN coating, and the evaluation of applicable working conditions of GE15 type self-lubricating spherical plain bearings through swing tests. The results have revealed that TiN coatings can maintain a certain friction distance without wear. Increasing friction speed and load can make TiN coatings more prone to wear. A thick transfer film can protect the TiN coating from wear. The main wear mechanism is attributed to fatigue wear induced by the repeated formation and peeling of transfer films. The GE15 bearing has achieved a self-lubricating fabric wear of approximately 0.04 mm when the swinging for 500 m (25,000 times) is under a specific condition of 27 kN and 0.2 Hz without damaging the inner ring of the bearing. The bearing is suitable for swing conditions with applied loads below 27 kN. This study provides a fundamental understanding of designing self-lubricating spherical plain bearings made of titanium alloys.