Search Results (244)

The existing PDC (polycrystalline diamond compact)–cone hybrid bit bearing adopts a unilateral support structure, which is prone to stress concentration in the journal area, resulting in fracture and wear failure of the bearing, thus reducing the service life of the hybrid bit. In this paper, a new type of double supported bearing hybrid bit is proposed. The static strength analysis of unilateral and bilateral support bearing structures is carried out by finite element simulation, and the stress and strain distribution of the two structures under loads of 20–100 kN is obtained. Experimental devices for unilateral and bilateral support bearing structures are designed and manufactured to complete 50–100 kN static pressure loading experiments. The results show that the stress and strain of unilateral and bilateral support bearing increased linearly with the increase of load. Compared with unilateral bearing, when the load was 100 kN, the maximum Mises stress of bilateral bearing decreased from 358.80 MPa to 211.10 MPa, with a decrease of 41.16%. The maximum contact stress decreased from 415.20 MPa to 378.10 MPa, a decreased of 8.94%, and the maximum principal strain decreased from 1.101 × 10⁻³ to 9.71 × 10⁻⁴, a decrease of 11.81%. The axial strain in the danger zone was reduced by 14.68% and 17.35%, respectively. It is found that the contact stress of the simulation data is highly correlated with the bearing life, and the service life of the bilateral bearing bit is increased by 8.94%. The simulation data and experimental results provide data support for the production of hybrid bits with bilateral bearing support. Full article

The performance of the porous gas bearing depends on the geometric characteristics, material, fluid properties, and the properties of the porous media, which is a restrictor that controls the gas flow. Its application in industrial environments must support higher loads, higher supply pressure, and, consequently, higher pressure in the lubricant fluid film. Because porous media has a relatively low elastic modulus, it is necessary to consider its deformation when designing porous gas bearings. The design of porous gas bearings is a multi-objective problem in engineering because the optimization objectives commonly are to maximize the load capacity or static stiffness coefficient and minimize the airflow; these objectives conflict. This work presents a multi-objective optimization algorithm based on the nature-inspired Flower Pollination Algorithm enhanced with Non-Dominated Sorting Genetic Algorithm II. The algorithm is applied to optimize the design of a porous gas bearing, maximizing the resultant force and the static stiffness coefficient and minimizing the airflow. The results indicate a better performance of the Multi-Objective Flower Pollination Algorithm than the Multi-Objective Cuckoo Search. The results show a relatively short running time of 6 min for iterations and a low number of iterations of 50. Full article

Methods for determining the characteristics of self-acting (aerodynamic) gas bearings have been developed for many years, but many researchers and engineers still question how sophisticated a model of such bearings should be to obtain reliable results. This is the subject of this article, which presents a numerical analysis of aerodynamic gas bearings using two alternative methods: a specialized program based on the finite difference method, and a universal CFD program using the finite volume method. Gas bearings with a nominal diameter of 49 mm, designed for a 10 kW turbogenerator operating at a rotational speed of 40,000 rpm, are analyzed. The vapor of the low-boiling medium, designated HFE-7100, is used as the bearing lubricant. The calculations focus on determining the position of the bearing journal where the bearing achieved the required load capacity and checking the bearing characteristics beyond the nominal operating point. The most important results obtained by the two independent methods are compared, and recommendations are made for those interested in the numerical analysis of self-acting gas bearings. Full article

The present study aims to efficiently predict the wear volume of a journal bearing under start–stop operating conditions. For this purpose, the wear data generated with coupled mixed-elasto-hydrodynamic lubrication (mixed-EHL) and a wear simulation model of a journal bearing are used to develop a neural network (NN)-based surrogate model that is able to predict the wear volume based on the operational parameters. The suitability of different time series forecasting NN architectures, such as Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU), and Nonlinear Autoregressive with Exogenous Inputs (NARX), is studied. The highest accuracy is achieved using the NARX network architectures. Full article

In high-speed and heavy-load conditions, ordinary rigid tilting pad journal bearings experience significant contact stress at the pad pivot points, leading to severe pad deformation and increased wear. A flexible structure tilting pad bearing (FSTPB) is presented in this paper, using spring supports to replace the traditional pivot supports and flexible hinge supports. A theoretical calculation model for tilting pad radial journal bearings considering flexible structure deformation is established, and the impact of elastic deformation on the performance of the flexible structure tilting pad bearings is discussed. Based on theoretical research, vibration experiments on flexible tilting pad bearings under different loading conditions were conducted. The influence of various structural parameters on the vibration characteristics of the flexible tilting pad radial bearings was studied. The results indicate that, compared to ordinary tilting pad bearings, flexible structure tilting pad bearings exhibit excellent vibration reduction characteristics at high speeds. Reducing the bearing clearance, lowering the stiffness of the flexible structure, and increasing the offset angle of the flexible structure contribute to enhancing the operational stability of the bearing–rotor system. Full article

The development of electric gerotor pumps is a complex multiphysical optimization problem. To develop optimal systems, accurate simulation models are required to increase digital reliability. An important challenge is the accurate prediction of the pump behavior for extreme temperatures in automotive applications from $-40$ °C to 110 °C, where the viscosity of the fluid changes significantly. Therefore, simulation-based methods (numerical methods for calculating viscous friction) were developed and validated by measurements, including climatic chamber tests. The results show a strong correlation between simulated and measured performance characteristics, especially in terms of volumetric flow rate ($<5\%$), pump torque and efficiency ($<7\%$) at different temperature and viscosity conditions over a wide speed range (1000–5000 rpm) and different system pressures (0.5–5 bar). A novel method for simulating the cold start behavior of pumps (journal bearing approach for outer gear in pump housing) was introduced and validated by measurements. The methods presented significantly reduce the need for physical testing and accelerate the development process, as the pump behavior at each operating point can be accurately predicted before a hardware prototype is built. This improves the understanding of gerotor pump characteristics and provides insights to further improve the model-based development of electric oil pumps for the automotive industry. Full article

As the transmission component in mechanical systems, hydrodynamic journal bearing is widely used in large electromechanical equipment. The instability of the hydrodynamic journal bearing often results in mechanical wear and damage, which may cause maintenance shutdowns and significant financial losses. Accordingly, assessing the hydrodynamic journal bearing online is a highly effective approach to guaranteeing reliability. To analyze oil film thickness distribution under various assembly characteristics, this paper proposes a Fluid–Solid coupling analysis method based on hydrodynamic lubrication theory and Hertzian elastic deformation theory. The novelty is that the difference between the oil film thicknesses at the same measuring angle within the two opposing faces of the bearing shell is taken as the assessment parameter, which can directly indicate the deviation degree of the stator axis. Comparison of simulation and experimental results validated that the proposed method exhibits exceptional accuracy in practical applications. Full article

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. Full article

The development of reusable liquid rocket turbopumps has gradually highlighted the disadvantages of rolling bearings, particularly the contradiction between long service life and high rotational speed. It is critical to explore a feasible bearing scheme offering a long wear life and high stability to replace the existing rolling bearings. In this study, liquid nitrogen is adopted to simulate the ultra-low temperature environment of liquid rocket turbopumps, and theoretical evaluations of the lubrication performance of thrust-type foil bearings in liquid nitrogen are conducted. A link-spring model for the bump foil structure and a thin-plate finite element model for the top foil structure are established. The static and dynamic characteristics of the bearings are analyzed using methods including the finite difference method, the Newton–Raphson iteration method, and the finite element method. Detailed analysis includes the effects of factors such as rotational speed, fluid film thickness, thrust disk tilt angle, and the friction coefficient of the bump foil interface on the static and dynamic characteristics of thrust-type foil bearings. The research results indicate that thrust-type foil bearings have a good load-carrying capacity and low frictional power consumption. The adaptive deformation of the foil structure increases the fluid film thickness, preventing dry friction due to direct contact between the rotor journal and the bearing surface. When faced with thrust disk tilt, the direct translational stiffness and damping coefficient of the bearing do not undergo significant changes, ensuring system stability. Based on the results of this study, the exceptional performance characteristics of thrust-type foil bearings make them a promising alternative to rolling bearings for the development of reusable liquid rocket turbopumps. Full article

In this paper, the effect of micro-dimple textures (produced by a laser) on the tribological properties of bearings is investigated. This study offers guidelines to reduce the friction torque of the bearing pair and addresses the problem of difficult start-ups after shutdowns. Micro-pits with different texture diameters and depths were machined on the surface of journal bearings. Then, the impact of several different texture parameters on the tribological performance of the bearing pairs was studied using an orthogonal experimental design. Subsequently, the surface morphology of the bearings before and after the friction and wear test was observed using scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). These observations were then used to determine the type/state of friction and wear, which also improves our understanding of how texture affects the service life of bearings. The results indicate that the bearings’ micro-pit surface hardness follows an approximate parabolic spatial distribution that decreases along the micro-pit wall. Furthermore, the laser processing of surface textures was found to cause hardening in certain areas, and the chemical composition of elemental carbon and oxygen at the inner surface of processed bearings increased by 31.1% and 7.9%, respectively. Moreover, abrasive wear was identified as the primary form of wear. The textured surface’s antifriction mechanism primarily functioned to trap particles, which acted as a secondary lubrication source and altered the lubrication states by serving as a medium for supplied lubricants. The results confirm that a suitable selection of texture parameters can not only effectively reduce the friction coefficient without shortening the service life of the bearing pair but also facilitate the smooth start-up of the rotor–bearing system. Full article

Due to the complexity of lubricating characteristics in the variable-sectional and multiscale clearance, the absence of an effective prediction method and theoretical basis of multi-foil aerodynamic journal bearing with bump-backing foils needs to be further developed. Hence, a modified efficient static characteristics model has been established, of which the one-dimensional curved beam theory is integrated and the elasto-hydrodynamic influence is intelligently concerned. It can be used to well predict the influential mechanisms of operational, geometric, and physical parameter effects on the static characteristics, and the important variation laws are systemically clarified. It aims to furnish a more effective and computationally efficient method and theoretical foundation for this significant type of bearing and promote its engineering design and performance optimization. Full article

CuAl8Fe5Ni4Zn4Sn1 (OF 2238) is a new lead-free copper alloy for plain-bearing applications that was first officially presented in a scientific journal in 2020. Soon after its invention, the use of the alloy for connecting rod bushings in heavy-duty internal combustion engines was promoted and validated with customers. The aim of this article is to describe the material properties of the new alloy in more detail than previously and explain how the advantageous properties of CuAl8Fe5Ni4Zn4Sn1 are generated. At the beginning of this article, the general development trends in the field of copper alloys for sliding applications are presented, into which the new alloy from this publication can be classified. In the main part of this publication, the authors go through the production chain of CuAl8Fe5Ni4Zn4Sn and show how the entire manufacturing process contributes to obtaining a material with a combination of high strength, ductility and sufficient toughness. This starts with fine microstructures after casting, followed by homogenisation and refinement during hot extrusion and work hardening chiefly during cold drawing. What is most surprising, however, is the finding that a strong hardening effect can be achieved in the new alloy by precipitation of fine κ-phase at temperatures of about 400 °C and air cooling without prior solution treatment. These results make it clear that there is great potential for further material developments to support material efficiency and even to expand the application limits. Full article

This paper introduces a rigorous and comprehensive approach to the assessment of marine shafting systems through the utilization of an advanced π-Theorem-based scaling methodology. Integrating journal-bearing similarity assessment and shaft-line scaling methodology with advanced dimensional analysis, the study aims to provide a methodology foundation for systematic replication and analysis of marine shafting systems through scaled models. The proposed scaling methodology ensures geometric and mechanical similarity in terms of shaft-line deflection, considering key scaling parameters such as shaft length, diameter, weight, loads, rotational speed, material properties, bearing locations, and offsets. The advanced dimensional analysis computes specific non-dimensional ratios to guarantee a close resemblance between a real-size system and a scaled lab model. The methodology is analytically derived and validated with numerical simulations for a case study, conducting comparative analysis, evaluating discrepancies, and utilizing the integrated framework for experimentation. Full article

The production and quality of automotive-grade galvanised steel are affected by the limited service life of the pot roll bearings used in continuous galvanising lines. The journal bearings are subjected to severe degradation as they react with the molten Zn bath, and coatings can provide corrosion protection to the bearing materials. This research investigates the performance of Al₂O₃ coatings applied via the HVOF thermal spray process to stainless steel 316L substrates. Immersion tests were conducted in baths of different compositions, namely GI (Zn-0.3 wt.% Al) and ZMA (Zn-1.5 wt.% Al-1.5 wt.% Mg). Material characterisation after testing showed evidence of coating degradation after 1 week, as the coating tended to crack and detach from the substrate, allowing the molten Zn to attack the underlying steel. The coefficient of thermal expansion of Al₂O₃ and steel was measured, and a difference of 13 × 10⁻⁶ K⁻¹ was found, leading to the development of cracks in the coatings. Zn penetration through cracks was determined to be the main failure mechanism of the Al₂O₃ coatings, which otherwise remained inert to Zn-Al. Conversely, the coatings immersed in Zn-Al-Mg reacted with the Mg in the molten metal bath, showing that changing bath composition affected the performance of the coatings in molten Zn alloy. Full article

(1) Background: To better understand the dynamic characteristics of a ball bearing with an elastic ring squeeze film damper (ERSFD) under sudden unbalance, a novel dynamic model was established by fully considering the coupling between the ERSFD, bearing outer ring (the journal), rotor, and disc (loading bearing); (2) Methods: An improved secant method was developed to determine the initial eccentricity values of the bearing’s outer ring and the disc. The dynamic response of the outer ring under different speed ratios, damping ratios, and mass ratios was solved using the variable-step Runge–Kutta method; (3) Results: In comparison, a low-speed ratio, high damping ratio, and low mass ratio were more conducive to suppressing the bearing vibration. When the imbalance was suddenly introduced, the displacement amplitude of the eccentricity, transmissibility, amplitude–frequency response, and the radius of the outer ring center locus increased; (4) Conclusions: This work provides a reference for further studying the nonlinear vibration of rolling bearings coupled with an ERSFD. Full article