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A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (28 February 2022) | Viewed by 46414

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Prof. Dr. Hubert Schwarze

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Institute of Tribology and Energy Conversion Machinery, Faculty of Mathematics/Informatics and Mechanical Engineering, Clausthal University of Technology, Leibniz Street 32, 38678 Clausthal-Zellerfeld, Germany
Interests: tribology; lubrication; rheology; dynamically loaded bearings; rotor dynamics
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Dr. Thomas Hagemann

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Institute of Tribology and Energy Conversion machinery, Clausthal University of Technology, Clausthal-Zellerfeld, Germany
Interests: bearings; thermal effects in hydrodynamic journal bearings; non-laminar regime; thermal and mechanical deformations
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Special Issue Information

Dear Colleagues,

Advances in the design and development of lubricated bearings has been a task for tribology engineers for decades, as the requirements for efficiency, power density, and robustness have been continuously increasing throughout the history of rotating machines. Today there are numerous applications of bearings that operate under different boundary conditions, with a wide variety of bearing sizes, speeds, and loads. Each of these aspects involves specific challenges that range from the manufacturing process to the demands in operation. The latter typically include a sufficiently low wear level and acceptable vibrations to ensure safe and stable operation.

Besides the general task of optimizing well-known bearing solutions, new areas of application often arise. Typical examples include sliding planetary bearings in wind turbines and aircraft engines, which have recently come into focus. Solving the problems that arise during the operation of all these bearings in complex drive trains requires innovative approaches based on the experience and physical understanding of the particular phenomena by the tribology engineer.

The intention of this Special Issue is to share advances in understanding specific phenomena, improved design, and other novel aspects in the field of lubricated roller- and sliding bearings. It covers materials, fluid flow, and the interaction of the bearing with other components of the machine. Both experimental and theoretical investigations are highly welcome.

Prof. Dr. Hubert Schwarze
Dr. Thomas Hagemann
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

bearing
rolling
sliding
modeling
mixed lubrication
hydrodynamic lubrication
hydrostatic lubrication
journal bearings
thrust bearings
materials
lubricants
molecular

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Advances in Lubricated Bearings, 2nd Edition in Lubricants

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Editorial

Jump to: Research

3 pages, 164 KiB

Open AccessEditorial

Advances in Lubricated Bearings

by Hubert Schwarze and Thomas Hagemann

Lubricants 2022, 10(7), 156; https://doi.org/10.3390/lubricants10070156 - 14 Jul 2022

Viewed by 1826

Abstract

Advances in the design and development of lubricated bearings have been a goal of tribology engineers over decades, as the requirements on efficiency, power density, and robustness continuously increase in the history of rotating machinery [...] Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

Research

Jump to: Editorial

11 pages, 11614 KiB

Open AccessArticle

Experimental Investigation of a Large Tilting-Pad Journal Bearing—Comparison of a Flooded and Non-Flooded Design

by Michael Stottrop, Nico Buchhorn and Beate Bender

Lubricants 2022, 10(5), 83; https://doi.org/10.3390/lubricants10050083 - 3 May 2022

Cited by 12 | Viewed by 3403

Abstract

In tilting-pad journal bearings (TPJB), power loss corresponds to the internal friction in the shearing of the oil. Besides the lubrication gap, intermediate spaces between the pads account for a notable amount of frictional losses. Against the background of increasing demands for efficiency and sustainable use of resources, the reduction of power loss takes a key position in the further development of bearings. In our research, we compare two bearing lubrication concepts of a five-pad TPJB. Our objective is to work out the influence of different lubrication methods and bearing housing designs on the bearing operation characteristics. We conduct experimental testing of a 500 mm TPJB in two different bearing configurations with respect to the lubrication concept: an oil-flooded and non-flooded bearing design. In the flooded bearing design, oil is supplied via spray-bars and axial seals ensure the inter-pad spaces to be completely filled with oil. The non-flooded design comes without axial seals but oil drain channels to avoid oil accumulation in the bearing. In the latter design, oil is fed in via leading edge grooves (LEG). For the non-flooded bearing design, the experimental data show that the unloaded pads are not completely filled with oil and therefore, no pressure build-up occurs. The absence of additional load on the lower pads compared to the flooded design results in an increase of minimum film thickness. With the non-flooded design, power loss at high speeds is reduced to almost half. As a result, the efficiency of the entire turbomachinery application can be considerably improved. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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14 pages, 9795 KiB

Open AccessArticle

Investigation of the Wettability Properties of Different Textured Lead/Lead-Free Bronze Coatings

by Amani Khaskhoussi, Giacomo Risitano, Luigi Calabrese and Danilo D’Andrea

Lubricants 2022, 10(5), 82; https://doi.org/10.3390/lubricants10050082 - 3 May 2022

Cited by 12 | Viewed by 2575

Abstract

Hydraulic components are often subjected to sliding contacts under starved or mixed lubrication. The condition of starved lubrication occurs during the start-up phase of the hydraulic machines or at low working temperature, causing friction and wear of components such as the cylinder block or the valve plate. The aim of this paper was to evaluate the hydrophobicity and oleophilic behavior of lead/lead-free bronze coatings under different texture conditions obtained by varying the diameter and the density of the dimples. The wettability tests were performed using sessile drop tests with oil and water liquids. The dimple parameters were analyzed using confocal microscopy, while the XRF analyses were performed to evaluate the composition of the bronze coatings. Based on the wettability measurements using oil and water, it was possible to assess that the porous surface acted as oil reservoirs that could prolong the life of lubricating oil layer, and may have resulted in a superior wear resistance. Furthermore, a relevant hydrophobicity was highlighted, suggesting that the surface texturing promoted the water-repellent barrier action on the surface. The experimental results showed that the discrepancy in surface properties in oil and water was raised when using the lead bronze coating. These coupled oleophilic and hydrophobic behaviors could play a beneficial role in sustaining the durability of a lubricating oil layer under a condition of continuous water-droplet impact. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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18 pages, 4648 KiB

Open AccessArticle

Impact of Graphene Nano-Additives to Lithium Grease on the Dynamic and Tribological Behavior of Rolling Bearings

by Mohamed G. A. Nassef, Mina Soliman, Belal Galal Nassef, Mohamed A. Daha and Galal A. Nassef

Lubricants 2022, 10(2), 29; https://doi.org/10.3390/lubricants10020029 - 18 Feb 2022

Cited by 24 | Viewed by 4841

Abstract

In recent years, reduced graphene oxide (rGO) received considerable interest as a lubricant nano-additive for enhancing sliding and rolling contacts. This paper investigates the tribological and dynamic behavior of ball bearings lubricated by lithium grease at different weight percentages of rGO. Full bearing tests were conducted for experimental modal analysis, vibration analysis, ultrasonic analysis, and infrared thermography. Modal analysis indicated considerable improvements of the damping ratio values up to 50% for the bearings with rGO nano-additives. These findings were confirmed by the corresponding reductions in vibrations and ultrasound levels. The steady-state temperatures of bearings running with lithium grease reached 64 °C, whereas the temperature of bearings lubricated by grease with 2 wt.% rGO measured only 27 °C. A Timken Load test was conducted on grease samples with and without rGO additives. Grease samples having 2, 3.5, and 5 wt.% rGO showed the highest OK load with an increase of 25%, 50%, and 100% as compared to values of lithium grease. For comparison, all tests were conducted on samples of the same grease blended with graphite and MWCNTs’ nano-additives. The results proved the superiority of graphene in enhancing the load-carrying capacity and damping of grease in rolling bearings. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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12 pages, 3376 KiB

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

by Myron Chernets, Mykhaylo Pashechko, Anatolii Kornienko and Andriy Buketov

Lubricants 2022, 10(1), 13; https://doi.org/10.3390/lubricants10010013 - 17 Jan 2022

Cited by 5 | Viewed by 3289

Abstract

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

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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18 pages, 9686 KiB

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Operating Behavior of Sliding Planet Gear Bearings for Wind Turbine Gearbox Applications—Part II: Impact of Structure Deformation

by Thomas Hagemann, Huanhuan Ding, Esther Radtke and Hubert Schwarze

Lubricants 2021, 9(10), 98; https://doi.org/10.3390/lubricants9100098 - 1 Oct 2021

Cited by 18 | Viewed by 3629

Abstract

The use of planetary gear stages intends to increase power density in drive trains of rotating machinery. Due to lightweight requirements on this type of machine elements, structures are comparably flexible while mechanical loads are high. This study investigates the impact of structure deformation on sliding planet gear bearings applied in the planetary stages of wind turbine gearboxes with helical gears. It focuses on three main objectives: (i) development of a procedure for the time-efficient thermo-elasto-hydrodynamic (TEHD) analysis of sliding planet gear bearing; (ii) understanding of the specific deformation characteristics of this application; (iii) investigation of the planet gear bearing’s modified operating behavior, caused by the deformation of the sliding surfaces. Generally, results indicate an improvement of predicted operating conditions by consideration of structure deformation in the bearing analysis for this application. Peak load in the bearing decreases because the loaded proportion of the sliding surface increases. Moreover, tendencies of single design measures, determined for rigid geometries, keep valid but exhibit significantly different magnitudes under consideration of structure deformation. Results show that consideration of structure flexibility is essential for sliding planet gear bearing analysis if quantitative assertions on load distributions, wear phenomena, and interaction of the bearing with other components are required. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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19 pages, 37537 KiB

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Operating Behavior of Sliding Planet Gear Bearings for Wind Turbine Gearbox Applications—Part I: Basic Relations

by Thomas Hagemann, Huanhuan Ding, Esther Radtke and Hubert Schwarze

Lubricants 2021, 9(10), 97; https://doi.org/10.3390/lubricants9100097 - 1 Oct 2021

Cited by 19 | Viewed by 5820

Abstract

The application of sliding planet gear bearings in wind turbine gearboxes has become more common in recent years. Assuming practically applied helix angles, the gear mesh of the planet stage causes high force and moment loads for these bearings involving high local loads at the bearing edges. Specific operating behavior and suitable design measures to cope with these challenging conditions are studied in detail based on a thermo-hydrodynamic (THD) bearing model. Radial clearance and axial crowning are identified as important design parameters to reduce maximum pressures occurring at the bearing edges. Furthermore, results indicate that a distinct analysis of the gear mesh load distribution is required to characterize bearing operating behavior at part-load. Here, operating conditions as critical as the ones reached at nominal load might occur. Wear phenomena can improve the shape of the gap in the circumferential as well as in axial direction incorporating a significant reduction of local maximum pressures. The complexity of the combination of these aspects and the additionally expected impact of structure deformation gives an insight into the challenges in the design processes of sliding planet gear bearings for wind turbine gearbox applications. Full article

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20 pages, 4044 KiB

Open AccessArticle

CFD Analysis of Journal Bearing with a Heterogeneous Rough/Smooth Surface

by Mohammad Tauviqirrahman, J. Jamari, Arjuno Aryo Wicaksono, M. Muchammad, S. Susilowati, Yustina Ngatilah and Caecilia Pujiastuti

Lubricants 2021, 9(9), 88; https://doi.org/10.3390/lubricants9090088 - 7 Sep 2021

Cited by 15 | Viewed by 3300

Abstract

In the present study, a computational investigation into acoustic and tribological performances in journal bearings is presented. A heterogeneous pattern, in which a rough surface is engineered in certain regions and is absent in others, is employed to the bearing surface. The roughness is assumed to follow the sand-grain roughness model, while the bearing noise is solved based on broadband noise source theory. Three types of heterogeneous rough/smooth journal bearings exhibiting different placement and number of the rough zone are evaluated at different combinations of eccentricity ratio using the CFD method. Numerical results show that the heterogeneous rough/smooth bearings can supply lower noise and larger load-carrying capacity in comparison with conventional bearings. Moreover, the effect on the friction force is also discussed. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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18 pages, 11458 KiB

Open AccessArticle

Design and Analysis of an Aerostatic Pad Controlled by a Diaphragm Valve

by Federico Colombo, Luigi Lentini, Terenziano Raparelli, Andrea Trivella and Vladimir Viktorov

Lubricants 2021, 9(5), 47; https://doi.org/10.3390/lubricants9050047 - 27 Apr 2021

Cited by 8 | Viewed by 2702

Abstract

Because of their distinctive characteristics, aerostatic bearings are particularly suitable for high-precision applications. However, because of the compressibility of the lubricant, this kind of bearing is characterized by low relative stiffness and poor damping. Compensation methods represent a valuable solution to these limitations. This paper presents a design procedure for passively compensated bearings controlled by diaphragm valves. Given a desired air gap height at which the system should work, the procedure makes it possible to maximize the stiffness of the bearing around this value. The designed bearings exhibit a quasi-static infinite stiffness for load variation ranging from 20% to almost 50% of the maximum load capacity of the bearing. Moreover, the influence of different parameters on the performance of the compensated pad is evaluated through a sensitivity analysis. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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23 pages, 11160 KiB

Open AccessArticle

Run-Up Simulation of a Semi-Floating Ring Supported Turbocharger Rotor Considering Thrust Bearing and Mass-Conserving Cavitation

by Christian Ziese, Cornelius Irmscher, Steffen Nitzschke, Christian Daniel and Elmar Woschke

Lubricants 2021, 9(4), 44; https://doi.org/10.3390/lubricants9040044 - 16 Apr 2021

Cited by 6 | Viewed by 3081

Abstract

The vibration behaviour of turbocharger rotors is influenced by the acting loads as well as by the type and arrangement of the hydrodynamic bearings and their operating condition. Due to the highly non-linear bearing behaviour, lubricant film-induced excitations can occur, which lead to sub-synchronous rotor vibrations. A significant impact on the oscillation behaviour is attributed to the pressure distribution in the hydrodynamic bearings, which is influenced by the thermo-hydrodynamic conditions and the occurrence of outgassing processes. This contribution investigates the vibration behaviour of a floating ring supported turbocharger rotor. For detailed modelling of the bearings, the Reynolds equation with mass-conserving cavitation, the three-dimensional energy equation and the heat conduction equation are solved. To examine the impact of outgassing processes and thrust bearing on the occurrence of sub-synchronous rotor vibrations separately, a variation of the bearing model is made. This includes run-up simulations considering or neglecting thrust bearings and two-phase flow in the lubrication gap. It is shown that, for a reliable prediction of sub-synchronous vibrations, both the modelling of outgassing processes in hydrodynamic bearings and the consideration of thrust bearing are necessary. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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18 pages, 18097 KiB

Open AccessArticle

Influence of Active Cooling at the Trailing Edge on the Thermal Behavior of a Tilting-Pad Journal Bearing

by Nico Buchhorn, Michael Stottrop and Beate Bender

Lubricants 2021, 9(3), 26; https://doi.org/10.3390/lubricants9030026 - 2 Mar 2021

Cited by 6 | Viewed by 4010

Abstract

In tilting-pad journal bearings (TPJB) with a non-flooded lubrication concept, higher maximum pad temperatures occur than with a flooded bearing design due to the lower convective heat transfer at the pad edges. In this paper, we present an approach to influence the thermal behavior of a five-pad TPJB by active cooling. The aim of this research is to investigate the influence of additional oil supply grooves at the trailing edge of the two loaded pads on the maximum pad temperature of a large TPJB in non-flooded design. We carry out experimental and numerical investigations for a redesigned test bearing. Within the experimental analysis, the reduction in pad temperature is quantified. A simulation model of the bearing is synthesized with respect to the additional oil supply grooves. The simulation results are compared with the experimental data to derive heat transfer coefficients for the pad surfaces. The experimental results indicate a considerable reduction of the maximum pad temperatures. An overall lower temperature level is observed for the rear pad in circumferential direction (pad 4). The authors attribute this effect by a cooling oil carry-over from the previous pad (3). Within the model limits, a good agreement of the simulation and experimental results can be found. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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14 pages, 3754 KiB

Open AccessArticle

Improvement of Tilting-Pad Journal Bearing Operating Characteristics by Application of Eddy Grooves

by Eckhard Schüler and Olaf Berner

Lubricants 2021, 9(2), 18; https://doi.org/10.3390/lubricants9020018 - 10 Feb 2021

Cited by 10 | Viewed by 3065

Abstract

In high speed, high load fluid-film bearings, the laminar-turbulent flow transition can lead to a considerable reduction of the maximum bearing temperatures, due to a homogenization of the fluid-film temperature in radial direction. Since this phenomenon only occurs significantly in large bearings or at very high sliding speeds, means to achieve the effect at lower speeds have been investigated in the past. This paper shows an experimental investigation of this effect and how it can be used for smaller bearings by optimized eddy grooves, machined into the bearing surface. The investigations were carried out on a Miba journal bearing test rig with Ø120 mm shaft diameter at speeds between 50 m/s–110 m/s and at specific bearing loads up to 4.0 MPa. To investigate the potential of this technology, additional temperature probes were installed at the crucial position directly in the sliding surface of an up-to-date tilting pad journal bearing. The results show that the achieved surface temperature reduction with the optimized eddy grooves is significant and represents a considerable enhancement of bearing load capacity. This increase in performance opens new options for the design of bearings and related turbomachinery applications. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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22 pages, 4361 KiB

Open AccessArticle

Stability Effects of Non-Circular Geometry in Floating Ring Bearings

by Giovanni Adiletta

Lubricants 2020, 8(11), 99; https://doi.org/10.3390/lubricants8110099 - 18 Nov 2020

Cited by 7 | Viewed by 2238

Abstract

The present study theoretically evaluates the stability potential of noncircular geometries when they are adopted in the outer bearing of floating ring bearings (FRB). A numerical study is carried out to evaluate the stability about the static equilibrium position of a balanced, symmetrical, rigid rotor, horizontally placed, and supported at both ends by identical FRBs. In the analysis, the outer bearing of these FRBs is alternatively shaped with common circular bore (CB), two lobe-wave bore (2LWB) or lemon bore (LB), assuming a linearization of the film forces. A minor part of the study consists of partially supporting the results of the above study by means of a nonlinear, transient analysis. Despite limiting to the theoretical aspect, dealt with under several simplifying hypotheses, the investigation highlights the influence of the examined non-circular geometries on the stability of the static equilibrium position, when these geometries are adopted for shaping the outer housing of the FRB. The paper shows that contrasting effects are obtained, depending on the chosen geometrical parameters. In the paper, the acronyms CB, 2LWB, and LB are used to indicate the FRB layouts respectively equipped with outer circular, wave, and lemon bearing. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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