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

Deadline for manuscript submissions: closed (31 October 2023) | Viewed by 11418

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Special Issue Editors

Dr. Sang-Shin Park

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Guest Editor

School of Mechanical Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea
Interests: energy system; tribology; system design

Dr. Tae Ho Kim

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Guest Editor

School of Mechanical Systems Engineering, Kookmin University, Seoul, Republic of Korea
Interests: rotordynamics; bearing; turbomachinery; vibration; lubrication
Special Issues, Collections and Topics in MDPI journals

Dr. Junho Suh

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Guest Editor

Department of Mechanical Engineering, Pusan National University, Busan SW7 2AZ, Republic of Korea
Interests: rotordynaics; tribology; journal bearing, rolling element bearing; non-contact fluid seal, contact rubber seal
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The importance of tribology has been increasingly emphasized over the years as we face critical technical and social issues related to energy and the environment. In this regard, tribology will continue to play a vital role in the development of novel technologies to maximize the efficiency as well as the performance of machines and devices. In this Special Issue of Lubricants, selected papers from the 3rd Korea-Tribology International Symposium (K-TRIB2023) will be published. Contributions can be articles describing original research, methods, hypothesis and theory, opinions, and more traditional reviews. The aim of K-TRIB 2023 is to provide a platform for scientists and engineers from all over the world to share the latest information on a wide range of topics relevant to tribology. The topics will include all topics related to lubricants as well as other major themes of tribology.

Dr. Sang-Shin Park
Dr. Tae Ho Kim
Dr. Junho Suh
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

fluid film lubrication
lubricants
additives
grease

Published Papers (7 papers)

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Research

15 pages, 5680 KiB

Open AccessFeature PaperArticle

Tribological Synergism of Anodic Aluminum Oxide Surface Containing Micro-Holes and Nanopores under Lubricated Reciprocation

by Minhaeng Cho

Lubricants 2023, 11(12), 533; https://doi.org/10.3390/lubricants11120533 - 15 Dec 2023

Viewed by 1433

Abstract

Micro-drilled aluminum surfaces containing micro-holes were anodized to produce nanopores over the machined and lapped surfaces. The anodized nanopores had an approximate diameter of 30–40 nm and a depth distribution of 20–30 μm from the surface. The diameter and depth of the machined micro-holes were 125 μm and 300 μm, respectively. Anodization itself did not change the surface roughness because the nanopores were very small. Ball-on-disk reciprocating tests were performed under lubricated conditions for 2 h using a frequency of 2 Hz, a load of 2 N, and a travel distance of 5 mm. The results showed that both the micro-drilled and anodized surfaces greatly reduced the coefficient of friction compared with the lapped bare surface; however, the coefficient of friction of the hole-textured specimen was not maintained till the end. Contrary to expectations, the lubricant retention capability of the textured structure declined because of hole failure that occurred during oscillation. This gradually increased friction until the end of the reciprocating test. When the micro-drilled surface was anodized, the coefficient of friction decreased again, implying that non-anodized micro-holes alone were ineffective for reducing friction. The surface hardness of Al increased owing to anodization, and thus the micro-holes remained intact. Therefore, it is concluded in this study that a prerequisite for friction reduction in Al is to increase the hardness to minimize the failure of micro-holes, which can be achieved by anodization. The synergistic lubricant retention capability can be maintained by the presence of both nanopores and micro-holes. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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18 pages, 8481 KiB

Open AccessArticle

Static Performance Measurements and Model Predictions of Gas Foil Thrust Bearing with Curved Incline Geometry

by Sung Ho Hwang, Syed Muntazir Mehdi and Tae Ho Kim

Lubricants 2023, 11(11), 480; https://doi.org/10.3390/lubricants11110480 - 7 Nov 2023

Cited by 1 | Viewed by 1633

Abstract

Gas foil thrust bearings (GFTBs) have been successfully used to support the axial load of oil-free microturbomachinery with low drag friction due to the low viscosity of gas or air used as a bearing lubricant. However, the widespread use of GFTBs in various high-power turbomachinery still needs reliable test data and an accurate predictive model. This research measures the height profile of a test GFTB to determine its actual incline geometry and estimate the drag torque of the GFTB. The measured GFTB height profile demonstrates that the incline geometry is closer to a quadratic curve than a line, which has been conventionally used to model GFTBs mathematically. The newly developed GFTB test rig is used to measure the lift-off speed, drag torque, and maximum load capacity of the test GFTB. A series of rotor speed-up tests estimate that the lift-off speeds of the GFTB increase with the increase in preloads. The maximum load capacity is determined by increasing the static load on the GFTB until a sudden sharp peak in the drag torque appears. The new GFTB model using quadratic incline geometry is in suitable agreement with the measured height profile of the GFTB incline and measured drag torque during the load capacity test. In addition, a comparison of the predicted GFTB performances reveals that the quadratic incline geometry model predicts a higher load capacity than the linear model. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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14 pages, 5017 KiB

Open AccessArticle

An Analysis of Edge Chipping in LiTaO₃ Wafer Grinding Using a Scratch Test and FEA Simulation

by Haeseong Hwang, Seungho Han and Hyunseop Lee

Lubricants 2023, 11(7), 297; https://doi.org/10.3390/lubricants11070297 - 16 Jul 2023

Viewed by 1361

Abstract

Lithium tantalite (LiTaO₃) is a representative multifunctional single-crystal material with electro-optical, acoustic, piezoelectric, pyroelectric, and nonlinear optical properties used as a substrate for surface acoustic wave (SAW) devices. To enhance SAW device performance, thinner LiTaO₃ substrates with improved surface roughness are desired. Chemical mechanical polishing (CMP) is employed to achieve the desired surface roughness after grinding. However, the thinning process increases the risk of substrate fracture, especially at the edges, resulting in edge chipping. Edge chipping can lead to complete substrate failure during SAW device fabrication, requiring an effective wafer geometry to prevent it. The study utilizes scratch tests and finite element analysis (FEA) to identify the optimal edge shape (C-cut, trimmed, and thinned) for preventing edge chipping on LiTaO₃ wafers. The C-cut edge refers to the rounding of the wafer’s edge, while the trimmed edge refers to the machining of the wafer’s edge to be perpendicular to the wafer surface. As a result of the scratch tests, we observed edge-chipping lengths of 115 and 227 μm on the C-cut and trimmed edges, respectively, while the thinned edge (half C-cut) resulted in complete wafer fracture. In the finite element analysis (FEA), edge-chipping lengths of 80, 120, and 150 μm were obtained on the C-cut, trimmed, and thinned edges (half C-cut), respectively. In conclusion, it has been confirmed that the C-cut, trimmed, and thinned edge shapes are effective in preventing edge chipping. However, considering that the C-cut edge shape becomes thinner through grinding, using the trimmed edge shape appears to be the most effective. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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20 pages, 6857 KiB

Open AccessArticle

Effect of Ferromagnetic Metal Base on Friction and Wear of 3D-Printed Aluminum Alloy Surface under Magnetorheological Fluid Action

by Deyong Li, Rui Li and Chul-Hee Lee

Lubricants 2023, 11(7), 273; https://doi.org/10.3390/lubricants11070273 - 23 Jun 2023

Cited by 1 | Viewed by 1027

Abstract

This study aimed to enhance the friction performance and controllable range of magnetorheological devices by investigating the impact of different materials on the tribological properties within a magnetorheological fluid (MRF) under the influence of a magnetic field. A novel friction-combined structure was proposed, consisting of a ferromagnetic metal base and a metal surface shell fabricated using 3D printing technology. The design offered several advantages: the ferromagnetic base significantly improved the magnetic field control range, the 3D-printed surface shell allowed easy replacement with different materials and textures, and it reduced both development and application costs. In this experimental study, composite samples consisting of metal 3D-printed surfaces and substrates made of different materials were used to evaluate the friction and wear characteristics of the MRF under different magnetic field conditions. Computer numerical control (CNC)-machined surfaces were also included for comparison. The results showed that the ferromagnetic matrix affected the magnetic field size and distribution of the energized coil, resulting in an increase in the friction coefficient, but also an increase in wear. Furthermore, the combination of 3D-printed surfaces with ferromagnetic substrates had a more pronounced effect on the friction coefficient compared to CNC-machined surfaces. Based on these findings, this research concluded that 3D-printed surfaces outperform CNC-machined surfaces in this specific environment. In addition, the proposed design, which combined ferromagnetic bases with 3D-printed surfaces, shows potential for improving the friction performance of friction components. The increase rate of friction coefficient from 0.1459 at no current to 0.2089 at 2.5A was 43.18%. This offers a novel application of 3D printing technology in magnetorheological devices. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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12 pages, 4773 KiB

Open AccessArticle

Tribological Study on Photocatalysis-Assisted Chemical Mechanical Polishing of SiC

by Hyunseop Lee

Lubricants 2023, 11(5), 229; https://doi.org/10.3390/lubricants11050229 - 18 May 2023

Cited by 6 | Viewed by 1529

Abstract

Silicon carbide (SiC) is widely used as a power semiconductor substrate material, even if it takes a large amount of processing time to secure an appropriate surface as a wafer for devices after chemical mechanical polishing (CMP). Therefore, studies on SiC CMP have focused on shortening the processing time by increasing material removal efficiency. Among the methods of SiC CMP that have been widely studied recently, the photocatalysis-assisted CMP (PCMP) method is known to efficiently increase the material removal rate (MRR) of SiC under UV light and photocatalysts. However, a limited number of comparative studies have been conducted on PCMP from a tribology perspective. In this article, a comparative study was conducted from a tribology perspective on CMP, mixed abrasive slurry CMP (MAS CMP), and PCMP. The experimental results demonstrated that SiC PCMP has higher friction and processing temperature than MAS CMP and general CMP, which may be caused by photocatalytic oxidation and the TiO₂ particles used as photocatalysts. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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20 pages, 12533 KiB

Open AccessArticle

Sonochemical Synthesis of CuO Nanoplatelets and Their Tribological Properties as an Additive in Synthetic Oil Using Reciprocating Tribometer

by Siraj Azam and Sang-Shin Park

Lubricants 2023, 11(4), 185; https://doi.org/10.3390/lubricants11040185 - 21 Apr 2023

Cited by 5 | Viewed by 1609

Abstract

This Research aimed to improve the tribological properties of commercially available lubricating oil (5W-40) by incorporating CuO nanoplatelets (NPs) synthesized using a simple and cost-effective sonochemical method. To evaluate the performance of the nanolubricant, a reciprocating tribometer was indigenously designed and developed to measure the coefficient of friction (COF) and wear tracks between two AISI 1045 steel surfaces. The CuO NPs were characterized using XRD to confirm their purity and phase, while SEM and FE-TEM were utilized to study their morphology and composition. Raman spectroscopy was used to reveal three distinct Raman active peaks of CuO at 283, 330, and 616 cm⁻¹. Zeta potential measurements demonstrated good dispersion quality, with a value of 92.0 mV for 0.1% concentration. SEM and FE-TEM analysis of the nanolubricant showed the formation of a tribo-film over the CuO NPs and adding 0.1% CuO NPs reduced COF by 32%. These findings suggest that incorporating synthesized CuO NPs in commercially available lubricating oil can enhance its tribological properties, leading to improved machine efficiency and lifespan, as well as reduced energy demand. Overall, the study demonstrates the potential benefits of using CuO nanoplatelets as an additive in lubricating oil, which could have significant implications for the development of more efficient nanolubricants. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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27 pages, 15080 KiB

Open AccessArticle

Thermal Preload for Predicting Performance Change Due to Pad Thermal Deformation of Tilting Pad Journal Bearing

by Yon-Do Chun, Jiheon Lee, Jiyoung Lee and Junho Suh

Lubricants 2023, 11(1), 3; https://doi.org/10.3390/lubricants11010003 - 20 Dec 2022

Cited by 2 | Viewed by 1929

Abstract

Thermal deformation of journal bearings operating under high-temperature conditions can have a significant effect on changes in bearing performance. However, no attempt has been made to quantify this amount of thermal deformation and link it to the performance change of the bearing. The aim of this study is to investigate the quantitative performance change due to thermal deformation of the tilting pad journal bearing (TPJB) pad in terms of the change in preload amount. The variable viscosity Reynolds equation and the energy equation were coupled using the relationship between viscosity and temperature, and the solution was obtained using the finite element method. Heat transfer between the spinning journal, oil film and pads is considered, and a three-dimensional (3D) finite element (FE) model was used to calculate the thermal deformation of the bearing structure. The steady state of the rotor-bearing system was predicted using a bearing performance prediction algorithm with three closed loops. State variables for this steady-state prediction include the amount of thermal deformation of the structure. In order to investigate the amount of thermal deformation of the bearing pad in terms of bearing performance, the concepts of thermal offset preload and thermal performance preload were suggested and the change in thermal preload under various conditions was investigated. Full article

(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)

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