Abstract: This article provides a summary of the 2019 seminar on high-speed and heavy-duty bearings and self-lubricating coating technology. More than 30 experts and scholars from China and Ukraine attended this meeting. The meeting focused on the discussion of high-speed and heavy-duty bearings and self-lubricating coating technology. Two academicians from the delegation of the Ukrainian Academy of Sciences gave thematic reports on the research and development technology of new materials such as ultra-high temperature ceramics and microwave materials. Two professors from the delegation of Ningbo University also gave reports on "Research on Micro Failure Mechanism of Bearing Materials under Rolling Contact Fatigue" and "Research on Microscale Control and Life Extension Technology of Rolling Mill Heavy Duty Bearings". This meeting showcased the new research achievements of experts from China and Ukraine in surface coating technology and bearing life extension.
Keywords: high-speed and heavy-duty bearings; Extend life; Self lubricating coating; meeting
Bearings are important fundamental components of aviation engines, and complex and harsh environments such as high temperature, high pressure, fatigue, and wear seriously affect the service life of bearings. Improving the service life of aviation engine bearings has always been a hot topic of scientific research. This seminar on high-speed and heavy-duty bearings and self-lubricating coating technology is a seminar and exchange between experts and scholars from China and Ukraine on bearing failure mechanisms and self-lubricating coating technology in extreme environments. The aim of the conference is to provide academic opinions for the development of aerospace and mechanical industries.
This academic conference was successfully held on June 10, 2019 at the Institute of Advanced Technology of Ningbo University. The conference is hosted by Ningbo University, organized by the School of Mechanical Engineering and Mechanics of Ningbo University, and co organized by the Zhejiang Key Laboratory of Parts Rolling Forming Technology, Ningbo Mechanical Engineering Society, and Journal of Ningbo University (Science and Engineering Edition). The meeting was chaired by Associate Professor Peng Wenfei, Vice Dean of the School of Mechanical Engineering and Mechanics at Ningbo University.
At the opening ceremony, Professor Shao Qianjun, Vice President of Ningbo University, Professor Zheng Rongyue, Dean of the School of Mechanical Engineering and Mechanics, and Director Ye Xuguang, Department of the Ningbo Association for Science and Technology, respectively delivered welcoming speeches, warmly welcoming the visit of Ukrainian experts. Associate Professor Ye Hongguang, Director of the China Research Center at the Institute of Materials Studies of the National Academy of Sciences of Ukraine, also delivered an enthusiastic speech. Experts and scholars from China and Ukraine exchanged views on the cooperation and development of surface coating technology and bearing life extension during this meeting.
1. Meeting Overview
1.1 Ultra high temperature ceramics
Ultra high temperature ceramics, mainly composed of refractory compounds such as borides, silicon carbide, or nitrides, have excellent impact resistance, wear resistance, and high-temperature oxidation resistance under extreme conditions. Therefore, they play a key role in reactor vessels in nuclear rocket engines. Therefore, the research and development of ultra-high temperature ceramic materials has important strategic significance for China.
The research by Ukrainian Academician Grygolyev indicates that the activation sintering of ultra-high temperature ceramics is a solid-state sintering of eutectic systems. At high temperatures, the thermal properties of the components are significantly different from those of the single-phase state, and the interatomic bonds are significantly weakened, resulting in an increase in the thermal vibration amplitude of the atoms. This phenomenon is the main reason for the increase in boundary volume diffusion activity in eutectic systems and increases the rate of heating (powder sintering, creep, etc.). At present, Academician Grigoriev has developed a new ceramic technology that obtains zirconium boron based compounds through vacuum sintering instead of conventional hot pressing technology, which can achieve the same mechanical properties as ceramics obtained under high pressure and have a relatively low temperature (1900-1950 ℃).
He found in the compression experiment of ultra-high temperature ceramics that as the creep process progresses, ZrB2 SiC ceramics can maintain a 65% reduction without being damaged, with an activation energy of 6.3eV. In addition, at a temperature of 1800 ℃, ceramics undergo high-temperature strengthening, with a strength of 800-1000MPa. At present, the ultra-high temperature ceramics developed by Academician Grigoriev have been widely used in fields such as turbine engine components, spacecraft materials, basalt fibers, coal boilers in power plants and thermal power plants.
1.2 Microwave Materials
Microwave materials are used in microwave frequency band circuits (mainly in the UHF and SHF frequency bands, 300MHz~300GHz). They are ceramic materials that serve as dielectric materials and can perform one or more functions. They are widely used in fields such as satellite broadcasting, radar, and military fighter jets.
For microwave materials, a higher relative dielectric constant can effectively solve the problem of equipment miniaturization; High quality factor values can effectively enhance the sensitivity of communication systems; The small variation of resonant frequency with temperature can improve the stability of the device. Based on these characteristics of microwave materials, Academician Birous has developed single-phase and multiphase microwave media and dielectric resonators that meet performance requirements. His related research results have been applied to devices in modern communication systems. In addition, in his research, the nano dispersed M-type barium ferrite BaFe12O19 particles obtained by aqueous solution precipitation method have broad application prospects in the medical field [3]. The nano thermal therapy (HT) method related to it can effectively damage malignant tumor cells, and magnetized particles have good effects on improving the repair of ulcerated wounds and the treatment of periodontitis. Currently, his research work has been used in many countries to treat malignant tumors.
1.3 Electronic radiation technology
With the development of modern technology, functional materials with complex characteristics are becoming increasingly important. Given that traditional material preparation processes cannot combine materials with different characteristics, electron radiation technology fills the gap in this field. Researchers can effectively utilize aluminum foil materials and vapor phase coating technology to prepare multifunctional materials.
Professor Ustinov, General Manager of Pratt&Whitney Company in Ukraine and Director of the Barton Institute, has developed quasi crystalline Al Cu Fe alloys based on electron beam physical vapor deposition (EB-PVD) technology. This alloy has extremely unusual characteristics such as high hardness, low heat conduction, low surface energy, and low friction coefficient, which can reduce surface wear in dry friction areas and prevent vacuum cold welding. This technology can also effectively solve problems such as mold surface damage and changes in product geometric dimensions during the manufacturing process of hot pressed plastic products.
In addition, traditional fusion techniques are difficult to obtain compounds that cross metal connect, making it difficult to manufacture structures composed of steel and titanium in pipeline connections. Ustinov prepared titanium steel bimetallic compounds using diffusion welding method, which can meet the requirements of installation and connection, and have the advantages of high strength and plasticity.
1.4 Copper based self-lubricating and wear-resistant materials
The preparation requirements for copper based self-lubricating wear-resistant materials include: (1) the copper matrix can increase strength and hardness by adding materials that can withstand loads and high contact pressures, while reducing the inherent plasticity of copper; (2) Solid lubricants must be added to form a protective layer at the friction contact to reduce wear.
Professor Kavarychenko of the Kiev Institute of Technology in Ukraine conducted a comparative study on the wear mechanism and properties of copper based composites with different amounts of solid lubricants (MoS2 or MoSe2) added at different temperatures in air and vacuum. The self-lubricating composite friction material SKAMIPM-301, which he participated in the research and development, has ensured the reliable operation of the friction unit of the R-400 ultra-high frequency radiation measurement system of the Mir orbital space station within 5 years.
Professor Cavalichenko studied the tribological behavior of metal materials such as aluminum (1100), molybdenum, stainless steel (304), tantalum, titanium, and copper (182) during sliding without lubrication. It was found that aluminum has a low wear resistance Z, which may be due to its affinity with copper, high ductility, and low shear strength; The friction coefficient values of molybdenum, stainless steel, and tantalum are relatively large, mainly due to the accumulation of oxide chips; Titanium has good solubility and is prone to wear with copper, but its high strength does not cause serious sliding damage.
1.5 Hot coating materials
In the design and application of modern aircraft, special coating materials used under extreme conditions play an important role. Associate Professor Antoniuk, Deputy Chief Materials Engineer of Antonov State owned Enterprise in Ukraine, conducted a comparative study on the tribological properties of traditional electroplating coatings used in the aviation industry and new wear-resistant coating materials developed by Ukraine (plasma, ion plasma, etc.), as well as the impact of new and old coatings on the fatigue performance of titanium alloys. The results indicate that the new coating has better wear resistance compared to traditional coatings. Fatigue test studies have found that the new coating can increase the fatigue strength of titanium alloys, such as plasma coating, which can make the fatigue strength of the sample reach the level of titanium alloy BT22.
Associate Professor Antoniuk also introduced coating preparation techniques with high tribological properties and resistance to alternating loads. This technology can be applied to different metal, non-metal or high melting point materials, with high application efficiency and low porosity. This coating has high wear resistance and corrosion resistance, and has minimal impact on the structural strength and fatigue performance of the substrate.
1.6 Mechanism of Rolling Contact Fatigue Failure
Bearings play an important role in high-speed trains, wind turbines, aerospace and other fields. It can be said that bearings are the core of the mechanical industry, but the probability of bearing failure is high. According to reports, nearly 40% of faults in wind turbines are related to bearings in the gearbox, and replacement or maintenance costs are high.
Professor Li Shuxin from Ningbo University found that the microstructure and morphology of the failure surface of bearings under rolling contact fatigue are different. The failure modes of bearings are mainly classified as axial cracks, surface pitting, surface white etching layer, and subsurface white etching zone. After undergoing hundreds of thousands of cycles, a large number of pitting pits will appear on the surface of the material. Professor Li Shuxin's research found that cyclic alternating shear stress is the main cause of pitting corrosion. She first conducted a composition analysis of the white etched layer (WEL) on the surface and found that the hardness increased, but its main component was still body centered cubic (BCC) martensite, with no phase transformation in the structure. Then, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and focused ion beam (FIB) were used to observe and analyze the white etched area (WEA) on the subsurface. It was found that the WEA structure underwent nanocrystalline transformation and martensite to austenite transformation. She attributed the nanocrystallization to dynamic recrystallization under large shear deformation, which mainly includes plastic deformation localization, grain elongation, and the formation of subgrains and equiaxed grains. In addition, the transformation of martensite into austenite is also caused by shear dominated large plastic deformation, causing the transformation of body centered cubic crystals (BCCs) to face centered cubic crystals (FCC).
After Z, Professor Li Shuxin pointed out that although there has been some progress in the research on the micro failure mechanism of bearing materials under rolling contact fatigue, further research is needed on how to solve the problem of bearing microstructure changes.
1.7 Heavy load bearing of rolling mill
Based on information collected from enterprises such as Baosteel, Ansteel, Wuhan Iron and Steel, and Benxi Steel, it was found that rolling mill bearings have short service life and are prone to large-scale fatigue peeling; On the operation side, the failure rate of the bearing is significantly higher than that of the drive side; 90% of the bearings experience fatigue peeling from the rows and second rows of rollers on the roller body side and their corresponding outer roller paths.
In response to the above issues, Professor Xu Xuedao from Ningbo University, based on the theory of microscale rolling mill control, conducts behavior control within the range of 1mm, 0.01mm, or even 0.001mm for the rolling mill system, including the elastic and thermal deformation of components, as well as the clearance between moving pairs. The theory of elastic microscale behavior control is based on the assumption of rigid components. Generally, under medium and low loads, the stiffness of the components is relatively high, and the results obtained as rigid bodies during design are consistent with reality. However, for heavy-duty mechanisms or mechanisms with relatively rigid components, the elastic deformation on the components far exceeds the allowable limit of stiffness assumptions, affecting or damaging the static reliability of the mechanism.
By analyzing the comprehensive principles and changes in degrees of freedom of the micro scale equivalent roll system of rolling mills under no-load and heavy-duty conditions, Professor Xu Xuedao elucidated the abnormal eccentric loading mechanism of rolling mill bearings, thrust bearings, and axial adjustment threads of rolling mills, providing a scientific method for the development and design of the micro scale controllable static rod system of rolling mills, and providing new ideas and approaches for effectively solving major equipment accidents such as rolling mill bearings.
In his report, he analyzed the microscale behavior and performance of a tripod high rigidity rolling mill, a square column high rigidity rolling mill, a spatial self positioning high rigidity rolling mill, a red ring rolling mill, and a DANELI chuck rolling mill under no-load and rolling conditions, and used a self-developed bearing boundary element special calculation program to calculate the bearing load characteristics. In the design of rolling mills, the roll system has self positioning characteristics in the rolling state, ensuring the controllable microscale behavior of the rolling mill. The microscale dynamic design theory of rolling mills is a new supplement to the traditional rolling mill design theory that focuses on strength and stiffness requirements, and has an important guiding role for modern rolling mill design.
1.8 Surface coating of heavy-duty sliding bearings
Common surface treatment processes for improving the service life of bearings include electroplating, magnetron sputtering, bonding self-lubricating pads, and embedding solid self-lubricating materials. However, electroplating pollutes the environment, resulting in low production efficiency of magnetron sputtering films and low utilization efficiency of target materials. Pads composed of aramid fibers are not resistant to high temperatures, and the embedded structure reduces the strength of the bearing structure. The surface treatment of bearings urgently requires a new material that meets the requirements of green and large-scale production.
Dr. Cao Jun from Ningbo University has developed a polymer coating material with a wide temperature range and sustained wear and friction reduction performance, and used liquid spraying technology to conduct comparative studies on the thickness, tribological properties, and fatigue strength of MoS2/PI polymer coatings. The results showed that the fatigue strength of MoS2/PI polymer coating was greater than 97MPa, and compared with uncoated bearings, the service life of bearings below 6000r · min-1 was increased by 446.29%. Its tribological, mechanical, and anti-corrosion properties were better than those of the electroplating layer. This technology has been promoted and used in Anhui Meida Electromechanical Industry Co., Ltd. and Shanghai Xiangsheng Baker Bearing Co., Ltd.
2. Summary
With the development of the mechanical industry, especially high-speed trains and aerospace industries, the research and development of bearing technology that meets the service requirements in extreme environments such as high-speed and heavy loads is crucial for improving the safety, reliability, and lifespan of aviation engines. The convening of this conference has provided many valuable research results and technologies for the research and application development of high-temperature bearing materials, as well as material selection, design, life assessment, and structural integrity assessment.
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