Wall-Breaker of Main Bearing for 8m-Class Mega Shield Machine Developed

The astonishing thrust generated by the cutterhead of a giant tunnel boring machine, exceeding ten meters in diameter, is ultimately borne by a main bearing several meters in diameter; similarly, the main bearing of a high-speed aero-engine must operate flawlessly under extreme conditions of high temperature, high speed, and extreme stress.

Bearings, seemingly ordinary industrial components, are a touchstone for measuring a nation's industrial foundation and technological strength.

During the 14th Five-Year Plan period, a crucial battle for independent control over high-end bearings quietly commenced and achieved key breakthroughs.

Led by the Institute of Metal Research, Chinese Academy of Sciences (hereinafter referred to as the Institute of Metal Research), and in collaboration with more than 20 research institutions and enterprises, a "wall-breaker" main bearing for ultra-large tunnel boring machines with a diameter of 8 meters was developed. This breakthrough overcomes key technologies in the development of high-speed, high-precision machine tool bearings and high-temperature, high-reliability aero-engine main bearings, establishing a complete chain from "design-materials-manufacturing-application" for high-end bearings. This marks a crucial step forward for my country in achieving independent control in the field of high-end basic components.

Rewriting Bearing Lifespan from the "Gene"

During the planning of key tasks for the 14th Five-Year Plan, the Institute of Metal Research team conducted research at over 30 units in 13 provinces across China. They discovered that the bearing industry faces severe challenges—since my country introduced its first tunnel boring machine in 1997 and began domestic production in the early 21st century, it has achieved self-sufficiency in almost all components, except for main bearings, which rely on imports.

The anxiety of enterprises is even more direct. Tunnel boring machines cost hundreds of millions of yuan, and imported main bearings are not only expensive and have long delivery cycles, but also carry the risk of supply disruptions. The infrastructure projects behind them cost tens of billions of yuan, and even if domestically produced main bearings are manufactured, no one dares to risk the project halting if they fail.

Faced with this "bottleneck" problem, the "national team" must step up.

After careful consideration, the Chinese Academy of Sciences (CAS) officially launched the "Independent and Controllable Manufacturing of High-End Bearings" strategic pilot science and technology project. The Institute of Metal Research (IMR) integrated 12 teams within its own institute, covering fields such as bearing steel, heat treatment, and ceramics, along with the resources of seven other research institutes within CAS. It also partnered with over 20 companies, including CCCC Tianhe Machinery Equipment Manufacturing Co., Ltd. (hereinafter referred to as CCCC Tianhe) and Luoyang Xinqianglian Slewing Bearing Co., Ltd., to establish a three-pronged parallel mechanism: administrative command, technical command, and Party committee support.

A crucial battle covering the entire lifecycle of bearings was thus launched.

"In bearing manufacturing, materials are the foundation, the 'genes.' Without good genes, all subsequent processes are castles in the air." This is the consensus of the team led by Li Dianzhong, Academician of the Chinese Academy of Sciences and researcher at the IMR.

Under the leadership and influence of senior scientists such as Li Yiyi, Academician of the Chinese Academy of Sciences and researcher at the IMR, the IMR has cultivated the field of special steel for decades, laying a solid theoretical and technological foundation.

Under this guidance, Li Dianzhong and Hu Xiaoqiang, a researcher at the Institute of Metal Research, led their team to undertake a special research project, focusing on the core indicator of "oxygen content" in bearing steel.

Oxygen in steel forms inclusions, becoming the source of fatigue cracks in bearings and directly affecting their lifespan. Reducing the oxygen content requires starting with the fundamental theories of metallurgical physicochemistry and reshaping the entire process.

This was a tough battle against the microscopic world. The research team delved into the formation mechanism and evolution of inclusions in bearing steel during the metallurgical process, innovatively developing key technologies such as trace rare earth addition, low-oxygen purification casting, and inclusion refinement and dispersion control.

Team members spent long periods working on the production line, observing, analyzing, and debugging alongside engineers and technicians. If they failed, they started again; if the data was unsatisfactory, they optimized the process repeatedly… They ultimately mastered the "genetic code" of high-performance bearing steel, successfully developing ultra-pure, highly homogeneous, and long-life bearing steel materials.

Third-party testing revealed that the fatigue life of this new bearing steel far exceeds that of a well-known imported brand, reaching international advanced levels.

This breakthrough signifies that domestically produced high-end bearings now possess a robust "body."

"We are not merely improving a material; through the research and application of low-oxygen rare-earth steel, we are building a stronger 'physique' for China's key basic components, forming a killer weapon," Li Dianzhong remarked. "This is our responsibility."

A 41-ton "giant ship" overcomes the micrometer-level "chasm"

The successful development of top-grade bearing steel is just the beginning.

Transforming high-quality steel into high-performance, stable, and reliable bearings tests the collaborative innovation capabilities across the entire chain, from design and manufacturing to application.

At that time, my country's imported equipment was limited by foreign technology, and the machining precision of large rollers could only reach level two, meaning the error in the diameter of several hundred rollers could not exceed ±2.5 micrometers. However, to manufacture rollers that meet the requirements of tunnel boring machines, the machining precision had to reach level one, meaning the column diameter error could not exceed ±1 micrometer.

The 1.5-micrometer difference between the two is equivalent to 1/40th the diameter of a human hair, but in the eyes of the research team, it was an insurmountable chasm.

To address this, the research team at the Institute of Metal Research proactively "went out," forming a collaborative research and development consortium with over 20 related companies, closely integrating industry, academia, and application.

"Scientists understand materials science, engineers understand manufacturing processes, and users understand actual working conditions. Only by deeply integrating the wisdom of these three parties can we manufacture truly usable bearings," summarized an engineer involved in the project.

The consortium launched a full-chain technical research effort targeting specific application scenarios such as main bearings for ultra-large diameter tunnel boring machines, main bearings for aero-engines, and main bearings for machine tools.

In July 2022, the project entered its "final push" phase. At the assembly site in Luoyang, Henan, researchers encountered another challenge: surface hardening machine tools and high-precision grinding machines could not meet the processing requirements of 8-meter bearings, while imported processing equipment was either banned from sale to my country or prohibitively expensive, requiring a two-year waiting period for production. A profound sense of frustration gripped everyone's hearts.

The Party Committee of the Institute of Metal Research decided to immediately form the "Li Xun Large Heavy-Duty Bearing Research Task Force," named after its first director. Led by Li Yiyi, Li Dianzhong, Hu Xiaoqiang, and others, and with the strong support of partner companies, the task force, in collaboration with various units, meticulously modified existing machine tools and painstakingly refined parameters on-site, tackling the most challenging problem in just two months.

The team broke through the then-current limit on the largest size of domestic quenching machine tools, achieving deep quenching control of the raceway surface of an 8-meter-class ultra-large diameter main bearing through equipment modification and process innovation.

By the end of September that year, this 41-ton 8-meter-class main bearing passed acceptance testing, with all technical performance indicators comparable to imported products of the same type.

At this point, the researchers, who had been working continuously, could finally breathe a sigh of relief. After returning home, Hu Xiaoqiang, suffering from severe eye swelling due to prolonged fatigue, said, "Only after the task was completed could I finally let out the pent-up frustration."

Demonstrating Real-World Achievements on the Front Lines of Engineering

Ultimately, products must withstand the test on the front lines of engineering projects.

With the support of the "Independent and Controllable Manufacturing of High-End Bearings" project, tunnel boring machines (TBMs) equipped with 3-meter main bearings developed independently by the Institute of Metal Research (IMR) have been successfully applied to the Shenyang Metro project. This marks the first time that domestically produced main bearings with a fully independent supply chain have been used in an infrastructure project, signifying the technology's transition from the laboratory to real-world application. The successful acceptance of the 8-meter main bearing signifies the complete completion of the domestic production chain for large-scale TBMs in my country.

In October 2025, during a working meeting between the Chinese Academy of Sciences and the State-owned Assets Supervision and Administration Commission of the State Council (SASAC), the IMR signed a cooperation agreement with CCCC Tianhe to demonstrate the application of domestically produced 8-meter main bearings. TBMs equipped with 8-meter main bearings will play a significant role in projects such as highway tunnels in Jiangxi Province.

The "Independent and Controllable Manufacturing of High-End Bearings" project has solved the challenges of domestic production of main bearings for high-end machine tools, large tunnel boring machines, and aero-engines. It has provided valuable insights for tackling key high-end basic components in my country, representing a positive practice of "connecting the technology chain, building the innovation chain, and linking the industrial chain," and vividly demonstrating the advantages of the new national system and collaborative innovation among government, industry, academia, research, and application.

"But this is not the end," Li Dianzhong explained. The main bearing industrialization base has now been officially established, laying a solid foundation for overcoming the "last mile" of tunnel boring machine domestic production. The radiating effect of the technology is also extending—the team is exploring the application of high-end bearing technology to wind power, tower cranes, port machinery, and even high-precision medical devices.

The team is ready to meet the next challenge of key technologies. The road ahead remains full of challenges, but this successful practice has proven that as long as we are committed to the country, grounded in reality, and pass on the torch, the Chinese people are fully capable of forging their own "steel spine" in key core technologies.