December 15, the reporter learned from the Institute of Metals of the Chinese Academy of Sciences, the Institute's researcher Li Dianzhong, Chinese Academy of Sciences, Li Yi Yi team led the research and development of super-large shield machine with a diameter of 8 meters main bearing successfully. The main bearing is the first set of the largest diameter and single weight shield machine with the largest main bearing manufactured in China, will be installed in the independent research and development of the domestic diameter of 16 meters super-large shield machine.

 

 

 

 

15 years of research to break through key problems

Aircraft engines, shield machines, high-grade CNC machine tools and other high-end equipment are inseparable from the bearings. At present, although China has achieved the localization of shield machine, but the core key component of its cutter drive system - the main bearing is still dependent on imports. In the process of shield tunneling, the main bearing "holds" the cutter, rotates to cut the excavation surface and provides rotational support for the cutter. It works at a very slow speed of less than 3 revolutions per minute, which means that the maximum axial force during the operation of the 8m diameter main bearing will reach 100,000 kN, the radial force 10,000 kN and the overturning moment 100,000 kN-m.

"If an adult Asian elephant weighs four tonnes, the axial maximum force on the main bearing will be equivalent to the weight of 2,500 Asian elephants." Li Dengzhong compared it to the 8m diameter main bearing, which is already the largest diameter rating and weighs 41 tonnes. What's more, once the main bearing is loaded into the shield and excavation begins, it cannot be "driven backwards". "The shield can only go forward, not backward, and if the bearings fail, the damage will be huge."

Such high load-bearing capacity and high reliability standards require the bearing steel used to manufacture the main bearings to be highly pure, homogeneous, strong and wear-resistant, and also place high demands on the design, machining accuracy and grease of the main bearing sets.

Chinese Academy of Sciences in 2020 launched a "high-end bearing independent controlled manufacturing" strategic science and technology pioneer special project, the Chinese Academy of Sciences Institute of Metals, the Chinese Academy of Sciences Lanzhou Institute of Chemical Physics and other seven scientific research units to form the establishment of the team, the joint CCCC Group's CCCC Tianhe Machinery Equipment Manufacturing Co. Ltd. and other more than 20 units to collaborate in the research.

Previously, in the development of bearings, China has been faced with two major problems - the manufacture of bearing materials and large roller processing accuracy is not off, the whole process technology chain is not through. To make a breakthrough, we need to solve the problem from the source of material manufacturing, so the research team set its sights on rare earth bearing steel.

A large number of studies have shown that the addition of trace amounts of rare earths in steel can significantly improve the toughness and plasticity, wear resistance, heat resistance, corrosion resistance and so on. "We also call rare earths 'industrial vitamins', and only 100 or so grams of rare earths are needed in 1 ton of rare earth steel." As the bearing pioneer special person in charge, Li Dianzhong introduced, rare earth is China's advantageous strategic resources, but previously on the research and application of rare earth steel repeatedly frustrated. After the addition of rare earths in the steel, it is easy to have serious blockage of the sprue, and will lead to dramatic fluctuations in the performance of steel and poor stability.

A team of researchers at the Institute of Metals, Chinese Academy of Sciences, has finally found the answer to this problem - the oxygen content - after 15 years. By reducing the oxygen content in rare-earth steels and rare-earth metals, their properties are extraordinarily stable. The key technology of "low-oxygen rare-earth steel" allows rare-earth bearing steel to increase its fatigue life by more than 40 times in tension and 40% in rolling contact. With the help of this technology, domestic enterprises have manufactured tens of millions of sets of high-quality bearings.

Excellent performance of many indicators

However, only rely on the quality of rare earth bearing steel is not enough, bearing processing accuracy, grease materials, bearing heat treatment and other issues are also critical.

Due to the limitation of processing equipment, the processing accuracy of large rollers in China can only reach the second level, compared with the more stringent standards of the first level of precision processing is still a gap. Shield machine main bearing development technology master, the Chinese Academy of Sciences Institute of Metals researcher Hu Xiaoqiang joint enterprises to carry out research, so that China's bearing industry breakthrough a large roller precision machining technology, and to achieve the shield machine main bearing processing and manufacturing, assembly and commissioning, testing and evaluation of the whole process of independent control, while driving the development of related domestic equipment.

The stable operation of bearings cannot be achieved without good lubricating materials. Through the structural design of core additives and the development of controllable preparation technology, the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences has formed an independent ratio and combination composition of main bearing lubricating grease, and developed a grease that can still maintain good lubrication under impact loads and make the rollers wear less.

"Our team came from a materials background, but during the development of the shield machine main bearing, we stepped out of the scientific research 'comfort zone' and completed the transition from 'what we can do' to 'what we should do '. Materials should become materials, materials should become tools, and tools should work well." Li Dengzhong said, through the multidisciplinary team and enterprise joint collaborative research, the team broke the industry barriers of materials and machinery manufacturing, "the successful development and application of the main bearing, is the concentration of domestic technology and equipment capabilities."

At present, the 8m-class main bearing is the first set of main bearings for shield machines with the largest diameter and the largest single weight in China. A number of its indicators are better than similar foreign products, the content of a non-metallic inclusions within the material is only a few hundred thousandths, compared to imported products reduced by an order of magnitude; rare earth steel material inclusions are small and round, the size is smaller than imported bearing steel, fatigue strength is also more than imported products to improve more than 100 MPa.

National Bearing Quality Inspection and Testing Center testing and expert group review that the main bearing of the technical performance indicators and imports of similar main bearings are comparable, to meet the super-large? The main bearing has been developed to meet the needs of super-large machine installation applications. The successful development of the main bearing signifies that China has mastered the independent design, material preparation, precision machining, installation and commissioning and testing and evaluation of the integrated technology of the shield machine main bearing.

At present, the pilot project has solved 12 core key technical problems in the material preparation, precision processing and complete set design of the main bearing, and developed a total of 10 sets of shield machine main bearings from 3m to 8m in diameter. Previously, the 3m diameter shield main bearings have been installed in shield machines produced by BHI Group and were successfully applied in the Shenyang metro project in April 2022. Subsequently, the 8m-class main bearings will be installed on the 16m-diameter super-large shield machine for tunneling works.

端）