The "Chinese Heart" of the super-large shield machine approached the R&D team of the Institute of Metal Research, Chinese Academy of Sciences

The "Chinese heart" of the super large shield machine

Approaching the R&D team of the Institute of Metal Research, Chinese Academy of Sciences

　　Crossing mountains and ridges, crossing rivers and seas... The shield machine, known as the "king of construction machinery in the world", is an artifact for excavating tunnels, and it has shown its power in the fields of subway, high-speed rail, water conservancy and other infrastructure construction.

　　As a big country in infrastructure construction, although my country has realized the localization of shield machines, the core component of shield machines, the main bearing, has long relied on imports.

The exciting thing is that this status quo will be reversed.

　　Recently, the main bearing for super-large shield machine with a diameter of 8 meters was successfully developed by the scientific research team of the Institute of Metal Research, Chinese Academy of Sciences.

This is the first set of main bearings for shield machines with the largest diameter and single weight manufactured in my country, which has opened up the "last mile" of national production and independent controllable manufacturing of super-large shield machines.

It is understood that the 41-ton main bearing will be installed on a super-large shield machine with a diameter of 16 meters for tunnel excavation.

　　So, where is the difficulty in the design and manufacture of the main bearing, known as the "heart" of the shield machine?

How is its key core technology overcome?

The reporter recently interviewed the comrades in charge of the research and development team of the Institute of Metal Research, Chinese Academy of Sciences.

　　Long-term dependence on imports of high-end bearings is the pain point of my country's bearing industry

　　The shield machine was "stuck in the neck" by the main bearing

　　For many mechanical equipment, bearings are a very critical existence.

Bicycles, automobiles, high-speed rails, wind turbines, aero engines, etc., which are common around us, are inseparable from this core component if they need to rotate.

Its main function is to support the mechanical rotating body, reduce the friction coefficient during the movement, and ensure the rotation accuracy.

　　Take the shield machine as an example.

The main bearing is the core and key component of the cutter head drive system of the shield machine, known as the "heart" of the shield machine.

During the tunneling process of the shield machine, the main bearing "handholds" the cutter head to rotate and cut the tunnel face, and provides rotational support for the cutter head.

If the cutter head of a shield machine is compared to a shovel being excavated, then the main bearing is equivalent to the hands that control it.

　　Li Dianzhong, a researcher at the Institute of Metals, Chinese Academy of Sciences, specializes in the study of metal materials, and is also the person in charge of the strategic pilot technology project of "Independent and Controllable Manufacturing of High-end Bearings".

As a professional, he is well aware of the importance of bearings to a country's industry, especially high-end bearings represented by shield machine main bearings, marine engineering bearings, high-speed rail bearings, and wind turbine bearings.

"It can be said that high-end bearings are related to the security of the national economy and represent the manufacturing level of a country's basic components." Li Dianzhong told reporters.

　　However, the long-term dependence on imports of high-end bearings is a pain point for my country's bearing industry, and it is also one of the blocking points for my country's industry to be "stuck".

　　It is understood that the 15.03-meter super-large-diameter shield machine "Zhenxing" used for the excavation of the Nanjing and Yanlu cross-river passages, the 16.07-meter super-large-diameter shield machine "Canal" used for the excavation of the East Sixth Ring Road in Beijing, and the Zhuhai Xingye The localization rate of a large number of shield machines such as "Xingye", China's first ultra-large-diameter synchronous roadheader "Xingye", used for excavation of the Jiangyin Jingjiang River-crossing channel, and the 16.09-meter-diameter shield machine "Juli No. 1" has reached 98%, but the main bearing still relies on imports.

　　"Relying on imports, we not only cannot buy the best bearings, but also are subject to others in terms of technical services, delivery cycles and prices." Li Dianzhong said, this is also the "pain" in the hearts of researchers in related fields.

　　Why can't our country produce its own high-end bearings?

　　"The key lies in the fact that the materials used to manufacture the bearings and the processing accuracy of the large rollers are not good enough, and the technical chain of the whole process is not connected." Li Dianzhong told reporters that this is precisely the long-standing unfinished task of independent and controllable manufacturing of super-large-diameter main bearings for shield machines. main reason.

　　According to reports, during the excavation process of large-scale shield machines, they can only move forward, not backwards. Once the main bearing fails, serious losses will be caused. At least, ground structures will be demolished in the excavation area, and the new receiving shaft will be "planed out" after the shield machine Replacing the main bearing; in severe cases, the constructed tunnel will be invalidated, and the shield machine will be buried deep underground forever.

Therefore, the main bearing should have extremely high bearing capacity and reliability.

This puts forward very high requirements for the bearing steel used in the manufacture of the main bearing of the shield machine, as well as the complete design of the main bearing, machining accuracy, lubricating grease, etc.

　　National demand is the research direction.

In 2020, the Chinese Academy of Sciences launched the "High-end Bearing Independent Controllable Manufacturing" strategic pilot science and technology project. Seven scientific research units affiliated to the Chinese Academy of Sciences, including the Institute of Metals, the Chinese Academy of Sciences, and the Lanzhou Institute of Chemical Physics, formed an institutionalized team. Together with China Communications Construction Group Co., Ltd. More than 20 units including CCCC Tianhe Machinery Equipment Manufacturing Co., Ltd. have jointly tackled key problems, and successively solved 12 key core technical problems in main bearing material preparation, precision machining, and complete set design, and developed bearings with diameters ranging from 3 meters to 8 meters. There are a total of 10 sets of main bearings of the shield machine, which can be used for shield machines from 6 meters to 16 meters, opening up the "last mile" of independent and controllable manufacturing of shield machines.

　　"The reality tells us that we still need to make our own high-end bearings and go out of our own technical route." Li Dianzhong told reporters, "If we only rely on copying foreign technical routes, it will not only be easy to 'look the same in spirit', but will always be Run after someone else."

　　High purity, high homogeneity, high toughness, high wear resistance

　　Low-oxygen rare earth steel "touch stone into gold"

　　The "stuck neck" problem of high-end bearings is rooted in the material, and the difficulty lies in the material.

　　It is understood that the main bearing materials of the shield machine mainly include bearing steel, lubricating oil, cage and so on.

Among them, the core issue is the bearing steel material.

　　So, what is the standard of good steel?

Hu Xiaoqiang, a researcher at the Institute of Metals, Chinese Academy of Sciences and chief engineer of shield machine main bearing technology, listed several key words for reporters: high purity, high homogeneity, high strength and toughness, and high wear resistance.

　　High purity means that the steel has high purity and few impurities; high homogeneity means that the composition and hardness of different parts of the parts are relatively uniform; high strength and toughness means good strength and toughness, high bearing capacity and stability; high resistance Grinding refers to the use of bearings with small wear and tear and long service life.

　　"A main bearing with a diameter of 8 meters can carry a maximum axial force of 105 kN during operation. If an adult Asian elephant weighs 4 tons, this axial force is equivalent to the gravity of 2,500 adult Asian elephants. "Hu Xiaoqiang further explained.

　　Ordinary steel obviously cannot meet the requirements, and it is necessary to find a special steel that can meet the above criteria.

Li Dianzhong thought of rare earths.

　　"A large number of studies have shown that adding trace amounts of rare earths to steel can significantly improve the ductility, wear resistance, heat resistance, corrosion resistance, etc. of steel." Li Dianzhong told reporters that in the industrial field, rare earths are known as "industrial vitamins." , and rare earth is precisely the superior resource of our country.

　　However, rare earth steel encounters two major problems in industrial production: one is that the process is not smooth, and there is a serious clogging of the gate; the other is that after the rare earth is added to the steel, the performance of the steel fluctuates violently, and there is a problem of poor stability.

And this is also the reason why the research and application of rare earth steel in my country changed from hot to cold.

　　Of course, Li Dianzhong and the others are also facing the same problem.

"We have tried commercial rare earths of various purity, but the performance of the rare earth steel produced in combination with steel is still unstable." Li Dianzhong recalled that in order to find out the reason, he and his team members almost traveled all over my country's rare earth producing areas, and went to Observe the rare earth smelting process at the production site.

　　Finally, after running around again and again, they discovered the crux of the problem: it turned out that there was a conceptual deviation between the rare earths produced by the processing plant and the rare earths he needed.

　　"In order to make the rare earth more pure, the manufacturer separates the iron, carbon and other elements in it, and this is an indispensable component for steelmaking, but ignores the oxygen element that should be removed." Li Dianzhong He told reporters that after a lot of research, they found that the root cause of rare earth steel performance fluctuations and gate clogging is the oxygen content. It also has a great impact on the performance of rare earth steel."

　　After a large number of experiments, calculations and characterizations, they revealed the main mechanism of action of rare earths in steel, and prepared low-oxygen rare earth steels with superior performance and good stability by controlling the oxygen content.

　　The secret of the key technology of low-oxygen rare earth steel is to control both the oxygen content of molten steel and the oxygen content in the added rare earth, so it is also called "double hypoxic".

　　"Among the 12 key core technologies, the successful development of low-oxygen rare earth steel is the key." Li Dianzhong told reporters that only about 100 grams of rare earth need to be added to 1 ton of steel, and the cost only increased by more than ten yuan. But the fatigue life can be increased by an order of magnitude.

Compared with the bearing steel without adding rare earth, the tension and compression fatigue life of the rare earth bearing steel is increased by more than 40 times, and the rolling contact fatigue life is increased by 40%, which effectively solves the bottleneck problem in the industrial application of rare earth steel.

　　In this technical battle of rare earth steel, scientific researchers "turned stone into gold".

After the approval of relevant departments, the Institute of Metals, Chinese Academy of Sciences took the lead in formulating a number of rare earth steel industry standards, and gradually popularized and applied them.

At present, the comprehensive mechanical properties of rare earth bearing steel produced by relevant cooperative enterprises are better than those of imported products.

　　Breakthrough roller precision machining technology

　　The main bearing with a diameter of 8 meters has a service life of more than 10,000 hours

　　As the New Year approached, Hu Xiaoqiang went to a bearing processing and manufacturing company in Luoyang, Henan Province again to discuss on-site the process of manufacturing the main bearing of the shield machine.

And this is also the place where Hu Xiaoqiang has traveled the most times in recent years.

　　According to reports, the main bearing of the shield machine is usually composed of rings, cages, rollers and other components.

"The composition is not complicated, but the process is very complicated." Hu Xiaoqiang told reporters that to turn high-end materials into high-end bearings, more than 100 processes such as forging, machining, and heat treatment are required. As a result, the service life of the bearing is not long and the performance is out of control. "If you want to make a good bearing, you must not lose the chain in every link."

　　The roller is the key element to bear the load when the main bearing of the shield machine is running, and it is also the weakest part in the large roller bearing.

High-end bearings have extremely high requirements on the machining accuracy of the rollers.

　　"Rollers are the most numerous elements in a bearing, including radial rollers, main thrust rollers and auxiliary thrust rollers." Hu Xiaoqiang said that there are more than 400 in the main bearing of a shield machine with a diameter of 3 meters. There are more rollers in the 8-meter main bearing, and there are nearly a thousand rollers.

Its manufacturing quality has a great influence on the working performance of the bearing and is the main factor affecting the service life of the bearing.

"The diameter error, surface finish and other indicators of these hundreds of rollers must be controlled within 1 micron. Exceeding this value will lead to deviations in the operation of the shield machine."

　　Hu Xiaoqiang once conducted research and analysis on the quality and production of the rollers together with the team members, and found that the rollers in the imported main bearings have very high precision, whether it is in terms of roughness, hardness uniformity, or plain lines on the working surface. It looks very good, but due to the limitation of equipment in China, the machining accuracy of large rollers can only reach the second level, and the first-level precision machining cannot be achieved.

　　Go deep into the production line, and jointly collect intelligence with key enterprises to tackle key problems... Hu Xiaoqiang and his team members successfully overcome the problems of high-precision machining and precision maintenance of the main bearing, and developed a first-class roller with a diameter of more than 100 mm, which made a breakthrough in my country's bearing industry The first-class large-scale roller precision machining technology has been achieved.

　　This is just one example.

That's it, with the support of the pilot project, the Institute of Metals of the Chinese Academy of Sciences has integrated 12 teams including bearing steel, heat treatment, and cages, and gathered the strength of 7 research institutes of the Chinese Academy of Sciences to form a whole-life team covering R&D, materials, manufacturing, evaluation and service. Cycle's full-chain team has achieved innovation from 0 to 1, from materials to components.

　　"In the beginning, if we wanted to make a good bearing, we had to travel almost half of China." Li Dianzhong said, for example, forging in Guangdong, turning in Shandong, heat treatment in Liaoning, grinding in Zhejiang, and assembly in Heilongjiang and Zhejiang. , The bearing field test will return to Guangdong again.

Now, it has realized the independent and controllable "one-stop" service of the whole process of processing and manufacturing, assembly and debugging, testing and evaluation.

　　Bearing development took 3 years.

The scientific research team used 1467.4 tons of rare earth bearing steel to develop 41 large rings, 7996 rollers, and 492 copper-steel composite cages, and 369,000 welds were welded.

In the end, domestically produced shield machine main bearings with diameters ranging from 3 meters to 8 meters were born one by one.

　　At present, the main bearing with a diameter of 3 meters for the shield machine has been successfully applied in the Shenyang subway project.

The main bearing of the ultra-large shield machine with a diameter of 8 meters has also been delivered to the relevant shield machine manufacturer. "The service life will exceed 10,000 hours, and the continuous excavation length will exceed 10 kilometers." Li Dianzhong told reporters that the next step of the research team The goal is to create main bearings for shield machines with a service life of more than 15,000 hours and a tunneling length of more than 15 kilometers, and to develop main bearings for shield machines with different diameters according to requirements.

　　Connecting the technology chain, creating the innovation chain, and connecting the industrial chain... This is a vivid practice of my country's self-reliance in science and technology, supporting and guaranteeing the development of the entire life cycle of the industry, and it also provides a good paradigm for my country's high-end basic parts and components.

(Reporter Wang Zhen from China Discipline Inspection and Supervision News)