A photo taken in September 2021 shows metal bearing equipment used for the Shenyang subway. CHINESE ACADEMY OF SCIENCES 

China has successfully made its first giant main bearing for tunnel boring machines, a major engineering breakthrough that experts said would allow the country to reduce its imports of the core component for building underground infrastructure such as subways.

The bearing has a diameter of 8 meters and weights 41 metric tons. It is the largest and heaviest bearing China has made and it would be installed on an ultra-massive tunnel boring machine with a diameter of 16 meters, according to the Institute of Metal Research of the Chinese Academy of Sciences.

Tunnel boring machines are instruments of national significance as they are used in building tunnels underground and under bodies of water, said Li Dianzhong, a researcher from the institute and the chief scientist for the project.

In general, metal bearings are used to reduce friction and wear between running surfaces. Many types of industrial equipment, including those used for aircraft engines, cars, high-speed rail and wind turbines, require high-performance bearings.

"Therefore, high-end bearings are key for the national economy and security, and they represent a nation's manufacturing capability in basic components," he said.

The main bearing for tunnel boring machines needs to withstand a massive amount of force as the huge equipment digs through earth, with only a handful of nations possessing the engineering capability to make it.

In 2020, the Chinese Academy of Sciences launched a major research project, combining the expertise of seven CAS institutes and over 20 other companies and organizations, to jointly tackle the challenge.

After overcoming 12 core challenges, from materials manufacturing to design and precision machining, the research team created bearings sized from 3 to 8 meters in diameter for the boring machines. The 3-meter version has since been used in subway construction in Shenyang, Liaoning province.

On Sept 30, the 8-meter bearing passed expert appraisals — they concluded that the performance of the domestically made bearing is on par with imported ones.

"The creation of the 8-meter bearing is a testament to China's research and manufacturing prowess," Li said. (China Daily)