"Make New glory for China" - the development process of the world's largest diameter shield machine main bearings

In large-scale tunnel construction, shield tunneling machine is an indispensable "magic weapon". As the core component of shield machine, main bearing is the key to ensure the safe and reliable operation of equipment. Recently, China Railway Construction Heavy Industry Group Co., LTD. (hereinafter referred to as "Railway Construction Heavy Industry") successfully developed the world's largest diameter shield machine main bearing with a diameter of 8.61 meters and weighing 62 tons, once again setting a new milestone for Chinese manufacturing.

"Casting indestructible Shields"

During the driving process of the shield machine, the 8.61m main bearing needs to withstand the test of extremely harsh working conditions. In order to ensure that the main bearing is strong enough, the first challenge faced by the R&D team is the material and process.

"For the inner gear ring of the main bearing, it needs to reach the standard of Rockwell hardness greater than 58 and thickness of not less than 8 mm to withstand the load of over 10,000 tons." Research and development team manufacturing process leader Xie Jindong pointed out

This 8mm ring is called the "shield" and is the key to the resistance of the main bearing to heavy pressure. The conventional domestic medium carbon bearing steel hardening process can only reach the Rockwell hardness of 55, surface hardening depth of 5 mm, therefore, the R & D team jointly with steel enterprises, after dozens of technical discussions and tests, finally determined the steel standard suitable for the manufacture of large diameter main bearings.

In order to overcome the problem that the monolithic quenching process could not be applied to the 8.61 m main bearing, the developers tried a variety of methods. Finally, inspired by the ancient "earth covered burning blade" manufacturing process, the R & D team successfully developed a new high temperature resistant medium to solve the problem of uneven temperature in the quenching area.

"Pursuing the ultimate flatness"

Another challenge is how to precisely control the flatness of the floating ring. The floating ring is one of the core components of the main bearing, and its inner wall must be smooth enough to avoid the failure of the entire system due to local damage.

Compared with the previous 3-meter diameter main bearing, the weight of the 8.61-meter main bearing has increased by about 8 times, and the inner wall circular area has increased by nearly 9 times. However, the control requirements for flatness are still strict, and the error cannot exceed 20 microns, which is equivalent to the wall fluctuation cannot exceed one-fifth of the thickness of an A4 paper.

At the beginning of the development, the floating ring will appear obvious distortion after a long time of processing and adjusting the flatness. Through many on-site consultations of experts, it was finally found that the reason was overheating deformation caused by long-term and large-area contact friction between the grinding wheel and the floating ring.

To solve this problem, the team modified the wheel to reduce the contact area by adjusting the shape of the wheel, while ensuring that the wheel trajectory covers every part of the inner wall. This improvement enabled the team to successfully manufacture floating rings that met the flatness requirements.

"A New Chapter in Independent Design"

In order to adapt to a variety of complex working conditions, each shield machine needs to be customized according to engineering requirements, which means that the main bearing must be customized accordingly. Before this, although the main bearing can be manufactured, the design process depends on foreign manufacturers, which is time-consuming and costly. The R&D team decided to implement their own design. They made it as they went along, using experimental data to reverse design methods. The process was fraught with challenges, for example, when a key calculation formula stuck and the team got stuck. After countless calculation adjustments, a series of parameters are finally determined and the formula is successfully verified.

In order to further improve the design accuracy, the team used years of construction experience and data to build a simulation model, successfully developed a special design and simulation software for the main bearing, and realized a closed-loop design verification system. In October 2023, the domestic 8.61-meter main bearing successfully rolled off the assembly line, marking that the Railway Construction Heavy Industry broke through the four major technical problems of material, process, design and verification, and realized the localization of the design and manufacture of the main bearing product spectrum with a diameter of 3 meters to 8.61-meter.