The main bearing of the shield machine, also known as the rotary table bearing or slewing support of the shield machine,
It is one of the core components of the shield machine, installed between the cutterhead and the shield body of the shield machine. Its main function is to support the weight of the shield machine cutterhead, withstand the huge axial force, radial force, and overturning moment generated by the cutterhead during excavation, and provide stable rotational support for the cutterhead to ensure that it can rotate and cut soil according to design requirements, achieving the excavation function of the shield machine.
Structural features: Large size and high precision: The main bearings of shield tunneling machines usually have a large diameter, usually around 3 to 6 meters, to adapt to different diameters of shield tunneling machine cutterheads. At the same time, in order to ensure the rotational accuracy and stability of the cutterhead, the manufacturing accuracy of the main bearing is extremely high, such as the radial and axial runout tolerances of the bearing are usually controlled within a few threads.
Multi row roller structure: The common main bearings of shield tunneling machines adopt a three row roller structure, including two rows of tapered rollers and one row of cylindrical rollers. Among them, two rows of tapered rollers mainly bear axial force and overturning moment, while one row of cylindrical rollers mainly bear radial force. This multi row roller structure can effectively distribute the load, improve the bearing capacity and service life.
Special sealing design: Due to the complex geological conditions underground, the main bearing of the shield machine needs to have good sealing performance to prevent soil, water, and other impurities from entering the bearing and affecting its normal operation. The main bearing usually adopts a combination of multiple lip seals and labyrinth seals to form a reliable sealing system. At the same time, special sealing grease is injected into the sealing structure to further improve the sealing effect.
Working principle: The main bearing of the shield machine is connected to the cutterhead and shield body through the inner and outer rings. When the drive system of the shield machine is started, the drive motor drives the inner or outer ring of the main bearing to rotate through transmission devices such as reducers, which in turn drives the cutterhead to rotate. During the rotation of the cutterhead, the rollers of the main bearing roll in the raceway, transmitting the load generated by the cutterhead to the shield body while ensuring the rotational accuracy and stability of the cutterhead. The lubrication system inside the main bearing continuously supplies lubricating oil between the rollers and raceways, reducing friction and wear, lowering the operating temperature of the bearing, and ensuring reliable operation of the main bearing under high load and long-term working conditions.
Technical requirements: High bearing capacity: Based on the excavation capacity of the shield machine and the diameter of the cutterhead, the main bearing needs to be able to withstand axial and radial forces of tens or even hundreds of tons, as well as overturning moments of thousands of Newton meters.
Long service life: A single excavation task of a shield machine usually takes several months or even years, requiring the main bearings to operate stably and without failure throughout the entire excavation process. Therefore, its design service life is generally more than 10 years, and it can withstand multiple load cycles during its service life.
Good reliability and stability: Once the main bearing fails during the shield tunneling process, it will cause the entire shield construction to come to a halt, resulting in huge economic losses and project delays. Therefore, the main bearing needs to have extremely high reliability and stability, and be able to work normally in complex geological conditions and harsh working environments.
In the past, the development status of China’s shield tunneling machine industry was constrained by the long-term dependence on imports for the main bearings of shield tunneling machines. In recent years, with the continuous improvement of China’s scientific and technological level, some domestic enterprises and research institutions have increased their investment in the research and development of shield machine main bearings, achieving certain breakthroughs. At present, some domestic enterprises have independently developed shield machine main bearings that meet certain engineering requirements, and have been applied in some domestic shield construction projects, gradually realizing the localization replacement of shield machine main bearings.
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