Comprehensive Guide to Slewing Bearings for Shield Machines

What is Shield Machine?

A shield machine, also known as a tunnel boring machine (TBM), is a heavy piece of machinery used for constructing tunnels. It is designed to excavate and remove material from tunnel sites, while simultaneously installing precast tunnel segments to create a stable tunnel structure. Shield machines are used in a wide range of construction projects, including subways, railways, and underground utility networks. They work by employing a rotating cutter head mechanism, which digs through and breaks apart the soil or rock, enabling the creation of tunnels in various geological conditions.

How Shield Machines Work？

Shield machines, also known as tunnel boring machines (TBMs), are specialized pieces of equipment designed to excavate and construct tunnels with high precision and efficiency. They are widely used in various construction projects, such as subways, railways, and underground utility networks. The following is a general overview of how shield machines work:

1. Cutter head excavation: At the front of the shield machine, there is a rotating cutter head. The cutter head is equipped with cutting tools (such as disc cutters and scraper tools) that excavate the ground by chipping, grinding, or cutting. As the cutter head rotates, it applies pressure against the tunnel face, breaking away soil, rock, and other materials.

2. Material removal: The excavated materials, also known as muck, are removed from the tunnel face through a series of processes. First, the muck falls onto a conveyor belt running inside the shield machine or is transferred by a screw conveyor system. The conveyor system transports the muck to the rear of the machine, from where it is loaded onto trains or trucks for disposal or further processing.

3. Tunnel support and lining installation: As the shield machine advances, it installs precast tunnel lining segments behind it to create a stable tunnel structure. These lining segments are guided into position by an erector mechanism, which uses a set of hydraulic jacks to hold, lift, and place them accurately and quickly. Once the segments are in place, they are held together by locking mechanisms such as bolts or compression joints, forming a continuous ring to support the tunnel walls.

4. Advancing the shield machine: After a segment of the tunnel lining is installed, the shield machine moves forward to continue the excavation process. This advancement is achieved through a set of hydraulic jacks that push against the newly installed tunnel lining segments, propelling the machine forward in small increments.

5. Steering and guidance: Shield machines are designed to maintain precise alignment as they move through the tunnel. An advanced guidance system, typically based on lasers and electronic sensors, monitors the machine's position and alignment in real-time. The shield machine operators use this information to make steering adjustments, such as modifying the thrust of the hydraulic jacks or altering the cutter head orientation, to maintain the desired tunnel path.

In summary, shield machines work by excavating the tunnel face using a rotating cutter head, removing the excavated material through a conveyor system, and installing precast tunnel lining segments to form a stable tunnel structure. The machine advances by pushing itself forward with hydraulic jacks and follows a predefined tunnel path using advanced guidance systems.

Where in Shield Machines are Slewing Bearings Used?

In shield machines, slewing bearings are essential components that enable smooth and precise rotation in various parts of the machinery. They are most commonly used in the following areas:

1.Cutter Head Assembly: Slewing bearings play a crucial role in the cutter head assembly by enabling the cutter head to rotate smoothly and apply the necessary torque to the excavation face for tunneling.

2.Segment Erector Mechanism: Slewing bearings can also be found in the segment erector mechanism of the shield machine. They facilitate rotation during the installation of tunnel lining segments, ensuring proper alignment and placement of the segments to form a stable tunnel structure.

By providing support, load handling, and precise rotational movement, slewing bearings significantly contribute to the efficient functioning of shield machines in tunnel construction projects.

What are the Types of Slewing Bearings for Shield Machines?

There are several types of slewing bearings suitable for shield machines, designed to meet specific load and application requirements. Some common types used in shield machines include:

1. Single-row ball slewing bearings: These bearings consist of a single row of balls and are suitable for low to medium load capacities, both axial and radial, as well as low moment loads. They enable smooth rotation and are often used for smaller shield machines or those with less demanding requirements.

2. Double-row ball slewing bearings: These bearings feature two rows of balls, providing higher load-carrying capacity and increased stiffness compared to single-row ball slewing bearings. They are commonly used in larger shield machines or those experiencing higher forces during the tunneling process.

3. Crossed roller slewing bearings: In these bearings, cylindrical rollers are arranged at right angles to each other, offering increased stiffness and load-carrying capacity while maintaining a compact design. They are particularly suitable for applications requiring high precision, minimal deflection, and rigorous performance demands, which are often encountered in shield machines.

The specific type of slewing bearing chosen for a shield machine will depend on various factors, such as the size and design of the machine, tunnel dimensions, and the expected forces and loads during the excavation process. Customized solutions are often required to meet the distinct needs of individual projects.

Dimensions of Slewing Bearings for Shield Machines