The modeling characteristics and structural composition of shield tunneling cutt

source：http://www.xrocktools.com/ Release Time：2015-01-11 10:10:07

For shield tunneling machines, the excavation system refers to the excavation cutterhead and its drive system. The excavation system has a decisive impact on the construction efficiency of the shield machine, and the difference in selection also has a significant impact on the cost of the shield machine. The selection of the cutterhead can affect 4% to 8% of the total cost, especially the equipment torque of the excavation equipment, which is one of the most basic parameters of the shield machine. The shield tunneling machine excavation cutterhead is a disc-shaped excavator that rotates or shakes, consisting of cutting tools for excavating the formation, a panel for stabilizing the excavation surface, an excavation groove, a driving mechanism for rotation or shaking, a bearing mechanism, etc.

1. Factors affecting shield tunneling wear

Under the propulsion force of the shield machine, the shield cutting tool exerts a certain pressure on the excavation surface soil. As the cutterhead rotates, the tool rubs against the soil and sand abrasive, resulting in wear. The wear of cutting tools is related to geological conditions, the material of shield tunneling tools, and their installation position on the cutterhead, and increases with the increase of cutting mileage. The cutting tools arranged around the cutter head wear out quickly, are prone to breakage, and have a short lifespan due to their high linear velocity and long cutting path. The main forms of tool damage include tool wear and detachment. The wear of cutting tools is influenced by the material, hardness, applied thrust, geological conditions, and the depth, speed, and time of cutting by the tool; The detachment of cutting tools is mainly related to the installation method, and is also affected by the wear of the tool handle, gravel, and obstacles during construction. Shield tunneling machines encounter various geological formations during excavation, ranging from silt, clay, sand layers, sand and gravel layers to soft and hard rocks. During the excavation process, the cutting tools are subjected to complex forces and the working environment is harsh. The wear of cutting tools is closely related to the construction layer. Strata such as silty clay, silty clay, and clayey silt have little wear on cutting tools, while sand and gravel formations have severe wear on cutting tools, even causing them to break. This situation has been confirmed in the already constructed projects.

2. Analysis of wear and tear of shield cutting tools in the structural components of shield tunneling machines

3.1 Knife ring fracture

The material used for the cutting ring is not suitable for the geological lithology. When the compressive strength of the rock is high, the hardness requirements for the cutting ring itself are also high, and the impact resistance of the cutting ring decreases accordingly, which will cause the cutting ring to fracture, known as impact fatigue fracture. When the interference fit of the clearance exceeds the specified value, the significant temperature difference between the inside and outside of the tool during excavation will cause the tool ring to break, known as internal stress fracture. Poor cooling effect of cutting tools during excavation, especially in mud, clay geology or rock fracture zones where the tools are wrapped, will cause the cutting ring to break, known as internal stress fracture.

3.2 Bearing damage and eccentric wear of the cutting ring

The sealing effect of engineering cutting tools is poor, including sealing clearance, rubber elasticity and hardness, mechanical seal flatness, mechanical seal surface hardness and wear resistance, etc. After mud and sand enter the interior of the cutting tool, the bearing is damaged and the cutting ring experiences eccentric wear; The thermal expansion coefficient of lubricating grease exceeds the specified limit, causing the sealing grease to overflow when the tool is heated, mud and water to enter the tool bearing during cooling, or the internal air is not completely discharged during assembly, resulting in bearing damage and eccentric wear of the tool ring; When the assembly clearance of the rotating parts of the cutting tool is unreasonable and the torque of the cutting ring exceeds the specified value, the bearing accelerates wear and is damaged; When the rotational torque is lower than the specified value, it causes excessive free clearance between the seal and the sealing surface, resulting in seal failure, mud and water entering, causing bearing damage and eccentric wear of the cutting ring.

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