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Created on 08.31
Selection, Types, and Functions of Pipe Jacking Tools
During underground drive, excavation equipment encounters various geological strata, such as clay, sand, soft rock, and hard rock. As excavation progresses and the cutterhead rotates, the shield scraping cutters are subjected to continuous and variable forces, including squeezing, thrusting, scraping, impact, and friction. This primarily manifests as intense wear and impact on the cemented carbide tips, shear failure at the brazing (welding) joints, and abrasive-impact wear on the cutter body.
Therefore, tool selection must first consider the geological applicability of the tools. In engineering projects, the properties of different rock and soil masses vary significantly; thus, tools must be selected and reasonably configured according to specific geological conditions. Geological characteristics, tool structural and performance parameters, rock/soil fragmentation and spalling behavior, and boring parameters of the machine are critical bases for tool selection and layout, closely influencing the cutting and rock-breaking efficiency of the tools.
Currently, the tools in use are generally classified into two main categories based on their functions: rolling cutters and scraping cutters.
Rolling Cutters (Disc Cutters)
01
Rolling cutters refer to rock-breaking tools that not only revolve with the cutterhead but also perform self-rotation at the same time. According to the number of cutter rings, they can be classified into: single-disc cutters, twin-disc cutters, and multi-disc cutters, etc.
Disc Cutters
- Single-disc cutters possess strong rock-breaking capability and are primarily used for hard rock tunneling; they can also be retrofitted as carbide-button disc cutters.
- Twin-disc cutters are generally installed in the central area of the cutterhead.
- For raise boring cutters, the cutter teeth are welded directly onto the cutter body. When the teeth are damaged, the entire raise boring cutter assembly must be replaced, resulting in relatively high operating costs.
Scraping Cutters
02
Scraping cutters refer to rock-breaking tools that only rotate with the cutterhead and do not self-rotate. There is a wide variety of scraping cutters; currently, the most commonly used scraping cutters on tunnel boring machines (TBMs) include face scrapers, gage scrapers, pre-cutting cutters (rippers), and copy cutters (overcut cutters).
Center Fishtail Cutters
The fishtail cutter cuts into the soil at the center of the cutterhead ahead of other cutters to loosen the ground. By improving the fluidity of the soil mass in the central area, it facilitates the excavation for other cutters, reduces their cutting resistance, and minimizes their wear and tear.
Scrapers (Scraping Cutters)
Scrapers are installed on the curved periphery of the cutterhead. They are used to cut soft soil as well as soft rock, and to clear scraped muck. In hard rock conditions, they can function as muck scrapers to clear debris.
Pre-cutting Cutters (Rippers / Shell-shaped Cutters)
During soil excavation, pre-cutting cutters cut into the soil mass before the main scraping cutters do. By slicing and dividing the soil into blocks, they create favorable cutting conditions for the subsequent scraping cutters.
Protection Cutters (Gage & Wear Protection)
Protection cutters come in various shapes and sizes, including disc cutter housing protection cutters, cutterhead periphery protection cutters, foam port protection cutters, and cutter seat protection cutters. Their primary function is to leverage the high hardness of their embedded cemented carbide to protect critical areas of the cutterhead during shield tunneling.
Copying Cutter
The Copying Cutter (Overcutting Cutter) is designed for curve advancement, turning, and path correction; it is installed on the edge of the cutter head and its extension distance is controlled by a hydraulic cylinder.
Scratching tools are primarily suitable for excavating soft clay, sandy soil, and sandy-gravelly strata; rolling tools are suitable for excavating medium-hard and hard rock strata.
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