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Created on 09.04
TBM tunneling core component – Cutting Tool
TBM tunneling core component – Cutting Tool
TBM Composition – Cutting Tools
TBM cutting tools are used for excavating and machining rock and soil masses; they represent both a critical and wear-prone component of a Tunnel Boring Machine (TBM).
Their operating condition directly affects both the tunneling efficiency of the Tunnel Boring Machine (TBM) and the cost of tunnel excavation. The cutting tools of a TBM mainly include disc cutters, toothed cutters, scrapers, and other types. Based on their positions on the cutterhead, these tools are classified into center cutters, face cutters, and gauge cutters. The center cutter is located at the center of the cutterhead; for hard-rock TBMs and composite shield machines, the center cutter typically employs one or multiple double-edged disc cutters, while the face cutters and gauge cutters use single-edged disc cutters.
1. Disc cutter
The disc cutter is a tool commonly used by TBMs for excavating rock masses; it primarily consists of a cutter ring, a cutter body, a cutter body seal, and a cutter shaft. Depending on the number of cutter rings installed on the cutter body, the cutter can be configured as single-edged, double-edged, or multi-edged. Among these, the single-edged disc cutter is currently the most widely used type of cutter in full-face TBM applications and has been proven in engineering practice to be the most effective for rock breaking.
During operation, under the influence of the machine's thrust and torque, the cutter ring of the disc-type face mill penetrates the rock mass, and the rock-breaking process is accomplished through continuous rolling engagement with the rock mass. The disc-type face mill is primarily manufactured from special steel materials; the entire tool—particularly its cutter ring—must possess sufficient strength, stiffness, toughness, wear resistance, and high-temperature resistance.
Figure | Disc-type hob structure diagram
With the continuous advancement of technology and the increasing use of high-strength materials, the diameter of disc cutters and the loads they bear have been steadily increasing. Cutter diameters range from 11 in, 12 in, 14 in, 15.5 in, 16.5 in, 17 in, and 19 in to a maximum of 20 in (500 mm); the corresponding loads are shown in Table 2.4. Currently, cutters with diameters of 17 in or 19 in are most commonly used. The use of large-diameter disc cutters allows for an appropriate increase in the spacing between cutters on the cutterhead, reduces the number of cutters required, and enhances the cutterhead's propulsion force. This not only improves rock-breaking efficiency but also extends the service life of the cutting tools, reduces the frequency of cutter replacement during tunnel excavation, thereby increasing the total excavation time and improving overall excavation efficiency.
Figure | Schematic diagram of the rock-breaking mechanism using a rolling cutter
Early disc-shaped milling cutters featured a V-shaped cutter ring cross-section with cutting edge angles typically set at 60°, 75°, 90°, or 120°. Larger cutting edge angles were generally employed when excavating hard rock, whereas smaller angles were used for softer rock formations. However, due to the rapid wear and high susceptibility to fracture associated with the V-shaped cutter ring design, which increased tunnel excavation costs, this design was gradually replaced by cutter rings with conventional cutting surfaces.
Figure | Cutting Tool
2. Toothed cutter
The toothed cutter is primarily used for excavating soft soil layers such as sandy, silty, or clayey strata; it serves as the main excavation tool for shield machines and composite shield machines. The toothed cutter is mounted on the cutterhead panel; its operating principle differs from that of a disc cutter – rather than rolling over the tunnel face to fracture the rock, the toothed cutter excavates the excavated material as the cutterhead rotates and is propelled by the cutterhead's thrust.
Figure | Blade
3. Blade
The scraper, which is categorized into a front scraper and an edge scraper, serves as the excavation tool for shield machines and composite shield machines. The cutting principle of the front scraper is relatively straightforward: it utilizes the thrust transmitted from the cutterhead to penetrate the soil at the excavation surface; as the cutterhead rotates, the scraper cuts through the soil under the action of a tangential force. The edge scraper, located at the edge of the cutterhead, collects the rock debris excavated by the disc cutter; as the cutterhead rotates, this debris is conveyed through the chute on the cutterhead into a belt conveyor.
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