The cutterhead is a critical component of a shield machine; during the tunneling process, it serves the functions of crushing rock and soil, facilitating muck flow, and providing support to the tunnel face.
Mechanical Structure
Currently, shield machine cutterhead structures primarily fall into three categories: spoke-type, disc-type, and a composite structure combining both spokes and discs. Large and medium-sized shield machine cutterheads typically employ a central support configuration. The particle passing rate-the proportion of the cutterhead's open area-is approximately 67% for spoke-type cutterheads and 33% for disc-type cutterheads.
Cutter Materials and Key Technologies
The "teeth" of a shield machine are the cutters mounted on its front-end cutterhead. On the working surfaces of these cutters-where direct "confrontation" with rock is required-hard alloys are utilized; these materials possess a hardness second only to that of diamond. Shield machine cutters must possess sufficient hardness to ensure wear resistance, adequate strength to prevent fracture, and sufficient toughness to withstand impact forces. One of the critical factors determining this strength and toughness is the precise control of grain size during the preparation of tungsten carbide powder. Advanced technologies in this field allow for the production of WC (tungsten carbide) grains with sizes as fine as 9 micrometers. Other key related technologies include novel multi-field, multi-scale regulated brazing techniques featuring ultrasonic and nano-modification composite reinforcement, as well as new laser additive manufacturing methods for high-carbon, high-hardness disc cutters.
Auxiliary and Intelligent Systems
A ring of hydraulic jacks is positioned behind the cutterhead of the shield machine. A foam mixture is injected to facilitate the cutterhead's agitation of rock and to soften the soil, thereby reducing the difficulty of the tunneling operation. Modern cutterhead configurations often feature designs optimized for soft ground, incorporating the capability for atmospheric-pressure cutter replacement. The cutterhead is equipped with sensing elements capable of monitoring the operational status of the cutters in real time. By increasing the cutterhead's opening ratio, integrating a high-pressure, high-flow central flushing system, and deploying a cutterhead "muck-caking" early warning system-supplemented by retractable camera devices-it is possible to observe the conditions within the cutterhead's working zone without requiring personnel to enter the chamber under pressure.
