TBM Tools and Rock-Breaking Principles

Currently, the cutters used in shield tunneling machines are generally divided into two main categories: scraping cutters and rolling cutters.

Scraping Cutters (Scrapers, Rippers): Scraping cutters refer to rock-breaking cutters that only rotate with the cutterhead and do not rotate on their own axis. There is a wide variety of scraping cutters. Currently, the commonly used scraping cutters on shield tunneling machines include gauge scrapers, scrapers, bucket teeth, precutters, ripping cutters, fish-tail cutters, etc.

Rolling Cutters (Disc Cutters / Rollers): Rolling cutters refer to rock-breaking cutters that not only rotate with the cutterhead but also rotate on their own axis simultaneously.

According to the shape of the cutting edge, rolling cutters can be divided into: toothed cutters (steel teeth and insert teeth) and disc cutters (steel ring disc cutters and insert ring disc cutters).

According to the installation position, rolling cutters can be divided into: center cutters, face cutters, gauge cutters, and reaming cutters.

The rolling cutters used in shield tunneling machines are mainly disc cutters, which can be further classified into single-edge, double-edge, and multi-edge variants.

According to the outer diameter of the cutting edge, they are divided into specifications such as 13, 15, 17, and 19 inches, with the 17-inch series being the most widely used currently. (Inches: 1 inch = 25.4 mm; 17 inches = 17 x 25.4 mm).

Under the thrust applied by the longitudinal hydraulic cylinders, the cutterhead forces the disc cutters mounted on it to penetrate into the rock. Driven by the rotation system, the cutterhead carries the rolling cutters to revolve around the central axis of the cutterhead. At the same time, each rolling cutter rotates around its own cutter shaft, causing the cutters to continuously roll and crush on the rock face. The cutterhead applies both thrust and rolling force (torque) to the cutter rings. The thrust forces the cutter ring into the rock mass, while the rolling force causes the cutter ring to roll across it. Through the extrusion and shearing actions of the rolling cutters on the rock mass, the rock is fractured, cutting a series of concentric circles on the rock face.