| 摘要 |
A pneumatic percussion boring device, which is particularly intended for boring tunnel-like holes in the ground, comprises a percussion boring tool which is mounted in a tubular housing, a percussion piston which, in operation, reciprocates in the housing and acts on the tool, and a displacement piece which is mounted on the boring tool for laterally displacing the soil through which the boring is being made. The displacement piece tapers in the direction of boring and is formed around its periphery with a series of annular cutting edges. The displacement piece is preferably stepped with each step being of an increasing diameter in a rearward direction with one of the cutting edges extending around the outer periphery of each step. The forwardly directed face of each step may be undercut with a concave annular depression which increases the sharpness of the cutting edge at the outside of the step.
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