Importance

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Abstract

A drawing device 4 is mounted in a drawing shaft 3, and pipe replacement device A connected with new pipes is arranged on the side of starting shaft 2, wherein the drawing device 4 and the pipe replacement device A is connected through pull-rods 5 inserted into existing pipes with each other. The pipe replacement device A is comprised of a cutting part 11 including cutter bodies 14 (shanks 14a to 14i) arranged in the axial direction and at angular intervals in the circumferential direction, an expanding part 12 having expanding rollers 18a to 18f, and a connecting part 13. Each cutter body 14 has a plurality of cutting edges, wherein distances between the respective cutting edges and the center of the circle become larger in order from the forward side toward the backward side. While the pipe replacement device A is traveled in the inside of cast iron pipes, the inner wall of cast iron pipes is cut by the cutter bodies 14 to form grooves. Splitting of existing pipes into arc-shaped pieces 1a is made starting from the grooves. Arc-shaped pieces 1a are pressed into the ground, by which a tunnel 7 surrounded by arc-shaped pieces 1a and portions of consolidated earth is formed, while new pipes 6 are introduced into the tunnel 7, and besides the new pipes 6 are protected by protective armors formed of arc-shaped pieces 1a.

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First Claim