Title:
FLAT OVAL SHEATH WITH SPIRAL RIB AND ITS MANUFACTURE AND MANUFACTURING DEVICE
Document Type and Number:
Japanese Patent JP3305657
Kind Code:
B2
Abstract:
PROBLEM TO BE SOLVED: To obtain the sheath with both of strength and flexibility, and which is easy to house a PC steel with plural cross-sections of a tube.
SOLUTION: This sheath 4 is manufactured as follows, that is, the spiral steel tube with ribs swelled on its outer peripheral surface, is deformed by being held and pressed with forming rolls having circular-arc shaped forming surfaces formed symmetrically up and down. The sectional shape of the spiral tube, is deformed from a circle to an oval while keeping the outer peripheral length of a base tube and by changing remarkably the curvature of a forming surface successively and stage by stage. Further, the forming surface is inclined to a horizontal surface, and a twist in the axial direction of the tube, is straightened through finish forming forming to a flat oval having straight line parts parallelling up and down the forming surface. In this case, the outer peripheral surface is strengthened by a spiral rib 41, and the cross-section is formed by the flat oval consisting of two parallel straight line parts 43 and semicircular parts 44 at both ends.
Inventors:
Takeshi Fujii
Application Number:
JP20122498A
Publication Date:
July 24, 2002
Filing Date:
June 30, 1998
Export Citation:
Assignee:
Kurimoto Iron Works Co., Ltd.
International Classes:
E04C5/10; B21C37/12; B21C37/15; B21C37/26; B21D3/02; B21D5/12; (IPC1-7): B21C37/15; B21C37/12; B21C37/26; B21D3/02; B21D5/12; E04C5/10
Domestic Patent References:
| JP59218216A | ||||
| JP57184511A |
Attorney, Agent or Firm:
Junzo Aono