| 摘要 |
<p>PURPOSE:To smoothly enlarge the diameter of a helical tube with certainty by constituting a wire rod for locking side edge portions of a band-like body in such a manner as to be released from a helical tube at a high speed when a thrust force applied to the band-like body reaches an upper limit value, and correcting the upper limit value if a difference between the maximum of the thrust force and the minimum thereof exceeds a predetermined value. CONSTITUTION:The side edge portions of a band-like body 10 are locked by a wire rod 30, thus obtaining a helical tube, 10' which is inserted into a sewer 81 and the diameter of which is enlarged. In enlarging the diameter, an oil pressure of the tube manufacturing machine 20 is increased in the case of a large frictional coefficient of a band-like body 10. However, the oil pressure may not be increased because of the sliding of the bank-like body 10 locked in the wire rod 30 and the non-released wire rod 30. In this state, a speed of axial motion of a portion to be enlarged become higher than a releasing speed of the wire rod 30 from the helical tube 10', and a truncated portion L becomes short and a load exerted on the tube manufacturing machine 20 is increased. At last, tube manufacturing becomes impossible. When control of a difference between the maximum of the thrust force applied to the bank-like body 10 and the minimum thereof reaches its limit, the upper limit value of the thrust force is corrected to a smaller value. Therefore, the releasing speed of the wire rod 30 from the helical tube 10' is increased and the length of the truncated portion L returns to a normal length.</p> |
