PURPOSE: To reduce the thickening of wall thickness at the top part of a pipe, and to improve product yield, by feeding back the data of wall thickness at the top part of a pipe stayed in a cold state, and using the data as the roll gap controlling data in a plug mill.
CONSTITUTION: The temperature in the axially longitudinal direction of a blank pipe P1 obtained from a thermometer 6 faced to a moving zone of the pipe P1 at the inlet side of a plug mill 1, and the distribution of wall thickness in the axially longitudinal direction of the top part of a pipe P5 obtained from a wall thickness detector 7 faced to the top part of the pipe P5 placed on an inspection table 5 are respectively read by a controlling part CN. Further, a roll gap pattern G(X,T) of the mill 1 is calculated and set by the controlling part CN to conform the wall thickness at the top part of pipe P2 to a desired wall thickness in order to eliminate a thinning phenomenon of the wall thickness generating at the top of a pipe P3 at the exit side of a reeler 2, basing on the other data inputted previously. In this case, the pattern G(X,T) is used in calculation as the sum of a standard pattern G0(X,T) and a correcting pattern ΔG(X,T) for eliminating the deviation generating at the top part of a pipe P5 from a target value of the wall thickness in a cold state.
SHIMODA TAKESHI
SANO MASAKAZU
