PURPOSE: To make the wall thickness and roundness of a product highly accurate, by providing a tension detector to a mandrel bar, and keeping a tension of mandrel bar constant by changing the rotating speed of barrel-shaped rolls in accordance with the variation of the tension.
CONSTITUTION: A piercing mill has a rolling device consisting of a plug 2 held by a mandrel bar 1 and two barrel-shaped rolls 3a, 3b, and rolls a blank pipe 6 by the plug 2 and the rolls 3a, 3b. A tension detector 10 detecting a tension TB acting on the mandrel bar 1 and a load cell 11 detecting a rolling load of the roll 3b are provided to the device. Respective detecting signals S1, S2 are transmitted to a calculator 12 to calculate so that the mandrel tension conforms with a tension value set by a tension setter 16. This signal is transmitted to a motor through a speed controller 17 and a motor power source 18 to change the rotating speeds of rolls 3a, 3b thereby the tension TB acting on the mandrel bar 1 is kept constant.
JPS5775209A | 1982-05-11 |