PURPOSE: To make an immediate countermeasure to prevent thickness deviation and to decrease the generation of a defective seamless pipe by monitoring the generating condition of the thickness deviation in accordance with the moment force to be exerted to a mandrel bar in the process for production of the seamless pipe.
CONSTITUTION: The moment force occurring in the whirling of a plug 2 is exerted to the mandrel bar 3 in the stage of piercing of the seamless pipe. The generation of the thickness deviation of the seamless pipe is detected by usng a strain bar, etc. in accordance with the deformation of the bar 3 owing to the moment force. The bar 3 presses each roll in each bar steadyer 50. An oil pressure fluctuation arises in the hydraulic circuit of hydraulic cyliners 55, 57 in this stage. The generation of the thickness deviation of the seamless pipe is detected from an increase in the amplitude of the hydraulic pressure fluctuation. The counter measure for preventing the heat deviation of a blank material, adjusting the position of cross helical rolls 1 of a piercer, etc. is made when the generation of the thickness deviation is detected.
YOSHIKAWA EIJI
MIYASHITA KEN
ISHIZU HISATSUGU
