Method for producing seamless steel tube and production facility therefor

Abstract

In the production of a seamless steel tube by piercing-rolling a heated billet with a piercing machine to form the billet into a hollow blank, and without reheating the hollow blank, by successively subjecting the hollow blank to elongation-rolling with an elongation-rolling mill and diameter-adjusting rolling by a diameter-adjusting rolling mill, it is made possible to prevent non-uniform longitudinal temperature distribution from occurring in a steel tube after diameter-adjusting rolling and enable energy saving to be accomplished by including a step 1 of measuring a temperature of the hollow blank along a longitudinal direction at the exit of the elongation-rolling mill; and a step 2 of spraying water onto the hollow blank to cool the hollow blank at the entrance of the diameter-adjusting rolling mill according to a measured longitudinal temperature distribution of the hollow blank, whereby the longitudinal temperature distribution of the hollow blank becomes uniform.

1 . A method for producing a seamless steel tube by piercing-rolling a heated billet by a piercing machine to form the billet into a hollow blank, and without reheating the hollow blank, by successively subjecting the hollow blank to elongation-rolling with an elongation-rolling mill and diameter-adjusting rolling with a diameter-adjusting rolling mill, the method comprising the steps of:
 (step 1) measuring a temperature of the hollow blank along a longitudinal direction at the exit of the elongation-rolling mill; and   (step 2) cooling the hollow blank by spraying water onto the hollow blank at the entrance of the diameter-adjusting rolling mill according to a measured longitudinal temperature distribution of the hollow blank, whereby the longitudinal temperature distribution of the hollow blank becomes uniform.   
     
     
         2 . The method for producing a seamless steel tube according to  claim 1 , wherein subsequently to the diameter-adjusting rolling, quenching is performed without reheating. 
     
     
         3 . The method for producing a seamless steel tube according to  claim 1 , wherein in the step 2, an amount of water to be sprayed onto the hollow blank is adjusted for each of regions that are virtually allotted along a longitudinal direction of the hollow blank. 
     
     
         4 . The method for producing a seamless steel tube according to  claim 2 , wherein in the step 2, an amount of water to be sprayed onto the hollow blank is adjusted for each of regions that are virtually allotted along a longitudinal direction of the hollow blank. 
     
     
         5 . A production facility for a seamless steel tube including a piercing machine for piercing-rolling a heated billet to form the billet into a hollow blank, and an elongation-rolling mill for elongation-rolling the hollow blank without reheating the hollow blank and a diameter-adjusting rolling mill for diameter-adjusting rolling the hollow blank without reheating the hollow blank, the production facility comprising:
 a thermometer which is disposed at the exit of the elongation-rolling mill and is used for measuring a temperature of the hollow blank along a longitudinal direction; and   a water-cooling apparatus which is disposed at the entrance of the diameter-adjusting rolling mill and serves for spraying water onto the hollow blank to cool the hollow blank according to a longitudinal temperature distribution of the hollow blank measured by the thermometer, whereby the longitudinal temperature distribution of the hollow blank becomes uniform.