Method of and apparatus for continuous casting of steel strip

Abstract

A continuous casting method and apparatus in which a distributor deposits a strand of molten steel upon a cooled surface of casting roll to a thickness of 1.0 to 6.0 mm, the cooling strand passes through the nip or gap between a fist counterroll and the casting roll and hardening strip is then passed through at least a first further nip between one or more further counterrolls and the surface of the casting roll. The height of the molten metal in the distributor is controlled to be constant by detecting the surface of the melt and regulating the outflow from an intermediate receptacle into the distributor and/or from the casting ladle into the intermediate receptacle so that the peripheral speed of the casting roll is matched to the speed with which the strand emerges from the distributor onto the casting roll.

We claim:  
     
         1 . A method of continuously casting steel strip comprising the steps of: 
 (a) feeding a continuous stream of molten steel from a distributor across a length of a cooled casting roll and upstream of a first counter roll, thereby forming a hardening layer of a thickness of about 1.0 to 6.0 mm of said molten steel on a surface of said casting roll;    (b) controlling a speed with which said molten steel is fed onto said surface by regulating a ferrostatic height of molten steel in said distributor, said layer partially hardening on said surface to form a shell;    (c) compressing said shell between said surface of said casting roll and said counter roll in a first nip between said casting roll and said counter roll to impart a first cross sectional contour to said hardening layer; and    (d) thereafter compressing said hardening layer in a second nip between said casting roll and a further counter roll downstream of said first counter roll to reduce the thickness of the layer on said surface thereby imparting a cross sectional contour to said layer to form said steel strip.    
     
     
         2 . The method defined in  claim 1  wherein said steel strip is hardened throughout its thickness upon emerging from said second nip.  
     
     
         3 . The method defined in  claim 2  wherein said steel strip is guided between guide and counterrolls into a horizontal orientation following the last of the counterrolls juxtaposed with said surface.  
     
     
         4 . The method defined in  claim 2  wherein a thickness reduction in said first nip is effected of about 5% to 20%.  
     
     
         5 . The method defined in  claim 2  wherein a thickness reduction is effected in said second nip by about 10 to 50%.  
     
     
         6 . The method defined in  claim 2 , further comprising the step of controlling a peripheral speed of said casting roll to match a speed with which said molten steel is fed onto said surface.  
     
     
         7 . The method defined in  claim 2  wherein said counterrolls are driven with peripheral speeds 0.5 to 1.5% higher than a peripheral speed of said casting roll.  
     
     
         8 . The method defined in  claim 2 , further comprising the steps of cooling said counterrolls.  
     
     
         9 . The method defined in  claim 2  wherein a perspective height of the melt in said distributor is continuously measured and supply of melt to said distributor is controlled to maintain said height constant.  
     
     
         10 . The method defined in  claim 9  wherein said melt is delivered by an intermediate receptacle receiving said melt from a casting ladle to said distributor by a tube dipping into the melt in said distributor.  
     
     
         11 . The method defined in  claim 2  wherein a speed of said melt discharged from said distributor is controlled at least in part by controlling a subatmospheric pressure applied to said distributor.  
     
     
         12 . The method defined in  claim 2 , further comprising the step of blanketing said melt at least from said distributor to a last of said counterrolls with an inert gas to prevent oxidation of said melt and slag formation.  
     
     
         13 . The method defined in  claim 12  wherein said melt is fed to said distributor from a tundish and the melt in said tundish is also blanketed with said inert gas.  
     
     
         14 . The method defined in  claim 2 , further comprising the step of internally cooling said casting roll and counterroll by passing coolant through cooling bores or grooves in said casting roll and said cooling rolls.  
     
     
         15 . The method defined in  claim 14 , further comprising the step of additionally cooling or cleaning said casting roll by directing water spray jets thereagainst.  
     
     
         16 . The method defined in  claim 3 , further comprising the steps of cooling the guide and counterrolls with which said strip is guided into said horizontal orientation.  
     
     
         17 . The method defined in  claim 2  wherein said strip is at a temperature in a range between 1100° and 1400° C. upon casting onto said casting roll.  
     
     
         18 . An apparatus for continuously casting steel strip comprising: 
 a casting roll having a cooled peripheral surface;    a distributor having a slot-shaped outlet extending along said surface for depositing a molten steel strand on said surface whereby said strand cools on said surface to form a shell and hardening into a steel strip;    a first counterroll juxtaposed with said surface for compressing said shell and thereby reducing a thickness of said strip in a first nip;    at least one second counterroll juxtaposed with said surface downstream of said first nip and defining with said surface a second nip for compressing said strip whereby said strip is solidified through a thickness thereof upon emergence from said second nip;    a tundish receiving molten metal from a casting metal and delivering said molten metal to said distributor through a tube immersed in molten metal in said distributor; and    a sensor responsive to a height of molten metal in said distributor for controlling delivery of a molten metal from said tundish to said separator to maintain said height substantially constant, said casting roll being driven with a peripheral speed matched to a speed with which molten steel is delivered by said distributor to said surface.    
     
     
         19 . The apparatus defined in  claim 18 , further comprising guide and counterrollers downstream of said casting roll, receiving said strip and bending said strip into a horizontal orientation, said guide and counterrollers being of smaller diameter than said rolls, composed of solid material and constituted of a CuNiBe alloy.  
     
     
         20 . The apparatus defined in  claim 18  wherein at least one of said rolls is composed of CuNiBe alloy.  
     
     
         21 . The apparatus defined in  claim 18  wherein a plurality of said counterrolls are interconnected to form a segment having a common control for positioning the counterrolls of said segment.  
     
     
         22 . The apparatus defined in  claim 18 , further comprising means for blanketing the molten steel at least in said distributor and along said casting roll with an inert gas.