Method for deep decarburisation of steel melts

Abstract

The vacuum pump ( 10 ) comprises at least one rotor shaft ( 12 ) having a rotor section ( 14 ) with a rotor ( 16 ), a bearing section ( 18 ) with a bearing ( 20 ), and a shaft sealing system ( 22 ) that is axially situated between the rotor section ( 14 ) and the bearing section ( 18 ). The shaft sealing system ( 22 ) axially comprises, on the side of the rotor, a gas seal ( 32 ) and, on the side of the bearing, an oil seal ( 34 ). The shaft sealing system ( 22 ) additionally comprises, between the gas seal ( 32 ) and the oil seal ( 34 ), a separating chamber, which surrounds the rotor shaft ( 12 ) and is ventilated by at least one separating chamber ventilation duct ( 60, 62 ). This enables the pressure differential that decreases via the gas seal and t he pressure differential that decreases via the oil seal to be adjusted. An appropriate adjustment can prevent oil on the bearing side from passing through the oil seal toward the separating chamber.

1 - 4 . (canceled)  
     
     
         5 . A method for decarburizing molten steel in an RH unit, comprising: 
 circulating the steel between a container and a vacuumscontainer that has been placed under a vacuum, the steel constituting a steel bath when present in the vacuum container;    blowing oxygen or an oxygen-containing gas onto the steel bath by means of blowing lances at a spacing from the top surface of the bath and aimed at the steel bath present in the vacuum container, the blowing in of the oxygen or an oxygen-containing gas beginning in correspondence with the increase of the CO, which is available in the vacuum container after having been freely released in the steel bath on account of the natural decarburization, and the amount of blown in oxygen being an amount that has been determined by taking into account a relationship of the start carbon content to the start oxygen content in the charge that is to be subjected to decarburization as specified by the formula and that corresponds to an amount of oxygen required for decarburization as calculated by the formula        O   Dec   =a ·( C   ini   /O   ini ) 2   +b ·( C   ini   /O   ini )+ c      Q o   2   =[O   Dec   +O   End Dec   ·]G   Ch    ρo 2 ;    setting a start pressure P Start in the vacuum container for the beginning of the blow process as a function of the start carbon content C ini of the steel melt in accordance with the formula        P   start   =a·C   ini   2   +b·C   ini   +c;  and    concluding the blowing in of oxygen upon the reaching of the boundary conditions (CO+CO 2 )≧5% of the exhaust gas amount as well as CO 2 /(CO+CO 2 )≧30%, whereby        O   Dec   =a ·( C   ini   /O   ini ) 2   +b ·( C   ini   /O   ini )+ c      Q o   2   =[O   Dec   +O   End Dec   ]·G   Ch    ρo 2      P   start   =a·C   ini   2   +b·C   ini   +c                                                  Q o 2     oxygen amount to be blown in (Nm 3 )         O Dec     for the oxygen portion required for the decarburization         O End Dec     oxygen amount available in the charge at the end             of the decarburization process (ppm)         C ini     start carbon content of the steel melt (ppm)         O ini     start oxygen content of the steel melt (ppm)         G Ch     weight of the charge         ρ o 2     thickness factor of oxygen = 1.428 Kg/Nm 3                                                      
     
     
         6 . A method according to  claim 5 , wherein blowing oxygen or an oxygen-containing gas onto the steel bath includes impacting the bath top surface of the steel bath present in the vacuum container with a compact oxygen blow stream that exits the blow jet with a high velocity.  
     
     
         7 . A method according to  claim 6 , wherein impacting the bath top surface of the steel bath present in the vacuum container with a compact oxygen blow stream that exits the blow jet with a high velocity includes impacting the bath top surface of the steel bath present in the vacuum container with a compact oxygen blow stream that exits the blow jet with an ultrasonic velocity.  
     
     
         8 . A method according to  claim 7 , wherein impacting the bath top surface of the steel bath present in the vacuum container with a compact oxygen blow stream that exits the blow jet with a high velocity includes blowing oxygen or an oxygen-containing gas from a blow jet with a working area that is variable via displacement of a position cone is configured such that the ultrasonic flow of the blow stream produced in the blow jet is maintained in the event of reduced counter pressure in the vacuum container.