Tundish control

Abstract

Microwave transmission and reception, and analysis thereof, are used to monitor the level of molten metal, paradigmatically steel, in a tundish receiving molten metal (steel) from a ladle or other vessel and passing it to the head of a continuous caster, while the steel in the tundish is covered with slag. The control factors may include level, weight or volume limits in the tundish derived from historical or real-time data, including data representing a predictable or developing vortex in the well feeding the continuous caster. The system is particularly useful in minimizing transition mix during change from one metal specification or grade to another.

1 . Method of managing a tundish to control the transition between a first grade of molten steel and a second grade of molten steel to be solidified sequentially in a continuous caster by draining said first and second grades of molten steel through a well in said tundish to a mold at the head of said continuous caster, wherein said first grade of molten steel is initially in said tundish and covered by a layer of slag in said tundish, comprising 
 (a) draining said first grade of steel to a level in said tundish as monitored in step (b) which level is (i) slightly higher than the predetermined level at which a vortex is expected to form above said well, or (ii) where vortex formation is indicated as in step (b), whichever is the first level to be reached;    (b) while draining said first grade of steel, monitoring the level of said first grade of steel in said tundish by directing microwave radiation into said tundish from above said layer of slag and analyzing reflections of said microwave radiation from said slag and said steel, (i) to determine the level of said steel and (ii) to detect a microwave pattern indicative of vortex formation in said tundish, and    (c) when step (a) is completed, adding said second grade of molten steel to said tundish at a rate at least that of the rate of draining said first grade of steel.    
   
   
       2 . Method of  claim 1  wherein said predetermined level of said first grade of steel at which a vortex is expected to form is at least ten inches above the bottom of said tundish.  
   
   
       3 . Method of  claim 1  wherein said level of said first grade of steel slightly higher than said predetermined level at which a vortex is expected to form is from 1% to 10% higher than said level at which a vortex is expected to form, and wherein said predetermined level at which a vortex is expected to form is at least partly derived from a historical microwave analysis of steel flow patterns above said well.  
   
   
       4 . Method of  claim 1  whereby a transition mix of said first and second grades of steel is formed in said tundish, and including monitoring the level of said transition mix, by microwave analysis, in said tundish while adding said second grade of steel.  
   
   
       5 . Method of  claim 4  followed by continuing, by microwave analysis, to monitor the level of said transition mix of steel in said tundish until it is substantially replaced by said second grade of steel, and thereafter monitoring, by microwave analysis, the level of said second grade of steel in said tundish.  
   
   
       6 . Method of maintaining the level of molten metal within predetermined limits in a tundish, said molten metal being beneath a layer of slag, while said tundish substantially continuously feeds said molten metal to a continuous caster including a mold comprising 
 monitoring the level, volume, or weight of said molten metal in said tundish by microwave analysis and controlling the flow of said molten metal into and out of said tundish to maintain said level, volume or weight within said predetermined limits.    
   
   
       7 . Method of  claim 6  wherein said molten metal is molten steel, said monitoring by microwave analysis comprises monitoring a well in said tundish for vortex formation, and wherein said predetermined limits include a lower level limit below which a vortex is likely to form.  
   
   
       8 . Method of  claim 6  wherein said molten metal is aluminum.  
   
   
       9 . Method of  claim 6  including monitoring said well by monitoring vibrations around said well or in the mold of said continuous caster, generating a signal representing said vibrations, and utilizing said signal in the control of said flow of said molten metal.  
   
   
       10 . Method of  claim 6  conducted substantially continuously while a plurality of molten metal heats are fed from at least one vessel to said tundish.  
   
   
       11 . Method of  claim 7  wherein said controlling of flow out of said tundish is also dependent on at least one of (a) steel level in said mold, (b) based on historical records, whether a vortex is likely to form at the level, volume or weight of steel in said tundish, (c) slag level in said tundish, (d) slag volume in said tundish, (e) slag weight in said tundish, (f) iron oxide content in said slag, (g) the composition of steel in said tundish, (h) the rate of solidification of said steel in said mold (i) vibration in said tundish or tundish nozzle, (j) turbulence in the mold of said continuous caster, (k) casting rate, and (l) value of steel being cast.  
   
   
       12 . Method of  claim 11  conducted during transition from the feeding of steel from said tundish having a first set of specifications to a steel having a second set of specifications.  
   
   
       13 . Method of inhibiting the formation of a vortex over a well in a vessel containing molten steel covered by slag comprising (a) directing microwave radiation toward said slag in an area over said well, (b) receiving reflections of said microwave radiation, (c) analyzing said reflections to identify a pattern thereof indicative of the incipient formation of a vortex in said well as predictable from a reference base, and (d) adding additional molten steel to said vessel when said pattern is identified.  
   
   
       14 . Method of  claim 13  wherein said vessel is a tundish.  
   
   
       15 . Method of  claim 13  wherein said additional molten steel of step (d) has a specification different from the original molten steel in said vessel.  
   
   
       16 . Method of  claim 13  including measuring the level of said molten steel by microwave analysis and maintaining said level within limits predetermined by historical data as correlating said level to the formation of an incipient vortex over said well.  
   
   
       17 . Method of  claim 13  wherein said microwave radiation is pulsed.  
   
   
       18 . Method of controlling operation of a tundish while said tundish is feeding molten steel to a continuous caster comprising (A) establishing a data base of historical or desirable continuous caster operation factors comprising at least one of (i) strand speed in said continuous caster (ii) steel temperature in the head of said continuous caster (iii) vibration in the head of said continuous caster (iv) rate of freezing in the mold of said continuous caster, (B) establishing a data base of historical or desirable tundish operation factors comprising at least one of (i) steel level in said tundish below which a vortex is likely to form (ii) a range of molten steel weight in said tundish to facilitate a desired substantially steady state inflow and outflow of molten steel (iii) volume of steel in said tundish to facilitate desired substantially steady state inflow and outflow of molten steel (iv) level of steel in said tundish to facilitate desired substantially steady state inflow and outflow of molten steel (v) level of slag in said tundish tolerable for operation of said tundish (vi) volume of slag in said tundish tolerable for operation of said tundish (vii) weight of slag in said tundish tolerable for operation of said tundish (C) by microwave analysis, monitoring the level, weight or volume of molten steel in said tundish, and (D) controlling the feed rate of molten steel to said continuous caster to maintain said level, weight or volume of molten steel in said tundish as determined in step (C), using control points based upon at least one operation factor from step (A) and at least one operation factor from step (B).  
   
   
       19 . Method of  claim 18  including monitoring slag weight, volume or level in said tundish by microwave analysis and using said slag weight, volume or level as a factor in controlling said feed rate to said continuous caster.  
   
   
       20 . Method of  claim 18  wherein said at least one operation factor from step (B) utilized in step (D) is steel level below which a vortex is likely to form.