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      Grinding technology of limestone with ball mills
      6. Ball charge of the raw mills:  
      For the producer, the most important is to have a certain residue on 1 or 2 sieves.
      For example, 15%R90µ.    
      It means that we don't need fineness (surface - Blaine) => no need to produce superfine particles.
      For that, the ball charge are relatively coarse, the retention time of the material inside the mill is
      very short and the circulating load of the separator is high.
      There is not method to calculate the ball charge of a raw mill.
      All is based on the experience.  
      The total ball charge is normally between 300 gr/ball and 400gr/ball average.
      A typical airswept mill coarse ball charge is the following: 
      Ø 90mm 16%    
      Ø 80mm 17%    
      Ø 70mm 11%    
      Ø 60mm 13%    
      Ø 50mm 14%    
      Ø 40mm 13%    
      Ø 30mm 16%    
      A typical double rotator mill fine ball charge will be the following:
      1st chamber:    
      Ø 80mm 20%    
      Ø 70mm 13%    
      Ø 60mm 8%          
      Ø 50mm 8%      
      2nd chamber:    
      Ø 50mm 11%    
      Ø 40mm 19%    
      Ø 30mm 21%    
      Naturally, the ball charge optimisation depends directly of a mill survey.
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