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      Ball Charges Composition              
                             
      1 Introduction:                
          - This page intends to introduce the ball charge composition calculator.      
          - But first, it is important to emphasize that the composition of a ball charge of a cement mill depends  
            on many parameters and a composition miscalculated can significantly affect the performance of the installation.
          - It is also better to do a complete audit before to modify a ball charge.      
            A complete explanation of the sampling campaign inside the mill is available here:     
               
     
           
          - It is also advisable to let the experienced people calculate a grinding charge.      
     
      2 Cement mill with 2 compartments:            
        2.1 First compartment:              
          - The first compartment (or first chamber) is also known as coarse chamber or crushing chamber.  
          - It is equipped with lifting lining in order to increase the ascending trajectory of the balls.    
          - The diameter of the balls is mostly from 90mm to 60mm with some exception (100mm for harder materials).
          - Balls smaller than 60mm have a limited efficiency and must be avoid.      
          - Balls are working by impact.            
        2.1.1 Factors influencing the composition of the charge:          
          - 1) The granulometry of the fresh feed:             
            This is probably the most important factor.           
            Important remark: we take into consideration the fresh feed at mill inlet.      
          - 2) The hardness of the clinker:            
            Do not confuse with the grindability of the clinker.          
            On this subject, see the explanation on the following link:        
               
     
           
            A good and easy test to know the clinker hardness is the well known Slegten hardness test.    
          - 3) The kind of lining:              
            The lining is generally made with a lifting effect but we can define three types of situation: weak lifting effect,
            normal lifting effect or agressive lifting effect.          
          - 4) The specific power consumption of the chamber:          
            The value is normally comprised between 8 and 12 kWh/t.        
          - 5) Other less important factors:            
            The percentage of slag in the feed.            
            The percentage of additives (like limestone) in the feed.        
            The percentage of moisture in the total feed.          
            The type of clinker (grey or white).            
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        2.1.2 Some examples of ball charges:            
          - 1) The ball charge with the same number of balls for each diameter:      
            This is a classical ball charge where all the diameters have the same number of balls.    
            The make-up of this ball charge is 100% balls of 90mm.        
            Here is an example of calculation:            
           
     
     
                   
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
            In conclusion, this ball charge must be only used in case of crushing problems due to coarse    
            granulometry, big hardness or worn-out lining because it is very coarse.       
            It is also recommended to check the level of material in order to avoid problems of breakage.  
          - 2) The ball charge with the same number of balls for each diameter except the biggest size:    
            This charge is quite well used.             
            Here is an example of calculation:            
           
     
     
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
             
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        2.2 Second compartment:              
          - The second compartment (or second chamber) is also known as finishing chamber or grinding chamber.  
          - Balls in this compartment are working by attrition.          
          - This chamber is equipped with classifying lining or lining plates without any classification. In the past, and in 
            open circuit configuration, there were also retaining rings (as Danula rings from FLS) in some mills.  
          - The diameter of the balls is mostly from 60-50mm to 17-15mm depending of the lining.    
          - Balls of 15mm are only used in open circuit configuration.        
          - Balls of 60, 50 and 40mm diameter are only used in case of classification and are called the barrage (dam). 
            This barrage allows to crush the biggest particles of material which (eventually) are coming from the 1st chamber.
          - The barrage constitutes 10-15% of the total charge.          
          - Without classification, such a barrage is completely useless and the charge is only composed of smaller balls.
          - In case of open circuit, cylpebs are an alternative to balls, especially when the  cement plant wants to increase
            the cement fineness in term of Blaine (Specific Surface Area).        
        2.2.1 Factors influencing the composition of the charge:          
          - The fineness of the cement.            
          - The fineness of the cement at second chamber inlet and outlet.        
          - The L/D (Length/Diameter) ratio.            
          - The type of lining.              
          - The type of circuit: open or closed.            
          - The type of separator (first, second or third generation).        
          - Other factors like the ventilation and the coating can also affect the Grinding Engineer in his choice.  
        2.2.2 Procedure to calculate the second chamber ball charge:        
          - Considering a classifying lining with a barrage (dam) of 10-15% with balls of 60, 50 and 40mm, the rest of the
            ball charge is made with balls of 40, 30, 25, 20 and 17mm (in closed circuit).      
          - The percentage of each diameter has been determined in laboratory tests, each diameter having a maximum 
            of efficiency for a given particle size of clinker.          
          - In function of the working conditions, the quantiy of each diameter is then adjusted.    
      3 Cement mill with 3 compartments:            
          - For open circuit cement mills.            
        3.1 First compartment:              
          - Is similar to a 2 compartments mill.            
        3.2 Second compartment:              
          - The second chamber is very short and is working like a barrage (dam) between the first and the finishing chamber.
          - Balls of 50, 40 and 30mm are generally used to compose the ball charge of this compartment (cylpebs of   
            similar size can also be used but it is very rare nowadays).        
        3.3 Third compartment:              
          - Three chambers mills are only utilized in case of open circuit.        
          - The lining is often without classification but it is less important because of the second compartment.  
          - Balls of 25, 20, 17 and 15mm constitute the finishing ball charge with the target to create fineness.  
          - Cylpebs are also used in this case.            
      4 Cement mill with only 1 compartment:            
          - These mills also called monochambers mills are used in case of pregrinding system in front of the mill or when
            the fresh feed is only composed of slag.          
          - Normally, big balls of 90, 80 and 70 are not needed.          
          - The calculation of the ball charge follows the same principle as the second chamber of a conventional mill.
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      5 Raw mills:                
          - It does not really exist methods to determine the ball charge of a raw mill. All is based on the experience.
          - Normally, the raw mills are monochamber (airswept) or birotator (central discharge).     
            Compounds mills are uncommon.            
          - The tendancy is to have less big balls in comparizon with cement mills because the material is easier to crush
            and less small balls because the target is not fineness but only a residue on 90µ.    
          - 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.          
          - The total ball charge is normally between 300 gr/ball and 400gr/ball average.      
          - Monochamber mills have a coarser ball charge without 25mm balls.      
          - A typical airswept mill coarse ball charge is the following:         
           
     
                 
                         
                         
                         
                         
                         
                         
                         
          - A typical double rotator mill fine ball charge will be the following:      
           
     
                   
                             
                             
                             
                             
                             
                             
                             
                             
                             
                             
            Naturally, the ball charge optimisation depends directly of a mill survey.      
                             
            See the infography which explains how to use the calculator clicking on the button below
                             
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