The fields with the red border are required.
    www.thecementgrindingoffice.com
    All rights reserved © 2012-2016 The Cement Grinding Office
      Grindability and Hardness Tests            
                           
      4 Grindability tests:              
      4.1 Bond grindability test:              
        - The test developed by Fred C. Bond in 1952/1961 is widely used worldwide.      
      4.1.1    Machinery required:              
        - Mill diameter 305 mm (12") and length 305 mm (12") with rounded corners and a smooth internal lining.
        - Speed of rotation: 70 rpm.            
        - Ball charge:                
            43 balls of 36,83 mm            
            67 balls of 29,72 mm            
            10 balls of 25,4 mm            
            71 balls of 19,05 mm            
            94 balls of 15,94 mm            
            total: 20,125 kg of balls            
        - balance and sieves are obviously required.          
        - Some pictures of laboratory Bond mills here below:        
         
     
             
                   
                   
                   
                   
          (From Edemet: www.edemet.cl)    
                   
                   
                   
                   
                   
                   
         
     
             
                   
                   
                   
                   
          (From Bico: www.bicoinc.com)    
                   
                   
                   
                   
                   
                   
         
     
             
                   
                   
                   
                   
                   
                   
          (From metcon Laboratories: metcon.com.au)  
                   
                   
                   
                   
                   
                   
                   
    www.thecementgrindingoffice.com
      4.1.2   Sample required:              
        - Initially, a few kilos of representative fresh feed are required        
        - The sample is passed through a #6 Mesh sieve, i.e. 3,35 mm.        
        - From the sample 100% passing on 3,35 mm, 700 ml are collected and go into the mill.    
      4.1.3   Test procedure:              
        - A first cycle is started, the mill realizes 100 revolutions and is stopped.      
        - The ground material is removed from the mill and is sieved on the selected test mesh screen (for example #100 or 106µ).
        - The undersized fraction is weighed.            
        - The oversized fraction returns again into the mill with a fresh quantity of 3,35 mm passing material corresponding to the
          weight of the 106µm passing material in order to get 700 ml of material into the mill.    
        - An other cycle is ready to begin.            
        - But before, it is necessary to specify the number of revolutions. It is calculated taking into account a theorical 250% 
          circulating load. It means that the Rejects (oversized fraction)/Fines (undersized fraction) ratio is equal to 2,5.
          That also means that the feed/fines ratio is equal to 3,5 and the undersized fraction represents 28,6% of the fresh feed.
        - After the second cycle, the same procedure is repeated until the weight of undersized product per mill revolution reaches
          the equilibrium, i.e. be a constant value.          
        - Generally, 6 to 12 cycles are necessary to achieve the test.        
      4.1.4   Results:                
        - The average of net undersized mass per revolution from the last three cycles is taken to calculate Gbp which is the
          ball mill grindability:              
         
     
             
                   
                   
        - The work index (Wi) is then calculated with the following formula:      
         
     
           
                 
                 
                 
          where Pf = test sieve product in µ,            
          Gbp = the mill grindability in gr/rev,            
          P80 = sieve with 80% of passing of the product and          
          F80 = sieve with 80% of passing of the feed.          
      4.1.5   Usual values of the work Index:            
         
     
           
                 
                 
                 
      4.2 Hardgrove test:              
        - This test was developed in the 1930's.            
        - The target was to measure empirically the relative difficulty of grinding coal to obtain the required particle size 
          for complete combustion in the pulverized coal boiler furnace.        
        - Later on the use of the Hardgrove grindability Test (HGI) has been has extended to other materials.  
      4.2.1    Machinery required:              
        - The test is performed in laboratory mill which is corresponding to the ASTM D409 standard.  
        - Link: http://www.lixingfeng.com/doc/ASTM_D409-02.pdf        
        - The grinder consists of a bowl mill with a ± 29 kg weight on the upper part and a grinding track with 8 balls of 1 inch
          in the lower part.              
        - balance and sieves are obviously required.          
        - Some pictures of laboratory Hardgrove mills here below:        
         
     
           
                 
                 
                 
                 
                 
                 
                 
          (From Trade2CN: trade2cn.com)  
                 
                 
                 
                 
                 
                 
                 
                 
                 
         
     
           
                 
                 
                 
                 
                 
          (From ACARP: acarp.com.au)  
                 
                 
                 
                 
                 
                 
                 
    www.thecementgrindingoffice.com
      4.2.2   Sample required:              
        - Initially, a few kilos of representative fresh feed are required with a maximum size of 4,75 mm.  
        - From this sample, 50gr between 0,6 and 1,18 mm are prepared.        
      4.2.3   Test procedure:              
        - The 50 gr sample is introduced in the circular path. 8 balls are placed above the material and the upper grinding 
          element is inserted onto the balls. The mill drive is started up.        
        - The mill performs 60 rotations.            
        - After that, the ground coal is screened carefully on a 0,075 mm sieve.      
        - The undersize and oversize are weighed with accuracy of 0,01 g.        
        - The total weight of screening test product can differ from the original weight at most by 0,75 g for the test to be agreed.
      4.2.4   Results:                
        - This undersized weight is converted to a HGI value using the following formula:    
         
     
               
                     
          with m = mass of the undersized test product in grams.        
        - Greater is HGI and easier is the material grindability.        
        - HGI can be transformed into Bond work index using the following formulas:      
         
     
                 
          (proposed by Bond in 1951)        
                       
         
     
                 
          (modified by Bond in 1961)        
                       
         
     
                 
          (proposed by McIntyre and Plitt, 1980 for Wi > 8,5)      
                       
         
     
               
          (proposed by Hower, 1992 for carbonates)    
                     
        - The most used of these formulas is the one modified in 1961 by Bond and is expressed in kWh/sh.tons (short tons).
      4.2.5   Usual values of the HGI:              
         
     
                   
                           
                           
                           
                           
                           
                           
                           
                           
                           
                           
                           
      4.3 Zeisel test:                
        - This test was developed in year 1953.            
        - The apparatus is similar to the HGI test.          
      4.3.1    Machinery required:              
        - The test is performed in laboratory mill which is corresponding to the ASTM D409 standard.  
        - balance and sieves are obviously required.          
        - A view of the laboratory Zeisel mill here below:          
         
     
             
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
      4.3.2   Sample required:              
        - Initially, a few kilos of representative fresh feed are required.        
        - From this sample, 30gr between 0,8 and 1 mm are prepared.        
      4.3.3   Test procedure:              
        - The 30 gr sample is introduced in the circular path. 8 balls are placed above the material and the upper grinding 
          element is inserted onto the balls. The mill drive is started up.        
        - The test is divided in various steps.            
        - The number of revolutions (between 100 and 200) is defined so that the step generates a proportion of fines to be 
          removed of 50%.              
        - In contrast to the HGI test, specific surface area (Blaine) is measured.      
        - After each step, Blaine is measured from the sample. The 0,125 mm undersized fraction is removed and weighed.
          A fresh sample with the same weight of the removed fraction is added to the sample for the next step.  
        - The test is concluded when the grams of product produced/number of rotations ratio is the same for 3 steps.
      4.3.4   Results:                
        - The result is obtained between the quantities of specific energy in kWh/ton which have to be expended to generate 
           specific levels of Blaine fineness.            
        - The Zeisel grindability result is expressed in kJ/kg.          
        - Here below, a usual graph with Zeisel test results:          
         
     
         
               
               
               
               
               
               
               
               
               
               
               
               
               
      4.3.5   Field of application:              
        - Many german companies are using this method in their laboratory.      
        - This test seems to be well adapted for VRM (Vertical Roller Mills).      
      4.4 Other tests:                
        - Innumerable companies have their own grindability test.        
        - This test is generally performed in batch mill (similar to the Bond mill).      
                           
    www.thecementgrindingoffice.com
    All rights reserved © 2012-2016 The Cement Grinding Office