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      The study of the granulometry along the ball mill
         
      1 Introduction
      In order to have a good idea of the ball mill's efficiency (linings, ball charge, diaphragms, ventilation), we have to do a 
      granulometric analysis inside the mill.
      This analysis includes three steps:
      - The sampling campaign inside the mill
      - The sieving of the samples in the laboratory
      - The results analysis with the curve and its interpretation
      For this presentation, we consider a classical 2 chambers mill as example.
         
      2 The Sampling Campaign
        First Chamber
        As described in the Mill Inspection Procedure, we need the following:
       
    sachets-ch1.jpg
    collector.jpg
     
        Procedure:
      - Take 4 samples (inlet, 2 intermediate samples, at the intermediate diaphragm) of ± 3kg each
      - Ideally for each sample, take materiel in three points as shown on the drawing here below
       
    samplepoints.JPG
     
      - Dig a hole 30 cm deep removing the balls at the sampling point and collect the sample with the collector. 
       
     
        Don't reject the unground particles from the sample!
        Second Chamber
        We need the following tools:
       
    sachets-ch2.jpg
    tamis.jpg
     
       
     
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        Procedure:
      - Take 7 samples (1st at inlet, 5 intermediate samples at equal distance and the last at the outlet diaphragm) of 0,5-
        1kg each
      - As the 1st chamber, take materiel in three points as shown on the drawing here below
       
    samplingch2.JPG
     
      - Dig a hole 30 cm deep removing the balls at the sampling point and collect the sample with the collector near the
        intermediate diaphragm (where there are the biggest balls in case of classifying lining). In the area of the smallest
        balls, use the shovel with the sieve and a bag below the sieve to retain the material
       
    echantillonnage-ch2.jpg
     
        Don't reject the unground particles from the sample!
      - Send all the samples to the laboratory
         
      3 The Sieving in the laboratory
      - We recommand the following sieves: 50mm, 25mm, 10mm, 5mm, 2,5mm, 1mm, 0,5mm, 212µ, 90µ.
      - Of course, similar sieves can be used.
      - Some plants adopt smaller sieve like 63µ, 45µ or/and 32µ because cement quality reason
      - As an example, we will take the first sample of the 1st chamber:
        Weight of the sample: 3,105 kg (3105gr)
        We will sieve manually for the biggest sieves (50mm, 25mm, 10mm and 5mm) and with the whole sample.
        Why the whole sample? Because the sample is generally a mixture of some big particles with fine particles. Then,
        it is difficult to homogenize the sample and to reduce it representatively.
       
     
        Results:
        1st sieving (with 50mm sieve): 326gr of material are retained - It means that we have 326gr higher than 50mm
        2nd sieving (with 25mm sieve): 236gr of material are retained - It means that we have 236gr between 25mm and 50mm
        3rd sieving (with 10mm sieve): 226,7gr of material are retained - It means that we have 226,7gr between 10mm and 25mm
        4th sieving (with 5mm sieve): 124,2gr of material are retained - It means that we have 124,2gr between 5mm and 10mm
        Summary of this first screening phase:
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        2192,1gr of the sample are lower than 5mm
        This part of the sample will be homogenized manually or with a homogenizer and we only will take a small part for the 
        second step of the sieving. It depends of the laboratory and the sieving device, but it is often between 100 and 500gr.
        The sieving device will be a sieve shaker (vibrating) or better, an air jet sieving for the possible agglomerated particles.
       
     
        For our example, let's take 100gr of material.
        Summary of the second step:
       
     
        Now, we have to link both steps in order to have the complete result of the sample 1 of chamber 1.
        For that, we use the follwing equation:
       
     
       
       
        With:
        A = total residue cumulated in gr on a sieve
        B = passing of the 1st step in gr
        C = initial weight of the second step sample in gr
        D = residue cumulated in gr on a sieve for the 2nd step in gr
        E = residue cumulated of the last sieve of the 1st step in gr
        Results on the table below:
       
     
        We do the same procedure for all the samples taken inside the mill.
        The interpretation of the results is following on the next page
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