standard bond ball mill grindability test method-procedure
The standard feed is prepared by stage crushing to all passing a 6 mesh sieve, but finer feed can be used when necessary. It is screen analyzed and packed by shaking in a 1000-cc graduated cylinder, and the weight of 700 cc is placed in the mill and ground dry at 250 per cent circulating load.
The grinding charge consists of 285 iron balls weighing 20, 125 grams. It consists of about 43-1. 45- in. balls, 67-1. 17 in. balls, 71-0. 75-in. balls and 90-0. 61 in. balls with a calculated surface area of 842sq. in.
Tests are made at all sieve sizes below 28 mesh. After the first grinding period of 100 revolutions, the mill is dumped, the ball charge is screened out, and the 700 cc of material is screened on sieves of the mesh size tested, with coarser protecting sieves if necessary. The under size is weighed, and fresh unsegregated feed is added to the oversize to bring its weight back to that of the original charge. Then it is returned on to the balls in the mill and ground for the number of revolutions calculated to produce a 250 per cent circulating load, dumped and rescreened. The number of revolutions required is calculated from the results of the previous period to produce sieve undersize equal to 1/3.5 of the total charge in the mill.
The grinding period cycles are continued until the net grams of sieve undersize produced per mill revolution reaches equilibrium and reverses its direction of increase or decrease. Then the undersize product and circulating load are screen analyzed, and the average of the last three net grams per revolution (Gbp) is the ball mill grindability.
When F is the size in microns which 30 per cent of the new ball mill feed passes, P is the microns which 80 per cent of the last cycle sieve undersize product passes, and P1 is the opening in microns of the sieve size tested, then ball mill work index Wi is calculated from the following revised (1960) equation:
The average value of P at 100 mesh is 114 microns, at 150 mesh it is 76 microns, at 200 mesh it is 50, and at 325 mesh it is 26.7. These values of P are to be used in this equation when P cannot be found from size distribution analyses.
The accompanying procedure and table can be used to shorten the calculations required with the new formula. The values of 44.5/(P1)0.23 are listed for each mesh size, and the values of (Gbp)0.82 can be found by interpolation from the table. The average P values are listed in the last column and should be used for tests whenever the actual P value is not available from screen analyses.
bond work index tests - grinding solutions ltd
The Bond Low-Energy Impact test can be used to determine the Crusher Work index (CWi), also known as the Impact Work Index. The test determines the impact energy at which a specimen fails and allows approximation of net power requirements for sizing crushers. The open and closed sized settings for given product sizes can also be determined.
The Bond Ball Mill Work Index (BBWi) test is carried out in a standardised ball mill with a pre-defined media and ore charge. The Work Index calculated from the testing can be used in the design and analysis of ball mill circuits