efficiency as where, is the surface energy per unit area wn is the energy absorbed by the material. we can experimentally find ηc. the range of ηc is between 0.06 1.00%. if ηm is the mechanical efficiency, the energy input is since wn= ηmw finally, the grinding energy used per unit mass is where m is mass of material being ground, is the sphericity, 3
the results are shown in figure 3-17. it is seen that for a reduction ratio of 1.32, the relative efficiency of crushing a multi-layer of particles is 72%. note that crushing ratios in a ball mill are not well defined, but are believed to range up to 1.5 or even 2.0.
the yield achieved with the micro-ball mill was 100% but was 80% for the air-jet mill, which reduced the size of pluronic f-68 from 70 μm to sizes ranging between 23 39 μm median diameters. ball milling produced particles less than 10 μm after 15 min.
procedure can be carried out in any laboratory ball mill. horst and bassarear 1976 gave a similar procedure, but lasting a bit longer, where reference ore data and data of the ore for which the value of the bond index is determined, are also compared. smith and lee 1968 have compared the data obtained through the standard bond
figure 1: uniaxial compression test machine. 3- standard bond tests. the bond's standard ball mill is used to determine the work index value of differ ent samples. the bond work index is defined as the kilowatt-hours per short ton required to break from infinite size to a product size of 80% passing 100 µm.
efficiency of grinding and mechanical activation of solids in planetary ball mills fig. 3: module of mechanical activation based on two planetary mills mpc-3 in addition, a series of centrifugal flow mills for dry milling was developed at the isscm sb ras fig. 4 .
factors affecting ball mill grinding efficiency. also related to both material and media retention is the discharge arrangement. south african experience indicates that the faster the pulp removal, the better, as evidenced by the evolution from grates with pulp lifters, to peripheral, and finally, to openend discharge design mokken, 1978 .
in a review of suryanarayana and al-aqeeli 2013 it is reported that only 15% of the studies used stirred media mill for mechanical alloying and 80% utilized mainly planetary ball mill or shaker mill and further 5% other mill types. furthermore, among the 15% stirred media mills most of them are low velocity vertical attritors and not high-speed horizontal ones.
according to this definition, given that the energy utilization in a ball mill is between 1×10 −3 and 4×10 −3 m 2 /j, and that the crack resistance value is between 30 and 60 j/m 2, the theoretical efficiency of the ball mill should be in the range of 1.5 12%.