In the design of the beneficiation plant, the processing capacity of the ball mill is generally determined based on experiments and experience. The processing capacity of ball mills and rod mills is often calculated using the volume method or power consumption method.
The selection of ball mills should meet the following requirements:
1. Rod mills are primarily used for coarse grinding, with the particle size of the ground product typically ranging from 1 to 3 mm, and for heavy selection plants, it can be as fine as 0.5 mm. If the particle size is too fine, the grinding efficiency significantly decreases. Due to the influence of the movement of the grinding rods within the mill, the diameter of the rod mill should generally not exceed ф4500 mm, and the length of the grinding rods should not exceed 6000 mm. When rod mills and ball mills operate together, the ratio of rod mill to ball mill should be 1:2.
2. Grid-type ball mills are mostly used for coarse grinding, generally in the first stage of single-stage or two-stage grinding. In closed-circuit operation, the grinding fineness is generally 50% to 70% -0.074 mm. Ball mills are often paired with spiral classifiers.
3. Overflow ball mills can be utilized for the first stage of grinding, as well as for the second stage of grinding or regrinding of intermediate products. Currently, they are predominantly used for the second stage or regrinding of intermediate products in China, with classification equipment typically paired with hydraulic cyclones. When the mill is employed for the first stage of grinding, it is sometimes also paired with spiral classifiers. Large ball mills (generally larger than ф4000 mm) often incorporate overflow ball mills and hydraulic cyclones to form a grinding circuit, which simplifies the structure of the mill and facilitates maintenance.
4. When selecting autogenous mills, semi-autogenous mills, and pebble mills, special attention should be paid to whether the raw ore has good autogenous grinding media. The autogenous media index of the ore can be determined using an autogenous media measuring instrument, and data processing should be conducted to determine whether it has good autogenous media, which will help decide whether to conduct autogenous, semi-autogenous, and pebble semi-industrial tests. After the semi-industrial tests, empirical formulas are used for the selection calculations of autogenous mills, semi-autogenous mills, and pebble mills.
