To distinguish it from an autogenous mill, grinding mills that require the addition of metal media (balls or rods) are generally referred to as conventional grinding mills, such as ball mills and rod mills. To achieve higher grinding efficiency and improve the economic benefits of mineral processing, it is necessary to select the appropriate grinding mill based on the particle size requirements of the feed material and the properties of the raw ore, according to the characteristics of various grinding mills. The main characteristics and applicable scope of ball mills and rod mills commonly used in mineral processing plants are as follows:

(1) Grid-type ball mill. Due to its unique grid plate and the presence of the lifting bucket in the fan-shaped chamber, it achieves low-level forced discharge of ore. The finely ground ore particles do not remain in the ball mill for too long and can be discharged in time. Over-grinding is less severe, and the grinding speed is fast and the efficiency is high.

(2) Overflow-type ball mill. The hollow shaft diameter at the discharge end of this mill is slightly larger than that at the feed end, causing a certain inclination of the slurry surface towards the discharge end. When the slurry level is higher than the lowest generatrix of the discharge port, the slurry overflows. This is a non-forced high-level discharge, resulting in a slow discharge speed, a long residence time of the ore within the mill, and a lower effective media effect. Therefore, overflow-type ball mills suffer from severe over-grinding, and their throughput is lower than that of grate-type mills of the same specifications. They are generally suitable for fine grinding or the second stage of a two-stage grinding process.

(3) Rod Mill. The media in a rod mill are steel rods, which fall horizontally and come into contact with the ore surface, selectively crushing the ore (i.e., crushing it sequentially from large to small pieces). Therefore, over-grinding is less severe, and the grinding product has a uniform particle size, making it suitable for coarse grinding or gravity separation plants that require less over-grinding of the grinding product.