According to the discharging method, the ball mill can be divided three types overflow type, end discharging method, and central peripheral discharging type. Peripheral discharging mill has high speed of discharging, and coarse products size for the less degree of crush. The central peripheral discharge type which can feed materials from both ends, has more higher speed of discharging and more coarse product size. The rod mill can be applied in both dry and wet type operation. The peripheral discharge is also used for wet grinding. We often use special machine to add rod medium. We should also regularly check up the wear of rod, take out of broken and bent rod in order to avoid its interference with the work of normal rod. So the efficiency of rod is low, generally 80%-88%.
First, the structure of rod mill and ball mill is basic same. The difference is that the former simplified aspect ratio (L/D) is larger, generally 1.5-2.0. Its discharging part has no lattice board and is larger than the overflow type ball mill’s discharging part which is convenient to discharging, load and remove the broken or bent rods. In order to prevent the skew of steel bar when the simplified rotating, the inner surface of rod mill conical cover is set to flat after covered with lining plate. Rod mill uses long round steel bar as grinding media. The length of bar is generally shorter 100-150 mm than the length of simplified, and its diameter is generally 60mm-120mm. too thick bar is easy to smash the lining plate, and too thin is easy to broken.
Second, the line contact between the rods and bars, rods and materials has strong selectivity in the operation. So the particle size is uniform, generally 1-3mm, and the degree of crush is light. The rod mill is 1.36 times the rod density of ball mill of the same material when the simplified is stationary. The filling rate of rod mill medium is low, typically 30%-35%, and the rotating rate is also low, generally 60%-75%. The feeding size should not be greater than 25mm, otherwise the rod will skew, bend and even broken. The grinding efficiency will also decline accordingly.
