Classification of drum ball mills
The main process in production of cement, lime, ceramic materials, etc, is grinding of different materials to particles sized less than tenths of mm. The grinding process specific power consumption is large.
However, only some part of energy consumed by grinding machine is spent on material grinding. Significant part of energy is lost as heat, sound, and operating members wear. Taking into consideration that large masses of materials (hundred millions of tons) are subjected to fine grinding, the economic significance of the improvement of such a process and equipment becomes evident.
Drum (ball and rod), medium-speed impact, vibratory and jet-type mills are used for material grinding in modern production.
In drum mills the material is ground inside a hollow rotating drum into which grinding media are placed (balls, rods). When the drum rotates, the grinding media and material (hereafter referred to as "charge") first move along the circular trajectory, and then, having detached from the wall, along parabole.
The material is ground as a result of abrasion during relative movement of balls and particles, and impact of balls against material when they fall from some height.
The drum mills are classified:
- in terms of operation mode
- intermittent action
- continuous action;
- in terms of grinding method
- dry grinding
- wet grinding
- in terms of material charging and discharging method
- charged and discharged via a hatch,
- charged and discharged via hollow spigots,
- charged via a spigot and discharged via drum walls
The mill drum is driven via a girth gear or a spigot.
The drum mills can operate in unclosed or closed cycles. In the latter case the material removed from the mill is screened (separated), and coarse particles (over-size) are returned into the mill for remilling. When such operation pattern is used the material ground to the required particle size is continuously removed from the mill which improves its efficiency.
The ball mills are characterised by their inner drum diameter and the drum operating length. Some specifications of drum mills, drum diameter, drum length, weight, power are shown in the Table.
When drum mills operate, dust may be emitted to the environment, and increased production noise is possible. So, all material movement channels in grinding units shall be covered tight with casings. During mill operation it is necessary to check the condition of actuators before each shift and replace them in a timely manner.
The production rooms shall be equipped with a ventilation and dedusting system which would prevent from environmental pollution with grinding products. To reduce noise, rubber gaskets shall be used between the mill housing and lining plates. The machine control panels shall be installed in soundproofed booths. The personnel shall wear personal protective equipment (face masks and special ear protectors) when in the production premises.