Grate ball mill primarily consists of six parts, viz, the barrel, feeding part, discharging part, bearing part and lubrication system. The lining plate is installed inside the barrel, whose materials are from manganese steel, chrome steel, cast iron and rubber. There’s a hole in the barrel for the use of maintaining and changing the liner.
Overflow ball mill is basically similar to the grate ball mill in structure. It is also composed of six parts. The difference is that there’s no grid plate device in the discharging part and the overflow ball mill is simpler than the grate ball mill in structure.
The overflow ball mill appeared earlier than the grate ball mill, the hollow shaft diameter of the discharging part is larger than the feeding one, which enables the ore pulp overflow from the discharging part. As the pulp overflowes from the discharging port, the pulp level becomes lower than the height difference inside the ball mill forms which makes the pulp shift from the self-supporting port to the discharging part. It can greatly promote the productivity and improve the quality of the grinding products. In order to avoid the grinding medium or the coarse ore block from discharging with the pulp together, the boomerang spiral is installed in the quill shaft of the discharging port.
Compared with the grate ball mill, the overflow ball mill discharges slower. It is suitable for fine grinding and requires prompt adjustment due to its sensitivity towards the change of the outside elements. Besides, its structure is simple and the maintenance is convenient.
While there are many small holes in the grid plate of the discharging port in the grate ball mill for the convenience to discharge the ore pulp. One side of the grid plate close to the discharging port installs a pulp bot. It is a kind of radial square beam. The space between the grid plate and the end cover is divided into several fan chambers, leading to the quill shaft journal. When the mill starts rotating, the square beam plays a part in elevating the pulp. Elevating the pulp is discharged by the small holes in the grid plate, then the pulp gets discharged via the grinding mill. Therefore, the main features of this machine are discharging by force and with high productivity. It is usually adopted in the first grinding work. This can get relatively high processing ability. But the product’s granularity is coarser than that of the overflow ball mill.
In production, the discharging concentration of the grade ball mill is higher than the overflow one, because the former has the forcedly discharging function. If the concentration is dilute, the flow rate will speed up, and the impact times between the particles and the grinding medium will decrease. All those will not only reduce the grinding efficiency but also speed up the abrasion of the liner and the steel ball, meanwhile the granularity tends to become coarse (known as “running coarse”)