Mining: What is a grinding mill and how does it work?

In the mining industry, a grinding mill is a machine used to break solid materials into smaller pieces. These machines are used to grind and crush large rocks or ore into smaller particles, which are then processed further to extract valuable minerals. Grinding mills are commonly used in mineral processing plants, where they play a crucial role in the comminution process.

There are many different grinding mills, such as Raymond mill, ultrafine mill, vertical roller mill, ball mill, etc.

The grinding mill is mainly used in powder making, what I have said above, those machines are used in stone powder making, according to the powder fineness different, there are coarse powder mills: hammer mill; fine mill: Raymond mill, ball mill; and superfine powder mill: ultra fine mill, vertical roller mill.

The different working principles of grinding mill as follows:

Raymond Mill

Raymond mill Working principle:

Raymond mill is mainly composed of main unit, analyzer, fan, dischargeing cyclone separator, powder cyclone separator and air duct. Among them, the main unit consists of frame, blow shell, shovel, grinding roller and grinding ring.

1. The lump material will be conveyed into the storage bin by the bucket elevator after it is crushed into the required particle size by the jaw crusher.
2. Then electro vibrating feeder will uniformly transfer the material into the grinding chamber of the host machine.
3. The material is upthrown and fed into the space between the grinding roller and grinding ring in the process of synchronous rotation of the shovel and the grinding roller and forms a cushion material layer.
4. The material on this layer is grinded between the grinding roller and the grinding ring. Thus, the purpose of powder production is achieved.
5. The grinded powder will be carried by the airflow of the fan into the analyzer for classification.
6. The powder with the qualified fineness will enter the large cyclone collector, together with the airflow through the pipes, for classification, and then, will be discharged by the discharging device, as the finished product.
7. The airflow is sucked into the air blower through the air return pipe on the upper part of the large cyclone collector.
8. The unqualified powder will be thrown to the external wall by the airflow and separated from the airflow.
9. The coarse powder will fall into the grinding chamber for regrinding due to its own gravity.
10. The whole airflow system is closed and cyclic, and it flows under the positive and negative pressure circularly.

Ultra Fine Mill

Working principle of HGM Ultra fine Mill

When the grinding mill is at work, all the grinding rollers are rolling in the ring, and the materials are driven to the edge of the turnplate by the centrifugal force and fall down into the grinding chambers where the materials are repeatedly pressed, crushed and grinded by the rollers.

The high-pressure air blower constantly inhales air within the grinding mill and, in turn, the airflow with crushed materials are brought to the classifier whose high-speed impeller will screen the airflow: the unqualified particle size will fall and return to the mill for being reground while the qualified particle size mixed with air will go into the cyclone powder collector. Most of the qualified powders will fall and exit from the discharging valve at the bottom; a small proportion of the fine powders, with airflow, moves to the dust cleaner, and clings to the surface of the filter bags. At the same time, the fine powders clinging to the surface fall down by the sudden vibration of the filter bags, which is caused by the instantly ejected high-pressure gas controlled by the pulse valve. The materials from the above two lots are sent by the conveyor at the bottom to get finished powders packed. In addition, filtered clean air will be emitted from the air outlet of muffler in the end.

Vertical Roller Mill:

Working Principle of Vertical Roller Mill

The motor makes grinding revolve under action of reduction gear. Materials, after being measured by belt scale, are sent to center of grinding disc by feeding screw. Because of centrifugal force, the materials would move towards the fringe of disc and then enter the grinding zone between grinding roller and disc to be ground. The materials which have been ground would keep moving toward fringe of grinding disc until they spill out of the disc. Through air inducing ring on the fringe of grinding disc, airflow sends these spilling materials to powder concentrator for classifying powders. The coarse powders which don’t meet the requirement of fineness would fall to the disc for another grinding while these qualified powders, as finished products, would be collected into dust collector and finally sent to finished product silo by conveying system for storage and packaging.