How coal gets crushed in ball mills?

In ball mills, coal is crushed through a combination of impact and attrition forces. Here's a step-by-step outline of how the process typically works:

1. Feeding Coal: The raw coal is first fed into the ball mill through a chute or a feeding device.

2. Grinding Process:

   • Impact: As the mill rotates, the grinding media (balls) inside the mill are lifted and then dropped onto the coal. This impact force helps to fracture and crush the coal into smaller particles.
   • Attrition: As the balls move around, they also create frictional forces against the coal. This further grinds the coal particles, wearing them down over time into finer particles.

3. Size Reduction: The coal gets progressively smaller as it is repeatedly impacted by the balls. The mill continues to rotate, ensuring that the coal is continuously subjected to the crushing forces.

4. Discharge: Once the coal has reached the desired fineness, it exits the ball mill through a discharge grate or screen. The finer particles pass through, while any larger pieces may be returned to the mill for further grinding.

5. Collection: The pulverized coal is then collected for further processing or for use in applications such as power generation, where it is burned in boilers.

The efficiency of this process can be influenced by various factors such as the speed of the mill, the size of the balls, the size of the coal feed, and the design of the mill itself.