Q1: In case of a ball mill,

ANS:A - coarse feed requires a larger ball.

In the context of a ball mill:

• Coarse feed requires a larger ball.

Explanation:

• Ball Mill Operation: In a ball mill, grinding occurs when a particle is crushed between two pieces of grinding media. Ball mills are used for grinding materials into fine powders.
• Feed Size and Ball Size:
  • Coarse Feed: A larger feed size generally requires larger balls to achieve effective grinding. This is because larger balls have more kinetic energy and can crush larger particles more effectively.
  • Fine Feed: Smaller balls are typically used for finer grinding because they provide more points of contact with the material, allowing for more efficient grinding of finer particles.
• Operating Speed and Critical Speed:
  • Critical Speed: The critical speed of a ball mill is the rotational speed at which the centrifugal force is equal to the gravitational force acting on the ball, preventing the ball from falling back on the cylinder wall. Operating above the critical speed can lead to excessive wear and inefficiencies.
  • Operating Speed: Typically, the operating speed of a ball mill is below the critical speed to ensure efficient grinding and minimize wear.

• Coarse feed requires a larger ball to effectively crush larger particles, while finer feed requires smaller balls for efficient grinding of smaller particles.