ANS:C - impact

Maximum size reduction in a ball mill is primarily achieved through impact action.

Explanation:

• Impact Action: In a ball mill, the grinding media (balls) and the material being ground are subjected to impacts as the balls cascade and tumble within the mill cylinder. These impacts cause the particles to break or deform, leading to size reduction.
• Other Actions:
  • Attrition: Attrition occurs when the grinding media rub against each other or against the mill lining. While attrition contributes to size reduction, it is typically secondary to impact in a ball mill.
  • Compression: Compression is not a primary mechanism in a ball mill because the grinding media (balls) do not compress the material directly. Instead, particles are crushed or deformed by impacts.
  • Cutting: Cutting action is not applicable to ball mills, as they do not involve shearing or cutting of materials.
• Effective Size Reduction:
  • Impact action in a ball mill is effective for reducing the size of particles because it involves high-energy collisions between the grinding media and the material.
  • The efficiency of size reduction in a ball mill depends on factors such as the speed of rotation, the size and number of balls, and the characteristics of the material being ground.