Step 1: Understanding the Concept:
Selection of a mill depends on the physical properties of the material (hardness, abrasiveness, moisture) and the desired final particle size.
Step 2: Detailed Explanation:
1. Ball Mill: It works on the principle of Impact and Attrition. It consists of a rotating cylinder containing balls (made of steel or porcelain). It is highly effective for hard and abrasive materials because the crushing action occurs within a closed system, and the balls can withstand significant wear.
2. Hammer Mill: Good for brittle materials, but abrasive materials will cause high wear and tear on the hammers.
3. Cutter Mill: Used for fibrous or waxy materials (crude drugs) via a shearing action.
4. Roller Mill: Used for crushing soft materials or in the production of ointments.
Step 3: Final Answer:
The ball mill is the most robust and efficient choice for reducing the size of hard and abrasive pharmaceutical substances.