In comminution (size reduction), how does production rate change as product fineness is increased when the energy input to the machine is held constant?

Introduction / Context:
Size reduction operations (crushing, grinding, milling) consume substantial power. Throughput, specific energy, and target fineness are tightly coupled. Understanding these trade-offs is essential for selecting mills, setting operating points, and estimating operating costs.

Given Data / Assumptions:

• Energy input to the machine is fixed (power constraint).
• Target product becomes finer (smaller characteristic size).
• Same material and feed characteristics.

Concept / Approach:
Work input generally increases nonlinearly as the required product size decreases. Rittinger’s law ties energy to new surface area (dominant at fine grinding), while Bond’s law is often used for ball mills over a broad range. For a fixed power draw, achieving finer product consumes more energy per unit mass; therefore, less mass can be processed per unit time, reducing production rate.

Step-by-Step Solution:
Hold power constant → fixed energy per time.Finer product → higher energy per mass required.Thus, mass processed per time (production rate) must fall.

Verification / Alternative check:
Plant data routinely show throughput drops when grind is tightened (e.g., moving from 150 microm to 75 microm cut).

Why Other Options Are Wrong:
Increases/Unchanged: contradict energy-per-mass rise at finer sizes.Depends only on machine: material grindability and energy–size laws dominate, not just machine choice.

Common Pitfalls:
Confusing power (kW) with energy per unit mass required to hit a finer P80; they are not interchangeable.

Final Answer:
Decreases