Trommel operating speed: revolving screens (trommels) normally run in which rpm range for effective screening?

Introduction / Context:
Trommels separate material by rotating a perforated cylinder. The operating speed must be high enough to tumble the material yet well below the critical speed to avoid centrifuging and loss of screening action.

Given Data / Assumptions:

• Medium-size industrial trommels handling aggregates/ores.
• Target: typical rpm range rather than an exact design value.

Concept / Approach:
Typical practice places operating speed at a small fraction of critical (often 30–50% of N_crit depending on lifters and fill). For many diameters, this translates to the 15–20 rpm range, providing adequate cascading and retention without excessive carryover.

Step-by-Step Solution:
Consider typical diameters (1–3 m) and critical-speed relation → N_crit tens of rpm.Choose operating fraction (~0.3–0.5 of critical) → gives mid-teens to ~20 rpm.Select the 15–20 rpm range.

Verification / Alternative check:
Manufacturer curves and plant standards often list 12–22 rpm, depending on feed and screen design.

Why Other Options Are Wrong:
1–2 rpm: too slow; poor cascading and throughput.40–50 or 60–75 rpm: near or above practical limits for most trommel sizes; risk of centrifuging.

Common Pitfalls:
Ignoring lifter bars or internal flights, which allow slightly lower speeds for the same performance.

Final Answer:
15 – 20