Screening at fine sizes: as average particle size decreases during separation on a screen, what happens to the screening task?

Introduction / Context:
Screens separate solids by size using apertures. At small particle sizes, several physical effects reduce efficiency and capacity. Recognising this trend helps engineers choose between fine screens and alternatives such as classification or filtration.

Given Data / Assumptions:

• Dry or wet screening of granular solids.
• Particle sizes approach the aperture size or become very fine.
• No major changes in moisture other than typical fines behavior.

Concept / Approach:
As particles get smaller, they are more prone to agglomeration, electrostatic effects, and surface forces. Near-size particles bridge or peg the apertures. The probability of passage drops and blinding increases. Both capacity (throughput per area) and efficiency (sharpness of cut) tend to decrease.

Step-by-Step Solution:
Reduce size toward aperture → more near-size particles.Near-size particles lodge, agglomerate, or track apertures → blinding/pegging increases.Net effect → screening becomes progressively more difficult; capacity and efficiency fall.

Verification / Alternative check:
Plant experience shows that fine screening demands agitation aids (inclination, vibration intensity), spray water (wet screening), anti-blinding devices, or switching to classification when fines dominate.

Why Other Options Are Wrong:
“Easier” or “capacity/effectiveness increased” contradict the physical realities of fines handling.“None of these” is unnecessary because the correct trend is well established.

Common Pitfalls:
Ignoring moisture; even a little dampness can exacerbate fines agglomeration and blinding dramatically.

Final Answer:
screening becomes progressively more difficult.