Screening efficiency describes how effectively particles that should pass and particles that should remain are directed to the correct product streams. Feed PSD, near-size content, surface loading, bed depth, moisture and open apertures directly influence the result.
Undersize, oversize and product streams
Undersize is the finer fraction expected to pass the selected aperture. Oversize is the coarser fraction retained on the surface. Unlike general sample D-values, these terms describe streams in a defined screening duty.
Real products can contain misplaced particles. Performance evaluation combines representative PSD results and mass flows for the feed and every outlet stream.
Why is near-size difficult?
Near-size particles are close to the screen aperture. They need suitable orientation and repeated presentation to pass, so they can remain longer on the surface or report to the wrong fraction.
A larger near-size population can make separation more demanding at the same nominal aperture. The complete feed distribution is therefore evaluated rather than one average or characteristic size.
Feed distribution, screen loading and bed depth
Balanced distribution across the width and over time allows effective use of the available surface. Local overloading can leave other regions underused and reduce particle contact with apertures.
As bed depth increases, particles in lower layers may have less opportunity to reach the surface. Very low loading can underuse capacity. No universal optimum is stated; material, surface and motion are verified together.
Moisture and fine-powder behaviour
Moisture can increase cohesion and surface adhesion, particularly in fine mineral powders. Agglomerated fines can behave as larger particles and cover apertures.
Natural and process moisture, temperature, storage time and feed conditioning should be evaluated with representative material for a dry-screening duty.
Blinding and pegging
| Condition | General definition | Possible effect |
|---|---|---|
| Blinding | Fine or sticky material covers apertures | Reduced open area and passage of fines |
| Pegging | Near-aperture particles become trapped in openings | Local closure of passage area and product deviation |
The response depends on material, aperture, surface, feeding and cleaning conditions. No single vibration setting suits every application.
How is performance monitored?
- Collect representative samples from feed and outlets
- Measure every stream with a consistent PSD method
- Record mass flows and sampling time
- Inspect aperture cleanliness and surface wear
- Relate moisture and feed-rate changes to samples
- Do not attribute a declining trend to vibration alone
Why is no formula published here?
Screening efficiency can be expressed in different ways according to the product objective and sample definitions. A single percentage formula without a verified mass balance can lead to false interpretation.
This article therefore explains the principles; project calculations use defined product boundaries and validated analyses.
