Near-size particles are particles with dimensions within approximately 75% to 125% of the screen aperture size, making them the most difficult fraction to separate and the primary cause of screen blinding. These particles are close enough to the cut point that their passage through the screen depends on orientation, velocity, and the number of times they contact the screening surface. Near-size particles are the limiting factor in vibratory screening performance.
In any bulk material feed, particles range from much smaller than the aperture (easy throughs) to much larger (easy overs). The near-size fraction occupies the middle ground where separation becomes probabilistic rather than certain. A particle at 90% of aperture size may pass through on a favorable presentation but bounce over the opening on an unfavorable one. Particles at 100-125% of aperture size are prime candidates for plugging and pegging. On ScreenerKing, Sweco, Kason, and Russell Finex separators, managing near-size particles requires optimizing amplitude, frequency, lead angle, and screen media selection.
Near-Size Particle Behavior by Size Ratio
| Particle-to-Aperture Ratio | Classification | Screening Behavior | Impact on Screen |
|---|---|---|---|
| Less than 50% | Easy throughs | Pass through on first contact | No blinding risk |
| 50-75% | Moderate throughs | Pass through within 2-3 contacts | Minimal blinding risk |
| 75-100% | Near-size (undersize) | Require multiple presentations; orientation-dependent | Moderate plugging risk |
| 100-125% | Near-size (oversize) | Cannot pass through but attempt to enter openings | High plugging/pegging risk |
| Greater than 125% | Easy overs | Travel directly to discharge | No blinding risk |
Why This Matters in Vibratory Screening
- Screening efficiency — The near-size fraction determines overall screening efficiency. A feed with 5% near-size content screens easily; a feed with 40% near-size content requires significantly more screen area, dwell time, or multiple passes.
- Separator sizing — Machines must be sized to accommodate the near-size fraction, not just total feed volume. Higher near-size content requires larger screening area or additional decks.
- Screen blinding — Near-size particles are the primary cause of plugging and pegging. Understanding the near-size content in your feed helps determine whether ball decks or ultrasonic deblinding is necessary.
- Mesh selection — When near-size content is high, operators may choose a slightly larger or smaller mesh to shift the near-size fraction into an easier separation range.
Related Glossary Terms
- Plugging — Near-size particles lodging within screen openings
- Pegging — Near-size particles wedging into openings from above
- Particle Size Distribution — The full size range including near-size fraction
- Screening Efficiency — Limited primarily by near-size particle behavior
- Stratification — Layer formation that brings fines to the screen surface
Near-Size Particle FAQs
What are near-size particles in screening?
Near-size particles are those with at least one dimension within approximately 75% to 125% of the screen aperture. They are the hardest to classify because passage through the screen depends on orientation and the number of contacts with the screening surface.
How do near-size particles affect screening efficiency?
Near-size particles reduce screening efficiency in two ways. First, they take the longest to pass through because they must be presented at exactly the right orientation. Second, they cause plugging and pegging, which progressively blocks screen openings. Materials with high near-size content require longer residence time, more screen area, or deblinding aids.
Handling Difficult Near-Size Separations
ScreenerKing engineers help select the right mesh size, deblinding system, and separator configuration for high near-size applications.