Particle size distribution (PSD) is a measurement that describes the range of particle sizes present in a bulk material, typically expressed as the percentage of material within each size fraction. PSD is the single most important material property for sizing vibratory screening equipment, selecting screen mesh, and predicting separation performance. Without an accurate PSD, it is impossible to correctly specify a separator or set realistic throughput and efficiency expectations.
PSD is determined through sieve analysis (also called a screen analysis or gradation test), where a weighed material sample is passed through a stack of test sieves arranged from coarsest on top to finest on the bottom. The material retained on each sieve is weighed, and the results are expressed as percentages of the total sample. The PSD reveals the proportion of near-size particles, the amount of oversize and undersize in the feed, and whether the material is narrowly or broadly distributed. ScreenerKing engineers use PSD data to recommend the correct separator model, screen mesh, and operating parameters for Sweco, Kason, Midwestern, and ScreenerKing applications.
Example Sieve Analysis Report
| Sieve (Mesh) | Opening (Microns) | Weight Retained (g) | % Retained | Cumulative % Passing |
|---|---|---|---|---|
| 20 | 841 | 5.2 | 5.2% | 94.8% |
| 40 | 420 | 22.8 | 22.8% | 72.0% |
| 60 | 250 | 35.4 | 35.4% | 36.6% |
| 80 | 177 | 18.6 | 18.6% | 18.0% |
| 100 | 149 | 10.2 | 10.2% | 7.8% |
| Pan | — | 7.8 | 7.8% | 0.0% |
Why This Matters in Vibratory Screening
- Separator sizing — The PSD determines the volume of material that must pass through each screen deck. A feed with 70% undersize needs more screening area than a feed with 30% undersize at the same total feed rate.
- Near-size content — The percentage of near-size particles (75-125% of aperture) is the most critical factor for screening difficulty. High near-size content requires more screen area, deblinding aids, or slower feed rates.
- Mesh selection — PSD data shows exactly where the cut point should be set and how much material falls in each fraction, guiding screen cloth mesh selection for each deck.
- Capacity estimation — Screener manufacturers use PSD data along with bulk density to calculate expected throughput capacity for each application.
Related Glossary Terms
- Near-Size Particles — The fraction that determines screening difficulty
- Bulk Density — Weight per unit volume, used with PSD for sizing
- Grading/Classification — Separating material into PSD-defined fractions
- Screening Efficiency — Accuracy of separation, predicted from PSD
- Stratification — Size-based layer formation dependent on PSD
Particle Size Distribution FAQs
What is particle size distribution?
Particle size distribution (PSD) describes the proportions of different particle sizes in a bulk material sample. It is determined by sieve analysis and is the most important property for sizing vibratory screeners and selecting screen mesh.
How is particle size distribution measured?
The most common method is sieve analysis: a weighed sample is passed through a stack of test sieves from coarsest to finest, and the material retained on each sieve is weighed. Results are reported as cumulative or differential percentages. For particles below 45 microns, laser diffraction or image analysis may be used.
Need Help Sizing Your Separator?
Send ScreenerKing your sieve analysis data and we will recommend the right separator model, screen mesh, and configuration for your application.