What is a particle size distribution?
A particle size distribution shows which size intervals occur in a sample and in what proportions. One maximum size describes only the largest lump; it does not show whether most material is coarse, intermediate or fine. Metso treats maximum size and distribution values such as d50 and d80 as separate material properties in process assessment.
Two feeds can share a 40 mm top size while one is mainly 30–40 mm and the other mainly 2–8 mm. They will not behave alike in a crusher chamber, grinding duty or on a belt. A selection brief therefore needs the distribution curve, not one size alone.
What does sieve analysis measure?
In sieve analysis, a representative sample passes through a stack arranged from larger to smaller apertures. The fraction retained on each sieve is weighed; fraction percentage, cumulative retained and cumulative passing are calculated. RETSCH describes weighing the retained fractions as the most common evaluation.
ASTM E11-24 defines requirements and tolerances for woven-wire sieve cloth and test-sieve construction. E11 alone is not a complete procedure for every material. The material-specific method, preparation, sieving time and applicable sector standard must also be stated.
How is a cumulative passing curve read?
The horizontal axis shows sieve aperture and the vertical axis the total percentage passing that aperture. “80 percent passing” means that 80 percent of the sample, on the stated basis, is at or below that size; 20 percent is coarser.
For a simple example, suppose 100 percent passes 16 mm, 85 percent passes 8 mm, 55 percent passes 4 mm and 20 percent passes 2 mm. The 80-percent-passing size lies between 4 and 8 mm. Its exact value is read using the axis and interpolation method declared in the report, not guessed as a convenient whole number.
What is the difference between D80, F80 and P80?
D80 is the characteristic size below which 80 percent of the distribution lies. In comminution circuits, F80 is the 80-percent-passing feed size and P80 is the corresponding product size. With the same units and comparable measurement bases, F80/P80 can indicate size reduction; it does not by itself guarantee capacity or energy use.
The distribution basis belongs with any D-value. Sieve analysis is commonly mass-based, while laser diffraction often reports volume-based Dv10, Dv50 and Dv90. Malvern Panalytical explains that number-, volume- and intensity-weighted results can differ and data from different methods are not automatically equivalent.
How does the distribution change equipment selection?
For jaw and hammer crushers, the largest lump matters for inlet suitability, but coarse-intermediate-fine proportions also affect chamber loading, passage and product distribution. A ball mill needs feed and target product curves, not only one top size. A belt conveyor considers both lump size and the volume and cross-section formed by the material.
Metso’s crushing and screening handbook tracks particle size distributions for material streams in circuit calculations. A catalogue capacity for one distribution should not be transferred directly to another. Even at the same tonnes per hour, more coarse particles, more fines or intermittent feed can behave differently.
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Why is a representative sample as important as the analysis?
Accurate balances and sieves cannot repair a biased sample. Coarse and fine particles can segregate in a stream; one scoop from the top of a pile may not represent the whole. RETSCH calls a representative subsample a basic condition for reproducible sieving and shows that random sampling can create major variation within the same material.
Record where, when and under which operating condition the sample was taken. When reducing a bulk sample to laboratory quantity, do not hand-pick particles; use a suitable divider or a validated splitting method. Preparation also belongs in the report because moisture loss or breaking agglomerates can change the result.
What should be reported together?
Include sampling location and date, material condition, moisture, method, distribution basis, sieve apertures, mass of every fraction, cumulative passing values, total sample and any loss. When D80, F80 or P80 is reported, state the unit and the curve from which it was read.
One sample may not cover design variability. Normal production, the realistic coarsest feed, wet-season conditions or recipe changes may need separate samples. The project can then be assessed against the range the line will meet, not one apparently average curve.
Safety and the limits of this guide
This article is not an instruction to take a hand sample from a running belt, crusher or mill. Samples should come only from a designed safe point under manufacturer instructions and the site risk assessment. Where inspection or intervention exposes personnel to moving equipment, authorised workers must isolate energy and verify a safe state under the applicable procedure. OSHA 1910.147 describes energy control where unexpected start-up or stored energy can injure workers during servicing.
Follow the safety data sheet and workplace rules for dusty, hot, reactive or harmful materials. The examples are educational and state no capacity, feed size, product fineness or performance value for an İnovate model.
Sources
Sources were checked on the article publication date. These are general technical references, not documentation of İnovate product specifications.
- Metso — Basics in Minerals Processing Handbook
- RETSCH — Expert Guide: Sieve Analysis
- ASTM International — ASTM E11-24 Test Sieves
- Malvern Panalytical — Definition and Measurement Methods of Particle Size Distribution
- Metso — Crushing and Screening Handbook, 7th Edition
- OSHA — Control of Hazardous Energy (Lockout/Tagout), 29 CFR 1910.147
