Reading powder sizes: 15–45 µm, −45+15 and Dv50

15–45 µm is a size-band designation. The conventional notation −45+15 µm expresses an upper cut and a lower cut. Neither label alone specifies the test method, permitted oversize or undersize, or the full particle-size distribution. Put those requirements in the agreed specification.

Dv10, Dv50 and Dv90 answer a different question

For a volume-weighted distribution, Dv10, Dv50 and Dv90 are the diameters below which 10%, 50% and 90% of the measured particle volume lies. Dv50 is the volume median, not the arithmetic mean or the largest particle.

Why sieve and laser results can differ

Sieving separates particles through apertures. Laser diffraction reports equivalent spherical diameters. Particle shape and measurement method therefore affect the comparison, particularly with irregular powders. A laser Dv90 above a nominal sieve endpoint does not, by itself, establish that a batch fails a sieve specification.

When comparing two certificates, first check whether both use the same method and reporting basis. Also check sample preparation and whether a reported D10 actually means Dv10. Do not silently convert a label written in mesh into micrometres without identifying the applicable sieve standard.

What to include on the purchase order

• Material, exact grade, manufacturing route and required size band.
• Measurement method, units and reporting basis.
• Accepted fractions above and below the band, if applicable.
• Required percentile limits and sampling or preparation conditions.
• The agreed rule for resolving differences between methods.

WOCO’s historical WC10Co4Cr certificate sample carries a batch identifier and a 15–45 µm label. Use it to discuss report format; obtain the report for the supplied batch when accepting an order.

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