In April, we published an article in "Powder-Bulk Solids"
Given that the calibration process highlights the actual performance of a given
We recently had a real-life example of the the difference between actual sieve performance and certification statistics. A customer recently acquired four 45 micron (#325) ASTM certified sieves. Given that their manufacturing process was critical, they decided to check the four sieves with calibration beads. The results on each sieve showed a mean aperture of 49 microns. Because the certification spec allowed a variation of up to 3 microns in average opening size (allowing up to 48 microns in average opening) They returned the sieves to the manufacturer for re-certification. All four sieves passed. The customer also had them double-checked by an outside laboratory. Each of the four sieves tested the same; consistent with a real-world sample as well as bead calibration results.
What to do? --- Whom to believe? --- What ARE these sieves?
In light of this, let's consider the most recent ASTM specification (ASTM E 11-09). The customer's sieves were 8 inches in diameter, which represented
The bead calibration tolerance is about 1 micron in mean opening resulting from a sieve test using a calibrated sphere sample.
This real-life situation makes it clear that certification, while an insurance
Calibration performs a live sieve test and yields the actual results.This leads us to the conclusion that calibration with glass spheres is the optimal procedure for determining the suitability of a test sieve as well as checking and controlling a process.
We can compare mesh sieve performance to the results on the same
To date, calibrated spheres are the best method for this and for determining the actual calibration of any test sieve.
As with most of the things I rail about here, real world conditions often lead to confusion about theory and when analyzed question established practice.
I hope this has been helpful. Call me at 703-876-4030 if you want to discuss the certification/calibration dichotomy.
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