This is another Adventure of Pequeño: The 150 Micron Particle, I wonder why I get myself into these fantasies. However, once I start I feel constrained to press on.

In an earlier encounter, our little friend Pequeño, was on a determined quest to make it through sieves -- particularly those through which were said be too small for him to pass. In this scenario, Pequeño along with some of his family and friends -- all small particles about 150 microns in size -- are on their way to a sieve test.

## Harry's Sieve Stack

Harry is a Quality Control Manager. He loads a stack of sieves onto a sieve shaker. From the top, the sieves are:

#80 – 180 micron

#100 – 150 micron

#120 – 125 micron

#140 – 106 micron

He dumps Pequeño and large quantities of other sized particles into the top sieve. Pequeño’s first impression is that getting through the first #80 sieve is no problem. Then, the Shaker starts (violent motion – up/down and circular).

## Passage Through A Sieve Stack

Almost immediately, Pequeño and his little 150 micron companions get to the #100 sieve . If the sieve is perfect, they should make make it to the 125 micron sieve. However, um it is not perfect; just certified to be within standard ASTM tolerances. He quickly finds lots of over-sized holes of 193 micron, His grand uncle, a 180 micron relative, gets through this one and meets him on the #120 (125 micron) sieve. That is smaller than Pequeño and most of his family.

As the shaker continues its vigorous movement, he looks for the certified largest allowable opening on the #120 sieve. That is 168 microns, through which he and and some of his colleagues should find easy passage. ----- If they don't shut off that damnable shaker, they will find some of these and pass through the 125 micron sieve.

As it turns out, the #140 (106 micron) sieve gives Pequeño trouble; only a few of his undersized cohorts squeeze through the max 141 micron opening.

Harry is depending on Brad’s (the professional Sieve Certifier) previous work to retain all particles like Pequeño on the #120 to125-micron sieve and would thus never expect to find Pequeño sitting on the 106-micron sieve.

## The ASTM Sieve Calibration Conundrum

Brad’s job is to make sure that sieves meet the Calibration Sieve Category  (the highest standard)  and thus apply a sufficiently rigorous standard to his measurements. It still leaves a high probability of 168 Micron holes on the #120 sieve.

Harry’s job is to run the sieve tests to see if his product meets predetermined particle size distributions. This specification did not call for Pequeño to pass beyond #120 (125 micron) sieve.

It turns out that the ASTM standard that Brad certified left a lot of wiggle room for Pequeño’s passage to a sieve specified as smaller than his natural size. This leaves Harry with some tough QC questions.

I appreciate your taking this journey with me to follow Pequeño’s  quest to get through ever-smaller sieves.

Check out the next article in the series here: Does Calibration Light the Way to the Sieving Holy Grail?

Feel free to share this ramble with associate who have to deal with sieve test results

Art

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