Is Sieve Calibration Really the Holy Grail? Part II: Inside a Sieve Test
As I start on this second installment of The Adventures of Pequeño: The 150 Micron Particle, I wonder why I get myself into these serial onslaughts. However, a promise is a promise, so I shall press on.
You will recall from Part I: Sieve Certification, our little friend Pequeño, a particle on a determined quest to make it through sieves -- particularly those through which he should be too large 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 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).
Almost immediately, Pequeño and his little companions get to the #150 sieve -- his size. If the sieve is perfect, he might not make it to the 125 micron sieveHowever, it is not perfect; just certified to be within standard ASTM tolerances. He quickly finds over-sized holes, which lead the way to the 125 micron sieve, which is supposed to be 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 #125 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, he’ll find one of these and pass through to the 125 micron sieve along with some of his cadre.
As it turns out, the #140 (106 micron) sieve gives Pequeño trouble; only a few of his ever-shrinking cohort squeeze through the max 141 micron opening.
Harry is depending on Brad’s (the professional Sieve Certifier from Part I) 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.
Brad’s job was 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 question.
I appreciate your taking this journey with me to follow Pequeño’s (hopefully unsuccessful) quest to get through ever-smaller sieves. In the next installment, we’ll explore what happens to him and his clan of similar sized particles after they transit the sieves.
Let's see what happens to Pequeño in Part III of this Saga.
Until then feel free to contact me with questions, concerns and/or suggestions,
P.S. If these musings on lab test equipment are interesting -- subscribe.
P.P.S. If you need to see the available sieve types sizes and mesh click on the button.