The ongoing debate between the value of a sieve certification process and sieve calibration has long intrigued me.
As I delved deeper, I realized that the certification process serves as a form of insurance. It not only confirms that the mesh aligns with ASTM or ISO specifications, despite allowable variations, but also satisfies the traceability requirements set by ISO standards.
However, the inspection reports only minimally predict a sieve's performance. I recall a situation in which a customer with a high-powered QC program had trouble matching the performance of 
a new shipment of mid-point sieves. [Mid-point sieves must conform to a much tighter tolerance than the standard spec.] After an exhaustive investigation, the old batch of sieves was determined to be at the low end of the spec while the new ones were at the high end. The mid-point certification reports did not indicate this discrepancy.
The customer then used a procedure that compared the performance between the two batches. That process finally pinpointed the problem. This is what I think calibration is all about -- ensuring predictable performance in an operating environment.
Calibration methods range from comparing sieve results against a master set of sieves (Master Stack) to evaluating results against a known sample (Master Sample), each tailored to specific applications.
Another innovative calibration technique involves the use of calibration spheres or beads, which gauge 
a particular sieve's performance against a high-precision traceable standard. This method provides a precise quantitative measure of the sieve's anticipated performance, resulting in a mean sieve opening size.
Since the high-precision beads are traceable to an ISO-recognized standard, this calibration method not 
only meets ISO or internal company QC audit demands but also provides a singular performance indicator unlike the certification report. In many cases, utilizing the calibration bead method eliminates the necessity for Master Stacks or Master Samples.
Whitehouse Scientific has developed a unique sieve calibration process that achieves a mean sieve size accuracy of approximately +/- one micron. This innovative method took them about three years to perfect, ensuring a traceable and precise calibration process. For more details on this advanced calibration technique, check out Sieve Calibration
I hope this sparks some thought-provoking questions and encourages further discussion. Thank you for taking the time to read this.
Continuing to ponder,
Cho
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