Yes Harry, there is a Santa Clause. Or, more specifically, there really is a Holy Grail for ensuring consistent particle size analysis.
If you’ve been following along, you know it was proven by Pequeño and his family of 150 micron particles who tried to bust our friend Harry’s quality control by attempting to slip through the mesh in Harry’s test sieves and defeat sieve certification.
(If you missed this drama, check out previous posts in the Holy Grail series.)
Now that we have indeed confirmed that, yes, sieve calibration really is the Holy Grail that sieve testers have been looking for, let’s get to work and dive a little deeper. Let’s examine some methods of sieve calibration.
Walk like an Egyptian
Sieving has been around since the days of the Egyptians, who used a sieving system to measure and distribute grain. And although the reeds they used as mesh got the job done, I’m sure they’d appreciate how far technology has taken the sieve calibration process. I mean, we consider it the Holy Grail for sieve performance!
And today, growing pressure for ISO 9000 certification has put a heightened interest in methods of ensuring quality sieves. There are several proven methods of sieve calibration, but let’s examine what really works and what doesn’t.
Master sieve stack
One method is using a master stack of sieves that includes each sieve size used in your process.
1. Two samples of your material would be selected.
2. One sample would be shaken through the master stack, and the results calculated.
3. Then, the second sample would be shaken through your working sieves (similar to the master stack), and these results would also be calculated.
By comparing results you could check for variances between the master stack and working sieves, then replace any working sieves that are out of whack. Sound simple? Well maybe. But it’s not a magic bullet. It’s sometimes hard to get an exact match if any of the master sieves need replacing.
Another sieve testing process it to create master samples of all the material that are subject to a sieve test. Working sieves put on a sieve shaker and loaded with the selected sample of the master sample.
The shaker does its job—and then how much of the material is retained in the sieve is looked at and measured. The results are studied for acceptable tolerances. Then sieves are replaced that produced results outside these tolerances.
Sounds OK, but master samples are hard to maintain.
Neither of these first approaches really hits the mark and gives you an accurate reading of just which sieve is troublesome. What to do, what to do? Oh, wait. There is better way.
Sphere this. Sphere this.
Just as our friends Harry and Brad learned in the previous Pequeño saga, there is a solution to optimal sieve calibration. It’s called Calibration with Micro-spheres.
Not only is it easy to do, but using these micro-spheres gives a truly objective measure of a sieve's performance and condition.
Calibration micro-spheres are created in exact sizes for the sieves that need to be calibrated. These beads can be used to accurately determine mean aperture for each sieve to be tested.
Let’s break down how it works:
1. Select a sieve to be calibrated, mount it on a receiver pan, and tare the combination.
2. Pour a vial of the appropriate micro-spheres into the sieve, weight it and record the weight
3. Shake it, shake it, work it for a couple of minutes.
4. Empty the receiver.
5. Weight the sieve and empty receiver.
6. Using the difference in the weights, calculate percent retained.
7. Find the percent retained on the chart and plot the mean aperture.
This approach works best, and it gives all working sieves a mean aperture number in microns, which can be a true predictor of performance.
To learn more about our calibration spheres, check out this button below.
I think you’ll see why these spheres truly are key to sieve calibration becoming the Holy Grail.
We have a video about Calibration vs Certification on the CSC Sieves page. Click on the Video button to get there.
Please share this with associates who might be interested.
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It as been a long journey since we met Pequeño in November 2011. I hope it has been worth the wait.
I remain a mystified,
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