In our business, we use the word “sieve” to describe a piece of equipment that separates desired elements from unwanted material using a woven wire screen or mesh net. To others, “sieve” can mean something very different.
Particle Size Sieves
Sieves – the screen or mesh kind – work by separating some particles from the others in their sample based on their size. Particles smaller than the holes in the mesh will be allowed through, while bigger particles will be caught in the net.
Sieves in the Computer World
In the computer programming world, “sieve” is a programming language used to create email filters. You could say its operation is based on the same concept as our sieves, separating certain emails from the entire batch, though not necessarily by the size of the email.
There are Even Sieves in Sports
The sports arena uses “sieve” to describe a goalie that causes his team to lose the game by allowing many goals to be scored by an opposing team. Here, the goalie is like the wire mesh in a sieve. He should be keeping some particles – or balls – in this case, from getting through, but in reality, the balls are slipping through the holes.
Mathematicians Have Their Own Kinds of Sieves
Mathematicians use sieves for a rather different purpose than the one we’re used to. To them, a “sieve” can be used to find prime numbers. Take the Sieve of Eratosthenes, which has to be the coolest name for a sieve I think I’ve ever heard. This sieve was named after Eratosthenes of Cyrene, a Greek mathematician in ancient times, and is known as one of the most efficient ways to find small primes (any prime number less than 1000). Like the mesh sieves that we use, this type of sieve is used to separate some numbers (in this case, small primes) from others based on certain criteria.
Dreams of a New Particle Size Sieve
We think it would be special if our particle sizing sieves acted more like the computer programming or mathematic version of the word – not the sports definition. That’s why we offer sieves that are manufactured to ASTM standards, and calibration beads to test their accuracy.
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Visitors to our web pages often arrive with the question, “What is the Function of a Sieve Shaker?”
The simple answer is “to expose the particles in a sample to all the openings in each sieve in a stack”. A sieve stack is the result of fitting each sieve to be used in a given particle size analysis into the one above. The sieve with the largest mesh holes is at the top with each subsequent sieve of a tighter mesh size than the one above it.
A sieve stack can consist of anywhere between 1 and 18 sieves. The number and mesh sizes of the sieves in a sieve stack are dictated by industry/application standards or the stated production standards of specific products.
In concept, the optimal motion of a sieve shaker is circular and vertical or, in other words, orbital. Initially, the motion was defined as “rotating the sieve in a person’s hand and tapping it on the side”. The first practical mechanical shakers were made of a rotating orbital table and a hammer that imparted, at a fixed interval, a vertical force. This was called the Ro/Tap©, which stands for “rotating and tapping”. The name became the copyright of W.S Tyler.
These first shakers tended to be very noisy. Developments to overcome the noise and provide an orbital motion of sufficient violence included:
- A sieve plate sitting on a cam driven by a belt and electric motor
- Offset weights mounted on springs
- Horizontal leaf springs, and a magnet and a rotating electrical field
- Rubber posts compressed and released by a magnet field
- Place noisy shaker in sound damping enclosure
The effectiveness of any sieve shaker is related to characteristics of the material being sieve tested. The minimum size to be separated, the resistance to agglomeration and static electric factors influence the selection of a shaker.
For example, the analysis of dry silica sand is easy for separations down to 50 microns. Most sieve shakers will do an adequate job on this type of product. If the material tends to clump or agglormerate, a shaker that can give the stack a periodic vertical shock will give better results. If the material has a high static electricity characteristic, methods such as wet sieving may be needed.
When particles to be separated are smaller than 50 microns, other techniques may be needed to effectively separate these small particles. Use of ultrasonic agitation techniques often works. Another method involves the use of a vacuum to pull small particles through the sieve openings. Such vacuum equipment usually processes one sieve at a time.
The purpose of sieve shaker is clear: to expose the sample to all the openings in a sieve in a manner that will expedite the passing of particles smaller then the openings. However, as in most of the instrument world where I work, the selection of the appropriate sieve shaker depends on the size and characteristics of the sample to be separated.
I hope this brought some understanding of the function of sieve shakers and the elements that go into selection of the optimal model.
Why do I take on these dilemma-ridden subjects?
A still bewildered commentator.
Thanks for visiting!
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Hiram is a Quality Control Supervisor of a plant manufacturing specialty pellets. This is about his struggle with particle-size sieve testing and results analysis.
The principal quality factors of the product and process are related to:
- Moisture of the raw material and of the finished product
- Finished material color
- Particle size distribution at the grinder output and of the finished product
Hiram’s responsibilities include testing each variable and comparing the results to the standards for each of five different products, which are produced in batches. Stan, the production Superintendent, expects Hiram to report any anomalies within one half hour of batch completion, to facilitate addressing problems before delivering pellets to customers.
The plant normally produces 15 batches a day. Sieve tests require a nine-sieve stack for grinder output and a six-sieve stack for process output.
Those familiar with pulling out distribution results form sieve tests will know the procedure well:
- - Measure and weigh a sample, record the weight
- - Load it and start the shaker
- - Wait 5 to 10 minutes.
- - Remove the stack and brush out the residue in each sieve on a balance
- - Record the weight.
- - Take each weight and divide by the total recorded weight.
If the procedure is performed correctly, the weights retained will equal 100%.
Weight collection and result calculation take between 10 and 15 minutes. Preparing and reporting these sieve results takes four to five hours a day.
Remember that Hiram needs to get the results to Stan within one half hour.
Like all of us, Hiram is under constant pressure to control his costs. Including all QC Tests, he needs about 12 man-hours a day. The process is at the same time exacting, tedious and boring. He has one full-time person and must borrow an employee from another department for the remainder.
The borrowed person is changed frequently, which necessitates training both his full-timer as well as a new part-timer as needed. To minimize errors, Hiram must provide close supervision.
If one of his people is on vacation or sick, Hiram often must fill in personally.
The whole sieve analysis process was a pain. We can almost feel sorry for Hiram.
Is there more to the story?
Click here to see.
Still trying to figure it out,
We are back with Hiram, the QC Supervisor in a specialty pellet plant. We pick up the story after the QC department was hit hard by the flu season.
Not only was his main sieve tester out for an extended period, but the borrowed part-timer was also afflicted. He thus had to rely on temps, which made training a continuous process as well as exponentially increasing the level of required supervision. Hiram also found that he was increasingly performing the testing himself, taxing his abilities to perform his normal responsibilities.
Hiram began to wonder if there was a better way to accomplish his particle size sieve analysis.
Hiram then turned to Google.
He found some alternatives, including fully automatic systems, in which the sample is thrown in followed by a printed result. Considering the cost-control constraints mentioned in Chapter I, such a method was too expensive.
He did find a reasonable approach that eased weight collection and result calculation. The meticulous residual sample weighing and removal from each sieve continued to be a part of the system. Still this was a considerable improvement from the previous method, requiring less training and supervision.
Hiram was glad that he had made the change. Business was growing, so extra batches were added each week resulting in the need for overtime. The extra tests were manageable as was the additional supervision. At least the calculations were consistent and reliable.
Now a new challenge for Hiram came roaring in. Business was so good that a new shift was needed. At least 2 ½ new people will require training and supervision. Even if he convinces his trained full-timer to work this new night shift, he has to train a another set of people for the first shift with its attendant supervision issues.
Hiram figures he will be at the plant most nights to monitor the second-shift staff. Remember Stan still needs accurate results within ½ hour of each batch being completed.
What to do?
Go to Google again!!!
What did Hiram find this time?
Click here to find out.
I wonder what's next.
The CSC Sieve Analyzer
The CSC Sieve Analyzer was designed to deliver a record of a sieve test results, eliminate operator error and significantly reduce the time to process and calculate these results.
Since ancient times until current days, outcomes of sieve tests have been recorded as the amount of material that is retained on each sieve used; usually expressed as the weight or percent retained. Some applications use the amount passed as an alternative.
The original process requires the emptying the material in each sieve onto a balance and recording the weight. These weights are used to calculate the retained amounts and percentages…. A tedious and error prone process.
Changes with the CSC Sieve Analyzer
With the advent of smart electronic balances and small computers some relief from this process has been achieved in the lab. Also totally automatic, comparatively high cost, systems are available.
The CSC Sieve Analyzer changes this landscape. This instrument is a self-contained sieve analysis machine. It can be used in the lab and on the production floor. Therefore, it can serve the needs of occasional sieving as well as 24/7 production requirements.
It is this simple to use
– take a sieve off the stack place it on the Sieve Analyzer,
– press start,
– wait a second for the beep and
– get the next sieve
The Sieve Analyzer almost totally eliminates training and is as close to fool proof that we could get.
Since our first beta test units were delivered, the test evaluators would not return the units because the Sieve Analyzer out-performed their wildest expectations in saving money and time and eliminating errors, customers have found the CSC Sieve Analyzer an indispensable tool.
Test results are displayed on the graphics screen and can be printed on a local printer or sent to a computer or LIMS system.
It stores the characteristics of each sieve in a stack and calculates the total weight of the sample. This does away with the need to weigh samples before starting the shaking process.
We feel that the CSC Sieve Shaker is an important addition to the productivity and data integrity of any sieving process.
Check out this video.
I know that if you use it you will be as excited as we are about the CSC sieve Analyzer. If you would like to see how this instrument will save time and money and enhance your sieving operation join us for 15 minutes of analysis with a sieving consultant.
Please forward this to those colleagues who live with problems of sieve test analysis.
This time I’m not necessarily befuddled, just excited
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As I've said many times measuring Moisture Content, Surface Tension and Particle Size often confounds me.
Moisture measurements are nothing compared to the measurements needed to check out the Universe. Came across this video and thought you'd fnd it interesting and fun.
Sieves make understanding the world around us not just possible, but also easier.
And with the advancement of sieves, not only are we able to separate dry particle, but also sift molecules from fluid as well. With molecular sieves developed by MIT, we can now strip a molecule’s individual parts gives us a better understanding of how things come together and work, such as diseases or even DNA.
These sieves use microfabrication technology, or a nanopore system, to separate proteins from fluid. The individual pores are so small and uniform that millions can fit into a chip the size of a fingernail.
Compared to gel electrophoresis, this process of sifting proteins is far more predictable and efficient, making it easier for scientist to learn more about these molecules and giving them a more accurate idea.
By using sieves in molecular studies, scientist can not only detect diseases, but make note of “biomarker” proteins associated with them, giving them the ability to detect a disease even before symptoms show.
Not just that, but with such an extensive, in-depth look into these particles, cures aren’t such a far-fetched possibility.
Thought you'd appreciate a short flight into the other things that can get done with sieving techniques, far removed for our Wire Mesh Sieve world of 20 microns and up. Check out the newest in the Cinderella world of Wire mesh.
These advanced applications of sieving concepts add new dimensions to my normal bewilderment.
We hope this was interesting.
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Yes Harry, there is a Santa Clause. Or, more specifically, there really is a Holy Grail for ensuring consistent particle size analysis. And .
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 appreciat 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. The, 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 sack 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 sieves performance and condition.
Calibration mirco-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 viedo 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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You may remember Pequeño and his family of very small 150 micron (150µ) particles being very determined to defeat sieve certification.
Episode I had Pequeño watching Brad measure a small number of mesh openings for a certified 150µ (#100) sieve and concluded that there were many places for him and his friends to sneak through.
Episode II introduced Harry theQuality Control Manager, who put Pequeño and a load of assorted-sized particles into a sieve stack for a test. As he predicted, Pequeño got through the #100 sieve. In fact, he got through the 125µ sieve as well. Given that he depended on the certification, Harry had no Idea that Pequeño and family were perched on a 106µ sieve -- two down in the stack from the certified #100 sieve.
Episode III had us observing the process of cleaning sieves after a test. Pequeño observed that Harry was very careful to gently brush away any residue in the sample. He noticed however, that Harry more aggressively pushed particles stuck in the mesh openings, he inadvertently widened them. This in turn would give Pequeño even more opportunities to get through openings that were certified to be as small or smaller than his 150µ size.
Here in Episode IV, the final episode of Pequeño’s saga, we return to Harry, the QC Manager who has been experiencing problems with his sieving results. Inconsistencies, disputes with production and customer complaints are plaguing him. He has been depending on his sieve certifications to insure that his test standards adequately assure correct and consistent results. (He had no Idea that Pequeño and family were doing their mischief).
Harry checked with other colleagues in the sieve testing game and got advice ranging from performing his own microscopic sieve inspections to setting up master stacks to compare individual sieve performance.
Appropriate visual inspection requires an optical comparator (expensive and tedious to operate) or sending the sieves out to be recertified (which removes the sieves out of service for several days). Even then, Harry was not sure that this would detect or identify his problem. (Pequeño felt that this would be good for his cause of getting through smaller than150µ mesh.)
Harry was leaning toward a master stack that would allow him to check each sieve’s actual performance against a standard he developed. Pequeño was concerned that his life may become more complicated. As Harry investigated the best way to develop the master stack, he discovered calibrated micro-spheres designed to define mesh size over the entire sieve.
These calibrating spheres would let him easily check the actual operating characteristic of an individual sieve. This check results in a mean aperture number that clearly defines how a sieve operates.
As Harry analyzed further, he concluded that he could select his master stack sieves using calibration microspheres and check his production sieves against the master results.
As he continued to ponder how this would work, Harry realized that he would not need a master stack. He could set up a program to establish the mean opening of new sieves, check them again when he seemed to have inconsistent sieving results and thus pinpoint problem sieves.
When Harry launched this calibration program, Pequeño and his family had limited opportunity to get past the #100 sieves. Further, Harry now knows if Pequeño is riding high.
The answer to the title question is: Yes -- Sieve Calibration Really is the Holy Grail!
Check out this rash declaration.
I trust that these episodes about Pequeño, his family, Brad and Harry were informative, helpful and somewhat entertaining. You can see more about Calibrating Sieves by clicking on the button.
I remain stunned by this field of test equipment.
P.S. If these musings on lab test equipment are engaging, please consider forwarding them to associates and subscribing.
We continue to search for answers to the question "Is Sieve Calibration Really the Holy Grail?" As promised,we present Episode III of the Pequeño saga. You may remember him as a very small (150-micron) particle with many similar-sized family members who are determined to defeat sieve certification.
In the first episode, he and his family were on the way to a sieve analysis. They had the objective of foiling the sieve test by passing through sieves with certified openings of less than 150 microns.
Episode II described Pequeño & Co.’s experiences in an actual sieve test wherein they got past the 150-micron sieve. Many even transited the 125-micron sieve, which is 16% smaller. The 106-micron sieve finally stopped most of them.
We now rejoin the story after the violent shaking stopped. The testers removed the sieves from the stack and emptied the contents onto a balance to obtain a retained-weight distribution for each one. When they came to the 106-micron sieve, Pequeño and couple of his siblings did not drop to the balance, because they were wedged into some of the openings.
When the analysis was completed, a tech used a brush to remove any residual material in the 106-micron sieve. Most everything was cleaned out, but Pequeño was among the particles that were still wedged into openings. The tech saw them on a visual check and gently pushed them through.
This unfortunately caused the mesh to spread, creating 150-micron openings in this 106-micron sieve -- much greater than the largest allowable opening of 141 that Brad (the Professional Sieve Certifier from the first episode) certified.
The next time, Pequeño and his 150-micron siblings are used in a stack that includes the following sieves:
#80 - 180 Micron
#100 - 100 Microns
#120 - 125 Microns
#140 - 106 microns
It is likely that many of them will find their way through the 106-micron sieve and fall on to the next-smallest-size sieve screen. This additional transit, is a result of the cleaning process. Most would assume, given that it is certified, that the 125-micron sieve would catch all of the150-micron particles. Not so. Worse still, a number of these will now pass through this 106-micron certified sieve, which has nominal openings 30% smaller than Pequeño.
Harry, the QC Manager from Episode II, has always relied on the certification process to insure that his sieves would perform to high standards. He never evaluated the process from the view of a small particle with the mindset: “I want to get through everything and do not care how much error I create.”
Only when repeated tests indicated result anomalies would Harry suspect a problem with sieve performance. After he experienced Pequeño and his siblings’ onslaught, Harry began to consider better methods of predicting and checking real-world sieve performance than certification.
Part IV of this series will explore alternatives for Harry to assess corruption of test results, perpetrated by Pequeño and family.
Until the next time, I continue to find new things in the world of material testing that baffle me.
Again we hope to be entertaining and helpful.
P.S. If these musings on lab test equipment are engaging, please consider forwarding them to associates and subscribing.
P.P.S. Click on the button to learn more about Sieve Calibration.