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!
P.S. If you are not subscribed to these Test Equipment rants and muses, sign up at the top of the page.