Quiet Sieve Shakers
Recently in a quiet, reflective moment, I recalled my first work with sieve shakers. Horizontal motion with tapping was the basic shaker design. The Ro-Tap® was King, and there were few alternatives. Different shakers for special applications, such as the Mary Jane and one that was hung from the ceiling, were the exception.
With The Ro-Tap® Came Copious Noise
When sieving was under way - an unpleasant occurrence - the lab became a zoo of noise. Ear plugs were common.
However, the big advantage of this sieve shaker was that it worked on a large variety of material and over nearly the full gamut of sieve mesh. The question of what shaker to use was never an issue.
New Techniques Came On The Scene
About the time I got involved, a few manufactures, Endecotts being one, began to build shakers based on orbital motion concepts that could duplicate the Ro-Tap® results without the noise. With these new shakers, a lab could comfortably conduct business during a sieve test.
Comparable results were obtained by experimenting with vertical amplitude, stop-start intervals that had the effect of whacking the sieve stack, and a few other tricks.
When experience showed that quiet shakers were passing the comparability test, the quiet sieve shaker became an option.
New models were introduced. These included simple, low noise, economy shakers that worked on easy-to-sieve materials.
Historically Ro-Tap® Dominated Industry Standards
The biggest obstacle to universal adoption of this new generation of quiet shakers, was the influence of industry sieve testing standards. The standards were built on years of test data. This test data was developed using Ro-Tap® type shakers.
As a result, the first applications of these new quiet sieve shakers were for materials without extensive historical particle distribution data and no ingrained sieving standards. The lack of noise easily sold orbital motion shakers for these materials.
Resources Were Committed To Constructing Comparative Results.
Because of dramatically reduced noise levels, more and more sieve testers took the time to find how to match quiet shaker results with established standards. Experiments with combinations of orbital speed, amplitude adjustments and stop/start intervals were conducted until sieve test results matched those obtained by established Ro-Tap® methods.
Increasingly, labs were concluding that the tweaking necessary to achieve comparable results was worth the effort. A quiet sieving lab became a priority.
Experience had shown that the Ro-Tap® motion could be effective for sieve mesh from 20 microns to 50 millimeters - a pretty wide range.
Orbital shakers also had this range covered. As more of these quiet shakers were put into operation, it became clear that the new, quiet designs were adequate for most sieve testing jobs.
New Techniques Expanded the World of Quiet Sieving
In the process, additional techniques were developed to deal with special sieving problems, such as agglomeration, electrostatic binding, and blinding. These problems were not adequately solved with speed, amplitude and interval adjustments. Some, but not all, of these problems had been solved with standard Ro-Tap® set-ups.
For small particle sizes down to 3 or 4 microns, orbital techniques as well as Ro-Tap® technology had unsolved issues.
Several new designs and systems unfolded to deal with these issues.
Sonic Sifting was one of these. With this technique the sample is alternately suspended on a shaft of air. Consistent results down to 2 micron separations are feasible with Sonic Sifting.
Another technique is called vacuum sieving. With this method the particles are pulled through a sieve. It was developed principally as a method of dealing with getting particles through a very small sieve apertures, and to mitigate blinding.
Some of the other product problems associated with agglomeration and blinding have been attacked using water to wash the sample through the sieve. Other solutions involve adding material to sieves to break up clumps.
These solutions are essentially quiet.
The Ro-Tap® type shakers continue to be used where long time standards dictate shaker selection. The noise issues are often overcome by using large, sound-deadening enclosures.
Advancements in orbital shakers, sonic sifters, and vacuum technology as well as systems such as the wet washing and adding materials to break-up agglomeration provide the base for a future of increasingly quiet sieving applications.
In summary, the emergence of new sieve shaker technologies has made it possible for "quiet" to be one of the specifications for new sieving equipment.
I have been there for most of this transition. I am enthusiastic about the results.
If you find this story interesting or useful, please share it with associates who work with sieve testing.
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P.P.S. CSC has a wide variety of particle size analysis instruments as well as quiet sieve shakers. Check them out.