If you use sieving to determine the particle size distribution of various materials, you likely understand the appeal of the sonic sieving method. Test sieves are an efficient, productive, and economical means of characterizing the gradation of dry granular materials. However, the sieving method is not without limitations.
- The particles of some materials become less manageable for sieving as they approach size ranges finer than 20µm or so.
- Hygroscopic materials tend to agglomerate (clump) more.
- Low-density materials respond less to mechanical sieving action and don’t readily fall through mesh openings.
- Lightweight particles respond to static charges more and tend to “fly away.”
- Ordinary sieve shakers with mechanical tapping or vibratory actions can have problems processing problematic materials, and fine sizes for conventional woven wire sieves stop at 20µm (No. 635).
Accurate Particle Sizing for Fine Materials
Sonic sifting addresses these issues head-on while preserving the economy and simplicity of sieving to measure grain size. The original Sonic Sifter was developed by Charles Ward over 60 years ago and used 3in (76mm) diameter acrylic frame sieves to characterize small samples of powders in the 850µm (No. 20) to 5µm range. The proven method and equipment are still widely used for sizing such diverse materials as pharmaceuticals, paint pigments, fine sands, and mineral aggregate powders, cosmetics, and powdered metal. A Sonic Sifter has even tested lunar soil samples brought back by the Apollo 11 moon mission!
The larger model Gilsonic UltraSiever® Sonic Sifter accepts 8in (203mm) diameter sieves can test larger volumes of material with particle sizes up to 4.75mm (No. 4).
In this report from the U.S. Army Corps of Engineers, it outlines some advantages of sonic sieving.
The Sonic Sieving Method
A sieve stack is enclosed on both ends by flexible latex diaphragms, forming a closed air column, preventing sample loss, and collecting fines during separation. A loudspeaker positioned at the top of the sifter acts as an audio generator, vertically oscillating the air column 3,600 times per minute. Sonic energy lifts each particle off the sieve surface, and it lands, presenting a different orientation to a different sieve opening.
The amplitude setting is variable and determines the intensity of the sieving action. Amplitude levels are programmable to gradually ramp up to and down from a preset level, preventing damage to sensitive samples and reducing electrostatic build-up. Test times can be as little as one to three minutes, and operation is quiet and dust-free.
Efficient Operation
The programmable operation allows gentle separation of fractions with less material attrition and more precise control than vibratory or mechanical sieve shakers. Output energy from the audio generator, testing times, pauses, and ramp/dwell intervals can be programmed to precisely tailor the testing cycle to materials of different textures and densities. Vertical and horizontal mechanical tappers are switchable for use separately or together if needed. Vertical tapping prevents the blinding of mesh and assists the passage of near-size particles. Horizontal tapping reduces the agglomeration of material caused by static or hygroscopic attraction.
Key Features of Sonic Sifters:
- Quiet operation
- Portable and compact, sifters can easily be relocated anywhere in the lab
- Fast test times for complete separations
- Adjustable amplitude is programmable for optimum separations
- Programmable ramp and dwell times protect sensitive materials
- Selectable vertical and horizontal tapping promotes sharp fraction separation
Special Sieves Enhance Performance
3in (76mm) diameter sieves for sonic sifters have clear acrylic frames for easy observation of the particle separation process. Each frame is machined for a close fit when nesting with other sieves, protecting the air column, and reducing sample loss.
- ASTM E11 Acrylic Frame Test Sieves fitted with conventional woven-wire cloth are also available. These sieves meet ASTM E11 requirements and are available in opening sizes from 5.60mm to 20µm (No. 3 ½ to No. 635).
- ASTM E161 Precision Electroformed Acrylic Frame Test Sieves feature precisely sized nickel mesh to bring out the best performance characteristics of the sonic sifter and are the best choice for testing fine powders down to 5µm. Production of electroformed cloth starts with the electrodeposition of nickel on a stainless steel grid to produce a precisely sized flat and square opening. They are available in opening sizes from 150μm to 5μm with tolerances less than ±2µm. Precision electroformed sieves are consistently more accurate than woven-wire sieves.
- 8in (203mm) diameter test sieves for the larger Gilsonic UltraSiever® offer seven times more surface area for higher volume samples and can separate materials with up to 4.75mm (No. 4) top-size. These test sieves have conventional stainless steel frames and feature precision electroformed mesh (ASTM Precision Electroformed Sieves) or woven-wire cloth (ASTM Test Sieves and ISO 3310-1 Test Sieves). Note: An Adapter Set (sold separately) for the UltraSiever® allows the use of ISO 200mm test sieves.
- When purchasing any of Gilson's Acrylic Frame, ASTM, or ISO Test Sieves, each sieve is supplied with a Certificate of Compliance.
If you’re finding it difficult to produce accurate particle size distributions for fine materials efficiently, Contact Tech Support with questions and discuss a free demonstration test to see if the Sonic Sifter is right for your application.
