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Test Sieves, Sieve Shakers, & Sifters Technical Specifications

Sieves are perforated vessels designed to separate fine from coarse materials. Standard sieve analysis is probably the fastest and most widely used quality control procedure due to its simplicity. This process ensures the sampling of organic or inorganic materials meet ASTM standard tests. Particle size distribution is critical to the way the material performs in use. Industries served include food, powdered metal, chemical, and mineral processing.

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Click Here for Test Sieve Selection Guide

Click Here for ASTM E 11-04 Standard Specifictions

Click Here for ASTM E 11-09 Standard Specifications

Click Here for Test Sieving: Principles and Procedures

Test Sieves - What is Sieving?
Test Sieves - Glossary of Sieving Terminology
Test Sieves - General Sieve Specifications
Test Sieves - Principles and Procedures for Test Sieves
Test Sieves - Sieve Care and Cleaning

What is Sieving?

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A simplistic definition of sieving is the separation of fine material from coarse material by means of a meshed or perforated vessel. Professor Terence Allen characterizes sieving as "The aperture of a sieve may be regarded as a series of gauges which reject or pass particles as they are presented to the aperture." This theory was actually in practice during the early Egyptian era as grains were sized with 'sieves' of woven reeds and grasses.

The level of sophistication increased with the rise of the industrial revolution and the need for more sophisticated methods for classifying material by their particle size. As requirements for sized material rose, technology in producing uniform sieving media increased. Woven wire cloth was introduced as an alternative, providing greater accuracy and durability. At present, this woven cloth is available in a range of sizes from 125 mm (5") openings to 20 micrometer openings. All mesh sizes are covered by of both national and international standards.

The need for particle size analysis in the finer size ranges (i.e. 38 micrometers and less) prompted the development of the electrodeposited sieve. These sieves, sometimes called electroformed or micromesh, are currently being produced with openings as fine as 3 micrometers. The mesh openings are extremely uniform in both size and shape and maintain exacting tolerances.

Standard sieve analysis is probably the fastest and most widely used quality control procedure in any powder process control industry. Used frequently as a mediating device between the production and sales divisions of a process corporation or between the sales force and the customer, test sieve analysis work enjoys the universal recognition of being the best 'quick and dirty' test procedure for rapid particle size distribution data. The outcome of the analysis is easily calculated and interpreted for comparison between laboratories. Startup cost to institute a basic sieving quality control program is minimal, and operators at most levels of training are capable of performing a successful sieve analysis. With these factors in mind, it is easy to see why testing sieves are as ubiquitous as they are in industry. Materials from crushed ore chunks of over 114.3 mm (4 ") in diameter to slurred alumina and porcelain powders of less than 20 micrometers are all analyzed with test sieves on a regular basis.

Whether hand or machine sieving, wet or dry preparations, analysis or production work, testing sieves have found a niche in the quality control laboratory. Given this overall acceptance of test sieves as a viable analytical device and the widespread presence of the sieve in laboratories of all industries, any shortcomings of such an analytical device would be magnified. For all of the advantages available to the test sieve user, limitations must be recognized and accounted for in the presentation and analysis of the data.

Test sieves are individuals. Being fabricated of a woven mesh material, variations in the weave are common. The chances of locating two sieves with an identical distribution of opening sizes are extremely remote. Due to these variations, the reproducibility of test results between sieves can be adversely affected. The stringent standards imposed by ASTM, ISO or other regulating bodies have established tolerance factors which allow for the permissible variations in the weave while striving to maintain a level of uniformity in the performance of the 'test grade' sieve cloth (See ASTM E-11 Specifications).

With this variation of opening sizes present, some smaller than the nominal and some larger, the time interval of the sieve analysis becomes extremely important. If, for example, a sieve has several openings far above the nominal opening size for the particular mesh size, and the test is run for 30 minutes, the probability of larger-than-nominal particles finding those oversize openings is much greater than if the test was run for only 15 minutes. Similarly, if the sample of powder contains a large percentage of elongated or needle like particles, a longer test interval would provide a greater likelihood that the elongated particles will orient themselves 'on end' and pass through the openings. If the sieving cloth has a wide range of opening sizes, the sieving of this type of material has a compounded error.

Another factor which must be considered is the reaction of the material to ambient conditions. The most accurate test sieve available would be of minimal use if the relative humidity in the test lab was 99%. Extremely dry conditions can cause fine powders to adhere to the sieve components and each other with strong electrostatic charges. Additional types of sieving problems are discussed in the glossary section.

Glossary of Sieving Terminology

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Sieving terminology is frequently used and abused in writing specifications for materials. Listed below are some of the most frequently used terms and a general discussion of their meaning:

Agglomerate: natural tendency of materials to clump or ball together. This condition is very common in materials with high moisture, fat or oil content or those with fibrous or extremely irregular topography.

Blinding: plugging of the screen openings with particles either exactly the same size as the sieve opening or by fine particles which build up on the wire mesh and eventually close off the openings. Frequently referred to as pegging.

Cover: stamped or spun lid that tightly covers the top of a sieve to prevent the loss of the material sample during sifting or mechanical agitation.

Electrostatic Charges: accumulation of electrical charges on the particles and sieve components causing clinging, agglomeration or blinding. This condition is frequently seen in hydrocarbon-based materials, plastics, reactive metals, paint pigments and powders with a large fraction finer than 20 micrometers.

Extended Rim Pan: a sieving pan with a skirt designed to nest within a sieve stack, allowing multiple tests to be performed simultaneously. Frequently called a nesting pan or spacer.

Flow Additive: powdered substance added to the sample to reduce agglomeration, neutralize static charges and improve the flow characteristics of the sample. Common additives are fine silica, activated charcoal, talc, and other commercially produced natural or synthetic substances. Generally, the additive is pre- screened to a known average particle size, blended with the sample (approximately 1% additive by weight) and then screened with the additives value removed from the reported data.

Frame: a rigid sidewall used to form the body of the testing sieve. Common depths are 50.8 mm (2" full height) for 8" sieves and 25.4 mm (1" half height). Special application sieves of other depths are also in use.

Mesh: screening medium with openings of uniform size and shape made of woven, punched or electrodeposited material.

Pan: stamped or spun receiver of materials passing through the finest sieve.

Skirt: section of test sieve below the sieve mesh that allows for mating or nesting of the sieves in a test stack.

Support Mesh: coarse sieve cloth mounted under fine sieve cloth in a test sieve to provide extra strength. This is widely used in wet sieving operations to protect the fragile fine sieve cloth. Frequently called backing cloth or rolled backing cloth.

Test Sieve: screening medium (mesh) with openings of uniform size and shape mounted on a rigid frame, usually for laboratory testing or small scale production applications. The frames can be made of various materials, the most common of which are brass and stainless steel in a cylindrical configuration, having a diameter of 3", 5", 6", 8", 10", 12" or larger.

Wet Sieving: the separation of fines from the coarse portion of a sample while suspended in an aqueous solution introduced to a testing sieve. The liquid medium is used to negate static charges, break down agglomerates and lubricate near-size particles. After the fines have been washed through the sieve, the residue is oven-dried and re-weighed.

General Sieve Specifications

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The U.S. Standard Sieve Series is a metric system based series first suggested by the American Society for Testing and Materials in 1913. The opening sizes in this sieve series are in the ratio of the fourth root of two. This numerical relationship was first suggested by Professor P .R. Rittinger, a German researcher, in 1867.

In the fourth root of two series, every opening size is 1.189 times the opening size of the next smaller sieve. This relationship continues into sieve opening area measurement. The U. S. Sieve Series provides that the area of each sieve opening size is 1 1/2 times the area of the preceding sieve size.

By using every other sieve in this number series, the relationship becomes based on the square root of two (1.414), with the area of the opening being twice that of the preceding sieve size. Thus, by skipping two sizes, you create an area ratio of 3 to 1, or by skipping three sizes, you create a ratio of 4 to 1.

When selecting sieves from this series, any number of sieves can be used for an analysis. Care must be taken in selecting each sieve between two points, every other sieve, every fourth sieve, etc., to keep within the mathematical progression of the series. After World War II, the International Standards Organization (ISO) was formed in an attempt to establish world standards. Though the U.S. Sieve Series had proven to be effective and was in use throughout the world, members of the ISO would not accept the U.S. Sieve Series as a world standard. The ISO chose to adopt the Preferred Number Series based on the roots of ten. The Preferred Number Series was suggested by Charles Renard of France in 1879. His system is based on the tenth, twentieth and fortieth roots of ten (designated R-10, R-20 and R-40).

A compromise was reached between the ISO and the proponents of the U.S. Sieve Series when it was discovered that every third value in the R-40/3 table is in a step ratio of 1.1885, sufficiently close to the fourth root of two (1.1892) used in the U.S. Sieve Series. In 1970, slight adjustments were made in the U.S. Sieve Series to align the series perfectly with the ISO specifications.

Principles and Procedures for Test Sieves

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In obtaining meaningful sieve analysis data, six major steps are recommended. 1) Obtain a representative sample of the material to be evaluated. 2) Prepare the sample for evaluation; this may involve washing and/or drying the sample. 3) Reduce the sample to a size suitable for the sieve analysis procedure. 4) Perform the actual sieve analysis procedure. 5) Compute the data and convert the data into a usable format. 6) Organize the data and assemble the information for presentation.

Granular and powder materials are prone to segregation during movement and storage of the products. This segregation can be due to the disparity of the particle sizes and the varied densities for blended products. When forming a stockpile of material, the larger, coarser particles are heavier and tend to roll to the lowest portion and outer perimeter of the cone. The finer particles are lighter and more angular and remain concentrated at the top and through the vertical center of the cone. Obtaining samples from only the outer perimeter or from the top of the cone would not provide a sample which would be representative of the entire batch.

Sample extraction and preparation is the most commonly overlooked variable in sieve standardization programs. Testing bias can be added at many places along the progression from the raw materials received from a supplier, samples taken at each stage of production, sample reduction procedures and samples when the product is ready for shipment to the customer. The way the samples are extracted from the original bulk volume varies with the way the materials are received, produced or stored. The ideal sampling method is one, which provides the most representative sample with the least amount of material required.

The following paragraphs were first published in the ASTM technical publication STP 447 A. The collaborative efforts of the authors have produced a section on sampling technique which will aid in obtaining representative test samples from larger test sources.

Sampling from a chute or belt

Accuracy in sampling is obtained where material is flowing from a chute or belt conveyor. The ideal place to collect the sample is where the material drops from the chute or belt. If the material stream is small enough, use a pail or other suitable receptacle which can be swung completely across the flowing stream in a brief interval of time and with uniform movement. The sampling receptacle should not be allowed to overflow, because the overflow would tend to reject a higher proportion of the larger particles that exist in a representative sample. Mechanical sampling devices are available for selecting samples automatically from a stream at uniform time intervals.

Sampling from carload shipments of coarse bulk material

For coarse materials, such as crushed stone and gravel, shipped in railroad cars, a recommended method is to dig three or more trenches at least 30.48 cm (1 foot) deep and approximately 30.48 cm (1 foot) wide at the bottom. Equal portions are taken at seven equally spaced points along the bottom of the trench by pushing a shovel downward into the material and not by scraping horizontally. Samples from trucks, barges, or boats should be taken in the same manner as from railroad cars, except that the number of trenches should be adjusted to the size of the transportation unit and tonnage involved.

Sampling from carload shipments of fine bulk materials

One established method for sampling a carload of bulk granular material is to take eight equal samples, (approximately 700 to 1000 grams each) from the bottom of a 30.48 cm (1 foot) conical excavation. Samples should be suitably spaced to represent the length and width of the car and then combined into a single gross sample.

Sampling bulk shipments of fine material with a sampling tube

An alternate and simpler method of sampling a carload, or other bulk quantity of fine or granular material is by use of a sampling tube which, for this purpose, should be 38.1 mm (1 1/2 inches) by approximately 1.829 m (6 feet). Five or six insertions of the tube will produce approximately, a 2 pound (907 g) sample.

Sampling from a carload of bagged material

One method of sampling a carload of material shipped in bags is to select, at random, a number of bags equal to the cube root of the total number of bags in the car and to take suitable portions (800 to 1000 grams for minus 6 mm material) from each of the selected bags for a combined gross sample.

Sampling from a pile

In sampling from a pile, particularly material like crushed stone or coal containing large particles, it is extremely difficult to secure samples that are truly representative. At the apex of a conical pile, the proportion of fines will be greater, while at the base; the percentage of coarse particles will be greater. Therefore, neither location will be representative of the whole. In a shoveling process, every fifth or tenth shovel, etc., should be taken depending on the amount of the sample desired. The sample should consist of small quantities taken at random from as many parts of the pile as are accessible and taken in a manner that the composite will have the same grading as the larger amount.

Reduction of gross sample to test size for sieve analysis

After the gross sample has been properly obtained, the next step is to reduce it to a suitable size for sieve analysis without impairing in any way the particle size distribution characteristics of the original sample. This phase of the operation should follow the applicable procedures described in the succeeding sections and should be performed with as much care as was used in the collection of the gross sample and in performing the sieve test.

Coning and quartering

Pile the gross sample in a cone, place each shovel full at the apex of the cone, and allow it to run down equally in all directions. This will mix the sample. Then spread the sample in a circle and walk around the pile, gradually widening the circle with a shovel until the material is spread to a uniform thickness.

Mark the flat pile into quarters, and reject two opposite quarters. Mix again into a conical pile, taking alternate shovel-fulls from the two quarters saved. Continue the process of piling, flattening, and rejecting two quarters until the sample is reduced to the required size.

Sample splitters and reducers

Gross samples, if not too large, may be reduced to test sample size by one or more passes through a sample splitter or Jones type riffle, which will divide a sample in half while maintaining the particle size distribution of the original sample. By repeated passes, the sample can be split into quarters, eighths, and soon until the size of the sample desired is obtained. For larger gross samples, sample reducers are available which will select a representative 1/16 part with a single pass. After just two passes through such a unit, a representative one pound sample can be obtained from an original 256 pounds. Three passes will give a one pound sample from two tons of material. Always make sure that the passages in the splitter or reducer are at least three times the size of the largest particle in the sample. Do not attempt to arrive at exactly the amount of material specified for the test. If a 50 gram sample is desired, arrive as near to this amount as practicable, because it will make no difference in the test percentage results whether the sample is slightly larger or smaller. In attempting to arrive at an exact weight, the tendency is to discriminate by the removal of sizes that are not representative of the whole, thus destroying the representative quality of the sample.

Size of Sample in the Test

There is a natural tendency, although incorrect, to use an excessively large sample in the test. In most cases, a smaller sample will provide a more accurate analysis. Beware, however, that the more you split, the greater the chance of error. Testing sieves are a go or no go gauge; if the sample is too large it will not permit each of the particles an opportunity to present themselves to the screen surface. Often the limiting factor for reducing the sample size is the accuracy of the weighing device used to determine the amount of material retained on the sieve.

Generally a 25 to 100 gram sample is recommended. However, if it is necessary to establish the correct sample size, utilize the following procedure: Using a sample splitter, reduce samples to weights (i.e. 25, 50, 100, 200 grams). Analyze these various sample sizes on a selected nest of sieves for a period of five minutes preferably using a mechanical sieve shaker. If the test with the 100 gram sample shows approximately the same percentage passing the finest sieve as the 50 gram sample, whereas the 200 gram sample shows a lower percentage, this would indicate that the 200 gram sample is too large and the 100 gram sample would be satisfactory. Then run the 100 gram sample on the same set of sieves for the same time period to see if repetitive results are obtainable.

A useful table of recommended sample sizes for tests with 200 mm or 8" diameter sieves is presented in Table 4. Note that the table gives sample sizes listed by volume. Recommended sample weights in grams can be determined by multiplying the values in Column 3 and 4 by the bulk density (grams per cubic centimeter) of the material to be tested rounded out within a reasonable tolerance. If the actual bulk density of a certain material is not known, the typical density factor for the most nearly similar material listed in Table 5 may be used.

To perform the actual sieve analysis, sieves should be chosen in a sequence as described earlier. Use every sieve, every other sieve, or every third sieve, etc. between the desired size parameters. The use of sieves in this sequential order will allow for better data presentation and a more meaningful analysis of the test results. Care should also be taken in selecting the proper sieves to avoid overloading any sieve with an especially large material peak. For example, a specification may require 96% of the sample be retained above a #50 mesh sieve. The proper way to perform an analysis of this nature is to use 'relief screens', that is, sieves in the 30, 35, 40 and 45 mesh ranges to remove some of the burden from the critical cut point of 50 mesh. If the relief sieves are not used, the particles of exactly 50 mesh size or slightly larger may become wedged in or forced through the sieve openings by the mass of material resting above them. Large concentrations of material on one sieve reduce the opportunity for near size material to pass through the sieve resulting in a larger portion of the material retained on the test sieve. The sieve cut point would be inaccurate and the sample would not meet the specifications for the test.

The selected sieves should be assembled with the coarsest sieve at the top of the stack, and the balance of the stack in increasing magnitude of fineness (increasing sieve numbers with smaller openings). The stack should include a cover on the top sieve and a pan below the finest sieve. The sieve stack can either be shaken then wrapped by hand, or mounted in a sieve shaker with a motorized or electrostatic drive mechanism.

While many applications still use the hand-shaken method for sieving, motor driven shakers have proven to be much more consistent, minimizing variations related to operator procedures. In powder analysis below the 100 mesh range, the sieve shaker should be equipped with a device to impart a shock wave to the sieve stack at regular intervals. This hammer or rapping device is necessary to reorient the particles on the sieve and impart some shear forces to near-size particles blocking the sieve openings.

Recommended Time Intervals

The duration of the sieving interval is usually regulated by industry standards, or by in-house control specifications. Commonly, 10, 15 or 20 minute tests are used as arbitrary sieving intervals. To determine the best interval for a new material, or to double check the accuracy of existing specifications, the following procedure can be used. Select the desired sieves for the analysis. 1) Weigh up a sample of the material to be tested and introduce it to the completed sieve stack. 2) Shake the sieve stack for a period of 5 minutes. 3) Weigh the residue in the pan and calculate the percentage in relation to the starting weight. 4) Reassemble the stack and shake for one additional minute. 5) Repeat the weigh-up procedure and calculate the percentage. If the percentage of fines increased more than 1% between 5 minutes and 6 minutes, reassemble the stack and shake for an additional minute. The data can be plotted as percentage throughput vs. time for each data point you calculate. When the change in the percentage of fines passing in the 1 minute period drops below 1 %, the test can be considered complete. Record the total testing time for subsequent analyses.

Another type of sieve analysis is the wet sieve test. In this method, the sample is weighed and then washed through the finest sieve in the stack with water, a wetting agent (water based), or some other compatible solvent. After thoroughly washing the fines from the raw sample, the residue is dried either over a hot plate or in an oven. The temperature of the sieve should be maintained below 149C (300F) to avoid loosening of the sieve cloth or failure of the solder joint. After drying, the residue is then sieved normally on the balance of the sieve stack. The loss in weight not accounted for on the coarse screens is assumed to be fines or soluble material.

Wet sieve analysis is especially helpful when working with naturally agglomerated materials, Ultra-fine powders with severe static changes, and in samples where fine particles tend to cling to the coarse fractions in the blend. The disadvantages associated with wet sieving are primarily the time period required to perform the analysis due to the additional washing and drying time and the possible damage to the sieve mesh by overloading. A common practice with wet sieving operations is brushing or forcing the sample through the mesh while the liquid medium is directed on the sieve. This pressure can distort the sieve openings or tear the mesh at the solder joint through stress. Therefore, this procedure is not recommended. Once the sieving interval is complete, whether dry or wet sieving is used, the residue on each sieve is removed by pouring the residue into a suitable weighing vessel. To remove material wedged in the sieve's openings, the sieve is inverted over a sheet of paper or suitable collector and the underside of the wire cloth brushed gently with a nylon paint brush with bristles cut to a 25.4 mm (1") length. The side of the sieve frame may be tapped gently with the handle of the brush to dislodge the particles between brush strokes. At no time should a needle or other sharp object be used to remove the particles lodged in the wire cloth. Special care should be taken when brushing sieves finer than 80 mesh. Brushing can cause distortions and irregularities in the sieve openings. The procedure is repeated for each sieve in the stack and contents of the pan.

The individual weights retained on the sieves should be added and compared to the starting sample weight. Wide variations or sample losses should be determined immediately. If the finished sample weight varies more than 2% from the initial weight, the analysis and sample should be discarded and the test performed another sample. If the sample weights are acceptable, complete the calculations and report the individual weights retained on each sieve.

Presentation and analysis of the resulting data is frequently made easier by plotting on one of a number of graph formats. The most common graphic presentation is the plotting of the cumulative percentage of material retained on a sieve (plotted on a logarithmic scale) versus percentage (plotted on a linear scale). The resulting curve allows a quick approximation of the sieve size at the fifty-percentile point of accumulation. The curve also shows the smoothness of the distribution by revealing the presence of bimodal blends in the sample. Other plotting techniques include log-log and direct plotting of micron size versus percentage retained.

Care should be exercised in the analyzing the data in relation to the length of time the test was run. If the sample contains a large amount of elongated or nearsize particles, the test results can be misleading. The longer the sieving interval, the greater the opportunity for these problem particles to pass through the sieve's openings. Ideally each fraction should be inspected microscopically after sieving to determine the integrity of the sieve cut point.

Sieve Care and Cleaning

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Click Here on How to Care and Clean Precision Sieves Care and Clean Precision Sieves

Click Here on How to Care and Clean Sonic Sifter Wire Cloth Sieves Care and Clean Sonic Sifter Wire Cloth Sieves

Click Here on How to Care and Clean Metal Framed Wire Cloth Sieves Care and Clean Metal Framed Wire Cloth Sieves

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