| Â
| |
| | were not significantly better than those
|
| Sieving in its most elemental definition
| |
| | achieved by using Mid-Point Sieves.
|
| is the separation of fine material from
| |
| | Mesh-Certified Sieves, Mid-Point Sieves,
|
| coarse material by means of a meshed or
| |
| | and sieves carrying the Manufacturing
|
| perforated surface. The technique was
| |
| | Conformance Certificate are all made with
|
| used as far back as the early Egyptian
| |
| | mesh that already conforms to official
|
| days as a way to size grains. These early
| |
| | standards. However, there are three lower
|
| sieves were made of woven reeds and
| |
| | grade levels of sieve mesh available when
|
| grasses. Today the sieve test is the
| |
| | tolerance levels are not as stringent.
|
| technique used most often for analyzing
| |
| | The first is Market Grade. These sieves
|
| particle-size distribution.
| |
| | have a weave that uses a larger diameter
|
| Although at first look the sieving
| |
| | wire resulting in a high strength
|
| process appears to be elementary, in
| |
| | square-mesh cloth suitable for general
|
| practice, there is a science and art
| |
| | purpose screening. There are no official
|
| involved in producing reliable and
| |
| | standards for Market Grade test sieves.
|
| consistent results. In order to better
| |
| | The second, Mill Grade, is a class of
|
| understand sieving, there are several
| |
| | woven mesh using smaller wire, which
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| areas of sieve specifications that should
| |
| | results in larger open areas in the
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| to be explained, including:
| |
| | screen mesh. There is also a Twill Weave
|
| 1. What Are Test Sieves?
| |
| | in which the weft and warp wires
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| Test sieves are measuring devices used to
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| | alternatively run over and under two
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| determine the size and size distribution
| |
| | wires rater than over and under alternate
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| of particles in a material sample using
| |
| | wires as in standard mesh. As none of
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| wire mesh of different openings to
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| | these have official standards against
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| separate particles of different sizes.
| |
| | which to measure the expected
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| Test sieves usually consist of wire mesh
| |
| | performance, none of these are provided
|
| held in a frame. In most laboratory
| |
| | with a mesh certificate.
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| applications the frame is round and is
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| | 5. Sieve Calibration
|
| made from stainless steel or brass. The
| |
| | Quality control of the sieving process is
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| standard frame sizes are three, six,
| |
| | essential, and for people involved in
|
| eight, ten, or twelve inch diameters and
| |
| | material processing and particle
|
| metric equivalents. The woven mesh can be
| |
| | characterization, sieve calibration can
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| made of stainless steel, brass, or
| |
| | be a confusing topic. It is beneficial to
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| bronze. For most applications stainless
| |
| | understand what sieve calibration is, why
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| steel is the most common material used.
| |
| | a working sieve should be calibrated, and
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| 2. What Are the Limitations of the Test
| |
| | how to calibrate a sieve.
|
| Sieve Procedure?
| |
| | A. What Is Sieve Calibration?
|
| The main limitation with the construction
| |
| | Sieve calibration is the process of
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| of test sieves is the inherent nature of
| |
| | checking a working sieve's performance.
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| a woven product including control of sag
| |
| | (A working sieve is a test sieve that is
|
| when mounted and the uniformity of
| |
| | used regularly to perform a particle size
|
| construction of the holding frame. It is
| |
| | analysis.)
|
| also essential to maintain consistent
| |
| | B. Why Calibrate a Working Sieve?
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| sizing across all the openings in a piece
| |
| | Since working sieves are used daily for
|
| of mesh.
| |
| | tests, they are also cleaned regularly.
|
| Because of the inherent variations of
| |
| | Although frequent use in itself can cause
|
| openings in any woven product there are
| |
| | changes in mesh openings, much of the
|
| limitations to the degree of uniformity
| |
| | damage sustained to working sieves occurs
|
| achieved in the opening size across the
| |
| | during cleaning. Often, the operator
|
| mesh in a sieve. This results in a
| |
| | hurries to clear the mesh of residual
|
| practical limit to the range of openings
| |
| | particles by strongly tapping the frame.
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| and to the precision of results from a
| |
| | This tapping can distort the mesh.
|
| specific sieve.
| |
| | Operators also use brushes to remove
|
| The sieve test requires particles to pass
| |
| | residual particles after a test. This
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| through the sieve mesh. The practical
| |
| | process often distorts sections of the
|
| limit for using a test sieve procedure is
| |
| | sieve mesh. These alterations of the
|
| a particle size of 20? (microns).
| |
| | sieve will change the results obtained in
|
| 3. What Are the Test Sieve Standards?
| |
| | subsequent tests, hence the need for
|
| The first sieve testing standards were
| |
| | calibration.
|
| developed by W.S. Tyler Company before
| |
| | Excessive damage such as tears or large
|
| 1920. This original work predated any
| |
| | distortions of the mesh weave can be
|
| published activity by the standards
| |
| | detected by visual inspection. Damaged
|
| organizations and the Tyler designation
| |
| | sieves can be taken out of service when
|
| is the de facto standard in many
| |
| | the damage is observed. When the change
|
| industries. In 1925, ASTM International
| |
| | is small, visual observation may not
|
| prepared the official standard for Test
| |
| | detect a variation in the test results
|
| Sieve Size, Test Sieve Construction, and
| |
| | attributable to the sieve's change. A way
|
| Test Sieve Mesh in the United States.
| |
| | to determine if changes have occurred is
|
| European Standards were developed by a
| |
| | to compare the sieve's performance
|
| German university group in 1977 and are
| |
| | against a known standard. This is sieve
|
| known by the designation DIN 4188. These
| |
| | calibration.
|
| were followed by British Standards (BS
| |
| | In addition, in operations with tight
|
| 410). The International Standards (ISO
| |
| | particle size specifications, calibration
|
| 565) were developed by the International
| |
| | of new test sieves is performed to
|
| Standards Organization in Europe. This
| |
| | establish a performance baseline for the
|
| was designed to be the universal
| |
| | sieve.
|
| international standard. However, in
| |
| | C. How is a Test Sieve Calibrated?
|
| practice, all of the standards are in
| |
| | The base point of a sieve calibration
|
| operation.
| |
| | process is the use of a fixed standard
|
| Sieve testing standards relate to the
| |
| | and there are a number of approaches
|
| construction of the sieve frame and mesh
| |
| | used. The most common is the use of a
|
| mounting as well as the tolerances
| |
| | master stack of sieves, a master sample,
|
| allowed in the variability of mesh
| |
| | or calibration spheres or beads.
|
| openings. Basic principles are common to
| |
| | A master stack of sieves includes one of
|
| all of the standards and variations in
| |
| | each of the sieves used in the processes.
|
| terminology and in details are small.
| |
| | A master stack should consist of
|
| These small differences, however, can
| |
| | Mesh-Certified sieves. In the event of
|
| often lead to confusion. The following is
| |
| | tight tolerances for the sieve tests it
|
| a synopsis of the principles behind these
| |
| | is recommended that Mid-Point sieves be
|
| standards.
| |
| | used. The following steps are used for
|
| Test sieve frame standards include the
| |
| | this method:
|
| following:
| |
| | 1. Prepare two samples of the material
|
| 1. Rigid construction
| |
| | selected for the calibrations process
|
| 2. Cloth (mesh) mounted without
| |
| | 2. Place the master stack of sieves on a
|
| distortion, looseness, or waviness
| |
| | sieve shaker
|
| 3. Joint between mesh and frame to be
| |
| | 3. Load one of the samples into the top
|
| filled or constructed so that particles
| |
| | sieve
|
| will not be trapped
| |
| | 4. Run on a sieve shaker for the
|
| 4. Frame will be of non-corrosive
| |
| | predetermined time
|
| material and seamless
| |
| | 5. Prepare a percent-retained analysis of
|
| 5. Bottom of the frame sized to easily
| |
| | the result
|
| slide into the top of same sized sieve,
| |
| | 6. Place the stack of working sieves
|
| thus enabling stacking
| |
| | (sieves with sizes to match master stack)
|
| 6. Cloth opening to be a minimum of 0.5
| |
| | 7. Repeat steps three through five for
|
| inches less than nominal diameter
| |
| | the second sample of the material
|
| The wire cloth (mesh) standards include
| |
| | 8. Compare the results of the two
|
| the following list of nominal size
| |
| | analyses
|
| openings in inches, millimeters
| |
| | 9. Check variance from the master stack
|
| (microns), and sieve number. The
| |
| | against acceptable tolerances
|
| following specific dimensional examples
| |
| | 10. Replace the working sieves that are
|
| come from the ASTM E11 Standard:
| |
| | out of tolerance
|
| 1. Permissible variation of average
| |
| | Some users only calibrate one sieve at a
|
| openings (depending on opening size and
| |
| | time and compare it to one sieve from the
|
| ranges from ± 2.9% of nominal size for
| |
| | master set. This procedure can be done
|
| 125 mm mesh to ± 15% for 20? mesh)
| |
| | before putting new working sieves in
|
| 2. Not more than 5 % of the openings can
| |
| | service.
|
| exceed 1.04 times the nominal size for
| |
| | In some processes master samples are
|
| 125 mm mesh to 1.45 times the nominal
| |
| | maintained of all material that is
|
| opening for 20? mesh
| |
| | subject to sieve testing. The results
|
| 3. Maximum individual opening (for any
| |
| | expected from working sieves were
|
| opening) ranges from 1.0472 times the
| |
| | established through the use of a master
|
| nominal size for 125 mm mesh to 1.75
| |
| | sieve stack or other calibration
|
| times the normal mesh for 20? mesh
| |
| | techniques. In this method a sample from
|
| 4. Wire diameters are specified and range
| |
| | the master is used and the following
|
| from 8 mm for 125 mm mesh to 0.020
| |
| | steps are taken:
|
| millimeters for 20? mesh
| |
| | 1. Place the stack of working sieves to
|
| More recently, methods based on laser and
| |
| | be checked on a sieve shaker
|
| energy technologies, sedimentation
| |
| | 2. Load the selected sample from the
|
| techniques, image analysis, and
| |
| | master sample into the top sieve
|
| centrifuge-type methods have gained
| |
| | 3. Run the sieve shaker for the
|
| acceptance. However, procedures using
| |
| | predetermined time
|
| test sieves are still widely used. The
| |
| | 4. Prepare a percent retained analysis of
|
| sieve-test result remains the basis or
| |
| | the result
|
| standard against which newer techniques
| |
| | 5. Compare the results to acceptable
|
| are checked. In addition, the equipment
| |
| | tolerances for the sieves in this stack
|
| cost for the test sieve procedure is
| |
| | 6. Replace the working sieves that are
|
| significantly lower than the capital
| |
| | out of tolerance
|
| investment needed for newer methods.
| |
| | The used sample may be returned to the
|
| 4. What Are Sieve Certifications?
| |
| | original master sample. Depending on the
|
| Sieve certifications are statements that
| |
| | type of material, deterioration may occur
|
| a test sieve meets or exceeds published
| |
| | during the sieve test. Where this occurs
|
| criteria. It is an assurance that a new
| |
| | the test sample is discarded after use.
|
| sieve will perform in a predictable way.
| |
| | As with the use of a master stack, some
|
| The closer the tolerance required in a
| |
| | users only calibrate one sieve at a time
|
| manufacturing process, the higher the
| |
| | and compare it to a performance tolerance
|
| level of certification needed. Similarly,
| |
| | chart for that sieve size. This procedure
|
| a master set of test sieves against which
| |
| | can also be used for new working sieves
|
| working sieves (sieves in everyday use)
| |
| | before putting them into service.
|
| are checked for wear and predicted
| |
| | Calibration spheres, in sizes for each of
|
| performance need a high level of
| |
| | the sieves to be calibrated, are used to
|
| certification. When test sieves are part
| |
| | determine the actual results obtained by
|
| of a process that is required to meet
| |
| | each sieve tested. This method is simple
|
| traceability prerequisites, such as a
| |
| | and gives a precise result on the mean
|
| specific ISO level, a certification will
| |
| | aperture size. The result is traceable to
|
| document the needed traceability.
| |
| | NIST and NPL standards. It is a good
|
| Many sieve manufacturers provide a
| |
| | check for standards reporting and for
|
| certificate which states that the sieve
| |
| | setting internal standards. The procedure
|
| was manufactured in conformance with a
| |
| | for this calibration is as follows:
|
| specific standard (e.g., ASTM, ISO). This
| |
| | 1. Select the sieve to be calibrated
|
| Manufacturing Conformance Certificate
| |
| | 2. Empty the contents of the bottle
|
| does not reference nor does it certify
| |
| | containing the appropriate standard onto
|
| conformance of the mesh. Most
| |
| | the sieve
|
| manufacturers supplying a Conformance
| |
| | 3. Shake evenly over the surface for one
|
| Certificate will analyze the mesh and
| |
| | minute
|
| provide a mesh certification for an extra
| |
| | 4. Calculate the percent passing through
|
| charge.
| |
| | and read the mean aperture for a
|
| A Mesh-Certified Sieve will be provided
| |
| | calibration graph
|
| with a certificate that states the sieve
| |
| | The method specified by ASTM is to
|
| was manufactured in accordance with a
| |
| | optically inspect a sample of the
|
| specified standard and it was submitted
| |
| | openings, measure the apertures and the
|
| for laboratory analysis and is certified
| |
| | wire, and compare the results with the
|
| to conform to that specific specification
| |
| | ASTM E11 Standard. Traditionally, this
|
| standard (e.g., ASTM, ISO).
| |
| | has been accomplished visually using a
|
| There is a third level of tolerance which
| |
| | microscope. However, there are new
|
| certifies that the manufacturing standard
| |
| | computer-based image analysis systems
|
| is met and that the mesh was submitted
| |
| | that are beginning to have limited use
|
| for laboratory analysis. It also
| |
| | for sieve calibration.
|
| certifies that its openings fall in the
| |
| | 6. Summary
|
| middle of the specific standard
| |
| | Sieves have a long history as the base
|
| specification (e.g., ASTM, ISO). This is
| |
| | for measuring and analyzing particle size
|
| effectively a 30% better tolerance than
| |
| | in material. In spite of the advent of
|
| the mesh of a Fully-Certified sieve. This
| |
| | new technology-based methods, procedures
|
| is known as a Mid-Point Sieve. These
| |
| | based on sieves continue to be the main
|
| three levels of sieve certification
| |
| | basis for particle size determination. In
|
| enable the comparability of performance
| |
| | order to produce reliable and consistent
|
| of one sieve to another of the same size.
| |
| | results, it is evident that sieving
|
| Until the development of the Mid-Point
| |
| | requires an understanding of not just
|
| Sieve, high levels of comparability were
| |
| | one, but a combination of integral
|
| achieved by providing sieves that were
| |
| | factors such as test sieves, limitations
|
| optically matched to a user's standard
| |
| | of the test sieve procedure, test sieve
|
| sieve. A time consuming and costly
| |
| | standards, sieve certifications, and
|
| procedure was needed to accomplish this
| |
| | sieve calibration.
|
| level of comparability and the results
| |
| |
|
