Standard Practice for Measuring Fluidization Segregation Tendencies of Powders

SIGNIFICANCE AND USE
Fluidization segregation can cause vertical segregation within bins used to hold and transport powders. This can affect final product quality in industrial applications.
By measuring a powder’segregation tendency, one can compare results to other powders with known history, or determine if the given powder may have a tendency to segregate in a given process.
Fine powders generally have a lower permeability than coarse bulk solids and therefore tend to retain air longer. Thus, when a bin is being filled with a fluidizable powder, the coarser particles settle or are driven into the bed while the finer particles remain fluidized near the surface.
Fluidization, which serves as a driving force for this mechanism of segregation, is likely to occur when fine powders are pneumatically conveyed into a bin, the bin is filled or discharged at high rates, or if sufficient air flow counter to the flow of powder is present within the bin.
Note 1—The quality of the result produced by this practice is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D 3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this practice are cautioned that compliance with Practice D 3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D 3740 provides a means of evaluating some of those factors.
Practice D 3740 was developed for agencies engaged in the testing and/or inspection of soil and rock. As such it is not totally applicable to agencies performing this practice. However, users of this practice should recognize that the framework of Practice D 3740 is appropriate for evaluating the quality of an agency performing this practice. Currently there is no known qualifying national authority that inspects agencies that perform this practice.
SCOPE
1.1 This practice covers an apparatus and procedure for simulating the segregation tendencies of powders by means of the fluidization mechanism.
1.2 Powders must be capable of being fluidized in order to be tested by this practice.
1.3 Temperature- and humidity-sensitive powders may need to be tested at different temperatures and moisture contents, as would happen in an industrial environment. Further, the gas supply (type, temperature, and humidity) should also match the industrial conditions.
1.4 This standard is not applicable to all bulk solids and segregation mechanisms: while fluidization is a common segregation mechanism experienced by many fine powders, other segregation mechanisms not evaluated by this standard might induce segregation in practice.
1.5 The extent to which segregation will occur in an industrial situation is not only a function of the powder and its tendency to segregate, but also the handling equipment (for example, bin design), process (for example, transfer rates), and environment.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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Status
Historical
Publication Date
31-Oct-2005
Current Stage
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ASTM D6941-05e1 - Standard Practice for Measuring Fluidization Segregation Tendencies of Powders
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Designation: D6941 − 05
StandardPractice for
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Measuring Fluidization Segregation Tendencies of Powders
This standard is issued under the fixed designation D6941; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
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´ NOTE—Section 7.10 and Figure 2 were corrected editorially in July 2007.
1. Scope D3740 Practice for Minimum Requirements for Agencies
Engaged in Testing and/or Inspection of Soil and Rock as
1.1 This practice covers an apparatus and procedure for
Used in Engineering Design and Construction
simulating the segregation tendencies of powders by means of
the fluidization mechanism.
3. Terminology
1.2 Powders must be capable of being fluidized in order to
3.1 Definitions:
be tested by this practice.
3.1.1 Definitions of terms used in this test method shall be
1.3 Temperature- and humidity-sensitive powders may need in accordance with Terminology D653.
to be tested at different temperatures and moisture contents, as
3.1.2 fluidization, n—the state in which a powder exhibits
would happen in an industrial environment. Further, the gas fluid-like properties.
supply(type,temperature,andhumidity)shouldalsomatchthe
3.1.3 fluidization segregation, n—a mechanism that causes
industrial conditions.
vertical segregation, that is, horizontal layering of fine and
coarse particles, as resulting from fluidization of the bulk solid.
1.4 This standard is not applicable to all bulk solids and
segregation mechanisms: while fluidization is a common
3.1.4 segregation, n—a process through which blended or
segregation mechanism experienced by many fine powders,
uniform powders or bulk solids become non-uniform, with
other segregation mechanisms not evaluated by this standard
regions of varying composition, for example, particle size.
might induce segregation in practice.
3.2 Definitions of Terms Specific to This Standard:
1.5 The extent to which segregation will occur in an
3.2.1 high flow-rate, n—the first stage flow-rate used to
industrial situation is not only a function of the powder and its
initiate fluidization.
tendency to segregate, but also the handling equipment (for
3.2.2 low flow-rate, n—the second stage flow-rate used to
example, bin design), process (for example, transfer rates), and
maintain fluidization.
environment.
3.2.3 representative sample, n—a quantity of the bulk solid
1.6 This standard does not purport to address all of the
to be tested that is representative of that solid in an industrial
safety concerns, if any, associated with its use. It is the
application being studied. Parameters of interest that may
responsibility of the user of this standard to establish appro-
affect whether or not a sample is representative include:
priate safety and health practices and determine the applica-
moisture, particle size distribution, raw material variation,
bility of regulatory limitations prior to use.
method of production, aging, chemical composition.
2. Referenced Documents
4. Summary of Practice
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2.1 ASTM Standards:
4.1 A representative sample of a powder is placed in the
D653 Terminology Relating to Soil, Rock, and Contained
apparatus.
Fluids
4.2 Pressurizedgas(usuallyair)isblownfromthebottomat
a series of flow-rates for specified times, creating a state of
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This practice is under the jurisdiction of ASTM Committee D18 on Soil and
fluidization of the powder.
Rock and is the direct responsibility of Subcommittee D18.24 on Characterization
and Handling of Powders and Bulk Solids.
4.3 Once the airflow is stopped, the powder in the test
Current edition approved Nov. 1, 2005. Published November 2005. Originally
chamber is divided into three samples from the bottom, center,
approved in 2003. Last previous edition approved in 2004 as D6941–04. DOI:
and top of the column.
10.1520/D6941-05E01.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.4 The samples are then available to be tested for differ-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ences relevant to the application, for example, particle size or
Standardsvolume information, refer to the standard’s Document Summary page on
the ASTM website. chemical assay.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6941 − 05
reliable results. Reliable results depend on many factors; Practice D3740
5. Significance and Use
provides a means of evaluating some of those factors.
5.1 Fluidization segregation can cause vertical segregation
Practice D3740 was developed for agencies engaged in the test
...

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