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ASTM D6941-05e1

ASTM D6941-05e1

Standard Practice for Measuring Fluidization Segregation Tendencies of Powders

Fecha:
2012-12-10 /Historical
Superseeded by:
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.

Keywords:
fluidization; powder; segregation
47,89
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