1、Designation: D6941 051 D6941 12Standard Practice forMeasuring Fluidization Segregation Tendencies of Powders1This standard is issued under the fixed designation D6941; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTESection 7.10 and Figure 2 were corrected editorially in July 2007.1. Scope Scope*1.1 This practice covers an apparatus and proc
3、edure for simulating the segregation tendencies of powders by means of thefluidization mechanism.creating several specimens of a powder sample that, if the powder is one that segregates by the fluidizationmechanism, should be different from one another.1.2 A powder sample is fluidized then, after th
4、e fluidizing gas is turned off, it is separated into three or more specimens thatcan be analyzed for parameters of interest. The difference in these parameters between the specimens is an indication of thesegregation potential of the powder.1.3 Powders must be capable of being fluidized in order to
5、be tested by this practice.1.4 Temperature- and humidity-sensitivemoisture-sensitive powders may need to be tested at different temperatures andmoisture contents, as would happen in an industrial environment. Further, the gas supply (type, temperature, and humidity) shouldalso match the industrial c
6、onditions.1.5 This standard is not applicable to all bulk solids and segregation mechanisms: while fluidization is a common segregationmechanism experienced by many fine powders, other segregation mechanisms not evaluated by this standard might inducesegregation in practice. Practice D6940 covers an
7、other common mechanism: sifting.1.6 The extent to which segregation will occur in an industrial situation is not only a function of the powder and its tendencyto segregate, but also the handling equipment (for example, bin design), process (for example, transfer rates), and environment.1.7 The value
8、s stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.8 This practice offers a set of instructions for performing one or more specific operations. This document cannot replaceeducation or experience and should be used in conjunction with p
9、rofessional judgment. Not all aspects of this practice may beapplicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which theadequacy of a given professional service must be judged, nor should this document be applied without consideration
10、 of a projectsmany unique aspects. The word Standard in the title of this document means only that the document has been approved throughthe ASTM consensus process.1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof th
11、e user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and Contained FluidsD2216 Test Methods for Laboratory Determination o
12、f Water (Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used inEngineering Design and ConstructionD6940 Practice for Measuring Sifting Segregation Tendencies of Bulk Solids1 This practice is unde
13、r the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.24 on Characterization andHandling of Powders and Bulk Solids.Current edition approved Nov. 1, 2005Nov. 1, 2012. Published November 2005December 2012. Originally approved in 2003. Last prev
14、ious edition approved in 20042005as D694104.051. DOI: 10.1520/D6941-05E01.10.1520/D6941-12.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandardsvolume information, refer to the standards Document S
15、ummary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recomme
16、nds that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700,
17、 West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions:3.1.1 Definitions of terms used in this test method shall be in accordance with For common definitions of technical terms in thisstandard, refer to Terminology D653.3.1.2 fluidization, nin powders, the state in which a po
18、wder exhibits fluid-like properties.3.1.3 fluidization segregation, nin powders, a mechanism that causes vertical segregation, that is, horizontal layering of fineand coarse particles, as resulting from fluidization of the bulk solid.3.1.4 segregation, nin powders, a process through which blended or
19、 uniform powders or bulk solids become non-uniform,with regions of varying composition, for example, particle size.3.2 Definitions of Terms Specific to This Standard:3.2.1 high flow-rate, nin powders, the first stage flow-rate used to initiate fluidization.3.2.2 low flow-rate, nin powders, the secon
20、d stage flow-rate used to maintain fluidization.3.2.3 representative sample, nin powders, a quantity of the bulk solid to be tested that is representative of that solid in anindustrial application being studied. Parameters of interest that may affect whether or not a sample is representative include
21、:include, but are not limited to: moisture, particle size distribution, raw material variation, method of production, aging, chemicalcomposition.4. Summary of Practice4.1 A representative sample of a powder is placed in the apparatus.test chamber.4.2 Pressurized gas (usually air) air), which is blow
22、n from the bottom at a series of flow-rates bottom, is ramped up from zeroto a pre-determined High Flow-rate, held there, ramped down to a pre-determined Low Flow-rate, then held there, all for specifiedtimes, creating a state of fluidization of the powder.4.3 The airflow is ramped down to zero over
23、 a specified time.4.4 Once the airflow is stopped, the The powder in the test chamber is divided into three samples from the bottom, center, andtop of the column.N specimens.4.5 The samplesspecimens are then available to be tested for differences relevant to the application, for example, particle si
24、zeor chemical assay.5. Significance and Use5.1 Fluidization segregation can cause vertical segregation within bins used to hold and transport powders. This can affect finalproduct quality in industrial applications.5.2 By measuring a powders segregation tendency, one can compare results to other pow
25、ders with known history, or determineif the given powder may have a tendency to segregate in a given process.5.3 Fine powders generally have a lower permeability than coarse bulk solids and therefore tend to retain air longer. Thus, whena bin is being filled with a fluidizable powder, the coarser pa
26、rticles settle or are driven into the bed while the finer particles remainfluidized near the surface.5.4 Fluidization, which serves as a driving force for this mechanism of segregation, is likely to occur when fine powders arepneumatically conveyed into a bin, the bin is filled or discharged at high
27、 rates, or if sufficient air flow counter to the flow of powderis present within the bin.NOTE 1The quality of the result produced by this practice is dependent on the competence of the personnel performing it, and the suitability of theequipment and facilities used. Agencies that meet the criteria o
28、f Practice D3740 are generally considered capable of competent and objectivetesting/sampling/inspection/etc. Users of this practice are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliableresults depend on many factors; Practice D3740 provides a means of
29、 evaluating some of those factors.Practice D3740 was developed for agencies engaged in the testing and/or inspection of soil and rock. As such it is not totally applicable to agenciesperforming this practice. However, users of this practice should recognize that the framework of Practice D3740 is ap
30、propriate for evaluating the qualityof an agency performing this practice. Currently there is no known qualifying national authority that inspects agencies that perform this practice.6. Apparatus6.1 The apparatus including critical dimensions is shown in Fig. 1. It consists of the following:6.2 Gas
31、Supply with Flow MeterA gas supply supply of dry, non-toxic and non-flammable gas capable of fluidizing thepowder is required (15 to 30 psig 100 to 200 kPa range, 25 psig 170 kPa recommended, maximum flow rate 10 000 required.The recommended gas supply pressure is 170 kPa 25 psig with a range from 1
32、00 to 200 kPa 15 to 30 psig. The recommendedgas supply flow rate is 10 000 cm3/min recommended). or higher. The gas flow rate mustshall be adjustable during the test-an test.An automated controller may be used for this purpose.NOTE 2Generally, clean, dry air is used. If air is not suitable (that is,
33、 it reacts with or adversely affects the powder being tested) another gas, suchas nitrogen, may be used.D6941 1226.3 CylindersTest ChamberThree transparent cylinders are stacked, identified (from the bottom) as the bottom, center, andtop cylinders. The bottom cylinder sits against the diffuser in th
34、e This consists of three or more cylinders stacked above thedistributor, which is at the top of the air supply plenum. The top cylinder mates to the expansion chamber. When the cylinders arestacked together, they make up the test chamber, These cylinders which, when stacked together have a total hei
35、ght of at least 195mm, are connected at the top to a conical expansion chamber. The test chamber is where the powder is placed. The assembled testchamber dimensions are 24 mm I.D. by at least 185 mm tall. The test chamber should have at least 25 mm additional height toallow expansion of the powder b
36、ed. The cylinders must be held together so they do not separate during the tests and so leakagedoes not occur, while still able to be separated at the end of the test in a way to allow for sample recovery. This can be done anumber of ways, including taping the sections together.sample is placed.6.3.
37、1 CylindersEach circular cylinder is transparent and has a diameter of 24 6 1 mm I.D. They are stacked, identified as #1(the bottom) to #N (the top). The bottom cylinder (#1) sits against the distributor in the air supply plenum. The top cylinder (#N)mates to the expansion chamber. The cylinders sha
38、ll be held together in a manner that prevents separation during the test andprevents leakage. This method must allow separation of the cylinders upon completion of the test to allow specimen recovery.6.4 Expansion ChamberThe expansion This conical extension of the test chamber allows the powder to d
39、isengage from theair stream. It must be sufficiently tall to prevent the expanded powder bed from contacting the filter at its top and sufficiently steepto cause the powder to slide back into the test chamber when the airflow is turned off.6.5 FilterThe filter prevents powder from being blown out of
40、 the apparatus. apparatus while allowing the gas to pass through.The filter material should be appropriate for the application and should not contaminate the powder (which may affect the analysisof the samples),specimens), and should provide sufficient containment of the powder (from both a safety p
41、erspective and a lossof powder perspective).FIG. 1 ApparatusFIG. 2 Timing ProfileD6941 1236.6 DiffuserDistributorThe diffuser distributesdistributor diffuses the air uniformly into the test chamber; therefore, asufficient pressure drop across the diffuser is required.distributor is required. The por
42、e size of the porous media in the distributordoes not have to be smaller than the smallest particle size of the test sample, but should be small enough to prevent particle seepageinto the plenum.NOTE 3A sintered metal disk, such as 5 m filtration grade porous stainless steel sheet available from Mot
43、t Industrial, Farmington CT, sheet, maybe an appropriate material for the diffuser.distributor. Some cohesive powders do not fluidize well, and simply form an air channel through the test bed,allowing the air to flow past stationary powder. In this case additional airflow will not serve to fluidize
44、the powder. If this occurs, this test is not valid.However, a diffuserdistributor with a lower permeability may serve to distribute the air better more uniformly, thereby reducing channeling.7. Procedure7.1 Clean the apparatus and allow all parts to dry.7.2 Stack the cylinders one above the other, s
45、ecure them together, and align the bottom cylinder (#1) on the diffuser.distributor.7.3 Place the apparatus on a table or bench that is free from vibration, in a suitable laboratory environment to approximate theindustrial environment. Make sure that the apparatus is level.7.4 Obtain a representativ
46、e, about 100 mL sample of the powder to be tested. Measure its temperature and, if appropriate, itsmoisture (water) content using Test Method D2216 or another method specified by the requesting agency.7.5 Carefully spoon or scoop the powder into the test chamber. Fill the cylinder it to a height of
47、185 170 6 5 mm.7.6 Attach the expansion chamber and filter.7.7 If the requesting agency has not specified values of High Flow-rate and Low Flow-rate for the powder to be tested, an initialtest of the powder is required prior to running this test; See Annex A1, “Determining Inputs.”7.8 Start the airf
48、low using the flow meter, and uniformly ramp up the airflow over 30 6 3 s to the High Flow-rate.7.9 Hold the airflow at the High Flow-rate for 30 s. 6 3 s.7.10 Uniformly ramp down the airflow over 30 6 3 s to the Low Flow-rate. Keep the airflow at this rate for 120 6 3 s.7.11 Uniformly ramp down the
49、 flow-rate to zero over 30 s. 6 3 s.7.12 Once the flow rate is reduced to zero, gently tap the side of the expansion chamber to allow residual dust to fall back intothe test chamber.7.13 Allow additional time after stopping the airflow for the powder to settle completely.NOTE 4Settlement is considered complete when the top powder surface no longer appears to move (typically several minutes for fine powders).7.14 Carefully separate the cylinders and place the entire contents of each cylinder into its own appropriate sample container.specimen conta
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