1、Designation: D 6941 05e1Standard Practice forMeasuring Fluidization Segregation Tendencies of Powders1This standard is issued under the fixed designation D 6941; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTESection 7.10 and Figure 2 were corrected editorially in July 2007.1. Scope1.1 This practice covers an apparatus and procedure forsim
3、ulating the segregation tendencies of powders by means ofthe fluidization mechanism.1.2 Powders must be capable of being fluidized in order tobe tested by this practice.1.3 Temperature- and humidity-sensitive powders may needto be tested at different temperatures and moisture contents, aswould happe
4、n in an industrial environment. Further, the gassupply (type, temperature, and humidity) should also match theindustrial conditions.1.4 This standard is not applicable to all bulk solids andsegregation mechanisms: while fluidization is a commonsegregation mechanism experienced by many fine powders,o
5、ther segregation mechanisms not evaluated by this standardmight induce segregation in practice.1.5 The extent to which segregation will occur in anindustrial situation is not only a function of the powder and itstendency to segregate, but also the handling equipment (forexample, bin design), process
6、 (for example, transfer rates), andenvironment.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regu
7、latory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and Construction3. Termi
8、nology3.1 DefinitionsDefinitions of terms used in this testmethod shall be in accordance with Terminology D 653.3.1.1 fluidization, nthe state in which a powder exhibitsfluid-like properties.3.1.2 fluidization segregation, na mechanism that causesvertical segregation, that is, horizontal layering of
9、 fine andcoarse particles, as resulting from fluidization of the bulk solid.3.1.3 segregation, na process through which blended oruniform powders or bulk solids become non-uniform, withregions of varying composition, for example, particle size.3.2 Definitions of Terms Specific to This Standard:3.2.1
10、 high flow-rate, nthe first stage flow-rate used toinitiate fluidization.3.2.2 low flow-rate, nthe second stage flow-rate used tomaintain fluidization.3.2.3 representative sample, na quantity of the bulk solidto be tested that is representative of that solid in an industrialapplication being studied
11、. Parameters of interest that mayaffect whether or not a sample is representative include:moisture, particle size distribution, raw material variation,method of production, aging, chemical composition.4. Summary of Practice4.1 A representative sample of a powder is placed in theapparatus.4.2 Pressur
12、ized gas (usually air) is blown from the bottom ata series of flow-rates for specified times, creating a state offluidization of the powder.4.3 Once the airflow is stopped, the powder in the testchamber is divided into three samples from the bottom, center,and top of the column.1This practice is und
13、er the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.24 on Characterizationand Handling of Powders and Bulk Solids.Current edition approved Nov. 1, 2005. Published November 2005. Originallyapproved in 2003. Last previous edition approved in 2
14、004 as D 694104.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandardsvolume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor
15、 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.4 The samples are then available to be tested for differ-ences relevant to the application, for example, particle size orchemical assay.5. Significance and Use5.1 Fluidization segregation can cause vertical segregationwithin bins
16、 used to hold and transport powders. This can affectfinal product quality in industrial applications.5.2 By measuring a powders segregation tendency, one cancompare results to other powders with known history, ordetermine if the given powder may have a tendency tosegregate in a given process.5.3 Fin
17、e powders generally have a lower permeability thancoarse bulk solids and therefore tend to retain air longer. Thus,when a bin is being filled with a fluidizable powder, the coarserparticles settle or are driven into the bed while the finerparticles remain fluidized near the surface.5.4 Fluidization,
18、 which serves as a driving force for thismechanism of segregation, is likely to occur when fine pow-ders are pneumatically conveyed into a bin, the bin is filled ordischarged at high rates, or if sufficient air flow counter to theflow of powder is present within the bin.NOTE 1The quality of the resu
19、lt produced by this practice is depen-dent on the competence of the personnel performing it, and the suitabilityof the equipment and facilities used. Agencies that meet the criteria ofPractice D 3740 are generally considered capable of competent andobjective testing/sampling/inspection/etc. Users of
20、 this practice are cau-tioned that compliance with Practice D 3740 does not in itself assurereliable results. Reliable results depend on many factors; Practice D 3740provides a means of evaluating some of those factors.Practice D 3740 was developed for agencies engaged in the testingand/or inspectio
21、n of soil and rock. As such it is not totally applicable toagencies performing this practice. However, users of this practice shouldrecognize that the framework of Practice D 3740 is appropriate forevaluating the quality of an agency performing this practice. Currentlythere is no known qualifying na
22、tional authority that inspects agencies thatperform this practice.6. Apparatus6.1 The apparatus including critical dimensions is shown inFig. 1. It consists of the following:6.2 Gas Supply with Flow MeterA gas supply capable offluidizing the powder is required (15 to 30 psig 100 to 200kPa range, 25
23、psig 170 kPa recommended, maximum flowrate 10 000 cm3/min recommended). The gas flow rate must beadjustable during the test-an automated controller may be usedfor this purpose.NOTE 2Generally, clean, dry air is used. If air is not suitable (that is,it reacts with or adversely affects the powder bein
24、g tested) another gas,such as nitrogen, may be used.FIG. 1 ApparatusD694105e126.3 CylindersThree transparent cylinders are stacked,identified (from the bottom) as the bottom, center, and topcylinders. The bottom cylinder sits against the diffuser in theair supply plenum. The top cylinder mates to th
25、e expansionchamber. When the cylinders are stacked together, they makeup the test chamber, where the powder is placed. The as-sembled test chamber dimensions are 24 mm I.D. by at least185 mm tall. The test chamber should have at least 25 mmadditional height to allow expansion of the powder bed. Thec
26、ylinders must be held together so they do not separate duringthe tests and so leakage does not occur, while still able to beseparated at the end of the test in a way to allow for samplerecovery. This can be done a number of ways, including tapingthe sections together.6.4 Expansion ChamberThe expansi
27、on chamber allowsthe powder to disengage from the air stream.6.5 FilterThe filter prevents powder from being blownout of the apparatus. The filter material should be appropriatefor the application and should not contaminate the powder(which may affect the analysis of the samples), and shouldprovide
28、sufficient containment of the powder (from both asafety perspective and a loss of powder perspective).6.6 DiffuserThe diffuser distributes the air uniformly intothe test chamber; therefore, a sufficient pressure drop across thediffuser is required.NOTE 3A sintered metal disk, such as 5 m filtration
29、grade porousstainless steel sheet available from Mott Industrial, Farmington CT, maybe an appropriate material for the diffuser. Some cohesive powders do notfluidize well, and simply form an air channel through the test bed,allowing the air to flow past stationary powder. In this case additionalairf
30、low will not serve to fluidize the powder. If this occurs, this test is notvalid. However, a diffuser with a lower permeability may serve todistribute the air better thereby reducing channeling.7. Procedure7.1 Clean the apparatus and allow all parts to dry.7.2 Stack the cylinders one above the other
31、, secure themtogether, and align the bottom cylinder on the diffuser.7.3 Place the apparatus on a table or bench that is free fromvibration, in a suitable laboratory environment to approximatethe industrial environment.7.4 Obtain a representative, 100 mL sample of the powderto be tested.7.5 Carefull
32、y spoon or scoop the powder into the testchamber. Fill the cylinder to a height of 185 mm.7.6 Attach the expansion chamber and filter.7.7 If the requesting agency has not specified values of HighFlow-rate and Low Flow-rate for the powder to be tested, aninitial test of the powder is required prior t
33、o running this test;See Annex A1, “Determining Inputs.”7.8 Start the airflow using the flow meter, and uniformlyramp up the airflow over 30 s to the High Flow-rate.7.9 Hold the airflow at the High Flow-rate for 30 s.7.10 Uniformly ramp down the airflow over 30 s to the LowFlow-rate. Keep the airflow
34、 at this rate for 120 s.7.11 Uniformly ramp down the flow-rate to zero over 30 s.7.12 Once the flow rate is reduced to zero, gently tap theside of the expansion chamber to allow residual dust to fallback into the test chamber.7.13 Allow additional time after stopping the airflow for thepowder to set
35、tle completely.NOTE 4Settlement is considered complete when the top powdersurface no longer appears to move (typically several minutes for finepowders).7.14 Carefully separate the cylinders and place the entirecontents of each cylinder into its own appropriate samplecontainer.8. Analysis of Samples8
36、.1 If needed, use appropriate sample splitting methods toreduce the size of the samples in each of the three cylinders toa suitable size for analysis. Use proper subdivision techniques,such as the use of a rotary riffler.NOTE 5Collecting sub-samples from the sample jars by scooping orthieving may be
37、 prone to errors. Analysis of multiple samples from asingle location yields further confidence in the results.8.2 Analyze the samples with respect to the parameters ofinterest: for example, particle size, particle shape, chemicalassay, bulk density, color, solubility, or any other differencesthat ma
38、y affect the suitability of the powder.8.3 The trend from the top to the bottom of the tester is anindication of segregation potential. Typically, if fluidizationsegregation has occurred, the top cylinder is fines-rich, whilethe bottom is coarse-rich.FIG. 2 Timing ProfileD694105e138.4 The difference
39、 between the top and bottom samples canbe used as an indicator of segregation potential when asingle-valued result is needed for comparison of differentsamples.8.5 Segregation test results for a new powder should becompared to prior tests on other powders, whose segregationproperties are well known
40、and understood.9. Report9.1 Report the following information:9.1.1 Date test was run,9.1.2 Operator,9.1.3 Name of project or client including project number ifused,9.1.4 Generic name of powder tested,9.1.5 Temperature and relative humidity of room wheretests performed,9.1.6 High Flow-rate,9.1.7 Low
41、Flow-rate, and9.1.8 Any observations of interest during running of tests,including indications of poor fluidization, such as channelingor lifting of a solid plug of the powder, and the need for tappingto break up a mass of powder to promote fluidization.10. Keywords10.1 fluidization; powder; segrega
42、tionANNEX(Mandatory Information)A1. DETERMINING INPUTSA1.1 Determining Flow Rates and TimesA1.1.1 The goal of the fluidization segregation test is tobring the powder to a completely fluidized state, then allowslow deaeration (settlement) of the powder. For this to occur aspecific flow-rate/time prof
43、ile is used. See Fig. 2 for the generalflow-rate/time profile.A1.1.2 To determine the proper High Flow-rate, slowlyincrease the flow-rate until all of the powder is in a state offluidization.NOTE A1.1This state is characterized by observing bubbles or turbu-lence within the bottom cylinder. When sta
44、rting with a deaerated bed ofpowder in the test chamber, as the air begins to flow, initially the bed willremain stationary. As the airflow increases, the bed will begin to expand.This expansion behavior is highly powder dependent-in some cases thetop surface may start to “bubble,” while with cohesi
45、ve powders the entirebed may lift as a plug. As the flow-rate increases further, eventually, all ofthe powder within the test chamber should become fluidized. Tapping theside of the test chamber may be necessary to break up a mass of powderto promote fluidization. In many cases, once the powder beco
46、mesfluidized, the flow-rate can be decreased while keeping the powderfluidized.A1.1.3 To determine the proper Low Flow-rate, immedi-ately after determining the High Flow-rate, slowly reduce theflow-rate until powder movement in the tester stops, thenincrease the rate again just to the point where mo
47、tion isinitiated within the top cylinder. This point is the LowFlow-rate.NOTE A1.2The second stage of the fluidization segregation test is toreduce and hold the airflow at a Low Flow-rate corresponding to theminimum fluidization velocity. This stage is characterized by observingsome turbulence or bu
48、bbling in the top cylinder. Under these conditions,powder movement might not occur in the center or bottom test chambers.A1.1.4 Upon completion of A1.1.2 and A1.1.3, empty thetester of the powder, and refill the tester with fresh powder forthe actual test.A1.2 Determining Inputs for Multiple Powders
49、A1.2.1 Often times the goal of these tests is to compare onepowder to another. Variations in the powder may result indifferent fluidization behaviors. However, if the differences inthe powders are small, usually the same rates can be used foreach powder. Use the same flow-rates and times when com-paring slight variations on one powder. In running each test, thetest chamber should be observed to ensure that at the HighFlow-rate, all the powder has become fluidized, while at theLow Flow-rate the top surface still shows signs of movement.A1.2.2 Vastly different
