1、Designation: D6940 10Standard Practice forMeasuring Sifting Segregation Tendencies of Bulk Solids1This standard is issued under the fixed designation D6940; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers an apparatus and procedure forsimulating the segregation tendencies of bulk solids by meansof the sifting mech
3、anism.1.2 Temperature- and humidity-sensitive bulk solids mayneed to be tested at different temperatures and moisturecontents, as would happen in an industrial environment.1.3 The maximum particle size should be limited to 3 mm,to reduce the likelihood of binding the slide gate.1.4 This standard is
4、not applicable to all bulk solids andsegregation mechanisms: while sifting is a common segrega-tion mechanism experienced by many bulk solids, othersegregation mechanisms not evaluated by this standard mightinduce segregation in practice. Practice D6941 covers anothercommon mechanism: fluidization.1
5、.5 The extent to which segregation will occur in anindustrial situation is not only a function of the bulk solid andits tendency to segregate, but also the handling equipment (forexample, bin design), process (for example, transfer rates), andenvironment.1.6 The values stated in SI units are to be r
6、egarded asstandard. No other units of measurement are included in thisstandard.1.7 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 dete
7、rmine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requi
8、rements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD6941 Practice for Measuring Fluidization SegregationTendencies of Powders3. Terminology3.1 DefinitionsFor common definitions of terms in thisstandard, refer to Terminology D653.3.1
9、.1 funnel flow pattern, na flow sequence in a bin orhopper characterized by having some bulk solids movingthrough stagnant bulk solids. In general, there is no flow alongthe hopper walls.3.1.2 segregation, na process through which blended oruniform powders or bulk solids become non-uniform, withregi
10、ons of varying composition, for example, particle size.3.1.3 sifting segregation, na mechanism in which finerparticles preferentially percolate into a zone within the bulksolid.3.2 Definitions of Terms Specific to This Standard:3.2.1 collection cup, na collection cup holds a specimenof bulk solid on
11、ce it is discharged from the apparatus.3.2.2 inner hopper, nthe inner hopper is transparent. Ithas a steep inner conical section designed to sit within the outerhopper.3.2.3 outer hopper, nthe outer hopper consists of ashallow transparent hopper designed to provide funnel flow formost bulk solids. I
12、t has an attached slide gate/guide cylinderand support legs.3.2.4 representative sample, na quantity of the bulk solidto be tested that is representative of that solid in an industrialapplication being studied. Parameters of interest that mayaffect whether or not a sample is representative include,
13、but arenot limited to: moisture, particle size distribution, raw materialvariation, method of production, aging, chemical composition.4. Summary of Practice4.1 A representative sample of a bulk solid is placed in theupper hopper of the apparatus.4.2 The bulk solid is discharged to form a pile within
14、 thelower hopper, allowing segregation to take place.1This practice is under 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 July 1, 2010. Published Augu
15、st 2010. Originallyapproved in 2003. Last previous edition approved in 2004 as D694004. DOI:10.1520/D6940-10.2For 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 stan
16、dards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 The segregated material is discharged in a funnel flowpattern intend
17、ed to recover zones of segregated material in aknown sequence. Specimens are collected from the dischargestream.4.4 The specimens are then available to be tested fordifferences relevant to the application, for example, particlesize or chemical assay.5. Significance and Use5.1 Sifting segregation can
18、 cause horizontal segregation (forexample, center-to-periphery) within bins used to hold andtransport bulk solids. This can affect final product quality inindustrial applications.5.2 By measuring a bulk solids segregation tendency, onecan compare results to other bulk solids with known history, orde
19、termine if the given bulk solid may have a tendency tosegregate in a given process.5.3 Sifting, which is a process by which smaller particlesmove through a matrix of larger ones, is a common method ofsegregation. Four conditions must exist for sifting to occur:5.3.1 A Difference in Particle Size bet
20、ween the IndividualComponentsThis ratio can be as low as 1.3 to 1. In general,the larger the ratio of particle sizes, the greater the tendency forparticles to segregate by sifting.5.3.2 A Suffciently Large Mean Particle SizeSifting seg-regation can occur with a mean particle size in the 50 m rangean
21、d can become a dominant segregation mechanism if themean particle size is above 100 m.5.3.3 Suffciently Free Flowing MaterialThis allows thesmaller particles to sift through the matrix of larger particles.With cohesive materials, the fine particles are bound to oneanother and do not enter the voids
22、among the coarse particles.5.3.4 Interparticle MotionThis can be caused during for-mation of a pile, by vibration, or by a velocity gradient acrossthe flowing material.5.4 All four of these conditions must exist for siftingsegregation to occur. If any one of these conditions does notexist, the mater
23、ial will not segregate by this mechanism.NOTE 1The quality of the result 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 D3740 are generally considered capabl
24、e of competent andobjective testing/sampling/inspection/etc. Users of this practice are cau-tioned that compliance with Practice D3740 does not in itself assurereliable results. Reliable results depend on many factors; Practice D3740provides a means of evaluating some of those factors.Practice D3740
25、 was developed for agencies engaged in the testingand/or inspection 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 D3740 is appropriate forevaluating the quality of an agency p
26、erforming this practice. Currentlythere is no known qualifying national authority that inspects agencies thatperform this practice.6. Apparatus6.1 The apparatus is shown in Fig. 1, and all criticaldimensions are specified in Fig. 2. The apparatus consists ofthe following:6.2 An upper hopper assembly
27、 consisting of an inner hopperseated within an outer hopper. This outer hopper providessupport for the inner hopper, and has a slide gate to start/stopmaterial flow. The outer hopper also has support legs, whichmate to the lower hopper assembly.NOTE 2Although only the inner hopper is used to contain
28、 the bulksolid being tested, placing this hopper inside the outer hopper provides ameans to locate and support it, as well as a means to fill and empty thehopper (by using the slide gate). In addition, this outer hopper can be usedfor alternate test procedures that involve recycling material to and
29、from ahopper of similar type. In this case a second inner hopper is also required.6.3 A lower hopper assembly consisting of a second outerhopper. This outer hopper provides support for the upperhopper assembly, has a slide gate to start/stop material flow,and a guide cylinder for dispensing material
30、 into collectingcups. The outer hopper also has support legs to support theentire segregation tester.6.4 A collecting cup with a minimum capacity of 55 mL, tocollect specimens as they discharge from the lower hopper. Thecollecting cups must fit within the apparatus.7. Procedure7.1 Clean the apparatu
31、s and allow all parts to dry.7.2 With inner hopper removed, place one outer hopper ontop of the other. Make sure that the centerlines of the twohoppers are aligned.7.3 Place the inner hopper into the upper outer hopper.7.4 Close the slide gates on both outer hoppers.7.5 Place the apparatus on a tabl
32、e or bench that is free fromvibration, in a suitable laboratory environment to approximatethe industrial environment. Ensure that the apparatus is level.7.6 Obtain a representative, one-liter sample of the bulksolid to be tested. The maximum particle size should be limitedto 3 mm, to reduce the like
33、lihood of binding the slide gate.7.7 Carefully spoon or scoop the bulk solid into the upperinner hopper. Free fall of material into the hopper should beminimized.7.8 Open the upper slide gate to the full open position,allowing the entire sample to fall into the lower hopper.7.9 Cohesive materials ma
34、y not readily flow through thisapparatus. For moderately cohesive materials that flow poorlythrough this apparatus, some light tapping on the hopper maybe required to maintain flow. Extremely cohesive materials,which do not flow with light tapping, should not be tested toavoid damage to the apparatu
35、s (further, extremely cohesivematerials generally do not readily segregate).7.10 When the upper inner hopper is empty, close the upperhopper slide gate, remove the upper hopper assembly and set itaside.7.11 With the lower hopper slide gate still closed, place acollecting cup over the open end of the
36、 guide cylinder so thatthe bottom of the cup is in contact with the bottom of the guidecylinder.NOTE 3The bottom of the guide cylinder must remain in contact withthe base of the cup.7.12 With the cup and guide cylinder together, open thelower hopper slide gate and allow the guide cylinder to fill.NO
37、TE 4Do not lower the cup at this time. Doing so will result inmaterial spillage and will void this practice.D6940 1027.13 When the guide cylinder is full, close the lower hopperslide gate completely, and then lower the collecting cup.7.14 Discharge from the lower outer hopper will be in afunnel flow
38、 pattern for most bulk solids. An exception mightoccur for free flowing, low friction materials such as beads orglass spheres. If the material is sliding along the walls duringdischarge (“mass flow”), then the test results will not be valid;in this case, roughen the hopper surface (for example, atta
39、chsandpaper) and begin the procedure again.7.15 Discharge the specimen in the collecting cup into aproperly identified specimen jar.7.16 Repeat 7.11-7.15 until the lower hopper is empty.Approximately 19 specimens will be obtained.8. Analysis of Specimens8.1 If needed, use appropriate splitting metho
40、ds to reducethe size of the specimens in each of the specimen jars to asuitable size for analysis. Use proper subdivision techniques,such as the use of a rotary riffler.NOTE 5Collecting sub-specimens from the specimen jars by scoopingor thieving may be prone to errors. Analysis of multiple specimens
41、 froma single location yields further confidence in the results.8.2 Analyze the specimens or sub-specimens with respect tothe parameters of interest: particle size, particle shape, chemi-cal assay, bulk density, color, solubility, or any other differ-ences that may affect the suitability of the bulk
42、 solid.FIG. 1 ApparatusD6940 1038.3 The trend from the beginning to the end of discharge isan indication of segregation potential. Normally, if siftingsegregation has occurred upon filling, fines discharge initially,with increasing coarse to the end.NOTE 6In some cases, the very last specimen may al
43、so be high infines, for a variety of reasons. For example, if the initial zone of finesexceeds the diameter of the outlet, not all fines will discharge at thebeginning, and may discharge at the very end. Another reason for fines atthe end is due to sifting of the material from the moving flow channe
44、l intothe stagnant zone during discharge; this layer often discharges at the veryend. (To investigate this later scenario, scoop material directly into thelower outer hopper in a way to maintain a good blend in the hopper, thencontinue from 7.11. If the last specimen is fine, segregation within the
45、flowchannel is occurring.)8.4 The difference between the first and last specimens canbe used as an indicator of segregation potential when asingle-valued result is needed for comparison of differentspecimens.NOTE 7Generally the last collection cup will not be as full as theother cups. If the last cu
46、p of material is less than half the volume of theother cups, then the reported difference should be the difference betweenthe first and last full cups (that is, next to last cup).8.5 Segregation test results for a new bulk solid should becompared to prior tests on other bulk solids, whose segregatio
47、nproperties are well known and understood.9. Report9.1 Record as a minimum the following general informa-tion:9.1.1 Requesting agency or client or identifying number orboth for job or project,9.1.2 Technician, and9.1.3 Date test was run.9.2 Record as a minimum the following test data:9.2.1 Generic n
48、ame of sample,9.2.2 Chemical name of sample, if known,9.2.3 Sample moisture (water) content, if determined.Record value to nearest 0.1 %. Indicate method used todetermine moisture if not Test Method D2216,9.2.4 Temperature and relative humidity of room wheretests performed,9.2.5 Number of specimen j
49、ars collected,9.2.6 Number of last full specimen jar, and9.2.7 Any observations of interest during running of tests,including the need for tapping to initiate or maintain flow.10. Keywords10.1 bulk solids; segregation; siftingFIG. 2 Dimensions of ApparatusD6940 104SUMMARY OF CHANGESCommittee D18 has identified the location of selected changes to this practice since the last issue, D694004,that may impact the use of this practice. (Approved July 1, 2010)(1) Replaced most instances of “sample” with “specimen.”(2) Added reference to Test Method D2216 and Pra
