1、Designation: D6940 18Standard 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 practice offers a set of instructions for performingone or more specific operations. This document cannot replaceeducation or experience and should be used in conjunction withprofessional judgment. Not all aspect
7、s of this practice may beapplicable in all circumstances. This ASTM standard is notintended to represent or replace the standard of care by whichthe adequacy of a given professional service must be judged,nor should this document be applied without consideration ofa projects many unique aspects. The
8、 word “Standard” in thetitle of this document means only that the document has beenapproved through the ASTM consensus process.1.8 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 a
9、ppro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.9 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for th
10、eDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determinatio
11、n of Water(Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD6941 Practice for Measuring Fluidization Segregation Ten-dencies of Powders3. Terminology3.1 De
12、finitions:3.1.1 For common definitions of terms in this standard, referto Terminology D653.4. 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 thelower hopper, allowing segregation to t
13、ake place.4.3 The segregated material is discharged in a funnel flowpattern intended to recover zones of segregated material in aknown sequence. Specimens are collected from the dischargestream.1This practice is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsib
14、ility of Subcommittee D18.24 on Characterizationand Handling of Powders and Bulk Solids.Current edition approved June 1, 2018. Published July 2018. Originally approvedin 2003. Last previous edition approved in 2010 as D694010. DOI: 10.1520/D6940-18.2For referenced ASTM standards, visit the ASTM webs
15、ite, 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Dr
16、ive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations i
17、ssued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14.4 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 cause horizontal segregation
18、 (forexample, center-to-periphery) within bins used to hold andtransport bulk solids. This can affect final product quality orsubsequent processes in industrial applications.5.2 By measuring a bulk solids segregation tendency, onecan compare results to other bulk solids with known history, ordetermi
19、ne 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 between
20、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 rangeand can
21、 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 among
22、 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 material w
23、ill not segregate by this mechanism.NOTE 1The quality of the result produced by this practice isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D3740 are generally considered capable of co
24、mpetentand objective testing/sampling/inspection/etc. Users of this practice arecautioned 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 was deve
25、loped 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 performing
26、 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 consisti
27、ng 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 the bulk
28、solid 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 from ahop
29、per 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 into col
30、lectingcups. 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 apparatus and all
31、ow 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 table or benc
32、h 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 likelihood of
33、 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 may not rea
34、dily 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 apparatus (furthe
35、r, 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 guide cy
36、linder 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.NOTE 4Do no
37、t lower the cup at this time. Doing so will result inmaterial spillage and will void this practice.7.13 When the guide cylinder is full, close the lower hopperslide gate completely, and then lower the collecting cup.D6940 1827.14 Discharge from the lower outer hopper will be in afunnel flow pattern
38、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, attachsandpap
39、er) 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 methods to red
40、ucethe 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 froma si
41、ngle 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 solid.8.
42、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 also be high infines, for a variety
43、of reasons. For example, if the initial zone of finesexceeds the diameter of the outlet, not all fines will discharge at theFIG. 1 ApparatusD6940 183beginning, and may discharge at the very end. Another reason for fines atthe end is due to sifting of the material from the moving flow channel intothe
44、 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 flowchann
45、el 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 the othercups. If the last cup of mate
46、rial is less than half the volume of the othercups, then the reported difference should be the difference between thefirst 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 segregationproperti
47、es are well known and understood.9. Report: Records9.1 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 name or initials, and9.1.3 Date test was run.9.2 Record as a minimum the following test spe
48、cimeninformation (data):9.2.1 Generic name of powder tested,9.2.2 Chemical name of sample, if known,9.2.3 Sample moisture (water) content, if determined. Re-cord value to nearest 0.1 %. Indicate method used to determinemoisture if not Test Method D2216,9.2.4 Temperature (to the nearest 1C) and relat
49、ive humidity(to the nearest 1 %) of room where tests performed,9.2.5 Number of specimen jars 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 184SUMMARY OF CHANGESCommittee D18 has identified the location of selected changes to this practice since the last issue, D694010,that may impact the use of this practice. (June 1, 2018)(1) Added 1.7 and 1.9. (2) M
