1、Designation: D 6940 04Standard Practice forMeasuring Sifting Segregation Tendencies of Bulk Solids1This standard is issued under the fixed designation D 6940; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers an apparatus and procedure forsimulating the segregation tendencies of bulk solids by meansof the sifting me
3、chanism.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 i
4、s 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.1.5 The extent to which segregation will occur in anindustri
5、al 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 This standard does not purport to address all of thesafety concerns, if any, associated with its use
6、. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 3740 Practice
7、 for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and Construction3. Terminology3.1 DefinitionsDefinitions of terms used in this testmethod shall be in accordance with Terminology D 653.3.1.1 funnel flow pattern, na flow sequ
8、ence 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, withregions of varying composition, for exam
9、ple, 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 sample ofbulk solid once it is discharged from the apparatus
10、.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. It has an attached slide gate/guide cyl
11、inderand 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:moisture, particle size distribution, r
12、aw material variation,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 thelower hopper, allowing segregation to take place.4.3 The s
13、egregated material is discharged in a funnel flowpattern intended to recover zones of segregated material in aknown sequence. Samples are collected from the dischargestream.4.4 The samples are then available to be tested for differ-ences relevant to the application, for example, particle size orchem
14、ical assay.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 Jan. 1, 2004. Published February 2004. Originallyapproved in 2003. Las
15、t previous edition approved in 2003 as D 694003.2For 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 AST
16、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 Sifting segregation can cause horizontal segregation (forexample, center-to-periphery) within bins used to hold andtransport bulk solids. This can affect final product qual
17、ity inindustrial applications.5.2 By measuring a bulk solids segregation tendency, onecan compare results to other bulk solids with known history, ordetermine 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 thr
18、ough 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 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 forpar
19、ticles 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 become a dominant segregation mechanism if themean particle size is above 100 m.5.3.3 Suffciently Free Flowing MaterialThis allows thesmaller p
20、articles 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 the coarse particles.5.3.4 Interparticle MotionThis can be caused during for-mation of a pile, by vibration, or by a velocity gradient acrossth
21、e 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 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 p
22、erforming 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 this practice are cau-tioned that compliance with Practice D 3740 does not in
23、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 inspection of soil and rock. As such it is not totally applicable toagencies performing
24、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 national authority that inspects agencies thatperform this practice.6. Apparatus6
25、.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 consisting of an inner hopperseated within an outer hopper. This outer hopper providessupport for the inner hopper, and has a slide gate to sta
26、rt/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 bulksolid being tested, placing this hopper inside the outer hopper provides ameans to locate and support it, as well as a means to fill an
27、d 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 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
28、. 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 collectingcups. The outer hopper also has support legs to support theentire segregation tester.6.4 A collecting cup with a minimum capacit
29、y of 55 mL, tocollect samples as they discharge from the lower hopper. Thecollecting cups must fit within the apparatus.7. Procedure7.1 Clean the apparatus 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 twoho
30、ppers 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 bench that is free fromvibration, in a suitable laboratory environment to approximatethe industrial environment.7.6 Obtain a representative,
31、one liter sample of the bulksolid to be tested. The maximum particle size should be limitedto 3 mm, to reduce the likelihood 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 s
32、lide gate to the full open position,allowing all of the material to fall into the lower hopper below.7.9 Cohesive materials may not readily flow though thisapparatus. For moderately cohesive materials that flow poorlythough this apparatus, some light tapping on the hopper may berequired to maintain
33、flow. Extremely cohesive materials, whichdo not flow with light tapping, should not be tested to avoiddamage to the apparatus (further, extremely cohesive materialsgenerally do not readily segregate).7.10 When the upper inner hopper is empty, close the upperhopper slide gate, remove the upper hopper
34、 assembly and set itaside.7.11 With the lower hopper slide gate still closed, place acollecting cup over the open end of the 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 th
35、e cup.7.12 With the cup and guide cylinder together, open thelower hopper slide gate and allow the guide cylinder to fill.NOTE 4Do not 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 ga
36、te completely, then lower the collecting cup.7.14 Discharge from the lower outer hopper will be in afunnel flow 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 (“m
37、ass flow”), then the test results will not be valid;D6940042in this case, roughen the hopper surface (for example, attachsandpaper) and begin the procedure again.7.15 Discharge the sample in the collecting cup into aproperly identified sample jar.7.16 Repeat 7.11-7.15 until the lower hopper is empty
38、.Approximately 19 samples will be obtained.8. Analysis of Samples8.1 If needed, use appropriate sample splitting methods toreduce the size of the samples in each of the sample jars to asuitable size for analysis. Use proper subdivision techniques,such as the use of a rotary riffler.NOTE 5Collecting
39、sub-samples from the sample jars by scooping orthieving may be 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, bu
40、lk density, color, solubility, or any other differencesthat may affect the suitability of the bulk solid.8.3 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 increa
41、sing coarse to the end.NOTE 6In some cases, the very last sample may also be high in fines,for a variety of reasons. For example, if the initial zone of fines exceedsthe diameter of the outlet, not all fines will discharge at the beginning, andmay discharge at the very end. Another reason for fines
42、at the end is dueto sifting of the material from the moving flow channel into the stagnantzone during discharge; this layer often discharges at the very end. (Toinvestigate this later scenario, scoop material directly into the lower outerFIG. 1 ApparatusD6940043hopper in a way to maintain a good ble
43、nd in the hopper, then continuefrom 7.11. If the last sample is fine, segregation within the flow channelis occurring.)8.4 The difference between the first and last samples can beused as an indicator of segregation potential when a single-valued result is needed for comparison of different samples.N
44、OTE 7Generally the last collection cup will not be as full as theother cups. If the last cup 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 f
45、or a new bulk solid should becompared to prior tests on other bulk solids, whose segregationproperties are well known and understood.9. Precision and Bias9.1 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
46、Generic name of bulk solid tested,9.1.5 Temperature and relative humidity of room wheretests performed,9.1.6 Number of jars collected,9.1.7 Number of last full jar, and9.1.8 Any observations of interest during running of tests,including the need for tapping to initiate or maintain flow.FIG. 2 Dimens
47、ions of ApparatusD694004410. Keywords10.1 bulk solids; segregation; siftingD6940045ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the
48、validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your
49、comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. In
