1、Designation: D7971 15Standard Guide forMeasuring Roundness of Glass Spheres Using a FlowingStream Digital Image Analyzer1This standard is issued under the fixed designation D7971; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the determination of the roundness ofglass spheres used in pavement marking systems using a
3、flowing stream digital analyzer. Typical gradations for pave-ment marking systems are defined in ranges from Type 0through 5 in AASHTO M247.1.2 This guide provides for the presentation of roundnessdata in a variety of formats to the requirement of the agencypavement marking material specification. F
4、or most specifica-tions the standard format is to present the roundness data asPercent True Spheres relative to a series of standard ASTMsieve sizes.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not
5、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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:
6、2B215 Practices for Sampling Metal Powders2.2 AASHTO Standard:3AASHTO M247 Standard Glass Beads Used in TrafficMarkings2.3 ISO Standards:ISO 92766 Representation of results of particle size analy-sis Part 6: Descriptive and quantitative representationof particle shape and morphologyISO 133221 Partic
7、le size analysis Image analysis meth-ods Part 1: Static image analysis methods3. Terminology3.1 Flowing Stream Digital Analyzer:3.1.1 A computer controlled particle analyzer employing ahigh resolution digital imaging device and computer imageprocessing software to do photo optical single particle co
8、untingand particle size analysis.3.2 Roundness of Glass Beads:3.2.1 Roundness, in the context of this guide, refers to thepercentage of true spheres in a sample as a ratio of the totalnumber of particles measured.3.2.2 Methods:3.2.2.1 These are specific observations and calculations ofthe streaming
9、particles that combine to form a protocol formeasuring the percentage of true spheres within the sample.3.3 Aspect Ratio:3.3.1 Aspect ratio, often referred to as b/l or w/l, is one ofthe several methods of determining roundness and is illustratedin Fig. 1.3.3.2 Aspect ratio will be the recommended m
10、ethod for themajority of roundness measurements, especially when thereexists a reasonable expectation that all of the particles beingmeasured have rounded surfaces and mostly resemble theshape of a sphere.3.4 Sphericity (also referred to as circularity):3.4.1 Sphericity is one of a number of methods
11、 of determin-ing roundness and is illustrated in Fig. 2.3.4.2 SPHT-value or sphericity is calculated from the mea-surements of1. the area* A* of the particle projection (particle image),2. multiplied by four Pi (4) and3. divided by the perimeter P of the particle projectionsquared (P2).3.4.3 SPHT re
12、sult values are between 0 and 1 (including 1)and following ISO 92766.NOTE 1A high percentage of the volume of glass beads are producedfrom crushed and sized recycled glass. The most common method ofproduction involves passing the particles in a reverse free fall through agas-rich, highly luminous, n
13、atural gas flame wherein they reach their1This guide is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.44 on Traffic Coatings.Current edition approved April 1, 2015. Published April 2015. DOI:
14、 10.1520/D7971-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Association of Sta
15、te Highway and TransportationOfficials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,http:/www.transportation.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1melting point. Due to natures insistence that all li
16、quids exhibit tension attheir surface, the particles are then forced to reconfigure into a shapewhich maintains the smallest ratio of surface area to volume. This shapeis a sphere. One of the main quality control concerns of this productionmethod is ensuring that all the particles pass through the f
17、lame andbecome spheres. If not, the particles will remain in the state in which theyare introduced and will consist of irregular shapes with sharp edges. Alarge variance between sphericity and aspect ratio could reveal thatsphericity is the better method in this particular case.3.5 Nominal Covered A
18、rea:3.5.1 Nominal covered area (Fig. 3) (set value of obscura-tion percentage) = Aobscured/Atotal measurement field.3.5.2 Nominal covered area (set value of obscuration) iscalculated using the obscured area by particles divided by thetotal measurement area.3.5.3 The higher the nominal covered area,
19、the more coin-cidental particles that are captured. With more coincidentalparticles measured, the more non-round particles detected.3.5.4 The task file setting for nominal covered area shouldnot exceed a certain percentage. Values of nominal coveredarea (fld = field density) of 0.8 % for smaller gra
20、des (20 to 100mesh, Type 0 and Type 1 outlined inAASHTO M247) and 1 %for larger grades (10 to 25 mesh, Type 2, Type 3, Type 4 andType 5) should not be exceeded. Lower values are possible.Values of 0.3 % to 0.5 % will lead to more accurate results. Forexample, a measurement with 0.7 % nominal covered
21、 arealeads to 18 % non-round particles, a measurement with 0.3 %nominal covered area would show 17 % non-round particles.4. Significance and Use4.1 The roundness of glass beads has a significant influenceon the retroreflective efficiency of a pavement marking system.4.2 The guide is for the characte
22、rization of the roundness ofglass beads for the purpose of compliance testing againststandard specification for glass beads in pavement markingapplications.4.3 While there are potential industrial applications for thisguide beyond the measurement of roundness of glass beads forpavement markings, tho
23、se are beyond the scope of thisstandard.5. Summary of Guide5.1 The glass particles are run through a flowing streamdigital image analyzer, a measuring system for determining theroundness of dry, free flowing and harmless bulk products. Thetotal recommended measuring range of sizes is be-tween 110 m
24、and 2.36 mm. The method uses photo opticalsingle particle counting technology for the image processing.The measurement time depends on the quantity of material tobe measured, the width of the metering feeder and the meangrain size. The quantity of material to be measured depends onthe grain size and
25、 width of the metering feeder. Typicalmeasuring times are approximately 2 to 10 min.6. Apparatus6.1 Typical ApparatusSee Fig. 4.7. Operating Conditions7.1 Environmental Temperaturebetween 10 and 40C.7.2 Air Humidity80 % maximum relative humidity attemperatures up to 30C, linear decrease to 50 % maxi
26、mumrelative humidity at a temperature of 40C,7.3 Height of Installation and Operationmaximum3000 m above sea level.7.4 Installation LocationPlace the particle analyzer on afirm, horizontal, vibration free surface.7.5 Light ConditionsAvoid strong direct external light onthe particle measurement shaft
27、 or on the cameras.FIG. 1 Aspect RatioFIG. 2 SphericityFIG. 3 Nominal Covered AreaD7971 1527.6 This method is designed for indoor or outdoor use asprescribed by the manufacturers design and instructions.8. Hazards8.1 General Safety InformationOperate the instrument inaccordance with the manufacturer
28、s recommendations follow-ing all required safety precautions.9. Sampling, Test Specimens, and Test Units9.1 In order to obtain representative samples when samplingfrom packaged containers, blenders or storage tanks, methodsoutlined in Practices B215 shall be followed.9.2 The approximate number of pa
29、rticles in a test samplemeasured by weight varies greatly between Type 0 and Type 5as outlined in AASHTO M247. Table 1 represents the mini-mum recommended sample size for each glass bead type.9.3 Compared to sieve analysis for gradation and Round-O-Meter analysis for roundness, dynamic image analyze
30、rs haveno upper limits for the amount of sample required. As shouldbe expected, the larger the sample size of an individual type,the higher the degree of accuracy and reliability. Larger samplesizes lengthen the duration of the test. The end user shouldtherefore balance the tolerance of test time du
31、ration against thedesire for accuracy. ISO 133221 can be referenced for asufficient number of particles for a certain precision and correctrepresentation of the size distribution. Since the segregation ofparticle shape in a bulk material is lower than the segregationfor particle size, users are on t
32、he safe side when they follow thesampling recommendations for particle size.10. Preparation of Apparatus10.1 Follow the manufacturers instructions for the particleanalyzer being used.11. Calibration and Standardization11.1 The particle analyzer, in most cases, will be calibratedby the manufacturer p
33、rior to shipping. Re-calibration mightbecome necessary occasionally, for example, after the trans-portation of the instrument or if required by quality manage-ment regulations. In this case, follow the calibration proceduresas outlined in the manufacturers instruction manual.12. Conditioning12.1 Sam
34、ple Preparation:12.1.1 Use a sample splitter, if necessary, to reduce theamount of sample to the appropriate size.12.1.2 Pour entire glass bead sample into the glass beaker orsuitable container.12.1.3 Assure glass beads are moisture free and free flow-ing.NOTE 2Check with the instrument manufacturer
35、 for suggestions onhow best to set up any software that comes with their instrument. Settingup the instrument software properly will speed up any glass sphereroundness measurements and allow for meaningful reports.13. Procedure13.1 Load the sample into the feeder of the flowing streamdigital image a
36、nalyzer. The analyzer software will allow theuser to carry out his measurements quickly and without error.All measuring and analysis parameters are determined initiallyand set into the computer program. Different task files arecreated for different specifications.13.1.1 When assigning sieve ranges t
37、o be used in a task file,the user must use the ASTM mesh sieve choice, not the W. S.Tyler mesh. The quantity of the material to be measured has tobe placed into the funnel of the metering feeder. The materialhandling mechanisms must not restrict or segregate productflow in an way that allows for a n
38、on-representative flow ofproduct through the measurement zone.13.2 After the task file has been defined, only a minimalnumber of operative steps are required for carrying out ameasurement. They are: a) filling a quantity of the material tobe measured into the funnel to the metering feeder, b) callin
39、gthe measurement and choosing the task file, c) confirming thesuggested comments or entering new comments, d) starting themeasurement, and e) reading the result or printing a record.The measured result is available a few moments after theFIG. 4 Typical ApparatusTABLE 1 Sample Size by Type AASHTO M24
40、7Type 0 15 gType 1 15 gType 2 20 gType 3 30 gType 4 45 gType 5 60 gD7971 153measurement is completed and can be displayed in manyforms, and be printed and saved with the help of the PC.14. Report14.1 Report the percentage true spheres of particles in eachsize classification.15. Precision and Bias15.
41、1 PrecisionNo precision statement accompanies thisguide.15.2 BiasBias cannot be determined because there is nostandard reference material available.16. Keywords16.1 PLEASE PROVIDE A FEW KEYWORDS.ASTM International takes no position respecting the validity of any patent rights asserted in connection
42、with any item mentionedin this standard. Users of this standard are expressly advised that determination of the 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 te
43、chnical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your 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 consider
44、ation 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
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