1、Designation: D720 91 (Reapproved 2010)Standard Test Method forFree-Swelling Index of Coal1This standard is issued under the fixed designation D720; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method2is a small-scale test for obtaininginformat
3、ion regarding the free-swelling properties of a coal.The results may be used as an indication of the cakingcharacteristic of the coal when burned as a fuel. This test is notrecommended as a method for the determination of expansionof coals in coke ovens.1.2 WarningBreathing of asbestos dust is hazar
4、dous.Asbestos and asbestos products present demonstrated healthrisks for users and for those with whom they come into contact.In addition to other precautions, when working with asbestos-cement products, minimize the dust that results. For informa-tion on the safe use of chrysoltile asbestos, refer
5、to, Safe Useof Chrysotile Asbestos: A Manual on Preventive and ControlMeasures.31.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated wit
6、h 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:4D2013 Practice for Preparing Coal Samples for Analysis3. Significan
7、ce and Use3.1 This test method, in addition to indicating the cakingproperties of a coal when burned as a fuel, can be used to givea broad indication of the degree of oxidation of a coal.4. Apparatus4.1 This test method can be made with either electric or gasheating. When using electric heating, the
8、 results obtained mustbe the same as those obtained when using the gas heatingmethod. The apparatus common to both electric and gasmethods shall consist of the following:4.1.1 Crucible, translucent silica, low-form, with a flat,close-fitting silica ring-handle lid and an extra pierced lid foruse in
9、determining the crucible temperature, conforming to thefollowing requirements:Weight, g 11.0 to 12.75External height, mm 26 6 0.5External diameter at top, mm 41 6 0.75Internal diameter at base, min, mm 11Capacity (approximate), cm3174.1.2 Sight Tube, as shown in Fig. 1, for viewing the cokebuttons s
10、o that the effect of parallax will be eliminated. Makethe tube of any rigid and preferably opaque material andsupport vertically on a ring stand.4.1.3 Thermocouple and Potentiometer.4.1.4 Weight, 500 g.4.2 The electric apparatus shall consist of the following:4.2.1 Furnace, consisting of a base, a h
11、eating element, anda chimney. The unit is shown in Fig. 2.4.2.1.1 ChimneyFig. 2 shows the chimney design. Makethe unit from firebrick and coat with firebrick bonding mortar.Maintain the chimney under compression by a sheet-metalenvelope (Fig. 2) to prevent cracking. Make the envelope in1This test me
12、thod is under the jurisdiction of ASTM Committee D05 on Coaland Coke and is the direct responsibility of Subcommittee D05.15 on MetallurgicalProperties of Coal and Coke.Current edition approved May 15, 2010. Published July 2010. Originallyapproved in 1943. Last previous edition approved in 2004 as D
13、720 91 (2004)1.DOI: 10.1520/D0720-91R10.2This test method is an adaptation of the Crucible Swelling Test for Coal of theBritish Standards Institution. For information concerning the experimental work onwhich this adaptation is based, see paper by Ostborg, H. N., Limbacker, H. R., andSherman, R. A.,
14、“An Experimental Investigation of the British Standard Method forthe Crucible Swelling Test for Coal,” Proceedings, Am. Soc. Testing Mats., Vol 42,1042, p. 851. See also a paper by Selvig, W. A., and Ode, W. H., “An Investigationof a Laboratory Test for Determination of the Free-Swelling Index of Co
15、al,” U.S.Bureau of Mines Report of Investigation 4238, Revision of R. I. 3989, 1948.3Safe Use of Chrysotile Asbestos: A Manual on Preventive and ControlMeasures Chrysotile Institute 1200, McGill College Suite 1640 Montreal, QuebecCanada H3B 4G74For referenced ASTM standards, visit the ASTM website,
16、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.fo
17、ur pieces, each piece covering a corner. The pieces shalloverlap at the center of the flat faces and be held together bybolts and springs. Place two layers of asbestos paper betweenthe chimney brick and the envelope. Cut two grooves in theupper inside chimney walls to accommodate the cruciblesupport
18、. In cases in which the furnace is located in a draftyarea, it is advisable to shield the chimney to prevent largefluctuations in furnace temperature.4.2.2 Crucible SupportA convenient crucible supportconsists of a cradle support made from nickel-chromium wiresuspended from a metal ring. The height
19、of the support insidethe furnace can be adjusted by loosening the two screws thathold the wire legs of the support in place.4.2.3 Electric Controls, consisting of a rheostat, an a-cammeter, and two timers. These components shall conform tothe following specifications:Ammeter a-c, 0 to 10-A rangeRheo
20、stat 100 W, 10 VVariable transformer 7.4 A, 120 VTimer mechanical, 05 min minimum span, with a holdposition, and electrical contact closed duringtiming cycle4.2.3.1 One timer shall actuate the rheostat, at a predeter-mined setting, after 112 min of operation. Preset the rheostat toreduce the rate of
21、 heating of the furnace so that a temperatureof 820 6 5C (1508 6 9F) is achieved at the end of 212 min.A variable transformer is desirable for establishing the inputvoltage to the furnace.4.3 The gas apparatus shall consist of the following:4.3.1 Burner AssemblyA gas burner with a grid of exter-nal
22、diameter, 30 to 42 mm (1.18 to 1.65 in.), a draft shield, anda triangular crucible support as shown in Fig. 3. Make the draftshield, conforming to the dimensions shown in Fig. 3 from theasbestos-cement pipe, and at the top it shall have three slots, 25mm (1 in.) in depth, in which the wires of the c
23、rucible supportrest. Support the draft shield on a ring stand, so that thedistance between the base of the crucible and the top of theburner grid may be adjusted by raising or lowering the draftshield. Make the triangular crucible support from three piecesof translucent silica tubing each 63 mm (2.5
24、 in.) in length, 6 to6.5 mm (0.24 to 0.26 in.) in external diameter, and mounted onchromium-nickel wire so that the diameter of the inscribedcircle is approximately 32 mm (1.26 in.). The twisted ends ofthe triangle may be joined together by a loop of wire tofacilitate removal of the hot crucible.4.3
25、.2 FlowmeterA capillary flowmeter with water ma-nometer placed in the gas line before the burner as a guide tothe control of the rate of gas flow (Fig. 3).5. Calibration5.1 Electric Furnace:5.1.1 Turn the main power switch on and set the timer to theHOLD position. Adjust the variable transformer so
26、that theammeter reads 5.8 A. Allow at least 45 min for the furnacetemperature to reach equilibrium.5.1.2 Set the timer just beyond the 112-min mark. At 112min, lower an empty crucible with pierced lid into the furnace.Measure the temperature at the inside base of the crucible witha thermocouple and
27、a potentiometer. The unprotected junctionof the thermocouple must be in contact with the inside base ofthe crucible.At the end of 112 min, the temperature should read800 6 10C (1472 6 18F). Adjust the variable transformer asnecessary to provide this temperature.5.1.3 A temperature of 820 6 5C (1508
28、6 9F) must beattained at the end of 212 min. The second timer shall be usedhere. The control unit rheostat must be properly adjusted toreduce the heating rate at the end of 212 min. If the rheostat isset initially so that at the end of 112 min the ammeter readingis reduced by 0.6 or 0.7 A, the speci
29、fied temperature at the endof 212 min should be attained. Several trials will no doubt benecessary before the proper temperatures at 112 and 212 minare reached; however, the information given above provides ageneral guide for calibration. The silica crucible and covermust be at room temperature befo
30、re each calibration run.5.1.4 After each calibration attempt or sample run, switchthe timer to the HOLD position, and allow about 1 min for thefurnace to reach equilibrium.5.2 Gas Burner:5.2.1 With the burner assembly arranged as shown in Fig. 3,and with an empty crucible in position, light the burn
31、er about15 min before making a determination to allow the draft shieldto rise to an equilibrium temperature.5.2.2 After placing a crucible in position adjust the flow ofgas and the relative positions of the burner and the draft shieldso that the temperature of the inner surface of the bottom of thec
32、rucible reaches 800 6 10C (1472 6 18F) in 112 min and820 6 5C (1508 6 9F) in 212 min. These desired tempera-tures may usually be obtained by setting the draft shield so thatthe bottom of the crucible is approximately 10 mm (0.4 in.)above the burner grid, and then adjusting the gas flame.Determine th
33、e crucible temperature by means of a thermo-couple and a potentiometer. Insert the thermocouple throughthe pierced crucible lid so that the unprotected junction of thethermocouple is in contact with the base of the crucible.6. Preparation of Sample6.1 Grind the sample of coal to pass a 250-m (No. 60
34、)sieve and prepare it in accordance with the requirements ofPractice D2013.FIG. 1 Sight TubeD720 91 (2010)26.1.1 The test should be performed within 24 h of the timethat a sample is pulverized to 60 mesh.NOTE 1For some coals, size consist of the sample is a variable thatcan affect the size of the co
35、ke button produced.7. Procedure7.1 Preparation of Coke Buttons:7.1.1 Electric MethodWeigh1goftheprepared sampleinto a cold crucible and level by lightly tapping the crucibletwelve times on a solid surface, rotating it between taps. Coverthe crucible with a solid lid. Set the control-unit timer just
36、pastthe 112-min mark and set a separate timer at the 212-min mark.As the control-unit timer passes the 112-min mark, lower thecrucible into the furnace and at the same time start the 212-mintimer. The rheostat will be actuated at the end of 112 min. Therun will be finished at the end of 212 min. Rem
37、ove the cokebutton carefully and remove the carbon residue remaining inthe crucible by ignition. Make three buttons in this manner foreach sample of coal tested.7.1.2 Gas MethodWeigh1goftheprepared sample intoa cold crucible, and level by lightly tapping the crucible twelvetimes on a solid surface,
38、rotating it between taps. Cover thecrucible with a solid lid and place it upright in the silicatriangle supported in the draft shield, directly over the gasflame. Heat the covered crucible in the gas flame for the timerequired for the flame of the burning volatile matter to die out,but in any case f
39、or not less than 212 min. Remove the cokebutton carefully and remove the carbon residue remaining inthe crucible by ignition. Make three buttons in this manner foreach sample of coal tested.7.2 Measurement of Coke Button:7.2.1 View each coke button through the sight tube andcompare it with the serie
40、s of standard profiles shown in Fig. 4.Place the standard profile with which a button is to becompared exactly in the center of the field of vision as viewedfrom the top of the tube. Place the button on the profile androtate it on its axis until, viewed with the eye placed immedi-ately over the top
41、of the tube, the maximum cross-sectionalFIG. 2 Furnace Base and ChimneyFIG. 3 Details of Burner AssemblyD720 91 (2010)3area is obtained. Record the number of the standard profilemost nearly matched by the maximum cross-sectional area ofthe button as the swelling index. If any button deviates by more
42、than one unit from the other two buttons, make a newdetermination.7.2.2 Some coals give buttons that do not conform in shapeto the standard profiles. For such coals, measure the maximumcross-sectional areas of the buttons and determine the indexfrom the relationship of the areas of the standard prof
43、iles toswelling indexes as shown in Fig. 5. For measuring thecross-sectional areas, mount the buttons on graph paper ruledinto square centimetres and square millimetres, and trace theoutlines of the buttons on the paper while viewing through thesight tube shown in Fig. 1. The buttons may be mountedc
44、onveniently by means of modeling clay. The squares insidethe outline may be counted, and fractions of squares along theboundary line estimated.NOTE 2To take care of buttons whose cross-sectional area is greaterthan that of standard profile 9, the curve shown in Fig. 5 has been extendedFIG. 4 Full-Sc
45、ale Standard Profiles and Corresponding Index NumbersFIG. 5 Relationship of Areas of Standard Profiles to Swelling IndexesD720 91 (2010)4to include about 700 mm2(1.08 in.2) which is the maximum cross-sectional area of the silica crucibles used in the test.7.2.3 Mechanical or electronic devices may b
46、e used todetermine the standard profiles if they give results equivalent tothose obtained with measurement techniques described in 7.2.1and 7.2.2.7.2.4 If the residue is coherent but nonswollen, place it on aflat surface and carefully place a 500-g weight on the button. Ifthe button disintegrates, r
47、eport the swelling index as one half.If the button supports the weight or merely cracks into two orthree hard coherent pieces, report the number as one.8. Report8.1 Report the average swelling index of a series of threebuttons expressed to the nearest one-half unit. If this testmethod is to be used
48、for International Classification of hardcoal by type, make five buttons. Report the swelling index aszero if the residue from the test sample is noncoherent.9. Precision and Bias59.1 PrecisionThe relative precision of this test method forthe determination of free-swelling index covers the index rang
49、efrom one to nine.NOTE 3A test result is considered to be an average of three FSIdeterminations.9.1.1 RepeatabilityThe difference in absolute value be-tween two consecutive tests results, carried out on the samesample in the same laboratory by the same operator using thesame apparatus, should not exceed the repeatability intervalI(r) more than 5 % of such paired values (95 % confidencelevel). When such a difference is found to exceed the repeat-ability interval, there is reason to question one or more of thetest results. The repeatabi
