1、Designation: D3874 13Standard Test Method forIgnition of Materials by Hot Wire Sources1This standard is issued under the fixed designation D3874; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method is intended to differentiate, in apreliminary fashion, among materials with respect to theirresistance to ignition because of
3、 their proximity to electrically-heated wires and other heat sources.21.2 This test method applies to molded or sheet materialsavailable in thicknesses ranging from 0.25 to 6.4 mm (0.010 to0.25 in.).1.3 This test method applies to materials that are rigid atnormal room temperatures. That is, it appl
4、ies to materials forwhich the specimen does not deform during preparation,especially during the wire-wrapping step described in 10.1.Examples of deformation that render this test method inappli-cable include:1.3.1 Bowing, in either a transverse or a longitudinaldirection, or twisting of the specimen
5、, during the wire-wrapping step, to a degree visible to the eye.1.3.2 Visible indentation of the wrapped wire into thespecimen.1.4 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in parentheses are forinformation only. (See SI10 for further details.)1.5 Th
6、is test method measures and describes the response ormaterials, products, or assemblies to heat and flame undercontrolled conditions, but does not by itself incorporate allfactors required for fire hazard or fire risk assessment of thematerials, products, or assemblies under actual fire conditions.1
7、.6 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 determine the applica-bility of regulatory limitations prior to use.1.7 Fire testing
8、 is inherently hazardous. Adequate safe-guards for personnel and property shall be employed inconducting these tests.NOTE 1Although this test method and IEC 60695-2-20, differ inapproach and in detail, data obtained using either are technically equiva-lent.2. Referenced Documents2.1 ASTM Standards:3
9、D1711 Terminology Relating to Electrical InsulationE176 Terminology of Fire StandardsIEEE/ASTM SI-10 American National Standard for MetricPractice2.2 IEC Standards:IEC 60695-2-20 Fire Hazard TestingSection 20: Glowing/Hot-wire Based Test Methods, Hot-wire Coil IgnitabilityTest on Materials4IEC 60695
10、-4 Fire Hazard TestingPart 4: TerminologyConcerning Fire Tests42.3 ISO StandardsISO 13943 Fire SafetyVocabulary53. Terminology3.1 Definitions:3.1.1 Use Terminology E176 and ISO 13943 and IEC60695-4 for definitions of terms used in this test method andassociated with fire issues. Where differences ex
11、ist indefinitions, those contained in Terminology E176 shall be used.Use Terminology D1711 for definitions of terms used in thistest method and associated with electrical insulation materials.3.2 Definitions of Terms Specific to This Standard:3.2.1 ignition, ninitiation of flaming produced by combus
12、-tion in the gaseous phase that is accompanied by the emissionof light.1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.17 on Fire and Thermal Properties.Current edition approved Nov
13、. 1, 2013. Published December 2013. Originallyapproved in 1988. Last previous edition approved in 2012 as D3874 12. DOI:10.1520/D3874-13.2K. N. Mathes, Chapter 4, “Surface Failure Measurements”, EngineeringDielectrics, Vol. IIB, Electrical Properties of Solid Insulating Materials, Measure-ment Techn
14、iques, R. Bartnikas, Editor, ASTM STP 926, ASTM, Philadelphia, 1987.3For 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 w
15、ebsite.4Available from International Electrotechnical Commission (IEC), 3 rue deVaremb, Case postale 131, CH-1211, Geneva 20, Switzerland, http:/www.iec.ch.5Available from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland,
16、 http:/www.iso.ch.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 In this test method, a rectangular bar-shaped testspecimen, with the cente
17、r portion wrapped with a coil of heaterwire, is supported horizontally at both ends. The circuit is thenenergized by applying a fixed power density to the heater wire,which rapidly heats up. The behavior of the test specimen isobserved. until one of the following happens: (a) the materialunder test
18、ignites, (b) the material under test melts, (c) 120 s ofexposure have gone by without ignition or melting. The time toignition and the time to melt through, as applicable, arerecorded.5. Significance and Use5.1 During operation of electrical equipment, includingwires, resistors, and other conductors
19、, it is possible for over-heating to occur, under certain conditions of operation, or whenmalfunctions occur. When this happens, a possible result isignition of the insulation material.5.2 This test method assesses the relative resistance ofelectrical insulating materials to ignition by the effect o
20、f hotwire sources.5.3 This test method determines the average time, inseconds, required for material specimens to ignite under thespecified conditions of test.5.4 This method is suitable to characterize materials, subjectto the appropriate limitations of an expected precision of615 %, to categorize
21、materials.5.5 In this procedure the specimens are subjected to one ormore specific sets of laboratory conditions. If different testconditions are substituted or the end-use conditions arechanged, it is not always possible by or from this test to predictchanges in the fire-test-response characteristi
22、cs measured.Therefore, the results are valid only for the fire test exposureconditions described in this procedure.6. Apparatus6.1 Heater WireThe heater wire shall be a No. 24 AWG,Nichrome (Nickel-Chrome) wire, that is iron free, with thefollowing nominal properties: a wire composition of 20 %chromi
23、um-80 % nickel, a diameter of 0.5 mm (0.020 in.), anominal cold resistance of 5.28 /m (1.61/ft), and a length-to-mass ratio of 580 m/kg (864 ft/lb).6.2 Calibrate each spool of test wire for energizedresistance, in accordance with the method outlined in AnnexA1. Such calibration is necessary due to t
24、he typical variabilityof wire lots in composition, processing, sizing, and metallurgy.6.3 Supply CircuitThe supply circuit, which is a means forelectrically energizing the heater wire, shall comply with 6.3.1 6.3.4.6.3.1 The supply circuit capacity shall be sufficient tomaintain a continuous linear
25、50 to 60 Hz power density of atleast 0.31 W/mm (8.0 W/in.) over the length of the heater wireat or near unity power factor. The power density of the supplycircuit at 60 A and 1.5 V shall approximate 0.3 W/mm.6.3.2 The supply circuit shall have a means of voltageadjustment to achieve the desired curr
26、ent as determined fromAnnex A1. Such means of voltage adjustment shall provide asmooth and continuous adjustment of the power level.6.3.3 The supply circuit shall have a means of voltageadjustment of measuring the power to within 62%.6.3.4 The test circuit shall be provided with an easilyactuated on
27、-off switch for the test power, and with timers torecord the duration of the application of test power.6.4 Test ChamberUse as a test chamber a draft-free closedchamber having a volume of at least 0.3 m3(10.5 ft3). The ratiobetween any two transverse dimensions of the chamber shallnot exceed 2.5. The
28、 test chamber shall be positively vented tothe outside of the test facility before and after the test, but itshall remain closed and unvented during the test. The chambershall be equipped with an observation window.6.5 Test FixtureTwo supporting posts shall be positioned70 mm (234 in.) apart to supp
29、ort the specimen in a horizontalposition, at a height of 60 mm (238 in.) above the bottom of thetest chamber, in the approximate center of the test chamber.6.6 Specimen-Winding FixtureA fixture shall be providedto uniformly position the wire, with a spacing of 6.35 6 0.05mm (0.250 6 0.002 in.) betwe
30、en turns and with a windingtension of 5.4 6 0.02 N (1.21 6 0.0045 lbf).7. Safety Precautions7.1 It is possible that fumes and products of incompletecombustion are liberated from the specimen when conductingthis test. Avoid the inhalation of such fumes and products ofcombustion and exhaust them from
31、the test chamber after eachrun.7.2 Take precautions to safeguard the health of personnelagainst the risk of explosion or fire, the inhalation of smoke, orother products of combustion, or the exposure to the residuespotentially remaining on the specimen after testing.8. Test Specimens8.1 The test spe
32、cimen shall consist of a bar measuring 12.56 0.2 by 125 6 5mm(12 by 5 in.) and of the thickness to betested.9. Conditioning9.1 Condition the specimens and heater wire as follows:9.1.1 Sample ConditioningPrior to testing, maintain thesamples in a dry condition. If this is not practical, dry thesample
33、s in an air-circulating oven at 70 6 2C (158 6 3.5F)for seven days and cool over a desiccant, such as silica gel, fora minimum of 4 h. Prior to testing, condition the dry samplesfor at least 40 h at 23 6 2C (73 6 3.5F) and 50 6 5%relative humidity. Maintain the test facilities at 50 6 5%relative hum
34、idity and 23C.9.1.2 Heater Wire Conditioning and CalibrationFor eachtest, use a length of previously calibrated wire measuringapproximately 250 mm (10 in.). Prior to testing, anneal eachstraight length by energizing the wire to dissipate 0.26 W/mmof length (6.5 W/in. of length) for 8 to 12 s to reli
35、eve theinternal stresses within the wire. Calibrate the wire in accor-dance with Annex A1 to determine the correct current level.D3874 13210. Procedure10.1 Wrap the center portion of the test specimen with a testwire, conditioned in accordance with 9.1.2, using the windingfixture as specified in 6.6
36、 and a winding force of 5.4 6 0.02 N(1.21 6 0.0045 lbf). Apply five complete turns spaced 6.35 60.05 mm (14 in.) between turns.10.2 Position the specimen on the test fixture such that thelength and width are horizontal. Securely connect the free endsof the wire to the test circuit. The connection is
37、 to be capableof transmitting the test power without significant losses, andinsofar as possible, not mechanically affect the specimenduring the test.10.3 Start the test by energizing the circuit to dissipate 0.26W/mm (6.5 W/in.) through the nickel-chrome wire. The 0.26W/mm shall be maintained during
38、 the test.10.4 Continue heating until the test specimen ignites (see3.2.1). When ignition occurs, shut off the power and record thetime to ignition. Discontinue the test if ignition does not occurwithin 120 s. For specimens that melt through the wire withoutignition, discontinue the test when the sp
39、ecimen is no longer inintimate contact with all five turns of the heater wire.10.5 Note the following observations:10.5.1 The time to ignition of each specimen, and10.5.2 The time for each specimen to melt through the wireif appropriate.11. Report11.1 Report the following information:11.1.1 Complete
40、 identification of the material tested includ-ing type, source, and manufacturers code number,11.1.2 Testing room conditions,11.1.3 Number of specimens tested,11.1.4 Thickness of specimens tested,11.1.5 Time to ignition for each specimen or the time atwhich the wire turns no longer contact the speci
41、men,11.1.6 Calculation and record of the average time forignition,11.1.7 Calibrated test current, and11.1.8 Geometry of test chamber.12. Precision and Bias12.1 It is likely that, when care is taken to adhere to this testmethod, the average determined will fall within 615 % of thevalue obtained by an
42、 interlaboratory evaluation.12.2 A statement of bias for this test method is not practi-cable since there is no standard reference material availablewith a known characteristic of true resistance to ignition.13. Keywords13.1 hot wire; ignition; resistance to ignitionANNEX(Mandatory Information)A1. T
43、EST WIRE CALIBRATIONA1.1 GeneralA1.1.1 Due to normal variations in metals, it is essential thateach spool of test wire be calibrated with respect to energizedresistance according to the following procedure. A mathemati-cal relationship is developed between current and powerdissipation, based on perf
44、ormance under the calibration experi-ment. Essentially, the voltage over a carefully measured lengthof wire, and the current through the wire are measured over arange of values to establish the power-current relationship. Ithas been found that the variation of electrical resistance of thetest wire w
45、ithin the spool is not significant.A1.2 Apparatus and EquipmentA1.2.1 Position approximately 250 mm (10 in.) of test wireas a horizontal open loop connected to the supply contacts ofthe hot wire ignition equipment (see Fig. A1.1). Place anammeter in the circuit. Fit a voltmeter with small voltage-me
46、asuring probes for measuring voltage across a measuredlength of the wire.A1.3 ProcedureA1.3.1 Position the voltmeter probes near the ends of thetest wire prior to connecting the wire, with the wire in ahorizontal straight position. Carefully measure and record thelength of the wire between the conta
47、ct points of the clips.Connect the wire to the test apparatus and energize to currentlevels, from 1 to 8 A in increments of 1 A. Record current andvoltage at each level.FIG. A1.1 Test ApparatusD3874 133A1.4 CalculationA1.4.1 For each measurement, calculate the linear powerdensity as follows:W 5EILwh
48、ere:W = linear power density, W/mm (or W/in.),E = measured voltage, V,I = measured current, A, andL = measured length between voltage clips, mm (or in.).A1.4.2 Construct a calibration curve of current as a functionof linear power density. The desired calibrated current for thegiven spool of test wir
49、e is then obtained from a calibrationcurve as that current corresponding to 0.26 W/mm (6.5 W/in.)(see Fig. A1.2).A1.4.3 Note that when current is equal to zero, the powershall be equal to zero.SUMMARY OF CHANGESCommittee D09 has identified the location of selected changes to this test method since the last issue,D387412, that may impact the use of this test method. (Approved November 1, 2013)(1) Revised A1.4.3.Committee D09 has identified the location of selected changes to this test method since the last issue,D387410, that may impact the use of this
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