1、Designation: D3874 10An American National StandardStandard 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
2、 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. Scope*1.1 This test method is intended to differentiate, in apreliminary fashion, among materials with respect to theirresi
3、stance to ignition because of 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 t
4、emperatures. That is, it applies 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 longitudinal direc-ti
5、on, or twisting of the specimen, during the wire-wrappingstep, 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 IE
6、EE/ASTM SI-10 for further details.)1.5 This 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
7、assemblies under actual fire conditions.1.6 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
8、limitations prior to use.1.7 Fire testing 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.
9、 Referenced Documents2.1 ASTM Standards:3D1711 Terminology Relating to Electrical InsulationE176 Terminology of Fire StandardsIEEE/ASTM SI-10 International System of Units (SI) TheModernized Metric System2.2 IEC Standards:IEC 60695-2-20 Fire Hazard TestingSection 20:Glowing/Hot-wire Based Test Metho
10、ds, Hot-wire CoilIgnitability Test on Materials4IEC 60695-4 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 andIEC 60695-4 for definitions of terms used in this test me
11、thodand associated with fire issues. Where differences exist 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:
12、3.2.1 ignition, ninitiation of flaming produced by com-bustion in the gaseous phase that is accompanied by theemission of light.4. Summary of Test Method4.1 In this test method, a rectangular bar-shaped test speci-men, with the center portion wrapped with a coil of heater wire,is supported horizonta
13、lly at both ends. The circuit is then1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.21 on Fire Performance Standards.Current edition approved March 1, 2010. Published April 2010. O
14、riginallyapproved in 1988. Last previous edition approved in 2004 as D387404. DOI:10.1520/D3874-10.2K. N. Mathes, Chapter 4, “Surface Failure Measurements”, EngineeringDielectrics, Vol. IIB, Electrical Properties of Solid Insulating Materials, Measure-ment Techniques, R. Bartnikas, Editor, ASTM STP
15、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 website.4Available from International E
16、lectrotechnical 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, http:/www.iso.ch.1*A Summary of Chang
17、es section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.energized by applying a fixed power density to the heater wire,which rapidly heats up. The behavior of the test specimen isobserved. until
18、one of the following happens: (a) the materialunder test 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 e
19、quipment, includingwires, resistors, and other conductors, 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 ofel
20、ectrical insulating materials to ignition by the effect of hotwire sources.5.3 This test method determines the average time, in sec-onds, required for material specimens to ignite under thespecified conditions of test.5.4 This method is suitable to characterize materials, subjectto the appropriate l
21、imitations of an expected precision of 615%, to categorize 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 tes
22、t to predictchanges in the fire-test-response characteristics 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 thefol
23、lowing nominal properties: a wire composition of 20 %chromium-80 % nickel, a diameter of 0.05 mm (0.020 in.), anominal cold resistance of 5.28 V/m (1.61V/ft), and a length-to-mass ratio of 580 m/kg (864 ft/lb).6.2 Calibrate each spool of test wire for energized resis-tance, in accordance with the me
24、thod outlined in Annex A1.Such calibration is necessary due to the typical variability ofwire lots in composition, processing, sizing, and metallurgy.6.3 Supply CircuitThe supply circuit, which is a meansfor electrically energizing the heater wire, shall comply with6.3.1-6.3.4.6.3.1 The supply circu
25、it capacity shall be sufficient tomaintain a continuous linear 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 shal
26、l have a means of voltageadjustment to achieve the desired current 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
27、.4 The test circuit shall be provided with an easilyactuated on-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 tw
28、o transverse dimensions of the chamber shallnot exceed 2.5. The 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 su
29、pporting posts shall be positioned70 mm (234 in.) apart to support 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
30、wire, with a spacing of 6.35 6 0.05mm (0.250 6 0.002 in.) between 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
31、 of such fumes and products ofcombustion and exhaust them from 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
32、on the specimen after testing.8. Test Specimens8.1 The test specimen 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 thesamp
33、les in a dry condition. If this is not practical, dry thesamples in an air-circulating oven at 70 6 2 C (158 6 3.5 F)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(736 3.5 F) and 50 6 5%relati
34、ve humidity. Maintain the test facilities at 50 6 5%relative humidity and 23 C.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 dissipa
35、te 0.26 W/mmof length (6.5 W/in. of length) for 8 to 12 s to relieve theinternal stresses within the wire. Calibrate the wire in accor-dance with Annex A1 to determine the correct current level.10. Procedure10.1 Wrap the center portion of the test specimen with a testwire, conditioned in accordance
36、with 9.1.2, using the windingfixture as specified in 6.6 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 fre
37、e endsof the wire to the test circuit. The connection is to be capableD3874 102of 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.) throug
38、h the nickel-chrome wire. The 0.26W/mm shall be maintained during 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 t
39、hrough the wire withoutignition, discontinue the test when the specimen 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 appropriat
40、e.11. Report11.1 Report the following information:11.1.1 Complete 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 specim
41、en or the time atwhich the wire turns no longer contact the specimen,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 ave
42、rage determined will fall within 615 % of thevalue obtained by an 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;
43、ignition; resistance to ignitionANNEX(Mandatory Information)A1. TEST 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
44、 is developed between current and powerdissipation, based on performance 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 fo
45、und that the variation of electrical resistance of thetest wire within 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). Plac
46、e anammeter in the circuit. Fit a voltmeter with small voltage-measuring 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. Car
47、efully measure and record thelength of the wire between the contact 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.A1.4 CalculationA1.4.1 For each measurement, calculate the linear
48、powerdensity as follows:W 5EILwhere: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 curren
49、t for theFIG. A1.1 Test ApparatusD3874 103given spool of test wire 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 Since the calibration curve must pass through thezero point (current equal 0, power equal 0), and since it isknown that the ideal functional relationship is of the formI 5 c=W, then it is possible to mathematically compute thevalue of c to yield the best least squares approximation to thecalibration data by square root regression. Calculate the valueof c as follows:c 51r5n=
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