1、Designation: D 3874 04An American National StandardStandard Test Method forIgnition of Materials by Hot Wire Sources1This standard is issued under the fixed designation D 3874; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. 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 test method is intended to differentiate, in apreliminary fashion, among materials with respect to theirre
3、sistance 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
4、 temperatures. 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-
5、tion, 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
6、IEEE/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, o
7、r 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 regulator
8、y limitations prior to use.1.7 Fire testing of products and materials is inherentlyhazardous, and adequate safeguards for personnel and propertyshall be employed in conducting these tests. Fire testinginvolves hazardous materials, operations, and equipment.NOTE 1Although this test method and IEC 606
9、95-2-20, differ inapproach and in detail, data obtained using either are technically equiva-lent.2. Referenced Documents2.1 ASTM Standards:3D 1711 Terminology Relating to Electrical InsulationE 176 Terminology of Fire StandardsIEEE/ASTM SI-10 International System of Units (SI) TheModernized Metric S
10、ystem2.2 IEC Standards:IEC 60695-2-20 Fire Hazard TestingSection 20:Glowing/Hot-wire Based Test Methods, Hot-wire CoilIgnitability Test on Materials4IEC 60695-4 Fire Hazard TestingPart 4: TerminologyConcerning Fire Tests42.3 ISO StandardsISO 13943 Fire SafetyVocabulary53. Terminology3.1 Definitions:
11、3.1.1 Use Terminology E 176 and ISO 13943 andIEC 60695-4 for definitions of terms used in this test methodand associated with fire issues. Where differences exist indefinitions, those contained in Terminology E 176 shall beused. Use Terminology D 1711 for definitions of terms used inthis test method
12、 and associated with electrical insulationmaterials.3.2 Definitions of Terms Specific to This Standard: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-s
13、haped test speci-men, with the center portion wrapped with a coil of heater wire,is supported horizontally 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 ofSubcommitt
14、ee D09.21 on Fire Performance Standards.Current edition approved Sept. 1, 2004. Published September 2004. Originallyapproved in 1988. Last previous edition approved in 2004 as D 3874 03.2K. N. Mathes, Chapter 4, “Surface Failure Measurements”, EngineeringDielectrics, Vol. IIB, Electrical Properties
15、of Solid Insulating Materials, Measure-ment Techniques, 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
16、 the standards Document Summary page onthe ASTM website.4Available from International Electrotechnical Commission (IEC), 3 Rue deVaremb, Geneva, Switzerland.5Available from International Organization for Standardization (ISO), 1 Rue deVaremb, Case postale 56, CH-1211, Geneva 20, Switzerland.1Copyrig
17、ht 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 one of the following happens: (a) the materialunder te
18、st 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 conduct
19、ors, 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 effec
20、t 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 limitations of an expected precision of 615%, to catego
21、rize 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 characte
22、ristics 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 %c
23、hromium-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 method outlined in Annex A1.Such calibration is necessar
24、y 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 circuit capacity shall be sufficient tomaintain a continuou
25、s 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 shall have a means of voltageadjustment to achieve the des
26、ired 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%.6.3.4 The test circuit shall be provided with an easilyac
27、tuated 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 two transverse dimensions of the chamber shallnot exceed
28、 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 supporting posts shall be positioned70 mm (234 in.) apar
29、t 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 wire, with a spacing of 6.35 6 0.05mm (0.250 6 0.002 i
30、n.) 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 of such fumes and products ofcombustion and exhaust t
31、hem 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 on the specimen after testing.8. Test Specimens8.1 The
32、 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 thesamples in a dry condition. If this is not practical, dry
33、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%relative humidity. Maintain the test facilities at 50 6 5%re
34、lative 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 dissipate 0.26 W/mmof length (6.5 W/in. of length) for 8 to 1
35、2 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 with 9.1.2, using the windingfixture as specified in 6
36、.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 free endsof the wire to the test circuit. The connection
37、is to be capableD3874042of 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 maintai
38、ned 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 through the wire withoutignition, discontinue the test w
39、hen 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 appropriate.11. Report11.1 Report the following information:11.1.
40、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 specimen or the time atwhich the wire turns no longer contact
41、 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 average determined will fall within 615 % of thevalue obta
42、ined 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; ignition; resistance to ignitionANNEX(Mandatory Informa
43、tion)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 is developed between current and powerdissipation, bas
44、ed 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 found that the variation of electrical resistance of thet
45、est 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). Place anammeter in the circuit. Fit a voltmeter with small
46、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. Carefully measure and record thelength of the wire between
47、 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 powerdensity as follows:W 5EILwhere:W = linear power de
48、nsity, 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 theFIG. A1.1 Test ApparatusD3874043given spool of
49、 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 51r5ne=WiIi2e=WieIneWi2e=Wi2where: Iiand Wiare the individual valu
