1、Designation: D2304 10D2304 18Standard Test Method forThermal Endurance of Rigid Electrical Insulating Materials1This standard is issued under the fixed designation D2304; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、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 Scope*1.1 This test method2 provides procedures for evaluating the thermal endurance of rigid electrical insulating mater
3、ials.Dielectric strength, flexural strength, or water absorption are determined at room temperature after aging for increasing periods oftime in air at selected-elevated temperatures. A thermal-endurance graph is plotted using a selected end point at each agingtemperature. A means is described for d
4、etermining a temperature index by extrapolation of the thermal endurance graph to aselected time.1.2 This test method is most applicable to rigid electrical insulation such as supports, spacers, voltage barriers, coil forms,terminal boards, circuit boards and enclosures for many types of application
5、 where retention of the selected property after heataging is important.1.3 When dielectric strength is used as the aging criterion, it is also acceptable to use this test method for some thin sheet(flexible) materials, which become rigid with thermal aging, but is not intended to replace Test Method
6、 D1830 for those materialswhich must retain a degree of flexibility in use.1.4 This test method is not applicable to ceramics, glass, or similar inorganic materials.1.5 The values stated in metric units are to be regarded as standard. Other units (in parentheses) are provided for information.1.6 Thi
7、s standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to
8、 use. A specific warning statement is given in 10.3.411.3.4.1.7 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations is
9、suedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D149 Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials atCommercial Power FrequenciesD229 Test Methods for Rigid Shee
10、t and Plate Materials Used for Electrical InsulationD570 Test Method for Water Absorption of PlasticsD790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating MaterialsD1830 Test Method for Thermal Endurance of Flexible Sheet Materials Used for Elect
11、rical Insulation by the Curved ElectrodeMethodD5423 Specification for Forced-Convection Laboratory Ovens for Evaluation of Electrical Insulation2.2 IEEE:4No. 1 General Principles Upon Which Temperature Limits Are Based in the Rating of Electric EquipmentNo. 98 Guide for the Preparation of Test Proce
12、dures for the Thermal Evaluation of Electrical Insulating Materials1 This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of SubcommitteeD09.07 on Flexible and Rigid Electrical Insulating Materials.Current
13、 edition approved Oct. 1, 2010May 1, 2018. Published October 2010May 2018. Originally issued as D2304 64 T. Last previous edition approved in 20022010as D2304 97D2304 10.R02. DOI: 10.1520/D2304-10.10.1520/D2304-18.2 This test method is a revision of a procedure written by the Working Group on Rigid
14、Electrical Insulating Materials of the Subcommittee on Thermal Evaluation, IEEEElectrical Insulation Committee, which was presented as CP 59-113 at the IEEE Winter General Meeting Feb. 16, 1959. See references at end of this test method.3 For referencedASTM standards, visit theASTM website, www.astm
15、.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.4 Available from the Institute of Electrical and Electronics Engineers, 445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-13
16、31.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior
17、editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*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-
18、2959. United States1No. 101 Guide for the Statistical Analysis of Test Data3. Terminology3.1 Definitions:3.1.1 Arrhenius plot, na graph of the logarithm of thermal life as a function of the reciprocal of absolute temperature.3.1.1.1 DiscussionThis is normally depicted as the best straight line fit,
19、determined by least squares, of end points obtained at aging temperatures.It is important that the slope, which is the activation energy of the degradation reaction, be approximately constant within theselected temperature range to ensure a valid extrapolation.3.1.2 temperature index, na number whic
20、h permits comparison of the temperature/time characteristics of an electricalinsulating material, or a simple combination of materials, based on the temperature in degrees Celsius which is obtained byextrapolating the Arrhenius plot of life versus temperature to a specified time, usually 20 000 h.3.
21、1.3 thermal life, nthe time necessary for a specific property of a material, or a simple combination of materials, to degradeto a defined end point when aged at a specified temperature.3.1.4 thermal life curve, na graphical representation of thermal life at a specified aging temperature in which the
22、 value of aproperty of a material, or a simple combination of materials, is measured at room temperature and the values plotted as a functionof time.3.2 Definitions of Terms Specific to This Standard:3.2.1 rigid electrical insulating material, nan electrical insulating material having a minimum flex
23、ural modulus of 690 MPaand minimum use thickness of 0.5 mm (0.02 in.). It is generally used as terminal boards, spacers, coil forms, voltage barriers, andcircuit boards.4. Hazards4.1 High Voltage:4.1.1 Lethal voltages are a potential hazard during the performance of this test. It is essential that t
24、he test apparatus, and allassociated equipment electrically connected to it, be properly designed and installed for safe operation.4.1.2 Solidly ground all electrically conductive parts which it is possible for a person to contact during the test.4.1.3 Provide means for use at the completion of any
25、test to ground any parts which were at high voltage during the test or havethe potential for acquiring an induced charge during the test or retaining a charge even after disconnection of the voltage source.4.1.4 Thoroughly instruct all operators as to the correct procedures for performing tests safe
26、ly.4.1.5 When making high voltage tests, particularly in compressed gas or in oil, it is possible for the energy released atbreakdown to be sufficient to result in fire, explosion, or rupture of the test chamber. Design test equipment, test chambers , andtest specimens so as to minimize the possibil
27、ity of such occurrences and to eliminate the possibility of personal injury. If thepotential for fire exists, have fire suppression equipment available. See 11.3.4.5. Summary of Test Method5.1 Test specimens are aged in air at three or preferably four temperatures above the expected use temperature.
28、 The agingtemperatures are selected so that the thermal life is at least 100 h at the highest aging temperature and 5000 h at the lowest agingtemperature.Athermal-life curve is plotted for each aging temperature. The values of thermal life determined from the thermal-lifecurve are used to plot the t
29、hermal-endurance graph.Atemperature index is determined from the thermal-endurance graph for eachaging criterion used. (It is possible to obtain different values for the thermal index of a material with different aging criteria.)6. Significance and Use6.1 Thermal degradation is often a major factor
30、affecting the life of insulating materials and the equipment in which they areused. The temperature index provides a means for comparing the thermal capability of different materials in respect to thedegradation of a selected property (the aging criterion). This property needs to directly or indirec
31、tly represent functional needs inapplication. For example, it is possible that a change in dielectric strength will be of direct, functional importance. However, moreoften it is possible that a decrease in dielectric strength will indirectly indicate the development of undesirable cracking(embrittle
32、ment). A decrease in flexural strength has the potential to be of direct importance in some applications, but also has thepotential to indirectly indicate a susceptibility to failure in vibration. Often, it is necessary that two or more criteria of failure beused; for example, dielectric strength an
33、d flexural strength.6.2 Other factors, such as vibration, moisture and contaminants, have the potential to cause failure after thermal degradationtakes place. In this test method, water absorption provides one means to evaluate such considerations.6.3 For some applications, the aging criteria in thi
34、s test method will not be the most suitable. Other criteria, such as elongationat tensile or flexural failure, or resistivity after exposure to high humidity or weight loss, have the potential to serve better. TheD2304 182procedures in this test method have the potential to be used with such aging c
35、riteria. It is important to consider both the natureof the material and its application. For example, it is possible that tensile strength will be a poor choice for glass-fiber reinforcedlaminates, because it is possible that the glass fiber will maintain the tensile strength even when the associate
36、d resin is badlydeteriorated. In this case, flexural strength is a better criterion of thermal aging.6.4 When dictated by the needs of the application, it is possible that an aging atmosphere other than air will be needed and used.For example, thermal aging can be conducted in an oxygen-free, nitrog
37、en atmosphere.7. End Point7.1 An expression of the thermal life of a material, even for comparative purposes only, inevitably involves the choice of anend point. The end point could be is one of the following 4 criteria: a fixed magnitude of the property criterion, a percentagereduction from its ini
38、tial magnitude, the minimum magnitude obtainable with time (that is, when change with time ceases), or afixed degrading change rate (that is, a fixed value for the negative derivative of property with respect to time).7.2 Experience has shown that the choice of an end point can affect the comparativ
39、e thermal life. A choice of end points needsto, therefore, be is guided by the limiting requirements imposed on the insulation by the manner and conditions of use in thecomplete system. End points are not specified in this test method. The first concern is to determine the values of the chosenproper
40、ties as a function of time of thermal exposure at specified temperatures. The properties are determined at various intervalsof time until a practical minimum or maximum magnitude, whichever is applicable, is reached. The data that result are thusuniversal, that is, usable for any subsequently chosen
41、 end point as determined by the specific application of the rigid electricalinsulation.7.3 The specification for each material needs to state the end point to be used.8. Aging Ovens8.1 The accuracy of the test results will depend on the accuracy with which the exposure temperature of the test specim
42、ens isknown. Experience has shown, as indicated in Table 1, that the thermal life is approximately halved for a 10C increase in exposuretemperature.8.2 Use aging ovens that conform to the requirements of Type I of Specification D5423.9. Test Specimen9.1 The accuracy of the test results depends signi
43、ficantly upon the number of specimens exposed at each temperature and thedispersion of the test results. The larger the individual deviations from the mean, the greater is the number of test specimens neededto achieve satisfactory accuracy. Experience has shown that a minimum of five test specimens
44、needs to be used at each exposuretemperature. A separate group of test specimens is required for each exposure period.TABLE 1 Temperature and Exposure Time in DaysExposureTemperature,CEstimated Hottest-Spot Temperature Range, C100 to120125 to145150 to170175 to195200 to240300 . . . . 10290 . . . . 20
45、280 . . . . 40270 . . . . 70260 . . . . 140250 . . . 10 280240 . . . 20 490230 . . . 40 .220 . . 10 70 .210 . . 20 140 .200 . 10 40 280 .190 . 20 70 490 .180 10 40 140 . .170 20 70 280 . .160 40 140 490 . .150 70 280 . . .140 140 490 . . .130 280 . . . .120 490 . . . .D2304 1839.2 It is possible tha
46、t the The rate of deterioration will be significantly influenced by specimen thickness. Consequently it isimportant to test specimens of the same nominal thickness when comparing the thermal degradation of two or more materialsunless information relating degradation to thickness is available that in
47、dicates the contrary. This test method specifies the specimensize, including thickness, for each property selected.PROCEDURES10. Oven Aging (Thermal Exposure)10.1 Factors such as moisture, chemical contamination, and mechanical stress or vibration usually do not in themselves causefailure, but are f
48、actors that have the potential to result in failure only after the material has been weakened by thermal deterioration.For this reason, exposure to elevated temperatures is the primary deteriorating influence considered in this test method.10.2 Table 1 is intended as a guide for the selection of the
49、rmal exposure. Select times and temperatures from those given in thistable. The exposure times given are approximately equal to the average estimated life at each exposure temperature based onthermal aging data obtained on insulating materials and systems. It is recognized that the The potential exists that this table willbe revised as a result of experience. The potential that either the time or the temperature will be adjusted to make the best use ofavailable oven facilities.10.3 Age at a minimum of three and preferably four temperatures. Choose the lowest temper
