1、Designation: D2756 07 (Reapproved 2017)Standard Test Method forWeight Loss of Electrical Insulating Varnishes1This standard is issued under the fixed designation D2756; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st 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 covers the measurement of the loss inweight of cured electrical insulating varnishes on exposure toele
3、vated temperature in air.1.2 The values stated in SI units are the standard.1.3 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, health, and environmental pract
4、ices and deter-mine the applicability of regulatory limitations prior to use.For specific precaution statements, see Section 7.NOTE 1IEC 60216 Part 2 is technically equivalent to this standard.1.4 This international standard was developed in accor-dance with internationally recognized principles on
5、standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D115 Test Methods for Testing Solvent Con
6、taining Var-nishes Used for Electrical InsulationD1711 Terminology Relating to Electrical InsulationD1932 Test Method for Thermal Endurance of FlexibleElectrical Insulating VarnishesD2518 Specification for Woven Glass Fabrics for ElectricalInsulation (Withdrawn 2013)3D5423 Specification for Forced-C
7、onvection Laboratory Ov-ens for Evaluation of Electrical Insulation2.2 IEC Standards:IEC 60216 Guide for the determination of thermal endur-ance properties of electrical insulating materialsPart 2:Choice of test criteria43. Terminology3.1 Definitions: For definitions of terms used in this testmethod
8、, refer to Terminology D1711.4. Summary of Test Method4.1 Specimens are prepared by coating glass cloth withvarnish to be tested. The specimens are aged at elevatedtemperatures and the loss in weight is determined after aspecific time.5. Significance and Use5.1 Weight loss is useful for indicating:5
9、.1.1 A form of degradation at elevated temperatures in air,and5.1.2 Evolution of volatiles that have the potential to affectother components.6. Apparatus6.1 Air-Circulating Oven, capable of meeting the require-ments of Specification D5423, Type II.6.2 Glass Cloth, heat-cleaned, Style No. 116, as des
10、cribed inSpecification D2518.6.3 Balance, capable of weighing to nearest 0.001 g.6.4 Desiccator Jar, with a suitable desiccant.7. Safety Precautions7.1 Do not use varnish at temperatures above the flash pointwhen inadequate ventilation and the possibility of flames orsparks exist. Store all varnishe
11、s, reagents and solvents in sealedcontainers. Apply these precautions to the handling of thecalled for reagents and solvents.8. Sampling8.1 Sample the varnish in accordance with Test MethodsD115.1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating
12、Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Products.Current edition approved Nov. 1, 2017. Published November 2017. Originallyapproved in 1968. Last previous edition approved in 2012 as D2756 07 (2012).DOI: 10.1520/D2756-07R17.2For referenced ASTM stand
13、ards, 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.3The last approved version of this historical standard is referenced onwww.astm.org.4Av
14、ailable from International Electrotechnical Commission (IEC), 3 rue deVaremb, Case postale 131, CH-1211, Geneva 20, Switzerland, http:/www.iec.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 1
15、9428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Tec
16、hnical Barriers to Trade (TBT) Committee.19. Test Specimens9.1 Prepare the test specimens as described in Test MethodD1932. Make one panel for each test temperature. Use anaverage of ten readings to determine the thickness of thepanels.9.2 Cure the varnish in accordance with manufacturersrequirement
17、s.9.3 Cut two specimens, 100 by 125 mm (4 by 5 in.) fromeach panel to be used for the tests.9.4 Cut an uncoated piece of cloth, 100 by 125 mm (4 by 5in.)10. Procedure10.1 Dry two cured specimens for each test temperature andone uncoated specimen for 2 h at 110C (230F). Place them ina desiccator and
18、allow them to cool to room temperature.Weigh each specimen to the nearest 0.001 g. The weight of thecoated specimen will be the initial weight.10.2 Subtract the weight of the uncoated specimen from theweight of each coated specimen. This is the initial weight of thevarnish solids on which the percen
19、t weight loss is based.10.3 Select at least four temperatures between 150C(300F) and 250C (480F) for weight loss aging. Suggestedtemperatures are: 150C (300F), 200C (390F), 220C(430F), and 250C (480F).10.4 Hang the cured specimens in the aging ovens, takingthe necessary precautions to assure good ai
20、r flow parallel to thesurface of the specimens. Avoid specimen collisions in theovens. (See Note 2).10.5 After 96 h (Note 3) remove the specimens from theoven and place them in a desiccator. After cooling to roomtemperature, weigh the specimens. Subtract the weight of theglass and the aluminum foil
21、tab, if used. This is the finalweight.NOTE 2It has been found that the use of battery clips over aluminumfoil identification tabs works very well to hold the specimens and preventwhipping around in the ovens. The use of the foil tabs also prevents thebattery clips from picking up any varnish, which
22、could introduce an errorin the measurement.NOTE 3When more information is required, it is desirable to use anumber of selected time periods (for example: 4, 24, 48, 96 h, and in somecases, even longer periods of time). A curve of weight loss versus thelogarithm of time is plotted to show the instant
23、aneous rate of the loss. Acomparison of the initial rate and subsequent or final rate providesinformation as to the degradative mechanisms involved.10.6 Calculate the percent weight loss as follows:Weight loss, % 5W12 W2!/W1#3100 (1)where:W1= initial weight of varnish solids, andW2= final weight.11.
24、 Report11.1 Report the following information:11.1.1 Identity of varnish,11.1.2 Cure cycle on specimen, and11.1.3 Percent weight loss after 96 h at the selected tem-peratures.12. Precision and Bias12.1 The data in Table 1 are the combined results of the sixlaboratories which participated in the round
25、-robin test for thistest method.512.2 This test method has no bias because the weight loss ofvarnishes is defined solely in terms of this method.13. Keywords13.1 varnish; weight lossSUMMARY OF CHANGESCommittee D09 has identified the location of selected changes to this standard since the last issue(
26、D2756 02) that may impact the use of this standard. (Approved May 1, 2007.)(1) Revised Sections 3, 5, 7, and 10.5Supporting data are available from ASTM Headquarters. Request RR:D09-1015.TABLE 1 Round-Robin Test ResultsHours at 200 C Avg. Weight Loss, %Interlaboratory StandardDeviation24 21.0 1.2348
27、 26.0 1.6496 31.2 2.04D2756 07 (2017)2ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the r
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31、y contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 07 (2017)3
