1、Designation: D2756 07 (Reapproved 2012)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 and health practices and determi
4、ne the applica-bility of regulatory limitations prior to use. For specificprecaution statements, see Section 7.NOTE 1IEC 60216 Part 2 is technically equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D115 Test Methods for Testing Solvent Containing Var-nishes Used for Electrical
5、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of FlexibleElectrical Insulating VarnishesD2518 Specification for Woven Glass Fabrics for ElectricalInsulation (Withdrawn 2013)3D5423 Specification for Forced-Convection Laboratory Ov-ens for Evaluat
6、ion 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, refer to Terminology D1711.4. Summary
7、 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:5.1.1 A form of degradation at elevated
8、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 described inSpecification D2518.6.3 Balanc
9、e, 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 varnishes, reagents and solvents in sealedconta
10、iners. Apply these precautions to the handling of thecalled for reagents and solvents.8. Sampling8.1 Sample the varnish in accordance with Test MethodsD115.9. Test Specimens9.1 Prepare the test specimens as described in Test MethodD1932. Make one panel for each test temperature. Use anaverage of ten
11、 readings to determine the thickness of thepanels.1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Varnishes, Powders and Encapsulat-ing Compounds.Current
12、 edition approved April 1, 2012. Published April 2012. Originallyapproved in 1968. Last previous edition approved in 2007 as D2756 07. DOI:10.1520/D2756-07R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of
13、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.4Available from International Electrotechnical Commission (IEC), 3 rue deVaremb, Case postale 131, CH-1211, Geneva 20,
14、 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 19428-2959. United States19.2 Cure the varnish in accordance with manufacturersrequirements.9.3 Cut two specimens, 1
15、00 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 allow them to cool to room
16、 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 percent weight loss is based.10.
17、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 air flow parallel to thesurf
18、ace 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 tab, if used. This is the
19、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 could introduce an errorin
20、 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 instantaneous rate of the loss. A
21、comparison 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. Report11.1 Report the fol
22、lowing 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-robin test for thistest m
23、ethod.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 test method since the last issue,D2756 02, that may impa
24、ct the use of this test method. (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 26.0 1.6496 31.2 2.0
25、4D2756 07 (2012)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 riskof infringement of
26、 such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for a
27、dditional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to
28、 the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at
29、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 (2012)3
