1、Designation:F26960(Reapproved 2014)Standard Test Method forSag of Tungsten Wire1This standard is issued under the fixed designation F269;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses
2、 indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a determination of the sagproperties of tungsten wire 0.030 in.(0.76 mm)and over indiameter.1.2 The values stated in inch-pound units are
3、 to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of t
4、he user of this standard to consult andestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2.Apparatus2.1 Bell Jar EnvelopeAsuitable envelope surrounding thetest apparatus.The envelope may consist of a glass bell jar,preferably of
5、 a heat resistant glass(WarningA protectivemedium shall be provided over an exposed glass to preventinjury by flying glass in the event of an explosion),or may beconstructed of metal,in which case a transparent window shallbe provided in order that the behavior of the specimen undertest may be obser
6、ved.The envelope may be rigidly supportedin a fixed position or may by suspended in such a manner thatit can be raised or lowered into position over the test apparatus.Ameans shall be provided for maintaining within the envelopean atmosphere and steady supply flow of hydrogen.A flowmeter shall be in
7、corporated in the hydrogen line so thatmeasurement and control of the gas flow may be maintained.The hydrogen line shall discharge at the upper levels of theenvelope and shall be baffled by a suitable diffusing device sothat no direct stream of the gas will play upon the testspecimens.2.2 Specimen S
8、upportA suitably designed support andclamping device for holding the specimen within the envelopeduring testing.This support,which may be rigidly fixed orcapable of being raised into or lowered from the envelope,shall be made from a suitable metallic conductor so thatelectrical current from the powe
9、r supply may be used to heatthe test specimen.An insulated clamping fixture shall beprovided at the top of the support so that the hairpin testspecimen will be firmly held.This clamping device shall becapable of rotating 90 on its axis in order that the testspecimen may be heated both in a vertical-
10、position with itsapex down and in a horizontal position.A means shall beprovided for accomplishing this rotation without requiring theremoval of the test specimen from the clamping fixture.2.3 WeightsAset of weights comprising loads of 3,4,6,7,9,10,and 13 lb(1.4,1.8,2.7,3.2,4.1,4.5,and 5.9 kg).Ahook
11、shall be provided for attaching the required weight to the apexof the test specimen.This hook should be made from tungstenwire and should be capable of supporting the heaviest weightat the elevated temperature of testing,without fear of breaking.NOTE1A tungsten wire with a diameter of 0.080 in.is re
12、commendedfor use as a hook.2.4 Cathetometer or any other suitable instrument for mea-surement of the vertical displacement of the test specimen thatresults from the sag test.This instrument shall have a suitablescale so that movement of the specimen of as little as 0.5 mmmay be read.2.5 Power Supply
13、A supply of electric current sufficient toheat the test specimen to the required test temperatures.Ameter shall be provided in this supply to permit measurementof the current to an accuracy of 62%.3.Materials3.1 Hydrogen used for the test atmosphere shall have apurity meeting the following requireme
14、nts:3.1.1 Moisture(water),not more than 2.5 g/1000 ft3(2.5g/28 m3)as indicated by a dew point of 65C or below.3.1.2 Oxygen,not more than 10 ppm.3.1.3 Hydrocarbons(plus CO and CO2),not more than 20ppm.3.1.4 Nitrogen,not more than12%.4.Test Specimen4.1 SurfaceThe specimen of tungsten wire to be tested
15、 forsag shall have a clean,bright surface and shall be at least 15 in.in length.1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.03 on MetallicMaterials.Current edition approved June 1,2014.Published July 2014.Origin
16、ally approvedin 1952.Last previous edition approved in 2009 as F269 60(2009).DOI:10.1520/F0269-60R14.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.2 FormingWith the aid of external heat,the test speci-men shall be bent into a hairpin-shape until the distancebetween the ends is 1 in.The hairpin is formed by bending thewire around a pin whose diameter is approximately twice thatof the test specimen.NOTE2Note more than 20%of the hair
