1、Designation: D374/D374M 16 An American National StandardStandard Test Methods forThickness of Solid Electrical Insulation1This standard is issued under the fixed designation D374/D374M; the number immediately following the designation indicates the yearof original adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 These test method
3、s cover the determination of thethickness of several types of solid electrical insulating materi-als employing recommended techniques. Use these test meth-ods except as otherwise required by a material specification.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separ
4、ately as standard. The values stated ineach system are not necessarily exact equivalents; therefore,each system shall be used independently of the other. It ispossible that combining values from the two systems will resultin non-conformance with the standard.1.3 This standard does not purport to add
5、ress 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1711 Termino
6、logy Relating to Electrical InsulationD6054 Practice for Conditioning Electrical Insulating Mate-rials for Testing (Withdrawn 2012)3E252 Test Method for Thickness of Foil, Thin Sheet, andFilm by Mass Measurement3. Terminology3.1 Refer to Terminology D1711 for definitions pertinent tothis standard.3.
7、2 Definitions of Terms Specific to This Standard:3.2.1 1 micron, m, na dimension equivalent to0.03937 mils.3.2.2 1 mil, na dimension equivalent to 0.0010 in.3.2.3 absolute uncertainty (of a measurement), nthesmallest division able to be read directly on the instrument usedfor measurement.3.2.4 micro
8、meter, nan instrument for measuring any di-mension with absolute uncertainty of 1 mil 25 m or smaller.4. Summary of Test Methods4.1 This standard provides eight different test methods forthe measurement of thickness of solid electrical insulationmaterials. The test methods (identified as Test Method
9、s Athrough H) employ different micrometers that exert variouspressures for varying times upon specimens of different geom-etries. Tables 1 and 2 display basic differences of each testmethod and identify test methods applicable for use on variouscategories of materials.5. Significance and Use5.1 Some
10、 electrical properties, such as dielectric strength,vary with the thickness of the material. Determination ofcertain properties, such as relative permittivity (dielectricconstant) and volume resistivity, usually require a knowledgeof the thickness. Design and construction of electrical machin-ery re
11、quire that the thickness of insulation be known.6. Apparatus6.1 Apparatus AMachinists Micrometer Caliper4withCalibrated Ratchet or Friction Thimble:6.1.1 Apparatus A is a micrometer caliper without a lockingdevice but is equipped with either a calibrated ratchet or afriction thimble. By use of a pro
12、per manipulative procedureand a calibrated spring (see AnnexA1), the pressure exerted onthe specimen is controllable.6.1.2 Use an instrument constructed with a vernier capableof measurement to the nearest 0.1 mil 2 m.6.1.3 Use an instrument with the diameter of the anvil andspindle surfaces (which c
13、ontact the specimen) of 250 6 1 mil6.35 6 0.05 mm.1These test methods are under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and are the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved June 1, 2016. Published August
14、2016. Originallyapproved in 1933. Last previous edition approved in 2004 as D374 99 (2004)which was withdrawn January 2013 and reinstated in June 2016. DOI: 10.1520/D0374_D0374M-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.or
15、g. 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.4Hereinafter referred to as a machinists micrometer.Copyright ASTM International, 100 Barr Harbo
16、r Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.1.4 Use an instrument conforming to the requirements of7.1, 7.2, 7.5, 7.6.1, and 7.6.2.6.1.5 Periodically, test the micrometer for conformance tothe requirements of 6.1.4.6.2 Apparatus BMachinists Micrometer Without aRatchet:6.2
17、.1 Apparatus B is a micrometer caliper without a lockingdevice.6.2.2 Use an instrument constructed with a vernier capableof measurement to the nearest 0.1 mil 2 m.6.2.3 Use an instrument with the diameter of the anvil andspindle surfaces (which contact the specimen) 250 6 1 mil6.35 6 0.05 mm.6.2.4 U
18、se an instrument conforming to the requirements of7.1, 7.2, 7.5.1, 7.5.2, 7.5.3, 7.6.1, and 7.6.3.6.2.5 Periodically, examine and test the micrometer forconformance to the requirements of 6.2.4.6.3 Apparatus CManually-Operated, Dead-Weight, DialType Thickness Gauge:56.3.1 Use a dead-weight dial-type
19、 gauge in accordance withthe requirements of 7.1, 7.3, 7.4, 7.6.1, 7.6.4, that has:6.3.1.1 Apresser foot that moves in an axis perpendicular tothe anvil face,6.3.1.2 The surfaces of the presser foot and the anvil (whichcontact the specimen) parallel to within 0.079 mil 2 m or 0.1mil 2.54 m (see 7.3)
20、,6.3.1.3 A vertical dial spindle,6.3.1.4 A dial indicator essentially friction-free and capableof repeatable readings within 60.05 mil 61.2 m at zerosetting, or on a steel gauge block,6.3.1.5 A frame, housing the indicator, of such rigidity thata load of 2.92 lbf 13 N or 3 lbf 13.34 N applied to the
21、 dialhousing, out of contact with the presser foot spindle (or anyweight attached thereto) will produce a deflection of the framenot greater than the smallest scale division on the indicatordial, and,6.3.1.6 A dial diameter at least 2 in. 50 mm and graduatedcontinuously to read directly to the neare
22、st 0.079 mil 2 m or0.1 mil 2.54 m. If necessary, equip the dial with a revolutioncounter that displays the number of complete revolutions of thelarge hand.6.3.1.7 An electronic instrument having a digital readout inplace of the dial indicator is permitted if that instrument meetsthe other requiremen
23、ts of 6.3.6.3.2 The preferred design and construction of manuallyoperated dead-weight dial-type micrometers calls for a limit onthe force applied to the presser foot. The limit is related to thecompressive characteristics of the material being measured.6.3.2.1 The force applied to the presser foot s
24、pindle and theweight necessary to move the pointer upward from the zeroposition shall be less than the force that will cause permanentdeformation of the specimen. The force applied to the presserfoot spindle and the weight necessary to just prevent movementof the pointer from a higher to a lower rea
25、ding shall be morethan the minimum permissible force specified for a specimen.6.4 Apparatus DMotor-Operated Dead-Weight DialGauge:6.4.1 Except as additionally defined in this section, use aninstrument that conforms to the requirements of 6.3.Anelectronic instrument having a digital readout in place
26、of thedial indicator is permitted if that instrument meets the otherrequirements of 6.3 and 6.4.6.4.2 Use a motor operated instrument having a presser footspindle that is lifted and lowered by a constant speed motorthrough a mechanical linkage such that the rate of descent (fora specified range of d
27、istances between the presser foot surfaceand the anvil) and the dwell time on the specimen are withinthe limits specified for the material being measured. Design themechanical linkage so that the only downward force upon thepresser foot spindle is that of gravity upon the weighted spindleassembly wi
28、thout any additional force exerted by the lifting/lowering mechanism.6.4.2.1 The preferred design and construction of motoroperated dead-weight dial-type micrometers calls for a limit onthe force applied to the presser foot. The limit is related to thecompressive characteristics of the material bein
29、g measured.6.4.2.2 The force applied to the presser foot spindle and theweight necessary to move the pointer upward from the zeroposition shall be less than the force that will cause permanentdeformation of the specimen. The force applied to the presserfoot spindle and the weight necessary to just p
30、revent movementof the pointer from a higher to a lower reading needs to bemore than the minimum permissible force specified for aspecimen.5Herein referred to as a dial gauge.TABLE 1 Test Methods Suitable for Specific MaterialsMaterial Test MethodPlastic sheet and film A B C or DPaper (all thicknesse
31、s) EPaper (over 2 mils 50 m thickness) F or GRubber and other elastomers HTABLE 2 Test Method Parameter DifferencesTestMethodApparatusDiameter ofPresser Footor Spindle,mils mmPressure onSpecimen,approximate,PSI kPaapproximateA Machinist micrometer withcalibrated ratchet or thimble250 6 not specified
32、B Machinist micrometerwithout ratchet/thimble250 6 unknownC Dead-weight dial type benchmicrometerManual125 to 5003 to 130.5 to 1304 to 900D Dead-weight dial type benchmicrometerMotoroperated125 to 5003 to 130.5 to 1304 to 900E Dead-weight dial type benchmicrometerMotoroperated250 6 25 172F Dead-weig
33、ht dial type benchmicrometerManual250 6 25 172G Machinist micrometer withcalibrated ratchet or thimble250 6 25 172H Dead-weight dial type benchmicrometerManual250 6 4 27D374/D374M 1627. Calibration (General Considerations for Care and Useof Each of the Various Pieces of Apparatus forThickness Measur
34、ements)7.1 Good testing practices require clean anvil and presserfoot surfaces for any micrometer instrument. Prior to calibra-tion or thickness measurements, clean such surfaces by insert-ing a piece of smooth, clean bond paper between the anvil andthe presser foot and slowly moving the bond paper
35、between thesurfaces. During measurements, check the zero setting fre-quently. It is possible that failure to repeat the zero setting willbe evidence of dirt or contamination on the surfaces.NOTE 1Avoid pulling any edge of the bond paper between thesurfaces to reduce the probability of depositing any
36、 lint particles on thesurfaces.7.2 The parallelism requirements for machinists microm-eters demand that observed differences of readings on a pair ofscrew-thread-pitch wires or a pair of standard 250 mil 6.35mm or 236 mil 6 mm nominal diameter plug gauges be notgreater than 0.079 mil 2 m or 0.1 mil
37、2.5 m. Spring-wirestock or music-wire of known diameter are suitable substitutes.The wire (or the plug gauge) has a diameter dimension that isknown to be within 60.05 mil 61.3 m. It is possible thatdiameter dimensions will vary by an amount approximatelyequal to the axial movement of the spindle whe
38、n the wire (orthe plug gauge) is rotated through 180.7.2.1 Lacking a detailed procedure supplied by the instru-ment manufacturer, confirm the parallelism requirements ofmachinists micrometers using the following procedure:7.2.1.1 Close the micrometer on the screw-thread-pitch wireor the plug gauge i
39、n accordance with the calibration procedureof 7.6.2 or 7.6.3 as appropriate.7.2.1.2 Observe and record the thickness indicated.7.2.1.3 Move the screw-thread-pitch wire or the plug gaugeto a different position between the presser foot and the anviland repeat 7.2.1.1 and 7.2.1.2.7.2.1.4 If the differe
40、nce between any pair of readings isgreater than 0.1 mil 2.5 m, the surfaces are NOT parallel.7.3 Lacking a detailed procedure supplied by the instrumentmanufacturer, confirm the requirements for parallelism ofdial-type micrometers given in 6.3.1.2 by placing a hardenedsteel ball (such as is used in
41、a ball bearing) of suitable diameterbetween the presser foot and the anvil. Mount the ball in afork-shaped holder to allow the ball to be conveniently movedfrom one location to another between the presser foot and theanvil. The balls used commercially in ball bearings are almostperfect spheres havin
42、g diameters constant within a few micro-inches micrometres.NOTE 2Exercise care with this procedure. Calculations using theequations in X1.3.2 show that it is possible that the use of a 24-oz0.68 kg weight on a ball between the hardened surfaces of presser footand anvil will result in dimples in the
43、anvil or presser foot surfaces causedby exceeding the yield stress of the surfaces.7.3.1 Observe and record the diameter as measured by themicrometer at one location.7.3.2 Move the ball to another location and repeat themeasurement.7.3.3 If the difference between any pair of readings isgreater than
44、0.1 mil 2.5 m, the surfaces are NOT parallel.7.4 Lacking a detailed procedure supplied by the instrumentmanufacturer, confirm the flatness of the anvil and the spindlesurface of a micrometer or dial gauge by use of an optical flatwhich has clean surfaces. Surfaces shall be flat within 0.05 mil1.3 m.
45、7.4.1 After cleaning the micrometer surfaces (see 7.1), placethe optical flat on the anvil and close the presser foot asdescribed in 7.6.2 or 7.6.3 or 7.6.4 or 7.6.5 as appropriate.7.4.2 When illuminated by diffused daylight, interferencebands are formed between the surfaces of the flat and thesurfa
46、ces of the micrometer. The shape, location, and number ofthese bands indicate the deviation from flatness in incrementsof half the average wavelengths of white light, which is takenas 0.079 mil 2 m or 0.1 mil 2.5 m.7.4.2.1 A flat surface forms straight parallel fringes at equalintervals.7.4.2.2 A gr
47、ooved surface forms straight parallel fringes atunequal intervals.7.4.2.3 A symmetrical concave or convex surface formsconcentric circular fringes. Their number is a measure ofdeviation from flatness.7.4.2.4 An unsymmetrical concave or convex surface formsa series of curved fringes that cut the peri
48、phery of themicrometer surface. The number of fringes cut by a straightline connecting the terminals of any fringes is a measure of thedeviation from flatness.7.5 Machinists Micrometer Requirements :7.5.1 The requirements for zero reading of machinistsmicrometers are met when ten closings of the spi
49、ndle onto theanvil, in accordance with 7.6.2.3 or 7.6.3.3 as appropriate,result in ten zero readings. The condition of zero reading issatisfied when examinations with a low-power magnifyingglass show that at least 66 % of the width of the zerograduation mark on the barrel coincides with at least 66 % ofthe width of the reference mark.7.5.2 Proper maintenance of a machinists micrometer re-quires adjusting the instrument for wear of the micrometerscrew so that
