1、Designation: D 374M 99 (Reapproved 2005)METRICAn American National StandardStandard Test Methods forThickness of Solid Electrical Insulation (Metric)1This standard is issued under the fixed designation D 374M; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the determination of thethickness of several types of
3、 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 SI units are the standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated wi
4、th 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:2D 1711 Terminology Relating to Electrical InsulationD 6054 Practic
5、e for Conditioning Electrical Insulating Ma-terials for TestingE 252 Test Method for Thickness of Thin Foil and Film byWeighing3. Terminology3.1 Refer to Terminology D 1711 for definitions pertinent tothis standard.3.2 Definitions of Terms Specific to This Standard:3.2.1 absolute uncertainty (of a m
6、easurement), nthesmallest division that may be read directly on the instrumentused for measurement.3.2.2 micrometer, nan instrument for measuring any di-mension with absolute uncertainty of 25 m or smaller.3.2.3 1 micron, m, na dimension equivalent to0.0000010 m.4. Summary of Test Methods4.1 This st
7、andard provides eight different test methods forthe measurement of thickness of solid electrical insulationmaterials. The test methods (identified as Methods A throughH) employ different micrometers that exert various pressuresfor varying times upon specimens of different geometries.Table 1 and Tabl
8、e 2 display basic differences of each testmethod and identify methods applicable for use on variouscategories of materials.5. Significance and Use5.1 Some electrical properties, such as dielectric strength,vary with the thickness of the material. Determination ofcertain properties, such as relative
9、permittivity (dielectricconstant) and volume resistivity, usually require a knowledgeof the thickness. Design and construction of electrical machin-ery require that the thickness of insulation be known.6. Apparatus6.1 Apparatus A Machinists Micrometer Caliper3withCalibrated Ratchet or Friction Thimb
10、le: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 proper manipulative procedureand a calibrated spring (seeAnnexA1), the pressure exerted onthe specimen is controllable.6.1.2 Use an instrument const
11、ructed with a vernier capableof measurement to the nearest 2 m.6.1.3 Use an instrument with the diameter of the anvil andspindle surfaces (which contact the specimen) of 6.25 6 0.05mm.6.1.4 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 th
12、e micrometer for conformance tothe requirements of 6.1.4.6.2 Apparatus BMachinists Micrometer without aRatchet: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 T
13、ests.Current edition approved Sept. 1, 2005. Published October 2005. Originallyapproved in 1968. Last previous edition approved in 1999 as D 374M 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStanda
14、rds volume information, refer to the standards Document Summary page onthe ASTM website.3Hereinafter referred to as a machinists micrometer.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.2.1 Apparatus B is a micrometer caliper wit
15、hout a lockingdevice.6.2.2 Use an instrument constructed with a vernier capableof measurement to the nearest 2 m.6.2.3 Use an instrument with the diameter of the anvil andspindle surfaces (which contact the specimen) of 6.25 6 0.05mm.6.2.4 Use an instrument conforming to the requirements of7.1, 7.2,
16、 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 C Manually-Operated, Dead-Weight, Di-alType Thickness Gage:46.3.1 Use a dead-weight dial-type gage in accordance withthe requirements of 7.1, 7.3, 7.4,
17、 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 2 m (see 7.3),6.3.1.3 A vertical dial spindle,6.3.1.4 A dial indicator essentially friction-free an
18、d capableof repeatable readings within 61.2 m at zero setting, or on asteel gage block,6.3.1.5 A frame, housing the indicator, of such rigidity thata load of 13 N applied to the dial housing, out of contact withthe presser foot spindle (or any weight attached thereto) willproduce a deflection of the
19、 frame not greater than the smallestscale division on the indicator dial, and6.3.1.6 A dial diameter at least 50 mm and graduatedcontinuously to read directly to the nearest 2 m. If necessary,equip the dial with a revolution counter that displays thenumber of complete revolutions of the large hand.6
20、.3.1.7 An electronic instrument having a digital readout inplace of the dial indicator is permitted if that instrument meetsthe other requirements 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 pre
21、sser foot. The limit is related to thecompressive characteristics of the material being measured.6.3.2.1 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 spe
22、cimen. The force applied to the presserfoot spindle and the weight necessary to just prevent movementof the pointer from a higher to a lower reading shall be morethan the minimum permissible force specified for a specimen.6.4 Apparatus DMotor-Operated Dead-Weight DialGage:6.4.1 Except as additionall
23、y defined in this section, use aninstrument that conforms to the requirements of 6.3.Anelectronic instrument having a digital readout in place 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 footsp
24、indle that is lifted and lowered by a constant speed motorthrough a mechanical linkage such that the rate of descent (fora specified range of distances between the presser foot surfaceand the anvil) and the dwell time on the specimen are withinthe limits specified for the material being measured. De
25、sign themechanical linkage so that the only downward force upon thepresser foot spindle is that of gravity upon the weighted spindleassembly without any additional force exerted by the lifting/lowering mechanism.6.4.2.1 The preferred design and construction of motoroperated dead-weight dial-type mic
26、rometers calls for a limit onthe force applied to the presser foot. The limit is related to thecompressive characteristics of the material being 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
27、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 reading must be morethan the minimum permissible force specified for a specimen.7. Calibration (Genera
28、l Considerations for Care and Useof Each of the Various Pieces of Apparatus forThickness Measurements)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 s
29、mooth, clean bond paper between the anvil andthe presser foot and slowly moving the bond paper between thesurfaces. During measurements, check the zero setting fre-quently. Failure to repeat the zero setting may be evidence ofdirt on the surfaces.NOTE 1Avoid pulling any edge of the bond paper betwee
30、n the4Hereinafter referred to as a dial gage.TABLE 1 Methods Suitable for Specific MaterialsMaterial MethodPlastic sheet and film A B C or DPaper (all thicknesses) EPaper (over 50 m thickness) F or GRubber and other elastomers HTABLE 2 Method Parameter DifferencesMethod ApparatusDiameter ofPresser F
31、oot orSpindle, mmPressure onSpecimen, kPaapproximateA Machinist micrometer withcalibrated ratchet or thimble6 not specifiedB Machinist micrometer withoutratchet/thimble6 unknownC Dead-weight dial type benchmicrometermanual3to13 4to900D Dead-weight dial type benchmicrometermotor operated3to13 4to900E
32、 Dead-weight dial type benchmicrometermotor operated6 172F Dead-weight dial type benchmicrometermanual6 172G Machinist micrometer withcalibrated ratchet or thimble6 172H Dead-weight dial type benchmicrometermanual627D 374M 99 (2005)2surfaces to reduce the probability of depositing any lint particles
33、 on thesurfaces.7.2 The parallelism requirements for machinists microme-ters demand that observed differences of readings on a pair ofscrew-thread-pitch wires or a pair of standard 6-mm nominaldiameter plug gages be not greater than 2 m. Spring-wirestock or music-wire of known diameter are suitable
34、substitutes.The wire (or the plug gage) has a diameter dimension that isknown to be within 61.3 m. Diameter dimensions may varyby an amount approximately equal to the axial movement ofthe spindle when the wire (or the plug gage) is rotated through180.7.2.1 Lacking a detailed procedure supplied by th
35、e 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 gage in accordance with the calibration procedureof 7.6.2 or 7.6.3 as appropriate.7.2.1.2 Observe and record
36、the thickness indicated.7.2.1.3 Move the screw-thread-pitch wire or the plug gageto 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 difference between any pair of readings isgreater than 2.5 m, the surfaces are NOT parallel.7.3 Lacking a detai
37、led 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 a ball bearing) of suitable diameterbetween the presser foot and the anvil. Mount the ball in afork-shaped holde
38、r 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 having diameters constant within a fraction ofa micron.NOTE 2Exercise care with this procedure. Calculations using th
39、eequations in X1.3.2 show that the use of a 0.68-kg mass and a ballbetween the hardened surfaces of presser foot and anvil can result indimples in the anvil or presser foot surfaces caused by exceeding the yieldstress of the surfaces.7.3.1 Observe and record the diameter as measured by themicrometer
40、 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 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 t
41、he spindlesurface of a micrometer or dial gage by use of an optical flatwhich has clean surfaces. Surfaces shall be flat within 2 m.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
42、 appropriate.7.4.2 When illuminated by diffused daylight, interferencebands are formed between the surfaces of the flat and thesurfaces of the micrometer. The shape, location, and number ofthese bands indicate the deviation from flatness in incrementsof half the average wavelengths of white light, w
43、hich is takenas 0.2 m.7.4.2.1 A flat surface forms straight parallel fringes at equalintervals.7.4.2.2 A grooved 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 fl
44、atness.7.4.2.4 An unsymmetrical concave or convex surface formsa series of curved fringes that cut the periphery 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 Requirem
45、ents:7.5.1 The requirements for zero reading of machinistsmicrometers are met when ten closings of the spindle 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
46、 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 mayrequire adjusting the instrument for wear of the micrometerscrew so that the spindle has no perceptible
47、 lateral or longitu-dinal looseness yet rotates with a torque load of less than0.0018 Nm. If this is not achievable after disassembly, clean-ing, and lubrication, replace the instrument.7.5.3 After the zero reading has been checked, use thecalibration procedure of 7.6.2 or 7.6.3 (as appropriate for
48、themachinists micrometer under examination) to check for maxi-mum acceptable error in the machinists micrometer screw.7.5.3.1 Use selected feeler-gage blades with known thick-nesses to within 60.5 m to check micrometers calibrated inmetric units at approximately 50, 130, and 250-m points. Usestandar
49、d gage blocks at points greater than 25 m.7.5.3.2 At each point checked, take ten readings. Calculatethe arithmetic mean of these ten readings.7.5.3.3 The machinists micrometer screw error is withinrequirements if the difference between the mean value of7.5.3.2 and the gage block (or feeler-gage blade) thickness isnot more than 2.5 m.7.5.4 Calibration of Spindle Pressure in Machinists Mi-crometer with Ratchet or Friction Thimble:7.5.4.1 See Annex A1, which details the apparatus andprocedure required for this calibration.7.6 Calibration of
