ASTM D374M-99(2005)
(Test Method)Standard Test Methods for Thickness of Solid Electrical Insulation (Metric)
Standard Test Methods for Thickness of Solid Electrical Insulation (Metric)
SCOPE
1.1 These test methods cover the determination of the thickness of several types of solid electrical insulating materials employing recommended techniques. Use these test methods except as otherwise required by a material specification.
1.2 The values stated in SI units are the standard.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D374M −99(Reapproved 2005) An American National Standard
Standard Test Methods for
Thickness of Solid Electrical Insulation (Metric)
This standard is issued under the fixed designation D374M; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, 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.
1. Scope 4. Summary of Test Methods
1.1 These test methods cover the determination of the 4.1 This standard provides eight different test methods for
thickness of several types of solid electrical insulating materi- the measurement of thickness of solid electrical insulation
materials. The test methods (identified as Methods A through
als employing recommended techniques. Use these test meth-
ods except as otherwise required by a material specification. H) employ different micrometers that exert various pressures
for varying times upon specimens of different geometries.
1.2 The values stated in SI units are the standard.
Table 1 and Table 2 display basic differences of each test
1.3 This standard does not purport to address all of the
method and identify methods applicable for use on various
safety concerns, if any, associated with its use. It is the
categories of materials.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 5. Significance and Use
bility of regulatory limitations prior to use.
5.1 Some electrical properties, such as dielectric strength,
vary with the thickness of the material. Determination of
2. Referenced Documents
certain properties, such as relative permittivity (dielectric
constant) and volume resistivity, usually require a knowledge
2.1 ASTM Standards:
of the thickness. Design and construction of electrical machin-
D1711 Terminology Relating to Electrical Insulation
ery require that the thickness of insulation be known.
D6054 Practice for Conditioning Electrical Insulating Mate-
rials for Testing
6. Apparatus
E252 Test Method for Thickness of Foil, Thin Sheet, and
Film by Mass Measurement 6.1 Apparatus A— Machinist’s Micrometer Caliper with
Calibrated Ratchet or Friction Thimble:
3. Terminology 6.1.1 ApparatusAis a micrometer caliper without a locking
device but is equipped with either a calibrated ratchet or a
3.1 Refer to Terminology D1711 for definitions pertinent to
friction thimble. By use of a proper manipulative procedure
this standard.
andacalibratedspring(seeAnnexA1),thepressureexertedon
3.2 Definitions of Terms Specific to This Standard:
the specimen is controllable.
3.2.1 absolute uncertainty (of a measurement), n—the
6.1.2 Use an instrument constructed with a vernier capable
smallest division that may be read directly on the instrument
of measurement to the nearest 2 µm.
used for measurement.
6.1.3 Use an instrument with the diameter of the anvil and
spindle surfaces (which contact the specimen) of 6.25 6 0.05
3.2.2 micrometer, n—an instrument for measuring any di-
mm.
mension with absolute uncertainty of 25 µm or smaller.
6.1.4 Use an instrument conforming to the requirements of
3.2.3 1micron,µm,n—adimensionequivalentto0.0000010
7.1, 7.2, 7.5, 7.6.1, and 7.6.2.
m.
6.1.5 Periodically, test the micrometer for conformance to
the requirements of 6.1.4.
6.2 Apparatus B—Machinist’s Micrometer without a
These test methods are under the jurisdiction of ASTM Committee D09 on
Ratchet:
Electrical and Electronic Insulating Materials and are the direct responsibility of
Subcommittee D09.12 on Electrical Tests. 6.2.1 Apparatus B is a micrometer caliper without a locking
Current edition approved Sept. 1, 2005. Published October 2005. Originally
device.
approved in 1968. Last previous edition approved in 1999 as D374M – 99. DOI:
6.2.2 Use an instrument constructed with a vernier capable
10.1520/D0374M-99R05.
2 of measurement to the nearest 2 µm.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Hereinafter referred to as a machinist’s micrometer.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D374M−99 (2005)
TABLE 1 Methods Suitable for Specific Materials
6.3.2 The preferred design and construction of manually
Material Method operated dead-weight dial-type micrometers calls for a limit on
Plastic sheet and film A B C or D the force applied to the presser foot. The limit is related to the
Paper (all thicknesses) E
compressive characteristics of the material being measured.
Paper (over 50 µm thickness) F or G
6.3.2.1 The force applied to the presser foot spindle and the
Rubber and other elastomers H
weight necessary to move the pointer upward from the zero
position shall be less than the force that will cause permanent
TABLE 2 Method Parameter Differences deformation of the specimen. The force applied to the presser
footspindleandtheweightnecessarytojustpreventmovement
Diameter of Pressure on
Method Apparatus Presser Foot or Specimen, kPa
of the pointer from a higher to a lower reading shall be more
Spindle, mm approximate
than the minimum permissible force specified for a specimen.
A Machinist micrometer with 6 not specified
calibrated ratchet or thimble 6.4 Apparatus D—Motor-Operated Dead-Weight Dial
B Machinist micrometer without 6 unknown
Gage:
ratchet/thimble
6.4.1 Except as additionally defined in this section, use an
C Dead-weight dial type bench 3to13 4to900
micrometer—manual instrument that conforms to the requirements of 6.3.An
D Dead-weight dial type bench 3to13 4to900
electronic instrument having a digital readout in place of the
micrometer—motor operated
dial indicator is permitted if that instrument meets the other
E Dead-weight dial type bench 6 172
micrometer—motor operated requirements of 6.3 and 6.4.
F Dead-weight dial type bench 6 172
6.4.2 Use a motor operated instrument having a presser foot
micrometer—manual
spindle that is lifted and lowered by a constant speed motor
G Machinist micrometer with 6 172
calibrated ratchet or thimble
through a mechanical linkage such that the rate of descent (for
H Dead-weight dial type bench 627
a specified range of distances between the presser foot surface
micrometer—manual
and the anvil) and the dwell time on the specimen are within
thelimitsspecifiedforthematerialbeingmeasured.Designthe
mechanical linkage so that the only downward force upon the
6.2.3 Use an instrument with the diameter of the anvil and
presserfootspindleisthatofgravityupontheweightedspindle
spindle surfaces (which contact the specimen) of 6.25 6 0.05
assembly without any additional force exerted by the lifting/
mm.
lowering mechanism.
6.2.4 Use an instrument conforming to the requirements of
6.4.2.1 The preferred design and construction of motor
7.1, 7.2, 7.5.1, 7.5.2, 7.5.3, 7.6.1, and 7.6.3.
operated dead-weight dial-type micrometers calls for a limit on
6.2.5 Periodically, examine and test the micrometer for
the force applied to the presser foot. The limit is related to the
conformance to the requirements of 6.2.4.
compressive characteristics of the material being measured.
6.3 Apparatus C— Manually-Operated, Dead-Weight, Dial-
6.4.2.2 The force applied to the presser foot spindle and the
Type Thickness Gage: weight necessary to move the pointer upward from the zero
6.3.1 Use a dead-weight dial-type gage in accordance with position shall be less than the force that will cause permanent
the requirements of 7.1, 7.3, 7.4, 7.6.1, 7.6.4, that has: deformation of the specimen. The force applied to the presser
6.3.1.1 Apresser foot that moves in an axis perpendicular to footspindleandtheweightnecessarytojustpreventmovement
the anvil face, of the pointer from a higher to a lower reading must be more
6.3.1.2 The surfaces of the presser foot and the anvil (which than the minimum permissible force specified for a specimen.
contact the specimen) parallel to within 2 µm (see 7.3),
7. Calibration (General Considerations for Care and Use
6.3.1.3 A vertical dial spindle,
of Each of the Various Pieces of Apparatus for
6.3.1.4 Adial indicator essentially friction-free and capable
Thickness Measurements)
of repeatable readings within 61.2 µm at zero setting, or on a
steel gage block,
7.1 Good testing practices require clean anvil and presser
6.3.1.5 A frame, housing the indicator, of such rigidity that
foot surfaces for any micrometer instrument. Prior to calibra-
a load of 13 N applied to the dial housing, out of contact with
tion or thickness measurements, clean such surfaces by insert-
the presser foot spindle (or any weight attached thereto) will
ing a piece of smooth, clean bond paper between the anvil and
produce a deflection of the frame not greater than the smallest
thepresserfootandslowlymovingthebondpaperbetweenthe
scale division on the indicator dial, and
surfaces. During measurements, check the zero setting fre-
6.3.1.6 A dial diameter at least 50 mm and graduated
quently. Failure to repeat the zero setting may be evidence of
continuously to read directly to the nearest 2 µm. If necessary,
dirt on the surfaces.
equip the dial with a revolution counter that displays the
NOTE 1—Avoid pulling any edge of the bond paper between the
number of complete revolutions of the large hand.
surfaces to reduce the probability of depositing any lint particles on the
6.3.1.7 An electronic instrument having a digital readout in
surfaces.
place of the dial indicator is permitted if that instrument meets
7.2 The parallelism requirements for machinist’s microm-
the other requirements of 6.3.
eters demand that observed differences of readings on a pair of
screw-thread-pitch wires or a pair of standard 6-mm nominal
Hereinafter referred to as a dial gage. diameter plug gages be not greater than 2 µm. Spring-wire
D374M−99 (2005)
stockormusic-wireofknowndiameteraresuitablesubstitutes. 7.4.2.3 A symmetrical concave or convex surface forms
The wire (or the plug gage) has a diameter dimension that is concentric circular fringes. Their number is a measure of
known to be within 61.3 µm. Diameter dimensions may vary deviation from flatness.
by an amount approximately equal to the axial movement of
7.4.2.4 An unsymmetrical concave or convex surface forms
the spindle when the wire (or the plug gage) is rotated through
a series of curved fringes that cut the periphery of the
180°.
micrometer surface. The number of fringes cut by a straight
line connecting the terminals of any fringes is a measure of the
7.2.1 Lacking a detailed procedure supplied by the instru-
ment manufacturer, confirm the parallelism requirements of deviation from flatness.
machinist’s micrometers using the following procedure:
7.5 Machinist’s Micrometer Requirements :
7.2.1.1 Closethemicrometeronthescrew-thread-pitchwire
7.5.1 The requirements for zero reading of machinist’s
or the plug gage in accordance with the calibration procedure
micrometers are met when ten closings of the spindle onto the
of 7.6.2 or 7.6.3 as appropriate.
anvil, in accordance with 7.6.2.3 or 7.6.3.3 as appropriate,
7.2.1.2 Observe and record the thickness indicated.
result in ten zero readings. The condition of zero reading is
7.2.1.3 Move the screw-thread-pitch wire or the plug gage satisfied when examinations with a low-power magnifying
to a different position between the presser foot and the anvil
glass show that at least 66 % of the width of the zero
and repeat 7.2.1.1 and 7.2.1.2. graduation mark on the barrel coincides with at least 66 % of
the width of the reference mark.
7.2.1.4 If the difference between any pair of readings is
greater than 2.5 µm, the surfaces are NOT parallel. 7.5.2 Proper maintenance of a machinist’s micrometer may
require adjusting the instrument for wear of the micrometer
7.3 Lacking a detailed procedure supplied by the instrument
screw so that the spindle has no perceptible lateral or longitu-
manufacturer, confirm the requirements for parallelism of
dinal looseness yet rotates with a torque load of less than
dial-type micrometers given in 6.3.1.2 by placing a hardened
0.0018 Nm. If this is not achievable after disassembly,
steelball(suchasisusedinaballbearing)ofsuitable diameter
cleaning, and lubrication, replace the instrument.
between the presser foot and the anvil. Mount the ball in a
7.5.3 After the zero reading has been checked, use the
fork-shaped holder to allow the ball to be conveniently moved
calibration procedure of 7.6.2 or 7.6.3 (as appropriate for the
from one location to another between the presser foot and the
machinist’s micrometer under examination) to check for maxi-
anvil. The balls used commercially in ball bearings are almost
mum acceptable error in the machinist’s micrometer screw.
perfect spheres having diameters constant within a fraction of
7.5.3.1 Use selected feeler-gage blades with known thick-
a micron.
nesses to within 60.5 µm to check micrometers calibrated in
NOTE 2—Exercise care with this procedure. Calculations using the
metric units at approximately 50, 130, and 250-µm points. Use
equations in X1.3.2 show that the use of a 0.68-kg mass and a ball
standard gage blocks at points greater than 25 µm.
between the hardened surfaces of presser foot and anvil can result in
7.5.3.2 At each point checked, take ten readings. Calculate
dimples in the anvil or presser foot surfaces caused by exceeding the yield
the arithmetic mean of these ten readings.
stress of the surfaces.
7.5.3.3 The machinist’s micrometer screw error is within
7.3.1 Observe and record the diameter as measured by the
requirements if the difference between the mean value of
micrometer at one location.
7.5.3.2 and the gage block (or feeler-gage blade) thickness is
7.3.2 Move the ball to another location and repeat the
not more than 2.5 µm.
measurement.
7.5.4 Calibration of Spindle Pressure in Machinist’s Mi-
7.3.3 If the difference between any pair of readings is
crometer with Ratchet or Friction Thimble:
greater than 2.5 µm, the surfaces are NOT parallel.
7.5.4.1 See Annex A1, which details the apparatus and
procedure required for this calibration.
7.4 Lacking a detailed procedure supplied by the instrument
manufacturer, confirm the flatness of the anvil and the spindle
7.6 Calibration of Micrometers :
surface of a micrometer or dial gage by use of an optical flat
7.6.1 Calibrate all micrometers in a standard laboratory
which has clean surfaces. Surfaces shall be flat within 2 µm.
atmosphere maintained at 50 % relative humidity and 23°C or
...
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