ASTM D374M-99
(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.
1.3 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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An American National Standard
Designation: D 374M – 99
METRIC
Standard Test Methods for
Thickness of Solid Electrical Insulation (Metric)
This standard is issued under the fixed designation D 374M; 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 (e) 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
als employing recommended techniques. Use these test meth- materials. The test methods (identified as Methods A through
ods except as otherwise required by a material specification. H) employ different micrometers that exert various pressures
1.2 The values stated in SI units are the standard. for varying times upon specimens of different geometries.
1.3 This standard does not purport to address all of the Table 1 and Table 2 display basic differences of each test
safety concerns, if any, associated with its use. It is the method and identify methods applicable for use on various
responsibility of the user of this standard to establish appro- categories of materials.
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,
2. Referenced Documents
vary with the thickness of the material. Determination of
2.1 ASTM Standards: certain properties, such as relative permittivity (dielectric
D 1711 Terminology Relating to Electrical Insulation constant) and volume resistivity, usually require a knowledge
D 6054 Practice for Conditioning Electrical Insulating Ma- of the thickness. Design and construction of electrical machin-
terials for Testing ery require that the thickness of insulation be known.
E 252 Test Method for Thickness of Thin Foil and Film by
6. Apparatus
Weighing
6.1 Apparatus A— Machinist’s Micrometer Caliper with
3. Terminology
Calibrated Ratchet or Friction Thimble:
3.1 Refer toTerminology D 1711 for definitions pertinent to 6.1.1 ApparatusAis a micrometer caliper without a locking
this standard. device but is equipped with either a calibrated ratchet or a
3.2 Definitions of Terms Specific to This Standard: friction thimble. By use of a proper manipulative procedure
3.2.1 absolute uncertainty (of a measurement), n—the and a calibrated spring (seeAnnexA1), the pressure exerted on
smallest division that may be read directly on the instrument the specimen is controllable.
used for measurement. 6.1.2 Use an instrument constructed with a vernier capable
3.2.2 micrometer, n—an instrument for measuring any di- of measurement to the nearest 2 µm.
mension with absolute uncertainty of 25 µm or smaller. 6.1.3 Use an instrument with the diameter of the anvil and
3.2.3 1 micron, µm, n—a dimension equivalent to spindle surfaces (which contact the specimen) of 6.25 6 0.05
0.0000010 m. mm.
6.1.4 Use an instrument conforming to the requirements of
7.1, 7.2, 7.5, 7.6.1, and 7.6.2.
These test methods are under the jurisdiction of ASTM Committee D-9 on
6.1.5 Periodically, test the micrometer for conformance to
Electrical and Electronic Insulating Materials and are the direct responsibility of
the requirements of 6.1.4.
Subcommittee D09.12 on Electrical Tests.
6.2 Apparatus B—Machinist’s Micrometer without a
Current edition approved March 10, 1999. Published June 1999. Originally
Ratchet:
published as D374M - 68. Last previous edition D374M - 94.
Annual Book of ASTM Standards, Vol 10.01
Annual Book of ASTM Standards, Vol 10.02.
4 5
Annual Book of ASTM Standards, Vol 02.02. 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.
D 374M
TABLE 1 Methods Suitable for Specific Materials
equip the dial with a revolution counter that displays the
Material Method number of complete revolutions of the large hand.
6.3.1.7 An electronic instrument having a digital readout in
Plastic sheet and film A B C or D
Paper (all thicknesses) E
place of the dial indicator is permitted if that instrument meets
Paper (over 50 µm thickness) F or G
the other requirements of 6.3.
Rubber and other elastomers H
6.3.2 The preferred design and construction of manually
operated dead-weight dial-type micrometers calls for a limit on
TABLE 2 Method Parameter Differences
the force applied to the presser foot. The limit is related to the
Diameter of Pressure on compressive characteristics of the material being measured.
Method Apparatus Presser Foot or Specimen, kPa
6.3.2.1 The force applied to the presser foot spindle and the
Spindle, mm approximate
weight necessary to move the pointer upward from the zero
A Machinist micrometer with 6 not specified
position shall be less than the force that will cause permanent
calibrated ratchet or thimble
deformation of the specimen. The force applied to the presser
B Machinist micrometer without 6 unknown
ratchet/thimble
footspindleandtheweightnecessarytojustpreventmovement
C Dead-weight dial type bench 3to13 4to900
of the pointer from a higher to a lower reading shall be more
micrometer—manual
than the minimum permissible force specified for a specimen.
D Dead-weight dial type bench 3to13 4to900
micrometer—motor operated
6.4 Apparatus D—Motor-Operated Dead-Weight Dial
E Dead-weight dial type bench 6 172
Gage:
micrometer—motor operated
F Dead-weight dial type bench 6 172
6.4.1 Except as additionally defined in this section, use an
micrometer—manual
instrument that conforms to the requirements of 6.3. An
G Machinist micrometer with 6 172
calibrated ratchet or thimble electronic instrument having a digital readout in place of the
H Dead-weight dial type bench 627
dial indicator is permitted if that instrument meets the other
micrometer—manual
requirements of 6.3 and 6.4.
6.4.2 Use a motor operated instrument having a presser foot
spindle that is lifted and lowered by a constant speed motor
6.2.1 Apparatus B is a micrometer caliper without a locking
through a mechanical linkage such that the rate of descent (for
device.
a specified range of distances between the presser foot surface
6.2.2 Use an instrument constructed with a vernier capable
and the anvil) and the dwell time on the specimen are within
of measurement to the nearest 2 µm.
thelimitsspecifiedforthematerialbeingmeasured.Designthe
6.2.3 Use an instrument with the diameter of the anvil and
mechanical linkage so that the only downward force upon the
spindle surfaces (which contact the specimen) of 6.25 6 0.05
presserfootspindleisthatofgravityupontheweightedspindle
mm.
assembly without any additional force exerted by the lifting/
6.2.4 Use an instrument conforming to the requirements of
lowering mechanism.
7.1, 7.2, 7.5.1, 7.5.2, 7.5.3, 7.6.1, and 7.6.3.
6.4.2.1 The preferred design and construction of motor
6.2.5 Periodically, examine and test the micrometer for
operated dead-weight dial-type micrometers calls for a limit on
conformance to the requirements of 6.2.4.
the force applied to the presser foot. The limit is related to the
6.3 Apparatus C— Manually-Operated, Dead-Weight, Di-
compressive characteristics of the material being measured.
alType Thickness Gage:
6.4.2.2 The force applied to the presser foot spindle and the
6.3.1 Use a dead-weight dial-type gage in accordance with
weight necessary to move the pointer upward from the zero
the requirements of 7.1, 7.3, 7.4, 7.6.1, 7.6.4, that has:
position shall be less than the force that will cause permanent
6.3.1.1 Apresser foot that moves in an axis perpendicular to
deformation of the specimen. The force applied to the presser
the anvil face,
footspindleandtheweightnecessarytojustpreventmovement
6.3.1.2 The surfaces of the presser foot and the anvil (which
of the pointer from a higher to a lower reading must be more
contact the specimen) parallel to within 2 µm (see 7.3),
than the minimum permissible force specified for a specimen.
6.3.1.3 A vertical dial spindle,
6.3.1.4 Adial indicator essentially friction-free and capable
7. Calibration (General Considerations for Care and Use
of repeatable readings within 61.2 µm at zero setting, or on a
of Each of the Various Pieces of Apparatus for
steel gage block,
Thickness Measurements)
6.3.1.5 A frame, housing the indicator, of such rigidity that
7.1 Good testing practices require clean anvil and presser
a load of 13 N applied to the dial housing, out of contact with
foot surfaces for any micrometer instrument. Prior to calibra-
the presser foot spindle (or any weight attached thereto) will
tion or thickness measurements, clean such surfaces by insert-
produce a deflection of the frame not greater than the smallest
ing a piece of smooth, clean bond paper between the anvil and
scale division on the indicator dial, and
the presser foot and slowly moving the bond paper between the
6.3.1.6 A dial diameter at least 50 mm and graduated
surfaces. During measurements, check the zero setting fre-
continuously to read directly to the nearest 2 µm. If necessary,
quently. Failure to repeat the zero setting may be evidence of
dirt on the surfaces.
Hereinafter referred to as a dial gage. NOTE 1—Avoid pulling any edge of the bond paper between the
D 374M
surfaces to reduce the probability of depositing any lint particles on the
7.4.2.1 Aflat surface forms straight parallel fringes at equal
surfaces.
intervals.
7.4.2.2 A grooved surface forms straight parallel fringes at
7.2 The parallelism requirements for machinist’s microme-
unequal intervals.
ters demand that observed differences of readings on a pair of
screw-thread-pitch wires or a pair of standard 6-mm nominal 7.4.2.3 A symmetrical concave or convex surface forms
diameter plug gages be not greater than 2 µm. Spring-wire concentric circular fringes. Their number is a measure of
stock or music-wire of known diameter are suitable substitutes. deviation from flatness.
The wire (or the plug gage) has a diameter dimension that is
7.4.2.4 An unsymmetrical concave or convex surface forms
known to be within 61.3 µm. Diameter dimensions may vary
a series of curved fringes that cut the periphery of the
by an amount approximately equal to the axial movement of
micrometer surface. The number of fringes cut by a straight
the spindle when the wire (or the plug gage) is rotated through
line connecting the terminals of any fringes is a measure of the
180°.
deviation from flatness.
7.2.1 Lacking a detailed procedure supplied by the instru-
7.5 Machinist’s Micrometer Requirements:
ment manufacturer, confirm the parallelism requirements of
7.5.1 The requirements for zero reading of machinist’s
machinist’s micrometers using the following procedure:
micrometers are met when ten closings of the spindle onto the
7.2.1.1 Closethemicrometeronthescrew-thread-pitchwire
anvil, in accordance with 7.6.2.3 or 7.6.3.3 as appropriate,
or the plug gage in accordance with the calibration procedure
result in ten zero readings. The condition of zero reading is
of 7.6.2 or 7.6.3 as appropriate.
satisfied when examinations with a low-power magnifying
7.2.1.2 Observe and record the thickness indicated.
glass show that at least 66 % of the width of the zero
7.2.1.3 Move the screw-thread-pitch wire or the plug gage
graduation mark on the barrel coincides with at least 66 % of
to a different position between the presser foot and the anvil
the width of the reference mark.
and repeat 7.2.1.1 and 7.2.1.2.
7.5.2 Proper maintenance of a machinist’s micrometer may
7.2.1.4 If the difference between any pair of readings is
require adjusting the instrument for wear of the micrometer
greater than 2.5 µm, the surfaces are NOT parallel.
screw so that the spindle has no perceptible lateral or longitu-
7.3 Lacking a detailed procedure supplied by the instrument
dinal looseness yet rotates with a torque load of less than
manufacturer, confirm the requirements for parallelism of
0.0018 Nm. If this is not achievable after disassembly, clean-
dial-type micrometers given in 6.3.1.2 by placing a hardened
ing, and lubrication, replace the instrument.
steel ball (such as is used in a ball bearing) of suitable diameter
7.5.3 After the zero reading has been checked, use the
between the presser foot and the anvil. Mount the ball in a
calibration procedure of 7.6.2 or 7.6.3 (as appropriate for the
fork-shaped holder to allow the ball to be conveniently moved
machinist’s micrometer under examination) to check for maxi-
from one location to another between the presser foot and the
mum acceptable error in the machinist’s micrometer screw.
anvil. The balls used commercially in ball bearings are almost
7.5.3.1 Use selected feeler-gage blades with known thick-
perfect spheres having diameters constant within a fraction of
nesses to within 60.5 µm to check micrometers calibrated in
a micron.
metric units at approximately 50, 130, and 250-µm points. Use
NOTE 2—Exercise care with this procedure. Calculations using the
standard gage blocks at points greater than 25 µm.
equations in X1.3.2 show that the use of a 0.68-kg mass and a ball
7.5.3.2 At each point checked, take ten readings. Calculate
between the hardened surfaces of presser foot and anvil can result in
the arithmetic mean of these ten readings.
dimples in the anvil or presser foot surfaces caused by exceeding the yield
stress of the surfaces. 7.5.3.3 The machinist’s micrometer screw error is within
requirements if the difference between the mean value of
7.3.1 Observe and record the diameter as measured by the
7.5.3.2 and the gage block (or feeler-gage blade) thickness is
micrometer at one location.
not more than 2.5 µm.
7.3.2 Move the ball to another location and repeat the
7.5.4 Calibration of Spindle Pressure in Machinist’s Mi-
measurement.
crometer with Ratchet or Friction Thimble:
7.3.3 If the difference between any pair of readings is
7.5.4.1 See Annex A1, which details the apparatus and
greater than 2.5 µm, the surfaces are NOT parallel.
procedure required for this calibration.
7.4 Lacking a detailed procedure supplied by the instrument
7.6 Calibration of Micrometers:
manufacturer, confirm the flatness of the anvil and the spindle
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
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