ASTM D352-23

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Designation: D352 − 97 (Reapproved 2016) D352 − 23
Standard Test Methods for
Pasted Mica Used in Electrical Insulation
This standard is issued under the fixed designation D352; 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
1.1 These test methods cover the testing of bonded mica splittings and bonded mica paper to be used for commutator insulation,
hot molding, heater plates, and other similar insulating purposes.
1.2 These test methods appear in the following sections:
Test Sections
Compressive Creep 4 – 10
Dielectric Strength 38 – 41
Mica or Binder Content 19
Molding Test 31 – 36
Organic Binder 20 – 24
Resistivity 42 – 46
Silicone Binder 25 – 30
Stability Under Heat and Pressure 11 – 18
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.4 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 healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use. See 40.1 and 45.1 for specific hazard statements.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D149 Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at
Commercial Power Frequencies
D257 Test Methods for DC Resistance or Conductance of Insulating Materials
D1711 Terminology Relating to Electrical Insulation
These test methods are under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and are the direct responsibility of Subcommittee
D09.01 on Electrical Insulating Products.
Current edition approved May 15, 2016Aug. 1, 2023. Published May 2016August 2023. Originally approved in 1932. Last previous edition approved in 20082016 as
ε1
D352 – 97 (2008) – 97 (2016). . DOI: 10.1520/D0352-97R16. 10.1520/D0352-23.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D352 − 23
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms relating to electrical insulation, refer to Terminology D1711.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 binder content, n, (of pasted mica)—the percent by weight of binder relative to the original weight of a specimen as
determined by procedures specified herein.
3.2.1.1 Discussion—
Binder content includes any residual solvent. Pasted mica materials not fully cured (such as molding and flexible plates)
maypossibly contain appreciable quantities of solvent in the binder. This solvent is usually later removed when the material is cured
in the manufacture of electrical equipment. In such cases, the binder content after cure is less (by the amount of solvent removed)
than would be determined by this method. To determine the binder content after cure of materials that are not fully cured, but
subsequently will be, it is necessary, before initially weighing the specimen, to heat the specimen for a time and at a temperature
that depends upon the material from which the specimen is prepared.
3.2.2 compressive creep, n—the change in thickness of a bonded micaceous material resulting from exposure to elevated
temperature for a specified time while a specimen is under a specified compressive load.
3.2.3 mica content, n, (of pasted mica)—the percent by weight of mica relative to the original weight equal to 100 % minus the
binder content as determined by procedures specified herein.
COMPRESSIVE CREEP
4. Significance and Use
4.1 This test determines the compressive creep under laboratory conditions or under conditions that may beare possibly
encountered during manufacture of electrical equipment. It has special significance if the material to be tested is applied as
commutator segment insulation. It serves as a measure under specified conditions of the ability of the material to resist deformation
while under compressive load, during exposure to elevated temperature for a specified time. This test is suitable for acceptance
tests and for manufacturing control.
5. Apparatus
5.1 Hydraulic Press—A hydraulic press having temperature controlled, electrically heated platens, or a press with other provisions
for heating the specimen and controlling the temperature. The platens shall be at least 4 by 4 in. (102 by 102 mm) 102 mm) in
size. The press shall be capable of exerting a force of at least 4000 lb (18 kN). The apparatus shall be capable of maintaining a
specimen temperature of at least 200 6 5°C.200 °C 6 5 °C. It is preferable that the apparatus have platens with water ducts or
other provisions for cooling the specimen. (See Note 1 in 7.3.)
5.2 Pressure Gage—Gauge—A pressure gagegauge capable of determining the pressure on the specimen with an accuracy of
65 %.
5.3 Thickness Gage—Gauge—A thickness gagegauge capable of measuring the thickness of the specimen to the nearest 0.001 in.
(0.025 mm).
5.4 Potentiometer—Temperature measuring instrument and a No. 30 AWG or smaller thermocouple with overall accuracy of
6 2°C6 2 °C for measurement of specimen temperature.
5.5 Steel Plates—Two 4 by 4-in. (102 by 102-mm)102 mm) or larger polished steel plates of at least ⁄16-in. (1.6-mm)(1.6 mm)
thickness, surface ground so that the top and bottom surfaces of each piece are parallel, one plate each for the top and bottom of
the test specimen.
6. Test Specimen
6.1 The test specimen shall consist of a sufficient number of pieces of bonded micaceous plate, 2 by 2 in. (51 by 51 mm) 51 mm)
D352 − 23
in size, to form a stack approximately but not greater than 1.000 in. 1.000 in. (25.40 mm) in thickness. The pieces shall be selected
so as to be representative of the entire sheet. At least three specimens shall be tested for each lot of material.
7. Procedure
7.1 Center the stacked specimen between the 4 by 4-in. (102 by 102-mm)102 mm) steel plates and then center this assembly in
the press. Place the thermocouple between pieces near the middle of the stack. Carefully align the stack to form a right
parallelepiped. Apply a pressure of 1000 psi (7 MPa) to the specimen surfaces, and carefully determine the average thickness of
the stack by means of the gage.gauge. Where inside gagesgauges are used, measure the thickness at each of the four corners as
close to the specimen as possible. Measurements shall be made within 5 min.5 min.
7.2 Pack approximately 2 in. (51 mm) of thermal insulation material around the specimen without disturbing it. Heat the specimen
to 160 6 5°C or 200 6 5°C160 °C 6 5 °C or 200 °C 6 5 °C as specified. The time required to reach the specified temperature
shouldshall be not less than 30 min nor more than 75 min. The platen temperature shall not exceed the specified temperature by
more than the specified tolerance. If the specimen is heated by other means, the surrounding medium shall not exceed the specified
temperature by more than the specified tolerance. Allow the specimen to remain at the specified temperature for 2 h after reaching
that temperature, and at the same time maintain the 1000-psi pressure.
7.3 Remove the thermal insulation and, while maintaining the pressure, allow the specimen to cool until the temperature is
5°C5 °C above the temperature (room ambient) at which the original thickness was measured. Control the rate of cooling such that
it does not exceed the rate at which the temperature was raised. Then determine the thickness of the stack while under 1000-psi
compressive load.
NOTE 1—Experience has shown that in order to cool the specimen to the specified temperature within a reasonable time, forced-cooling means must be
employed. It is suggested that a fan be initially utilized to force air across the specimen for the first 5 min, after which cooling water may be allowed
it is allowable to circulate in ducts provided in the platens. The rate of water flow, if used, shouldshall be adjusted to give a cooling rate no greater than
the rate at which the specimen was initially heated.
8. Calculation
8.1 Calculate the percentage compressive creep, C, as follows:
C,%5 T 2 T' /T ×100 (1)
@~ ! #
where:
T = thickness of the stack at 1000 psi (7 MPa) before heating, and
T' = thickness of the stack at 1000 psi after heating.
9. Report
9.1 Report the following information:
9.1.1 The identity of the material,
9.1.2 The nominal thickness of the pasted mica,
9.1.3 The observed values of T and T',
9.1.4 The percentage compressive creep, and
9.1.5 The specimen temperature.
10. Precision and Bias
10.1 This method has been in use for many years but no statement for precision has been made and no activity is planned to
develop such a statement.
10.2 A statement of bias is not possible due to a lack of a standard reference material.
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STABILITY UNDER HEAT AND PRESSURE
11. Scope
11.1 The test for stability under heat and pressure determines mica or binder displacement, or both, under the specified conditions
of test.
11. Scope
11.1 The test for stability under heat and pressure determines mica or binder displacement, or both, under the specified conditions
of test.
12. Significance and Use
12.1 This test serves as a measure of the ability of bonded micaceous materials to maintain their physical integrity under exposure
to heat and pressure. It has special significance where the material to be tested is employed as commutator segment insulation. This
test is suitable for acceptance tests and for manufacturing control.
13. Nature of Test
13.1 This test method utilizes the application of a shearing force as well as a compressive force, which is accomplished by placing
the specimens between specified wedges, thereby causing the applied force to resolve into compression and shear components. This
test is particularly useful for material used in commutator assemblies where shearing as well as compressive forces are
encountered. Test results are expressed quantitatively as units of linear deflection.
14. Apparatus
14.1 Hydraulic Press, Pressure Gage,Gauge, and Thermocouple as described in Section 5, except that the hydraulic press shall
be capable of producing a force of 26 400 lb (118 kN) on the specimen,
14.2 Steel Wedges—Two steel wedges of the same size as the specimen by approximately ⁄4 in. (19 mm) thick, with one face
tapered at an angle of 3° with the horizontal and a center wedge as shown in Fig. 1. They shall be hardened and surface ground
top and bottom.
14.3 Dial Gages—Gauges—Two dial gagesgauges having 0.001-in. (0.02-mm)(0.02 mm) graduations and a range of at least ⁄2-in.
(13-mm),(13 mm), designed to be accurate at the specified test temperature, and suitably mounted on the steel wedges described
in 14.2.
NOTE 2—Where the dial gagesgauges are mounted through nonmetallic bushings, or if some other suitable method is used to interrupt the metallic thermal
path, it shall not be necessary to utilize gagesgauges designed to be accurate at the test temperature.
15. Test Specimen
15.1 The specimen shall consist of two rectangular pieces of bonded micaceous plate between 4 and 6 in. (2580 and 3870
mm3870 mm ) in area, the shorter side being not less than 1 ⁄2 in. (38 mm). in. (38 mm).
Minimum size of sheet: A = 3 in.; B = 18 in.
FIG. 1 Apparatus for Stability Test Under Heat and Pressure, Angular Method
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16. Procedure
16.1 Insert the specimen between the wedges, as shown in Fig. 1. Center the assembly in the press and carefully align, using just
enough pressure to hold the assembly together. Insert the thermocouple and fit it tightly in the hole provided in the center wedge.
Cement the thermocouple into the hole. Apply a pressure of 100 6 10 psi (690 6 70 kPa) on the top and bottom assembly surfaces.
16.2 Pack approximately 2 in. (51 mm) of thermal insulating material, such as glass or other inorganic fiber mat, around the
specimen without disturbing either the specimen or dial gages.gauges. Heat the specimen to 160 6 5°C or 200 6 5°C,160 °C 6
5 °C or 200 °C 6 5 °C, as specified, and allow to remain at the specified temperature for 5 +1, −0 min. Do not allow the platen
temperature to exceed the specimen temperature by more than 10°C.10 °C.
16.3 Adjust both gagesgauges to read zero. Apply and hold a pressure of 4400 psi (30 MPa) within 5 s on the top and bottom
assembly surfaces and maintain for 15 min at the specified temperature. Record the deflection as determined by the top and bottom
dial gagesgauges after 15 s, 30 s, 1, 2, 5, 10, and 15 min beginning with the instant that the 4400 psi pressure is obtained.
17. Report
17.1 Report the following information:
17.1.1 The identity of the material,
17.1.2 The dimensions of the specimen used,
17.1.3 The temperature used, and
17.1.4 The average deflection at each of the time intervals in accordance with 16.3.
18. Precision and Bias
18.1 See 10.1.
18.2 See 10.2.
MICA OR BINDER CONTENT
19. Significance and Use
19.1 Physical (such as the ability to hot mold, flexibility) and electrical (such as dielectric strength, resistivity) properties of
bonded micaceous materials are affected, among other things, by the propo
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