ASTM D7895/D7895M-14(2018)
(Test Method)Standard Test Method for Thermal Endurance of Coating Powders Used for Powder Coating Insulation Systems
Standard Test Method for Thermal Endurance of Coating Powders Used for Powder Coating Insulation Systems
SIGNIFICANCE AND USE
5.1 A major factor affecting the life of insulating materials is thermal degradation. It is possible that other factors, such as moisture and vibration, will cause failures after the material has been weakened by thermal degradation.
5.2 Electrical insulation is effective in electrical equipment only as long as it retains its physical and electrical integrity. The following are potential indicators of thermal degradation: weight change, porosity, crazing, and generally a reduction in flexibility. Thermal degradation is usually accompanied by an ultimate reduction in dielectric breakdown.
5.3 This test method is useful in determining the thermal endurance of coating powders applied over a steel substrate material.
SCOPE
1.1 This test method provides a procedure for evaluating thermal endurance of coating powders by determining the length of aging time at selected elevated temperatures required to achieve dielectric breakdown at room temperature at a pre-determined proof voltage. Thermal endurance is expressed in terms of a temperature index.
1.2 This test method is applicable to insulating powders used over a substrate material of steel.
1.3 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems is likely to result in non-conformance with the 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 7.
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.
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Designation: D7895/D7895M − 14 (Reapproved 2018)
Standard Test Method for
Thermal Endurance of Coating Powders Used for Powder
Coating Insulation Systems
This standard is issued under the fixed designation D7895/D7895M; 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 at Commercial Power Frequencies
D1711 Terminology Relating to Electrical Insulation
1.1 This test method provides a procedure for evaluating
D5423 Specification for Forced-Convection Laboratory Ov-
thermal endurance of coating powders by determining the
ens for Evaluation of Electrical Insulation
length of aging time at selected elevated temperatures required
2.2 IEEE Document
to achieve dielectric breakdown at room temperature at a
IEEE 101A Simplified Method for Calculation of the Re-
pre-determined proof voltage. Thermal endurance is expressed
gression Line
in terms of a temperature index.
1.2 This test method is applicable to insulating powders
3. Terminology
used over a substrate material of steel.
3.1 Definitions—For definitions of terms used in this test
1.3 Units—The values stated in either SI units or inch-
method refer to Terminology D1711.
pound units are to be regarded separately as standard. The
4. Summary of Test Method
values stated in each system are not necessarily exact equiva-
lents; therefore, each system shall be used independently of the
4.1 Specimens are aged in air at a minimum of three
other. Combining values from the two systems is likely to
temperatures above the expected use temperature of the mate-
result in non-conformance with the standard.
rial. Exposure to ambient stress conditions, followed by
dielectric proof voltage tests in an electrically conductive
1.4 This standard does not purport to address all of the
solution, are periodically conducted to determine the time of
safety concerns, if any, associated with its use. It is the
aging at each elevated temperature required to reduce the
responsibility of the user of this standard to establish appro-
breakdown voltage to a preselected percentage of the original
priate safety, health, and environmental practices and deter-
breakdown value. These thermal life values are used to
mine the applicability of regulatory limitations prior to use.
construct a thermal endurance graph by means of which it is
Specific precautionary statements are given in Section 7.
possible to estimate a temperature index, corresponding to a
1.5 This international standard was developed in accor-
thermal life as specified in the material specification or as
dance with internationally recognized principles on standard-
agreed upon between the user and the supplier. It is possible
ization established in the Decision on Principles for the
that a material will have multiple indices, each corresponding
Development of International Standards, Guides and Recom-
to a different thermal life as required by a given application.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
5. Significance and Use
2. Referenced Documents
5.1 Amajorfactoraffectingthelifeofinsulatingmaterialsis
thermal degradation. It is possible that other factors, such as
2.1 ASTM Standards:
moisture and vibration, will cause failures after the material
D149 Test Method for Dielectric Breakdown Voltage and
has been weakened by thermal degradation.
Dielectric Strength of Solid Electrical Insulating Materials
5.2 Electrical insulation is effective in electrical equipment
1 only as long as it retains its physical and electrical integrity.
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of The following are potential indicators of thermal degradation:
Subcommittee D09.01 on Electrical Insulating Products.
weight change, porosity, crazing, and generally a reduction in
Current edition approved Nov. 1, 2018. Published November 2018. Originally
flexibility. Thermal degradation is usually accompanied by an
approved in 2014. Last previous edition approved in 2014 as D7895/D7895M – 14.
ultimate reduction in dielectric breakdown.
DOI: 10.1520/D7895_D7895M-14R18.
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 Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),
the ASTM website. 445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7895/D7895M − 14 (2018)
5.3 This test method is useful in determining the thermal oughly instruct all operators as to the correct procedures for
endurance of coating powders applied over a steel substrate performing tests safely. When making high voltage tests,
material. particularly in compressed gas or in oil, it is possible for the
energy released at breakdown to be sufficient to result in fire,
6. Apparatus
explosion, or rupture of the test chamber. Design test
equipment,testchambers,andtestspecimenssoastominimize
6.1 Dielectric Breakdown Test Set—The set shall meet the
the possibility of such occurrences and to eliminate the
requirements of Test Method D149.
possibility of personal injury. If the potential for fire exists,
6.2 Ovens—Ovens shall meet the requirements of Specifi-
have fire suppression equipment available.
cation D5423, Type I.
8. Test Specimens
6.3 Electrically Conductive Solution:
6.3.1 An appropriate container shall be selected for the
8.1 The substrate material to be used for evaluating integral
electrically conductive solution.
bus-bar insulation systems shall be steel. It is preferred that the
6.3.2 Prepare a solution having a conductivity of at least
configuration of the substrate material be representative of the
2.5 mS (millisiemens).
end application. One configuration that has been found to be
useful is shown in Fig. 1. Alternative configurations are
NOTE 1—A solution comprised of tap water and a solute such as NaCl
acceptable if agreed to by all interested parties.
orNH Clhasbeenfoundtobeacceptable.Sincethewatersolutionisused
to detect (not cause) material decomposition/breakdown, the solution is
8.2 The substrate shall be coated with the powder and cured
acceptable for use as long as it meets the minimum conductivity
using the manufacturer’s standard process. One end of the
requirements. It is recommended to change the solution when it becomes
specimens shall be left uncoated for making an electrical
difficult to observe breakdown due to cloudiness or other contamination.
connection during the dielectric strength tests.
6.3.3 During testing, the conductive solution is at ground
potential. The ground connection, using an immersed
9. Number of Test Specimens
electrode, is made using Nichrome, stainless steel, or other
9.1 A set of specimens for thermal aging shall consist of at
non-corrosive metal.
least ten specimens. Prepare one set for each aging temperature
6.3.4 Fit the container with a cover to prevent evaporation
chosen.
of the solution when not in use.
9.2 The initial value (unaged) set shall consist of at least
7. Hazards
twenty specimens.
7.1 Warning—Lethal voltages are a potential hazard during
9.3 The minimum number of test specimens is 50. It is
the performance of this test. It is essential that the test
recommended to prepare extra specimens for situations such as
apparatus, and all associated equipment electrically connected
the need to add additional aging temperatures, or to have
to it, be properly designed and installed for safe operation.
replacement specimens available for any specimens that are
Solidly ground all electrically conductive parts which are
found during the screening test to be unsuitable for use in
possible for a person to contact during the test. Provide means
thermal aging.
for use at the completion of any test to ground any parts which
10. Calibration and Standardization
were at high voltage during the test, or have the potential for
acquiring an induced charge during the test, or retaining a 10.1 Expose the test material to at least three aging tem-
charge even after disconnection of the voltage source. Thor-
peratures. The preferred number of aging temperatures is four.
FIG. 1 Example Specimen Dimensions
D7895/D7895M − 14 (2018)
10.2 Minimum thermal life target values for the high and 13.2 Selectascreeningtestvoltagelevelthatisapercentage
low temperatures shall be selected based on application. of the average initial value.
10.3 Aging temperatures shall differ by at least 10°C.
13.3 Selectascreeningtestperiodoftimethatisexpectedto
causefailureinweakspecimenswithoutcausingdamagetothe
NOTE 2—Experience has shown that the suggested target thermal life
remaining specimens.
values listed in Table 1 are generally satisfactory.
NOTE 4—Experience has shown that a screening test voltage level of
11. Selection of Aging Cycles
75 % of the initial value for a period of 10 s is generally satisfactory.
11.1 To provide approximately equal exposures to the other
13.4 Suspend each specimen in the electrically conductive
conditionings, and to more accurately determine the property
solution in the same manner as described for the initial value
endpoint, the heat aging time per cycle shall be shorter for the
test. Apply voltage uniformly to the test electrode in accor-
higher aging temperatures and longer for the lower aging
dance with the guidelines of the Short-Time Test described in
temperatures.
12.2.1 of Test Method D149, unless another rate is specified,
until the screening voltage level is achieved. Maintain the
11.2 Cycle times shall be selected such that each set
voltage for the screening test period before removing the
undergoes an adequate (but not excessive) number of cycles
voltage from the specimen.
before completion. In order to obtain an appropriate number of
cycles, the following adjustments to the cycle time are recom-
13.5 Discard any
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7895/D7895M − 14 D7895/D7895M − 14 (Reapproved 2018)
Standard Test Method for
Thermal Endurance of Coating Powders Used for Powder
Coating Insulation Systems
This standard is issued under the fixed designation D7895/D7895M; 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 This test method provides a procedure for evaluating thermal endurance of coating powders by determining the length of
aging time at selected elevated temperatures required to achieve dielectric breakdown at room temperature at a pre-determined
proof voltage. Thermal endurance is expressed in terms of a temperature index.
1.2 This test method is applicable to insulating powders used over a substrate material of steel.
1.3 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated
in each system are not necessarily exact equivalents; therefore, each system shall be used independently of the other. Combining
values from the two systems is likely to result in non-conformance with the 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 7.
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
D1711 Terminology Relating to Electrical Insulation
D5423 Specification for Forced-Convection Laboratory Ovens for Evaluation of Electrical Insulation
2.2 IEEE Document
IEEE 101A Simplified Method for Calculation of the Regression Line
3. Terminology
3.1 Definitions—For definitions of terms used in this test method refer to Terminology D1711.
4. Summary of Test Method
4.1 Specimens are aged in air at a minimum of three temperatures above the expected use temperature of the material. Exposure
to ambient stress conditions, followed by dielectric proof voltage tests in an electrically conductive solution, are periodically
conducted to determine the time of aging at each elevated temperature required to reduce the breakdown voltage to a preselected
percentage of the original breakdown value. These thermal life values are used to construct a thermal endurance graph by means
of which it is possible to estimate a temperature index, corresponding to a thermal life as specified in the material specification
or as agreed upon between the user and the supplier. It is possible that a material will have multiple indices, each corresponding
to a different thermal life as required by a given application.
This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommittee
D09.01 on Electrical Insulating Varnishes, Powders and Encapsulating CompoundsProducts.
Current edition approved Nov. 1, 2014Nov. 1, 2018. Published November 2014November 2018. Originally approved in 2014. Last previous edition approved in 2014 as
D7895/D7895M – 14. DOI: 10.1520/D7895_D7895M-14.10.1520/D7895_D7895M-14R18.
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.
Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE), 445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7895/D7895M − 14 (2018)
5. Significance and Use
5.1 A major factor affecting the life of insulating materials is thermal degradation. It is possible that other factors, such as
moisture and vibration, will cause failures after the material has been weakened by thermal degradation.
5.2 Electrical insulation is effective in electrical equipment only as long as it retains its physical and electrical integrity. The
following are potential indicators of thermal degradation: weight change, porosity, crazing, and generally a reduction in flexibility.
Thermal degradation is usually accompanied by an ultimate reduction in dielectric breakdown.
5.3 This test method is useful in determining the thermal endurance of coating powders applied over a steel substrate material.
6. Apparatus
6.1 Dielectric Breakdown Test Set—The set shall meet the requirements of Test Method D149.
6.2 Ovens—Ovens shall meet the requirements of Specification D5423, Type I.
6.3 Electrically Conductive Solution:
6.3.1 An appropriate container shall be selected for the electrically conductive solution.
6.3.2 Prepare a solution having a conductivity of at least 2.5 mS (millisiemens).
NOTE 1—A solution comprised of tap water and a solute such as NaCl or NH Cl has been found to be acceptable. Since the water solution is used
to detect (not cause) material decomposition/breakdown, the solution is acceptable for use as long as it meets the minimum conductivity requirements.
It is recommended to change the solution when it becomes difficult to observe breakdown due to cloudiness or other contamination.
6.3.3 During testing, the conductive solution is at ground potential. The ground connection, using an immersed electrode, is
made using Nichrome, stainless steel, or other non-corrosive metal.
6.3.4 Fit the container with a cover to prevent evaporation of the solution when not in use.
7. Hazards
7.1 Warning—Lethal voltages are a potential hazard during the performance of this test. It is essential that the test apparatus,
and all associated equipment electrically connected to it, be properly designed and installed for safe operation. Solidly ground all
electrically conductive parts which are possible for a person to contact during the test. Provide means for use at the completion
of any test to ground any parts which were at high voltage during the test, or have the potential for acquiring an induced charge
during the test, or retaining a charge even after disconnection of the voltage source. Thoroughly instruct all operators as to the
correct procedures for performing tests safely. When making high voltage tests, particularly in compressed gas or in oil, it is
possible for the energy released at breakdown to be sufficient to result in fire, explosion, or rupture of the test chamber. Design
test equipment, test chambers, and test specimens so as to minimize the possibility of such occurrences and to eliminate the
possibility of personal injury. If the potential for fire exists, have fire suppression equipment available.
8. Test Specimens
8.1 The substrate material to be used for evaluating integral bus-bar insulation systems shall be steel. It is preferred that the
configuration of the substrate material be representative of the end application. One configuration that has been found to be useful
is shown in Fig. 1. Alternative configurations are acceptable if agreed to by all interested parties.
FIG. 1 Example Specimen Dimensions
D7895/D7895M − 14 (2018)
8.2 The substrate shall be coated with the powder and cured using the manufacturer’s standard process. One end of the
specimens shall be left uncoated for making an electrical connection during the dielectric strength tests.
9. Number of Test Specimens
9.1 A set of specimens for thermal aging shall consist of at least ten specimens. Prepare one set for each aging temperature
chosen.
9.2 The initial value (unaged) set shall consist of at least twenty specimens.
9.3 The minimum number of test specimens is 50. It is recommended to prepare extra specimens for situations such as the need
to add additional aging temperatures, or to have replacement specimens available for any specimens that are found during the
screening test to be unsuitable for use in thermal aging.
10. Calibration and Standardization
10.1 Expose the test material to at least three aging temperatures. The preferred number of aging temperatures is four.
10.2 Minimum thermal life target values for the high and low temperatures shall be selected based on application.
10.3 Aging temperatures shall differ by at least 10°C.
NOTE 2—Experience has shown that the suggested target thermal life values listed in Table 1 are generally satisfactory.
11. Selection of Aging Cycles
11.1 To provide approximately equal exposures to the other conditionings, and to more accurately determine the property
endpoint, the heat aging time per cycle shall be shorter for the higher aging temperatures and longer for the lower aging
temperatures.
11.2 Cycle times shall be selected such that each set undergoes an adequate (but not excessive) number of cycles before
completion. In order to obtain an appropriate number of cycles, the following adjustments to the cycle time are recommended:
th
11.2.1 If no specimens in a set fail by the end of the 4 cycle, double the heat aging period of the test cycle.
th
11.2.2 If three or more specimens in a set fail by the end of the 4 cycle, halve the heat aging period of the test cycle.
11.2.3 Use observations in the highest temperature set to select appropriate adjustments to the other temperature sets.
NOTE 3—Experience has shown that the suggested cycle times in Table 1 are generally satisfactory.
12. Initial Value Test
12.1 To determine an initial dielectric strength level, at least twenty specimens shall be selected at random from the sample and
subjected to a voltage breakdown test.
12.2 Connect o
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