ASTM D4733-17

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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: D4733 − 13 D4733 − 17
Standard Test Methods for
Solventless Electrical Insulating Varnishes
This standard is issued under the fixed designation D4733; 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 solventless varnishes used primarily as electrical, mechanical, and environmental protection for
electrical equipment.
1.2 These test methods are used on solventless varnishes that are applied by dipping (at atmospheric pressure conditions or
under vacuum or other certain pressure), spraying, or brushing for the purpose of impregnating or sealing electrical equipment. The
following test methods are included:
Property Tests (Uncured): Section
Density 7
Flash Point 8
Gel Time 9
Monomer Content 10
Rheological Properties (Non-Newtonian) 11
Brookfield Viscosity 12
Performance Property Tests (cured):
Bond Strength 13
Coating Thickness 14
Dielectric Strength 15
Dielectric Strength-Using Metal Panels 16
Permittivity and Dissipation Factor 17
Build 18
Property Tests (Uncured): Section
Density 7
Flash Point 8
Gel Time 9
Monomer Content 10
Rheological Properties (Non-Newtonian) 11
Rotational Viscosity 12
Performance Property Tests (cured):
Bond Strength 13
Coating Thickness 14
Dielectric Strength 15
Dielectric Strength-Using Metal Panels 16
Permittivity and Dissipation Factor 17
Build 18
1.3 The values stated in inch-pound units are to be regarded as the standard. The values in parentheses are for information only.
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 hazard statements are given in 8.3, 15.5.1, and 15.5.2.
NOTE 1—This test method is related to IEC 60455. Since both methods contain multiple test procedures, many procedures are technically equivalent
while others differ significantly.
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.
These test methods are 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 April 1, 2013Nov. 1, 2017. Published April 2013November 2017. Originally approved in 1987. Last previous edition approved in 20092013 as
D4733 – 03 (2009).D4733 – 13. DOI: 10.1520/D4733-13.10.1520/D4733-17.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4733 − 17
2. Referenced Documents
2.1 ASTM Standards:
D93 Test Methods for Flash Point by Pensky-Martens Closed Cup Tester
D115 Test Methods for Testing Solvent Containing Varnishes Used for Electrical Insulation
D149 Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at
Commercial Power Frequencies
D150 Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation
D168 Test Method for Coke Residue of Creosote (Withdrawn 2006)
D374 Test Methods for Thickness of Solid Electrical Insulation (Metric) D0374_D0374M
D923 Practices for Sampling Electrical Insulating Liquids
D1475 Test Method for Density of Liquid Coatings, Inks, and Related Products
D1711 Terminology Relating to Electrical Insulation
D2196 Test Methods for Rheological Properties of Non-Newtonian Materials by Rotational Viscometer
D2519 Test Method for Bond Strength of Electrical Insulating Varnishes by the Helical Coil Test
D3056 Test Method for Gel Time of Solventless Varnishes
D3278 Test Methods for Flash Point of Liquids by Small Scale Closed-Cup Apparatus
D3312 Test Method for Percent Reactive Monomer in Solventless Varnishes
D3487 Specification for Mineral Insulating Oil Used in Electrical Apparatus
D3636 Practice for Sampling and Judging Quality of Solid Electrical Insulating Materials
D6054 Practice for Conditioning Electrical Insulating Materials for Testing (Withdrawn 2012)
E176 Terminology of Fire Standards
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.
The last approved version of this historical standard is referenced on www.astm.org.
D4733 − 17
2.2 IEC Standards
IEC 60455 Resin Based Reactive CompundsCompounds Used for Electrical Insulation
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in these test methods, refer to Terminology D1711. For definitions of terms associated with
fire issues, refer to Terminology E176.
3.1.2 gel time, n—of solventless varnish, the time required at a specified temperature for a solventless varnish to be transformed
from a liquid state to a gel as measured with a suitable gel time apparatus.
3.1.3 thixotropy, n—the property of a material to thin upon isothermal agitation and to thicken upon subsequent rest.
3.1.4 varnish, electrical insulating, n—a liquid resin system that is applied to and cured on electrical components providing
electrical, mechanical, and environmental protection.
3.1.4.1 Discussion—
There are two types of electrical insulating varnish—solvent-containing and solventless. The solvent-containing varnish is
solution, dispersion, or emulsion of a polymer or a mixture of polymers in a volatile, nonreactable liquid. The solventless type is
a liquid resin system free of volatile, nonreactable solvents.
4. Significance and Use
4.1 The test methods referenced in these test methods are useful for control purposes during the manufacture and use of
solventless varnishes.
5. Sampling
5.1 Accurate sampling, whether of the complete contents or only parts thereof, is extremely important from the standpoint of
evaluating the quality of the product sampled. In most cases, the detection of contaminants that are not ordinarily dispersed
uniformly through the liquid being sampled such as water or solid particles, necessitates taking samples at specific locations where
the contaminants are likely to be found. For a liquid having a specific gravity less than one, water and other impurities are most
likely to be found on the bottom; whereas in the case of liquids having a specific gravity greater than one, these impurities are most
likely to be found on the surface.
5.2 Sampling Fluids Exhibiting Newtonian Viscosity:
5.2.1 Sample solventless varnishes having an approximate viscosity of 25 cP (0.025 Pa·s) or less at 100°F (37.8°C) using the
sampling device shown in Fig. 1 of Test Method D923. However, if the temperature of the material is below room temperature
or if the humidity is above 75 % relative humidity, sample using an aspirator-type sampling device as shown in Fig. 2 of Test
Method D923.
5.2.2 Sample solventless varnishes having a viscosity from 25 to 650 cP (0.025 to 0.65 Pa·s) at 100°F (37.8°C) and where
contact with the atmosphere must be avoided, use a pressure-type sampling device as shown in Fig. 3 of Test Method D923.
5.2.3 Sample solventless varnishes having a viscosity above 650 cP at 100°F at 73 6 10°F (23 6 5°C). Open the container and
mix slowly so as not to entrap air. When the material is homogeneous, take samples from two or three places on the surface and
mix together.
5.3 Sampling Fluids Exhibiting Non-Newtonian Viscosity:
5.3.1 Sample solventless varnishes exhibiting non-Newtonian viscosity in accordance with 5.2.3.
5.4 Use sample containers and sampling procedures in accordance with Test Method D923.
5.5 When a sampling method is needed to determine whether a lot meets the requirements of a material specification, use
Practice D3636 as a guide.
6. Conditioning
6.1 Condition test specimens at standard laboratory condition as specified in Practice D6054.
6.2 Deaerate specimens to be used for property evaluation before curing using the vacuum technique recommended by the
varnish manufacturer.
TEST METHODS
7. Density
7.1 Scope—This test method covers the measurement of the density using a pycnometer. It is particularly applicable where the
fluid has too high a viscosity for other methods of testing density. In this test method the density will be expressed as pounds per
gallon (grams per millilitre) at 70 to 77°F (20 to 25°C).
D4733 − 17
7.2 Procedure—Test for density in accordance with Test Method D1475.
7.3 Report—Report the following information:
7.3.1 Identification of the test sample,
7.3.2 The test temperature to the nearest 0.2°F (0.1°C),
7.3.3 Density to the nearest 0.01 lb/gal (0.001 g/mL), and
7.3.4 The mean, the range, and the number of replicate determinations.
8. Flash Point
8.1 Scope—This test method covers the determination of the flash point of solventless varnishes. There are two types of
materials involved:
8.1.1 Those varnishes having a flash point above 230°F (110°C), and
8.1.2 Those varnishes having a flash point below 230°F (110°C).
8.2 Summary of Test Method—A specified amount of sample is added to the instrument. The temperature of the material is
increased at a constant rate until a small flame ignites the vapor of the specimen in the tester and propagates a flame across its
surface. The temperature at ignition is taken as the flash point.
8.3 This standard is used to measure and describe the response of materials, products, or assemblies to heat and flame under
controlled conditions, but does not by itself incorporate all factors required for fire hazard or fire risk assessment of the materials,
products or assemblies under actual fire conditions.
8.4 Fire testing is inherently hazardous. Adequate safeguards for personnel and property shall be employed in conducting these
tests.
8.5 Procedure:
8.5.1 Test the materials of 8.1.1 in accordance with Test Methods D93.
8.5.2 Test the materials of 8.1.2 in accordance with Test Method D3278.
8.6 Report—Report information in accordance with the report section of the test method used.
9. Gel Time
9.1 Scope—This test method covers the determination of gel time of a solventless varnish mixed with a reactor or catalyst and
exposed to elevated temperatures.
9.2 Significance and Use—Knowledge of gel time is important for determining shelf life, batch uniformity, and processing
characteristics.
9.3 Procedure—Test for gel time in accordance with Test Method D3056.
9.4 Report—Report the following information:
9.4.1 Identification of the material,
9.4.2 The reactor or catalyst and quantity used shall be described if the reactor or catalyst is supplied in a separate package,
9.4.3 Gel time to the nearest 0.1 min,
9.4.4 Temperature of the bath, and
9.4.5 Liquid used in the bath.
10. Monomer Content
10.1 Scope—This test method covers the determination of the percent monomer having a vapor pressure exceeding 0.1 Torr (13
Pa) at 77°F (25°C).
10.2 Significance and Use—The percent of reactive monomer in a solventless varnish will affect the viscosity, handling, and
processing properties of the uncured resin. The amount of reactive monomer also has the potential to affect the physical and
electrical properties of the cured resin.
10.3 Procedure—Test for the monomer content in accordance with Test Method D3312.
10.4 Report—Report the following information:
10.4.1 Identification of the solventless varnish, and
10.4.2 Percent reactive monomer.
11. Rheological Properties (Non-Newtonian)
11.1 Scope—This test method covers the determination of the rheological properties of solventless varnishes that are
non-newtonian in character.
11.2 Significance and Use—This test method is used to test solventless varnishes that are thixotropic in nature and require
specific treatment of the sample in order to determine this property.
D4733 − 17
11.3 Procedure—Test for thixotropy in accordance with Test Method D2196, Method B or C.
11.4 Report—Report information as specified in Test Method D2196.
12. BrookfieldRo
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