ASTM D4881-05

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An American National Standard
Designation:D4881–05
Standard Test Method for
Thermal Endurance of Varnished Fibrous- or Film-Wrapped
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Magnet Wire
This standard is issued under the fixed designation D4881; 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 3.1.2 Refer to Terminology D1711 for definitions of other
terms.
1.1 This test method covers the determination of thermal
endurance of rectangular and square fibrous- or film-wrapped
4. Significance and Use
magnet wire coated with an insulating varnish.
4.1 Individual varnishes behave differently when applied to
1.2 The values given in SI units are the standard.The values
the same fibrous- or film-wrapped magnet wire when exposed
given in parentheses are for information only.
to elevated temperatures. Likewise, a varnish does not always
1.3 This standard does not purport to address all of the
behave the same when applied to different types of fibrous or
safety concerns, if any, associated with its use. It is the
film-wrapped magnet wires and when exposed to elevated
responsibility of the user of this standard to establish appro-
temperatures.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. A specific precau-
tionary statement is given in Section 5.
NOTE 1—There is no similar or equivalent IEC Standard.
2. Referenced Document
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2.1 ASTM Standards:
D1711 Terminology Relating to Electrical Insulation
D2307 Test Method for Thermal Endurance of Film-
Insulated Round Magnet Wire
D3353 Test Methods for Fibrous-Insulated Magnet Wire
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 varnish, electrical insulating, n— a liquid resin sys-
tem that is applied to and cured on electrical components
providing electrical, mechanical, and environmental protec-
tion.
3.1.1.1 Discussion—There are two types of electrical insu-
lating varnishes—solvent-containing and solventless. Solvent-
FIG. 1 Jig for Forming Wire
containing types are solutions, dispersions, or emulsions of a
polymer or a mixture of polymers in a volatile, nonreactable
5. Safety Precautions
liquid. Solventless types are liquid resin systems free of
volatile, nonreactable solvents.
5.1 It is unsafe to use varnish at temperatures above the
flash point without adequate ventilation, especially if the
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possibility exists that flames or sparks are present. Store
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
varnish in sealed containers.
Subcommittee D09.01 on Electrical Insulating Varnishes, Powders, and Encapsu-
lating Compounds.
6. Test Specimens
Current edition approved Sept. 1, 2005. Published September 2005. Originally
6.1 Construction of Test Specimens:
approved in 1988. Last previous edition approved in 2001 as D4881 – 01. DOI:
10.1520/D4881-05.
6.1.1 Cut two 250-mm (10-in.) lengths of wire for each
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
specimen to be made.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
6.1.2 Determine the thickness dimensions per Test Method
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. D3353.
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D4881–05
6.1.3 Form each length in a fixture as shown in Fig. 1. procedure in Test Method D2307 with the following excep-
6.1.4 Prepare a test specimen by placing the two formed tions:
wires together back to back and wrap tightly with a minimum 7.1.1 The described specimen holder and electrical connec-
of6turnsofglassyarnoverthemiddle6-in.(150-mm)section. tion device are not required. Instead, lay samples flat on a
The glass yarn shall have a gap between turns and there must vented tray during oven exposure.
be intimate contact of the two wires. 7.1.2 Test individual specimens by carefully attaching test
6.1.5 Prepare ten specimens for each test temperature. leads to each specimen.
6.2 Varnishing the Test Specimens:
8. Calculation
6.2.1 Adjust the consistency of a solvent-containing varnish
8.1 After all specimens have failed, calculate the endpoint
to give a 0.025 6 0.005-mm (0.0010 6 0.0002-in.) cured film
time at each test temperature in accordance with Test Method
on each side of a 0.13-mm (0.005-in.) copper strip withdrawn
D2307.
at a rate of 100 mm/min (4 in./min). Use solventless varnish as
8.2 Plot the results using the
...