ASTM D748-00

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An American National Standard
Designation: D 748 – 00
Standard Specification for
Natural Block Mica and Mica Films Suitable for Use in Fixed
1
Mica-Dielectric Capacitors
This standard is issued under the fixed designation D 748; 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 become available. Natural block mica and mica films that do
2 not conform to the requirements of this specification for
1.1 This specification covers natural block mica and mica
capacitor use may well be capable of meeting the requirements
films (cut and uncut) suitable for use in the manufacture of
for other critical electrical insulation purposes.
fixedmica-dielectriccapacitors,basedonelectrical,visual,and
4.2 The system of classifying electrical quality of natural
physical properties as determined by tests specified herein.
block and mica films (cut and uncut) covered by this specifi-
1.2 The values stated in inch-pound units are to be regarded
cation is based on a combination of electrical and physical
as the standard.
properties,andvisualqualitiesspecifiedherein,whichthemica
2. Referenced Documents
must possess. This system differs radically from past practices
and previous concepts of mica quality for capacitor use. The
2.1 ASTM Standards:
electrical classification system does not discriminate against
D 149 Test Method for Dielectric Breakdown Voltage and
the presence of spots and stains in even first quality electrically
Dielectric Strength of Solid Electrical Insulating Materials
3
selected mica, provided the mica conforms to specific and
at Commercial Power Frequencies
physical requirements. Appreciable amounts of air inclusions
D 150 Test Methods for A-C Loss Characteristics and
and waviness also are permitted in all electrical quality classes,
Permittivity (Dielectric Constant) of Solid Electrical Insu-
3
provided the mica meets specific electrical and physical
lating Materials
requirements. Mica meeting these requirements is acceptable
D 351 Classification for Natural Muscovite Block Mica and
3
without regard to color or origin. However, mica meeting these
Thins Based on Visual Quality
electrical and physical requirements but having lower visual
D 1082 Test Method for Power Factor and Dielectric Con-
3
qualitythanthatmeetingtherequirementsforthevisualquality
stant of Mica
classification is not considered generally as desirable.
3. Terminology
4.3 In capacitor fabrication, one or more pieces of cut film
or block mica having lower than required electrical and
3.1 For definitions pertaining to this specification see Clas-
physical properties may prevent meeting the end requirements
sification D 351.
ofthecapacitor.Itisthereforerequiredthateachpieceofblock
4. Significance and Use
(cut) or film (cut or uncut), or both, be tested for the electrical
requirementsandinspectedforthevisualrequirementslistedin
4.1 The properties included in this specification are those
this specification.
required to identify the types of natural block mica and mica
films (cut and uncut) suitable for use in the manufacture of
5. Forms
fixed mica-dielectric capacitors. There may be other require-
5.1 This specification covers the following three forms of
ments necessary to identify particular characteristics. These
natural mica, suitable for use in the manufacture of mica-
will be added to the specification as their inclusion becomes
dielectric capacitors:
generally desirable, and the necessary test data and methods
5.1.1 Form1—Full-knife trimmed natural block mica 0.007
to 0.035 in. (0.18 to 0.89 mm) in thickness.
1
This specification is under the jurisdiction of ASTM Committee D09 on
NOTE 1—Acertain percentage of block mica thinner than 0.007 in. may
Electrical and Electronic Insulating Materials and is the direct responsibility of
be accepted under this specification, upon agreement between the pur-
Subcommittee D09.19 on Dielectric Sheet and Roll Products.
chaser and the manufacturer.
Current edition approved Sept. 10, 2000. Published November 2000. Originally
{1
published as D 748 – 43. Last previous edition D 748 – 71 (1994) .
5.1.2 Form 2—Half-knife trimmed natural block mica
2
Coutlee, K. G., “Electrical Quality Classification of Raw Mica by a Rapid,
0.007 to 0.035 in. in thickness.
Direct-Reading Test Method,” Proceedings, ASTM, Vol 46, 1946, p. 1486.
3
Annual Book of ASTM Standards, Vol. 10.01.
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D748–00
5.1.3 Form 3—Films (cut or uncut) split or manufactured and coupling purposes whe
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