1、Designation:D74818Standard Specification forNatural Block Mica and Mica Films Suitable for Use in FixedMica-Dielectric Capacitors1This standard is issued under the fixed designation D748;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revisio
2、n,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This specification covers natural block mica2and micafilms(cut and uncut)suitable for use in the manufacture
3、 offixed mica-dielectric capacitors,based on electrical,visual,andphysical properties as determined by tests specified herein.1.2 The values stated in inch-pound units are to be regardedas standard.1.3 This international standard was developed in accor-dance with internationally recognized principle
4、s on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:3D149 Test Method for Dielectric Breakdow
5、n Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD351 Classification for Natural Muscovite Block Mica andThins Based on Visual QualityD1082 Test Method for Dissipation Factor and Permittivity(Dielectric Constant)of Mica3.Terminology3.1 For defin
6、itions pertaining to this specification see Clas-sification D351.4.Significance and Use4.1 The properties included in this specification are thoserequired to identify the types of natural block mica and micafilms(cut and uncut)suitable for use in the manufacture offixed mica-dielectric capacitors.It
7、 is possible that other re-quirements will be necessary to identify particular character-istics.These will be added to the specification as their inclusionbecomes generally desirable,and the necessary test data andmethods become available.It is possible that natural blockmica and mica films that do
8、not conform to the requirements ofthis specification for capacitor use are capable of meeting therequirements for other critical electrical insulation purposes.4.2 The system of classifying electrical quality of naturalblock and mica films(cut and uncut)covered by this specifi-cation is based on a c
9、ombination of electrical and physicalproperties,and visual qualities specified herein,which the micamust possess.This system differs radically from past practicesand previous concepts of mica quality for capacitor use.Theelectrical classification system does not discriminate againstthe presence of s
10、pots and stains in even first quality electricallyselected mica,provided the mica conforms to specific andphysical requirements.Appreciable amounts of air inclusionsand waviness also are permitted in all electrical quality classes,provided the mica meets specific electrical and physicalrequirements.
11、Mica meeting these requirements is acceptablewithout regard to color or origin.However,mica meeting theseelectrical and physical requirements but having lower visualquality than that meeting the requirements for the visual qualityclassification is not considered generally as desirable.4.3 In capacit
12、or fabrication,one or more pieces of cut filmor block mica having lower than required electrical andphysical properties will possibly prevent meeting the endrequirements of the capacitor.It is therefore required that eachpiece of block(cut)or film(cut or uncut),or both,be tested forthe electrical re
13、quirements and inspected for the visual require-ments listed in this specification.5.Forms5.1 This specification covers the following three forms ofnatural mica,suitable for use in the manufacture of mica-dielectric capacitors:5.1.1 Form 1Full-knife trimmed natural block mica 0.007to 0.035 in.(0.18
14、to 0.89 mm)in thickness.1This specification is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Products.Current edition approved March 15,2018.Published March 2018.Originally
15、approved in 1943.Last previous edition approved in 2014 as D748 14.DOI:10.1520/D0748-18.2Coutlee,K.G.,“Electrical Quality Classification of Raw Mica by a Rapid,Direct-Reading Test Method,”Proceedings,ASTM,Vol 46,1946,p.1486.3For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact
16、 ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDe