1、Designation:D 1928 96An American National StandardStandard Practice forPreparation of Compression-Molded Polyethylene TestSheets and Test Specimens1This standard is issued under the fixed designation D 1928;the number immediately following the designation indicates the year oforiginal adoption or,in
2、 the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1.Scope1.1 This pr
3、actice covers the preparation of compression-molded test sheets of Types I,II,III,and IV polyethyleneplastics(Specification D 1248).This practice includes bothbranched and linear polyethylenes.Two of the proceduresgiven provide for compression-molded sheets to be condi-tioned by first heating each m
4、aterial above its melting point fora period of time sufficient to erase its prior thermal history andthen cooling it from the melt state at a controlled rate whilemaintaining the required dimensions of the sheet.The thirdprocedure provides for molded test sheets to be prepared bycooling the platens
5、of the compression press,and hence themolten polyethylene plastic,at a controlled rate.Three coolingschedules are provided for as follows:1.1.1 Procedure A,in which the temperature of the initiallymolten plaque is lowered at a rate of 5 6 0.5C/h.NOTE1It is recognized that Procedure A may not be appl
6、icable tomaterial containing carbon black due to difficulties,at times,with sheetscontaining voids.If it is not possible to mold a void-free sheet,ProcedureB or C should be selected.1.1.2 Procedure B,in which the initially molten plaque ischilled very rapidly under specified conditions in water,and1
7、.1.3 Procedure C,in which the temperature of the platensof the molding press,and hence of the initially molten plaque,is lowered at a rate of 15 6 2C/min.1.2 This practice method also covers the preparation of testspecimens from compression molded test sheets.1.3This standard does not purport to add
8、ress all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific precau-tionary statements are given in 7.5.1.NOTE2
9、Although this practice and ISO 293-1986(E)differ in somedetails,data obtained using either method should be technically equiva-lent.2.Referenced Documents2.1 ASTM Standards:D 618 Practice for Conditioning Plastics and ElectricalInsulating Materials for Testing2D 638 Test Method for Tensile Propertie
10、s of Plastics2D 1248 Specification for Polyethylene Plastics Molding andExtrusion Materials2D 4703 Practice for Compression Molding ThermoplasticMaterials into Test Specimens,Plaques,or Sheets3D 4976 Specification for Polyethylene Plastics Molding andExtrusion Materials33.Terminology3.1 Definitions:
11、3.1.1 picture frame molda flat piece of metal of somedimensions usually of brass or steel that has its center portionremoved to give a shape and dimension of the final molding.The thickness of the metal is dependent on the desiredthickness of the finished molding,taking into consideration theshrinka
12、ge of the material to be molded.4.Significance and Use4.1 The conditions under which a polyethylene plastic isformed into a test sheet,particularly the rate of cooling,influence some of the properties of test specimens taken fromthe sheet.It is,therefore,necessary to control the cooling rateof the t
13、est sheet.This practice is intended to minimizeinterlaboratory variability of test results on compression-molded specimens arising from differences in rate of cooling.4.1.1 Procedures A and B are designed also to erase mod-erate differences in the prior thermal history by employing aconditioning per
14、iod of 1 h at a temperature about 25C abovethe melting point of the polyethylene plastic prior to cooling ata controlled rate.For Procedures A and B,the conditioningtemperature may have to be raised above this minimum valuein some cases to promote adhesion to the aluminum foil partingsheets.The foll
15、owing temperatures,which depend on the typeof polyethylene plastic as classified in Specification D 1248,have been found to be generally useful:Type I140C1This practice is under the jurisdiction of ASTM Committee D-20 on Plasticsand is the direct responsibility of Subcommittee D20.12 on Olefin Plast
16、ics.Current edition approved July 10,1996.Published September 1996.Originallypublished as D 1928 62 T.Last previous edition D 1928 90.2Annual Book of ASTM Standards,Vol 08.01.3Annual Book of ASTM Standards,Vol 08.03.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMNOTICE:This standard has either been superseded and replaced by a new version or discontinued.Contact ASTM International(www.astm.or
