ASTM_D_731_-_22.pdf

Designation:D73122Standard Test Method forMolding Index of Thermosetting Molding Powder1This standard is issued under the fixed designation D731;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,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 test method covers the measurement of the moldingindex(plasticity)of thermosetting plastics ranging in flow fromsoft to stiff by selection of appropriate molding pressureswithin the range from 3.7 to 36.5 MPa(530 to 5300 psi).1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles 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:2D256 Test Methods for Determining the Izod PendulumImpact Resistance of PlasticsD883 Terminology Relating to PlasticsD957 Practice for Determining Surface Temperature ofMolds for PlasticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 Definitions are in accordance with Terminology D883,unless otherwise specified.3.2 Definitions of Terms Specific to This Standard:3.3 plasticity,na measure of the resistance of a moltenthermosetting material to flow under heat and pressure.Ameasure of the apparent viscosity of the material.4.Summary of Test Method4.1 A cup mold is mounted in a semi-automatic type press.A predetermined quantity of test sample is charged into themold,controlled at a temperature dependent upon the testmaterial.The minimum force required to mold a cup having aflash or fin thickness within a specified tolerance is determined.This force along with the mold closing time is reported asmolding index.5.Significance and Use5.1 This test method provides a guide for evaluating themoldability of thermosetting molding powders.This testmethod does not necessarily denote that the molding behaviorof different materials will be alike and trials may be necessaryto establish the appropriate molding index for each material inquestion.5.2 The sensitivity of this test diminishes when the moldingpressure is decreased below 5.3 MPa(764 psi),so pressureslower than this are not ordinarily recommended.This is due tothe friction of moving parts and the insensitivity of the pressureswitch actuating the timer at these low pressures.6.Apparatus6.1 MoldA cup mold of the flash type,to produce amolded cup as shown in Fig.1,operated under controlledpressure and temperatures and provided with stops so that flashor fin thickness cannot be less than 0.14 mm(0.0055 in.).Thearea of the mold casting creating the molded flash shall belocated on top of the cup,flat,perpendicular to the axis of thecup,and in the form of an annular ring 3.17 mm(0.125 in.)inwidth.6.2 PyrometerA calibrated pyrometer,traceable to a na-tional standard(for example,NIST),and accurate to 61Cshall be used to determine the temperature of the moldsurfaces.For properly measuring mold temperatures,referencePractice D957.6.3 Heating SystemAny conventional means for heatingthe press platens,provided the heat source is constant enough1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.30 on Thermal Properties(Section D20.30.08).Current edition approved March 15,2022.Published March 2022.Originallyapproved in 1950.Last previous edition approved in 2018 as D731-18.DOI:10.1520/D0731-22.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact 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 theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1to maintain the molding temperature within 61C of thespecified temperature(see 9.2).6.4 Pressure SystemA se