1、Designation: D3641 14Standard Practice forInjection Molding Test Specimens of Thermoplastic Moldingand Extrusion Materials1This standard is issued under the fixed designation D3641; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he 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 practice covers the general principles to be fol-lowed when injection molding test specimens of therm
3、oplasticmolding and extrusion materials. This practice is to be used toobtain uniformity in methods of describing the various steps ofthe injection molding process and to set up uniform methods ofreporting these conditions. The exact conditions required toprepare suitable specimens will vary for eac
4、h plastic material.Any requirements or recommendations in the material specifi-cation that differ from this standard take precedence over thosein this standard. Always consult the referenced material docu-ment for specimen preparation. If no referenced documentexists, then consult the material suppl
5、ier for specimen prepa-ration guidance and note such in the test report.1.2 The methodology presented assumes the use of recipro-cating screw injection molding machines.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 Th
6、is 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 and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1This practice i
7、s equivalent to the following parts of ISO 294:PlasticsInjection Moulding of Test Specimens of Thermoplastic Mate-rials; 294-1: Part 1General Principles and Multipurpose Test Specimens(ISO Type A Mould) and Bars (ISO Type B Mould); ISO 294-2: Part2Small Tensile Bars (ISO Type C Mould); ISO 294-3: Pa
8、rt 3Plates(ISO Type D Moulds).2. Referenced Documents2.1 ASTM Standards:2D256 Test Methods for Determining the Izod PendulumImpact Resistance of PlasticsD570 Test Method for Water Absorption of PlasticsD638 Test Method for Tensile Properties of PlasticsD648 Test Method for Deflection Temperature of
9、PlasticsUnder Flexural Load in the Edgewise PositionD790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Materi-alsD883 Terminology Relating to PlasticsD955 Test Method of Measuring Shrinkage from MoldDimensions of ThermoplasticsD957 Practice for
10、 Determining Surface Temperature ofMolds for Plastics2.2 ISO Standards:3ISO 3167 PlasticsPreparation and Use of MultipurposeTest SpecimensISO 294-1: PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 1: General Principlesand Multipurpose Test Specimens (ISO Type A Mould)and B
11、ars (ISO Type B Mould)ISO 294-2: PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 2: Small Tensile Bars(ISO Type C Mould)ISO 294-3: PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 3: Plates (ISO Type DMoulds)3. Terminology3.1 DefinitionsDefinition
12、s of terms applying to this prac-tice appear in Terminology D883.3.2 Definitions of Terms Specific to This Standard:3.2.1 average injection velocity, nthe mean value of thevelocity of the molten plastic flow front within a cavity duringthe injection time that is calculated from the shot volume andin
13、jection time. (See Terminology D883.)3.2.1.1 DiscussionThe average injection velocity is calcu-lated as follows:1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.09 on Specimen Preparation.Current edition approved March 1, 2
14、014. Published March 2014. Originallyapproved 1991. Last previous edition approved 2012 as D3641 12. DOI: 10.1520/D3641-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, re
15、fer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor
16、Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Vav5VsTi3 Ac3 nwhere:Vav= average injection velocity, mm/s,Vs= shot volume, mm3,Ti= injection time, s,Ac= cross section of the cavity, mm2, (see 3.2.2) andn = number of cavities.The calculation is valid for molds containing a single
17、cavity or those containing identical multi-specimen cavitiesonly. This calculation does not apply for family molds.3.2.2 cross section of the cavity, nin a mold for testspecimens, the area of a planar section perpendicular to theflow pattern during filling of the mold that forms the criticalportion
18、of the test specimen.3.2.3 flash, nthin film of material formed at the partingline of a part during molding, caused by unintentional openingof the mold or by defective mating surfaces.3.2.4 switchover point, nthat point in the injection stage ofthe injection molding cycle when the control or level o
19、f theforwarding force applied to the screw and shot is switchedfrom that used during injection to that used during pack/hold.3.2.5 velocity-pressure transfer point (VPT), nthat pointin the injection stage of the injection molding cycle as definedby pressure, position, or time when the rate of ram tr
20、avel isswitched from speed control to pressure control.4. Summary of Practice4.1 Many factors in the injection molding process can havean influence on the character of the moldings and the numericalvalues of test results. Among these are geometry, size, andtemperature conditions of the heating chamb
21、er, pressures andspeeds used, size, shape, and length of runners and gates, moldtemperature and its uniformity, cavity surface finish, andtiming cycles used along with the method of sequencing fromstage to stage in the process. It is sometimes necessary topretreat materials before molding. For mater
22、ials that absorbwater, drying under prescribed conditions is recommended andthe user is advised to consult the applicable material standardfor the conditions. This practice attempts to control some ofthese variables, nullify others, and report those that arenecessary to obtain reproducible specimens
23、. Definite stock andmold temperatures, based on the relevant material specifica-tions or the material suppliers recommendations or pastexperience, and measured by standard techniques, are used forthe molding process. By a sequence of operations thepressures, timing settings, and mode of control are
24、establishedon the basis of their effects upon the molded part itself ratherthan upon any universal setpoints.5. Significance and Use5.1 It is well known that plastic test specimens moldedunder different conditions can have significantly differentproperties. This practice is designed to minimize thos
25、e differ-ences by establishing operating protocols without being unnec-essarily restrictive.5.2 Always refer to the ASTM material specification or ISOdesignation for the material for recommended molding condi-tions. If not available, consult the material supplier.5.3 This practice requires the use o
26、f adequate quantities ofplastic material to find desirable operating conditions and tomake the desired test specimens.6. Apparatus6.1 Injection Molding MachineThe machine selected foruse must be equipped with appropriate devices for the controland measurement of pressures, all relevant temperatures,
27、 andthe timing of certain cycle elements. Additional devices tomonitor cavity pressure and ram position and velocity are veryuseful and desirable in the effective control of the injectionmolding process to give reproducible results. The capacity ofthe machine shall be such that the total shot weight
28、 (specimensplus sprue and runners) is 20 to 80 % of rated capacity. Theinjection machine must be capable of maintaining the properinjection velocity range if specified in the material standard.NOTE 2Heat-sensitive materials may require using the high end of themachine shot capacity range in order to
29、 minimize residence time of themelt in the barrel.6.1.1 Control SystemThe various control systems shallmaintain the operating parameters of the injection moldingprocess from cycle to cycle within the following limits:plastic melt, or stock temperature 3Cmold temperature 3C, #80C5C, 80Cinjection pres
30、sure 2 %hold pressure 5 %injection time 0.1 shold time 5 %shot weight 2 %Suitable means of monitoring these parameters to ensurecontrol within the above limits shall be utilized.6.1.2 ScrewThe design of the screw will be determined bythe material being molded.Akey criterion of screw design is toprov
31、ide a melt that is as uniform as possible with respect tocomposition, temperature, and viscosity.6.1.3 ClampThe clamping force of the machine shall behigh enough to prevent flashing at all operating conditions.NOTE 3The minimum clamp force required is the product of thehighest possible cavity pressu
32、re and the projected surface area of thecavities (and runners). A force greater than this minimum will be requiredto prevent flashing.6.2 MoldThe design of the mold is one of the more criticalvariables affecting specimen properties. Optimum reproduc-ibility requires that identical molds be used by p
33、arties attempt-ing to obtain comparable results. However, in the absence ofidentical molds, adherence to certain features of design willhelp to minimize differences between results obtained bydifferent parties. It has been found that the use of unitized moldbases with interchangeable mold plates and
34、 gate inserts canprovide a great deal of flexibility and provide rapid transitionsbetween the moldings of different specimen configurations.(See Annex A1.)6.2.1 Cavity LayoutMulti-cavity molds with identicalcavities are recommended. The cavity layout shall be such thatthere is a uniform and symmetri
35、cal distribution of specimenD3641 142surface area on the overall mold surface. The use of singlecavity molds is discouraged. For large tensile test specimensand multipurpose bars, a two cavity “Z” layout is preferred, buta “T” layout is acceptable. For small tensile test specimens andbars, a four ca
36、vity double “T” layout is recommended. Otherspecimens have their unique cavity layout. (See Annex A1.)NOTE 4ISO 294-1 states that the “Z” cavity runner layout is preferredover the “T” cavity runner layout.NOTE 5Family molds designed to produce more than one partconfiguration with each shot are not r
37、ecommended. If molds of this natureare used, consideration shall be taken in the design to ensure that constantand uniform filling velocities are achieved in all cavities. Empiricaltechniques can be used to estimate these velocities. Additionally it iscautioned that the comparability of data obtaine
38、d on specimens molded inthis manner may be limited not only to a specific polymer type but also tospecific rheological characteristics.6.2.2 RunnersRunners will either be of the full-round typecut into both halves of the mold or of the trapezoidal type cutinto only one of the mold halves. They shall
39、 be a minimum of5 mm (0.2 in.) in diameter or of equivalent cross-sectional areaif trapezoidal.Asymmetrical cavity layout will permit identicalrunner systems to be used for each cavity and thus facilitateuniform filling of all cavities with all materials under allconditions. Runner draft angles for
40、trapezoidal runners shall befrom 10 to 30. The diameter of the sprue shall be a minimumof 4 mm on the nozzle side.NOTE 6The runner system for small bars is longer than conventionalto allow for approximately the same total shot volume between thedifferent interchangeable cavity plates so that the sho
41、t size does not haveto be adjusted significantly.NOTE 7If family molds with two or more identical specimen cavitiesor non-identical runner systems or if multi-cavity molds with non-identical runner systems are used, specimens from such cavities shall beidentified and not be commingled for testing un
42、less it has been demon-strated that there are no statistically significant differences in test resultsbetween the cavities.NOTE 8Limited data have shown that, for some materials(Polypropylenes, in particular), mechanical test values can be significantlyaffected by the cross sectional area of the run
43、ner. Specimens molded usingthe specified minimum runner size of 5 mm D (20 mm2) exhibited lowervalues of most mechanical properties than specimens molded usingrunners with cross-sectional areas of 50 and 80 mm2. Higher viscosity(lower MFR) materials appear to be more sensitive. This effect needs to
44、beconsidered when comparing data obtained from different sources.6.2.3 GatesUnless otherwise stated for specificspecimens, or material specifications, the gate depth shall be atleast two-thirds the depth of the bar-type cavities and the gatewidth shall preferably be equal to the width of the bar-typ
45、ecavities but no less than two thirds the width. Use the shortestpossible gate length, with a maximum length of 3 mm (0.12in.). Such large gates tend to give parts whose physicalproperties are less sensitive to varying molding conditions thansmaller ones. However, many existing test methods call for
46、somewhat smaller gates such as some of those listed in Table1.NOTE 9Certain materials require smaller gates to promote shearthinning so that mold cavities will be filled.6.2.4 CavitiesMachining tolerances of the cavity willdepend on the material to be molded and on the tolerancesallowed in the speci
47、fic test methods. Dimensioning of cavitieswith respect to anticipated shrinkage will result in cavityvariations from molder to molder. It also requires differentmolds for every material to be molded. It is preferred tomachine the cavity to the nominal dimensions of the specimenand to adjust the dime
48、nsions only when shrinkage leads to aspecimen that is out of specification for the desired testmethod. Draft angles in the sidewalls of the cavity willprobably be needed to facilitate part ejection but shall not begreater than 1 except in the shoulder of the multipurpose testspecimen (ISO 3167) that
49、 shall not be greater than 2. Amaximum draft angle of12 is preferred for all areas. Allinterior mold surfaces shall be finished to Society of PlasticsIndustry-Society of Plastics Engineers (SPI-SPE) No. A-3 orbetter. If cavity identification is required, this shall be locatedoutside of the test area. It is recommended that the end of anejector pin be used to incorporate an identifying symbol ratherthan the cavity surface.6.2.5 Ejector PinsEjector pins shall be located wherenecessary, but not in the test area of the specimen.
