1、Designation: D3641 12Standard 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 which differ from this standard take precedence overthose in this standard.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 b
5、e regarded as thestandard. The values given in parentheses are for informationonly.1.4 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 and health practices and
6、determine the applica-bility of regulatory limitations prior to use.NOTE 1This practice is 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
7、 (ISO Type B Mould); ISO 294-2: Part2Small Tensile Bars (ISO Type C Mould); ISO 294-3: Part 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
8、 Method for Tensile Properties of PlasticsD648 Test Method for Deflection Temperature of PlasticsUnder Flexural Load in the Edgewise PositionD790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating MaterialsD883 Terminology Relating to PlasticsD955 T
9、est Method of Measuring Shrinkage from MoldDimensions of ThermoplasticsD957 Practice for 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 Ma
10、terialsPart 1: General Principlesand Multipurpose Test Specimens (ISO Type A Mould)and Bars (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 Thermop
11、lastic MaterialsPart 3: Plates (ISO Type DMoulds)3. Terminology3.1 DefinitionsDefinitions 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 fron
12、t within a cavity duringthe injection time that is calculated from the shot volume andinjection time. (See Terminology D883.)3.2.1.1 DiscussionThe average injection velocity is cal-culated as follows:Vav5VsTi3 Ac3 nwhere:Vav= average injection velocity, mm/s,Vs= shot volume, mm3,Ti= injection time,
13、s,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 April 15, 2012. Published May 2012. Originallyapproved 1991. Last previous edition approved 2010 as D3641 10A. DOI:10.15
14、20/D3641-12.2For 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.3Available from American National Standards Insti
15、tute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Ac= cross section of the cavity, mm2, (se
16、e 3.2.2) andn = number of cavities.The calculation is valid for molds containing a single cavity or thosecontaining identical multi-specimen cavities only. This calculation doesnot apply for family molds.3.2.2 cross section of the cavity, nin a mold for testspecimens, the area of a planar section pe
17、rpendicular to theflow pattern during filling of the mold that forms the criticalportion 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, nth
18、at point in the injection stageof the injection molding cycle when the control or level of 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
19、 injection molding cycle as definedby pressure, position, or time when the rate of ram travel 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 tes
20、t results. Among these are geometry, size, andtemperature conditions of the heating chamber, 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
21、 in the process. It is sometimes necessary topretreat materials before molding. For materials 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 varia
22、bles, nullify others, and report those that arenecessary to obtain reproducible specimens. 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 pro
23、cess. By a sequence of operations the pres-sures, timing settings, and mode of control are established onthe basis of their effects upon the molded part itself rather thanupon any universal setpoints.5. Significance and Use5.1 It is well known that plastic test specimens moldedunder different condit
24、ions can have significantly differentproperties. This practice is designed to minimize those 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-
25、tions. If not available, consult the material supplier.5.3 This practice requires the use of 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
26、appropriate devices for the controland measurement of pressures, all relevant temperatures, 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 giv
27、e reproducible results. The capacity ofthe machine shall be such that the total shot weight (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-sensi
28、tive materials may require using the high end of themachine shot capacity range in order to 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
29、 limits:plastic melt, or stock temperature 63Cmold temperature 63C, #80C65C, 80Cinjection pressure 62%hold pressure 65%injection time 60.1 shold time 65%shot weight 62%Suitable means of monitoring these parameters to ensurecontrol within the above limits shall be utilized.6.1.2 ScrewThe design of th
30、e screw will be determined bythe material being molded.Akey criterion of screw design is toprovide 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 condit
31、ions.NOTE 3The minimum clamp force required is the product of thehighest possible cavity pressure 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 morecritical variables aff
32、ecting specimen properties. Optimum re-producibility requires that identical molds be used by partiesattempting to obtain comparable results. However, in theabsence of identical molds, adherence to certain features ofdesign will help to minimize differences between resultsobtained by different parti
33、es. It has been found that the use ofunitized mold bases with interchangeable mold plates and gateinserts can provide a great deal of flexibility and provide rapidtransitions between the moldings of different specimen con-figurations. (See Annex A1.)6.2.1 Cavity LayoutMulti-cavity molds with identic
34、alcavities are recommended. The cavity layout shall be such thatthere is a uniform and symmetrical distribution of specimensurface 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 preferr
35、ed, buta “T” layout is acceptable. For small tensile test specimens andbars, a four cavity double “T” layout is recommended. Otherspecimens have their unique cavity layout. (See Annex A1.)D3641 122NOTE 4ISO 294-1 states that the “Z” cavity runner layout is preferredover the “T” cavity runner layout.
36、NOTE 5Family molds designed to produce more than one partconfiguration with each shot are not recommended. 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 t
37、o estimate these velocities. Additionally it iscautioned that the comparability of data obtained 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-roundtype cut into bot
38、h halves of the mold or of the trapezoidal typecut into only one of the mold halves. They shall be a minimumof 5 mm (0.2 in.) in diameter or of equivalent cross-sectionalarea if trapezoidal. A symmetrical cavity layout will permitidentical runner systems to be used for each cavity and thusfacilitate
39、 uniform filling of all cavities with all materials underall conditions. Runner draft angles for trapezoidal runners shallbe from 10 to 30. The diameter of the sprue shall be aminimum of 4 mm on the nozzle side.NOTE 6The runner system for small bars is longer than conventionalto allow for approximat
40、ely the same total shot volume between thedifferent interchangeable cavity plates so that the shot 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 syste
41、ms are used, specimens from such cavities shall beidentified and not be commingled for testing unless 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 (Polypro-pylenes, in part
42、icular), mechanical test values can be significantly affectedby the cross sectional area of the runner. Specimens molded using thespecified 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 a
43、nd 80 mm2. Higher viscosity(lower MFR) materials appear to be more sensitive. This effect needs to beconsidered when comparing data obtained from different sources.6.2.3 GatesUnless otherwise stated for specific speci-mens, or material specifications, the gate depth shall be at leasttwo-thirds the d
44、epth of the bar-type cavities and the gate widthshall preferably be equal to the width of the bar-type cavitiesbut no less than two thirds the width. Use the shortest possiblegate length, with a maximum length of 3 mm (0.12 in.). Suchlarge gates tend to give parts whose physical properties are lesss
45、ensitive to varying molding conditions than smaller ones.However, many existing test methods call for somewhatsmaller gates such as some of those listed in Table 1.NOTE 9Certain materials require smaller gates to promote shearthinning so that mold cavities will be filled.6.2.4 CavitiesMachining tole
46、rances of the cavity willdepend on the material to be molded and on the tolerancesallowed in the specific 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
47、. It is preferred tomachine the cavity to the nominal dimensions of the specimenand to adjust the dimensions 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
48、but shall not begreater than 1 except in the shoulder of the multipurpose testspecimen (ISO 3167) that 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)
49、 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. For tensiletest specimens, it is recommended that the ejector pins belocated at the wide tab ends (shoulders). For bars, it isrecommended that the ejector pins be located at the “dead” endof the bar and ou
