1、Designation: D3641 10Standard 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.Those conditions should become a part of the specification forthe material, or be agreed upon between the purchaser and thesupplier.Any requirements or recommendations in the materialspecification which differ from this standard take precedenceover those in this standard.1.2 The m
5、ethodology 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 This standard does not purport to address all of thesafety concerns, if any, associ
6、ated 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 is equivalent to the following parts of ISO 294:PlasticsInjection Moulding of Test
7、 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: Part 3Plates(ISO Type D Moulds).2. Referenced Documents2.1 ASTM Standards:2D256 Tes
8、t 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 PlasticsUnder Flexural Load in the Edgewise PositionD790 Test Methods for Flexura
9、l Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating MaterialsD883 Terminology Relating to PlasticsD955 Test Method of Measuring Shrinkage from MoldDimensions of ThermoplasticsD957 Practice for Determining Surface Temperature ofMolds for Plastics2.2 ISO Standards:3ISO 3167 P
10、lasticsPreparation 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 Bars (ISO Type B Mould)ISO 294-2: PlasticsInjection Moulding of Test Specimensof Th
11、ermoplastic 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 DefinitionsDefinitions of terms applying to this prac-tice appear in Terminology D883.3.2 Definitions o
12、f 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 andinjection time. (See Terminology D883.)3.2.1.1 DiscussionThe average injection veloc
13、ity is cal-culated as follows:Vav5VsTi3 Ac3 nwhere:Vav= average injection velocity, mm/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 Aug. 1, 2010. Published September
14、 2010. Originallyapproved 1991. Last previous edition approved 2002 as D3641 02. DOI: 10.1520/D3641-10.2For 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
15、 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.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
16、, West Conshohocken, PA 19428-2959, United States.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 cavity or thosecontaining identical multi-specimen cavities only. This calcu
17、lation doesnot 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 of the test specimen.3.2.3 flash, nthin film of material formed at the partin
18、gline 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 stageof the injection molding cycle when the control or level of theforwarding force applied to the screw and shot is switchedfrom that used
19、 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 travel isswitched from speed control to pressure control.4. Summary of Practice
20、4.1 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 chamber, pressures andspeeds used, size, shape, and length of runners and gates, m
21、oldtemperature 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 materials that absorbwater this may mean drying under prescribed conditions. Thisp
22、ractice attempts to control some of these variables, nullifyothers, and report those that are necessary to obtain reproduc-ible specimens. Definite stock and mold temperatures, based onthe relevant material specifications or the material suppliersrecommendations or past experience, and measured by s
23、tan-dard techniques, are used for the molding process. By asequence of operations the pressures, timing settings, and modeof control are established on the basis of their effects upon themolded part itself rather than upon any universal setpoints.5. Significance and Use5.1 It is well known that plas
24、tic test specimens moldedunder different conditions 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
25、for the material for recommended molding condi-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
26、 machine selected foruse must be equipped with appropriate devices for the controland measurement of hydraulic pressure, all relevant tempera-tures, and the timing of certain cycle elements. Additionaldevices to monitor cavity pressure and ram position andvelocity are very useful and desirable in th
27、e effective control ofthe injection molding process to give reproducible results. Thecapacity of the machine should be such that the total shotweight (specimens plus sprue and runners) is 20 to 80 % ofrated capacity. The injection machine must be capable ofmaintaining the proper injection velocity r
28、ange if specified inthe material standard.NOTE 2Heat-sensitive materials may require using the high end of the30 to 80 % range in order to minimize residence time of the melt in thebarrel.6.1.1 Control SystemThe various control systems shouldbe able to maintain the operating parameters of the inject
29、ionmolding process from cycle to cycle within the followinglimits:plastic melt, or stock temperature 63Cmold temperature 63C, #80C65C, 80Cinjection pressure 62%hold pressure 65%injection time 60.1 shold time 65%shot weight 61%Suitable means of monitoring these parameters to ensurecontrol within the
30、above limits should be present.6.1.2 ScrewThe design of the 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
31、 behigh enough to prevent flashing at all operating conditions.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 d
32、esign of the mold is one of the morecritical variables affecting 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 minim
33、ize differences between resultsobtained by different parties. 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 An
34、nex A1.)6.2.1 Cavity LayoutMulti-cavity molds with identicalcavities are recommended. The cavity layout should be suchthat there is a uniform and symmetrical distribution of speci-men surface area on the overall mold surface. The use of singlecavity molds is discouraged. For large tensile test speci
35、mensand multipurpose bars, a two cavity “Z” layout is preferred, buta “T” layout is acceptable. For small tensile test specimens andD3641 102bars, a four cavity double “T” layout is recommended. Otherspecimens have their unique cavity layout. (See Annex A1.)NOTE 4ISO 294-1 states that the “Z” cavity
36、 runner layout is preferredover the “T” cavity runner layout.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 ar
37、e achieved in all cavities. Empiricaltechniques can be used to 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 Run
38、nersRunners may be of the full-round type cutinto both halves of the mold or of the trapezoidal type cut intoonly one of the mold halves. They shall be a minimum of 5 mm(0.2 in.) in diameter or of equivalent cross-sectional area iftrapezoidal. A symmetrical cavity layout will permit identicalrunner
39、systems to be used for each cavity and thus facilitateuniform filling of all cavities with all materials under allconditions. Runner draft angles for trapezoidal runners shouldbe 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 b
40、ars is longer than conventionalto allow for approximately 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
41、 if multi-cavity molds with non-identical runner systems are used, specimens from such cavities shall beidentified and should not be commingled for testing unless it has beendemonstrated that there are no statistically significant differences in testresults between the cavities.NOTE 8Limited data ha
42、ve shown that, for some materials (Polypro-pylenes, in particular), 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 speci
43、mens 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 beconsidered when comparing data obtained from different sources.6.2.3 GatesUnless otherwise stated for specific speci-mens, or material speci
44、fications, the gate depth should be atleast two-thirds the depth of the bar-type cavities and the gatewidth shall preferably be equal to the width of the bar-typecavities but no less than two thirds the width. Gates should beas short as possible with a maximum length of 3 mm (0.12 in.).Such large ga
45、tes tend to give parts whose physical propertiesare less sensitive to varying molding conditions than smallerones. However, many existing test methods call for somewhatsmaller gates such as some of those listed in Table 1. Alsocertain materials may require smaller gates to promote shearthinning so t
46、hat mold cavities can be filled.6.2.4 CavitiesMachining tolerances 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
47、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 dimensions only when shrinkage leads to aspecimen that is out of specification for the desired testmethod. Draft angles in the sidewalls of th
48、e 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 shall not be greater than 2. Amaximum draft angle of12 is preferred for all areas. Allinterior mold surfaces should be finished to Societ
49、y of PlasticsIndustry-Society of Plastics Engineers (SPI-SPE) No. A-3 orbetter. If cavity identification is required, this should 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 t
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1