1、Designation: D 3641 02Standard Practice forInjection Molding Test Specimens of Thermoplastic Moldingand Extrusion Materials1This standard is issued under the fixed designation D 3641; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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.1. Scope *1.1 This practice covers the general principles to be fol-lowed when injection molding test specimens of t
3、hermoplasticmolding 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
4、 each 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
5、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 This standard does not purport to address all of thesafety concerns, if any, a
6、ssociated 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
7、 Test Specimens of Thermoplastic Mate-rials2; 294-1: Part 1General Principles and Multipurpose Test Speci-mens (ISO Type A Mould) and Bars (ISO Type B Mould)2; ISO 294-2:Part 2Small Tensile Bars (ISO Type C Mould); ISO 294-3: Part3Plates (ISO Type D Moulds).2. Referenced Documents2.1 ASTM Standards:
8、D 256 Test Methods for Impact Resistance of Plastics andElectrical Insulating Materials3D 570 Test Method for Water Absorption of Plastics3D 638 Test Method for Tensile Properties of Plastics3D 648 Test Method for Deflection Temperature of PlasticsUnder Flexural Load3D 790 Test Methods for Flexural
9、Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Materi-als3D 883 Terminology Relating to Plastics3D 955 Test Method for Measuring Shrinkage from MoldDimensions of Molded Plastics3D 957 Practice for Determining Surface Temperature ofMolds for Plastics32.2 ISO Standards:ISO
10、 3167 PlasticsPreparation and Use of MultipurposeTest Specimens2ISO 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)2ISO 294-2: PlasticsInjection Moulding of Test Speci
11、mensof Thermoplastic MaterialsPart 2: Small Tensile Bars(ISO Type C Mould)2ISO 294-3: PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 3: Plates (ISO Type DMoulds)23. Terminology3.1 DefinitionsDefinitions of terms applying to this prac-tice appear in Terminology D 883.3.2 D
12、efinitions 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 andinjection time. (See Terminology D 883.)3.2.1.1 DiscussionThe average in
13、jection velocity is cal-culated as follows:Vav5VsTi3 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) and1This practice is under the jurisdiction of ASTM Committee D20 on Plastics andis the direct responsibi
14、lity of Subcommittee D20.09 on Specimen Preparation.Current edition approved April 10, 2002. Published June 2002. Originallypublished as D 3641 91. Last previous edition D 3641 97.2Available from American National Standards Institute, 25 W. 43rd St., 4thFloor, New York, NY 10036.3Annual Book of ASTM
15、 Standards, Vol 08.01.1*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.n = number of cavities.The calculation is valid for molds containing a single cavity or thosecont
16、aining 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 perpendicular to theflow pattern during filling of the mold that forms the criticalportion of the test specimen
17、.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 stageof the injection molding cycle when the control or level of theforwarding forc
18、e 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 travel isswitched from
19、 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 chamber, pressures andspe
20、eds 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 materials that absorbwate
21、r this may mean drying under prescribed conditions. Thispractice 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 suppl
22、iersrecommendations or past experience, and measured by stan-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 setpoi
23、nts.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 those differ-ences by establishing operating protocols without being unnec-essarily restrictive.5.2 Always re
24、fer 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 of adequate quantities ofplastic material to find desirable operating conditions and tomake the desired te
25、st specimens.6. Apparatus6.1 Injection Molding MachineThe 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
26、 position andvelocity are very useful and desirable in the 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
27、 be capable ofmaintaining the proper injection velocity range 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 shouldb
28、e able to maintain the operating parameters of the injectionmolding 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
29、 monitoring these parameters to ensurecontrol within the above limits should be present.6.1.2 ScrewThe design of the screw will be determined bythe material being molded. A key criterion of screw design is toprovide a melt that is as uniform as possible with respect tocomposition, temperature, and v
30、iscosity.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 pressure and the projected surface area of thecavities (and runners). A force greater than thi
31、s minimum will be requiredto prevent flashing.6.2 MoldThe design 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
32、, adherence to certain features ofdesign will help to minimize 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
33、the moldings of different specimen con-figurations. (See Annex 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 sing
34、lecavity 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 cavity double “T” layout is recommended. Otherspecimens have their unique cavity layout. (See An
35、nex 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 partD 36412configuration with each shot are not recommended. If molds of this natureare used, consideration shall be taken in the design
36、 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 obtained on specimens molded inthis manner may be limited not only to a specific polymer type
37、but also tospecific rheological characteristics.6.2.2 RunnersRunners 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.
38、 A symmetrical 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 trapezoidal runners shouldbe from 10 to 30. The diameter of the sprue shall be aminimum of 4
39、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 shot size does not haveto be adjusted significantly.NOTE 7If family molds with two or more iden
40、tical 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 should not be commingled for testing unless it has beendemonstrated that there are no statistically significant differences
41、in testresults between the cavities.6.2.3 GatesUnless otherwise stated for specific speci-mens, or material specifications, 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
42、 two thirds the width. Gates should beas short as possible with a maximum length of 3 mm (0.12 in.).Such large gates 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
43、as some of those listed in Table 1. Alsocertain materials may require smaller gates to promote shearthinning so that 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. Dimensi
44、oning 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 dimensions only when shrinkag
45、e 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 shall not be greater tha
46、n 2. Amaximum draft angle of12 is preferred for all areas. Allinterior mold surfaces should be finished to Society 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 tha
47、t 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
48、 ends (shoulders). For bars, it isrecommended that the ejector pins be located at the “dead” endof the bar and outside of the central 20 mm length of the ISOmold type B (80 mm bar). For plates, the ejector pins should beoutside the central area of 50 mm diameter.6.2.6 Cavity Pressure TransducersPres
49、sure transducersmay be mounted in conjunction with an ejector pin or directlyinto the cavity, coplanar to the mold surface. These may beused to monitor or control the mold filling characteristics. Inthe case of plates, the pressure transducer is mandatory formeasurement of molding shrinkage only and the mountingshall be as shown for ISO mold type D in Annex A1.Transducers may also be located in the main runner but thislocation will not provide suitable data for monitoring orcontrolling cavity flow.6.2.7 Mold CoolingCoolant channels shall
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