1、Designation: D 4703 07Standard Practice forCompression Molding Thermoplastic Materials into TestSpecimens, Plaques, or Sheets1This standard is issued under the fixed designation D 4703; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, 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 compression molding of ther-moplastic granules and milled stock for the prep
3、aration of testspecimens.21.2 While conditions for certain materials are given, theprimary source of specific conditions shall be the materialspecification standards for each type of material.1.3 The values stated in SI units are to be regarded as thestandard. The values given in brackets are for in
4、formation only.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 determine the applica-bility of regulatory limitations prior to use.
5、NOTE 1The main body of this practice is equivalent to ISO 293-1986.Annex A1 and ISO 293-1986 differ in some details; however, specimensprepared using Annex A1, Procedure A should be equivalent to thoseprepared using ISO 293-1986, Cooling Method D. Specimens preparedusing Annex A1, Procedure C should
6、 be equivalent to those preparedusing ISO 293-1986, Cooling Method B. However, due to the greatercooling rate tolerances of the ISO standard, specimens prepared inaccordance with ISO Cooling Method B may not be equivalent to AnnexA1, Procedure C.2. Referenced Documents2.1 ASTM Standards:3D 618 Pract
7、ice for Conditioning Plastics for TestingD 1248 Specification for Polyethylene Plastics ExtrusionMaterials for Wire and CableD 3350 Specification for Polyethylene Plastics Pipe andFittings MaterialsD 4976 Specification for Polyethylene Plastics Molding andExtrusion MaterialsISO 293-1986 PlasticsComp
8、ression Moulding TestSpecimens of Thermoplastic Materials43. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 average cooling rate (C/min), nthe cooling ratecalculated by dividing the difference between the molding anddemolding temperatures by the time required to cool the moldto
9、the demolding temperature.3.1.2 cooling rate (C/h), nthe rate of cooling obtained bycontrolling the flow of the cooling fluid in such a way thatduring each 10-min interval, the deviation from this specifiedcooling rate shall not exceed the specified tolerance.3.1.3 demolding temperature, nthe temper
10、ature of themold or the press platens at the end of the cooling time,measured in the nearest vicinity to the molded material.3.1.3.1 DiscussionFor positive molds, holes are normallydrilled in the mold for measuring the temperatures defined in3.1.3 and 3.1.4.3.1.4 molding temperature, nthe temperatur
11、e of the moldor the press platens during the preheating and molding time,measured in the nearest vicinity to the molded material.3.1.5 molding time, nthe time during which full pressureis applied while maintaining the molding temperature.3.1.6 picture frame mold, na flat piece of metal, usually ofbr
12、ass or steel, that has a center portion removed to provide thespecified shape and dimensions of the final molding. Thethickness of the metal is dependent on the desired thickness ofthe finished molding, taking into consideration the shrinkage ofthe material to be molded. The picture frame mold is so
13、me-times referred to as a chase.3.1.7 preheating time, nthe time required to heat thematerial in the mold up to the molding temperature whilemaintaining the contact pressure.4. Significance and Use4.1 The methods by which sample materials are preparedand molded influence the mechanical properties of
14、 the speci-men. Unlike injection molding, the objective of compressionmolding is to produce test specimens or sheets that are both1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.09 on Specimen Preparation.Current edition a
15、pproved April 1, 2007. Published April 2007. Originallyapproved in 1991. Last previous edition approved in 2003 as D 4703 03.2This practice was created as a coalescence of and replacement for PracticesD 1928, D 2292, D 3010, and D 3463.3For referenced ASTM standards, visit the ASTM website, www.astm
16、.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.4ISO/IEC Selected Standards for Testing Plastics, available from ASTM. Alsoavailable from American National Standards Institu
17、te (ANSI), 25 W. 43rd St., 4thFloor, New York, NY 10036.1*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.homogeneous and isotropic. Molded specimens may be madefrom pow
18、der or pellets such as are received directly from amaterial manufacturer, particles produced in a recycle recoveryoperation, or from a milled preform or sheet prepared on atwo-roll mill. The powder, pellets, particles, preform, or sheetare melted and molded in a mold designed to produce afinished sp
19、ecimen of a given geometry, size, and thickness, ormelted and molded in the form of a smooth plaque or sheet ofuniform thickness from which desired specimens are cut,punched, or machined. Working a compound on a two-roll millprior to molding will disperse and distribute the compoundadditives in a ma
20、nner that will affect the physical properties ofthe compound. The need for milling a sample prior to com-pression molding may be determined by reference to therelevant material specification or the material manufacturer. Itis important to treat different samples of the same type ofmaterial in the sa
21、me way: if milling was done prior to moldingon a material which is to be used as a standard for comparison,all new materials to be tested against this practice should beprepared and molded in a similar manner.4.2 The apparatus and exact conditions required to prepareadequate specimens may vary for e
22、ach plastic material. Appa-ratus and procedures which should be satisfactory for moldingmany different plastic materials are given in this practice inSections 5 and 6. The apparatus and procedures which havebeen found satisfactory for molding certain specific materialsare given in the Appendix. In a
23、ny case, the apparatus andprocedures to be used in producing compression-molded speci-mens of a given material may be obtained by reference to therelevant material specification and should be agreed uponbetween the purchaser and the supplier.5. Apparatus5.1 MillAny size two-roll mill having chrome-p
24、latedrolls, capable of maintaining a constant temperature within62C 63.6F of the temperature needed for the particularmaterial involved, and being adjustable in speed as needed forthe material to be worked, is adequate. Some recommendationsfor mills to be used for specific types of materials are giv
25、en inthe Appendix.5.2 Molds:5.2.1 Mold TypesSeveral different types of molds may beused for the compression molding of test specimens of ther-moplastics. In general, however, the molds used will fall intoone of two categories: a flash-type mold (see Figs. 1 and 2)ora positive-type mold (see Fig. 3).
26、 The characteristics of the testspecimens prepared by using different types of molds are notthe same. In particular, some mechanical properties may beaffected by the pressure applied to the material during cooling.5.2.2 Flash-Type MoldThe flash-type mold may be of thepicture-frame type, where a meta
27、l chase (the picture frame) issandwiched between two thin metal ferrotype plates (see Fig.1), or it may be of the machined-cavity type (see Fig. 2), wherethe mold consists of a cavity machined in a metal plate, with asingle metal ferrotype plate used as a top or cover. The cavity,or cavities, in the
28、 flash-type mold may be constructed to molda single plaque from which test specimens may be stamped ormachined, or the mold may be built to mold one or morespecimens to finished dimensions. Flash molds permit excessmolding material to be squeezed out and do not exert moldingpressure on the material
29、during cooling. Nevertheless, this typeof mold is useful for preparing test specimens or panels ofsimilar thickness or comparable levels of low internal stress.5.2.3 Positive-Type MoldThe positive-type mold consistsof a cavity machined in a plate or block of metal and a force orplunger which closely
30、 mates with the sidewalls of the cavity(see Fig. 3). Like the flash-type mold, the cavity may be builtto produce a plaque from which test specimens may bestamped or machined, or to mold a test specimen to finisheddimensions. Because of the manner in which the positive moldoperates, it is recommended
31、 that this mold type, either for aplaque or a finished specimen, be limited to a single cavity. Inthe positive-type mold, the full molding pressure, neglectingfriction, is exerted on the material during cooling. The thick-ness, stress and density of the resulting moldings depend on themold construct
32、ion, the size of the material charge, and themolding conditions. This type of mold produces test specimenswith high density, and it is particularly suitable for obtainingflat surfaces and for suppressing the formation of voids withintest specimens.5.2.4 Mold SurfacesThe surfaces of either type of mo
33、ldthat form the flat faces of the specimen should be finished tothe degree required by the test for which the specimen isintended. For most tests, a surface quality of SPI-SPE #2 isadequate.5The edges of the mold cavity should be visually freeof nicks and scratches which could cause premature failur
34、e ofthe specimen during testing.5.3 Press:5.3.1 The press shall have a clamping force capable ofapplying a pressure (conventionally given as the ratio of theclamping force to the area of the mold cavity) of at least 105Mold comparison kits are available from D-M-E Company, 29111 StephensonHighway, M
35、adison Heights, MI 48071.FIG. 1 Flash Picture-Frame MoldFIG. 2 Flash Mold with Machined CavityFIG. 3 Positive-Type MoldD4703072MPa 1450 psi, and shall be capable of maintaining pressurewithin 10 % of the specified pressure during the molding cycle.5.3.2 The platens of the press shall be capable of b
36、eingheated to at least 240C, and being cooled at a rate consistentwith the cooling method selected from Table 1.5.3.3 The platens or mold shall be heated either by high-pressure steam, by a heat-conducting fluid in an appropriatechannel system, or by using electric-heating elements. Theplatens or mo
37、ld are cooled by a heat-conducting fluid (usuallycold water) in a channel system.5.3.4 The heating and cooling systems in the mold platensshall be such that, when used with a particular mold, they shallbe capable of maintaining a temperature difference betweenpoints on the mold surfaces of no more t
38、han 65C duringheating or cooling.5.3.5 For quench cooling (Method C in Table 1), twopresses shall be used, one for heating during molding and theother for cooling unless it can be demonstrated that the pressused for heating can cool at the specified rate.NOTE 2For a specified cooling method, the flo
39、w rate of the heat-conducting fluid should be predetermined in a test without any material inthe mold.6. Procedure6.1 Preparation of Molding Material:6.1.1 Drying of Granular MaterialDry the granular ma-terial as specified in the relevant material specification, or inaccordance with the material sup
40、pliers instructions. If noinstructions are given, dry for 24 6 1hat706 2C in an oven.6.1.2 Preparation of PreformsDirect molding of testspecimens, plaques, and sheets from granules shall be thestandard procedure, provided that a sufficiently homogeneoussheet is obtained. Normally this means that the
41、 moldedspecimen, plaque, or sheet is free from surface irregularitiesand internal imperfections. Poly(vinyl chloride) (PVC) com-pounds and chlorinated poly(vinyl chloride) (CPVC) com-pounds will generally require milling to obtain a preform forthe final molding procedure.6.1.3 MillingDirect molding
42、from powder or granulesmay sometimes require melt homogenization using a hot-meltmilling or mixing procedure to achieve a satisfactory finalsheet. Where such is required, a two-roll mill will usuallyperform satisfactorily. Take the milled material from the milland cut or shape it to become a preform
43、 for the compressionmold in which it ultimately will be molded. Use millingconditions that do not degrade the polymer. Recommendedconditions for milling the material, particularly the stocktemperature and time on the rolls, may be obtained from therelevant material specification or the material manu
44、facturer.The preform prepared by milling should normally be thickerthan the specimen, plaque, or sheet to be molded to enable themolding to be done properly.6.2 Molding:6.2.1 Adjust the mold temperature to within 65C of themolding temperature indicated in the relevant material speci-fication. With p
45、icture-frame (Fig. 1) molds or large, heavymolds it may not be necessary or desirable to preheat the molditself. This will then require slight increases in the preheat timeof the cycle; the temperature stability of the material shall beconsidered.6.2.2 Place a weighed quantity of the material (granu
46、les orpreforms) in the preheated mold. If granular material is used,make sure that it is evenly spread over the mold surface. Themass of the material shall be sufficient to fill the cavity volumewhen it is melted and allow about a 10 % loss for a flash moldand about a 3 % loss for a positive mold. W
47、ith flash molds,cover the mold with the top ferrotype plate (see Figs. 1 and 2)and then place the mold in the preheated press.6.2.3 Close the press and preheat the material charge byapplying a contact pressure for a minimum of 5 min. Thenapply full pressure for a minimum of 2 min (molding time, see3
48、.1.5) and then cool down (see 6.3).NOTE 3Apreheating time of 5 min is the standardized time for evenlyspread material charges sufficient for sheets up to 2 mm in thickness. Forthicker moldings, adjust the time accordingly.NOTE 4At contact pressure the press is just closed with a pressure lowenough t
49、o avoid flow of the material. Full pressure means a pressuresufficient to shape the material and squeeze out the excess material.6.3 Cooling:6.3.1 GeneralWith some thermoplastics, the cooling rateaffects the ultimate physical properties. For this reason, thecooling methods are specified in Table 1. The method ofcooling shall always be stated together with the final physicalproperties. The appropriate cooling method is normally givenin the relevant material specification. If no method is indicated,Method B shall be used.6.3.2 Cooling MethodsThe appro
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