1、Designation: D4703 10Standard Practice forCompression Molding Thermoplastic Materials into TestSpecimens, Plaques, or Sheets1This standard is issued under the fixed designation D4703; 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 () 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 prepara
3、tion 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 parentheses are for in
4、formationonly.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.N
5、OTE 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:3D618 Practic
7、e for Conditioning Plastics for TestingD1248 Specification for Polyethylene Plastics ExtrusionMaterials for Wire and CableD3350 Specification for Polyethylene Plastics Pipe andFittings MaterialsD4976 Specification for Polyethylene Plastics Molding andExtrusion Materials2.2 ISO Standard:ISO 293-1986
8、PlasticsCompression 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
9、 the moldto 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,
10、 nthe temperature 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, nth
11、e temperature 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,
12、usually ofbrass 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 fram
13、e mold is some-times referred to as a chase.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 June 1, 2010. Published July 2010. Originally approvedin 1991. Last previous e
14、dition approved in 2007 as D4703 07. DOI: 10.1520/D4703-10.2This practice was created as a coalescence of and replacement for PracticesD1928, D2292, D3010, and D3463.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual B
15、ook 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 Institute (ANSI), 25 W. 43rd St., 4thFloor, New York, NY 10036.1*A Summary of
16、 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.3.1.7 preheating time, nthe time required to heat thematerial in the mold up to the molding temperature whilemaintaining the contact
17、pressure.4. Significance and Use4.1 The methods by which sample materials are preparedand molded influence the mechanical properties of the speci-men. Unlike injection molding, the objective of compressionmolding is to produce test specimens or sheets that are bothhomogeneous and isotropic. Molded s
18、pecimens may be madefrom powder 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 desi
19、gned to produce afinished specimen 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 t
20、he compoundadditives in a manner 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 sa
21、me type ofmaterial in the same 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 prepareadequ
22、ate specimens may vary for each 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
23、 given in the Appendix. In any 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 t
24、wo-roll mill having chrome-platedrolls, 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 speci
25、fic types of materials are given 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 po
26、sitive-type mold (see Fig. 3). 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 thepi
27、cture-frame type, where a metal 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.
28、The cavity,or cavities, in the 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 mo
29、ldingpressure on the material 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
30、 force orplunger which closely 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 m
31、oldoperates, it is recommended 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 moldin
32、gs depend on themold construction, 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
33、 surfaces of either type of moldthat 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 isFIG. 1 Flash Picture-Frame MoldFIG. 2 Flash Mold with Machined CavityFIG. 3 Positive-Type
34、 MoldD4703 102adequate.5The edges of the mold cavity should be visually freeof nicks and scratches which could cause premature failure 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 f
35、orce to the area of the mold cavity) of at least 10MPa (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 beingheated to at least 240C, and being cooled at a rate consistentwith the
36、 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 mold are cooled by a heat-conducting fluid (usuallycold water) in a channel
37、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 than 65C duringheating or cooling.5.3.5 For quench cooling (Method C in Tab
38、le 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 flow rate of the heat-conducting fluid should be predetermined in a test with
39、out 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 suppliers instructions. If noinstructions are given, dry for 24 6 1hat706 2C
40、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 moldedspecimen, plaque, or sheet is free from surface irregularitiesand i
41、nternal 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 from powder or granulesmay sometimes require melt homogenization using a h
42、ot-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 for the compressionmold in which it ultimately will be molded. Use millin
43、gconditions 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 manufacturer.The preform prepared by milling should normally be thickerthan th
44、e 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 picture-frame (Fig. 1) molds or large, heavymolds it may not be necessary o
45、r 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 (granules orpreforms) in the preheated mold. If granular material is used,make s
46、ure 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. With flash molds,cover the mold with the top ferrotype plate (see Figs. 1 a
47、nd 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, see3.1.5) and then cool down (see 6.3).NOTE 3Apreheating time of 5 min is the
48、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 to avoid flow of the material. Full pressure means a pressuresufficient to
49、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 appropriate cooling methodshall be selected from Table 1.6.3.2.1 In the case of q
