1、Designation: D4703 10aD4703 16Standard 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
2、revision, 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 thermoplastic granules and milled stock for the
3、 preparation of testspecimens.21.2 While conditions for certain materials are given, the primary source of specific conditions shall be the material specificationstandards for each type of material.1.3 UnitsThe values stated in SI units are to be regarded as the standard. The values given in parenth
4、eses are for informationonly. standard. No other units of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and heal
5、th practices and determine the applicability of regulatorylimitations prior to use.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 AnnexA1, ProcedureAshould be equivalent to those prepared using IS
6、O 293-1986, Cooling Method D. Specimens prepared using AnnexA1, Procedure C should be equivalent to those prepared using ISO 293-1986, Cooling Method B. However, due to the greater cooling rate tolerances ofthe ISO standard, specimens prepared in accordance with ISO Cooling Method B may not be equiv
7、alent to Annex A1, Procedure C.2. Referenced Documents2.1 ASTM Standards:3D618 Practice for Conditioning Plastics for TestingD1248 Specification for Polyethylene Plastics Extrusion Materials for Wire and CableD3350 Specification for Polyethylene Plastics Pipe and Fittings MaterialsD4976 Specificatio
8、n for Polyethylene Plastics Molding and Extrusion Materials2.2 ISO Standard:ISO 293-1986 ISO 293 PlasticsCompression Moulding Test Specimens of Thermoplastic Materials43. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 average cooling rate (C/min),nthe cooling rate calculated by
9、dividing the difference between the molding anddemolding temperatures by the time required to cool the mold to the demolding temperature.3.1.2 cooling rate (C/h),nthe rate of cooling obtained by controlling the flow of the cooling fluid in such a way that duringeach 10-min interval, the deviation fr
10、om this specified cooling rate shall not exceed the specified tolerance.3.1.3 demolding temperature, nthe temperature of the mold or the press platens at the end of the cooling time, measured inthe nearest vicinity to the molded material.3.1.3.1 Discussion1 This practice is under the jurisdiction of
11、 ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.Current edition approved Nov. 1, 2010April 1, 2016. Published January 2011April 2016. Originally approved in 1991. Last previous edition approved in 2010 asD4703 10.D4703 10a. DOI: 10.1520
12、/D4703-10A.10.1520/D4703-16.2 This practice was created as a coalescence of and replacement for Practices D1928, D2292, D3010, and D3463.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume in
13、formation, refer to the standards Document Summary page on the ASTM website.4 ISO/IEC Selected Standards for Testing Plastics, available from ASTM. Also available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor,New York, NY 10036.This document is not an ASTM standard and
14、 is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only t
15、he current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1For positive molds, hole
16、s are normally drilled in the mold for measuring the temperatures defined in 3.1.3 and 3.1.4.3.1.4 molding temperature, nthe temperature of the mold or 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 durin
17、g which full pressure is applied while maintaining the molding temperature.3.1.6 picture frame mold, na flat piece of metal, usually of brass or steel, that has a center portion removed to provide thespecified shape and dimensions of the final molding. The thickness of the metal is dependent on the
18、desired thickness of thefinished molding, taking into consideration the shrinkage of the material to be molded. The picture frame mold is sometimesreferred to as a chase.3.1.7 preheating time, nthe time required to heat the material in the mold up to the molding temperature while maintainingthe cont
19、act pressure.4. Significance and Use4.1 The methods by which sample materials are prepared and molded influence the mechanical properties of the specimen.Unlike injection molding, the objective of compression molding is to produce test specimens or sheets that are both homogeneousand isotropic. Mold
20、ed specimens may be madeSpecimens can be molded from powder or pellets such as are received directly froma material manufacturer, particles produced in a recycle recovery operation, or from a milled preform or sheet prepared on atwo-roll mill. The powder, pellets, particles, preform, or sheet are me
21、lted and molded in a mold designed to produce a finishedspecimen of a given geometry, size, and thickness, or melted and molded in the form of a smooth plaque or sheet of uniformthickness from which desired specimens are cut, punched, or machined. Working a compound on a two-roll mill prior to moldi
22、ngwill disperse and distribute the compound additives in a manner that will affect the physical properties of the compound. The needfor milling a sample prior to compression molding may be determined by reference to the relevant material specification or thematerial manufacturer. relevant material s
23、pecification or the material manufacturer shall be consulted to determine the need formilling a sample prior to compression molding. It is important to treat different samples of the same type of material in the sameway: if milling was done prior to molding on a material which is to be used as a sta
24、ndard for comparison, all new materials tobe tested against this practice shouldshall be prepared and molded in a similar manner.4.2 The apparatus and exact conditions required to prepare adequate specimens may will usually vary for each plastic material.Apparatus and procedures which should be sati
25、sfactory for molding many different plastic materials are given in this practice inSections 5 and 6. The apparatus and procedures which have been found satisfactory for molding certain specific materials are givenin the Appendix.Appendixes. In any case, the specific apparatus and procedures to be us
26、ed in producing compression-moldedspecimens of a given material mayshall be obtained by reference to the relevant material specification and should be agreed uponor by agreement between the purchaser and the supplier.5. Apparatus5.1 MillAny size two-roll mill having chrome-plated rolls, capable of m
27、aintaining a constant temperature within 62C(63.6F) of the temperature needed for the particular material involved, and being adjustable in speed as needed for the materialto be worked, is adequate. Some recommendations worked. Recommendations for mills to be used for some specific types ofmaterials
28、 are given in the Appendix.5.2 Molds:5.2.1 Mold TypesSeveral different types of molds may mold geometries can be used for the compression molding of testspecimens of thermoplastics. In general, however, the molds used will fall into one of two categories: a flash-type mold (see Figs.1 and 2) or a po
29、sitive-type mold (see Fig. 3). The characteristics of the test specimens prepared by using different types of moldsare not the same. In particular, some mechanical properties maycan be affected by the pressure applied to the material duringcooling.5.2.2 Flash-Type MoldThe flash-type mold may be of i
30、s, typically, the picture-frame type, where a metal chase (the pictureframe) is sandwiched between two thin metal ferrotype plates (see Fig. 1), or it maycan be of the machined-cavity type (see Fig.2), where the mold consists of a cavity machined in a metal plate, with a single metal ferrotype plate
31、 used as a top or cover. Thecavity, or cavities, in the flash-type mold maycan be constructed to mold a single plaque from which test specimens may be arestamped or machined, or the mold maycan be built to mold one or more specimens to finished dimensions. Flash molds permitexcess molding material t
32、o be squeezed out and do not exert molding pressure on the material during cooling. Nevertheless, thisThis type of mold is useful for preparing test specimens or panels of similar thickness or comparable levels of low internal stress.FIG. 1 Flash Picture-Frame MoldD4703 1625.2.3 Positive-Type MoldTh
33、e positive-type mold consists of a cavity machined in a plate or block of metal and a force orplunger which closely mates with the sidewalls of the cavity (see Fig. 3). Like the flash-type mold, the cavity maycan be built toproduce a plaque from which test specimens may be are stamped or machined, o
34、r to mold a test specimen to finished dimensions.Because of the manner in which the positive mold operates, it is recommended that this mold type, either for a plaque or a finishedspecimen, be limited to a single cavity. In the positive-type mold, the full molding pressure, neglecting friction, is e
35、xerted on thematerial during cooling. The thickness, stress and density of the resulting moldings depend on the mold construction, the size ofthe material charge, and the molding conditions. This type of mold produces test specimens with high density, and it is particularlysuitable for obtaining fla
36、t surfaces and for suppressing the formation of voids within test specimens.5.2.4 Mold SurfacesThe surfaces of either type of mold that form the flat faces of the specimen shouldshall be finished to thedegree required by the test for which the specimen is intended. For most tests, a surface quality
37、of SPI-SPE #2 is adequate. Theedges of the mold cavity should be visually free of nicks and scratches which could cause premature failure of the specimen duringtesting.NOTE 2For most tests, a surface quality of SPI-SPE #2 is adequate.5Visual nicks or scratches on the edges of the mold are to be avoi
38、ded as they can cause premature failure of the specimen duringtesting.5.3 Press:5.3.1 The press shall have a clamping force capable of applying a pressure (conventionally given as the ratio of the clampingforce to the area of the mold cavity) of at least 10 MPa (1450 psi), MPa, and shall be capable
39、of maintaining pressure within 10 %of the specified pressure during the molding cycle.5.3.2 The platens of the press shall be capable of being heated to at least 240C, and being cooled at a rate consistent with thecooling method selected from Table 1.5.3.3 The platens or mold shall be heated either
40、by by suitable means such as high-pressure steam, by a heat-conducting fluidin an appropriate channel system, or by using electric-heating elements. The platens or mold are cooled by a heat-conducting fluid(usually cold water) in a channel system.5.3.4 The heating and cooling systems in the mold pla
41、tens shall be such that, when used with a particular mold, they shall beshall be capable of maintaining a temperature difference between points on the mold surfaces of no more than65C during heatingor cooling.5.3.5 For quench cooling (Method C in Table 1), two presses shall be used, one for heating
42、during molding and the other forcooling unless it can be demonstrated that the press used for heating can cool at the specified rate.5 Mold comparison kits are available from D-M-E Company, 29111 Stephenson Highway, Madison Heights, MI 48071.FIG. 2 Flash Mold with Machined CavityFIG. 3 Positive-Type
43、 MoldTABLE 1 Cooling Methods RequirementsCooling MethodAverage CoolingRate (See 3.1.1),C/minCooling Rate(See 3.1.2),C/minRemarksA 10 5B 15 5C 60 30 Quench coolingD 5 0.5 Slow coolingD4703 163NOTE 3For a specified cooling method, the flow rate of the heat-conducting fluid should be predetermined in a
44、 test without any material in the mold.6. Procedure6.1 Preparation of Molding Material:6.1.1 Drying of Granular MaterialDry the granular material as specified in the relevant material specification, or inaccordance with the material suppliers instructions. If no instructions are given, dry for 24 6
45、1 h at 70 6 2C in an oven.6.1.2 Preparation of PreformsDirect molding of test specimens, plaques, and sheets from granules shall be the standardprocedure, provided that a sufficiently homogeneous sheet is obtained. Normally this means that the molded specimen, plaque, orsheet is free from surface ir
46、regularities and internal imperfections. Poly(vinyl chloride) (PVC) compounds and chlorinatedpoly(vinyl chloride) (CPVC) compounds will generally require milling to obtain a preform for the final molding procedure.NOTE 4Poly(vinyl chloride) (PVC) compounds and chlorinated poly(vinyl chloride) (CPVC)
47、 compounds will generally require milling to obtain apreform for the final molding procedure.6.1.3 MillingDirect molding from powder or granules maycan sometimes require prior melt homogenization using a hot-meltmilling or mixing procedure to achieve a satisfactory final sheet. Where such is require
48、d, a two-roll mill will usually performsatisfactorily. Take the milled material from the mill and cut or shape it to become a preform for the compression mold in whichit ultimately will ultimately be molded. Use milling conditions that do not degrade the polymer. Recommended conditions formilling th
49、e material, particularly the stock temperature and time on the rolls, maycan be obtained from the relevant materialspecification or the material manufacturer. The preform prepared by milling should normally be thicker than the specimen, plaque,or sheet to be molded to enable the molding to be done properly.NOTE 5The preform prepared by milling should normally be thicker than the specimen, plaque, or sheet to be molded to enable the molding to bedone properly.6.2 Molding:6.2.1 Adjust the mold temperature to within 65C of the molding tem
