1、Designation: D955 08 (Reapproved 2014)Standard Test Method ofMeasuring Shrinkage from Mold Dimensions ofThermoplastics1This standard is issued under the fixed designation D955; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method is intend
3、ed to measure shrinkage frommold cavity to molded dimensions of thermoplastics whenmolded by compression or injection processes with specifiedprocess conditions.1.2 This test method covers shrinkage measurements at 24and 48 hours.1.3 This method will give comparable data based on stan-dard specimens
4、 and can not predict absolute values in actualmolded parts with varying flow paths, wall thicknesses, pres-sure and temperature gradients and process conditions. Differ-ences in mold shrinkage may also be observed among the threespecimen geometries described in this test method.1.4 The values stated
5、 in SI units are to be regarded as thestandard. The values given in parentheses are given forinformation only.1.5 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 safet
6、y and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1This standard and ISO 294-3 are equivalent in the design ofspecimen D2. This test method is equivalent to ISO 294-4 where Type D2specimens and the procedure in Appendix X2 are used.2. Referenced Docu
7、ments2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD788 Classification System for Poly(Methyl Methacrylate)(PMMA) Molding and Extrusion CompoundsD883 Terminology Relating to PlasticsD3641 Practice for Injection Molding Test Specimens ofThermoplastic Molding and Extrusion Mat
8、erialsD4066 Classification System for Nylon Injection and Extru-sion Materials (PA)D4549 Classification System and Basis for Specification forPolystyrene and Rubber-Modified Polystyrene Moldingand Extrusion Materials (PS)D4703 Practice for Compression Molding ThermoplasticMaterials into Test Specime
9、ns, Plaques, or SheetsD4976 Specification for Polyethylene Plastics Molding andExtrusion MaterialsD5947 Test Methods for Physical Dimensions of SolidPlastics SpecimensD6778 Classification System and Basis for Specification forPolyoxymethylene Molding and Extrusion Materials(POM)D6779 Classification
10、System for and Basis of Specificationfor Polyamide Molding and Extrusion Materials (PA)E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ISO Standards:3ISO 293 PlasticsCompression Moulding Test Specimensof Thermoplastic MaterialsISO 294-1 PlasticsInj
11、ection Moulding of Test Specimensof Thermoplastic MaterialsPart 1: General Principles,and Moulding of Multipurpose and Bar Test specimensISO 294-3 PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 3: Small PlatesISO 294-4 PlasticsInjection Moulding of TestSpecimensPart 4: De
12、termination of Moulding Shrink-age3. Terminology3.1 DefinitionsGeneral definitions of terms applying tothis test method appear in Terminology D883.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsi
13、bility of Subcommittee D20.09 on Specimen Preparation.Current edition approved Aug. 1, 2014. Published August 2014. Originallyapproved in 1948. Last previous edition approved in 2008 as D955 - 08. DOI:10.1520/D0955-08R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
14、 ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards 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.Copyright AST
15、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1 jetting, nnon-uniform multi-directional flow frontapparent on the surface of the mold due to rapid filling of themold cavity.4. Summary of Test Method4.1 The principle of this test method is to
16、 compare moldcavity dimensions with specimen dimensions and report thedifferences in percent.5. Significance and Use5.1 Injection MoldingIn injection molding, the differencebetween the dimensions of a mold cavity and of the moldedspecimen may vary according to the design of the mold andoperation of
17、the molding process. Factors such as mold andmelt temperature, fill times, and packing conditions are knownto affect shrinkage significantly. Adherence to the specifiedmold design (see 7.1) and specifications outlined in PracticeD3641 or ISO 294-4 or the appropriate material specificationwill improv
18、e the reproducibility of the test.5.2 Compression MoldingIn compression molding, thedifference between the dimensions of a mold cavity and of themolded specimen may vary according to the design of the moldand operation of the molding process. Factors, such as theamount of material in charge, cooling
19、 time, and pressureapplication are known to affect shrinkage significantly. Adher-ence to the specified mold design (see 7.2) and specificationsoutlined in Practice D4703 or ISO 293 or the appropriatematerial specifications will improve the reproducibility of thetest.6. Sample Preparation6.1 Some ma
20、terials require special treatment before they aremolded. For example, thermoplastics, which absorb moisturemust be dried before molding. For required conditions forsample preparation, refer to the appropriate material specifica-tion or the manufacturers recommendations if no specificationis availabl
21、e. The preparation given to the material prior tomolding shall be recorded and reported.7. Apparatus7.1 Injection MoldSpecimens shall be molded in a twocavity mold conforming with dimensions as shown in Figs. 1and 2 for the 60 60-mm plaque specimen (Type D2), Fig. 3for the 12.7 by 127-mm bar specime
22、n (Type A) and Fig. 4 forthe 100 mm by 3.2-mm disk specimen (Type B). Pressuretransducers for monitoring the pressure in at least one cavityare mandatory for Type D2. Mold shrinkage measurementsshall be made on specimens that have been molded at one ofthe following cavity pressures 6 3 % from the se
23、lectedpressure: 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, or asspecified in the appropriate material specification. Pressuretransducers are recommended, but not mandatory for speci-mens Type A and Type B.7.2 Compression MoldA single cavity positive mold hav-ing cavity dimensions conforming to the dim
24、ensions of Fig. 2for the 60 60-mm plaque (Type D2) Fig. 3 for the 12.7 127-mm bar specimen (Type A) and Fig. 4 for the 100-mm 3.2-mm disk specimen (Type B), not including the sprue,runner or gate.Sp | sprueG | gateLc= distance between the lines along which the test specimens are cut from the runners
25、Molding volume = 20 000 mm3Projected area = 11 000 mm2FIG. 1 Type D2 (Mold Layout)D955 08 (2014)2NOTE 2Although scribe marks are not required, if they are used forinjection or compression molded specimens for the measurement ofshrinkage, the scribe marks shall be 1.0 mm long by 0.1 mm wide located4.
26、0 mm from each edge on one side of the mold.7.3 Injection PressA suitable injection molding machinethat shall fill the test molds when it is operated in the rangefrom 20 to 80 % of its rated shot capacity at the moldingparameters specified in Practice D3641, ISO 294-3 or theappropriate material spec
27、ification.NOTE 3If the injection machines of appropriate capacity are notavailable, the requirements of 7.3 may be met in machines of largercapacities by providing test molds with multiple cavities (maximum offour) to be filled from a common sprue and having a balanced fillingpattern, so that the to
28、tal weight of the shot, including sprue and runner willSp sprueG gateR runnerP pressure sensorl length of plate 602mmb widthofplate 602mmh thickness of plate 2.0 0.1 mmlGlength of gate 4.0 0.1 mmhGheight of gate (0.75 0.05) hlRlength of runner 25 to 40 mmbRwidth of runner $ (b+6)mmhgdepth of runner
29、at gatel* unspecified distance . . .lpdistance of pressure sensor from gate 52mmFIG. 2 Type D2 (Cavity Details)w = 12.7 0.2 mmt =3.20.05mml =1272mmG = GateP = Pressure TransducerFIG. 3 Bar SpecimenD955 08 (2014)3fall within the specified limits.7.4 Compression PressA suitable hydraulic press thatsha
30、ll deliver a pressure of 20 to 35 MPa (3000 to 5000 psi) tothe material in the mold.7.5 Measuring ToolsMeasuring tools (micrometers, ver-nier calipers, etc.) accurate to 0.025 mm (0.001 in.) formeasuring the molds and test specimens conforming to themeasuring tool requirements in Test Methods D5947.
31、8. Test Specimen8.1 The following specimen dimensions are applicable forboth compression and injection molding. Orientation effectsdue to flow direction do not generally pertain to compressionmolding.8.1.1 Specimen Type D2For mold shrinkage in both flowand cross flow the preferred specimen shall be
32、60 by 60 by2 mm depth conforming to the dimensions of Fig. 2.8.1.2 Specimen Type AFor shrinkage parallel to flow, a barmold having a cavity of 12.7 by 127 mm shall be used asshown in Fig. 3. The thickness shall be 3.2 mm unlessotherwise agreed upon by the seller and the purchaser. Themold shall have
33、 at one end a gate 6.4 mm in width by 3.2 mmin depth.8.1.3 Specimen Type BA disc shaped specimen, as shownin Fig. 4, having a cavity 100 mm in diameter by 3.2 mm inthickness with a gate 12.7 mm in width by 3.2 mm in depth,placed radially at the edge, shall be used.NOTE 4Although this specimen may be
34、 used to determine moldshrinkage in both the flow and cross flow directions, the filling patterndoes not produce uniform flow lengths and orientation. Consequently,there may be significant differences when measuring the specimen atdifferent points around the circumference. Values would not be expect
35、edto be in agreement with those obtained using the specimens described in8.1.1 and 8.1.2.9. Conditioning9.1 ConditioningConditioning of molded specimens shallbe done in the Standard LaboratoryAtmosphere, 23 6 2C and50 % 6 10 RH, if not otherwise specified in the appropriatematerials standard.9.2 Tes
36、t ConditionsConduct measurement in the standardlaboratory atmosphere of 23 6 2C and 50 % 6 10 RH, if nototherwise specified in the appropriate materials standard.10. Procedure10.1 Measure the length and width of the mold cavity at thecenter of each edge or at the molded scribe marks, to thenearest 0
37、.025 mm at 23 6 2C and 50 % 6 10 RH. Recordthese values as l and w, respectively.10.2 Mold at least five flat test specimens from the sampleto be tested.NOTE 5Flat is represented by a specimen with less than 3 % warp.Three percent warp is defined as 3 mm depth deflection, positive ornegative, per 10
38、0 mm in length.10.2.1 Thermoplastics Molded by InjectionMolding ofthermoplastic materials shall be conducted in accordance withthe appropriate material standard, Practice D3641 or ISO294-3. The temperature of the heating cylinder and the moldshall be maintained at a point which, on a cycle selected,
39、 willproduce temperature within the range recommended by thet =3.20.05mmD =1002mmG = GateP = Pressure TransducerFIG. 4 Disk SpecimenD955 08 (2014)4material molding standard. Begin with a short shot to ensurethe flow front is straight and not radial and that the flow islaminar and does not exhibit me
40、lt fracture (jetting). Collectsamples after the machine is at equilibrium.10.2.2 Thermoplastics Molded by CompressionForthermoplastics, molding shall be conducted in accordance withthe appropriate material standard or D4703.10.3 Treatment of Specimens after Removal from the Mold:10.3.1 In order to m
41、inimize warpage, separate the testspecimens from the runners in the gate area immediately afterremoval from the mold. Do not modify or alter the edges usedfor the measurement of dimensions. It is recommended to coolspecimens in a horizontal position at room temperature byplacing them on a material o
42、f low thermal conductivity tominimize warpage. After the first hour, condition the speci-mens at 23 6 2C and 50 % 6 5 RH, unless otherwisespecified in the material standard.10.3.2 Specification of Measurement Time:10.3.2.1 Twenty four hour shrinkage measurements shall bemade 24 6 0.5 h after the spe
43、cimen has been removed from themold.10.3.2.2 Forty eight hour shrinkage measurements shall bemade 48 6 0.5 h after the specimen has been removed from themold.11. Calculation and Report11.1Sw5 Wm2 Ws! 3100/Wm (1)where:Sw= the shrinkage perpendicular to flow, %,Wm= the mold dimension perpendicular to
44、flow,Ws= the specimen dimension perpendicular to flow, andS15 Lm2 Ls! 3100/Lm (2)where:S1= the shrinkage parallel to flow, %,Lm= the mold dimension parallel to flow, and,Ls= the specimen dimension parallel to flow.Report mold shrinkage in both flow and cross direction totwo significant figures.11.2
45、The report shall include the following:11.2.1 Details of any special material preparation, such asdrying, which the material received before molding;11.2.2 The molding procedure used, following the report asoutlined in Practice D3641 for injection molding and PracticeD4703 for compression molding.11
46、.2.3 The 24-hour shrinkage and the 48-hour shrinkageshall be expressed in percent (mm/mm) with each valuerepresenting the mean of determinations obtained on five ormore specimens.12. Precision and Bias12.1 Precision:12.1.1 Tables 1-3 summarize data from a round robin4conducted in 1988, using specime
47、ns Type A and Type B,involving five thermoplastics materials tested by eight labora-tories. Each material was supplied in granular form to each ofthe testing laboratories by a single supplier. The resins werehandled in accordance with the suppliers instructions and weremolded in accordance with Prac
48、tice D3641. Each test result isthe average of five individual determinations from successiveinjection molding cycles. Each laboratory obtained one testresult for each material.8NOTE 6A repeatability study was conducted in Europe using speci-men Type D2. The results, including suggested cavity hold p
49、ressure forvarious materials, are shown in Appendix X1.12.1.2 Repeatability estimates Srand r were made bytreating the five individual determinations from successiveinjection molding cycles as test results. Poorer precision (largervalues of Srand r) would be expected if the same operator wereto shutdown and then restart the injection molding machine onthe same day with the same mold, material and operating setpoints. Repeatability under such circumstances was not evalu-ated.12.1.3 The following explanations of r and R on
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