ASTM D955-2000 Standard Test Method of Measuring Shrinkage from Mold Dimensions of Thermoplastics《热塑塑料的模型尺寸收缩率测量的标准试验方法》.pdf

1、Designation: D 955 00Standard Test Method ofMeasuring Shrinkage from Mold Dimensions ofThermoplastics1This standard is issued under the fixed designation D 955; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis

2、ion. 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 test method is intended to measure shrinkage frommold cavity to molded dimensions of thermoplastics whenmolded by compre

3、ssion or injection processes with specifiedprocess conditions.1.2 This test method covers initial shrinkage measurements.The method also accommodates shrinkage at 24 and 48 h,which may be critical for some materials.1.3 This method will give comparable data based on stan-dard specimens and can not p

4、redict absolute values in actualmolded parts with varying flow paths, wall thicknesses, pres-sure gradients and process conditions. Differences in moldshrinkage may also be observed between the three specimengeometries described in this test method.1.4 The values stated in SI units are to be regarde

5、d 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 safety and health practices and det

6、ermine the applica-bility of regulatory limitations prior to use.NOTE 1This test method is technically identical to ISO 294-4 whereType D2 specimens are used except that pressure transducers are an optionin this test method and required in ISO 294-4.2. Referenced Documents2.1 ASTM Standards:D 374 Te

7、st Methods for Thickness of Solid Electrical Insu-lation2D 618 Practice for Conditioning Plastics and ElectricalInsulating Materials for Testing3D 788 Classification System for Poly(Methyl Methacrylate)(PMMA) Molding and Extension Compounds3D 883 Terminology Relating to Plastics3D 3641 Practice for

8、Injection Molding of Test Specimens ofThermoplastic Molding and Extrusion Materials4D 4066 Specification for Nylon Injection and ExtrusionMaterials4D 4181 Specification for Acetal (POM) Molding and Extru-sion Materials4D 4549 Specification for Polystyrene Molding and Extru-sion Materials (PS)5D 4703

9、 Practice for Compression Molding of Thermoplas-tic Materials into Test Specimens, Plaques, Sheets5D 4976 Specification for Polyethylene Plastics Molding andExtension Materials5D 5947 Test Methods for Physical Dimensions of SolidPlastics Specimens5E 691 Practice for Conducting an Interlaboratory Stu

10、dy toDetermine the Precision of a Test Method62.2 ISO Standards:ISO 293 PlasticsCompression Moulding Test Specimensof Thermoplastic Materials7ISO 294-3 PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 3: Small Plates7ISO 294-4 PlasticsInjection Moulding of TestSpecimensPart

11、 4: Determination of Moulding Shrink-age73. Terminology3.1 DefinitionsGeneral definitions of terms applying tothis test method appear in Terminology D 883.3.2 Definitions of Terms Specific to This Standard:3.2.1 demolding, nremoving the specimens from themold.1This test method is under the jurisdict

12、ion of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.Current edition approved Nov. 10, 2000. Published January 2001. Originallypublished as D 955 48T. Last previous edition D 955 89 (1996).2Annual Book of ASTM Standards, Vol 10.01.3Annu

13、al Book of ASTM Standards, Vol 08.01.4Annual Book of ASTM Standards, Vol 08.02.5Annual Book of ASTM Standards, Vol 08.03.6Annual Book of ASTM Standards, Vol 14.02.7Available from American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.1*A Summary of Changes section appea

14、rs at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Test Method4.1 The principle of this test method is to compare moldcavity dimensions with specimen dimensions and report thedifferences in pe

15、rcent.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 the molding process. Factors such as mold andmelt temperature, fill times, and packing

16、conditions are knownto affect shrinkage significantly. Adherence to the specifiedmold design (see 7.1) and specifications outlined in PracticeD 3641 or ISO 294-4 or the appropriate material will improvethe reproducibility of the test.5.2 Compression MoldingIn compression molding, thedifference betwe

17、en 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 time, and pressureapplication are known to affect shrinkage significantly. Adher-ence to the specif

18、ied mold design (see 7.2) and specificationsoutlined in Practice D 4703 or ISO 293 or the appropriatematerial specifications will improve the reproducibility of thetest.6. Sample Preparation6.1 Some materials require special treatment before they aremolded. For example, thermoplastics, which absorb

19、moisturemust be dried before molding. Refer to the manufacturersrecommendations for required conditions or appropriate mate-rial specification. The preparation given to the material prior tomolding shall be recorded and reported.7. Apparatus7.1 Injection MoldSpecimens shall be molded in a twocavity

20、mold conforming with dimensions as shown in Figs. 1and 2 for the 60 3 60-mm plaque specimen (Type D2), Fig. 3for the 12.7 3 127-mm bar specimen (Type A) and Fig. 4 forthe 100mm 3 3.2-mm disk specimen (Type B). The mold mayhave scribe marks included for the measurement of shrinkage.The scribe marks s

21、hall be 1.0 mm long by .01 mm wide located1.0 mm from each edge on one side of the mold. Pressuretransducers for monitoring the pressure in at least one cavityare mandatory for Type D2. Mold shrinkage measurementsshould be made on specimens that have been molded at one ofthe following cavity pressur

22、es 6 3 % from the selectedpressure: 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 c

23、onforming to the dimensions of Fig. 2for the 60 3 60-mm plaque (Type D2) Fig. 3 for the 12.7 3127-mm bar specimen (Type A) and Fig. 4 for the 100-mm 33.2-mm disk specimen (Type B), not including the sprue,runner or gate. The mold may have scribe marks included forthe measurement of shrinkage. The sc

24、ribe marks shall be 1.0mm long by 0.1 mm wide located 1.0 mm from each edge onone side of the mold.7.3 Injection PressA suitable injection molding machinethat will fill the test molds when it is operated in the range from20 to 80 % of its rated shot capacity at the molding parametersSp sprue molding

25、 volume = 30 000 mm3G gate projected area = 11 000 mm2lc = distance between the lines along which the test specimens are cut fromthe runnersFIG. 1 Type D2Sp sprueG gateR runnerP pressure sensor dimensions in mml length of plate 60 6 2b width of plate 60 6 2h thickness of plate 2.0 6 0.1lGlength of g

26、ate 4.0 6 0.1hGheight of gate (0.75 6 0.05) 3 h3lRlength of runner 25 to 40bRwidth of runner $ (b+6)hgdepth of runner at gate h + (1.5 6 0.5)l* unspecified distance . . .lpdistance of pressure sensor from gate 5 6 2FIG. 2 Type D2D955002specified in Practice D 3641, ISO 294-3 or the appropriatemateri

27、al specification.NOTE 2If 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

28、 the total weight of the shot, including sprue and runner willfall within the specified limits.7.4 Compression PressA suitable hydraulic press that willdeliver a pressure of 20 to 35 MPa (3000 to 5000 psi) to thematerial in the mold.7.5 Measuring ToolsMeasuring tools (micrometers, ver-nier calipers,

29、 etc.) accurate to 0.025 mm (0.001 in.) formeasuring the molds and test specimens conforming to themeasuring tool requirements in Test Methods D 374.8. Test Specimen8.1 Specimen Type D2For mold shrinkage in both flowand cross flow of compression and injection molding materialsthe preferred specimen

30、shall be 60 3 60 3 2 mm depthconforming to the dimensions of Fig. 2.8.2 Specimen Type AFor shrinkage parallel to flow, a barmold having a cavity of 12.7 3 127 mm may be used as shownin Fig. 3. The thickness shall be 3.2 mm unless otherwiseagreed upon by the seller and the purchaser. The mold shallha

31、ve at one end a gate 6.4 mm in width by 3.2 mm in depth.8.3 Specimen Type BA disc shaped specimen, as shown inFig. 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, may also be used.NOTE 3Although this specimen ma

32、y be 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 ex

33、pectedto be in agreement with those obtained using the specimens described inclauses 8.1 and 8.2.9. Conditioning9.1 ConditioningConditioning of molded specimens shallbe done in the Standard Laboratory Atmosphere, 23 6 2C and50 % 6 5 RH, if not otherwise specified in the appropriatematerials standard

34、.9.2 Test ConditionsConduct measurement in the standardlaboratory atmosphere of 23 6 2C and 50 % 6 5 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 thene

35、arest 0.025 mm at 23 6 2C and 50 % 6 5 RH. Record thesevalues as l and w, respectively.FIG. 3 Bar SpecimenFIG. 4 Disk SpecimenD95500310.2 Mold at least five flat test specimens from the sampleto be tests.NOTE 4Flat is represented by a specimen with less than 3 % warp.Three percent warp is defined as

36、 3 mm depth deflection, positive ornegative, per 100 mm in length.10.2.1 Thermoplastics Molded by InjectionMolding ofthermoplastic materials shall be conducted in accordance withthe appropriate material standard, Practice D 3641, or ISO294-3, or both. The temperature of the heating cylinder and them

37、old shall be maintained at a point which, on a cycle selected,will produce temperature within the range recommended by thematerial molding standard. Begin with a short shot to insureflow is straight and not partly radial and that the flow is laminarand does not exhibit melt fracture. Collect samples

38、 after themachine is at equilibrium.10.2.2 Thermoplastics Molded by CompressionFor ther-moplastics, molding shall be conducted in accordance with theappropriate material standard or D 4703.10.3 Treatment of Specimens After Demolding:10.3.1 In order to minimize warpage, separate the testspecimens fro

39、m the runners in the gate area immediately afterdemolding. Do not modify or alter the edges used for themeasurement of dimensions. It is recommended to cool speci-mens in a horizontal position at room temperature by placingthem on a material of low thermal conductivity to minimizewarpage. After the

40、first hour, condition the specimens at 23 62C and 50 % 6 5 RH, unless otherwise specified in thematerial standard.10.3.2 Dimensional Measurement Conditioning Time Speci-fication:10.3.2.1 Initial shrinkage measurement shall be made on thespecimen within one hour after the specimen has beendemolded.10

41、.3.2.2 Twenty four hour shrinkage measurements shall bemade 24 6 0.5 h after the specimen has been demolded.10.3.2.3 Forty eight hour shrinkage measurements shall bemade 48 6 0.5 h after the specimen has been demolded.11. Calculation and Report11.1Sw5 Wm2 Ws! 3 100/Wm (1)where:Sw= the shrinkage perp

42、endicular to flow, %,Wm= the mold dimension perpendicular to flow, %,Ws= the specimen dimension perpendicular to flow, andS15 Lm2 Ls! 3 100/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 shrink

43、age in both flow and cross direction totwo significant figures.11.2 The report shall include the following:11.2.1 Details of any special preparation, such as drying,which the material received before molding;11.2.2 The molding procedure used, following the report asoutlined in Practice D 3641 for in

44、jection molding and PracticeD 4703 for compression molding.11.2.3 The initial shrinkage, the 24 h shrinkage and the 48h shrinkage, if these were obtained, shall be expressed inpercent (mm/mm) with each value representing the mean ofdeterminations obtained on five or more specimens.12. Precision and

45、Bias12.1 Precision:12.1.1 Tables 1-3 summarize data from a round robin8conducted in 1988, using specimens 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

46、resins werehandled in accordance with the suppliers instructions and weremolded in accordance with Practice D 3641. Each test result isthe average of five individual determinations from successiveinjection molding cycles. Each laboratory obtained one testresult for each material.8NOTE 5A round robin

47、 was conducted in Europe using specimen TypeD2. When the results are published, they will be appended editorially tothis test method.12.1.2 Repeatability estimates Srand r were made bytreating the five individual determinations from successiveinjection molding cycles as test results. Poorer precisio

48、n (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

49、R only areintended to present a meaningful way of considering theapproximate precision of this test method. The data in Tables1-3 should not be rigorously applied to acceptance or rejectedof material, as those data are specific to the round robin andmay not be representative of other lots, conditions, materials,or laboratories. Users of this test method should apply theprinciples outlined in Practice E 691 to generate data specificto their laboratory and materials, or between specific laborato-ries. The principles of 11.1.3 through 11.3.3 then would