1、Designation: D 955 08Standard 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 () 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 compress
3、ion or injection processes with specifiedprocess conditions.1.2 This test method covers shrinkage measurements at 24and 48 h.1.3 This method will give comparable data based on stan-dard specimens and can not predict absolute values in actualmolded parts with varying flow paths, wall thicknesses, pre
4、s-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 in SI units are to be regarded as thestandard. The values given in parentheses are given forinformation
5、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 determine the applica-bility of regulatory limitations prior to use.NOTE 1This
6、 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 Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 788 Classification System
7、for Poly(Methyl Methacrylate)(PMMA) Molding and Extrusion CompoundsD 883 Terminology Relating to PlasticsD 3641 Practice for Injection Molding Test Specimens ofThermoplastic Molding and Extrusion MaterialsD 4066 Classification System for Nylon Injection and Ex-trusion Materials (PA)D 4549 Specificat
8、ion for Polystyrene and Rubber-ModifiedPolystyrene Molding and Extrusion Materials (PS)D 4703 Practice for Compression Molding ThermoplasticMaterials into Test Specimens, Plaques, or SheetsD 4976 Specification for Polyethylene Plastics Molding andExtrusion MaterialsD 5947 Test Methods for Physical D
9、imensions of SolidPlastics SpecimensD 6778 Classification for Polyoxymethylene (POM,Acetal)Molding and Extrusion MaterialsD 6779 Classification System for Polyamide Molding andExtrusion Materials (PA)E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2
10、 ISO Standards:3ISO 293 PlasticsCompression Moulding Test Specimensof Thermoplastic MaterialsISO 294-1 PlasticsInjection Moulding of Test Specimensof Thermoplastic MaterialsPart 1: General Principles,and Moulding of Multipurpose and Bar Test specimensISO 294-3 PlasticsInjection Moulding of Test Spec
11、imensof Thermoplastic MaterialsPart 3: Small PlatesISO 294-4 PlasticsInjection Moulding of TestSpecimensPart 4: Determination of Moulding Shrink-age3. Terminology3.1 DefinitionsGeneral definitions of terms applying tothis test method appear in Terminology D 883.3.2 Definitions of Terms Specific to T
12、his Standard:3.2.1 jetting, nnon-uniform multi-directional flow frontapparent on the surface of the mold due to rapid filling of themold cavity.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.09 on Specimen Preparation
13、.Current edition approved Nov. 1, 2008. Published December 2008. Originallyapproved in 1948. Last previous edition approved in 2000 as D 955 - 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards
14、 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.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM Intern
15、ational, 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 percent.5. Significance and Use5.1 Injection MoldingIn
16、 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 conditions are knownto affect shrinkage significantl
17、y. Adherence to the specifiedmold design (see 7.1) and specifications outlined in PracticeD 3641 or ISO 294-4 or the appropriate material specificationwill improve the reproducibility of the test.5.2 Compression MoldingIn compression molding, thedifference between the dimensions of a mold cavity and
18、 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 specified mold design (see 7.2) and specific
19、ationsoutlined 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 moisturemust be dried before molding.
20、For required conditions forsample preparation, refer to the appropriate material specifica-tion or the manufacturers recommendations if no specificationis available. The preparation given to the material prior tomolding shall be recorded and reported.7. Apparatus7.1 Injection MoldSpecimens shall be
21、molded in a twocavity 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 by 127-mm bar specimen (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 c
22、avityare 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 selectedpressure: 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, or asspecified in the appropriate material specification. Pressuretransducers
23、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 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-m
24、m disk specimen (Type B), not including the sprue,runner or gate.NOTE 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 located4.0 mm from each edge on one side
25、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 moldingSp | sprueG | gateLc= distance between the lines along which the test specimens are cut from the runnersMolding v
26、olume = 20 000 mm3Projected area = 11 000 mm2FIG. 1 Type D2 (Mold Layout)D955082parameters specified in Practice D 3641, ISO 294-3 or theappropriate material specification.NOTE 3If the injection machines of appropriate capacity are notavailable, the requirements of 7.3 may be met in machines of larg
27、ercapacities by providing test molds with multiple cavities (maximum offour) to be filled from a common sprue and having a balanced fillingpattern, so that the total weight of the shot, including sprue and runner willfall within the specified limits.7.4 Compression PressA suitable hydraulic press th
28、atshall deliver a pressure of 20 to 35 MPa (3000 to 5000 psi) tothe material in the mold.Sp sprueG gateR runnerP pressure sensorl length of plate 60 6 2mmb width of plate 60 6 2mmh thickness of plate 2.0 6 0.1 mmlGlength of gate 4.0 6 0.1 mmhGheight of gate (0.75 6 0.05) 3 hlRlength of runner 25 to
29、40 mmbRwidth of runner $ (b+6)mmhgdepth of runner at gatel* unspecified distance . . .lpdistance of pressure sensor from gate 5 6 2mmFIG. 2 Type D2 (Cavity Details)w = 12.7 6 0.2 mmt =3.26 0.05 mml = 127 6 2mmG = GateP = Pressure TransducerFIG. 3 Bar SpecimenD9550837.5 Measuring ToolsMeasuring tools
30、 (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 D 5947.8. Test Specimen8.1 The following specimen dimensions are applicable forboth compression and injection molding. Orien
31、tation 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 60 by 60 by 2mm depth conforming to the dimensions of Fig. 2.8.1.2 Specimen Type AFor shrinkage parallel to flow, aba
32、r mold 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 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,
33、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 used to determine moldshrinkage in both the flow and cross flow directions, the filling patterndoes not produce unif
34、orm flow lengths and orientation. Consequently,there may be significant differences when measuring the specimen atdifferent points around the circumference. Values would not be expectedto be in agreement with those obtained using the specimens described in8.1.1 and 8.1.2.9. Conditioning9.1 Condition
35、ingConditioning 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 Test ConditionsConduct measurement in the standardlaboratory atmosphere of 23 6 2C and 50 % 6 10 RH, if nototherwise spe
36、cified 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 0.025 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 sp
37、ecimens 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 100 mm in length.10.2.1 Thermoplastics Molded by InjectionMolding ofthermoplastic materials shall be conducted in accor
38、dance withthe appropriate material standard, Practice D 3641 orISO 294-3. The temperature of the heating cylinder and themold 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 en
39、surethe flow front is straight and not radial and that the flow islaminar and does not exhibit melt fracture (jetting). Collectsamples after the machine is at equilibrium.t =3.26 0.05 mmD = 100 6 2mmG = GateP = Pressure TransducerFIG. 4 Disk SpecimenD95508410.2.2 Thermoplastics Molded by Compression
40、For ther-moplastics, molding shall be conducted in accordance with theappropriate material standard or D 4703.10.3 Treatment of Specimens after Removal from the Mold:10.3.1 In order to minimize warpage, separate the testspecimens from the runners in the gate area immediately afterremoval from the mo
41、ld. 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 of low thermal conductivity tominimize warpage. After the first hour, condition the speci-mens at 23 6 2C and 50 %
42、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 specimen has been removed from themold.10.3.2.2 Forty eight hour shrinkage measurements shall bemade 48 6 0.5 h after
43、 the specimen has been removed from themold.11. Calculation and Report11.1Sw5 Wm2 Ws! 3 100/Wm (1)where:Sw= the shrinkage perpendicular 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 paralle
44、l 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 The report shall include the following:11.2.1 Details of any special material preparation, such asdrying, which
45、the material received before molding;11.2.2 The molding procedure used, following the report asoutlined in Practice D 3641 for injection molding and PracticeD 4703 for compression molding.11.2.3 The 24-hour shrinkage and the 48-hour shrinkageshall be expressed in percent (mm/mm) with each valuerepre
46、senting 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 specimens Type A and Type B,involving five thermoplastics materials tested by eight labora-tories. Each material was
47、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 Practice D 3641. Each test result isthe average of five individual determinations from successiveinjection molding
48、 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 pressure forvarious materials, are shown in Appendix X1.12.1.2 Repeatability estimates Srand r were made bytre
49、ating 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 only areintended to present a meaningful way of considering the4Supporting data are available from ASTM Headquarters. Request RR: D-20-11
