1、Designation: D 4894 07Standard Specification forPolytetrafluoroethylene (PTFE) Granular Molding and RamExtrusion Materials1This standard is issued under the fixed designation D 4894; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This specification covers granular resins and test meth-ods for polytetrafluoroethylene (PTFE) that have
3、 never beenpreformed or molded and are normally processed by methodssimilar to those used in powder metallurgy or ceramics, or byspecial extrusion processes. These PTFE resins are homopoly-mers of tetrafluoroethylene, or, in some cases, modified ho-mopolymers containing not more than one percent by
4、weight ofother fluoromonomers. The usual methods of processing ther-moplastics generally are not applicable to these materialsbecause of their viscoelastic properties at processing tempera-tures. The materials included herein do not include mixtures ofPTFE resin with additives such as colorants, fil
5、lers or plasti-cizers; nor do they include reprocessed or reground resin or anyfabricated articles. The methods and properties included arethose required to identify the various types of resins. Addi-tional procedures are provided in the Appendix for furthercharacterization of the resins.1.2 The val
6、ues stated in SI units as detailed in IEEE/ASTMSI-10 are to be regarded as the standard, and the practices ofIEEE/ASTM SI-10 are incorporated herein.1.3 The following precautionary caveat pertains only to theSpecimen Preparation section, Section 9, and the Test Methodssection, Section 10, of this sp
7、ecification: This specificationdoes not purport to address all of the safety concerns, if any,associated with its use. It is the responsibility of the user of thisstandard to establish appropriate safety and health practicesand determine the applicability of regulatory limitations priorto use. See N
8、otes 3 and 9 for specific cautionary statements.NOTE 1Information in this specification is technically equivalent torelated information in ISO 12086-1 and ISO 12086-2.2. Referenced Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 638 Test Method for Tensile Properti
9、es of PlasticsD 792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD 883 Terminology Relating to PlasticsD 1895 Test Methods for Apparent Density, Bulk Factor,and Pourability of Plastic MaterialsD 3295 Specification for PTFE Tubing, Miniature Beadingand
10、Spiral Cut TubingD 3892 Practice for Packaging/Packing of PlasticsD 4441 Specification for Aqueous Dispersions of Polytet-rafluoroethyleneD 4591 Test Method for Determining Temperatures andHeats of Transitions of Fluoropolymers by DifferentialScanning CalorimetryD 4745 Specification for Filled Compo
11、unds of Polytet-rafluoroethylene (PTFE) Molding and Extrusion MaterialsD 4895 Specification for Polytetrafluoroethylene (PTFE)Resin Produced From DispersionE11 Specification for Wire Cloth and Sieves for TestingPurposesE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsIEEE/AS
12、TM SI-10 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System2.2 ISO Standards:3ISO 12086-1 PlasticsFluoropolymer Dispersions andMoulding and Extrusion MaterialsPart 1: DesignationSystem and Basis for Specification1This specification is under the jurisdiction of ASTM C
13、ommittee D20 onPlastics and is the direct responsibility of Subcommittee D20.15 on ThermoplasticMaterials.Current edition approved Sept. 1, 2007. Published October 2007. Originallyapproved in 1989. Last previous edition approved in 2004 as D 4894 - 04.2For referenced ASTM standards, visit the ASTM w
14、ebsite, www.astm.org, orcontact 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 10036.1*
15、A Summary of 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.ISO 12086-2 Test Methods for Fluoropolymers3. Terminology3.1 Definitions:3.1.1 The terminology given in Terminology D 883
16、 is ap-plicable to this specification.3.2 Descriptions of Terms Specific to This Standard:3.2.1 bulk densitythe mass (in grams) per litre of resinmeasured under the conditions of the test.3.2.2 extended specific gravity (ESG)the specific gravityof a specimen of PTFE material molded as described in t
17、hisspecification and sintered (g.v.) for an extended period of time,compared to the sintering time for the measurement of standardspecific gravity (SSG), using the appropriate sintering schedulegiven in this specification.3.2.3 lot, none production run or a uniform blend of twoor more production run
18、s.3.2.4 preformingcompacting powdered PTFE materialunder pressure in a mold to produce a solid object, called apreform, that is capable of being handled. Molding andcompaction are terms used interchangeably with preformingfor PTFE.3.2.5 reground resinthat produced by grinding PTFEmaterial that has b
19、een preformed but has never been sintered.3.2.6 reprocessed resinthat produced by grinding PTFEmaterial that has been both preformed and sintered.3.2.7 sinteringas it applies to PTFE, a thermal treatmentduring which the PTFE is melted and recrystallized by coolingwith coalescence occurring during th
20、e treatment.3.2.8 skivinga machining operation during which a con-tinuous film of PTFE material is peeled from the lateral surfaceof a cylindrical sintered molding.3.2.9 standard specific gravity (SSG)the specific gravityof a specimen of PTFE material molded as described in thisspecification and sin
21、tered using the appropriate sinteringschedule given in this specification.3.2.10 thermal instability index (TII)a measure of thedecrease in molecular weight of PTFE material which has beenheated for a prolonged period of time.4. Classification4.1 This specification covers the following six types ofP
22、TFE generally used for compression molding or ram extru-sion, or both:4.1.1 Type IResin used for general-purpose molding andram extrusion.4.1.2 Type IIFinely divided resin with an average particlesize less than 100 micrometres.4.1.3 Type IIIModified resins, either finely divided orfree-flowing, typi
23、cally used in applications requiring improvedresistance to creep and stress-relaxation in end-use.4.1.4 Type IVFree-flowing resins. Generally made bytreatment of finely divided resin to produce free-flowingagglomerates.4.1.5 Type VPresintered. Resin that has been treatedthermally at or above the mel
24、ting point of the resin atatmospheric pressure without having been previously pre-formed.4.1.6 Type VIResin, not presintered, but for ram extrusiononly.NOTE 2See Tables 1 and 2 for division of Types by Grades, andfootnotes to Tables 1 and 2 (and Table X2.1 in Appendix X2.) for formerclassifications.
25、4.2 A line callout system is used to specify materials in thisstandard. The system uses predefined cells to refer to specificaspects of this specification, illustrated as follows:SpecificationStandard Number Block : Type : Grade : Class : Special notes: :Example: ASTMD489404III 2For this example, th
26、e line callout would be ASTMD 4894 04, III2, and would specify a granular polytetrafluo-roethylene that has all of the properties listed for that Type andGrade in the appropriate specified properties, Tables, or both,in this specification. In this case there is no Class item so thecell position for
27、class is left blank. A comma is used as theseparator between Standard Number and Type. Separators arenot needed between Type, Grade, and Class.4Provision forSpecial Notes is included so that other information will beprovided when required.An example would be in SpecificationD 3295 where dimensions a
28、nd tolerances are specified for eachAWG size within Type and Class. When Special Notes areused, they shall be preceded by a comma.4See the ASTM Form and Style Manual, available from ASTM Headquarters.TABLE 1 Detail Requirements for Tests on ResinsAType Grade Bulk Density, g/LParticle Size, Average D
29、iameter,mWater Content, max, %Melting Peak TemperatureInitial C Second CI 1 700 6 100 500 6 150 0.04A327 6 102 675 6 50 375 6 75 0.04A327 6 10II . . . . . . 800 . . . 0.04A327 6 103 580 6 80 200 6 75 0.04A327 6 10V . 6356 100 500 6 250 0.04 327 6 10 327 6 10VI . . . 650 6 150 800 6 250 0.04A327 6 10
30、A5C above the second melting peak temperature.D 4894 0725. Mechanical Properties5.1 The resins covered by this specification shall conform tothe requirements prescribed in Tables 1 and 2 when tested bythe procedures specified herein. Table 1 lists tests to be carriedout on resins. Table 2 lists test
31、s requiring specimens molded asdescribed in Section 9.6. Other Requirements6.1 The resin shall be uniform and shall contain no additivesor foreign material.6.2 The color of the material as shipped by the seller shallbe white.7. Sampling7.1 Sampling shall be statistically adequate to satisfy therequi
32、rements of 11.48. Number of Tests8.1 Lot inspection shall include tests for bulk density,particle size and standard specific gravity. Periodic tests shallconsist of all the tests specified in Tables 1 and 2 and shall bemade at least one per year.8.2 The tests listed in Tables 1 and 2, as they apply,
33、 aresufficient to establish conformity of a material to this specifi-cation. One set of tests specimens as prescribed in Section 7shall be considered sufficient for testing each sample. Theaverage of the results for the specimens tested shall conform tothe requirements of this specification.9. Speci
34、men Preparation9.1 Test Disks:9.1.1 Use the die shown in Fig. 1 for the molding of testdisks. The test resin shall be near ambient temperature prior tomolding (Note 5). WarningPTFE can evolve small quanti-ties of gaseous products when heated above 204C 400F.Some of these gases are harmful. Consequen
35、tly, exhaustventilation must be used whenever the resins are heated abovethis temperature, as they are during the sintering operationsthat are a part of this specification. Since the temperature ofburning tobacco exceeds 204C 400F, those working withPTFE resins should ensure that tobacco is not cont
36、aminated.9.1.2 Screen 14.5 g (for tensile properties) or 7.25 g (forelectrical properties discussed in Appendix X1.7) of PTFEresin through a No. 10 hand sieve into the die.Adjust the lowerplug height to allow the resin in the die can be leveled bydrawing a straightedge in contact with the top of the
37、 die acrossthe top of the die cavity. Insert the die in a suitable hydraulicpress and apply pressure gradually (Note 3) until a total of 34.5MPa 5000 psi is attained. Hold this pressure for 3 min.Remove the disk identification on the disk at this time.NOTE 3As a guide, increasing the pressure at a r
38、ate of 3.45 MPa 500psi/min is suggested until the desired maximum pressure is attained.9.1.3 Sinter the preforms in accordance with Table 3 (Note4).9.1.3.1 Use Procedure B for Types I, II and IV and Proce-dure C for Type III.NOTE 4Although the rate of heating application is not critical, thecooling
39、cycle is most important and the conditions cited in theseprocedures must be followed very closely. If they are not followed, thecrystallinity of the disks and the resulting physical properties will bemarkedly changed. Therefore, the use of a programmed oven is recom-mended for the most precise sinte
40、ring cycle control so that the hoodwindow will be left down during the entire sintering procedure, the latterbeing an important safety consideration.9.2 Test Specimens for Standard Specific Gravity (SSG) andExtended Specific Gravity (ESG):9.2.1 A cylindrical preforming die, 28.6 mm 118 in.internal d
41、iameter by at least 76.2 mm 3 in. deep, is used toprepare the preforms. End plug clearances shall be sufficient toensure escape of air during pressing.The test resin shall be nearambient temperature prior to molding (Note 5).NOTE 5For maximum precision, the weighing and preforming opera-tions shall
42、be carried out at 23 6 2C 73.4 6 3.6F (the “near ambient”temperature referred to herein). These operations shall not be preformed attemperatures below 21C 70F due to the crystalline transition thatoccurs in PTFE in this temperature region which leads to possible cracksin sintered specimens and diffe
43、rences in specimen density (as well aschanges in other physical properties). Problems caused by the effects oftemperature on the specific gravity or density of PTFE will be minimizedwhen the measurement is made using immersion procedures if a sensitivethermometer (for example, one reading 60.1C) is
44、used in the liquid andthe temperature is adjusted to be at least 22C.9.2.2 Weigh out 12.0 6 0.1 g of resin and place it in the die.Screen non-free-flowing resins through a No. 10 sieve. Breakup compacted resins by hand-shaking cold resin in a half-filledsealed glass container. Condition the resin in
45、 the sealed glasscontainer in a freezer or dry-ice chest. After breaking up resinlumps, allow the sealed container to equilibrate to near ambientTABLE 2 Detail Requirements for Tests on Molded SpecimensType Grade Thermal Instability Index, maxStandard Specific Gravity Tensile Strength minElongation
46、at break min %min max MPa psiI 1 50 2.13 2.18 13.8 2000 1402 50 2.13 2.18 17.2 2500 200II . . . 50 2.13 2.19 27.6 4000 300III 1 50 2.14 2.22 28.0 4060 4502 50 2.14 2.18 20.7 3000 300IV 1 50 2.13 2.19 25.5 3700 2752 50 2.13 2.19 27.6 4000 3003 50 2.15 2.18 27.6 4000 200V . NAANAANAANAANAANAAVIB. NAAN
47、AANAANAANAANAAANA: Not Applicable by molding techniques included in this specification.BExtrusions of this resin show different degrees of clarity from the others.D 4894 073temperature. Then screen and weigh the 12.0 6 0.1-g sample.Insert the die in a suitable hydraulic press and apply pressuregradu
48、ally (Note 3) until a pressure of 34.5 MPa 5000 psi isattained. Hold this pressure for 2 min. Remove the preformfrom the die. Write the sample identification number using anappropriate marker that will not effect the PTFE duringsintering on the preform at this time.9.2.3 Sinter the preforms in accor
49、dance with Table 3 (Note4).9.2.3.1 For SSG specimens use Procedure B for Types I, IIand IV and Procedure C for Type III.9.2.3.2 For ESG specimens use Procedure F for Types I, IIand IV and Procedure G for Type III.NOTE 6Improved precision in SSG and ESG test results has beenobtained with the use of an upright, cylindrical oven and an aluminumsintering rack. The cylindrical oven has an inside diameter of 140 mm 5.5in. and an inside depth of 203 mm 8 in. plus additional depth toaccommodate a 50.8-mm 2-in. thick cover, a
