ASTM D4894-98a
(Specification)Standard Specification for Polytetrafluoroethylene (PTFE) Granular Molding and Ram Extrusion Materials
Standard Specification for Polytetrafluoroethylene (PTFE) Granular Molding and Ram Extrusion Materials
SCOPE
1.1 This specification covers granular resins of polytetrafluoroethylene (PTFE) that have never been preformed or molded and are normally processed by methods similar to those used in powder metallurgy or ceramics, or by special extrusion processes. These PTFE resins are homopolymers of tetrafluoroethylene, or, in some cases, modified homopolymers containing not more than one percent by weight of other fluoromonomers. The usual methods of processing thermoplastics generally are not applicable to these materials because of their viscoelastic properties at processing temperatures. The materials included herein do not include mixtures of PTFE resin with additives such as colorants, fillers or plasticizers; nor do they include reprocessed or reground resin or any fabricated articles. The methods and properties included are those required to identify the various types of resins. Additional procedures are provided in the Appendix for further characterization of the resins.
1.2 The materials covered by this specification formerly were covered in Specification D1457 as Types I, IV, V, VI, VII and VIII.
1.3 The values stated in SI units as detailed in Practice E380 are to be regarded as the standard, and the practices of E380 are incorporated herein.
1.4 The following precautionary caveat pertains only to the Specimen Preparation section, Section 9, and the Test Methods section, Section 10, of this specification: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. See Notes 1, 3 and 9 for specific cautionary statements. Note 1-Most of the technical content of this standard is included as part of ISO 12086-1 and ISO 12086-2 Part 2. These standards have been approved for publication and are in the final editing process.
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Designation: D 4894 – 98a
Standard Specification for
Polytetrafluoroethylene (PTFE) Granular Molding and Ram
Extrusion Materials
This standard is issued under the fixed designation D 4894; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope * D 638M Test Method for Tensile Properties of Plastics
[Metric]
1.1 This specification covers granular resins and test meth-
D 792 Test Methods for Density Specific Gravity (Relative
ods for polytetrafluoroethylene (PTFE) that have never been
Density) and Density of Plastics by Displacement
preformed or molded and are normally processed by methods
D 883 Terminology Relating to Plastics
similar to those used in powder metallurgy or ceramics, or by
D 1505 Test Method for Density by the Density-Gradient
special extrusion processes. These PTFE resins are homopoly-
Technique
mers of tetrafluoroethylene, or, in some cases, modified ho-
D 1895 Test Methods for Apparent Density, Bulk Factor,
mopolymers containing not more than one percent by weight of
and Pourability of Plastic Materials
other fluoromonomers. The usual methods of processing ther-
D 3295 Specification for PTFE Tubing
moplastics generally are not applicable to these materials
D 3892 Practice for Packaging/Packing of Plastics
because of their viscoelastic properties at processing tempera-
D 4441 Specification for Aqueous Dispersions of Polytet-
tures. The materials included herein do not include mixtures of
,
4 5
rafluoroethylene
PTFE resin with additives such as colorants, fillers or plasti-
D 4591 Test Method for Determining Temperatures and
cizers; nor do they include reprocessed or reground resin or any
Heats of Transitions of Fluoropolymers by Differential
fabricated articles. The methods and properties included are
Scanning Calorimetry
those required to identify the various types of resins. Addi-
D 4895 Specification for Polytetrafluoroethylene (PTFE)
tional procedures are provided in the Appendix for further
4,5
Resins Produced From Dispersion
characterization of the resins.
E 11 Specification for Wire-Cloth Sieves for Testing Pur-
1.2 The values stated in SI units as detailed in IEEE/ASTM
poses
SI-10 are to be regarded as the standard, and the practices of
E 177 Practice for Use of the Terms Precision and Bias in
IEEE/ASTM SI-10 are incorporated herein.
ASTM Test Methods
1.3 The following precautionary caveat pertains only to the
IEEE/ASTM SI 10-1997 Standard for Use of the Interna-
Specimen Preparation section, Section 9, and the Test Methods
tional System of Units (SI): The Modern Metric System
section, Section 10, of this specification: This specification
2.2 ISO Standards:
does not purport to address all of the safety concerns, if any,
ISO 12086-1 Plastics—Fluoropolymer Dispersions and
associated with its use. It is the responsibility of the user of this
Moulding and Extrusion Materials—Part 1: Designation
standard to establish appropriate safety and health practices
System and Basis for Specification
and determine the applicability of regulatory limitations prior
ISO 12086-2 Test Methods for Fluoropolymers
to use. See Notes 3 and 9 for specific cautionary statements.
NOTE 1—Information in this specification is technically equivalent to 3. Terminology
related information in ISO 12086-1 and ISO 12086-2.
3.1 Definitions:
3.1.1 The terminology given in Terminology D 883 is ap-
2. Referenced Documents
plicable to this specification.
2.1 ASTM Standards:
D 618 Practice for Conditioning Plastics and Electrical
Insulating Materials for Testing
Annual Book of ASTM Standards, Vol 08.02.
Annual Book of ASTM Standards, Vol 08.03.
1 5
This specification is under the jurisdiction of Committee D-20 on Plastics and Specifications for other forms of polytetrafluoroethylene may be found in
is the direct responsibility of Subcommittee D20.15 Thermoplastic Materials. Specifications D 4441 and D 4895.
Current edition approved Nov. 10, 1998. Published March 1999. Originally Annual Book of ASTM Standards, Vol 14.02.
published as D 4894 – 89. Last previous edition D 4894 – 98. Available from American National Standards Institute, 11 W. 42nd St., 13th
Annual Book of ASTM Standards, Vol 08.01. Floor, New York, NY 10036.
*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.
D 4894
3.2 Descriptions of Terms Specific to This Standard: 4.1.4 Type IV—Free-flowing resins. Generally made by
3.2.1 bulk density—the mass (in grams) per litre of resin treatment of finely divided resin to produce free-flowing
measured under the conditions of the test. agglomerates.
3.2.2 extended specific gravity (ESG)—the specific gravity 4.1.5 Type V—Presintered. Resin that has been treated
of a specimen of PTFE material molded as described in this thermally at or above the melting point of the resin at
specification and sintered (g.v.) for an extended period of time, atmospheric pressure without having been previously pre-
compared to the sintering time for the measurement of standard formed.
specific gravity (SSG), using the appropriate sintering schedule 4.1.6 Type VI—Resin, not presintered, but for ram extrusion
given in this specification. only.
3.2.3 lot, n—one production run or a uniform blend of two
NOTE 2—See Tables 1 and 2 for division of Types by Grades, and
or more production runs.
footnotes to Tables 1 and 2 (and Table X2.1 in Appendix X2.) for former
3.2.4 preforming—compacting powdered PTFE material
classifications.
under pressure in a mold to produce a solid object, called a
4.2 A one-line system may be used to specify materials
preform, that is capable of being handled. Molding and
covered by this specification. The system uses predefined cells
compaction are terms used interchangeably with preforming
to refer to specific aspects of this specification, illustrated as
for PTFE.
follows:
3.2.5 reground resin—that produced by grinding PTFE
Specification
material that has been preformed but has never been sintered.
Standard Number Block : Type : Grade : Class : Special notes
3.2.6 reprocessed resin—that produced by grinding PTFE
:: : : :
material that has been both preformed and sintered.
Example: ASTM III 2
3.2.7 sintering—as it applies to PTFE, a thermal treatment
D4894–97
during which the PTFE is melted and recrystallized by cooling
with coalescence occurring during the treatment.
For this example, the line callout would be ASTM
3.2.8 skiving—a machining operation during which a con-
D 4894 – 97, III2, and would specify a granular polytetrafluo-
tinuous film of PTFE material is peeled from the lateral surface
roethylene that has all of the properties listed for that Type and
of a cylindrical sintered molding.
Grade in the appropriate specified properties, Tables, or both,
3.2.9 standard specific gravity (SSG)—the specific gravity
in this specification. In this case there is no Class item so the
of a specimen of PTFE material molded as described in this
cell position for class is left blank. A comma is used as the
specification and sintered using the appropriate sintering
separator between Standard Number and Type. Separators are
schedule given in this specification.
not needed between Type, Grade, and Class. Provision for
3.2.10 thermal instability index (TII)—a measure of the
Special Notes is included so that other information can be
decrease in molecular weight of PTFE material which has been
provided when required. An example would be in Specification
heated for a prolonged period of time.
D 3295 where dimensions and tolerances are specified for each
AWG size within Type and Class. When Special Notes are
4. Classification
used, they should be preceded by a comma.
4.1 This specification covers the following six types of
PTFE generally used for compression molding or ram extru- 5. Mechanical Properties
sion, or both:
5.1 The resins covered by this specification shall conform to
4.1.1 Type I—Resin used for general-purpose molding and
the requirements prescribed in Tables 1 and 2 when tested by
ram extrusion.
the procedures specified herein. Table 1 lists tests to be carried
4.1.2 Type II—Finely divided resin with an average particle
out on resins. Table 2 lists tests requiring specimens molded as
size less than 100 micrometers.
described in Section 3.1.1.
4.1.3 Type III—Modified resins, either finely divided or
free-flowing, typically used in applications requiring improved
resistance to creep and stress-relaxation in end-use. See the ASTM Form and Style Manual, available from ASTM Headquarters.
A
TABLE 1 Detail Requirements for Tests on Resins
Melting Peak Temperature
Particle Size, Average Diameter,
Type Grade Bulk Density, g/L Water Content, max, %
μm
Initial °C Second °C
A
I 1 700 6 100 500 6 150 0.04 327 6 10
A
2 675 6 50 375 6 75 0.04 327 6 10
A
II . . . . . . <100 0.04 327 6 10
A
III 1 400 6 125 <100 0.04 327 6 10
2 850 6 50 500 6 100 0.04 335 327 6 5
A
IV 1 650 6 150 550 6 225 0.04 327 6 10
A
2 >800 . . . 0.04 327 6 10
A
3 580 6 80 200 6 75 0.04 327 6 10
V . 635 6 100 500 6 250 0.04 327 6 10 327 6 10
VI . . . 650 6 150 800 6 250 0.04 335 327 6 5
A
>5°C above the second melting peak temperature.
D 4894
TABLE 2 Detail Requirements for Tests on Molded Specimens
Standard Specific Gravity Tensile Strength min
Type Grade Thermal Instability Index, max Elongation at break min %
min max MPa psi
I 1 50 2.13 2.18 13.8 2000 140
2 50 2.13 2.18 17.2 2500 200
II . . . 50 2.13 2.19 27.6 4000 300
III 1 50 2.14 2.22 28.0 4060 500
2 50 2.14 2.18 20.7 3000 300
IV 1 50 2.13 2.19 25.5 3700 275
2 50 2.13 2.19 27.6 4000 300
3 50 2.15 2.18 27.6 4000 200
A A A A A A
V . NA NA NA NA NA NA
B A A A A A A
VI . NA NA NA NA NA NA
A
NA: Not Applicable by molding techniques included in this specification.
B
Extrusions of this resin may show an increased degree of clarity.
6. Other Requirements 8.2 The tests listed in Tables 1 and 2, as they apply, are
sufficient to establish conformity of a material to this specifi-
6.1 The resin shall be uniform and shall contain no additives
cation. One set of tests specimens as prescribed in Section 3
or foreign material.
shall be considered sufficient for testing each sample. The
6.2 The color of the material as shipped by the seller shall
average of the results for the specimens tested shall conform to
be white.
the requirements of this specification.
7. Sampling
9. Specimen Preparation
7.1 The resin shall be sampled in accordance with an
9.1 Test Disks:
adequate statistical sampling program. Adequate statistical
9.1.1 Use the die shown in Fig. 1 for the molding of test
sampling prior to packaging shall be considered an acceptable
disks (Note 3). The test resin should be near ambient tempera-
alternative.
ture prior to molding (Note 6).
7.2 The producer shall take (and test) sufficient within-lot
NOTE 3—Caution: PTFE can evolve small quantities of gaseous prod-
samples to assure adequate in-process quality control and
ucts when heated above 204°C (400°F). Some of these gases are harmful.
continuing conformance to the property requirements of this
Consequently, exhaust ventilation must be used whenever the resins are
specification.
heated above this temperature, as they are during the sintering operations
that are a part of this specification. Since the temperature of burning
8. Number of Tests
tobacco exceeds 204°C (400°F), those working with PTFE resins should
ensure that tobacco is not contaminated.
8.1 Lot inspection shall include tests for bulk density,
particle size and standard specific gravity. Periodic tests shall 9.1.2 Screen 14.5 g (for tensile properties) or 7.25 g (for
consist of all the tests specified in Tables 1 and 2 and shall be electrical properties discussed in Appendix X1.7) of PTFE
made at least one per year. resin through a No. 10 hand sieve into the die. Adjust the lower
FIG. 1 Assembly and Details of Die for Molding Test Specimens
D 4894
plug height so that the resin in the die can be leveled by 12.0 6 0.1-g sample. Insert the die in a suitable hydraulic press
drawing a straightedge in contact with the top of the die across and apply pressure gradually (Note 4) until a pressure of 34.5
the top of the die cavity. Insert the die in a suitable hydraulic
MPa (5000 psi) is attained. Hold this pressure for 2 min.
press and apply pressure gradually (Note 4) until a total of 34.5
Remove the preform from the die. A wax pencil may be used
MPa (5000 psi) is attained. Hold this pressure for 3 min.
to write the sample identification on the preform at this time.
Remove the disk identification on the disk at this time.
9.2.3 Sinter the preforms according to Table 3 (Note 5).
NOTE 4—As a guide, increasing the pressure at a rate of 3.45 MPa (500
9.2.3.1 For SSG specimens use Procedure B for Types I, II
psi)/min is suggested until the desired maximum pressure is attained.
and IV and Procedure C for Type III.
9.1.3 Sinter the preforms according to Table 3 (Note 5).
9.2.3.2 For ESG specimens use Procedure F for Types I, II
9.1.3.1 Use Procedure B for Types I, II and IV and Proce-
and IV and Procedure G for Type III.
dure C for Type III.
NOTE 7—Improved precision in SSG and ESG test results has been
NOTE 5—Although the rate of heating application is not critical, the
obtained with the use of an upright, cylindrical oven and an aluminum
cooling cycle is most important and the conditions cited in these
sintering rack. The cylindrical oven has an inside diameter of 140 mm (5.5
procedures must be followed very closely. If they are not followed, the
in.) and an inside depth of 203 mm (8 in.) plus additional depth to
crystallinity of the disks and the resulting physical properties may be
accommodate a 50.8-mm (2-in.) thick cover, and is equipped with suitable
markedly changed. Therefore, the use of a programmed oven is recom-
heaters and controllers to sinter specimens according to the Procedures in
mended for the most precise sintering cycle control so that the hood
Table 3. The rack, as shown in Fig. 2, allows preforms to be placed
window may be left down during the entire sintering procedure, the latter
symmetrically in the center region of the oven. Place six preforms on each
being an important safety consideration.
of the middle oven rack shelves (if six or fewer preforms are to be
9.2 Test Specimens for Standard Specific Gravity (SSG) and sintered, place them on the middle rack, filling in with “dummies” as
needed). Place “dumm
...
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