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ASTM D3457 92 = 0759530 0535368 269 AMERICAN SOCIETY FOR TESTING AND MATERIALS
191 6 Race St Phlladelphia, Pa 191 03 Reprinted from the Annwl Book of ASTM Standards. Copyright ASTM
if not listed In the current wmblned index, will appear in the next edfin.
An American Nalional Standard #Tb Designation: D 1457 - 92
Standard Specification for Polytetrafluoroethylene (PTFE) Molding and Extrusion Materials'
This standard is issued under the fixed designaiion D 1457; 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 indicatcs the year of last reapproval. A superscript epsilon (0 indicates an editorial change since the last revision or reapproval.
This standard lias been approved for use by agencies o] !he Depur~nieni of Dejnsr IO repluce L-P-403c. Cunsiilt rlie DoD ín(1e.r if Specijicarions and Standards for the specijic year which has been adopted by tlie Deparlriierir ($Definse.
1. Scope 1.1 This specification covers molding and extrusion resins
of polytetrafluoroethylene (PTFE) that have never been melted after preforming or molding and are normally proccsscd by methods similar to those uscd in powder metallurgy or ceramics, or by ram extrusion or extrusion with a volatile aid. These PTFE resins are homopolymers of tetrafluoroethylene or copolymers containing not more than 1 % 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, plasticizers, any fabricated articles, or reprocessed or reground resin. The methods and properties included are those required to identify the various types of resins. Additional procedures are provided in Appendix X 1 for further characterization of the resins.
1.2 The values stated in SI units as detailed in Practice E 380 are to be regarded as the standard, and the practices of E 380 are incorporated herein.
1.3 The following precautionary caveat pertains only to the test methods portion, Section 13, of this specification: This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsi- bility OS the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents 2.1 ASTM Standards: D 6 18 Practice for Conditioning Plastics and Electrical
D 638 Test Method for Tensile Properties of Plastics2 D792 Test Methods for Specific Gravity (Relative Den-
D 883 Terminology Relating to P l a ~ t i c s ~ . ~ D 1505 Test Method for Density of Plastics by the
Insulating Materials for Testing2
sity) and Density of Plastics by Displacement2
Density-Gradient Technique2
I This specification is under the jurisdiction of ASTM Committee D-20 on Plastics and is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials, and subsection 12 on Fluoropolymen.
Current edition approved Oct. 30. 1992. Published December 1992. Origi- nally published as D 1457 - 56 T. Last previous edition D 1457 - 91a.
Anniral Book uf ASTM Standards, Vol 08.0 I . Anniial Book ojASTM Standards, Vol 08.04.
D 1895 Test Methods for Apparent Density, Bulk Facfor, and Pourability of Plastic Materials4
D 1898 Practice for Sampling of Plastics4 D 3297 Practice for Molding and Matching Tolerances for
PTFE Resin Partss D 3892 Practice for Packaging/Packing of Plastics5 D4052 Test Method for Density and Relative Density of
Liquids By Digital Density Meter6 D 459 1 Test Method for Determining Temperatures and
Heats of Transitions of Fluoropolymers by Differential Scanning Calorimetry5
E i l Specification for Wire-Cloth Sieves for Testing Purposes'
E 177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods*
E 380 Practice for Use of the International System of Units (SI)8
E 691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Methods
2.2 Military Standard? MIL-STD-I05 Sampling Procedures and Tables for In-
spection by Attributes
3. Terminology 3.1 Dejnitions: 3.1.1 General-The terminology given in Terminology
D 883 is applicable to this specification. 3.2 Descriptions of Tenns Specific to This Standasd: 3.2.1 bulk density, @)-the weight in grams of a volume
of 1000 mL of resin measured under the conditions of the test.
3.2.2 extended specific graviiy, (ri)-the specific gravity of a specimen of PTFE material molded as described in this specification and sintered for an extended period of time, compared to the sintering time for the measurement of SSG using the appropriate sintering schedule given in this specifi- cation.
3.2.3 preforming, (n)-compacting powdered PTFE mate- rial under pressure in a mold to produce a solid object, called a preform, that is capable of being handled. Molding and
Anarrnl Book ufASTM Siandurds, Vol 08.02. Anninul Book oJASTM Siandurds, Vol 08.03. Anriiial Book of ASTM Siandurdr, Vol 05.03.
Anriiral Book ofASThí Standards, Vol 14.02. Available from Standardization Documents Order Desk. Bldg. 4 Section D.
' Anniial Book ofASTM Staridard.s, Vols 14.02. 04.01. and 04.02.
700 Robbins Ave., Philadelphia, PA 191 11-5094. Attn: NPODS.
I
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_____ -~ ___-- ~ -- -~ _____ ASTM D1457 92 0759510 0515Lb9 LT5 m
D 1457
compaction are terms used interchangeably with preforming for PTFE.
3.2.4 reground resin, (n)-that produced by grinding PTFE material that has been molded or compacted but has never been sintered.
3.2.5 reprocessed resin, (n)-that produced by grinding PTFE material that has been molded or compacted and sintered.
3.2.6 sint,ering, (n)-as it applies to PTFE, is a thermal treatment during which the PTFE is melted and recrystallized by cooling with coalescence occurring during the treatment,
3.2.7 skiving, (n)-a machining operation during which a continuous film of' PTFE material is peeled from the lateral surface of a cylindrical sintered molding.
3.2.8 standard specific gravity (SSG), (n)-the specific gravity of a specimen of PTFE material molded as described in this specification and sintered using the appropriate sintering schedule given in this specification.
3.2.9 lhermal insiabilily index (TII), (n)-a measure of the decrease in molecular weight of PTFE material which has been heated for a prolonged period of time.
4. Classification 4.1 This specification covers the following seven types of
PTFE generally used for compression molding or extrusion, or both:
4.1.1 Type Z-Granular resin used for general-purpose molding and extrusion.
4.1.2 Type IIZ-Resin produced from a coagulated dis- persion and normally used with a volatile processing aid. Type III resins are divided into seven grades by such characteristics as bulk density, agglomerate size, melting peak temperature, standard specific gravity, tensile proper- ties, etc. Each grade is divided into four classes to indicate performance in the test for extrusion pressure as described in 13.8. 4.1.3 Type ZV-Finely divided resin with an average
particle size less than 100 pm, 4.1.4 Type V-A modified granular resin, either finely
divided or pelletized, typically used in applications requiring improved resistance to creep and stress relaxation in end use.
4.1.5 Type VI-Free-flowing resins. Generally made by treatment of finely divided resin to produce free-flowing agglomerates. Type VI resins are divided into three grades according to bulk density level.
4.1.6 Type VU-Presintered. Resin that has been treated thermally at or above the melting point of the resin at atmospheric pressure without having been previously molded or preformed.
4.1.7 Type Viii-Granular resin, not presintered for ram extrusion only. NOTE l-See Tables 1 and 2 for division of types by grades and
classes, See footnotes to Table 1 for former classifications. Type II was deleted from this specification in an earlier edition.
5. General Requirements
additives or foreign material.
be white.
5.1 The resin shall be uniform and shall contain no
5 2 The color of the material as shipped by the seller shall
6. Detail Requirements 6. I The resins covered by this specification shall conform
to the requirements prescribed in Tables 1 and 2, when tested by the procedures specified herein. Table 1 lists tests to be carried out on resins. Table 2 lists tests requiring a specimen molded as described in Section IO.
7. Test Specimens 7.1 Test specimens shall be cut from disks or billets
molded in accordance with the procedures given in Section 10.
8. Sampling 8.1 Unless otherwise agreed upon between the seller and
the purchaser, sample the resin in accordance with sections on the Random Sampling of Unstratified Materiais, Sam- pling Stratified Materials, Scope of Specific Sampling Proce- dures, and Sampling Molded Powder in Practice D 1898. Adequate statistical sampling prior to packaging shall be considered an acceptable alternative.
8.2 A lot of resin shall consist of one continuous produc- tion run or a uniform blend of two or more production runs. The producer shall take (and test) sufficient within-lot samples to assure adequate in-process quality control and continuing conformance to the property requirements of this specification.
9. Number of Tests 9.1 Unless otherwise agreed upon in writing by the
purchaser and seller, routine lot inspection tests shall consist of those specified in Table 1 except melting peak tempera- tures. Measurement of standard specific gravity (see Table 2) is to be part of the routine lot inspection tests. Periodic tests shall consist of all the tests specified in Tables I and 2 and shall be made at least once per year.
9.2 The tests listed in Tables 1 and 2, as they apply, are sufficient to establish conformity of a material to this specification. When the number of test specimens is not stated in the test method, single determinations may be made. If more than single determinations on separate portions of the same sample are made, the results shall be averaged. The single or average result shall conform to the requirements prescribed in this specification.
10. Sample Preparation 1 O, 1 Test Disks: 10.1.1 The die shown in Fig, 1 shall be used for the
molding of test disks (Note 2). Place flat aluminum disks, 0,08 to 0.38 mm (3 to 15 mils) thick and 76 mm (3 in.) in diameter, on both sides of the resin when molding Type I l i resins. NOTE 2: Caution-Although PTFE resin can be used continuously
at temperatures of 260°C (500°F) or intermittently up to 327'C (62 Ion, it can evolve small quantities of gaseous products when heated above 204'C (400'F). Some of these gases are harmful. Consequently, exhaust ventilation must be used whenever the resins are heated above this temperature. Since a burning cigarette would exceed 204°C (400'F), those working with PTFE resins should ensure that tobacco is not contaminated.
10.1.2 Screen 14.5 g (for tensile properties) or 7.25 g (for electrical properties discussed in Appendix X 1.7) of PTFE
2
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A S T M DL457 92 0759510 0515170 917
## D 1457 . TABLE 1 Detail Requirements for Tests on Resins
Particle Size Water Melting Peak Temperature Extrusion Pressure TypeA Grade Class "Ik Density' Average Content,
gIL Diameter, pl max, % Initial OC SecMid OC MPa psi N 327 f 10 NA NAJ IS 1
2 111 1 =
20
111 3.5
4
5 6
7
IVF ... VO 1
2 VI 1"
2' 3
VI1 ... VIII . . .
. . .
. . . A B C A B C D A B C A B C D B C D B
. . .
. . .
. . .
...
. . .
. . .
. . .
...
700 f 100 675 f 50 475 f 100 475 f 100 475 f 100 475 f 100 475 f 100 475 f 100 475 f 100 475 f 100 475 f 100 475 f 100 475 i 100 475 f 100 475 f 100 475 f 100 600 f 100 475 f 100 475 f 100 475 f 100
. . . 350 f 75 850 f 50 650 f 150 M O O 580 i: 80
635 f 100
500 f 150 375 f 75 500 f 150 500 f 150 500 f 150
500 f 150 500 f 150 500 i 150 425 i: 150 425 f 150 425 i 150 650 f 200 650 f 200 650 f 200 650 f 200 500 f 150 450 f 150 500 i 150 500 f 150
4 0 0 CI O0 500 f 50 525 f 200
200 f 75 500 f 200 900 f 100
50,O f 150
...
0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
N
N N N
N
N N
N N
N
N N
N N N
N N
N
N
N
N
335 N
N N
327 f 10 335
327 f 10
327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10 327 f 10
327 f 10
327 f 10 327 f 5 327 f 10 327 f 10 327 i 10
327 f 10 327 f 5
NA J
9.7 f 4.2K 24.1 f 10.3' 55.2 f 20.7M 9.7 f 4.2K 24.1 f 10.3' 55.2 f 20.7M 32.5 f 17.W
24.1 f 10.3' 55.2 f 20.7M 9.7 f 4.2K 24.1 f 10.3' 55.2 f 20.7M 15.6 f 8.0K 24.1 f 10.3' 34.5 f 13AM 32.5 f 17.5" 25.9 f 10.4'
NA
NA NA
NAJ NA J
NA
NA J
NA J
9.7 f 4.2K
NA
1410 f 610K 3500 f 1500' 8000 f 3000M 1410 f 610K 3500 f 1500' 8000 f 3000" 4710 f 2540" 1410 f 610K 3500 f 1500' 8000 i 3000M 1410 k 610K 3500 f 1500' 8000 f 3000" 2170 f 1160M 3500 f 1500' 5000 f 2000M 4710 f 2540M 3750 f 1500'
NA J
NA J
NA
NAJ NA J
NAJ
NA
NAJ 600 f 100 * Former Type I, Classes 1 through 5. Type II, Type IV, Classes 5,6, and 9, and Type V. Class 2 have been deleted because they are no longer listed as commercial
e Fmer ly Type I, Class 6. Formerly Type 111, Class 1. Formerly Type 111, Class 2.
E F m r l y Type 111, Class 3. Fomierly Type IV, Classes 1 through 4. Formerly Type V, Class 1. Formerly Type IV, Class 7. F m r l y Type IV. Class 8. Not applicable.
Tested at a reduction ratio of 400 to 1.
products.
KTested at a reduction ratio of 100 to 1. (Reduction ratio is the ratio of the cross-sectional area of the preform to the cross-sectional area of the die.)
M Tested at a reduction ratio of 1600 to 1. >5O above second melting peak temperature.
resin through a No. 10 hand sieve into the mold. Adjust the lower plug height so that the resin can be leveled by drawing a straightedge in contact with the across the top of the mold cavity. Insert the mold in a suitable hydraulic press and apply pressure gradually (Note 3) until a total of 13.8 MPa (2000 psi) for Type III resin or 34.5 MPa (5000 psi) for all other types is attained. After this point has been reached, hold the pressure on the disk for 3 min. Remove the disk from the die. A wax pencil may be used to write sample identification on the disk at this time.
NOTE 3-As a guide, increasing the pressure at a rate of 3.45 MPa (500 psi)/min is suggested until the desired maximum is attained.
10.1.3 Place the sintering oven in a laboratory hood (or equip it with an adequate exhaust system) and sinter preforms according to Table 3, Procedure B for Types I, III, IV, and VI, and Procedure C for Type V.
NOTE 4-Although the rate of pressure application is not critical, the cooling cycle is most important and the conditions cited in this procedure must be followed very closely. If they are not followed, the
crystallinity of the disks and the resulting physical properties will be markedly changed. Therefore, the use of a programmed oven is recommended for the most precise sintering cycle control so that the hood window may be left down during the entire sintering procedure, the latter being an important safety consideration.
10.2 Test Specimens for Standard SpeciJic Gravity and Thermal Instability Index:
10.2.1. A cylindrical preforming mold, 28.6 ( 1 % in.) internal diameter by at least 76.2 mm (3 in.) deep, is used to prepare the preforms. Clearance should be sufficient to ensure escape of air during pressing. Place flat aluminum foil disks, normally 0.013 mm (0.005 in.) thick and 28.6 m m ( I l/s in.) diameter, on both sides of the resin, when molding Type III resins. The test resin should be near ambient temperature prior to molding.
NOTE 5-For maximum precision, fhe weighing and preforming operations should be carried out in a constant-temperature room at 23 f I'C (73.4 f 1.8'F). The method should not be run below 22'C (71.6"F) due to the crystalline transition which leads to possible cracks in sintered
3
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TABLE 2 Detail Requirements for Tests on Molded Specimens
Thermal Insta- Standard Cpeclfic Gravity Tensile Strength, min Elongation at break, min, % min max MPa DSi
Type Grade bility Index, m a r -
. . . 50 2.13 2.18 13.8 2000 140 I 1 2
III I A
28
3c
4
5 6
7 IV0 . . . V E 1
2 VI 1
2 3
VI1 . . .
A . B C A 0 C D A B C A B C D B C D 0
. I .
... . . .
. . .
...
. . .
. . .
. < .
50
50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 15 15 15 50 50 50 50 50 50
NAO
NAO
2.13 2.19 2.19 2.19 2.14 2.14 2.14 2.14 2.17 2.17 2.17 2.14 2.14 2.14 2.14 2.14 2.160 2.14 2.140 2.13 2.16 2.14 2.13 2.13 2.15 NA o
NAG
2.18 2.24 2.24 2.24 2.20 2.20 2.20 2.20 2.23 2.23 2.23 2.23 2.23 2.23 2.23 2.20 2.190 2.20 2.160 2.19 2.22 2.1 8 2.19 2.19 2.18 NAG
NAO
17.2 18.6 18.6 18.6 20.7 20.7 20.7 20.7 20.7 20.7 20.7 18.6 18.6 18.6 18.6 20.7 20.7 20.7 20.7 27.6 20.7 28.0 25.5 27.6 27.6 NAG
NAG
2500 2700 2700 2700 3000 3000 3000 3000 3000 3000 3000 2700 2700 2700 2700 3000 3000 3000 3000 4000 3000 4060 3700 4000 4000 NAG
NAQ
400 400 400 400 200 200 200 200 200 200 200 200 200 200 200 200 200 200 200 300 300 500 275 300 200 NAG NAo VIIIF . . .
* Formerly Type 111, Class 1. ' Fomwrly Type 111, Class 2. Formerly Type Ili, Class 3. Formerly Type IV, Classes 1 through 4.
E Fwmerly Type V, Class 1. Extnislons of thls resin may show an Increased degree of clarity. Not applicable by molding techniques included in this specification.
B. Steel I
A. Steel D. Steel -D Assembly
FIG. 1 Assembly and Details of Die for Molding Test Specimens
specimens and differences in specimen density. Practice D 3297 pro- vides additional details.
10.2.2 Weigh out 12.0 f 0.1 g of resin and place it in a
preforming mold. Nonfree-flowing resins shall be screened through a No. 10 sieve, Compacted resins can be broken up by hand-shaking cold resin in a half-filled sealed glass
4 --`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
A S T M DI457 92 = 0759510 0515372 79T
TABLE 3 Sintering Procedures A A B C D E F G H I
Initial temperature, OC (OF)
Rate of heating, OC/h (OF/h)
Hdd temperature, "C (OF)
Hold time, min Coding rate, 'Cjh (OF/h)
Final or second hdd temper-
Second hold time, mln Period to room temper-
ature, OC (OF)
ature.c min. h
..
380 I 6 (716 f IO) NAa
380 f 6 (716 f IO) 30 + 2. -0 72 f 5 (132 f 9)
(572 f IO) NAs '12
300 f 6
290 (554)
120 f 10 (216 f 18) 380 f 6 (716 f IO) 30 + 2. -0 60 f 5 (108 f 9) 294 f 6 (561 f IO) 24 + 0.5, -0 '12
290 (554)
120 f 10 (216 f 18) 357 f 8 (675 f 15) 30 + 2, -0 60 f 5
294 f 6 (561 f IO) 24 + 0.5, -0 '/2
(108 f 9)
238 (460)
60 f 5
371 f 6 (700 f IO) 240 f 15 60 f 5 (108 f 9) 238 it 6 (460 f IO) NAa 6
(108 f 9)
238 (460)
60 f 5 (I08 f 9)
(685 i IO) 363 t 6
240 f 15 60 f 5
238 f 6 (460 i IO) NAE 6
(108 f 9)
290 (554)
120 f 10 (216 i 18) 380 f 6 (716 f IO) 360 f 5 60 f 5 (I08 f 9) 294 f 6 (561 f IO) 24 + 0.5, -0 '12
238 (460)
60 f 5
357 f 8 (675 f 15) 240 f 15 60 f 5
238 f 6 (460 f IO) NAa 6
(108 r 9)
(108 f 9)
238 (460)
60 f 5 (I08 f 9) 380 f 6 (716 f IO) 960 f 15 60 f 5
238 f 6 (460 f IO) NAE 6
(108 f 9)
238 (460)
60 f 5 (108 r 9) 371 f 6 (700 i IO) 120 f 5 60 f 5 (108 r 9) 238 f 6 (460 f 10) NAs 6
A Procedure A has been specifled in previous Issues of Specification C 1457 for Type 111 resins. For improved precision Procedure 8 should be used. Not applicable. Aftef the specimens have cooled, store them at ambient temperature (ideally 23 f IOC) and remote from any laboratory heat source (that is ovens, etc.).
container. Condition the resin in the sealed glass container in a freezer or dry-ice chest. After breaking up resin lumps, allow the sealed container to equilibrate to near ambient temperature. Then screen and weigh the 12.0 f O. 1 g sample. Insert the mold in a suitable hydraulic press and apply pressure gradually (Note 3) until a total load of 13.8 MPa (2000 psi) or 34.5 MPa (5000 psi) is attained. Hold the pressure on the preform for 2 min. Remove the preform from the mold. A wax pencil may be used to write the sample identification on the preform at this time.
10.2.3 Sinter the preforms by Procedure A or B for Type III, Procedure B for Types I, IV, and VI, and Procedure C for Type V given in Table 3. NOTE 6-Improved precision in the standard specific gravity test
results has been obtained with the use of an upright, cylindrical oven, and an aluminum sintering rack. The cylindrical oven has an inside diameter of 140 mm (5.5 in.) and a depth of 203 mm (8 in.) plus additional depth to accommodate a 50.8-mm (2-in.) cover and is equipped with adequate band heaters and controls to accomplish the sintering of specimens according to Procedure B, Table 3. The rack, as shown in Fig. 2, allows preforms to be placed symmetrically in the
!4 IN. (6.3 mm) DIAM. 4 SIDES REQUIRED
* N N
(1 24 mm)
5 REQUIRED
4?4" D, TYPE 3003-Hl4 20 GA. ALUMINUM- l u
NOTE: ALUMINUM PLATES
FIG. 2 Sintering Rack for SSG Samples
TACK WELDED TO RODS
center region of the oven. Place six preforms on each of the middle oven rack shelves. (If six or less preforms are to be sintered, place them on the middle rack, filling with dummy specimens as needed.) Place 'dummy' specimens on the top and bottom shelves. Specimens must be spaced evenly in a circle on each shelf, with none of them touching. An oven load must be no less than 18 pieces including the additional dummy pieces. Dummies are used to complete the load as necessary. (Dummies are defined as normal 12-g specimens that have previously been through the sintering cycle. Dummies must only be used for an additional two or three thermal cycles, due to eventual loss of thermal stability and physical form.)
10.2.4 Remove all flash from each specimen so that no air bubbles will cling to the edges when the specimen is immersed in the solution for weighing during the standard specific gravity and thermal instability index tests. It is recommended for this section and during testing that cotton gloves be worn while handling test specimens.
10.3 Tesi Billets: 10.3.1 Test specimens cut or skived from billets may be
used as alternatives to the test disks described in 10.1 and
1 FIG. 3 Preforming of PTFE Test Billet
5
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-__ _L_ . _ _ _ _ . ~ _ ~ _
A S T M D1457 92 0759510 0515173 626
D 1457
10.2 for Types I, IV, V, and VI resins. 10.3.2 Mold test billets in a mold similar to Fig. 3, having
an inside diameter of 57 mm (2.25 in.) and of sufficient height to contain the resin sample. Plug clearance should be sufficient to ensure escape of air during pressing. A 254-mm ( IO-in.) mold cavity fill depth will produce a billet approxi- mately 76 mm (3 in.) long from a resin charge of 400 f 50 g. The billet length may be varied in accordance with the testing to be done.
10.3,2.1 Adjust the lower plug position using a support ring for the mold shell so that the resin level will not come within 13 mm (0.5 in.) of the top of the mold cavity. Add the resin to the mold, insert the top plug, and apply hand pressure. Remove the support ring, and place the mold in a hydraulic press.
10.3.2,2 Apply an initial load to the mold of 3.45 MPa (SOO psi) 110 % and hold for 1 to 2 min. Increase the load smoothly to the final performing pressure in 3 to 5 min. Do not allow the mold shell to contact either press platen at any time during this preforming step. The final pressure attained should be as recommended by the manufacturer for the particular material, otherwise 34.5 MPa (5000 psi) for Type I and 17.2 MPa (2500 psi) for Types IV, V, and VI should be used. Hold under maximum pressure for 2 to 5 min. Release the pressure by gradually 'cracking' the pressure release valve without an apparent movement of the press platens. Remove the top pusher and force the preform vertically out of the mold shell using a continuous, smooth movement.
NOTE 7: Caution-Take care in removing the preform from the die. If a continuous smooth movement of the preform is not maintained, cracking of the preform may occur.
10.3.3 Place the preform in an oven. Sinter according to procedures in Table 3. Use Procedure D for Types I, IV, and VI, and Procedure E for Type V resins,
10.4 Sectioning and Skiving the Test Billet: 10.4.1 Divide the test billet into sections by making
traverse cuts by machining, or by a suitable alternate
FACE B 7 1 7
SECT.'II[ Approx. 38 mm ( I .5 in.)
U A FACE E
FACE F
1 1 SECT.=
procedure, in accordance with Fig. 4. The rough cuts between Sections i and I I may be made with a saw, but the Faces C and D must be prepared by machining.
10.4.2 Prepare five test specimens for the determination of tensile strength and elongation from 0.8-mm (Vx-in.) thick slices machined from Section I I , Face C, and machine a slice of suitable thickness for standard specific gravity measurements as described in 13.7.1. Take care to avoid wedge-shaped cuts. Use the remainder of Section II to prepare tape specimens by skiving O. I3 mm ( 5 mils). Discard the initial five revolutions of skived tape before taking the test sample. The tape may be used for the determination of tensile strength and elongation, as an alternative to ma- chined disks, If electrical properties, discussed in the Ap- pendix, are to be determined on tape, Sections II and III must be left together in order that a tape of sufficient width is obtained to allow the cutting of a 2-in. diameter electrical test specimen.
11. Conditioning Test Specimens 11.1 For tests of standard specific gravity and tensile
properties the molded test specimens shall be conditioned in accordance with Procedure A of Practice D 6 18, for a period of at least 4 h prior to test. The other tests require no conditioning of the molded test specimens.
12. Test Conditions 12.1 Tests shall be conducted at the Standard Laboratory
Temperature of 23 f 2°C. (73.4 2 3.6"F), unless otherwise specified in the testing methods or in this specification. Since this resin does not absorb water, the maintenance of constant humidity during testing is not important.
13. Test Methods 13.1 Melting Characteristics by Thermal Analysis-An
initial melting peak temperature (Fig. 5 ) greater than 5°C (4 1 O F ) above subsequent melting peak temperatures is indic- ative that the resin has not been melted previously. A resin that has been melted previously is not compatible with the scope of this specification except for Type VIL The peak
/-
dBCIJ:il) .\!;I> SL'IiSEi!I'P: I !IC.I.TiSi; -.-. . I'tdES . . .. . ._ ..
:. . . . . .. , . .! - 1 1 : ! :.:< - I'!.,. ............_.
TEMPERATURE L
FIG. 5 Melting Characteristics by Thermal Analysis
4
AT
t
FIG. 4 Sectioned PTFE Test Billet
6
--`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
~~
ASTM DI1457 92 = 0759530 0535L74 562 = D 1457
3àmm 4 I i l f i (-'I FUNNEL 4
Mai'i: Type 304 Stainless Steel i6 Gage (1.6 m m l 0.0625")
FIG. 6 Details of Funnel for Bulk Density Test
temperature obtained on the second and any subsequent melting is defined as the second melting peak temperature and occurs at about 327°C (621°F) for PTFE resins. If peak temperatures are difficult to discern from the curves, that is, if the peaks are rounded rather than pointed, straight lines should be drawn tangent to the sides of the peak. Where these lines intersect beyond the peak should be taken as the peak temperature. Multiple peaks during the initial melting test are not uncommon. Where more than one peak occurs, the presence of any peak corresponding to the second melting peak temperature may indicate the presence of some previously melted material.
13.2 Bulk Density: 13.2.1 Bulk density gives some indication, on a volu-
metric basis, of how the resin may perform during feeding of molding and extrusion equipment. PTFE resins have a tendency to compact during shipment and storage, and even though the material is broken up by screening or some other means, original 'as produced' results may not be duplicated. Because of this tendency to pack under small amounts of compression or shear, Test Method D 1895 is not applicable to these resins. The procedure given in the following para- graphs must be used to measure this property.
13.2.2 Apparatus: 13.2.2.1 Funnel-A funnel arrangement as shown in Fig.
6. 13.2.2.2 Feederlo-A feeder with a No. 8 wire screen
placed over approximately the top two thirds of the trough.
The funnel shall be mounted permanently in the feeder outlet.
13.2.2.3 Controller:' I
13.2.2.4 Volumetric Cup and Clip S a n d (see Fig. 7)-The volumetric cup shall be calibrated initially to 250 mL by filling with distilled water, placing a plane glass plate on top, drying the outside of the cup, and weighing. The net weight shall be 250 f 0.5 g. The top and bottom faces of the volumetric cup and the cup stand shall be machined plane and parallel.
13.2.2.5 Leveling Device-The leveler (see Fig. 8) shall be affixed permanently to the table and adjusted so that the sawtooth edge of the leveler blade passes within 0.8 mm ( ' h 2
in,) of the top of the volumetric cup. 13.2.2.6 Work Surface-The work surface for holding the
volumetric cup and leveler shall be essentially free from vibration. The feeder, therefore, must be mounted on an adjoining table or wall bracket,
13.2.2.7 Balance-The balance having an extended beam shall have a capacity of 500 g and a sensitivity of 0.1 g or equivalent .
13.2.3 Place the clean, dry volumetric cup on the ex- tended beam of the balance and adjust the tare to zero. Select about 500 mL of the resin to be tested, place it on the feeder screen and vibrate all of the resin through the screen and back into the sample container twice to break up any lumps. This screening step is not necessary for Type III resins. Put the cup in the cup stand and place the assembly such that the distance of free polymer fall from the feeder outlet to the top
l o A 'Vibra-Flow' Feeder,' Type FTOIA, available from FMC Corporation, Material Handling Division, FMC Building, Homer City, PA 15748, has been found satisfactory for this purpose.
I I A 'Syntron' controller, Type SCRlB, available from FMC Corporation, Material Handling Division, FMC Building, Homer City, PA 15748. has been found satisfactory for this purpose.
7
--`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
_ _ __ - _s _I-
A S T M DI457 92 - 0759530 0515375 Y T 9 - I
IO2 niiri (4") h a m Noies:
I Top and bottom mus1 be t la l and parallel wilhin 0.05mm (0.002"l.
2 Inside bol lom corner must be square as shown.
3 Star1 with Slainlers Steel lubing
or 53.98 mm (2.125") I.D. square up and machine to l inirhed dimensions after welding.
63mm (2$)0.0. x 50.80mm(2 000") 51 rnn . . .. .
T d L
E. and bottom must be f lat and
parallel within 0.05 mm (0.002").
3 Bottom 01 hole must be square wilh cenlerline and with IOD
I 7 fl 2 Remove o11 external sharp corners. /' .e'' !<'' ,
Weld al l oround and grind $mooth
VOLUMETRIC CUP
surlace of stand.
Mat'l: Type 3 0 4 Stainless CUP STAND Y-
Seamless Tubing Mat' l ; 17 S-T Aluminum (or equiv.)
FIG. 7 Volumetric Cup and Cup Stand for Bulk Density Test
2 1 0 x 5 3 ~ 6 mm ( 8 $r2& x y) 2.4mm($)gap l e f l between -- Type 304 Stainless Siée¡ Plate ar Sirap welded across toD for r ia ld i lv --- angler lor mounling saw blade
Use shimslock ar washers to lake up clearance in 2.4 mm (3/32"1 wide gap between angle and sow blad
\ Leveler Blade (Atkins Saw Blade No, 614-P)saw loolh
6mm( ~ 4 " l Diorn ~19mm(3/4"1 Long Brass Rive1 ( 2 req'd) 2.4 mm (3/32") Diom x 19mm (314") long Brass Colter Pin (2 req'd) for mounting saw blade firmly in posit ion
Drill hole thru angle and blade to 0.12mm (0.005") clearance with diom 01
1111 I cotter Din 2 5 r 2 5 ; 3 m m ( l x l ~ ~ ) Type 304 Sloinless Sleel'Angles ( 4 req'd - 2 each end)
51x 5 1 x 3 m m ( 2 x 2 x Q') Slainlers Sleel Gusseis
&4 req'd- 2 each end)
~
I I
k- 2 5 4 mm (10") -4 LEVELER STAND
Mat'kas Noted
*I 9.5 mm k- 2 5 4 mm (IO") -4
( 348'') Note: Base pla ie must bc
f l a l and parallel. Saw blade when mounted murt between blade and assembled be rqhare to and p a r h i e l wilh base ploie wilhin 0.12 mm (0.005") from end lo end.
Height of saw blade must allow 0.8mm (V32") or less clearance
cup and cup stand (as indicaled by phanlom lines.)
Welded Construction where indicaled
FIG. 8 Leveler Stand for Bulk Density Test
rim of the cup shall be 38.1 4 3.2 mm (1 */z in. f 1/18 in.). Increased fall causes packing in the cup and higher bulk density values. Set the controller so that the cup is filled in 20 to 30 s (usually about 70 on the controller). Pour the sample on the vibrating screen and fill the cup so that the resin forms a mound and overflows. Let the resin settle for about 15 s and then gently push the cup and its stand beneath the leveler. Exercise care to avoid agitation of the resin and cup before leveling. Weigh the resin to the nearest 0.1 g.
13,2.4 Calibration-Calculate the bulk density as follows:
13.2.5 Precision-The precision on a single determina- tion shall be between I 5 and 6 g/L (two U limits).
1 3.3 Part icle Size: 13.3.1 The fabrication of PTFE resins either by molding
or extrusion is affected significantly by particle or agglom-
Grams of resin x 4 = bulk density (g/L)
erate size and size distribution. (See Appendix X 1 for further details on particle characteristics.)
13,4 Wet-Sieve Method: 13.4.1 Principle of Method-The average particle or ag-
glomerate size of PTFE resins is determined by fractionation of the material with a series of sieves. Fractionation is facilitated by spraying with perchloroethylene (Note 8) which breaks up lumps and prevents clogging of the sieve openings. This method is recommended for Types I, IV, V, VI, VII, and VI11 resins, but not for Type III. NOTE 8: Warning-Perchloroethylene is under investigation by gov-
ernment agencies and industry for its carcinogenic effects. Precaution- Protective nitrile or butyl gloves should be worn to prevent skin contact and adequate ventilation provided to remove the vapors.
13.4.2 Apparalus: 13.4,2.1 Balance, capable of weighing to *O, 1 g. 13.4.2.2 Sieves-U.S. Standard Sieve Series, 203-mm (8-
8
--`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
ASTM DI457 92 0759530 0535176 335
TABLE 4 Sieving Requirements”
14 (1.40 mm) 18 (1.00 mm) 25 (710 pm) 35 (500 pm) 45 (335 pm) 60 (250 pm) 80 (180 pm)
120 (125 pm) 170 (90 pm) 200 (75 pm) 230 (63 pm) 270 (53 pm) 325 (45 pm) 400 (38 pm) Sample Size, g 10 f 0.1 50 f 0.1
x x X X x x x x x x x x x x x x x x x x x x x x x x x x X X x x x x
x x x x x x x x x x x x x x X
x x x x x x
A it is suggested that the sieves and sample size checked in a “Type” cdumn be used when perfmlng the sieve analysis on that particular type. However, other configurations of sieves may be used lo obtain equivalent results.
E A discusslon of the parllcle characteristics of finely divided resins is found in Appendix Xi.
in.) diameter conforming to Specification E 11, except that sieves shall be selected from Table 4.
13.4.2.3 Ventilated Hood. 13.4.2.4 Beakers-Six-tared, 150-mL beakers. NOTE 9-As an alternative, sieves may be tared, dried, and weighed
on a balance to avoid transferring of fractionated samples to the tared beakers.
13.4.2.5 Apparatus for Sieving and Spraying-A sug- gested arrangement of an apparatus for recirculating perchloroethylene is shown in Fig. 9 (a). This must be located in a ventilated hood or adequately ventilated area.
13.4.3 Reagents-Perchloroethylene, 20 L (5 gal). Other liquids may be used; however, their applicability and hazards associated with their use must be thoroughly investigated.
13.4.4 Procedure: 13.4.4.1 Select the appropriate sample size and combina-
tion of sieves from Table 4 for the type of resin under test. Adjust the flow rate of the perchloroethylene to 6 f 0.5 L/min.
13.4.4.2 Place the weighed resin on the top sieve and
Porloble Al l Pwipoie P o w
\\\ \\\\\\\\\ Table Top
b
lamp l o dlult Flon ole
antrifugal Pump
6 Li tar i per min ot Shower Head
opOble Of Deliverinq
13nn if ioü Ghae Tubing
201. ISooi.1 Corboy
Perchloroethylene
a
FIG. 9 Apparatus for Particle Size Test
spray it with perchloroethylene for 1 I 0.2 min. The shower-head shall be about level with the top of the sieve and be moved in a circular fashion. Take care to break up all of the lumps and to wash the material from the sides of the sieve.
13.4.4.3 Remove the top sieve and place it in the hood to dry.
13.4.4.4 Repeat the procedure specified in 13.4.4.2 and 13.4.4.3 iintil all the sieves have been sprayed. Air-dry the sieves in the hood for 30 min or longer, or oven-dry at 90°C (194°F) for 15 min and then cool to room temperature. Remove the resin from each sieve by tapping on a piece of paper as shown in Fig. 9 (b) . Pour each fraction into a tarcd bcakcr and wcigh t o k0.I g (see Note 9).
13.4.4.5 Record the weight of resin on each sieve. 13.4.4.6 Clean the sieve by inverting it over filter paper
and spraying with perchloroethylene. Take care to prevent the resin from getting into the perchloroethylene.
13.4.5 Calculation: 13.4.5.1 Calculate the net percentage of resin on each
sieve as follows: Net percent on sieve Y = F x weight of resin in grams on sieve Y where: F = 2 for 50-g sample, and F = 10 for 10-g sample.
13.4.5.2 Calculate the cumulative percentage of resin on each sieve as follows: Cumulative percent on sieve Y = sum of net percentages on sicvc i’
and sieves having numbers smaller than Y NOTE IO-Example: Cumulative percent on No. 35 sieve = net
percent on No. 18 + net percent on No. 25 + net percent on No. 35 sieves for a Type VI1 Resin.
13.4.5.3 Plot the cumulative percent versus the sieve opening size (or sieve number) on log probability paper as shown in the sample plot (Fig. IO). The sieve numbers and sieve opening sizes in micrometers are indicated below the figure. Draw the best straight line through the points and read the particle size at the 50 % cumulative percentage point (d50).
13.4.5.4 Calculate the average particle diameter, a as follows:
z= d,, 13.4.6 Precision-Because the resin particles have com-
plex shapes, and because on each sieve there is a distribution of particle sizes, the values for particle size and particle size distribution obtained will be only relative numbers. The 95 % confidence limits based on a limited series of tests are rt2.8 % for the average particle size.
13.5 Dry-Sieve Method: 13.5.1 Principle of Method-The average agglomerate size
of PTFE coagulated dispersion powders is determined by fractionation of the resin with a series of sieves. Fraction- ation is accomplished by mechanically shaking the material in the assembly of sieves for a predetermined period, This method is recommended for Type III resins.
13.5.2 Apparatus: 13.5.2. I Balance, capable of weighing to &O. 1 g. 13.5.2.2 Sieves-US. Standard Sieve Series (Table 4). 13.5.2.3 Sieve Shaker-A mechanical sieve shaking de-
9
--`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
- ~ _ _ ~ _- - --- - ASTM DI1457 92 0759530 0515377 273 =
dm D 1457
CUMULATIVE PERCENTAGE
Sieve No. Sieve Opening, pm Sieve No. Sieve Opening, pm 14 I20 I25 18 Io00 170 90 25 710 200 75 35 500 230 63 45 355 270 53 60 250 325 45 80 180 400 38
for Determination of Particle Size FIG. 10 Sample Plot of Cumulative Percent Sieve Opening Cire
I
vice capable of imparting uniform rotary and tapping action. 13.5.2.4 Freezer-Any commercial ice freezer. (A dry-ice
chest may be used.) 13.5.3 Proceúure; 13.5.3.1 Select the appropriate sample size and combina-
tion of sieves from Table 4 for the type of resin under test. Place the sample in an aluminum pan. Cool the pan and contents to less than 10°C (50°F). The dew-point tempera-, ture in the screening room must be less than the temperature in the cooling chamber. Obtain the tare weight on the selected sieves. Put the conditioned sample on the top sieve of the assembly and shake in the sieve shaker for 10 f 0.5 min. Determine the weight of resin retained on each sieve.
13.5.4 Calculaiion: 13.5.4.1 Calculate the same as in the wet-sieve method
(see 13.4.5). 13.5.5 Precision-The test precision is I 3 . 2 % (two 0
limits) for the combination of 25 + 35 + 45 - sieve fractions for a resin where this combination of sieves retains, on the average, 78 % of the sample.
13.6 Water Content: 13.6.1 Principle ofMelhod-A sample of PTEE resin of
known weight is dried in a vacuum oven in a tared aluminum weighing dish. When the resin is dry, it is removed from the oven, placed in a desiccator, allowed to cool, and then reweighed. From the weight lost during drying, the moisture content is determined and reported as percent moisture.
NOTE I I-If volatiles, other than moisture, are suspected, use the alternative method described in 13.6.5.
13.6.2 Apparatics: 13.6.2.1 Vacuum Oven. 13.6.2.2 Aluminum Weighing Dishes, with lids. 13.6.3 Procedure (Note 12)-Wash the aluminum
weighing dishes with water and rinse with acetone. When the acetone has evaporated from the dishes, dry them thoroughly in an oven at 50 to 80°C (122 to 176”F), then store in a desiccator until ready for use. Obtain the tare weight, B, of an aluminum weighing dish, plus lid, to the nearest 0.0001 g,
Place 35 to 40 g of PTFE resin in the tared aluminum weighing dish and record the weight, A, to the nearest 0.000 1 g (Note 13). Dry to constant weight in a vacuum oven (660 mm (25 in.) Hg) at 150°C (302”F), with the dish lid removed. Remove the dish from the oven, replace the lid on the weighing dish, and allow to cool in the desiccator for at least 30 min. Reweigh the dish (plus the resin and lid), C, and calculate the weight loss.
NOTE 12-From each group of samples, one sample is selected. and duplicate moisture determinations are run on it. If the difference between the duplicate results exceeds 0.01 %, the entire group of samples must be run over.
NOTE 13-When a group of samples is run at the same time, it is good practice to place the lids from the weighing dishes directly under their corresponding dishes while the samples are drying in the oven. This eliminates the possibility of introducing errors in the tare weights. Also, overnight drying in a circulating air oven may be used if the data can be shown to be equivalent to those obtained with the above procedure.
13.6.4 Crtl~iilufion-Calculate the percentage of moisture as follows:
where: A = weight of resin, dish, and lid, g, B = weight of dish and lid, g and C = weight of resin. dish, and lid after drying, g.
13.6.5 Precision-The precision of this test is k0.0063 % (two U limits).
13.6,6 Alternaiive M e h d . l i , r Diverininalion qf Wnrer IIJ Kur1 Fiscl~er ReugcJnrlZ-Weigh 35 f 1 g of resin into a glass-stoppered flask containing about 50 mL of pretitrated methanol. Shake to mix with a swirling motion for a few minutes. Titrate with standardized Karl Fischer reagent’ to a visual or electrometric end point.
Moisture, % = 11 - [ (A - C)/(A - il)] x 100
13.7 Specific Gravity: 13.1.1 Standard SpeciJic Gravity (SSG); 13.7.1.1 Determine the standard specific gravity of speci-
mens prepared by one of the procedures given in 10.2 or 10.3. (a) If specimens from 10.2 (12 g) are to be tested, use them “as is.” (6) If specimens from 10.3 (from billets) are to be tested, use the center portion of the sintered billet (Section II of Fig. 4). From it, cut an approximately cubical shape which weighs at least 10 g.
13.7.1.2 Make SSG determinations in accordance with the procedures described in Test Methods D 792, Annex A 1, Add two drops of a wetting agentI4 to the water in order to reduce the surface tension and ensure complete wetting of the specimen.
13.7.2 Spec@ Gravity by Density Gradient Technique- When the better precision of the SSG method is not required, the density gradient test described in Test Method D 1505 may be used,
13,8 Thermal Instability Index: 13.8.1 The thermal instability index (TII) test measures
the decrease in molecular weight of the resin after it has been
12Details of this method can be found in J. Mitchell. Jr. and D. M. Smith’s Aqiiarnciry, 2nd Ed., published by Interscience Publishers. Inc.. Ncw York, NY 1977.
IsKarl Fischer Reagent (Catalog No. So-K-3) is available from the Fischer
l4 Various liquid detergents have been found suitable for this purpose. Scientific Co., Pittsburgh, PA.
10 --`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
~
A S T I D1457 92 9 0759510 0535178 L O B
(,,,,c- U
WITH 2-WAY VALVE
TO AIR SUPPLY
Al R MOTOR-
VALVE
L
RAPID SPEED +
LINK BELT DRIVE
SLOW +SPEED
*SAFE1
r
U
CONSTANT TEMP ER ATU R E
GEAR REDUCER
FIG. 11 Paste Extruder and Accessories
heated for a prolonged period of time. When this test is to be run, duplicate specimens are prepared from the same sample or billet.
13.8.1.1 If 12-g specimens are used, determine SSG (13.7.1.1 and 13.7.1.2) on one specimen and extended specific gravity (ESG) on the other. Sinter the ESG specimen according to Procedure F for Types I, III, IV, and VI, and Procedure G for Type V, Table 3. Determine the ESG as in 13.7.1.2.
13.8.1.2 If billet specimens are used, use Section III as shown in Fig. 4 as the ESG specimen. Sinter according to Procedures in Table 3. Use Procedure H for Types I, IV, and VI, and Procedure I for Type V resins. Determine ESG as in 13.7.1.2.
1 3.8.2 Calculation-Calculate the thermal instability index (TII) as follows:
Tff = (ESG - SSG) X 1000 13.9 Tensile Properties: 13.9. I Procedure-Cut five tensile specimens from the
14.5-g disk prepared in 10.1, or from a billet, as prepared in Section 10 and cut or skived as in 10.4.2, with the microtensile die described in Fig. 13.15 Determine the tensile properties in accordance with the procedures described in Test Method D638, except that the initial jaw separation shall be 22.2 f O. 13 mm (0.875 i 0.005 in.) and the speed of testing shall be 50 mm (2 in.)/min. Clamp the specimens with essentially equal lengths in each jaw. Determine elonga-
The steel rule typc of die has been found satisfactory.
1457
&- -.. 2.370+ 0.001"- 4
GROSS SECTIONAL VIEW OF GYLINORICAL DIE
FIG. 12 Extruder Die Assembly
TABLE 5 Interchangeable Extrusion Dies - Land Length, mm (in.) Die Orifice, (Inside
Diameter), mm (in.) Reduction Ratio
1OO:l 3.18 (0.125) 25.35 (0.998) 400:l 1.59 (0.0625) 4.70 (0.188) 1600:l 0.79 (0.0312) 0.38 (0.015)
tion from the chart, expressed as a percentage of the initial jaw separation.
13.9.2 Precision-The single-operator, single-machine precision of tensile strength is 1.09 MPa (1 58 psi) (Is) and of elongation is 10.9 % (1s %), as defined in Practice E 177.
i 3. I O Exrrirsion Pressiirc. uf Typc I I I PTFE Rmins: 13.10.1 Dejinirion-Extrusion pressure is the pressure
that is observed duríng the extrusion of a lubricated Type 111 resin at one of the reduction ratio values established to represent processing under a low, intermediate, or high reduction ratio condition (see I3.10.2.2 and Table i).
13.10.2 Apparatus-(Equivalent apparatus may be substi- tuted):
13.10.2.1 Paste Exrruder (Fig. 1 i): (a) One paste extruder which may be used is a vertically
disposed, breech-loading extruder with a 3 1.8-mm ( 1 -25 in.) inside diameter extrusion cylinder. The barrel length is approximately 305 mm (12 in.), which is not critical so long as it will hold enough lubricated resin to extrude for about five min. The ram is 3 1.6 mm ( I .245 in.) outside diameter, with a groove near its free end to hold an O-ring that makes a tight seal between fhe ram and extruder cylinder. The extruder is equipped with devices for sensing and recording pressure on the face of the ram. The range of the pressure transducer in the ram face is greater than 69 MPa (10 O00 psi). Temperature-controlling equipment maintains the ex- truder at 30 & 1°C. A hydraulic system drives the ram at a speed of about 18 mm/min (0.7 in./min) to give an output rate of 19 g/min on a dry-resin basis (about 23.5 g/min of lubricated resin). The extruder-die assembly slides on tracks from under the ram to allow easy access for loading and cleaning the cylinder.
(b) An alternative muzzle-loaded paste extruder may be used which has a detachable die assembly that drops from the cylinder. The die assembly is dropped, a preformed charge of resin inserted up into the cylinder and the die assembly reattached.
13.10.2.2 Exirusion Dies (Fig. 12)-Dimensions for inter-
11
--`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
__-___-- -___ _ _ _ _ ~ ASTM DL457 92 a 0759530 0535379 044 m
STEEL RULE DIE
(INSIDE DIMENSIONS FOR DIE ARE T H E SAME AS TEST SPECIMEN)
TEST SPECIMEN
NOT TO SCALE
DIE TO BE SHARPENED ON INSIDE EDGF QNLY! (AS SHOWN IN M)
FIG. 13 Microtensile Die
changeable extrusion dies are given in Table 5 .
NOTE 14-Reduction ratio in this specification is the ratio of the cross-sectional area of the preform to the cross-sectional area of the die. This must not be confused with another definition wherein reduction ratio is the ratio of the cross-sectional area of the extruder cylinder to the cross-sectional area of the sintered extrudate.
13.10.2.3 Miscellaneous Equipment-Equipment is pro- vided for weighing, blending, conditioning (at 30"C), and preforming resin as well as extruder cleaning.
I3,10.3 Procedure: 13.10.3.1 Screen the dry resin through a 4-mesh sieve
onto a clean, dry, lint-free sheet of paper. 13.10.3.2 Transfer 200 f 0.5 g of the screened resin to a
clean, dry dass jar about 92 mm (3.625 in.) in diameter (approximately i -L capacity) having an airtight closure, or into a V-blender of laboratory size.
13.10.3.3 Determine the density of the lubricant, a kero- sene-type hydrocarbon liquid.I6 Determine the density at 25°C using, Test Method D 4052, a commercial density meter that will give four significant figures for the density,17 or a technically equivalent procedure. Calculate the mass of lubricant required by multiplying the density by 60.00 mL. Add the calculated mass i 0.0 I g of the lubricant to the resin in the jar or blender. It is convenient to make this addition while the jar containing the powder is on a balance that has a sensitivity at least as good as the -C 0.01 g required for the test. Avoid wetting the walls of the blending vessel with the liquid as this impairs mixing. When a jar is used, tape the lid in place to prevent loss of lubricant. Shake the jar briefly to
l6 Isopar Kœ, available from Exxon Co. has been found satisfactory for this
' 'A Mettler/Paar DMA 40 density meter has been found suitable for purPo=.
determining density to the required precision.
minimize the wetting of the jar wall with liquid. 13.10.3.4 Blend the mixture by placing the jar on rubber-
coated mill rolls and rolling it at 30 rpm for 25 & 5 min, by fastening the jar to a windmill type blender" and blending for 20 k 1 min, or by blending the mixture in the V-blender for i 5 +. 5 min. If a V-blender has been used, drop the resin from it into a jar of approximately I-L capacity and seal the jar.
13.10.3.5 Afier blending, place the jar with its contents, in a controlled atmosphere at 30 +. 1"C, to age for a minimum of 2 h. A water bath has been found to be satisfactory. This enables the lubricant to diffuse to the interior of individual particles and surfaces not reached during the blending process.
13.10.3.6 Place the proper extrusion die for the desired reduction ratio at the bottom of the extruder cylinder if using the paste extruder of 13.10.2. la.
13.10.3.7 Resin Prt$orm: (a) To preform the resin for the paste extruder of
13.10.2. i(a), slide the extruder-die assembly forward, mount a 31.8-mm (1.25411.) inside diameter extension tube about 610 mm (24 in.) in length at the breech end of the extruder cylinder. Quickly pour the lubricated resin through a funnel into the extension and force the resin into the extruder cylinder with a tamping rod. Apply the force with hard pressure and a very slow, even stroke.
(b) To preform the resin for the paste extruder of 13.10.2.l(b), mount a 31.8 mm (1.25 in.) inside diameter preforming tube about 610 mm (24 in.) in length with its cross section resting against a flat, smooth surface. Quickly pour the lubricated resin through a funnel into the tube and force the resin down in the tube, The force may be applied
I S A Gilson Spinning wheel mixer has been found suitable for this purpose.
12 --`,`,`,``,,```,````,,``````,```-`-`,,`,,`,`,,`---
A S T M DI457 72 0759510 0515LBO 866
d!# D 1457
with a hydraulically controlled tamping device to compact the resin with a slow, even stroke to a minimum of 690 kPa (100 psi) on the resin. Remove the preform from the preforming tube, insert the preform up into the cylinder of the extruder and attach the die assembly.
13.10.3.8 Use the fast speed drive to run the ram down into the cylinder cavity. When the first bit of beading emerges from the orifice, stop the descent of the ram.
13.10.3.9, Immediately change to slow drive, start the pressure-recording system and extrude the lubricated resin at a rate of 19.0 -I: 1 .O g/min (dry-resin basis).
13.10.3.10 Record the pressure developed on the face of the ram in contact with the resin in the cylinder as a function of time. The extrusion pressure is the average pressure required to extrude the sample as measured between the third and fourth minutes of the extrusion, provided it gives a continuous, smooth extrudate. This has been called the steady-state extrusion pressure.
13.10.4 Precision: 13.10.4.1 The test precision is to be determined by
round-robin testing.
14. Inspection
material meets the requirements of this specification.
15. Retest and Rejection
specification, it may be retested to establish conformity.
16. Packaging and Package Marking 16.1 Packaging-The resin shall be packaged in standard
commercial containers so constructed as to ensure accept- ance by common or other carriers for safe transportation to the point of delivery, unless otherwise specified in the contract or order.
16.2 Package Marking-Shipping containers shall be marked with the name of the resin, type, and quantity contained therein.
16.3 All packing, packaging, and marking provisions of Practice D 3892 shall apply to this specification.
17. Precision and Biaslg 17.1 Table 6 is based on a round robin conducted in
1985-1986 according to Practice E 691, involving seven materials tested by six laboratories. For each material, the sheeting from which the test specimens were to be cut was obtained from one source. Using a steel rule'die, one set of test specimens for each laboratory was cut by one of the laboratories. Sheeting and a duplicate die were furnished each participating laboratory and used to cut a second set of test specimens. Each test result was the average of five individual determinations. Each lab obtained four test results on each material, two test results each on the specimens furnished and two on the specimens cut by the laboratory doing the testing.
17.1.1 The properties used in the analysis are tensile
14.1 Inspection of the resin shall be to determine that the
15.1 If any resin fails to meet the requirements of this
l9 Supporting data are available from ASTM Headquarters.
TABLE 6 Precision ,mrnary, Tensile Strength and Elongation at Break
NOTE-/, = 2.8 x CV,; I, = 2.8 x CV,.
Tensile Strength
Mean psi CV,% CVR% I,% I R % Material
Granular PTFE 4801 2.79 8.85 7.81 24.78 Coagulated Dispersion PTFE 4807 2.71 3.37 7.59 9.46 PFA 4164 3.11 9.03 8.71 25.28 FEP 4144 2.98 7.98 8.34 22.34
Percentage Elongation at Break
Mean % E CV,% CV, % i ,% I, W Material
Granular PTFE 337 2.83 16.43 7.92 46.00 Coagulated Dispersion PTFE 300 2.17 13.74 6.08 38.47 PFA 336 3.27 9.66 9.16 27.05 FEP 319 2.21 7.60 6.19 21.28
strength and elongation at break. The stress-strain curves of the fluorocarbon polymers (but not the fluoropolymers: modified ETFE and poly(viny1idene fluoride), PVDF) are similar in shape. Data on ETFE and PVDF, therefore, were excluded from the analysis used for this precision and bias statement but are available for use in precision and bias statements and are to be included in the research report at ASTM. Based on advice from experts in statistical analysis of round robin data, and since use of fillers is excluded in the applicable standards, information from the testing on giass- fiber filled PTFE also is not included in Table 6. In addition, the experts advised that information from the samples cut in one laboratory and tested by all the laboratories should not be included in Table 6. The data are available in the report. NOTE 15: Caution-The following explanations of I, and IR (17.3
thru 17.3.3) are intended only to present a meaningful way of considering the approximate precision of this test method. The data in Table 6 should not be applied rigorously to acceptance or rejection of material, as those data are specific to the round robin and may not be representative of other lots, conditions, materials, or laboratories.
17.2 Users of this test method should apply the principles outlined in Practice E 691 to generate data specific to their laboratory and materials, or between specific laboratories, The principles of 17.3 thru 17.3.3 would then be valid for such data.
17.3 Concept of Ir and IR-if CVr and CVR have been calculated from a large enough body of data, and for test results that were averages from testing five specimens:
17.3.1 I,.- Repeatability-Comparing two test results for the same material, obtained by the same operator using the same equipment on the same day the two test results should' be judged not equivalent if they differ by more than the I , value for that material.
17.3.2 IR: Reproducibility-Comparing two test results for the same material, obtained by different operators using different equipment on different days the two test results should be judged not equivalent if they differ by more than the IR value for that material.
17.3.3 Any judgment in accordance with 17.3.1 and 17.3.2 would have an approximate 95 % (0.95) probability of being correct.
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- ~- ASTM DL457 92 m 0759530 05353d3 7T2 m
17.4 Bias is systematic error that contributes to the differ- ence between a test result and a true (or reference) value. 18. 1 coagulated dispersion PTFE; fluorocarbon polymer; There are no recognized standards on which to base an fluoropolymers; granular PTFE; polytetrafluoroethylene; estimate of bias for this test procedure,
18. Keywords
PTFE
APPENDIX
(Nonmandatory Information)
XI. ADDITIONAL USEFUL TESTS
X1.1 Scope X 1, I , I In addition to their use for specification purposes,
the tests described in this specification have utility for characterizing PTFE resins. Other useful properties of PTFE can be measured by adding a few details to the specification tests. Others, taken from earlier editions of this specification still have utility. The purpose of this Appendix is to provide the details needed to determine these additional characteris- tics. The scope is summarized in Table Xl.1.
X1.2 Referenced Documents
X i .2.1 ASTM Standards: D150 Test Methods for A-C Loss Characteristics and
Permittivity (Dielectric Constant) of Solid Electrical Insulating Materials2
D 638 Test Method for Tensile Properties of Plastics2 D 2990 Test Methods for Tensile, Compressive, and Fiex-
ural Creep and Creep-Rupture of Plastics4 D 3293 Specification for PTFE Resin Molded Sheets D3294 Specification for PTFE Resin Molded Basic
Shapes5 D 3308 Specification for PTFE Resin Skived Tapes D 3369 Specification for PTFE Resin Cast Films
X1.3 Dimensional Changes During Molding (Shrinkage and
X1.3.1 Measure the inside diameter (ID) to rC0.00254 mm (0.OOOi in,) of the die used to make the preform in 10.1, 10.2, or 10.3. Measure the diameter and height at the preform. After the piece has been sintered and before using it for other testing, remeasure the diameter and height.
Percent mold shrinkage = [(diameter of sintered piece/iD of die) - i ] 100 Percent preform shrinkage = [(diameter of sintered piece/ diameter of preform) - i ] 100 Percent growth = [(height of sintered piece/height of pre- form) - i ] 100 Positive values reflect an increase in the dimension during sintering. Negative values reflect a decrease in the dimension during sintering.
XI ,3.3 Precision-Data on precision are being assembled.
X1.4 Size and Distribution of Size of Particles or Agglomer-
X 1.4.1 Average Size of Fine-Particle Size PTFE-Wet- sieve analysis, while having disadvantages, can be used to measure the average size of Type IV and Type V PTFE
Growth)
XI .3,2 Calculation:
ates in PTFE Resins
resins. The procedure of 13.4.5 should be followed using the set of sicves listed in Table 4 and a sample size of 10.0 g.
X 1.4.2 Material Retained on No. 230 (63-pm) Sieve: X 1.4.2.1 Scope-A wet sieving is performed with the
apparatus used for the determination of particle size, except that only two sieves are employed. This method is applicable to ultrafine resins such as Type IV resins.
X1.4.2.2 Principle of Method-The resin is sieved on a No. 230 (63-pm) sieve by spraying with perchloroethylene which breaks up agglomerates and prevents clogging of the sieve openings (see Note 10).
X1.4.2.3 Apparatus-Same as in 13.5.2, except that the following sieves are used: U.S. Standard Sieves, No. 20 (850-pm), No. 230 (63-pm), and No. 325 (45-pm).
X 1.4.2.4 Procedure: (a) Weigh 10 k 0.01 g of resins, Assemble the sieves as
shown in Fig. 9(a) with the No. 20 on top of the No. 230. Adjust the flow rate of the perchloroethylene to 6 f 0.5 L/min.
(b) Place the weighed sample on the No. 20 sieve and spray with perchloroethylene for exactly 1 min using a timer. This step assists in breaking up agglomerates. Move the shower head in a circular fashion, taking care to break up all the agglomerates and to wash the material from the sides of the sieve.
(c) Remove the No. 20 sieve and spray the No. 230 sieve for exactly 6 min, using a timer. Wash the material to the side of the sieve during the last minute.
(d) Dry the sieve and retained resin in an oven for 20 min or longer at 80 to 120 O C . The No. 20 sieve does not require drying.
(e) Remove the material from the No. 230 sieve by inverting on a piece of filter paper and tapping to free dry polymer. A stiff brush may be used to help free all the material from the sieve. Pour the dried resin into a tared weighing dish and weigh to fO.01 g. Alternatively, determine the tare mass of the resin retained on the sieve from the difference between the gross mass after sieving and the tare mass of the sieve before sieving. A balance with a sensitivity of about 0.0 i g is required for good precision. (f) Calculate the percentage retained on the No. 230 sieve
as follows: Amount retained, % = (weight retained/sample weight) x 100.
X 1.4.3 Distribution of Particle or Agglomerate Sizes in PTFE Resin:
XI .4.3.1 Procedure-Using the graph plotted in accord- ance with 13.4.5.3 or 13.5.4, draw the best smooth curve through the data points and read the values for the sizes at
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cumulative percentages of 16 and 84. These values, identi- fied d16 and d84, are, respectively, the sizeof the resin at the average diameter (d) plus 1 sigma and (d) minus 1 sigma. Calculate a distribution factor (DF) and skewness (SKEW) as follows:
DF = d16/d50 SKEW = DF/d50/d84
X 1.4.3.2 Precision-Because the resin particles have com- plex shapes, and because on each sieve there is a distribution of particle sizes, the values for particle size and particle-size distribution obtained will be only relative numbers. The 95 % confidence limits based on a limited series of tests are f2.8 % for the average particle size and 6 '?6 for the particle size distribution function.
X1.5 Yield Behavior and Tangent Modulus at Rupture . X1.5.1 Most of the PTFE resins covered in this standard do not show a yield stress as defined in Test Method D 638. Rather than the stress having a zero slope, the rate of increase of stress with strain decreases and then increases again. An approximate yield stress can be reported as the stress at the intersection of the two lines that best represent the initial linear part of the stress strain curve and the second linear part of the curve.
X1.5.2 Tangent Modulus at Rupture-The shapes of tensile stress-strain curves for PTFE resins are highly de- pendent on the crystallinity of the test specimen. Values for tensile strength and elongation at break do not reflect these shapes clearly. The value of the tangent to the recorded stress-strain curve measured as the best straight line from the point of rupture back along the curve is a convenient measure of the relative crystallinity of the test specimen. High values for the tangent modulus at rupture (>7.6 MPa) (1 200 psi) indicate relatively low crystalline contents. As the crystallinity increases, the tangent modulus at rupture de- creases until it approaches zero at high levels of crystallinity.
X1.6 Heats of Fusion and Crystallization X 1.6.1 If the melting characteristics of the PTFE resin, as
determined by Section 13, are determined by Differential
Scanning Calorimetry (DSC) rather than in DTA mode, additional quantitative information can be obtained on the nature of the resin.
X 1.6.2 Following the procedures for determining heats of fusion (AHF) and heat of crystallization (AHc) by DSC, measure and report AHf for the initial and second endotherms and AHc for the exotherm that is observed during controlled cooling between the two heating steps. These heats of transition, especially SHc, provide additional characterization of crystalline content and relative molecular weight of PTFE resins. X1.7 Electrical Properties
X 1.7. I Determine dielectric constant and dissipation factor in accordance with Test Method D 150. Determine dielectric breakdown voltage and dielectric strength in ac- cordance with Test Method D 150. Typical property values for dielectric constant and dissipation factor are listed in Table X I .2. Standards for dielectric strength of sheet, basic shapes, skived tape, and film are described in Specifications D 3293, D 3294, D 3308, and D 3369, respectively. X1.8 Tensile Creep
X 1.8.1 Determine the tensile creep of Type V materials on Type II tensile bars die cut or machined from the sheets produced in X1.8.2. Make measurements in accordance with Test Method D 2990. Conditions of test shall be 5.52 MPa (800 psi) stress at the Standard Laboratory Temperature of 23 +. 2°C (73.4 f 3°F) for a test duration of a minimum of 100 h. Typical values for moldings ofType V resins would be a maximum of 4.0 % tensile creep strain after 100 h.
X1.8.2 Mold test sheets for Type V resins for tensile creep requirements in a picture frame mold having inside dimen- sions of 203 mm (8.0 in.) square and of sufficient height to contain the sample. A frame 102 mm (4 in.) in height has been found adequate when using 25-mm (I-in.) thick pusher plugs to produce a sheet approximately 3 mm ( 1 % in.) in thickness from a resin charge of 300 g. Take care to level the resin charge in the mold. The molded sheet thickness shall be 3 mm ( I '/8 in.).
X1.8.3 Sinter the preform according to Procedure E of Table 3.
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