ASTM D7474-08
(Practice)Standard Practice for Determining Residual Stresses in Extruded or Molded Sulfone Plastic (SP) Parts by Immersion in Various Chemical Reagents
Standard Practice for Determining Residual Stresses in Extruded or Molded Sulfone Plastic (SP) Parts by Immersion in Various Chemical Reagents
SIGNIFICANCE AND USE
Thermoplastic moldings contain residual stresses due to differential cooling rates through the thickness of the molding. Changes in residual stress have been found to occur with time after molding due to stress relaxation. Many part performance parameters as well as part failures are affected by the level of residual stress present in a part. Residual stresses cause shrinkage, warpage, and a decrease in environmental stress crack resistance. This practice estimates the relative magnitude of residual stresses in parts produced from the series of sulfone plastics (SP), namely polysulfone (PSU), polyethersulfone (PESU), and polyphenylsulfone (PPSU) materials.
No direct correlation has been established between the results of the determination of residual stresses by this practice and part performance properties. For this reason, this practice is not recommended as a substitute for other tests, nor is it intended for use in purchasing specifications for parts. Despite this limitation, this practice does yield information of value in indicating the presence of residual stresses and the relative quality of plastic parts.
Residual stresses cannot be easily calculated, hence it is important to have an experimental method, such as this practice, to estimate residual stresses.
This practice is useful for extruders and molders who wish to evaluate residual stresses in SP parts. This can be accomplished by visual examination after immersion in one or more chemical reagents to evaluate whether or not cracking occurs. Stresses will relax after molding or extrusion. Accordingly, both immersion in the test medium and visual examination must be made at identical times and conditions after processing, if comparing parts. It is important to note the differences in part history. Thus, this technique may be used as an indication for quality of plastic processing.
The practice is useful primarily for indicating residual stresses near the surface.
SCOPE
1.1 This practice covers the evaluation of residual stresses in extruded profile or molded SP parts. The presence and relative magnitude of residual stresses are indicated by the crazing of the specimen part upon immersion in one or more of a series of chemical reagents. The specified chemical reagents were previously calibrated by use of Environmental Stress Cracking (ESC) techniques to cause crazing in sulfone plastics (SP) at specified stress levels.
1.2 This practice applies only to unfilled injection molding and extrusion grade materials of high molecular weight as indicated by the following melt flow rates: PSU 9 g/10 min, max., PESU 30 g/10 m, max, and PPSU 25 g/10 min, max. Lower molecular weight (higher melt flow) materials will craze at lower stress levels than indicated in Tables 1-3. (See Specification D 6394 for melt flow rate conditions.)
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
Note 1—There is no equivalent ISO standard.
1.4 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.
General Information
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Standards Content (Sample)
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Designation:D7474–08
Standard Practice for
Determining Residual Stresses in Extruded or Molded
Sulfone Plastic (SP) Parts by Immersion in Various
Chemical Reagents
This standard is issued under the fixed designation D7474; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope D6394 Specification for Sulfone Plastics (SP)
2.2 ISO Standard:
1.1 This practice covers the evaluation of residual stresses
ISO 22088–3 Plastics—Determination of Resistance to En-
in extruded profile or molded SP parts. The presence and
vironmental Stress Cracking (ESC)—Part 3: Bent Strip
relative magnitude of residual stresses are indicated by the
Method
crazing of the specimen part upon immersion in one or more of
a series of chemical reagents. The specified chemical reagents
3. Terminology
were previously calibrated by use of Environmental Stress
3.1 Definitions—For definitions of technical terms pertain-
Cracking (ESC) techniques to cause crazing in sulfone plastics
ing to plastics used in this practice, see Terminology D883.
(SP) at specified stress levels.
1.2 This practice applies only to unfilled injection molding
4. Summary of Practice
and extrusion grade materials of high molecular weight as
4.1 The practice involves the exposure of finished plastic
indicated by the following melt flow rates: PSU 9 g/10 min,
parts to a specified series of chemical reagents which are
max., PESU 30 g/10 m, max, and PPSU 25 g/10 min, max.
known to produce cracking or crazing of Sulfone Plastic (SP)
Lowermolecularweight(highermeltflow)materialswillcraze
materials at specific stress levels, under otherwise constant
at lower stress levels than indicated in Tables 1-3. (See
conditions including a fixed time of one minute. Thus, the
Specification D6394 for melt flow rate conditions.)
exposure of finished parts to one or more chemical reagents
1.3 The values stated in SI units are to be regarded as the
under no load conditions allows the quantification of the
standard. The values given in parentheses are for information
residual stress levels in the finished parts. Since the evaluation
only.
is based on the subjective criteria of presence or absence of
NOTE 1—There is no equivalent ISO standard.
crazing, this practice only yields an approximate indication of
the level of residual stresses in the parts. This practice
1.4 This standard does not purport to address all of the
estimates the relative magnitude of residual stresses in parts
safety concerns, if any, associated with its use. It is the
produced from the series of sulfone plastics, namely polysul-
responsibility of the user of this standard to establish appro-
fone (PSU), polyethersulfone (PESU), and polyphenylsulfone
priate safety and health practices and determine the applica-
(PPSU) materials.
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents
5.1 Thermoplastic moldings contain residual stresses due to
2.1 ASTM Standards:
differential cooling rates through the thickness of the molding.
D543 Practices for Evaluating the Resistance of Plastics to
Changes in residual stress have been found to occur with time
Chemical Reagents
after molding due to stress relaxation. Many part performance
D883 Terminology Relating to Plastics
parameters as well as part failures are affected by the level of
D4000 Classification System for Specifying Plastic Materi-
residual stress present in a part. Residual stresses cause
als
shrinkage, warpage, and a decrease in environmental stress
crack resistance.This practice estimates the relative magnitude
ThispracticeisunderthejurisdictionofASTMCommitteeD20onPlasticsand
of residual stresses in parts produced from the series of sulfone
is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials.
plastics (SP), namely polysulfone (PSU), polyethersulfone
Current edition approved Aug. 1, 2008. Published September 2008. DOI:
(PESU), and polyphenylsulfone (PPSU) materials.
10.1520/D7474-08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
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D7474–08
TABLE 1 Liquid Reagents for Residual Stress Test for PSU
Mixture Composition
Mixture Critical Stress, MPa (psi)
% by volume Ethanol % by volume MEK
1 50 50 15.2 (2200)
2 43 57 12.1 (1750)
3 37 63 9.0 (1300)
4 25 75 5.5 (800)
TABLE 2 Liquid Reagents for Residual Stress Test for PESU
Mixture Composition
Mixture Critical Stress, MPa (psi)
% by volume Ethanol % by volume MEK
1 50 50 17.9 (2600)
2 40 60 10.3 (1500)
3 20 80 6.9 (1000)
4 0 100 5.9 (850)
TABLE 3 Liquid Reagents for Residual Stress Test for PPSU
Mixture Composition
Mixture Critical Stress, MPa (psi)
% by volume Ethanol % by volume MEK
1 50 50 22.8 (3300)
2 25 75 13.8 (2000)
3 10 90 9.0 (1300)
4 0 100 8.0 (1150)
5.2 No direct correlation has been established between the 7.3 Methyl Ethyl Ketone (MEK), and
results of the determination of residual stresses by this practice 7.4 Isopropyl alcohol, 70 %.
and part performance properties. For this reason, this practice
8. Safety Precaustions
is not recommended as a substitute for other tests, nor is it
8.1 Protective equipment and clothing must be utilized to
intended for use in purchasing specifications for parts. Despite
avoid contact of chemical reagents with the skin or eyes. Use
this limitation, this practice does yield information of value in
adequateventilationtoremovenoxiousortoxicfumes,orboth.
indicating the presence of residual stresses and the relative
quality of plastic parts.
9. Test Specimen
5.3 Residual stresses cannot be easily calculated, hence it is
9.1 Size of Specimen—The specimen shall be a complete
important to have an experimental method, such as this
molding or a cut piece of the extrusion or molding of sufficient
practice, to estimate residual stresses.
size to not influence the stresses being observed. Twisting and
5.4 This practice is useful for extruders and molders who
breaking must be avoided in separating cut pieces since the
wish to evaluate residual stresses in SP parts. This can be
slightest amount of such forces has the potential to change
accomplished by visual examination after immersion in one or
stresses and cause false results.
more chemical reagents to evaluate whether or not cracking
occurs. Stresses will relax after molding or extrusion. Accord-
10. Conditioning
ingly, both immersion in the test medium and visual examina-
10.1 It is not necessary to condition the part prior to testing
tion must be made at identical times and conditions after
by this practice. If conditioning is utilized for a controlled
processing, if comparing parts. It is important to note the
studyinaseriesofparts,recommendedconditioningisat23 6
differences in part
...
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