ASTM D4703-93
(Practice)Standard Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets
Standard Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets
SCOPE
1.1 This practice covers the compression molding of thermoplastic granules and milled stock for the preparation of test specimens.
1.2 While conditions for certain materials are given, the primary source of specific conditions shall be the material specification standards for each type of material.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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.
Note 1--The main body of this practice is equivalent to ISO 293-1986. Annex A1 and ISO 293-1986 differ in some details; however, specimens prepared using Annex A1, Procedure A should be equivalent to those prepared using ISO 293-1986, Cooling Method D. Specimens prepared using Annex A1, Procedure C should be equivalent to those prepared using ISO 293-1986, Cooling Method B. However, due to the greater cooling rate tolerances of the ISO standard, specimens prepared according to ISO Cooling Method B may not be equivalent to Annex A1, Procedure C.
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Designation: D 4703 – 93 An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Compression Molding Thermoplastic Materials into Test
Specimens, Plaques, or Sheets
This standard is issued under the fixed designation D 4703; 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 measured in the nearest vicinity to the molded material.
3.1.3.1 Discussion—For positive molds, holes are normally
1.1 This practice covers the compression molding of ther-
drilled in the mold for measuring the temperatures defined in
moplastic granules and milled stock for the preparation of test
2 3.1.3 and 3.1.4.
specimens.
3.1.4 molding temperature, n—the temperature of the mold
1.2 Certain ASTM standards require the use of Test Method
or the press platens during the preheating and molding time,
D 1928 for compression molding of polyethylene test speci-
measured in the nearest vicinity to the molded material.
mens. Determine whether such requirements exist before using
3.1.5 molding time, n—the time during which full pressure
this practice.
is applied while maintaining the molding temperature.
1.3 While conditions for certain materials are given, the
3.1.6 preheating time, n—the time required to heat the
primary source of specific conditions shall be the material
material in the mold up to the molding temperature while
specification standards for each type of material.
maintaining the contact pressure.
1.4 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information
4. Significance and Use
only.
4.1 The methods by which sample materials are prepared
1.5 This standard does not purport to address all of the
and molded influence the mechanical properties of the speci-
safety problems, if any, associated with its use. It is the
men. Unlike injection molding, the objective of compression
responsibility of the user of this standard to establish appro-
molding is to produce test specimens or sheets that are both
priate safety and health practices and determine the applica-
homogeneous and isotropic. Molded specimens may be made
bility of regulatory limitations prior to use.
either from pellets such as are received directly from a material
2. Referenced Documents manufacturer, particles produced in a recycle recovery opera-
tion, or from a milled preform or sheet prepared on a two-roll
2.1 ASTM Standards:
mill. The pellets, particles, preform, or sheet are melted and
D 1928 Test Method for Preparation of Compression-
3 molded in a mold designed to produce a finished specimen of
Molded Polyethylene Test Sheets and Test Specimens
a given geometry, size, and thickness, or melted and molded in
3. Terminology the form of a smooth plaque or sheet of uniform thickness from
which desired specimens are cut, punched, or machined.
3.1 Definitions of Terms Specific to This Standard:
Working a compound on a two-roll mill prior to molding will
3.1.1 average cooling rate (°C/min), n—the cooling rate
disperse and distribute the compound additives in a manner
calculated by dividing the difference between the molding and
that will affect the physical properties of the compound. The
demolding temperatures by the time required to cool the mold
need for milling a sample prior to compression molding may be
to the demolding temperature.
determined by reference to the relevant material specification
3.1.2 cooling rate (°C/h), n—the rate of cooling obtained by
or the material manufacturer. It is important to treat different
controlling the flow of the cooling fluid in such a way that
samples of the same type of material in the same way: if
during each 10-min interval, the deviation from this specified
milling was done prior to molding on a material which is to be
cooling rate shall not exceed the specified tolerance.
used as a standard for comparison, all new materials to be
3.1.3 demolding temperature, n—the temperature of the
tested against this practice should be prepared and molded in a
mold or the press platens at the end of the cooling time,
similar manner.
4.2 The apparatus and exact conditions required to prepare
This practice is under the jurisdiction of ASTM Committee D-20 on Plastics
adequate specimens may vary for each plastic material. Appa-
and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.
ratus and procedures which should be satisfactory for molding
Current edition approved Feb. 15, 1993. Published April 1993. Originally
published as D 4703 – 91. Last previous edition D 4703 – 92.
many different plastic materials are given in this practice in
This practice was created as a coalescence of and replacement for Practices
Sections 5 and 6. The apparatus and procedures which have
D 2292, D 3010, and D 3463.
3 been found satisfactory for molding certain specific materials
Annual Book of ASTM Standards, Vol 08.02.
D 4703
are given in the Appendix. In any case, the apparatus and
procedures to be used in producing compression-molded speci-
mens of a given material may be obtained by reference to the
relevant material specification and should be agreed upon
between the purchaser and the supplier.
FIG. 2 Flash Mold with Machined Cavity
TABLE 1 Cooling Methods
Average Cooling Cooling Rate
Cooling Method Rate (See 3.1.1), (See 3.1.2), Remarks
°C/min °C/min
A 10+5
B 15+5
C 60 + 30 Quench cooling
D 5 + 0.5 Slow cooling
FIG. 3 Positive-Type Mold
5. Apparatus
5.1 Mill—Any size two-roll mill having chrome-plated
dimensions. Because of the manner in which the positive mold
rolls, capable of maintaining a constant temperature within6
operates, it is recommended that this mold type, either for a
2°C (63.6°F) of the temperature needed for the particular
plaque or a finished specimen, be limited to a single cavity. In
material involved, and being adjustable in speed as needed for
the positive-type mold, the full molding pressure, neglected
the material to be worked, is adequate. Some recommendations
friction, is exerted on the material during cooling. The thick-
for mills to be used for specific types of materials are given in
ness, stress and density of the resulting moldings depend on the
the Appendix.
mold construction, the size of the material charge, and the
5.2 Molds:
molding conditions. This type of mold produces test specimens
5.2.1 Mold Types—Several different types of molds may be
with high density, and it is particularly suitable for obtaining
used for the compression molding of test specimens of ther-
flat surfaces and for suppressing the formation of voids within
moplastics. In general, however, the molds used will fall into
test specimens.
one of two categories: a flash-type mold (see Figs. 1 and 2) or
5.2.4 Mold Surfaces—The surfaces of either type of mold
a positive-type mold (see Fig. 3). The characteristics of the test
that form the flat faces of the specimen should be finished to
specimens prepared by using different types of molds are not
the degree required by the test for which the specimen is
the same. In particular, the mechanical properties depend on
intended. For most tests, a surface quality of SPI-SPE #2 is
the pressure applied to the material during cooling.
adequate. The edges of the mold cavity should be visually free
5.2.2 Flash-Type Mold—The flash-type mold may be of the
of nicks and scratches which could cause premature failure of
picture-frame type, where a steel chase (the picture frame) is
the specimen during testing.
sandwiched between two thin steel ferrotype plates (see Fig. 1),
5.3 Press:
or it may be of the machined-cavity type (see Fig. 2), where the
5.3.1 The press shall have a clamping force capable of
mold consists of a cavity machined in a steel plate, with a
applying a pressure (conventionally given as the ratio of the
single steel ferrotype plate used as a top or cover. The cavity,
clamping force to the area of the mold cavity) of at least 10
or cavities, in the flash-type mold may be constructed to mold
MPa (1450 psi), and shall be capable of maintaining pressure
a single plaque from which test specimens may be stamped or
within 10 % of the specified pressure during the molding cycle.
machined, or the mold may be built to mold one or more
5.3.2 The platens of the press shall be capable of being
specimens to finished dimensions. Flash molds permit excess
heated to at least 240°C, and being cooled at a rate consistent
molding material to be squeezed out and do not exert molding
with the cooling method selected from Table 1.
pressure on the material during cooling. Nevertheless, this type
5.3.3 The platens or mold shall be heated either by high-
of mold is useful for preparing test specimens or panels of
pressure steam, by a heat-conducting fluid in an appropriate
similar thickness or comparable levels of low internal stress.
channel system, or by using electric-heating elements. The
5.2.3 Positive-Type Mold—The positive-type mold consists
platens or mold are cooled by a heat-conducting fluid (usually
of a cavity machined in a plate or block of steel and a force or
cold water) in a channel system.
plunger which closely mates with the sidewalls of the cavity
5.3.4 The heating and cooling systems in the mold platens
(see Fig. 3). Like the flash-type mold, the cavity may be built
shall be such that, when used with a particular mold, they shall
to produce a plaque from which test specimens may be
be capable of maintaining a temperature difference between
stamped or machined, or to mold a test specimen to finished
points on the mold surfaces of no more than 65°C during
heating or cooling.
5.3.5 For quench cooling (Method C in Table 1), two
presses shall be used, one for heating during molding and the
Mold comparison kits are available from D-M-E Company, 29111 Stephenson
FIG. 1 Flash Picture-Frame Mold Highway, Madison Heights, MI 48071.
D 4703
enough to avoid flow of the material. Full pressure means a pressure
other for cooling unless it can be demonstrated that the press
sufficient to shape the material and squeeze out the excess material.
used for heating can cool at the specified rate.
6.3 Cooling:
NOTE 1—For a specified cooling method, the flow rate of the heat-
6.3.1 General—With some thermoplastics, the cooling rate
conducting fluid should be predetermined in a test without any material in
affects the ultimate physical properties. For this reason, the
the mold.
cooling methods are specified in Table 1. The method of
6. Procedure
cooling shall always be stated together with the final physical
6.1 Preparation of Molding Material:
properties. The appropriate cooling method is normally given
6.1.1 Drying of Granular Material—Dry the granular ma-
in the relevant material specification. If no method is indicated,
terial as specified in the relevant material specification, or in
Method B shall be used.
accordance with the material supplier’s instructions. If no
6.3.2 Cooling Methods—The appropriate cooling method
instructions are given, dry for 24 61hat70 6 2°C in an oven.
shall be selected from Table 1.
6.1.2 Preparation of Preforms—Direct molding of test
6.3.2.1 In the case of quench cooling (see Method C in
specimens, plaques, and sheets from granules shall be the
Table 1), transfer the mold assembly from the heating press to
standard procedure, provided that a sufficiently homogeneous
the cooling press as quickly as possible. If the heating press has
sheet is obtained. Normally this means that the molded
the capability to cool at the specified rate, it may be used for
specimen, plaque, or sheet is free from surface irregularities
the cooling step.
and internal imperfections. Poly(vinyl chloride) (PVC) com-
6.3.3 The demolding temperature shall be <40°C if no other
pounds and chlorinated poly(vinyl chloride) (CPVC) com-
instructions are given.
pounds will generally require milling to obtain a preform for
NOTE 4—Method D is recommended for producing test specimens free
the final molding procedure.
of any internal stress, or for slow cooling after annealing of previously
6.1.3 Milling—Direct molding from powder or granules
prepared sheets.
may sometimes require melt homogenization using a hot-melt
milling or mixing procedure to achieve a satisfactory final
7. Inspection of the Molded Specimens, Plaques, or
sheet. Where such is required, a two-roll mill will usually
Sheets
perform satisfactorily. Take the milled material from the mill
7.1 After cooling, check the molded specimens, plaques, or
and cut or shape it to become a preform for the compression
sheets for appearance (such as sink marks, shrink holes,
mold in which it ultimately will be molded. Use milling
discolorations) and for conformance to specified dimensions.
conditions that do not degrade the polymer. Recommended
Discard any test specimens or sheets having molding defects.
conditions for milling the material, particularly the stock
7.2 Make sure there is no degradation or unwanted
temperature and time on the rolls, may be obtained from the
crosslinking, using the method specified in the relevant mate-
relevant material specification or the material manufacturer.
rial specification, or as agreed upon between the interested
The preform prepared by milling should normally be thicker
parties.
than the specimen, plaque, or sheet to be molded to enable the
molding to be done properly. 8. Report
6.2 Molding:
8.1 Provide the following information in the processing
6.2.1 Adjust the mold temperature to within 65°C of the
report:
molding temperature indicated in the relevant material speci-
8.1.1 Reference to this practice and the relevant material
fication.
specification,
6.2.2 Place a weighed quantity of the material (granules or
8.1.2 Dimensions of the specimen and its intended use,
preforms) in the preheated mold. If granular material is used,
8.1.3 Complete identification of molding material (type,
make sure that it is evenly spread over the mold surface. The
designation, etc.),
mass of the material shall be sufficient to fill the cavity volume
8.1.4 Preparation of molding material:
when it is melted and allow about a 10 % loss for a flash mold
8.1.4.1 Drying conditions for granules and powder, and
and about a 3 % loss for a positive mold. With flash molds,
8.1.4.2 Processing conditions used in the preparation of
cover the mold with the top ferrotype plate (see Figs. 1 and 2)
preforms and their average thickness,
and then place the mold in the pr
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