ASTM D3641-97

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: D 3641 – 97
Standard Practice for
Injection Molding Test Specimens of Thermoplastic Molding
and Extrusion Materials
This standard is issued under the fixed designation D 3641; 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 * 2. Referenced Documents
1.1 This practice covers the general principles to be fol- 2.1 ASTM Standards:
lowed when injection molding test specimens of thermoplastic D 256 Test Methods for Impact Resistance of Plastics and
molding and extrusion materials. This practice is to be used to Electrical Insulating Materials
obtain uniformity in methods of describing the various steps of D 570 Test Method for Water Absorption of Plastics
the injection molding process and to set up uniform methods of D 638 Test Method for Tensile Properties of Plastics
reporting these conditions. The exact conditions required to D 648 Test Method for Deflection Temperature of Plastics
prepare adequate specimens will vary for each plastic material. Under Flexural Load
These conditions should become a part of the specification for D 788 Specification for Methacrylate Molding and Extru-
the material, or be agreed upon between the purchaser and the sion Compounds
supplier. D 790 Test Methods for Flexural Properties of Unreinforced
1.2 The methodology presented assumes the use of recipro- and Reinforced Plastics and Electrical Insulating Materi-
cating screw injection molding machines. Users of other types als
of machines will need to adapt this practice to their machines D 883 Terminology Relating to Plastics
with appropriate precautions. D 955 Test Method for Measuring Shrinkage from Mold
1.3 The values stated in SI units are to be regarded as the Dimensions of Molded Plastics
standard. The values given in parentheses are for information D 957 Practice for Determining Surface Temperature of
only. Molds for Plastics
1.4 This standard does not purport to address all of the D 3935 Specification for Polycarbonate (PC) Unfilled and
safety concerns, if any, associated with its use. It is the Reinforced Materials
responsibility of the user of this standard to establish appro- D 4066 Specification for Nylon Injection and Extrusion
priate safety and health practices and determine the applica- Materials
bility of regulatory limitations prior to use. D 4101 Specification for Propylene Plastic Injection and
Extrusion Materials
NOTE 1—This practice is equivalent to the following parts of ISO 294:
D 4181 Specification for Acetal (POM) Molding and Extru-
Plastics—Injection Moulding of Test Specimens of Thermoplastic Mate-
sion Materials
rials ; 294-1: Part 1—General Principles and Multipurpose Test Speci-
mens (ISO Type A Mould) and Bars (ISO Type B Mould) ; ISO 294-2: D 4507 Specification for Thermoplastic Polyester (TPES)
Part 2—Small Tensile Bars (ISO Type C Mould); ISO 294-3: Part
Materials
3—Plates (ISO Type D Moulds).
D 4549 Specification for Polystyrene Molding and Extru-
NOTE 2—Care should be taken in the design of the cavities for tensile
sion Materials (PS)
test specimens to assure that the flat, parallel test area between the radii
2.2 ISO Standards:
extending to the end tabs be of uniform dimensions and cross sectional
ISO 3167 Plastics—Preparation and Use of Multipurpose
area for the entire length. With some materials, lack of uniformity in
Test Specimens
dimensions or cross sectional area, or both, could lead to problems in
testing. In these cases, it may be advantageous to slightly thicken the tabs ISO 294-1: Plastics—Injection Moulding of Test Specimens
and fillet (radii area) of the specimen.
of Thermoplastic Materials—Part 1: General Principles
and Multipurpose Test Specimens (ISO Type A Mould)
and Bars (ISO Type B Mould)
ISO 294-2: Plastics—Injection Moulding of Test Specimens
This practice is under the jurisdiction of ASTM Committee D-20 on Plastics
of Thermoplastic Materials—Part 2: Small Tensile Bars
and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.
(ISO Type C Mould)
Current edition approved Dec. 10, 1997. Published May 1998. Originally
published as D 3641 – 91. Last previous edition D 3641 – 93.
Available from American National Standards Institute, 11 West 42nd St., 13th
Floor, New York, NY 10036.
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 08.03.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 3641
ISO 294-3: Plastics—Injection Moulding of Test Specimens sequence of operations the pressures, timing settings, and mode
of Thermoplastic Materials—Part 3: Plates (ISO Type D of control are established on the basis of their effects upon the
Moulds) molded part itself rather than upon any universal setpoints.
5. Significance and Use
3. Terminology
3.1 Definitions—Definitions of terms applying to this prac- 5.1 It is well known that plastic test specimens molded
under different conditions can have significantly different
tice appear in Terminology D 883.
3.2 Definitions of Terms Specific to This Standard: properties. This practice is designed to minimize those differ-
ences by establishing operating protocols without being unnec-
3.2.1 average injection velocity, n—the mean value of the
velocity of the molten plastic flow front within a cavity during essarily restrictive.
5.2 Always refer to the ASTM material specification or ISO
the injection time that is calculated from the shot volume and
injection time. (See Terminology D 883.) designation for the material for recommended molding condi-
tions. If not available, consult the material supplier.
3.2.1.1 Discussion—The average injection velocity is cal-
culated as follows: 5.3 This practice requires the use of adequate quantities of
plastic material to find desirable operating conditions and to
V
s
V 5
av make the desired test specimens.
T 3 A 3 n
i c
6. Apparatus
where:
V = average injection velocity, mm/s,
6.1 Injection Molding Machine—The machine selected for
av
V = shot volume, mm ,
use must be equipped with appropriate devices for the control
s
T = injection time, s,
and measurement of hydraulic pressure, all relevant tempera-
i
A = cross section of the cavity, mm , and
c
tures, and the timing of certain cycle elements. Additional
n = number of cavities.
devices to monitor cavity pressure and ram position and
velocity are very useful in the effective control of the injection
The calculation is valid for molds containing a single cavity or those
molding cycle. The capacity of the machine should be such that
containing identical multi-specimen cavities only and not for family
molds.
the total shot weight (specimens plus sprue and runners) is 20
to 80 % of rated capacity. The injection machine must be
3.2.2 cross section of the cavity, n—in a mold for test
capable of maintaining the proper injection velocity range if
specimens, the area of a planar section perpendicular to the
specified in the material standard.
flow pattern during filling of the mold that forms the critical
portion of the test specimen.
NOTE 3—Heat-sensitive materials may require using the high end of the
3.2.3 flash, n—thin fin of material formed at the parting line
30 to 80 % range in order to minimize residence time of the melt in the
of a part during molding, caused by unintentional opening of barrel.
the mold or by defective mating surfaces.
6.1.1 Control System—The various control systems should
3.2.4 switchover point, n—that point in the injection stage
be able to maintain the operating parameters of the injection
of the injection molding cycle when the control or level of the
molding process from cycle to cycle within the following
forwarding force on the screw is switched from that used
limits:
during injection to that used during pack/hold.
plastic melt, or stock temperature 63°C
3.2.5 velocity-pressure transfer point (VPT), n—that point
mold temperature 63°C, #80°C
65°C, >80°C
in the injection stage of the injection molding cycle as defined
injection pressure 62%
by pressure, position, or time when the rate of ram travel is
hold pressure 65%
switched from speed control to pressure control.
injection time 60.1 s
hold time 65%
shot weight 61%
4. Summary of Practice
4.1 Many factors in the injection molding process can have Suitable means of monitoring these parameters to ensure
an influence on the character of the moldings and the numerical
control within the above limits should be present.
values of test results. Among these are geometry, size, and
NOTE 4—The mold temperature may be measured using a calibrated
temperature conditions of the heating chamber, pressures and
surface pyrometer and the technique described in Practice D 957.
speeds used, size, shape, and length of runners and gates, mold
6.1.2 Screw—The design of the screw will be determined by
temperature and its uniformity, cavity surface finish, and
the material being molded. A key criterion of screw design is to
timing cycles used along with the method of sequencing from
provide a melt that is as uniform as possible with respect to
stage to stage in the process. It is sometimes necessary to
composition, temperature, and viscosity.
pretreat materials before molding. For materials that absorb
6.1.3 Clamp—The clamping force of the machine shall be
water this may mean drying under prescribed conditions. This
high enough to prevent flashing at all operating conditions.
practice attempts to control some of these variables, nullify
others, and report those that are necessary to the obtaining of
NOTE 5—The minimum clamp force required is the product of the
reproducible specimens. Definite stock and mold temperatures, highest possible cavity pressure and the projected surface area of the
cavities (and runners). A force greater than this minimum will be required
based on the relevant material specifications or the material
to prevent flashing.
supplier’s recommendations or past experience, and measured
by standard techniques, are used for the molding process. By a 6.2 Mold—The design of the mold is one of the more
D 3641
TABLE 1 Recommended Gate Sizes for Common Test
critical variables affecting specimen properties. Optimum re-
Specimens
producibility requires that identical molds be used by parties
Gate Size, mm
attempting to obtain comparable results. However, in the
Specimen Test Method
Depth Width
absence of identical molds, adherence to certain features of
Type I tension specimen 3.2 by 9.6 D 638
design will help to minimize differences between results
3.2 by 12.7 by 127 mm bar 3.2 by 6.4 D 256, D648, D790
obtained by different parties. It has been found that the use of
6.4 by 12.7 by 127 mm bar 6.4 by 6.4 D 256, D648, D790
3.2 by 51 mm disk 3.2 by 3.2 D 570
unitized mold bases with interchangeable mold plates and gate
3.2 by 102 mm disk 3.2 by 12.7 D 955
inserts can provide a great deal of flexibility and provide rapid
Multipurpose test specimen 2.5 by 14 (min) ISO 3167
transitions between the moldings of different specimen con-
figurations. (See Annex A1.)
6.2.1 Cavity Layout—Multi-cavity molds with identical
cavities are recommended. The cavity layout should be such
allowed in the specific test methods. Dimensioning of cavities
that there is a uniform and symmetrical distribution of speci-
with respect to anticipated shrinkage will result in cavity
men surface area on the overall mold surface. The use of single
variations from molder to molder. It also requires different
cavity molds is discouraged. For large tensile test specimens
molds for every material to be molded. It is preferred to
and multipurpose bars, a two cavity “Z” or “T” layout is
machine the cavity to the nominal dimensions of the specimen
acceptable. For small tensile test specimens and bars, a four
and to adjust the dimensions only when shrinkage leads to a
cavity double “T” layout is recommended. Other specimens
specimen that is out of specification for the desired test
have their unique cavity layout. (See Annex A1.)
method. Draft angles in the sidewalls of the cavity will
probably be needed to facilitate part ejection but shall not be
NOTE 6—ISO 294-1 states that the “Z” cavity runner layout is preferred
over the “T” cavity runner layout.
greater than 1° except in the shoulder of the multipurpose test
NOTE 7—Family molds designed to produce more than one part
specimen (ISO 3167) that shall be not greater than 2°. A
configuration with each shot are not recommended. If molds of this nature
maximum draft angle of ⁄2 ° is preferred for all areas. All
are used, consideration should be taken in the design to ensure that
interior mold surfaces should be finished to Society of Plastics
constant and uniform filling velocities are achieved in all cavities.
Industry-Society of Plastics Engineers (SPI-SPE) No. A-3 or
Additionally it is cautioned that the comparability of data obtained on
better. If cavity identification is required, this should be located
specimens molded in this manner may be limited not only to a specific
polymer type but also to specific rheological characteristics. outside of the test area. It is recommended that the end of an
ejector pin be used to incorporate an identifying symbol rather
6.2.2 Runners—Runners may be of the full-round type cut
than the cavity surface.
into both halves of the mold or of the trapezoidal type cut into
6.2.5 Ejector Pins—Ejector pins shall be located where
only one of the mold halves. They should be a minimum of 5
necessary, but not in the test area of the specimen. For tensile
mm (0.2 in.) in diameter or of equivalent cross-sectional area
test specimens, it is recommended that the ejector pins be
if trapezoidal. A symmetrical cavity layout will permit identical
located at the wide tab ends (shoulders). For universal bars, it
runner systems to be used for each cavity and thus facilitate
is recommended that the ejector pins be located at the “dead”
uniform filling of all cavities with all materials under all
end of the bar and outside of the central 20 mm length of the
conditions. Runner draft angles for trapezoidal runners should
ISO mold type B (80 mm bar). For plates, the ejector pins
be from 10 to 30°C. The diameter of the sprue shall be a
should be outside the central area of 50 mm diameter.
minimum of 4 mm on the nozzle side.
6.2.6 Cavity Pressure Transducers—Pressure transducers
NOTE 8—If family molds with two or more identical specimen cavities
may
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