ASTM D1896-99
(Practice)Standard Practice for Transfer Molding Test Specimens of Thermosetting Compounds
Standard Practice for Transfer Molding Test Specimens of Thermosetting Compounds
SCOPE
1.1 This practice covers a general procedure for transfer molding thermosetting materials into test specimens for Izod or Charpy impact, flexure, tension, compression, water-absorption, heat-aging, electrical, modulus in tension or flexure, and heat-deflection-temperature tests. Note 1-The utility of this practice has been demonstrated for the molding of thermosetting molding compounds exhibiting intermediate viscosity non-Newtonian flow.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety problems, 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 2-There are no ISO standards covering the primary subject of this practice.
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Designation:D1896–99
Standard Practice for
Transfer Molding Test Specimens of Thermosetting
Compounds
This standard is issued under the fixed designation D 1896; 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 * 3.1.2 transfer molding, n—a method of forming articles by
fusing a plastic material in a chamber and then forcing
1.1 This practice covers a general procedure for the transfer
essentially the whole mass into a hot mold where it solidifies.
molding of mechanical and electrical test specimens of ther-
3.2 Definitions of Terms Specific to This Standard:
mosetting molding materials.
3.2.1 breathing, v—theoperationofopeningamoldorpress
NOTE 1—The utility of this practice has been demonstrated for the
for a very short period of time at an early stage in the process
molding of thermosetting molding compounds exhibiting intermediate
of cure.
viscosity non-Newtonian flow.
3.2.2 Discussion—Breathing allows the escape of gas or
1.2 The values stated in either SI or inch-pound units are to
vapor from the molding material and reduces the tendency of
be regarded separately as standard. The vlaues stated in each
thick moldings to blister.
system may not be exact equivalents; therefore, each system
3.2.3 cavity (of a mold), n—the space within a mold to be
shall be used independently of the other. Combining values
filled to form the molded product.
from the two systems may result in nonconformance with this
3.2.4 clamp pressure, n—the pressure applied to the mold to
practice.
keep it closed, in opposition to the fluid pressure of the
1.3 This standard does not purport to address all of the
compressed molding material.
safety concerns, if any, associated with its use. It is the
3.2.5 fill time, n—the time required to fill each cavity used
responsibility of the user of this standard to establish appro-
in the mold. Fill times can be critical to well molded parts (see
priate safety and health practices and determine the applica-
Note 3 under 4.4).
bility of regulatory limitations prior to use.
3.2.6 minimum plunger pressure, n—theminimumpressure,
on the ram, required to just fill each cavity used in the mold at
NOTE 2—There is no similar, or equivalent, ISO standard.
a specified temperature and reasonable fill time.
2. Referenced Documents
3.2.7 vent, n—a hole, slot, or groove provided in a mold or
machine to allow air and gas to escape during molding,
2.1 ASTM Standards:
extrusion, or forming.
D 731 Test Method for Molding Index of Thermosetting
Molding Powder
4. Significance and Use
D 883 Terminology Relating to Plastics
4.1 Transfer molding is particularly suited to thermosetting
D 957 Practice for Determining Surface Temperature of
materials of intermediate plasticity. Fixed molding parameters
Molds for Plastics
cannot be specified for each type of material. Molding com-
D 3123 Test Method for Spiral Flow of Low-Pressure
pounds of the same type come in many different plasticities
Thermosetting Molding Compounds
measuredinaccordancewithTestMethodsD 731,D 3123,and
D 3795 Test Method for Thermal Flow and Cure Properties
D 3795. For this reason, a material may mold satisfactorily
of Thermosetting Plastics by Torque Rheometer
under one set of fixed parameters, while the same type of
3. Terminology
material with a different plasticity may require a different set of
parameters to produce satisfactory test specimens.
3.1 Definitions:
4.2 The mold shown in this practice provides for a set of
3.1.1 General—Definitions of terms applying to this prac-
fivespecimens.However,ifonlycertainspecimensaredesired,
tice appear in Terminology D 883.
the other cavities may be blocked by inserting gate blanks.
4.3 Typically, breathing of the mold may not be required to
This practice is under the jurisdiction of ASTM Committee D-20 on Plastics
release trapped volatile matter as the gas is free to flow from
and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.
the vent end of the mold. This is a particular advantage for
Current edition approved Dec. 10, 1999. Published February 2000. Originally
heat-resistant compounds and reduces the tendency for molded
published as D 1896 – 61 T. Last previous edition D 1896 – 93.
Annual Book of ASTM Standards, Vol 08.01.
specimens to blister at high exposure temperatures.
Annual Book of ASTM Standards, Vol 08.02.
*A Summary of Changes section appears at the end of this standard.
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D1896
4.4 Flow and knit lines in a molded piece are often sites of cavitiesordifferentconfigurationsofthetensionspecimenmay
mechanical or electrical weakness. Knit lines may be found in be used. Specimens may be eliminated by blocking the runners
some degree of severity throughout the molded piece. The to particular cavities and reducing injection pressure and shot
semisolid molding compound passing through the gate is size accordingly. The gates for each of the cavities in this mold
subjecttonon-Newtonianflowand,consequently,wrinklesand are 6.4 mm wide by 1.52 mm deep ( ⁄4 by 0.060 in.). Suitable
folds as it travels down the mold cavity. Fibers and other venting must be provided from each cavity.Surfaces of the
reinforcements in the molding compound align with the flow cavity should be finished to SPI-SPE #2. Chrome plating of
pattern and, consequently, may mold perpendicular to the axis the mold surface is recommended.
of the bar at the center and parallel at the surface of the bar.
NOTE 5—Althoughthemoldshownisgenerallyuseful,itispreferredto
Mold temperature, thermal conductivity and plasticity of the
use a multiple-identical-cavity mold with a symmetrical layout of runners
molding compound, degree of preheat, and plunger pressure
and cavities. In either case, it is important to describe the mold in the
are parameters that influence the time to fill the mold cavities report on the specimen preparation.
and the formation of knit lines.
5.3 Heating System—Any convenient method of heating the
NOTE 3—Ifthetemperatureofthemoldisheldconstantandtheplunger press platens and plunger cavity may be used, provided the
pressure varied for a designated thermosetting molding compound, two
heat source is constant enough to maintain the mold and
extreme characteristic conditions can be obtained. If the pressure is low,
plunger temperature within 63°C (5°F).
then the vent end of the cavity will not fully fill, and weld lines will form
5.4 Temperature Indicator—Typically, a surface pyrometer
by incomplete knitting of the material. If the pressure is too high, the mold
is used to measure the temperature of the mold surface as
cavity will fill fast, the outside of the specimen will case harden while the
specified in Practice D 957.
pressure is still forcing material out the vent, and a ball-and-socket grain
5.5 Preforming—Any preforming equipment or press may
structure will be obtained. A ball-a
...
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