ASTM D4703-16

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4703 − 10a D4703 − 16
Standard Practice for
Compression Molding Thermoplastic Materials into Test
Specimens, Plaques, or Sheets
This standard is issued under the fixed designation D4703; 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*
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 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information
only. standard. No other units of measurement are included in this 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.
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 in accordance with ISO Cooling Method B may not be equivalent to Annex A1, Procedure C.
2. Referenced Documents
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D1248 Specification for Polyethylene Plastics Extrusion Materials for Wire and Cable
D3350 Specification for Polyethylene Plastics Pipe and Fittings Materials
D4976 Specification for Polyethylene Plastics Molding and Extrusion Materials
2.2 ISO Standard:
ISO 293-1986 ISO 293 Plastics—Compression Moulding Test Specimens of Thermoplastic Materials
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 average cooling rate (°C/min),n—the cooling rate calculated by dividing the difference between the molding and
demolding temperatures by the time required to cool the mold to the demolding temperature.
3.1.2 cooling rate (°C/h),n—the rate of cooling obtained by controlling the flow of the cooling fluid in such a way that during
each 10-min interval, the deviation from this specified cooling rate shall not exceed the specified tolerance.
3.1.3 demolding temperature, n—the temperature of the mold or the press platens at the end of the cooling time, measured in
the nearest vicinity to the molded material.
This practice is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.
Current edition approved Nov. 1, 2010April 1, 2016. Published January 2011April 2016. Originally approved in 1991. Last previous edition approved in 2010 as
D4703 – 10.D4703 – 10a. DOI: 10.1520/D4703-10A.10.1520/D4703-16.
This practice was created as a coalescence of and replacement for Practices D1928, D2292, D3010, and D3463.
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 the ASTM website.
ISO/IEC Selected Standards for Testing Plastics, available from ASTM. Also available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor,
New York, NY 10036.
3.1.3.1 Discussion—
*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
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For positive molds, holes are normally drilled in the mold for measuring the temperatures defined in 3.1.3 and 3.1.4.
3.1.4 molding temperature, n—the temperature of the mold or the press platens during the preheating and molding time,
measured in the nearest vicinity to the molded material.
3.1.5 molding time, n—the time during which full pressure is applied while maintaining the molding temperature.
3.1.6 picture frame mold, n—a flat piece of metal, usually of brass or steel, that has a center portion removed to provide the
specified shape and dimensions of the final molding. The thickness of the metal is dependent on the desired thickness of the
finished molding, taking into consideration the shrinkage of the material to be molded. The picture frame mold is sometimes
referred to as a chase.
3.1.7 preheating time, n—the time required to heat the material in the mold up to the molding temperature while maintaining
the contact pressure.
4. Significance and Use
4.1 The methods by which sample materials are prepared and molded influence the mechanical properties of the specimen.
Unlike injection molding, the objective of compression molding is to produce test specimens or sheets that are both homogeneous
and isotropic. Molded specimens may be madeSpecimens can be molded from powder or pellets such as are received directly from
a material manufacturer, particles produced in a recycle recovery operation, or from a milled preform or sheet prepared on a
two-roll mill. The powder, pellets, particles, preform, or sheet are melted and molded in a mold designed to produce a finished
specimen of a given geometry, size, and thickness, or melted and molded in the form of a smooth plaque or sheet of uniform
thickness from which desired specimens are cut, punched, or machined. Working a compound on a two-roll mill prior to molding
will disperse and distribute the compound additives in a manner that will affect the physical properties of the compound. The need
for milling a sample prior to compression molding may be determined by reference to the relevant material specification or the
material manufacturer. relevant material specification or the material manufacturer shall be consulted to determine the need for
milling a sample prior to compression molding. It is important to treat different samples of the same type of material in the same
way: if milling was done prior to molding on a material which is to be used as a standard for comparison, all new materials to
be tested against this practice shouldshall be prepared and molded in a similar manner.
4.2 The apparatus and exact conditions required to prepare adequate specimens may will usually vary for each plastic material.
Apparatus and procedures which should be satisfactory for molding many different plastic materials are given in this practice in
Sections 5 and 6. The apparatus and procedures which have been found satisfactory for molding certain specific materials are given
in the Appendix.Appendixes. In any case, the specific apparatus and procedures to be used in producing compression-molded
specimens of a given material mayshall be obtained by reference to the relevant material specification and should be agreed upon
or by agreement between the purchaser and the supplier.
5. Apparatus
5.1 Mill—Any size two-roll mill having chrome-plated rolls, capable of maintaining a constant temperature within 62°C
(63.6°F) of the temperature needed for the particular material involved, and being adjustable in speed as needed for the material
to be worked, is adequate. Some recommendations worked. Recommendations for mills to be used for some specific types of
materials are given in the Appendix.
5.2 Molds:
5.2.1 Mold Types—Several different types of molds may mold geometries can be used for the compression molding of test
specimens of thermoplastics. In general, however, the molds used will fall into one of two categories: a flash-type mold (see Figs.
1 and 2) or a positive-type mold (see Fig. 3). The characteristics of the test specimens prepared by using different types of molds
are not the same. In particular, some mechanical properties maycan be affected by the pressure applied to the material during
cooling.
5.2.2 Flash-Type Mold—The flash-type mold may be of is, typically, the picture-frame type, where a metal chase (the picture
frame) is sandwiched between two thin metal ferrotype plates (see Fig. 1), or it maycan be of the machined-cavity type (see Fig.
2), where the mold consists of a cavity machined in a metal plate, with a single metal ferrotype plate used as a top or cover. The
cavity, or cavities, in the flash-type mold maycan be constructed to mold a single plaque from which test specimens may be are
stamped or machined, or the mold maycan be built to mold one or more specimens to finished dimensions. Flash molds permit
excess molding material to be squeezed out and do not exert molding pressure on the material during cooling. Nevertheless, this
This type of mold is useful for preparing test specimens or panels of similar thickness or comparable levels of low internal stress.
FIG. 1 Flash Picture-Frame Mold
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FIG. 2 Flash Mold with Machined Cavity
FIG. 3 Positive-Type Mold
5.2.3 Positive-Type Mold—The positive-type mold consists of a cavity machined in a plate or block of metal and a force or
plunger which closely mates with the sidewalls of the cavity (see Fig. 3). Like the flash-type mold, the cavity maycan be built to
produce a plaque from which test specimens may be are stamped or machined, or to mold a test specimen to finished dimensions.
Because of the manner in which the positive mold operates, it is recommended that this mold type, either for a plaque or a finished
specimen, be limited to a single cavity. In the positive-type mold, the full molding pressure, neglecting friction, is exerted on the
material during cooling. The thickness, stress and density of the resulting moldings depend on the mold construction, the size of
the material charge, and the molding conditions. This type of mold produces test specimens with high density, and it is particularly
suitable for obtaining flat surfaces and for suppressing the formation of voids within test specimens.
5.2.4 Mold Surfaces—The surfaces of either type of mold that form the flat faces of the specimen shouldshall be finished to the
degree required by the test for which the specimen is intended. For most tests, a surface quality of SPI-SPE #2 is adequate. The
edges of the mold cavity should be visually free of nicks and scratches which could cause premature failure of the specimen during
testing.
NOTE 2—For most tests, a surface quality of SPI-SPE #2 is adequate.
Visual nicks or scratches on the edges of the mold are to be avoided as they can cause premature failure of the specimen during
testing.
5.3 Press:
5.3.1 The press shall have a clamping force capable of applying a pressure (conventionally given as the ratio of the clamping
force to the area of the mold cavity) of at least 10 MPa (1450 psi), MPa, and shall be capable of maintaining pressure within 10 %
of the specified pressure during the molding cycle.
5.3.2 The platens of the press shall be capable of being heated to at least 240°C, and being cooled at a rate consistent with the
cooling method selected from Table 1.
5.3.3 The platens or mold shall be heated either by by suitable means such as high-pressure steam, by a heat-conducting fluid
in an appropriate channel system, or by using electric-heating elements. The platens or mold are cooled by a heat-conducting fluid
(usually cold water) in a channel system.
5.3.4 The heating and cooling systems in the mold platens shall be such that, when used with a particular mold, they shall be
shall be capable of maintaining a temperature difference between 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 other for
cooling unless it can be demonstrated that the press used for heating can cool at the specified rate.
Mold comparison kits are available from D-M-E Company, 29111 Stephenson Highway, Madison Heights, MI 48071.
TABLE 1 Cooling Methods Requirements
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
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NOTE 3—For a specified cooling method, the flow rate of the heat-conducting fluid should be predetermined in a test without any material in the mold.
6. Procedure
6.1 Preparation of Molding Material:
6.1.1 Drying of Granular Material—Dry the granular material as specified in the relevant material specification, or in
accordance with the material supplier’s instructions. If no instructions are given, dry for 24 6 1 h at 70 6 2°C in an oven.
6.1.2 Preparation of Preforms—Direct molding of test specimens, plaques, and sheets from granules shall be the standard
procedure, provided that a sufficiently homogeneous sheet is obtained. Normally this means that the molded specimen, plaque, or
sheet is free from surface irregularities and internal imperfections. Poly(vinyl chloride) (PVC) compounds and chlorinated
poly(vinyl chloride) (CPVC) compounds will generally require milling to obtain a preform for the final molding procedure.
NOTE 4—Poly(vinyl chloride) (PVC) compounds and chlorinated poly(vinyl chloride) (CPVC) compounds will generally require milling to obtain a
preform for the final molding procedure.
6.1.3 Milling—Direct molding from powder or granules maycan sometimes require prior melt homogenization using a hot-melt
milling or mixing procedure to achieve a satisfactory final sheet. Where such is required, a two-roll mill will usually perform
satisfactorily. Take the milled material from the mill and cut or shape it to become a preform for the compression mold in which
it ultimately will ultimately be molded. Use milling conditions that do not degrade the polymer. Recommended conditions for
milling the material, particularly the stock temperature and time on the rolls, maycan be obtained from the relevant material
specification or the material manufacturer. The preform prepared by milling should normally be thicker than the specimen, plaque,
or sheet to be molded to enable the molding to be done properly.
NOTE 5—The preform prepared by milling should normally be thicker than the specimen, plaque, or sheet to be molded to enable the molding to be
done properly.
6.2 Molding:
6.2.1 Adjust the mold temperature to within 65°C of the molding temperature indicated in the relevant material specification.
With picture-frame Picture-frame (Fig. 1) molds or large, heavy molds it may not be necessary or desirable to preheat the mold
itself. This do not necessarily require preheating of the mold itself, but this will then require slight increases in the preheat time
of the cycle; the cycle. If this is the case, the temperature stability of the material shall be considered.
6.2.2 Place a weighed quantity of the material (granules or preforms) in the preheated mold. If granular material is used, make
sure that it is evenly spread over the mold surface. The mass of the material shall be sufficient to fill the cavity volume when it
is melted and allow about a 10 % loss for a flash mold and about a 3 % loss for a positive mold. With flash molds, cover the mold
with the top ferrotype plate (see Figs. 1 and 2) and then place the mold in the preheated press.
6.2.3 Close the press and preheat the material charge by applying a contact pressure for a minimum of 5 min. Then apply full
pressure for a minimum of 2 min (molding time, see 3.1.5) and then cool down (see 6.3).
NOTE 6—A preheating time of 5 min is the standardized time for evenly spread material charges sufficient for sheets up to 2 mm in thickness. For thicker
moldings, adjust the time accordingly.
NOTE 7—At contact pressure the press is just closed with a pressure low enough to avoid flow of the material. Full pressure means a pressure sufficient
to shape the material and squeeze out the excess material.
6.3 Cooling:
6.3.1 General—With some thermoplastics, the cooling rate affects the ultimate physical properties. For this reason, the cooling
methods are specified in Table 1. The method of cooling shall always be stated together with the final physical properties. The
appropriate cooling method is normally given in the relevant material specification. If no method is indicated, Method B shall be
used.
6.3.2 Cooling Methods—The appropriate cooling method shall be selected from Table 1.
6.3.2.1 In the case of quench cooling (see Method C in Table 1), transfer the mold assembly from the heating press to the cooling
press as quickly as possible. If the heating press has the capability to cool at the specified rate, it may be used is not necessary
to transfer the mold assembly for the cooling step.
6.3.3 The demolding temperature shall be <40°C if no other instructions are given.
NOTE 8—Method D is recommended for producing test specimens free of any internal stress, or for slow cooling after annealing of previously prepared
sheets.
7. Inspection of the Molded Specimens, Plaques, or Sheets
7.1 After cooling, check the molded specimens, plaques, or sheets for appearance (such as sink marks, shrink holes,
discolorations) and for conformance to specified dimensions. Discard any test specimens or sheets having molding defects.
7.2 Make sure Ensure there is no degradation or unwanted crosslinking, using the method specified in the relevant material
specification, or as agreed upon between the interested parties.
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8. Report
8.1 Provide the following information in the processing report:
8.1.1 Reference to this practice and the relevant material specification,
8.1.2 Dimensions of the specimen and its intended use,
8.1.3 Complete identification of molding material (type, designation, etc.),
8.1.4 Preparation of molding material:
8.1.4.1 Drying conditions for granules and powder, and
8.1.4.2 Processing conditions used in the preparation of preforms and their average thickness,
8.1.5 Type of mold and plates used,
8.1.6 Molding conditions:
8.1.6.1 Preheating time,
8.1.6.2 Molding temperature, pressure, and time,
8.1.6.3 Cooling method used, and
8.1.6.4 Demolding temperature,
8.1.7 State of specimen, if applicable, and
8.1.8 Any other observations.
9. Precision and Bias
9.1 No statement is made about either the precision or the bias of this practice for preparation of compression-molded test
specimens since there is no numerical result.
10. Keywords
10.1 acrylonitrile-butadiene-styrene (ABS); chlorinated poly(vinyl chloride) (CPVC); compression molding; polyethylene (PE);
poly(vinyl chloride) (PVC); styrene-butadiene; test specimen preparation; thermoplastics
ANNEXES
(Mandatory Information)
A1. PROCEDURES FOR POLYETHYLENE
A1.1 Scope—This annex covers the preparation of compression-molded test sheets of Class 1, 2, 3, and 4 polyethylene plastics
(Specification D4976) and Types 0, I, II, III, and IV (Specifications D1248 and D3350). This annex includes both branched and
linear polyethylenes. Two of the procedures given provide for compression-molded sheets to be conditioned by first heating each
material above its melting point for a period of time sufficient to erase its prior thermal history and then cooling it from the melt
state at a controlled rate while maintaining the required dimensions of the sheet. The third procedure provides for molded test
sheets to be prepared by cooling the platens of the compression press, and hence the molten polyethylene plastic, at a controlled
rate. Three cooling schedules are provided for as follows:
NOTE A1.1—The specimen preparation procedures in this annex were originally published as ASTM Test Method D1928 - 96.
A1.1.1 Procedure A, in which the temperature of the initially molten plaque is lowered at a rate of 5 6 0.5°C/h.
NOTE A1.2—It is recognized that Procedure A may not be applicable to material containing carbon black due to difficulties, at times, with sheets containing
voids. If it is not possible to mold a void-free sheet, Procedure B or C should be selected.
A1.1.2 Procedure B, in which the initially molten plaque is chilled very rapidly under specified conditions in water, and
A1.1.3 Procedure C, in which the temperature of the platens of the molding press, and hence of the initially molten plaque, is
lowered at a rate of 15 6 2°C/min.
A1.2 Significance and Use—The conditions under which a polyethylene plastic is formed into a test sheet, particularly the rate
of cooling, influence some of the properties of test specimens taken from the sheet. It is, therefore, necessary to control the cooling
rate of the test sheet. These procedures are intended to minimize interlaboratory variability of test results on compression-molded
specimens arising from differences in rate of cooling.
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A1.2.1 Procedures A and B are designed also to erase moderate differences in the prior thermal history by employing a
conditioning period of l h at a temperature about 25°C above the melting point of the polyethylene plastic prior to cooling at a
controlled rate. For Procedures A and B, raise the conditioning temperature may have to be raised above this minimum value in
some cases to promote adhesion to the aluminum foil parting sheets. The following temperatures, which depend on the Class of
polyethylene plastic as classified in Specification D4976 (Type in D1248 and D3350), have been found to be generally useful:
Class 1 (Type I) 140°C
Class 2 (Type II) 150°C
Class 3 (Type III) 155°C
Class 4 (Type IV) 155°C
Type 0 140°C
A1.2.2 Values obtained on specimens from test sheets prepared in accordance with Procedure C of this annex are useful for the
identification of type or class of polyethylene plastics in accordance with Specifications D1248, D3350 and D4976.
A1.2.3 Results obtained on specimens from test sheets prepared by any of the procedures described do not necessarily reflect the
properties of articles fabricated by other methods, such as extrusion and injection molding.
A1.3 Apparatus: Apparatus:
A1.3.1 Two-Roll Mill, that can be heated to a temperature high enough to flux the materials to be tested. Heating maycan be by
steam, electricity, or other suitable means.
A1.3.2 Press, with platens that can be heated to at least 150°C for Class 1 (Type I) and 177°C for Class 2, 3 and 4 (Type II, III
and IV), and 140°C for Type 0 polyethylene plastics.
NOTE A1.3—Pressure is not a key parameter of the molding of polyethylene. Available data showsshow no additional variability imparted to low, medium
or high density polyethylene density measurements when ram force was varied from ten tons to twenty-eight tons.
A1.3.3 Molds, of the flash picture-frame variety (also known as chases) or flash molds with machined cavities shall be used.
A1.3.4 Backing Plates, flat, for the chases. The backing plates should be chases and strong enough to resist warping or distortion
under the molding conditions. Plates made from high thermal conductivity materials such as aluminum, copper or bronze plates
or polished steel, of 3.2 to 12.7 mm thick, are suitable.
A1.3.5 Aluminum Foil, 0.05 to 0.2 mm thick, for use as a parting agent in the molding operation.
NOTE A1.4—It is necessary to use aluminum foil of the specified thickness as a parting agent in the molding operation in Procedures A and B. Much
thinner foil is not stiff enough to resist the tendency of the plastic surface to wrinkle on fluxing, while thicker foil does not conform well enough to the
plastic surface. Aluminum alloy 1100, Temper O, is suitable.
A1.3.6 Oven, capable of maintaining a temperature of at least 175°C. Temperature 175°C with a temperature variation within the
oven should be less than 4°C, and the oven should be large enough to conveniently accommodate a one day production of molded
sheets.
A1.3.7 For Procedure A Only:
A1.3.7.1 DeviceControl System for lowering the oven temperature at a rate of 5.0 6 0.5°C (9.0 6 0.9°F)/h. 0.5°C/h.
NOTE A1.5—A suitable device may be made by connecting a motor-driven thermoregulator or a programmer through a relay to the oven heaters. An
alternative and equally satisfactory device comprises a controller and a small electric motor geared to lower the oven temperature at the specified rate.
A1.3.8 For Procedure B Only:
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A1.3.8.1 Cooling Tanks—Tanks into which water may run and continuously overflow and which with continuous water flow and
overflow, and are large enough to accommodate the chases but small enough to fit into a laboratory sink. Each tank shall contain
a mesh basket to hold the chases suspended in the cooling water. The basket should be made with as open a construction as possible
to facilitateshall have an open, unrestricted construction to maximize circulation of cooling water over all surfaces of the molding.
A1.3.9 For Procedure C Only:
A1.3.9.1 Polyester Film, or aluminum foil for use as a parting agent in the molding operation.
NOTE A1.5—Studies have shown that the type of parting sheet, that is, polyester film or aluminum foil, may cause minor but measurable differences in
certain properties.
(1) In cases of dispute, the type of parting sheet should shall be agreed upon by the parties involved.
A1.3.9.2 Device for lowering the temperature of the platens at a rate of 15 6 2°C/min.
A1.4 Roll Milling:
A1.4.1 Compression moldings can be made directly from the granules, pellets, or powders. However, if insufficient flow or
inadequate adhesion between particles is observed, materials can be roll milled to ensure homogeneity.
NOTE A1.6—During the milling operation, the addition of an antioxidant is desirable if the molded test sheet is not used subsequently for tests of thermal,
oxidative, or environmental stress cracking stability where such additives will interfere.
A1.4.2 Mill rolls shouldshall be hot enough to flux materials, but not so hot as to cause them to drip. The crepe should be slashed
or turned Slash or turn the crepe frequently to promote mixing. Materials should not be milled Do not mill the materials for more
than 5 min after gelling to minimize oxidative and thermal changes.
A1.5 Compression Molding Procedure: Compression Molding Procedure:
A1.5.1 A double pressing technique may sometimes be required to squeeze entrapped air out of mill-massed material; if the air
is not removed, conditioned sheets may develop voids. A single pressing is usually sufficient, however, to produce void-free test
sheets from most polyethylene plastics. single pressing is usually sufficient to produce void-free test sheets from most polyethylene
plastics. However, if voids are present, a double pressing technique shall be utilized to squeeze entrapped air out of mill-massed
material.
A1.5.2 A flash-type molding operation is involved. The subsequent conditioning step will not give good results unless excess
material is squeezed out on all sides and both surfaces of the chase.
NOTE A1.7—The presence of sink marks in the molded sheet, or the failure of the aluminum foil to adhere tightly all around the chase, usually indicates
that an insufficient amount of material has been charged. Failure of the aluminum foil to stick to the plastic can often be remedied by pressing and
subsequently conditioning at a higher temperature.
A1.5.3 The press temperature should be warm enough to result in To ensure good adhesion between the plastic and the aluminum
foil. Recommendedfoil, recommended minimum temperatures for the press platens are 150°C for Class 1 (Type I) and 177°C for
Class 2, 3 and 4 (Type II, III and IV), and 140°C for Type 0 polyethylene plastics.
A1.5.4 Weigh out the amount of plastic necessary to fill the blanked-out volume of the chase and provide an excess, for flash, of
not less than two and not more than 10 % of the weight of the final molding. For this purpose, the following densities maycan be
assumed:used:
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Class 1 (Type I) 0.92 g/cm
Class 2 (Type II) 0.93 g/cm
Class 3 (Type III) 0.95 g/cm
Class 4 (Type IV) 0.97 g/cm
Type 0 0.90 g/cm
The densities of most carbon black formulations are about 0.01 g/cm higher than those of the natural materials.
A1.5.5 For Procedures A and B:
A1.5.5.1 Compression molding is performed using parting sheets of aluminum foil. The foil shouldcan be cleaned by wiping with
acetone and then dried with clean, absorbent paper or cloth. Any Smooth out any wrinkles in the foil should be smoothed out before
use. While the foil is usually not suitable for reuse, it maycan be used again if undamaged.
A1.5.5.2 Safety Precautions—See acetone Material Safety Data Sheets for specific hazards information on these materials. The
OSHA requirements for 8-h time weighted average and acceptable ceiling concentration are found in 29 CFR, CH XVII, Table
Z-2.
A1.5.5.3 At ambient temperature, place the polyethylene plastic in the chase between parting sheets backed by smooth backing
plates. With the platens at the molding temperature, insert the assembly between the platens. With the platen closed and contact
pressure applied, allow the platens to heat back to within 65°C of the molding temperature then start a heating period of 5 min
after which apply full pressure as quickly as possible. The dwell time at full pressure and cooling rate are optional. After the
molding has been formed, remove the assembly from the press. Carefully pry the backing plates off without disturbing the parting
sheets, which should be adhering tightly to the chase and polyethylene plastic sheet. Handle the sheet, chase, and adhering parting
sheets as a unit from this point.
NOTE A1.8—The recommend full pressure is 5 MPa exerted over area of the molded cavity of a flash type mold (picture frame) or 10 MPa on a positive
type mold.
A1.5.5.4 If a second pressing is desired (see A1.5.1), proceed as follows: after molding as in A1.5.5.3, remove the assembly from
the press (take off the aluminum foil) and knock the molded sheet out of the chase. Discard the flash from this sheet. Cut the sheet
into at least four pieces of approximately equal size. Replace the pieces within the chase and between aluminum foil parting sheets.
The pieces shall not be spread Do not spread the pieces over the open volume of the mold but should be stacked mold, but stack
them so the press can squeeze out any air. Add enough milled crepe to make up for the flash lost in the first molding. Put smooth
backing plates behind the aluminum parting sheets and repeat the molding procedure specified in A1.5.5.3.
A1.5.6 For Procedure C:
A1.5.6.1 Compression molding is performed using parting sheets of uncoated polyester film or aluminum foil. Any Smooth any
wrinkles in the parting sheets should be smoothed out before use. While foil is usually not suitable for re-use, it maycan be used
again if undamaged.
A1.5.6.2 At ambient temperature, place the polyethylene plastic in the chase between parting sheets backed by smooth backing
plates. With the platens at the molding temperature insert the assembly between the platens. With the platens closed and contact
pressure applied, allow the platens to heat back up to within 65°C of the molding temperature then start a heating period of 5 min
after which apply full pressure as quickly as possible (see Note A1.9A1.8). After full pressure has been applied, continue the
heating from 3 to 5 min. At the end of this heating period, turn off the heat and cool the press platens at a rate of 15 6 2°C/min
until a platen temperature of 76°C is reached for Class 1, 2, 3, and 4 (Type I, II, III, and IV) polyethylene plastics and 45°C for
Type 0. Continue to cool the platens until their temperatures are 40°C or lower. Then open the press and remove the assembly from
the press (see Notes A1.10A1.9 and A1.11).
NOTE A1.9—The platen cooling rate can be varied by controlling the flow of water through the platens. The flow of water can be controlled by the use
of needle valves on the coolant inlet lines or in the coolant exit lines.
A1.5.6.3 The cooling rate of the platens maycan be determined by inserting a thermometer (the bulb wrapped with metallic wool
Available from U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
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to ensure contact) or a thermocouple into a hole drilled into the platen and measuring the temperature change of each platen during
the cooling cycle. Record the temperature each 30 s in the following temperature ranges:
Class 1 (Type I) 150°C to 76°C
Class 2 (Type II) 177°C to 76°C
Class 3 (Type III) 177°C to 76°C
Class 4 (Type IV) 177°C to 76°C
Type 0 140°C to 45°C
On linear graph paper plot temperature on the Y-axis versus time on the X-axis for the following temperature ranges:
Class 1 (Type I) 121°C to 76°C
Class 2 (Type II) 150°C to 90°C
Class 3 (Type III) 150°C to 90°C
Class 4 (Type IV) 150°C to 90°C
Type 0 121°C to 45°C
For each 30 s interval, the cooling rate shall be 15°C 6 2°C/min.
A1.5.6.4 Uniformity of temperature over the surface of the platens maycan be checked conveniently by using small temperature
probes to measure the surface temperature of the platens or the temperature of the plastic itself. With suitable platen design,
temperature differences within a particular cavity or picture frame can be kept to within 2°C.
A1.5.6.5 If non-uniform temperature distribution is observed, it maycan be minimized by the use of plates made from high thermal
conductivity materials such as aluminum, copper or bronze plates or polished steel, of 3.2 to 12.7 mm thick. On some presses, a
region of the outside perimeter of the mold may not be usable due to poor design of cooling channels. In extreme cases, a better
distribution of cooling water channels in the platen may be required.
NOTE A1.10—On some presses, a region of the outside perimeter of the mold may not be usable due to poor design of cooling channels. In extreme cases,
a better distribution of cooling water channels in the platen may be required.
NOTE A1.11—If regular tap water is used as the platen coolant, it will be necessary to flush the scale and rust from the platen channeling periodically.
This can be done by circulating boiler treater solution through the platen channels. The frequency of scale cleaning can be reduced by using air to purge
water from the platens prior to preheating.
A1.5.6.6 If a second pressing is desired (see A1.5.1) proceed as follows: after molding as in A1.5.6.2, remove the assembly from
the press (take off the parting sheets) and knock the molded sheet out of the chase. Discard the flash from this sheet. Cut the sheet
into at least four pieces of approximately equal size. Replace the pieces within the chase and between the parting sheets of uncoated
polyester film, cellophane, or aluminum foil. The pieces shall not be spread Do not spread the pieces over the open volume of the
mold but should be stacked stack them so the press can squeeze out any air. Add enough milled crepe to make up for the flash
lost in the first molding. Put smooth backing plates behind the parting sheets and repeat the molding procedure specified in
A1.5.6.2. Test values obtained from stress-crack tests will be at a substantially different level than samples prepared by Procedures
A or B.
A1.6 Conditioning (for Procedures A and B):
A1.6.1 General—Place the unit produced in accordance with A1.5.6.2 on a smooth thin metal plate on a rack in the oven. The
oven temperature shall be not less than 140°C for Class 1 (Type I), 150°C for Class 2 (Type II), 155°C for Classes 3 and 4 (Type
III and IV), and 140°C for Type 0 polyethylene plastics. In no case shall the temperature be greater than 175°C. Units Do not stack
units intended for cooling by Procedure B should not be stacked. B. Units for Procedure A maycan be stacked, with a light, smooth
metal plate between each pair (Note A1.13).
NOTE A1.12—Units shall reach the specified temperature and be maintained in the oven at the specified temperature for at least 1 h, and thereafter shall
be cooled in accordance with Procedure A or B.
NOTE A1.13—Care should be taken that all the units stacked for eventual cooling by Procedure A reach the oven temperature before cooling is started.
The ability of the oven to heat all units to the required temperature in 1 h should be checked with suitably placed thermocouples. The use of low pressures
during the conditioning procedure may assist in preventing the formation of bubbles and voids in black or other samples which show this tendency. Low
pressures can be applied by the use of a metal following plate which rests on the sample and not on the metal chase.
A1.6.2 Procedure A—Leave the unit or units in the oven and switch on the thermo-regulating device to cool the oven at a rate
of 5°C/h. Continue cooling at the specified rate and remove the samples at a temperature of 50°C or less.
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NOTE A1.14—Most properties of polyethylene plastics are quite stable after conditioning by Procedure A. However, the use of Procedure A may not be
suitable for preparation of test sheets for the mechanical tests of materials that are embrittled excessively by the slow cooling rate.
A1.6.3 Procedure B—The temperature of the water in the tank shall be 15 to 20°C. Running Use running cold tap water or stirred,
refrigerated water should be used (Note A1.15). After the unit at its specified temperature has been in the oven for 1 h remove it
from the oven, place it in the wire tray, and lower the whole unit quickly into the cooling tank. The Complete the entire operation
should be completed as quickly as possible. For this reason, possible by locating the cooling tank should be located near the oven.
The unit should be Place the unit in the cold water within 10 to 15 s after its removal from the oven. Only Place only one unit
at a time should be in the cooling tank unless it has been shown that the presence of more than one does not affect the results of
subsequent tests. Units shall remain immersed in the tank for at least 15 min. At the end of the cooling period remove the unit,
strip off the aluminum foil, and press the test sheet out of the chase.
NOTE A1.15—The effect of a variation in the water temperature in the cooling bath depends on the material and the property being measured. For example,
a change from 1 to 20°C has a noticeable effect on the density of almost all materials, whereas brittleness temperatures of most resins would be unaffected.
For this reason, Procedure B is strictly confined to quenching in 15 to 20°C water.
NOTE A1.16—Procedure B is not recommended for density measurements that are to be compared between laboratories, because this property changes
too rapidly with elapsed time after conditioning. Some of the other properties of interest do not appear to change as rapidly as does density, and Procedure
B has been found useful for preparing test sheets for such tests as brittleness temperature. The stability of tensile and stiffness properties will depend on
the polyethylene plastic.
A1.7 Test Specimen Preparation:
A1.7.1 Prepare test specimens from test sheets by any technique which will not disturb the thermal history introduced during sheet
preparation and which will provide test specimens of acceptable quality as judged by visual examination as described in A1.7.2.
Where possible, use one of the five techniques described in Annex A2 – Annex A7.
A1.7.2 Inspect prepared test specimens visually and use the following criteria for acceptability:
A1.7.3 Cut—Examine the freshly cut edges of the specimen. These should be specimen to ensure they are smooth, substantially
unbeveled, and free of feathery edges. For Class 3 and 4 (Type III and IV) materials, some whitening is not unusual and shouldis
not to be considered a defect. If edge defects are seen, sharpening of the blanking die or of the machining tool is indicated.
A1.7.4 Surface:
A1.7.4.1 Examine the top and bottom flat surfaces of the specimen adjacent to cut edges for evidence of cracking. No cracks
should be visible. any visible cracking. If cracks are seen, use of another specimen preparation technique is indicated.
A1.7.4.2 Examine the top and bottom fiatflat surfaces of the specimen for evidence of scratching or marring. Surfaces should be
generally blemish-free. surface blemishes, scratching, or marring. Blemishes can arise from such things as blemish-transfer from
the cover sheet when a blanking die is used, careless or improper technique in removing the specimen from the blanking die, or
careless handling in the machining operation. When such blemishes are seen, take immediate steps should be taken to correct the
situation.
A1.7.5 Form—Examine the specimen for evidences of bending or warping. None should be seen. warping and are cause for
rejection. Such deformations can arise through poor technique in removing specimens from blanking dies.
A1.8 Report:
A1.8.1 Report the following information:
A1.8.2 Identification of the material,
Round-robin data for this practice may be obtained from ASTM Headquarters. Request RR:D20-1047.
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A1.8.3 Date of preparation of test sheets and test specimens,
A1.8.4 Procedure used to prepare test sheets (Procedure A, B, or C),
A1.8.5 Technique used to prepare test specimens (Technique 1, 2, 3, 4, or 5 of the Annexes; or details of the particular technique
employed), and
A1.8.6 Deviations, if any, from the standard conditioning of Practice D618, Procedure A.
A2. SPECIMEN PREPARATION FOR POLYETHYLENE
A2.1 Five techniques are described for preparing test specimens from test sheets. These are designated 1 through 5 and are
generally in the order of choice for use as the task of preparing acceptable test specimens becomes progressively more difficult.
A2.1.1 Technique 1 employs a blanking die and impact curing of the sheet at 23°C.
A2.1.2 Technique 2 employs a blanking die and relatively slow curing of the sheet at 23°C by means of an arbor press or other
device providing suitable mechanical advantage.
A2.1.3 Technique 3 employs a blanking die and impact curing of the heated sheet.
A2.1.4 Technique 4 employs a blanking die and curing of the heated sheet by use of an arbor press, or equivalent.
A2.1.5 Technique 5 involves machining operations at 23°C.
A2.2 The necessity for having more than one technique comes from the fact that problems sometimes arise in attempting to
prepare acceptable specimens from sheets which exhibit either some degree of brittleness or exceptional toughness. As a general
rule, the simplest and most direct approach is preferable. Technique 1 or 2 would be used where possible, Technique 3 or 4 (heating
of the sheet prior to cutting) would be used only when 1 or 2, or both, did not produce acceptable specimens, and Technique 5
would be used only if none of the other four produced satisfactory results.
A2.2.1 Techniques 1, 2, and 5 are applicable for preparing specimens from sheets prepared by any one of the three Procedures,
A or B or C. However, precautions shall be taken when applying Techniques 3 and 4.
A2.2.1.1 Techniques 3 and 4 are applicable for sheets prepared by Procedure A, since the limited heating cycles for sheets do not
change the thermal history introduced by Procedure A significantly.
A2.2.1.2 Techniques 3 and 4 are not applicable for sheets prepared by Procedure B, since the heating treatment would invalidate
the thermal history introduced by Procedure B.
A
TABLE A2.1 Heating Schedules for Sheets
Class (Type) Temperature Heating Time for Oven Type
Polyethylene
Plastic
Gravity Recirculating
1 and 2 (I, II,
and 0) 76°C 10 ± 2 min 5 ± 1 min
3 and 4 (III and
IV) 95°C 10 ± 2 min 5 ± 1 min
A
TheseThese heating schedules are for sheets no thicker than 3.2 mm ( ⁄8 in.)
nominal. Thicker sheets maygenerally require a longer time at the temperatures
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