ASTM D731-22

Standard Test Method for Molding Index of Thermosetting Molding Powder

SIGNIFICANCE AND USE
5.1 This test method provides a guide for evaluating the moldability of thermosetting molding powders. This test method does not necessarily denote that the molding behavior of different materials will be alike and trials may be necessary to establish the appropriate molding index for each material in question.  
5.2 The sensitivity of this test diminishes when the molding pressure is decreased below 5.3 MPa (764 psi), so pressures lower than this are not ordinarily recommended. This is due to the friction of moving parts and the insensitivity of the pressure switch actuating the timer at these low pressures.
SCOPE
1.1 This test method covers the measurement of the molding index (plasticity) of thermosetting plastics ranging in flow from soft to stiff by selection of appropriate molding pressures within the range from 3.7 to 36.5 MPa (530 to 5300 psi).  
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 concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Mar-2022
• ICS: 83.080.10 - Thermosetting materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.30 - Thermal Properties

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D731 − 22
Standard Test Method for
1
Molding Index of Thermosetting Molding Powder
This standard is issued under the fixed designation D731; 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* 3.2 Definitions of Terms Specific to This Standard:
3.3 plasticity, n—a measure of the resistance of a molten
1.1 Thistestmethodcoversthemeasurementofthemolding
thermosetting material to flow under heat and pressure. A
index(plasticity)ofthermosettingplasticsranginginflowfrom
measure of the apparent viscosity of the material.
soft to stiff by selection of appropriate molding pressures
within the range from 3.7 to 36.5 MPa (530 to 5300 psi).
4. Summary of Test Method
1.2 The values stated in SI units are to be regarded as the
4.1 A cup mold is mounted in a semi-automatic type press.
standard. The values given in parentheses are for information
A predetermined quantity of test sample is charged into the
only.
mold, controlled at a temperature dependent upon the test
1.3 This standard does not purport to address all of the
material. The minimum force required to mold a cup having a
safety concerns, if any, associated with its use. It is the
flashorfinthicknesswithinaspecifiedtoleranceisdetermined.
responsibility of the user of this standard to establish appro-
This force along with the mold closing time is reported as
priate safety, health, and environmental practices and deter-
molding index.
mine the applicability of regulatory limitations prior to use.
5. Significance and Use
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
5.1 This test method provides a guide for evaluating the
ization established in the Decision on Principles for the
moldability of thermosetting molding powders. This test
Development of International Standards, Guides and Recom-
method does not necessarily denote that the molding behavior
mendations issued by the World Trade Organization Technical
of different materials will be alike and trials may be necessary
Barriers to Trade (TBT) Committee.
to establish the appropriate molding index for each material in
question.
2. Referenced Documents
5.2 The sensitivity of this test diminishes when the molding
2
2.1 ASTM Standards:
pressure is decreased below 5.3 MPa (764 psi), so pressures
D256 Test Methods for Determining the Izod Pendulum
lower than this are not ordinarily recommended. This is due to
Impact Resistance of Plastics
thefrictionofmovingpartsandtheinsensitivityofthepressure
D883 Terminology Relating to Plastics
switch actuating the timer at these low pressures.
D957 Practice for Determining Surface Temperature of
Molds for Plastics
6. Apparatus
E691 Practice for Conducting an Interlaboratory Study to
6.1 Mold—A cup mold of the flash type, to produce a
Determine the Precision of a Test Method
molded cup as shown in Fig. 1, operated under controlled
pressure and temperatures and provided with stops so that flash
3. Terminology
or fin thickness cannot be less than 0.14 mm (0.0055 in.). The
3.1 Definitions are in accordance with Terminology D883,
area of the mold casting creating the molded flash shall be
unless otherwise specified.
located on top of the cup, flat, perpendicular to the axis of the
cup, and in the form of an annular ring 3.17 mm (0.125 in.) in
width.
1
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
6.2 Pyrometer—A calibrated pyrometer, traceable to a na-
and is the direct responsibility of Subcommittee D20.30 on Thermal Properties
(Section D20.30.08).
tional standard (for example, NIST), and accurate to 61°C
Current edition approved March 15, 2022. Published March 2022. Originally
shall be used to determine the temperature of the mold
approved in 1950. Last previous edition approved in 2018 as D731 - 18. DOI:
surfaces. For properly measuring mold temperatures, reference
10.1520/D0731-22.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Practice D957.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
6.3 Heating System—Any conventional means for heating
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. the press platens, provided the heat source is constant enough
*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-
...

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: D731 − 18 D731 − 22
Standard Test Method for
1
Molding Index of Thermosetting Molding Powder
This standard is issued under the fixed designation D731; 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 test method covers the measurement of the molding index (plasticity) of thermosetting plastics ranging in flow from soft
to stiff by selection of appropriate molding pressures within the range from 3.7 to 36.5 MPa (530 to 5300 psi).
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 concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
D256 Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics
D883 Terminology Relating to Plastics
D957 Practice for Determining Surface Temperature of Molds for Plastics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions are in accordance with Terminology D883, unless otherwise specified.
3.2 Definitions of Terms Specific to This Standard:
3.3 plasticity—plasticity, n—a measure of the resistance of a molten thermosetting material to flow under heat and pressure. A
measure of the apparent viscosity of the material.
4. Summary of Test Method
4.1 A cup mold is mounted in a semi-automatic type press. A predetermined quantity of test sample is charged into the mold,
1
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.30Thermal Properties.30 on
ThermalThermal Properties Properties (Section D20.30.08).
Current edition approved May 1, 2018March 15, 2022. Published May 2018March 2022. Originally approved in 1950. Last previous edition approved in 20102018 as
D731 - 10.D731 - 18. DOI: 10.1520/D0731-18.10.1520/D0731-22.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*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
1

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D731 − 22
controlled at a temperature dependent upon the test material. The minimum force required to mold a cup having a flash or fin
thickness within a specified tolerance is determined. This force along with the mold closing time is reported as molding index.
5. Significance and Use
5.1 This test method provides a guide for evaluating the moldability of thermosetting molding powders. This test method does not
necessarily denote that the molding behavior of different materials will be alike and trials may be necessary to establish the
appropriate molding index for each material in question.
5.2 The sensitivity of this test diminishes when the molding pressure is decreased below 5.3 MPa (764 psi), so pressures lower
than this are not ordinarily recommended. This is due to the friction of moving parts and the insensitivity of the pressure switch
actuating the timer at these low pressures.
6. Apparatus
6.1 Mold—A cup mold of the flash type, to produce a molded cup as shown in Fig. 1, operated under controlled pressure and
temperatures and provided with stops so that flash or fin thickness cannot be less than 0.14 mm (0.0055 in.). The area of the mold
FIG. 1 Cup Mold
2

---------------------- Page: 2 ----------------------
D731 − 22
casting creating the molded flash shall be located on top of the cup, flat, perpendicular to the axis of the
...