ASTM D955-21

Standard Test Method of Measuring Shrinkage from Mold Dimensions of Thermoplastics

SIGNIFICANCE AND USE
5.1 Injection Molding—In injection molding, the difference between the dimensions of a mold cavity and of the molded specimen may vary according to the design of the mold and operation of the molding process. Factors such as mold and melt temperature, fill times, and packing conditions are known to affect shrinkage significantly. Adherence to the specified mold design (see 7.1) and specifications outlined in Practice D3641 or ISO 294-4 or the appropriate material specification will improve the reproducibility of the test.  
5.2 Compression Molding—In compression molding, the difference between the dimensions of a mold cavity and of the molded specimen may vary according to the design of the mold and operation of the molding process. Factors, such as the amount of material in charge, cooling time, and pressure application are known to affect shrinkage significantly. Adherence to the specified mold design (see 7.2) and specifications outlined in Practice D4703 or ISO 293 or the appropriate material specifications will improve the reproducibility of the test.
SCOPE
1.1 This test method is intended to measure shrinkage from mold cavity to molded dimensions of thermoplastics when molded by compression or injection processes with specified process conditions.  
1.2 This test method covers shrinkage measurements at 24 and 48 hours.  
1.3 This method will give comparable data based on standard specimens and can not predict absolute values in actual molded parts with varying flow paths, wall thicknesses, pressure and temperature gradients and process conditions. Differences in mold shrinkage may also be observed among the three specimen geometries described in this test method.  
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are given for information only.  
1.5 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.
Note 1: This standard and ISO 294-3 are equivalent in the design of specimen D2. This test method is equivalent to ISO 294-4 where Type D2 specimens and the procedure in Appendix X2 are used.  
1.6 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: 31-Mar-2021
• ICS: 83.140.10 - Films and sheets
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.09 - Specimen Preparation

Relations

• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D6778-20 - Standard Classification System and Basis for Specification for Polyoxymethylene Molding and Extrusion Materials (POM)
• Effective Date: 01-Feb-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D4066-13(2019) - Standard Classification System for Nylon Injection and Extrusion Materials (PA)
• Effective Date: 01-Nov-2019
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E2935-17 - Standard Practice for Conducting Equivalence Testing in Laboratory Applications
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017

Overview

ASTM D955-21: Standard Test Method of Measuring Shrinkage from Mold Dimensions of Thermoplastics provides procedures for determining the shrinkage of thermoplastics during injection and compression molding, by comparing mold cavity dimensions with those of molded specimens. This standard is essential for plastics engineers, quality control professionals, and manufacturers focused on the precision molding of thermoplastic components. It covers both immediate and delayed shrinkage measurements (24 and 48 hours) and applies to a range of materials and processing conditions, ensuring standardized evaluation across the plastics industry.

Key Topics

• Mold Shrinkage of Thermoplastics: Assesses how the dimensions of molded parts differ from the original mold dimensions due to factors like cooling, material type, and processing conditions.
• Scope of Application: Relevant for parts manufactured by compression and injection molding using standardized process parameters.
• Factors Affecting Shrinkage: Includes mold/melt temperature, fill and packing conditions (in injection molding), and material charge, cooling time, and pressure application (in compression molding).
• Measurement Protocols: Specifies the use of accurate measuring tools (such as micrometers or vernier calipers) and standard specimen types (plaque, bar, and disc).
• Sample Conditioning and Test Environment: Requires specimens to be conditioned and tested in a controlled laboratory atmosphere, typically at 23 ± 2°C and 50 ± 10% relative humidity, ensuring reproducibility and comparability.
• Data Reporting: Shrinkage results are reported as percentages in both flow and cross-flow directions for at least five specimens, at 24 and 48 hours after molding.

Applications

• Quality Control in Plastics Manufacturing: By following ASTM D955-21, manufacturers can monitor mold shrinkage to maintain tight dimensional tolerances in plastic parts such as automotive components, consumer goods, and medical devices.
• Material Comparison: This standard enables the comparison of shrinkage characteristics among different thermoplastic materials, supporting informed material selection for specific design requirements.
• Process Optimization: Understanding shrinkage behaviors helps optimize molding parameters, reducing defects such as warping or dimensional inaccuracy.
• Specification Compliance: Ensures alignment with customer or regulatory specifications for molded plastic products, particularly where critical tolerances are required.
• Interlaboratory Consistency: Adoption of this method facilitates reliable data exchange and performance benchmarking across multiple sites or organizations.

Related Standards

• ASTM D3641: Practice for Injection Molding Test Specimens of Thermoplastic Molding and Extrusion Materials
• ASTM D4703: Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets
• ASTM D5947: Test Methods for Physical Dimensions of Solid Plastics Specimens
• ISO 294-1, ISO 294-3, ISO 294-4: Series of international standards for injection molding of plastics and mold shrinkage determination
• ASTM D618: Practice for Conditioning Plastics for Testing
• ASTM D883: Terminology Relating to Plastics

Adherence to ASTM D955-21 and these related standards promotes uniform quality and reliability in thermoplastic parts, facilitating international trade and regulatory compliance. Employing these standardized test methods supports efficient problem-solving in plastics engineering and provides clear communication across supply chains regarding material performance and manufacturability.

Keywords: ASTM D955, mold shrinkage, thermoplastics, injection molding, compression molding, plastic testing, dimensional stability, material comparison, quality control.

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: D955 − 21
Standard Test Method of
Measuring Shrinkage from Mold Dimensions of
Thermoplastics
This standard is issued under the fixed designation D955; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method is intended to measure shrinkage from
mold cavity to molded dimensions of thermoplastics when D618Practice for Conditioning Plastics for Testing
D788Classification System for Poly(Methyl Methacrylate)
molded by compression or injection processes with specified
process conditions. (PMMA) Molding and Extrusion Compounds
D883Terminology Relating to Plastics
1.2 This test method covers shrinkage measurements at 24
D3641Practice for Injection Molding Test Specimens of
and 48 hours.
Thermoplastic Molding and Extrusion Materials
1.3 This method will give comparable data based on stan-
D4066Classification System for Nylon Injection and Extru-
dard specimens and can not predict absolute values in actual
sion Materials (PA)
molded parts with varying flow paths, wall thicknesses, pres-
D4549Classification System and Basis for Specification for
sure and temperature gradients and process conditions. Differ-
Polystyrene and Rubber-Modified Polystyrene Molding
encesinmoldshrinkagemayalsobeobservedamongthethree
and Extrusion Materials (PS)
specimen geometries described in this test method.
D4703Practice for Compression Molding Thermoplastic
Materials into Test Specimens, Plaques, or Sheets
1.4 The values stated in SI units are to be regarded as the
D4976Specification for Polyethylene Plastics Molding and
standard. The values given in parentheses are given for
Extrusion Materials
information only.
D5947Test Methods for Physical Dimensions of Solid
1.5 This standard does not purport to address all of the
Plastics Specimens
safety concerns, if any, associated with its use. It is the
D6778Classification System and Basis for Specification for
responsibility of the user of this standard to establish appro-
Polyoxymethylene Molding and Extrusion Materials
priate safety, health, and environmental practices and deter-
(POM)
mine the applicability of regulatory limitations prior to use.
D6779Classification System for and Basis of Specification
NOTE 1—This standard and ISO 294-3 are equivalent in the design of
for Polyamide Molding and Extrusion Materials (PA)
specimenD2.ThistestmethodisequivalenttoISO294-4whereTypeD2
E456Terminology Relating to Quality and Statistics
specimens and the procedure in Appendix X2 are used.
E691Practice for Conducting an Interlaboratory Study to
1.6 This international standard was developed in accor-
Determine the Precision of a Test Method
dance with internationally recognized principles on standard-
E2935Practice for Conducting Equivalence Tests for Com-
ization established in the Decision on Principles for the
paring Testing Processes
Development of International Standards, Guides and Recom-
2.2 ISO Standards:
mendations issued by the World Trade Organization Technical
ISO 293Plastics—Compression Moulding Test Specimens
Barriers to Trade (TBT) Committee.
of Thermoplastic Materials
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ThistestmethodisunderthejurisdictionofASTMCommitteeD20onPlastics contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2021. Published April 2021. Originally the ASTM website.
approvedin1948.Lastpreviouseditionapprovedin2014asD955-08(2014).DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D0955-21. 4th Floor, New York, NY 10036, http://www.ansi.org.
*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
D955 − 21
ISO 294-1Plastics—Injection Moulding of Test Specimens melt temperature, fill times, and packing conditions are known
of Thermoplastic Materials—Part 1: General Principles, to affect shrinkage significantly. Adherence to the specified
and Moulding of Multipurpose and Bar Test specimens mold design (see 7.1) and specifications outlined in Practice
ISO 294-3Plastics—Injection Moulding of Test Specimens D3641 or ISO 294-4 or the appropriate material specification
of Thermoplastic Materials—Part 3: Small Plates will improve the reproducibility of the test.
ISO 294-4 Plastics—Injection Moulding of Test
5.2 Compression Molding—In compression molding, the
Specimens—Part 4: Determination of Moulding Shrink-
difference between the dimensions of a mold cavity and of the
age
moldedspecimenmayvaryaccordingtothedesignofthemold
and operation of the molding process. Factors, such as the
3. Terminology
amount of material in charge, cooling time, and pressure
3.1 Definitions—Terms used in this standard are defined in
application are known to affect shrinkage significantly.Adher-
accordance with Terminology D883, unless otherwise speci-
ence to the specified mold design (see 7.2) and specifications
fied. For terms relating to precision and bias and associated
outlined in Practice D4703 or ISO 293 or the appropriate
issues,thetermsusedinthisstandardaredefinedinaccordance
material specifications will improve the reproducibility of the
with Terminology E456.
test.
3.2 Definitions of Terms Specific to This Standard:
6. Sample Preparation
3.2.1 jetting, n—non-uniform multi-directional flow front
apparent on the surface of the mold due to rapid filling of the 6.1 Somematerialsrequirespecialtreatmentbeforetheyare
mold cavity. molded. For example, thermoplastics, which absorb moisture
must be dried before molding. For required conditions for
4. Summary of Test Method
sample preparation, refer to the appropriate material specifica-
tionorthemanufacturer’srecommendationsifnospecification
4.1 The principle of this test method is to compare mold
cavity dimensions with specimen dimensions and report the is available. The preparation given to the material prior to
molding shall be recorded and reported.
differences in percent.
5. Significance and Use 7. Apparatus
5.1 Injection Molding—In injection molding, the difference 7.1 Injection Mold—Specimens shall be molded in a two
between the dimensions of a mold cavity and of the molded cavity mold conforming with dimensions as shown in Figs. 1
specimen may vary according to the design of the mold and and 2 for the 60 × 60-mm plaque specimen (Type D2), Fig. 3
operation of the molding process. Factors such as mold and for the 12.7 by 127-mm bar specimen (TypeA) and Fig. 4 for
Sp | sprue
G | gate
L = distance between the lines along which the test specimens are cut from the runners
c
Molding volume = 20 000 mm
Projected area = 11 000 mm
FIG. 1 Type D2 (Mold Layout)
D955 − 21
Sp sprue
G gate
R runner
P pressure sensor
l length of plate 60±2mm
b width of plate 60±2mm
h thickness of plate 2.0 ± 0.1 mm
l length of gate 4.0 ± 0.1 mm
G
h height of gate (0.75 ± 0.05) × h
G
l length of runner 25 to 40 mm
R
b width of runner $ (b+6)mm
R
h depth of runner at gate
g
l* unspecified distance . . .
l distance of pressure sensor from gate 5±2mm
p
FIG. 2 Type D2 (Cavity Details)
w = 12.7 ± 0.2 mm
t =3.2±0.05mm
l =127±2mm
G = Gate
P = Pressure Transducer
FIG. 3 Bar Specimen
the 100 mm by 3.2-mm disk specimen (Type B). Pressure pressure: 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, or as
transducers for monitoring the pressure in at least one cavity
specified in the appropriate material specification. Pressure
are mandatory for Type D2. Mold shrinkage measurements
transducers are recommended, but not mandatory for speci-
shall be made on specimens that have been molded at one of
mens Type A and Type B.
the following cavity pressures 6 3% from the selected
D955 − 21
t =3.2±0.05mm
D =100±2mm
G = Gate
P = Pressure Transducer
FIG. 4 Disk Specimen
7.2 Compression Mold—Asingle cavity positive mold hav- measuring the molds and test specimens conforming to the
ing cavity dimensions conforming to the dimensions of Fig. 2 measuring tool requirements in Test Methods D5947.
for the 60 × 60-mm plaque (Type D2) Fig. 3 for the 12.7 ×
8. Test Specimen
127-mm bar specimen (Type A) and Fig. 4 for the 100-mm ×
3.2-mm disk specimen (Type B), not including the sprue,
8.1 The following specimen dimensions are applicable for
runner or gate.
both compression and injection molding. Orientation effects
7.2.1 Although scribe marks are not required, if they are
due to flow direction do not generally pertain to compression
used for injection or compression molded specimens for the
molding.
measurement of shrinkage, the scribe marks shall be 1.0 mm
8.1.1 Specimen Type D2—For mold shrinkage in both flow
long by 0.1 mm wide located 4.0 mm from each edge on one
and cross flow the preferred specimen shall be 60 by 60 by
side of the mold.
2mm depth conforming to the dimensions of Fig. 2.
8.1.2 Specimen TypeA—Forshrinkageparalleltoflow,abar
7.3 Injection Press—A suitable injection molding machine
mold having a cavity of 12.7 by 127 mm shall be used as
that shall fill the test molds when it is operated in the range
shown in Fig. 3. The thickness shall be 3.2 mm unless
from 20 to 80% of its rated shot capacity at the molding
otherwise agreed upon by the seller and the purchaser. The
parameters specified in Practice D3641, ISO 294-3 or the
mold shall have at one end a gate 6.4 mm in width by 3.2 mm
appropriate material specification.
in depth.
NOTE 2—If the injection machines of appropriate capacity are not
8.1.3 Specimen Type B—Adisc shaped specimen, as shown
available, the requirements of 7.3 may be met in machines of larger
in Fig. 4, having a cavity 100 mm in diameter by 3.2 mm in
capacities by providing test molds with multiple cavities (maximum of
thickness with a gate 12.7 mm in width by 3.2 mm in depth,
four) to be filled from a common sprue and having a balanced filling
pattern,sothatthetotalweightoftheshot,includingsprueandrunnerwill
placed radially at the edge, shall be used.
fall within the specified limits.
NOTE 3—Although this specimen may be used to determine mold
7.4 Compression Press—A suitable hydraulic press that
shrinkage in both the flow and cross flow directions, the filling pattern
shall deliver a pressure of 20 to 35 MPa (3000 to 5000 psi) to does not produce uniform flow lengths and orientation. Consequently,
there may be significant differences when measuring the specimen at
the material in the mold.
different points around the circumference. Values would not be expected
7.5 Measuring Tools—Measuring tools (micrometers, ver-
to be in agreement with those obtained using the specimens described in
nier calipers, etc.) accurate to 0.025 mm (0.001 in.) for 8.1.1 and 8.1.2.
D955 − 21
9. Conditioning
W = the mold dimension perpendicular to flow,
m
W = the specimen dimension perpendicular to flow, and
s
9.1 Conditioning—Unless otherwise specified by relevant
material standard, condition molded specimens at 23 6 2°C
S 5 ~L 2 L ! 3100/Lm (2)
1 m s
and 50% 6 10% relative humidity in accordance with
where:
Practice D618.
S = the shrinkage parallel to flow, %,
9.2 Test Conditions—Unlessotherwisespecifiedbyrelevant
L = the mold dimension parallel to flow, and,
m
materialstandard,conductmeasurementat23 62°Cand50%
L = the specimen dimension parallel to flow.
s
6 10% relative humidity in accordance with Practice D618.
Report mold shrinkage in both flow and cross direction to
two significant figures.
10. Procedure
11.2 The report shall include the following:
10.1 Measurethelengthandwidthofthemoldcavityatthe
11.2.1 Details of any special material preparation, such as
center of each edge or at the molded scribe marks, to the
drying, which the material received before molding;
nearest 0.025 mm at 23 6 2°C and 50% 6 10% relative
11.2.2 The molding procedure used, following the report as
humidity. Record these values as l and w, respectively.
outlined in Practice D3641 for injection molding and Practice
10.2 Mold at least five flat test specimens from the sample
D4703 for compression molding.
to be tested.
11.2.3 The 24-hour shrinkage and the 48-hour shrinkage
shall be expressed in percent (mm/mm) with each value
NOTE 4—Flat is represented by a specimen with less than 3% warp.
Three percent warp is defined as 3 mm depth deflection, positive or representing the mean of determinations obtained on five or
negative, per 100 mm in length.
more specimens.
10.2.1 Thermoplastics Molded by Injection—Molding of
12. Precision and Bias
thermoplastic materials shall be conducted in accordance with
the appropriate material standard
...

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: D955 − 08 (Reapproved 2014) D955 − 21
Standard Test Method of
Measuring Shrinkage from Mold Dimensions of
Thermoplastics
This standard is issued under the fixed designation D955; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope Scope*
1.1 This test method is intended to measure shrinkage from mold cavity to molded dimensions of thermoplastics when molded
by compression or injection processes with specified process conditions.
1.2 This test method covers shrinkage measurements at 24 and 48 hours.
1.3 This method will give comparable data based on standard specimens and can not predict absolute values in actual molded parts
with varying flow paths, wall thicknesses, pressure and temperature gradients and process conditions. Differences in mold
shrinkage may also be observed among the three specimen geometries described in this test method.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are given for information only.
1.5 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
NOTE 1—This standard and ISO 294-3 are equivalent in the design of specimen D2. This test method is equivalent to ISO 294-4 where Type D2 specimens
and the procedure in Appendix X2 are used.
NOTE 1—This standard and ISO 294-3 are equivalent in the design of specimen D2. This test method is equivalent to ISO 294-4 where Type D2 specimens
and the procedure in Appendix X2 are used.
1.6 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
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D788 Classification System for Poly(Methyl Methacrylate) (PMMA) Molding and Extrusion Compounds
D883 Terminology Relating to Plastics
This test method 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 Aug. 1, 2014April 1, 2021. Published August 2014April 2021. Originally approved in 1948. Last previous edition approved in 20082014 as
D955 - 08.D955 - 08(2014). DOI: 10.1520/D0955-08R14.10.1520/D0955-21.
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
D955 − 21
D3641 Practice for Injection Molding Test Specimens of Thermoplastic Molding and Extrusion Materials
D4066 Classification System for Nylon Injection and Extrusion Materials (PA)
D4549 Classification System and Basis for Specification for Polystyrene and Rubber-Modified Polystyrene Molding and
Extrusion Materials (PS)
D4703 Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets
D4976 Specification for Polyethylene Plastics Molding and Extrusion Materials
D5947 Test Methods for Physical Dimensions of Solid Plastics Specimens
D6778 Classification System and Basis for Specification for Polyoxymethylene Molding and Extrusion Materials (POM)
D6779 Classification System for and Basis of Specification for Polyamide Molding and Extrusion Materials (PA)
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2935 Practice for Conducting Equivalence Tests for Comparing Testing Processes
2.2 ISO Standards:
ISO 293 Plastics—Compression Moulding Test Specimens of Thermoplastic Materials
ISO 294-1 Plastics—Injection Moulding of Test Specimens of Thermoplastic Materials—Part 1: General Principles, and
Moulding of Multipurpose and Bar Test specimens
ISO 294-3 Plastics—Injection Moulding of Test Specimens of Thermoplastic Materials—Part 3: Small Plates
ISO 294-4 Plastics—Injection Moulding of Test Specimens—Part 4: Determination of Moulding Shrinkage
3. Terminology
3.1 Definitions—General definitions of terms applying to this test method appear in Terms used in this standard are defined in
accordance with Terminology D883, unless otherwise specified. For terms relating to precision and bias and associated issues, the
terms used in this standard are defined in accordance with Terminology E456.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 jetting, n—non-uniform multi-directional flow front apparent on the surface of the mold due to rapid filling of the mold
cavity.
4. Summary of Test Method
4.1 The principle of this test method is to compare mold cavity dimensions with specimen dimensions and report the differences
in percent.
5. Significance and Use
5.1 Injection Molding—In injection molding, the difference between the dimensions of a mold cavity and of the molded specimen
may vary according to the design of the mold and operation of the molding process. Factors such as mold and melt temperature,
fill times, and packing conditions are known to affect shrinkage significantly. Adherence to the specified mold design (see 7.1) and
specifications outlined in Practice D3641 or ISO 294-4 or the appropriate material specification will improve the reproducibility
of the test.
5.2 Compression Molding—In compression molding, the difference between the dimensions of a mold cavity and of the molded
specimen may vary according to the design of the mold and operation of the molding process. Factors, such as the amount of
material in charge, cooling time, and pressure application are known to affect shrinkage significantly. Adherence to the specified
mold design (see 7.2) and specifications outlined in Practice D4703 or ISO 293 or the appropriate material specifications will
improve the reproducibility of the test.
6. Sample Preparation
6.1 Some materials require special treatment before they are molded. For example, thermoplastics, which absorb moisture must
be dried before molding. For required conditions for sample preparation, refer to the appropriate material specification or the
manufacturer’s recommendations if no specification is available. The preparation given to the material prior to molding shall be
recorded and reported.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D955 − 21
7. Apparatus
7.1 Injection Mold—Specimens shall be molded in a two cavity mold conforming with dimensions as shown in Figs. 1 and 2 for
the 60 × 60-mm plaque specimen (Type D2), Fig. 3 for the 12.7 by 127-mm bar specimen (Type A) and Fig. 4 for the 100 mm
by 3.2-mm disk specimen (Type B). Pressure transducers for monitoring the pressure in at least one cavity are mandatory for Type
D2. Mold shrinkage measurements shall be made on specimens that have been molded at one of the following cavity pressures
6 3 % from the selected pressure: 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, or as specified in the appropriate material
specification. Pressure transducers are recommended, but not mandatory for specimens Type A and Type B.
7.2 Compression Mold—A single cavity positive mold having cavity dimensions conforming to the dimensions of Fig. 2 for the
60 × 60-mm plaque (Type D2) Fig. 3 for the 12.7 × 127-mm bar specimen (Type A) and Fig. 4 for the 100-mm × 3.2-mm disk
specimen (Type B), not including the sprue, runner or gate.
NOTE 2—Although scribe marks are not required, if they are used for injection or compression molded specimens for the measurement of shrinkage, the
scribe marks shall be 1.0 mm long by 0.1 mm wide located 4.0 mm from each edge on one side of the mold.
7.2.1 Although scribe marks are not required, if they are used for injection or compression molded specimens for the measurement
of shrinkage, the scribe marks shall be 1.0 mm long by 0.1 mm wide located 4.0 mm from each edge on one side of the mold.
7.3 Injection Press—A suitable injection molding machine that shall fill the test molds when it is operated in the range from 20
to 80 % of its rated shot capacity at the molding parameters specified in Practice D3641, ISO 294-3 or the appropriate material
specification.
NOTE 2—If the injection machines of appropriate capacity are not available, the requirements of 7.3 may be met in machines of larger capacities by
providing test molds with multiple cavities (maximum of four) to be filled from a common sprue and having a balanced filling pattern, so that the total
weight of the shot, including sprue and runner will fall within the specified limits.
7.4 Compression Press—A suitable hydraulic press that shall deliver a pressure of 20 to 35 MPa (3000 to 5000 psi) to the material
in the mold.
Sp | sprue
G | gate
L = distance between the lines along which the test specimens are cut from the runners
c
Molding volume = 20 000 mm
Projected area = 11 000 mm
FIG. 1 Type D2 (Mold Layout)
D955 − 21
Sp sprue
G gate
R runner
P pressure sensor
l length of plate 60 ± 2 mm
b width of plate 60 ± 2 mm
h thickness of plate 2.0 ± 0.1 mm
l length of gate 4.0 ± 0.1 mm
G
h height of gate (0.75 ± 0.05) × h
G
l length of runner 25 to 40 mm
R
b width of runner $ (b + 6) mm
R
h depth of runner at gate
g
l* unspecified distance . . .
l distance of pressure sensor from gate 5 ± 2 mm
p
FIG. 2 Type D2 (Cavity Details)
w = 12.7 ± 0.2 mm
t = 3.2 ± 0.05 mm
l = 127 ± 2 mm
G = Gate
P = Pressure Transducer
FIG. 3 Bar Specimen
7.5 Measuring Tools—Measuring tools (micrometers, vernier calipers, etc.) accurate to 0.025 mm (0.001 in.) for measuring the
molds and test specimens conforming to the measuring tool requirements in Test Methods D5947.
D955 − 21
t = 3.2 ± 0.05 mm
D = 100 ± 2 mm
G = Gate
P = Pressure Transducer
FIG. 4 Disk Specimen
8. Test Specimen
8.1 The following specimen dimensions are applicable for both compression and injection molding. Orientation effects due to flow
direction do not generally pertain to compression molding.
8.1.1 Specimen Type D2—For mold shrinkage in both flow and cross flow the preferred specimen shall be 60 by 60 by 2 mm depth
conforming to the dimensions of Fig. 2.
8.1.2 Specimen Type A—For shrinkage parallel to flow, a bar mold having a cavity of 12.7 by 127 mm shall be used as shown in
Fig. 3. The thickness shall be 3.2 mm unless otherwise agreed upon by the seller and the purchaser. The mold shall have at one
end a gate 6.4 mm in width by 3.2 mm in depth.
8.1.3 Specimen Type B—A disc shaped specimen, as shown in Fig. 4, having a cavity 100 mm in diameter by 3.2 mm in thickness
with a gate 12.7 mm in width by 3.2 mm in depth, placed radially at the edge, shall be used.
NOTE 3—Although this specimen may be used to determine mold shrinkage in both the flow and cross flow directions, the filling pattern does not produce
uniform flow lengths and orientation. Consequently, there may be significant differences when measuring the specimen at different points around the
circumference. Values would not be expected to be in agreement with those obtained using the specimens described in 8.1.1 and 8.1.2.
9. Conditioning
9.1 Conditioning—Conditioning of molded specimens shall be done in the Standard Laboratory Atmosphere, Unless otherwise
specified by relevant material standard, condition molded specimens at 23 6 2°C and 50 % 6 10 RH, if not otherwise specified
in the appropriate materials10 % relative humidity in accordance with Practice D618standard.
9.2 Test Conditions—Conduct measurement in the standard laboratory atmosphere of Unless otherwise specified by relevant
material standard, conduct measurement at 23 6 2°C and 50 % 6 10 RH, if not otherwise specified in the appropriate
materials10 % relative humidity in accordance with Practice D618standard. .
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10. Procedure
10.1 Measure the length and width of the mold cavity at the center of each edge or at the molded scribe marks, to the nearest 0.025
mm at 23 6 2°C and 50 % 6 10 RH. 10 % relative humidity. Record these values as l and w, respectively.
10.2 Mold at least five flat test specimens from the sample to be tested.
NOTE 4—Flat is represented by a specimen with less than 3 % warp. Three percent warp is defined as 3 mm depth deflection, positive or negative, per
100 mm in length.
10.2.1 Thermoplastics Molded by Injection—Molding of thermoplastic materials shall be conducted in accordance with the
appropriate material standard, Practice D3641 or ISO 294-3. The temperature of the heating cylinder and the mold shall be
maintained at a point which, on a cycle selected, will produce temperature within the range recommended by the material molding
standard. Begin with a short shot to ensure the flow front is straight and not radial and that the flow is laminar and does not exhibit
melt fracture (jetting). Collect samples after the machine is at equilibrium.
10.2.2 Thermoplastics Molded by Compression—For thermoplastics, molding shall be conducted in accordance with the
appropriate material standard or D4703.
10.3 Treatment of Specimens after Removal from the Mold:
10.3.1 In order to minimize warpage, separate the test specimens from the runners in the gate area immediately after removal from
the mold. Do not modify or alter the edges used for the measurement of dimensions. It is recommended to cool specimens in a
horizontal position at room temperature by placing them on a material of low thermal conductivity to minimize warpage. After the
first hour, condition the specimens at 23 6 2°C and 50 % 6 5 RH, unless otherwise specified in the material standard.
10.3.2 Specification of Measurement Time:
10.3.2.1 Twenty four hour shrinkage measurements shall be made 24 6 0.5 h after the specimen has been removed from the mold.
10.3.2.2 Forty e
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