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 D6778-20 - Standard Classification System and Basis for Specification for Polyoxymethylene Molding and Extrusion Materials (POM)
• Effective Date: 01-Feb-2020

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
1
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
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
3
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
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1
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.
3
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
1

---------------------- Page: 1 ----------------------
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 mol
...

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
1
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
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
1
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.
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

---------------------- Page: 1 ----------------------
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
3
2.2 ISO Standards:
ISO 293 Plastics—Compression Mouldi
...