ASTM International - ASTM D4703-24

Standard Practice for Compression Molding Thermoplastic Materials into Test Specimens, Plaques, or Sheets

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Organization:	ASTM International
Publication Date:	1 December 2024
Status:	active
Page Count:	13
ICS Code (Thermoplastic materials):	83.080.20

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. Specimens 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 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 shall be prepared and molded in a similar manner.

4.2 The apparatus and exact conditions required to prepare adequate specimens will usually vary for each plastic material. Apparatus and procedures 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 Appendixes. In any case, the specific apparatus and procedures to be used in producing compression-molded specimens of a given material shall be obtained by reference to the relevant material specification or by agreement between the purchaser and the supplier.

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scope:

1.1 This practice covers the compression molding of thermoplastics (for example, granules, pellets) and milled stock for the preparation of test specimens.2

Note 1: Certain ASTM standards require the use of Procedure C in Annex A1 for compression molding of polyethylene 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 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

Note 2: ISO 293:2023 has been updated and is no longer equivalent to ASTM D4703. The practice is considered technically similar to ISO 293:2023 but differs in detail.
Listed are the differences between ISO?293-1986 and ASTM D4703-16: The main body of D4703-16 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.

1.5 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.