ASTM D6746-15 (2020) PDF

Full title and description

Standard Test Method for Determination of Green Strength and Stress Relaxation of Raw Rubber or Unvulcanized Compounds. This ASTM test method defines procedures to measure the characteristic known as "green strength" (tensile green strength and related stress-relaxation behavior) of raw or unvulcanized rubber compounds to aid evaluation of processing performance and formulation effects.

Abstract

This standard describes specimen preparation, test apparatus, test conditions (including rate of extension and temperature), and calculation/reporting procedures used to determine tensile green strength and stress relaxation of unvulcanized rubber compounds. Results help characterize processing behavior (e.g., handling, extrusion, calendering, molding prior to cure) and effects of polymer properties and compounding ingredients such as fillers, plasticizers, and peptizers.

General information

• Status: Active (D6746-15, reapproved/confirmed 2020).
• Publication date: D6746-15 originally issued 2015; designation reapproved/confirmed as D6746-15(2020) with a publication/confirmation date of 01 June 2020.
• Publisher: ASTM International (American Society for Testing and Materials).
• ICS / categories: 83.040.20 (Rubber compounding ingredients).
• Edition / version: Designation D6746-15 (2015) — reaffirmed/issued in 2020 as D6746-15(2020).
• Number of pages: 6 pages.

Scope

This test method covers methods to evaluate the green strength property of raw rubber or unvulcanized rubber compounds and procedures to measure stress relaxation under specified test conditions. The standard specifies SI units, identifies dependencies on specimen preparation, extension rate and temperature, and notes that single-point measurements cannot capture the full range of processing behavior across all conditions. It is intended for characterization of uncured rubber for processing and formulation control.

Key topics and requirements

• Definition and significance of green strength (tensile green modulus, tensile green strength) and its relationship to processing behavior.
• Specimen preparation requirements and geometry for unvulcanized test pieces.
• Apparatus and instrumentation for tensile and stress-relaxation measurements (tensile tester with controlled extension rate, grips, and environment control).
• Prescribed test conditions including temperature control and specified rates of extension; emphasis that results depend on these parameters.
• Procedures to measure stress relaxation following an imposed extension and calculation/reporting of relevant parameters (peak tensile green strength, modulus, relaxation curve characteristics, yield stress where applicable).
• Requirements for reporting test conditions, specimen details, and any deviations to ensure repeatable comparison.

Typical use and users

Used by rubber compounders, product formulators, quality control and quality assurance laboratories, R&D teams, and manufacturers of rubber goods to evaluate unvulcanized compound handling and processing behavior (mixing, extrusion, calendering, molding prior to cure). Also used by testing laboratories providing specification verification and by standards and compliance professionals in the rubber industry.

Related standards

Commonly used alongside other ASTM rubber test methods that address cured and uncured properties and physical testing, for example ASTM D412 (tensile properties of vulcanized rubber), ASTM D2240 (durometer hardness), and other D11 committee methods for compound characterization and processing tests. The D6746 designation replaces or revises earlier D6746 editions.

Keywords

green strength, tensile green strength, tensile green modulus, green stress relaxation, raw rubber, unvulcanized compounds, yield stress, stress relaxation, rubber compounding, processing behavior.

FAQ

Q: What is this standard?

A: ASTM D6746-15(2020) is a test method that specifies procedures to determine the green strength and stress-relaxation behavior of raw or unvulcanized rubber compounds.

Q: What does it cover?

A: It covers specimen preparation, test apparatus, controlled test conditions (temperature and extension rate), measurement procedures for tensile green strength and stress relaxation, and guidance on calculations and reporting. The standard emphasizes that results depend strongly on specimen preparation, rate of extension, and temperature.

Q: Who typically uses it?

A: Rubber compound formulators, processing engineers, QC/QA laboratories, test houses, and R&D groups within the rubber and elastomers industry.

Q: Is it current or superseded?

A: The edition in common use is D6746-15, which was reaffirmed/issued in 2020 as D6746-15(2020). The document is listed as active in vendor and standards catalogs as of its 2020 confirmation. Users should verify any newer revisions or withdrawals with ASTM directly before relying on the standard for compliance.

Q: Is it part of a series?

A: It is part of the suite of ASTM D11 committee standards covering rubber and rubber-like materials (Book of Standards, Volume 09.01). It relates to other D11 test methods addressing both uncured and cured rubber properties.

Q: What are the key keywords?

A: Green strength; tensile green modulus; tensile green strength; green stress relaxation; raw rubber; unvulcanized compounds; yield stress; rubber compounding ingredients.