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D5939-96 – Standard Test Method Technical Guide
The ASTM D5939-96 standard, formally titled “Standard Practice for Preparing Multipurpose Test Specimens and Bars of Thermoplastics by Injection Moulding,” provides a comprehensive framework for the consistent fabrication of injection moulded test specimens. By detailing essential mould designs and promoting uniform reporting of processing parameters, this practice ensures that material property data derived from these specimens are reproducible and comparable across laboratories. This practice is technically identical to ISO 294-1.
📐 Specimen Geometry and Mould Design Considerations
The standard specifies the general principles for injection moulding test specimens of thermoplastics, focusing on two primary geometries for reference data acquisition:
- Multipurpose Test Specimens: Conforming to ISO 3167 and ASTM D 5936, these are designed for a wide range of mechanical and thermal tests.
- Standard Bars: Precise bars measuring 80 mm × 10 mm × 4 mm, commonly used for Charpy impact testing (ISO 179 / D 5942) and flexural evaluations.
The design of the mould cavity is explicitly recognized as a critical variable for achieving reproducible results. The cavity is defined as the part of the hollow space of the mould that forms one specimen.
| 🟦 Specimen Type | 📏 Nominal Dimensions | 📐 Governing Specification | 🎯 Typical Applications |
|---|---|---|---|
| Multipurpose Test Specimen (Type A) | Overall length ≥ 150 mm (per ISO 3167) | ISO 3167 / D 5936 | Tensile, flexural, and impact testing |
| Injection Moulded Bar | 80 × 10 × 4 mm | D 5939 / ISO 294-1 | Charpy impact (ASTM D 5942) |
⚙️ Moulding Parameters and Process Control
Reproducibility is the cornerstone of this practice. It establishes a uniform methodology for describing and reporting the crucial parameters of the injection moulding operation. The special conditions required to prepare test specimens in a comparable state will vary for each material.
A critical equation governs the minimum clamping force required to keep the mould closed during injection:
💡 Key Parameter: The minimum clamping force (FM) must satisfy the condition: FM ≥ AP × Pmax × 10⁻³, where AP is the projected area of the cavities (mm²) and Pmax is the maximum hydraulic pressure in the cavity (MPa).
| ⚠️ Symbol | 📊 Definition | 🔢 Requirement / Units |
|---|---|---|
| FM | Clamping Force | kiloNewton (kN) |
| AP | Projected Area per cavity | mm² |
| Pmax | Maximum melt pressure in cavity | MPa |
| Condition | Minimum Clamping Force | FM ≥ AP × Pmax × 10⁻³ |
International round-robin testing, specifically cited for ABS, S/B, and PMMA in the standard, has demonstrated that mould design is among the most critical factors influencing specimen quality and consistency.
⚠️ Safety and Compliance: As per section 1.3 of the standard, this practice does not address all safety concerns. It is the responsibility of the user to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
📋 Standards Harmonization and Framework
ASTM D5939-96 is explicitly identical to ISO 294-1. It operates within a family of related standards for thermoplastic testing:
- ASTM D 3641: A comparable practice for injection molding. The standard cautions that neither D5939 nor D3641 should be substituted for the other.
- Auxiliary ASTM Practices: D 5935 (Single-Point Data), D 5936 (Multipurpose Specimens), D 5940 (Small Plates).
- International ISO Standards: ISO 294-2/-3 (Mould Types C/D), ISO 294-4 (Moulding Shrinkage), ISO 10350 (Single-Point Data), and the ISO 11403 series (Multipoint Data).
This framework ensures that specimens prepared under this practice yield data suitable for material databases and quality control systems on a global scale.
❓ Frequently Asked Questions
🔍 What is the primary scope of ASTM D5939-96?
The practice covers the general principles for injection moulding test specimens of thermoplastics, specifically multipurpose test specimens conforming to ISO 3167 / D 5936 and standard bars 80 mm × 10 mm × 4 mm.
💡 How does D5939-96 relate to international ISO standards?
This standard is technically identical to ISO 294-1. It provides the basis for preparing specimens that conform to ISO 3167, ensuring global harmonization of test data.
⚡ What is the significance of the Clamping Force equation in this standard?
The equation FM ≥ AP × Pmax × 10⁻³ sets the minimum clamping force required to prevent flash and ensure consistent cavity packing during the injection cycle. It is fundamental to reproducible moulding conditions.
📌 What is the relationship between D5939 and ASTM D 3641?
D5939 is identical to ISO 294-1, while D 3641 is a comparable ASTM practice. The standard explicitly states that neither standard should be substituted for the other, as they represent distinct, though related, methodologies for specimen preparation.