Overview
ISO 293:2023 - "Plastics - Compression moulding of test specimens of thermoplastic materials" defines the principles and procedures for preparing compression‑moulded test specimens and sheets from thermoplastics. The standard standardizes the main steps (including eight standardized cooling methods) to ensure reproducible, homogeneous and isotropic specimens. ISO 293:2023 is not applicable to reinforced thermoplastics.
Key topics and technical requirements
- Scope & purpose: Procedures for compression moulding of thermoplastic test specimens and sheets for machining or stamping. Emphasis on reproducibility and control of cooling during crystallization for semi‑crystalline polymers.
- Moulding press requirements: Clamping force sufficient to provide at least 12 MPa (pressure). Pressure must be maintained within ±10% during the cycle. Platens must be capable of heating to ≥320 °C and meeting specified cooling rates.
- Temperature and uniformity: Mould surface temperature variation limited to ±2 °C during heating and ±4 °C during cooling; moulding and demoulding temperatures are defined and measured near the material.
- Cooling control: Eight standardized cooling methods are described (including quench cooling, which requires two presses). The standard distinguishes average cooling rate and strictly controlled (linear) cooling rate and requires pre‑determination of coolant flow for each method.
- Mould types and fabrication: Two main mould types - flash (picture frame) moulds and positive moulds - with guidance on when to use each. Surface finish recommendation: 0.16 Ra (see ISO 21920‑2). For positive moulds, recommended fits (e.g., H7g6) and materials/toughness guidance (alloy steels, special stainless for PVC) are provided.
- Material preparation: Drying procedures for granules (including use of vacuum ovens where applicable) and preparation of preforms are specified to reduce variability.
- Specimen inspection & reporting: Requirements for inspection of moulded sheets/specimens and a specimen preparation report to document conditions.
Practical applications and users
ISO 293:2023 is intended for:
- Materials testing laboratories and QA/QC teams preparing standardized specimens for mechanical and thermal testing.
- Plastics manufacturers and compounders developing material data and process windows.
- R&D and product development groups validating material properties.
- Certification bodies and standardization committees referencing specimen preparation procedures.
Practical benefits include improved test reproducibility, controlled thermal histories for semi‑crystalline polymers (PE, PP, etc.), and consistent specimen geometry and surface quality.
Related standards
- ISO 21920‑2 (surface roughness guidance)
- ISO 286‑1 (tolerance fits such as H7g6)
- ISO 20753 (specimen types/dimensions referenced in the standard)
- Material‑specific International Standards that specify moulding temperatures and cooling methods
Keywords: ISO 293:2023, compression moulding, thermoplastic test specimens, cooling rate, moulding press, flash mould, positive mould, specimen preparation.
