ISO 188:2023

Overview

ISO 188:2023 - Rubber, vulcanized or thermoplastic - Accelerated ageing and heat resistance tests - specifies laboratory procedures to evaluate how vulcanized rubbers and thermoplastic elastomers (TPEs) change when exposed to elevated temperatures. The standard defines test principles, apparatus, calibration, test-piece preparation, ageing and heat-resistance conditions, procedures, expression of results, precision and reporting requirements. It replaces the 2011 edition and introduces additional oven types and editorial clarifications.

Key topics and technical requirements

• Scope and purpose: Defines accelerated ageing (higher-than-service temperatures to simulate long-term ageing) and heat-resistance tests (exposure at intended service temperatures).
• Four test methods (Clause 5):
  • Method A - cell or cabinet ovens with low air speed, laminar flow; air changes 3–10/h.
  • Method B - cabinet oven with forced circulation, laminar flow; air speed 0.5–1.5 m/s; air changes 3–10/h.
  • Method C - cabinet oven with forced circulation, turbulent flow and rotating test-piece carrier (5–10 rpm); average air speed ~0.5 m/s ±0.25; air changes 3–10/h.
  • Method D - cabinet oven, high air speed turbulent flow, stationary test pieces; air flow 0.25–3.0 m/s and air changes >30/h (suitable for short-term tests up to 168 h).
• Apparatus & setup:
  • Oven free space must be large enough that test-piece volume ≤10% of chamber free volume.
  • Test pieces suspended ≥10 mm from each other and ≥50 mm from cabinet walls (for forced-air ovens).
  • Temperature control and sensor placement near test pieces; incoming air heated to within ±1 °C before reaching samples.
  • No copper or copper alloys in heating chamber construction.
• Measured properties: Where unspecified, recommended properties include tensile strength, stress at intermediate elongation, elongation at break (ISO 37), and hardness (ISO 48‑2).
• Key cautions:
  • Air speed and air-exchange significantly affect results - use the same method when comparing materials.
  • Accelerated ageing is a simulation of natural ageing and may not replicate all mechanisms (e.g., effects of light, ozone, or mechanical stress).

Practical applications and users

ISO 188:2023 is used by:

• Rubber and TPE manufacturers for product development and quality control
• Independent testing laboratories validating material heat stability and lifetime estimates
• Automotive, aerospace, oil & gas, and seal/hose designers assessing material suitability for elevated-temperature service
• R&D teams performing comparative ageing studies and lifetime projections (with Arrhenius or WLF analysis per ISO 11346)

Benefits include standardized test methods for consistent evaluation of heat resistance, improved comparability when the same oven method is applied, and documented precision and reporting practices for certification and procurement.

Related standards

• ISO 11346 - guidance on Arrhenius/WLF lifetime estimation
• ISO 18899 - calibration of test equipment
• ISO 23529 - preparing and conditioning test pieces
• ISO 37 and ISO 48‑2 - tensile and hardness test methods (referenced for recommended measured properties)

Keywords: ISO 188:2023, accelerated ageing, heat resistance tests, rubber testing, thermoplastic elastomers, ageing oven, air speed, air exchange rate.