Overview
ISO 718:1990 specifies standardized test methods for thermal shock and thermal shock endurance of laboratory glassware in the condition received by the customer. The standard defines how to perform a controlled thermal shock test - heating glassware to an upper temperature and rapidly immersing it in a cold water bath - and how to determine the temperature-difference at which 50% of samples fail (thermal shock endurance). It does not apply to fused silica ware or annealed soda‑lime‑silicate containers (those are covered by ISO 7459).
Key topics and technical requirements
- Scope & exclusions: Applies to laboratory glassware except fused silica and annealed soda‑lime‑silicate containers.
- Definitions: thermal shock, thermal shock endurance (DT50), temperature variation and fluctuation.
- Apparatus:
- Test oven: electrically heated, air‑circulated, temperature range up to at least 300 °C; tight thermostatic control (±1 °C up to ~180 °C and ±2 °C toward higher temperatures as specified).
- Cold water bath: circulator and thermostat to maintain the lower temperature (t2) within 0–27 °C and close tolerance (≈±1 °C).
- Accessories: tongs with heat‑resistant tips, gauntlet‑type gloves, and a basket that holds multiple samples upright without scratching or floating.
- Sampling: Number of test items is predetermined by the applicable article standard or agreed between parties; random selection if not specified.
- Procedure:
- Heat samples in the oven to t1 and hold until thermal equilibrium (30 min normally; note: equilibrium time depends on glass thickness - guidance such as ~6 min/mm is provided).
- Transfer samples to the cold bath and immerse for 8 s to 2 min depending on item type (containers immersed to half height less neck; rim testing specified separately).
- Transfer timing must be controlled (≈5 s ±1 s per sample or per basket); temperature difference t1 − t2 is the test variable.
- For endurance, repeat with increasing temperature differences (5 °C increments up to 100 °C, 10 °C beyond) until all samples fail.
- Results & reporting:
- Items that do not chip, crack or break are considered to have passed at that temperature difference.
- Record number of failures at each ΔT and determine DT50 (temperature difference at which 50% fail) by linear regression; report standard deviation.
- Test report must reference ISO 718 and include product ID, sample size and method, ΔT values, pass/fail counts, DT50 and SD.
Applications and users
- Who uses it: laboratory glassware manufacturers, QC/QA laboratories, test houses, procurement teams, product designers and R&D groups evaluating glass thermal performance.
- Practical uses: quality control, batch validation, comparative product testing, failure analysis, and specification compliance for laboratory consumables and apparatus.
Related standards
- ISO 7459:1984 - Glass containers (thermal shock resistance and endurance) - referenced for annealed soda‑lime‑silicate containers.
Keywords: ISO 718, thermal shock, laboratory glassware, thermal shock endurance, test methods, cold water bath, test oven, DT50, glassware testing.
