What Is Heat Aging?
Thermal aging test is the test in which the change in the properties of the sample such as hardness, tensile strength and elongation at break is measured after being kept at a defined temperature for a defined period of time.
Purpose of Heat Aging
The aim is to comparatively evaluate to what extent the material maintains its properties over time at service temperature.
Which Products Is Heat Aging Applied To?
- Elastomer gaskets and hoses
- Cable insulation and sheaths
- Engine compartment rubber parts
- Plastic and elastomer components
In Which Sectors Is Heat Aging Used?
Standards Related to Heat Aging
- ISO 188
- ASTM D573
- IEC 60216 series (thermal resistance index)
- ISO 23529
Heat Aging Conditions
- Temperature
- Defined in the specification; is selected above the service temperature
- Time
- Defined in the standard; typically 70, 168 or 1000 hours
- Oven type
- Air circulation; The samples are hung so that they do not touch each other or the wall.
- measured change
- Percent change in hardness, tensile strength and elongation at break
Equipment for Heat Aging
- Air circulation aging ovens (dedicated to single material)
- Tensile tester and durometer
- Conditioning room
- Sample hanging arrangement
Sample Requirements for Heat Aging
- Initial properties should be measured in unaged samples
- Different types of rubber should not be aged in the same oven
- Samples should not touch each other
- The conditioning period after aging must be observed.
Duration of Heat Aging
Depending on the duration, from 1 week to several months.
Heat Aging Procedure
- 1Baseline characteristics are measured.
- 2The samples are hung in the oven.
- 3It is aged at a defined temperature and time.
- 4Samples are removed and conditioned.
- 5Features are remeasured.
- 6The percentage change is calculated.
Heat Aging Acceptance Criteria
The acceptance criterion is the maximum percentage change in properties given in the specification (for example, a maximum loss of 30% in elongation at break).
Evaluation of Results
Aging different types of rubber in the same oven creates cross-contamination (especially sulfur and plasticizer migration) and distorts the results. Accelerated hours cannot be directly converted to years of service; cycling requires multi-temperature rating type IEC 60216.
Heat Aging Report
- Standard applied
- Temperature and duration
- Oven and sample placement
- Before/after property values
- percent change
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Product and OEM specifications
Rubber Testing — What Does This Testing Field Cover?
The section below describes the field that the Heat Aging test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Rubber testing determines the mechanical behaviour of an elastomer and its resistance to environmental effects. Elastomers are assessed with a different logic from metals and plastics: the real question is not strength but ELASTIC RECOVERY and ageing behaviour.
The function of an elastomer is usually to deform and return: a gasket is compressed and provides a seal, a mount absorbs vibration, a hose expands under pressure. What is measured in the field is therefore not "how many newtons does it withstand" but "how far does it recover after deformation, and how long does it keep doing so".
COMPRESSION SET is therefore the most decisive measurement in the field. If a gasket cannot recover after being held compressed for a long period, it has lost its sealing function even though it has not torn at all. This measurement is made together with temperature, because permanent set increases rapidly with temperature.
Hardness is the most common measurement in the field, using the Shore A and IRHD scales. It is fast and practical but does not define the material on its own: two different compounds of the same hardness can show completely different ageing and fluid resistance. Hardness is valuable in monitoring compound consistency.
On the environmental resistance side, hot air ageing, swelling in fluids, ozone cracking and low temperature behaviour are examined. FLUID RESISTANCE is particularly critical: the same elastomer behaves differently in fuel, oil, coolant and brake fluid — swelling in one, shrinking in another, hardening in a third. The material is therefore tested with the actual fluid it will contact and at the actual temperature.
Ozone cracking is a silent cause of failure in parts used outdoors. Low concentrations of ozone in the atmosphere create surface cracks in unsaturated elastomers under strain; the part cracks while appearing to carry no load at all. An ozone chamber accelerates and reveals this behaviour.
Low temperature behaviour is the second silent risk. As an elastomer approaches its glass transition temperature it loses elasticity and behaves like a rigid plastic; a gasket starts to leak in the cold. Low temperature recovery and brittleness tests establish this limit.
A change of compound is not a silent change in this family. When filler content, plasticiser or the vulcanisation system changes, mechanical properties and fluid resistance shift together; verification is repeated.
Method groups in this field
Mechanical
Tensile stress-strain properties, tear strength, abrasion (rotating drum and Pico), fatigue and tear propagation.
Hardness
Shore A and IRHD indentation hardness; a rapid indicator of compound consistency.
Permanent deformation
Compression set and stress relaxation; decisive for sealing components.
Fluid resistance
Swelling in fuel, oil, coolant and chemicals, change in mass and volume, loss of hardness and strength.
Ageing
Hot air ageing, ozone cracking, the effects of UV and humidity.
Low temperature
Low temperature recovery, brittleness temperature and flexibility measurements.
Commonly confused in this field
- Hardness does not define the material; two compounds of the same hardness can show different ageing and fluid resistance.
- Fluid resistance must be tested with the actual fluid and the actual temperature; a general claim of oil resistance is insufficient.
- Without measuring compression set, no decision can be made about sealing life.
- Ozone cracking occurs under strain; a test with an unstrained specimen does not show the real risk.
- A change of compound requires verification to be repeated; a supplier may change its compound silently.
- A gasket whose low temperature behaviour is not stated produces unexpected leaks in cold climates.
Which decisions these results support
- Material selection for gaskets and sealing components
- Automotive and industrial component approval
- Verification of a compound change
- Root cause analysis of field leaks and cracking
- Declaration of the operating temperature range and fluid compatibility
Related Tests
Frequently Asked Questions About Heat Aging
How many years of service life does 168 hours of aging at 100 °C correspond to?
Life expectancy cannot be predicted from an experiment at a single temperature. Life estimation requires Arrhenius evaluation with multi-temperature approaches such as IEC 60216.