High-temperature weathering testing of sealing strips evaluates how rubber and thermoplastic gaskets withstand long-term exposure to heat, UV radiation, ozone, and humidity, which are the primary causes of hardening, cracking, and loss of sealing force. This article explains the tested sample types, key testing items, internationally recognized methods such as ISO 188, ASTM D573, ISO 4892, and GB/T 3512, and typical acceptance criteria used by accredited third-party laboratories. It serves as a practical reference for manufacturers, suppliers, and quality engineers in the automotive, construction, and industrial equipment sectors.
Technical Overview
Sealing strips, also known as weatherstrips or gaskets, are flexible elastomeric profiles installed at doors, windows, trunks, sunroofs, curtain walls, and equipment enclosures to block air, water, dust, noise, and vibration. They are commonly manufactured from EPDM rubber, PVC, silicone rubber, thermoplastic elastomers (TPE/TPV), chloroprene rubber (CR), or nitrile rubber (NBR). Because these products operate outdoors or near heat sources for many years, their long-term durability is dominated by high-temperature weathering resistance.
High-temperature weathering degradation of sealing strips is driven by several coupled mechanisms: thermal oxidation of the polymer backbone, ultraviolet-induced chain scission and crosslinking, ozone attack on stretched rubber surfaces, plasticizer and additive volatilization, and hydrolytic aging under humid conditions. The macroscopic consequences include hardness increase, loss of tensile strength and elongation, permanent compression set, surface cracking, discoloration, stickiness, and ultimately leakage, wind noise, corrosion, and energy loss in the assembled structure.
High-temperature weathering testing simulates these aging mechanisms under accelerated laboratory conditions in accordance with ISO, IEC, ASTM, EN, GB, UL, and JIS standards. By comparing properties before and after exposure, manufacturers can verify material formulation stability, validate design life, support supplier qualification, and demonstrate regulatory compliance through accredited third-party laboratories.
Testing Samples
Automotive Sealing Strips
Door seals, window channels, trunk and tailgate seals, hood seals, sunroof drains, and body sealing membranes for passenger vehicles, commercial vehicles, and new energy vehicles. EPDM and TPV are the dominant materials, and test temperatures typically range from 70 °C to 125 °C depending on the mounting position and heat exposure class.
Architectural Door and Window Seals
Gaskets and weatherstrips for aluminum or UPVC windows, doors, and glass curtain walls, usually made of EPDM, silicone rubber, or PVC. These products are evaluated against building hardware performance specifications in the EN 12365 series and related national standards, with emphasis on UV and heat aging stability over a 10 to 25 year service life.
Industrial and Appliance Seals
Sealing strips for electrical enclosures, HVAC ducting, refrigeration appliances, oven and machinery door gaskets, rail transit vehicles, and marine hatch seals. Silicone grades may require heat resistance testing at 180 °C to 300 °C, while enclosure gaskets for electrical equipment may be assessed under UL enclosure standards in addition to material aging tests.
Specimen Forms
- Standard dumbbell or ring specimens die-cut from vulcanized sheets or from the seal body, for tensile and hardness measurement before and after aging.
- Cylindrical discs or stacked buttons for compression set testing under constant deflection.
- Full cross-section profile segments or finished parts for appearance evaluation, dimensional stability, insertion force, and functional leak checks after aging.
- Stretched specimens mounted on fixtures for ozone exposure testing.
Testing Items
High-temperature weathering test programs for sealing strips typically combine the following items, with results reported as property changes relative to the unaged reference condition:
- Hot air aging: change in tensile strength, elongation at break, 100% modulus, and hardness after oven exposure at 70 °C to 150 °C for 70 h to 1000 h.
- Compression set at elevated temperature: permanent deformation of the seal after compression at service temperature, a direct indicator of long-term sealing force retention.
- Compression stress relaxation and sealing force decay measured continuously or at intervals during heat aging.
- Heat deformation and dimensional stability: shrinkage, warpage, and profile geometry change after thermal exposure.
- Thermal aging mass loss: volatilization of plasticizers and process oils, particularly critical for PVC and low-cost EPDM compounds.
- Ozone resistance at elevated temperature: dynamic and static cracking resistance of strained rubber surfaces.
- Artificial weathering by xenon arc or fluorescent UV lamps combined with elevated black panel temperature, humidity, and water spray.
- Damp heat aging, for example 85 °C and 85% relative humidity, for seals used in humid or electrical environments.
- Thermal cycling between low and high temperature extremes to assess fatigue and adhesion of coated or co-extruded layers.
- Appearance assessment after aging: cracking, blistering, blooming, discoloration, and tackiness, usually graded visually or under magnification.
Testing Methods
Hot Air Oven Aging
Accelerated heat aging is performed in forced-ventilation air ovens following ISO 188, ASTM D573, GB/T 3512, and JIS K 6257. Typical conditions for EPDM sealing strips include 100 °C or 125 °C for 168 h, while PVC grades are aged at 70 °C to 100 °C and silicone grades at 200 °C or above. After exposure, specimens are conditioned and tested for tensile properties per ISO 37, ASTM D412, and GB/T 528, and for hardness per ISO 48, ASTM D2240, and GB/T 531.1. Acceptance limits commonly specified in industry require tensile strength and elongation retention of at least 70% to 80% and hardness change within ±10 Shore A points.
Xenon Arc Weathering
Full-spectrum weathering is conducted with xenon arc lamps equipped with daylight filters according to ISO 4892-2, ISO 11341, ASTM G155, and GB/T 16422.2. A representative cycle uses an irradiance of 0.35 W/m² at 340 nm, a black standard temperature of 65 °C, a chamber temperature of 38 °C, and alternating light and water spray periods. Exposure durations of 500 h to 3000 h are selected according to the target service climate, and degradation is judged by color change, chalking, crack formation, and mechanical property retention.
Fluorescent UV Condensation Weathering
For screening tests and cost-sensitive programs, fluorescent UV lamps with UVA-340 lamps and condensation cycles are used per ISO 4892-3, ASTM G154, and GB/T 16422.3. Typical cycles alternate 8 h of UV at 60 °C black panel temperature with 4 h of condensation at 50 °C. This method is particularly effective for evaluating UV stabilizers and pigment systems in colored seals.
Ozone Resistance Testing
Strained specimens are exposed to controlled ozone atmospheres following ISO 1431-1, ASTM D1149, JIS K 6259, and GB/T 7762. Standard conditions include an ozone concentration of 50 pphm at 40 °C with specimens elongated 20% or 50% for 72 h to 168 h. Specimens must show no cracking when inspected under two-fold to seven-fold magnification, which validates the antiozonant package and wax protection of the compound.
Compression Set and Stress Relaxation
Compression set is measured under constant deflection, typically 25%, according to ISO 815-1, ASTM D395 Method B, and GB/T 7759, using test temperatures matching the service class such as 100 °C or 125 °C for 22 h, 70 h, or 168 h. Compression stress relaxation is determined per ISO 6914 and ASTM D6147 to quantify the decay of sealing force over time. Automotive and architectural specifications commonly limit compression set to 50% or less after the specified exposure.
Damp Heat and Thermal Cycling
Seals integrated into electrical and electronic products are evaluated with damp heat tests per IEC 60068-2-78 (steady state, for example 85 °C/85% RH for 1000 h) and IEC 60068-2-30 (cyclic humidity). Thermal shock and change-of-temperature tests per IEC 60068-2-14, for example between −40 °C and +90 °C or +120 °C for 50 to 200 cycles, reveal delamination of flocked or coated layers and embrittlement of the compound.
Evaluation and Reporting
Accredited third-party laboratories report aged and unaged values, percentage change in tensile strength, elongation at break, and hardness, compression set values, mass loss, visual defect grades, and photographic documentation. Statistical comparison with agreed acceptance criteria forms the basis of pass or fail conclusions and material ranking.
Applications
High-temperature weathering test reports are used across the entire product life cycle of sealing strips:
- Material development and compound qualification for new EPDM, TPV, and silicone formulations, including filler, plasticizer, and UV stabilizer optimization.
- Automotive supplier validation and production part approval, where heat aging, compression set, and weathering data are mandatory submission elements.
- Building product certification for window, door, and curtain wall gaskets, demonstrating durability consistent with EN 12365 and national building code requirements.
- Quality control and incoming inspection of seal extrusions, using shortened aging checkpoints to monitor batch-to-batch consistency.
- Failure analysis of field returns, comparing aged properties against specification to identify root causes such as thermal overload or formulation drift.
- Export compliance support, providing internationally recognized test evidence based on ISO, ASTM, and GB methods for global markets.
FAQ
What is a typical test condition for EPDM automotive sealing strips?
A common program combines hot air aging at 125 °C for 168 h per ISO 188 or GB/T 3512, compression set at 125 °C for 22 h or 70 h per ISO 815-1, and xenon arc weathering for 1000 h to 1500 h per ISO 4892-2. Exact temperatures and durations depend on the vehicle manufacturer specification and the mounting position of the seal.
How are pass or fail criteria defined?
Typical acceptance limits include tensile strength and elongation retention of at least 70% to 80% after aging, hardness change within ±10 Shore A, compression set not exceeding 50% to 70%, no visible cracks after ozone exposure, and no cracking or severe discoloration after artificial weathering. The governing specification of the OEM or building system owner always takes precedence.
Can testing be performed on finished seal profiles instead of flat sheets?
Yes. Full profile sections can be aged and then evaluated for appearance, dimensional change, and functional performance such as insertion and extraction force or leak resistance. However, tensile and compression set measurements usually require standardized specimens, either cut from the product where geometry permits or prepared from the same compound and cure condition.
How long does a complete high-temperature weathering program take?
Short-cycle oven aging and compression set tests can be completed within one to two weeks. Extended weathering exposures of 2000 h or more, damp heat tests of 1000 h, and thermal cycling programs may require two to four months. Scheduling should also account for pre-aging baseline measurements and post-aging conditioning time.
Which standards apply to architectural versus automotive sealing strips?
Architectural gaskets are commonly assessed under the EN 12365 series together with ISO and GB material aging methods, while automotive weatherstrips follow ISO, ASTM, GB, and JIS rubber test methods supplemented by each OEM engineering standard. Seals for electrical enclosures may additionally be evaluated under UL enclosure requirements and IEC 60068 environmental tests.
Why is compression set at high temperature so critical?
A seal functions by maintaining contact force over years of compression. Even if the material remains visually intact after heat aging, progressive stress relaxation leads to gaps, air and water leakage, and wind noise. Compression set and stress relaxation tests therefore predict real sealing performance more directly than tensile testing alone.