What is Rubber Aging?
Rubber aging refers to a wide range of laboratory tests designed to accelerate the aging process in rubber materials. The purpose of rubber aging is to predict the lifespan of rubber materials and understand how a rubber product may change over time while in service. This information allows manufacturers to modify rubber compounds formulations and product design to boost longevity or communicate product lifespan expectations to their customers.
Rubber Aging Tests
There are many ways to accelerate the rubber aging process in a controlled laboratory environment. Two common methods are fluid aging and heat aging.
Fluid Aging (ASTM D471)
Benefits of Fluid Aging
Fluid aging is excellent for rubber materials and products that will be exposed to fluids while in service. This type of testing enables manufacturers to predict how their materials will interact with a given fluid on an accelerated timeline and the effects of long-term exposure. The temperature of the fluid and the testing environment can also be customized to closely match the product’s intended service environment and gain a sharper understanding of real-world performance.
One popular method for fluid aging testing is ASTM D471: Standard Test Method for Rubber Property—Effect of Liquids. ASTM D471 is used in many industries, ranging from aerospace, oil, and gas to consumer and automotive. What makes ASTM D471 so valuable is its flexibility. Many of the standard fluids listed in the spec are industry reference oils, but the method outlined in ASTM D471 can be used with virtually any fluid, including jet fuels, acids, salt water, synthetic sweat, inks, and even animal waste.
To conduct the method described in ASTM D471, the rubber material is cut into sample specimens and suspended in a glass test tube filled with the designated fluid. ASTM D471 also provides alternative test setups for situations that call for exposure to just one surface of the sample, rather than full immersion. The full test assembly is heated to a specific temperature for a determined period of time.
Once the test period is completed, the sample specimens are removed from the fluid and examined for changes to physical properties and performance characteristics and signs of deterioration. This may include:
- Mass, volume, and dimensions.
- Stress/strain properties.
- Soluble matter extraction.
- Tensile strength, elongation, and hardness.
- Breaking resistance, burst strength, tear strength, and adhesion.
Heat Aging (ASTM D573)
Benefits of Heat Aging
Long-term exposure to heat can cause oxidation and thermal aging of vulcanized rubber, both of which can contribute to deterioration and weakened performance of rubber products and components. These effects are especially important to understand for products that operate in high-heat service environments, such as engine compartments, manufacturing, and even the great outdoors. Heat aging testing allows manufacturers to predict exactly how a rubber component may age over time when exposed to heat.
A popular standardized test procedure for heat aging is ASTM D573: Standard Test Method for Rubber—Deterioration in an Air Oven. The test is conducted on dumbbell-shaped specimens, which are placed in an oven and exposed to a prescribed temperature for a prescribed internal, usually three, seven, or 14 days.
After being exposed to heat, the samples are subjected to tensile strength and elongation testing. The resulting data is compared to the tensile and elongation performance of samples that have not been aged, so as to quantify the effects of aging on material properties.
Limitations to Rubber Testing
While many test specifications for accelerated aging are suitable for a wide range of rubber materials, there can be limitations depending on the test method. For example, ASTM D471 is ideal for vulcanized and finished rubber products, but the method is unsuitable for cellular rubbers, porous composition rubbers, and compressed sheet packing. A clear understanding of which tests are appropriate for which materials is vital.
Another limitation is clarity. ASTM D573 describes a reliable method for conducting aging testing on rubber materials, but the spec doesn’t give any specific insight into what can be extrapolated from test results. It’s best to work closely with testing experts who have experience designing test programs and interpreting data to glean valuable insight from the entire testing process.
Rubber Testing With Rubber Experts at ACE Labs
The testing experts at ACE Laboratories have years of experience with rubber aging tests. We are well versed in a wide range of industry standard tests and have also designed countless custom protocols to meet our customers’ needs. We can help you navigate the more ambiguous elements of accelerated aging testing and help you determine how to apply testing data to your design and production decisions.
To learn more about accelerated aging or get started on a project, talk to us >