From the blazing heat of the deserts, where temperatures exceed +115F, to the frigid polar ice caps, where lows dip to –80F, molded rubber applications have to perform regardless of the weather. Even greater temperature extremes are found in the operating environments of vehicles with internal combustion engines, which contain molded rubber parts – from automobiles and heavy trucks to oil rigs, ships, and even aerospace vehicles.
Not all materials can take the heat and the cold of such harsh environments. As a result, rubber materials must be selected and compounded to meet the operating demands of each molded rubber application to ensure flexibility and durability.
Temperature Ranges for Rubber Families
Rubber materials are generally categorized into five families:
- General purpose
- High performance
- Oil/hydrocarbon resistant
- High temperature resistant
- Low temperature resistant
Three of these families are best suited for molded rubber applications that must hold up in harsh environments and temperature extremes.
Selecting the Right Material for the Operating Environment
The operating temperature range is only one factor in selecting the right rubber material. Hydrocarbon and chemical resistance are also important in many molded rubber applications.
Engineers and chemists in rubber molding firms work with their manufacturing clients to determine the best material for the application and its operating environment. Some manufacturers will specify a material that they have already proven effective. Others will define the operating environment, including the temperature range and any exposure to chemicals, and leave the material recommendations up to the rubber molding firm.
The rubber molder will first select the best rubber material that meets as many of the required qualities as possible, choosing from some 80 organic elastomers. The chemist may also recommend any of 350 raw materials that may be added to the elastomer to enhance its properties. For example, a reinforcing agent such as carbon black may be added to enhance the physical properties of the rubber, such as tensile strength, elongation, chemical resistance, and compression set. Certain minerals may be added to give the elastomer super resistance to high temperatures. This custom formulation then will be mixed and compounded for testing to ensure it will stand up to harsh environments.
Molded Rubber Components That Operate Under Extreme Temperatures
- O-ring seals in fuels, lubricants and hydraulic systems
- Shaft seals
- Radiator seals
- Valve stem seals
- Weather sealing systems
- Aerospace de-icing bladders
- Electrical connectors
- Gaskets and ducts
Testing Temperature Extremes
After one or more compounds have been developed for the application, the rubber molder will test the material in a laboratory setting to expose it to high and low temperatures and evaluate its resiliency and ability to maintain necessary properties.
High Temperature Tests
To test heat resistance, the chemist may use heat aging testing of the rubber compound. This involves exposing the material to a given temperature, such as +400F, for a certain period of time, such as 100 hours. Then the chemist retests the material to determine to what extent the rubber’s properties may have changed.
A pull test may be conducted, where tensile strength is important. If the standard is for the part to hold up to a minimum of 2,000 PSI (pounds per square inch), the test on material after exposure to high heat will determine whether than strength is maintained or the material has degraded.
Low temperature Tests
If a molded rubber part must remain flexible in low operating temperatures, the chemist will conduct low-temperature flex testing. The chemist will also test for the glass transition temperature – the brittle point at which rubber becomes like glass from a chemical standpoint, which means it can no longer exhibit elastomeric properties.
Thermal retraction is another form of low temperature testing. TR-10 is the temperature at which a material retracts by 10 percent, which correlates with the brittle point. TR-70 correlates with low temperature compression set or how well the material rebounds after long exposures to low temperatures.
Once a compound has been developed to perform well in its expected operating environment, the manufacturer may want to go a step further and develop a prototype of the molded rubber part for further testing, including design for manufacturability and assembly.
For manufacturers now serving global markets, developing a new product that can perform in any climate is critical. Therefore, development vehicles and their various parts undergo a barrage of tests, including extreme temperature testing.
According to the Alliance of Automobile Manufacturers, “Automakers have built high-tech test chambers so engineers can evaluate products in different environments, ranging from -40 degrees to 130 degrees.” The Alliance explains, “An auto needs to withstand years of tough duty, so researchers keep studying how to extend a vehicle’s life … It takes 84,000 open-and-close cycles to simulate 10 years of customer use of a car door. This testing happens in a wide range of temperatures, just like real life.”
Materials Quality Tests
Once the custom rubber compound has been developed and approved, the rubber molding firm will provide appropriate testing to industry standards to ensure quality. These tests may be done in-house or through independent labs, using ASTM, sampling and material batch testing methods to ensure consistent quality.
For more information on rubber materials and their ability to perform under harsh conditions, including a chart of temperature and oil resistance for commonly used elastomers, download our complimentary e-book: The Use of Implantable Silicone in Medical Devices.