There are a lot of precise design elements that go into crafting rubber o-rings and seals. Regardless of any critical design factors, rubber seals must be compatible with their surrounding environment in order to function properly. If an o-ring is not compatible with its environment, it will eventually fail.
An important first step in seal design is to ensure environmental compatibility, which consists of multiple factors including chemical contact, temperature, pressure and friction. In order to make an informed decision on material selection and important design elements, this is what you need to know about environmental factors.
Materials must be chemically compatible.
Not all rubber materials are the same. In fact, each type of rubber has a different chemical makeup that is made to function under specific conditions. Many types of rubber are not compatible with certain chemicals that may be used in a sealing application. For example, silicone does not function well when exposed to butane, and butyl does not respond well to propane. Therefore, these materials should not be used in applications involving these chemicals.
It is important to research materials before the seal design process to ensure you are making the right choice for your application. Apple Rubber offers a Chemical Compatibility Guide, which lists out each rubber material and rates how compatible they are to various chemicals. This guide is an extremely helpful tool for the material selection process.
Extreme heat or cold can largely affect rubber compounds.
Certain rubber materials have better resistance to temperature than others. This is an important factor to be aware of during material selection to ensure the right type of rubber is chosen for the application. There are a variety of different tests that can be done to detect the temperature properties of a specific rubber compound, including brittleness, temperature retraction and torsional stiffness ratio.
For example, some forms of rubber can handle colder temperatures, while others may lose flexibility and crack. Certain elastomers will harden and resist deformation pressure when exposed to low-temperature limits, causing leak paths to form. Alternatively, some rubber compounds cannot withstand high temperatures and will fail after extended exposure. To check the temperature resistance of specific rubber materials, visit Apple Rubber’s O-Ring Material Selection Guide.
Look out for the impact of pressure.
When pressure is introduced to a rubber seal, the o-ring will naturally shift to the low-pressure side of the gland. This will cause the cross-section of the o-ring to distort and block the diametrical clearance gap between mating surfaces. If too much pressure is introduced and the seal cannot resist, part of the seal may be extruded into the diametrical gap, leading to premature failure, leakage and system contamination.
Every o-ring is designed to operate under specific ranges of pressure. This is important to note during the seal design process. To prevent o-ring extrusion, some engineers will increase the o-ring hardness, use backup o-rings to block the diametrical gap, reduce the diametrical gap clearance or lower the system pressure. These prevention methods could potentially save your seal from failure.
Friction is a critical operational factor.
Friction is an important factor to consider in moving applications. In some operations, friction can cause excessively high hydraulic pressure to develop, potentially tearing portions of the rubber seal that adhere to the gland wall. In addition to hydraulic pressure, running friction should also be considered. In continuously moving applications, running friction can generate heat, causing the o-ring to swell. If an o-ring experiences too much swelling, it will ultimately fail.
Some methods that are commonly used to control friction include increasing or decreasing the seal’s hardness, using a smaller cross-section, lubrication, compound additives, decreasing pressure and ensuring proper material selection. In order to effectively combat friction, it’s important to take into account the limits of the rubber to ensure the right seal is used for the application.
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