Standard Test Methods for Rubber O-Rings

 

Theory:

ASTM D1414 is used to test gaskets, seals and valves that are made with a Rubber O-Ring.  This simple circular elastomer design is interesting since O-rings are used in so many sealing applications. The versatility of an O-ring allows it to function in multiple modalities. Static rubber rings are used for gas sealing and specialized applications including vacuums.

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Rubber bands are also commonly tested under this standard to test their tensile strength and elongation characteristics.

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Rings under tension in high temperature environments can experience something called the Gough-Joule effect where they tend to contract in this scenario. Alongside Gough-Joule, quality managers may age their rubber specimens inside an environmental conditioning chamber to test other parameters. Cracking, flaking, general brittleness, and other characteristics can appear in the rubber O-rings when they are exposed to temperature cycles and solar radiation. 

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Top top grip has a counterweight to allow for even loading.

Solution:

The Rubber O-Ring test standard uses a special motorized fixture that rotates at fixed speed throughout the test. The speed is adjustable from 4-17 RPM and the fixture takes 220V (20W) power with a seperate power cable (included). The rotation keeps localized stress moments on the sample to a minimum. These materials tend to elongate extensively so attention must be made to the total stroke of the tensile tester. 

 

There is also another test that does not require the motorized fixture. If your O-ring specimens fall within the allowed criteria, they can be tested with a static fixture. In some cases, a special type of oil may be used to alleviate friction between the ID of the O-ring and the grip surface.

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The fixture ships complete with a power adapter for both US and International power outlets. A green LED light is located in the back to show that the motor is on and working.  The fixture attaches to the universal testing machine by means of a female 5/8 clevis coupling with a 5/16" locking pin. 

 

O-ring Roller Sizes:

The fixture can use interchangeable rollers at different sizes. The standard sizes that Universal Grip carries are 3.18, 4.5, 4.75, 6.35, 12.7, 15, 18.3, 22.3, and 25mm. 

 

Analysis:

Elongation and tensile strength are the two main calculations. Some advanced calculations including elongation modulus can also be derived from the data. It is recommended that groups of samples are tested and the data is compared using a method similar to Statistical Process Control.