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    O-Ring Properties

    O Ring Modulus Properties

    O Ring Permeability Properties

    O-ring Modulus is an indication of the toughness and resistance to extrusion of a compound. High modulus usually indicates a tougher, harder compound. Modulus is normally expressed as tensile strength at 100% elongation.

    In addition, Modulus is useful for quality control purposes.

    Gases diffuse into and through o-ring elastomer compounds, depending on the denseness of the base polymer molecule, the amount of fillers used, and the state of the cure.

    Generally, harder compounds which have more carbon black added have lower diffusion rates. Of the most popular compounds, Butyl has the lowest permeability, followed by Fluorocarbons.

    Fluorosilicone and silicones have such high rates of permeability that they should not be used to seal gases, particularly at high temperatures and pressures.

    For any given O-Ring, regardless of compound, the permeability depends on the amount of compression or squeeze, the area of the seal, and the pressure, temperature, and molecular weight of the gas being sealed.

    Low Temperature Resistance

    High Temperature Resistance

    Low Temperature combined with low operating pressure is hard for an o-ring to seal. A soft compound should be used to provide as much resilience as possible. The softer the compound the lower the load required to maintain a seal.

    At low temperatures, some compounds may exhibit changes in physical properties, however, they are not permanent. Unlike high temperature affects, low temperature changes can be reversed once the compound is warmed up.

    Neoprene, for example, crystalizes at low temperatures, loses its resilience, and flattens. But when heated above the crystallization temperature, it regains its physical properties again.

    In applications below -65 degrees Fahrenheit, soft silicone should be used. Compounds of other polymers are simply too stiff for colder temperatures, particularly for oil and gas.

    When it comes to o-rings, the higher the operating temperature, the more compounds can soften, depending on the compound.

    Every compound has a limit for maximum service temperature. The closer the compound gets to its vulcanization temperature, the more likely it is to crack, or lose resilience, and harden when cooled. Resulting in leakage.

    When considering a high temperature application, its important to ensure the compound’s temperature compatibility. As a material warms and softens it must maintain enough hardness to resist extrusion at service temperature.

    Tear Strength / Resistance

    O Ring Hardness

    Tear strength is another indicator of the toughness of a compound. Tear strength measures the force required to perpetuate a nick or cut in the material.

    Materials exhibiting poor tear resistance are not usually recommended for dynamic applications such as in mechanical seals. Tear resistance is less of a factor in static applications where no movement is involved to exacerbate a nick or tear caused during installation.

    Hardness of elastomer o-ring materials is determined using an industry standard instrument called the Shore A durometer.

    The lower the hardness of the material, the less force required for it to effect a seal, it will stretch easier, and can seal rough surfaces with lower compressive loads.

    The higher the hardness, the more force required for sealing, leakage chances are greater, and breakage is more common. On the positive side, there is less of a chance for extrusion.

    Whether the amount of hardness required is important or not is up to the type of application.

    O Ring - Tensile Strength

    O Ring Compression Set

    Tensile strength is used to measure an o-rings material’s resistance to breakage when stretched. Essentially, how much force does it require to break a specimen at ultimate elongation? Tensile strength is not usually considered an important factor in o-ring designs if the compound has over 1000 PSI. Regarding O-Rings, this property is mostly useful for quality control purposes. It proves as a good test for the quality of the nitrile compound.

    An o-rings Compression set is a very important sealing factor. It’s not uncommon for an o-ring to harden over time and hold a compressed shape. A good example of this is when you remove an o-ring that has been in service and it is square but started out round. This happens as an o-ring ages, or when it has been heated over time drying out the plasticizers .

    Simply put, Compression set is a measurement of the expected loss of resiliency or “memory” of a compound. Compression set is calculated as the ratio of non-recovered thickness, expressed as a percent, after the material has been compressed and heated for a certain amount of time.

    O Ring - Ultimate Elongation

    Volume , Swelling, Shrinkage

    Ultimate elongation is the percent increase in length at the breaking point over the original length. It is useful for knowing how much O-Rings of various cross-sections and compounds can be stretched without breaking in installation.

    In addition, elongation can also be useful for quality control purposes. O-rings that break prematurely are indicative of an excess of filler in the compound.

    When an o-ring elastomer compound is immersed in fluid, normally it tends to absorb the fluid, and the accompanying increase in volume modifies the hardness, resilience, and wear resistance. This is acceptable if there is no chemical attack, and excessive dimensional changes does not produce erosion of physical properties.

    Swelling happens when fluids are absorbed and has the same effect of adding plasticizers. This can make the seal more flexible at low temperatures if the fluid has good low temperature properties.

    Shrinkage happens when volatile fluids extract the plasticizers from the material. Evaporation or dryout during idle time periods and low temperature contraction can also cause shrinkage. Shrinkage can cause applications to leak due to loss of volume or when the seal loses squeeze.

     

    How an O-Ring FunctionsGland dimension designs:
    Aflas O-Rings

    Aflas O-Rings

    Aflas® material is an elastomeric based flouorubber

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    Neoprene O-Rings

    Neoprene O-Rings

    Neoprene is a family of synthetic rubbers

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    Viton O-rings

    Viton O-rings

    Viton® (FKM) is the most specified fluoroelastomer

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    American & Metric O-RINGS in a wide range of materials and sizes

  • O-Ring and Industrial Oring Kits
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    O-Ring materials include: Nitrile, Buna-N, Viton® Orings (Black), Viton® O-rings (Brown), Aflas®, Silicone, PTFE, molded PTFEo-rings, , PTFE encapsulated, Viton® o-rings, EPDM, Neoprene, Silicone o-ring, 4 Lobe Q-Rings, E.P.R., Kalrez. Sizes Range From: 1/32" to 26" I.D.

     
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    Aflas O-rings

    Aflas O-rings

     

    O-rings made of Aflas are generally utillized in chemical and high temperature applications.Aflas® material is an elastomeric based..

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    BUNA O-RINGS

    Buna O-rings

     

    Buna O-rings are the most common o-rings on the market. Ideal for water or hydrocarbons (Oil & Gas), they area staple in the industry.

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    EPDM O-Rings

    EPDM O-rings

     

    EPDM O-rings are a lower cost o-ring that performs well in a number of applications. EPDM is used to seal car windows,..

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    O-Ring Kits

    O-Ring Kits

     

    The most common AS-568 American standard sizes are contained in this o-ring kit. 27/ 30 / 32 different sizes Kits are availble.

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