Gasket Compression in Metal Housings and Assemblies

Gasket CompressionGasket compression in metal housings and assemblies can support sealing or contribute to gasket failure. That’s because rubber gaskets are resilient, but only to a point. Compressing a gasket within allowable limits forms a reliable seal. When a gasket is over-compressed, however, the rubber won’t rebound when the compressive stresses are removed. This creates a gap between the gasket and the surface of the housing or assembly. Gaps cause leaks, and seals that leak won’t support your designs.

Material scientists calls the permanent deformation of the gasket material “compression set”, a term that’s used widely but not always fully understood. Engineers need to know the basics of compression set, but they also need to consider its limitations as a test method. With housings and assemblies, it’s essential to account for the entire application environment, including variables such as temperature and vibration. Relaxation, a related phenomenon, is also associated with gasket compression. (more…)

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Nitrile Rubber for Sealing and Insulation

Nitrile RubberWhen is nitrile rubber the right choice for sealing and insulation? This common elastomer is known by many names, including Buna-N, NBR, and acrylonitrile butadiene. There are plenty of trade names for nitrile, too. No matter what you call it, nitrile rubber offers good resistance to oils, fuels, and chemicals. Temperature and environmental conditions are limiting factors, however, and may require the selection of a more expensive material such as Viton™.

In this article from Elasto Proxy, you’ll learn about nitrile’s advantages and disadvantages. You’ll also examine NBR compounds, compare commercial and specialty Buna-N, and consider some typical nitrile applications. Elasto Proxy supplies specialty nitrile products to a variety of industries and can create a custom sealing solution that meets your specific requirements. Nitrile isn’t the only oil-resistant elastomer, but it’s a cost-effective choice compared to some other compounds.

Nitrile Advantages and Disadvantages

Nitrile rubber provides good-to-excellent resistance to many oils and solvents. Examples include:

  • animal and vegetable oils
  • crude petroleum oil
  • kerosene and gasoline
  • liquified petroleum (LP) gases
  • motor oils
  • mineral oil based hydraulic fluids
  • silicone greases and oils

For engineers and buyers, it’s important to understand that nitrile’s resistance to petroleum oils is limited by temperature. According to most chemical resistance charts, nitrile resists petroleum oil at temperatures up to 250° F (121° C). If your application requires both oil resistance and higher temperature resistance, a fluorocarbon such as Viton™ may be required instead. Nitrile is also unsuitable for highly polar solvents such as acetone, which is used in some food processing and medical applications.

Nitrile’s advantages include good physical properties such as resistance to compression set, tearing, and abrasion. Typically, NBR or Buna-N comes in durometers (Shore A) ranging from 20 to 95 for applications that require a softer or harder rubber. Nitrile resists water, but provides poor resistance to weather, ozone, and aging. Acrylonitrile butadiene is also unsuitable for some applications because Buna-N won’t withstand temperatures that are colder than -40° F (-40° C).

Nitrile Compounds and Specialty Grades

Through compounding, material suppliers have developed different types of nitrile with enhanced material properties. For example, hydrogenated nitrile butadiene rubber (HNBR) can withstand slightly higher temperatures than NBR and provides improved resistance to polar fluids. Carboxylated nitrile butadiene rubber (XNBR) has a higher compression set than Buna-N and offers improved tear and abrasion resistance. Nitrile can also be blended with polymers such as polyvinyl chloride (PVC).

For engineers and buyers, choosing the right type of nitrile may involve comparing commercial rubber to specialty grades. Commercial grades generally cost less and are available in higher minimum order quantities (MOQs). Specialty grades generally cost more and have larger MOQs, but they’re custom compounds with improved properties. ASTM D2000 provides a standard way to describe elastomers and uses the designations BF, BG, BK, and CH with both standard and specialty nitrile. (more…)

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Commercial Grade Rubber vs. Specialty Rubber: Make the Right Choice

Commercial Grade RubberCommercial grade rubber provides sealing and insulation for a wide variety of applications. Compounds such as commercial grade EPDM, silicone, and neoprene also cost less than specialty rubber materials that meet standards, approvals, or regulatory requirements from organizations such as ASTM International, Underwriters Laboratories (UL), and the U.S. Food and Drug Administration (FDA).

For engineers, choosing the right rubber means understanding when a specialty material is required, and when a commercial grade rubber is sufficient. Engineers want to make sure that the products they design meet application requirements, but over-specifying an elastomer can incur unnecessary costs. In addition to paying more per unit of material, you may have to buy greater minimum order quantities (MOQs).

In this article from Elasto Proxy, we’ll consider the differences between commercial grade rubber and specialty rubber in terms of some real-world examples. You’ll also learn about some best practices that can strengthen your seal designs. (more…)

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EPDM Rubber for Sealing and Insulation

EPDM Rubber

When is EPDM rubber the right choice for sealing and insulation? EPDM seals and gaskets are used widely with vehicles and equipment, but this synthetic elastomer has unsatisfactory resistance to gasoline, diesel fuel, and motor oil. EPDM’s advantages are numerous, however, and this cost-effective compound is often a better choice than silicones – especially in outdoor environments.

If you’re wondering whether EPDM is the right choice for your sealing and insulation application, Elasto Proxy invites you to take a closer look at this M-class elastomer. The M in M-class indicates that EPDM is part of ASTM D1418, a common specification for characterizing rubber compounds. Often, design or product engineers use ASTM specs to designate the rubber material on a part drawing.

In this article, we’ll examine EPDM’s advantages and applications. We’ll also consider its disadvantages – and consider how EPDM rubber compares to some other materials. Finally, we’ll look at how EPDM is supplied and fabricated. (more…)

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