Many of the most challenging sealing applications require a heavy-duty gasket that can perform exceptionally well in the harshest of conditions. Such applications often call for gaskets made from a family of fluoroelastomers called FKM. While Viton® is the generic name for FKM, it actually is a brand name of DuPont for its synthetic rubber and fluoropolymer elastomer.
What Exactly is FKM?
The FKM family of elastomers consist of copolymers or terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP), hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2) and perfluoromethylvinylether (PMVE). Since DuPont was the first company to really market this material, its brand name Viton® has become the most commonly associated name with FKM.
Majority of synthetic rubbers are composed of long chains of carbon and hydrogen atoms. These rubbers are prone to swelling upon exposure to oil and have a limited temperature range. What’s more, they break down over time with UV exposure (through sunlight).
When fluorine is added to synthetic rubbers, it bonds tightly to the carbon atoms and makes the compound more resistant to other compounds while providing tremendous flexibility. This changes the properties of the material and makes FKM the high-performance rubber compound that is crucial to many applications.
FKM is known for excellent resistance to heat, chemicals, concentrated acids, oils, and aggressive fuels.
Material Grades for Viton® Gaskets
On the basis of material composition and applications, FKM comes in a number of different material grades. Some of these are:
General Use Grades:
Viton® A dipolymers are polymerized from two monomers – vinylidene fluoride (VF2) and hexafluoropropylene (HFP). It is the most widely used Viton® gasket material and has applications as rubber seals for aerospace and automotive lubricants and fuels.
Viton® B is a terpolymer, i.e. polymerized from three monomers – vinylidene (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). This material is primarily used in chemical processing, power industries, and utilities.
Viton® F is also a terpolymer, polymerized from three monomers – vinyl fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). F types offer the best fluid resistance out of all other Viton® types. They are extremely useful in applications that require resistance to fuel permeation.
Viton® GB and GBL
Viton GB and GBL are fluoroelastomer terpolymers that are polymerized from three monomers – vinyl fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). These fluoroelastomers use peroxide cure chemistry that leads to a superior resistance to acid, steam, and aggressive engine oils.
This fluoroelastomer is specially designed to retain the high heat and chemical resistance properties of general use Viton® grades while improving the low-temperature flexibility. Also, Viton® GLT offers an 8 to 12°C lower glass transition temperature, which is indicative of low-temperature performance in elastomer applications.
Key Properties of a Viton® Gasket
When it comes to gasket materials, good compression set resistance or the ability to spring back after the load is taken off is needed. Other desirable properties include a wide temperature range and good chemical resistance. FKM offers exceptional performance in all these regards.
FKM is graded as ‘HK’ as per the ASTM D2000 standard for classifying elastomers. Here, H indicates that the performance of an FKM Gasket deteriorates very little after prolonged exposure to temperatures of 250°C (480°F). FKM also works well in low-temperature conditions going as low as -40°C (-40°F).
Whereas, the K indicates the resistance to swelling. Since K is the lowest possible rating, it means that FKM swells less than almost all other elastomeric materials. FKM is also highly resistant to chemicals and can withstand ozone, typical automotive fuels, and hydrocarbon lubricating oils. However, FKM doesn’t give as great results against strong acids, alkalis, and ketones.
Applications of Viton® for Rubber Gaskets
Viton® gaskets were first used in the aerospace industry owing to their fuel resistance and low burning characteristics. Now, their application can be found in fluid power, automotive, appliance, and chemical industries. Moreover, with the introduction of FDA grades, the uses of FKM have been extended to the food processing and pharmaceutical industries as well.
Viton® Gaskets are highly recommended for harsh, high-temperature environments. They are often used with lubricating and fuel oils, gasoline, vegetable oils, alcohols, diluted acids, hydraulic oil, and kerosene because of their chemical resistance. In addition, Viton® applications can also be found in fuel seals, cap seals, T-seals, and radial lip seals in pumps. FKM gaskets also offer superior UV resistance that makes them a great choice in applications where prolonged sunlight exposure is expected.
We hope that you found this information useful. If you’re looking for FKM or Viton® gaskets for your application, Harkesh Rubber manufactures top-of-the-line products to fulfil your sealing needs. In fact, we can produce low-temperature FKM gaskets that can withstand up to -50°C! Simply contact us for your Viton® gaskets needs.