Viton Gaskets

Gasoline, diesel and hydraulic oil are some of the hardest fluids to seal against. They make most gasket materials swell, which increases pressure on the joint and leads to gasket failure. Nitrile rubber is one of the rare exceptions but its upper temperature limit is around 200⁰F. If you’re concerned that nitrile won’t be up to the job it’s time to move to Viton washers.

Viton™, FKM and FPM

The first thing to know about Viton is that it’s a trademark, (originally held by DuPont and now their spinoff, Chemours.) The technical term for this type of elastomer is a fluoroelastomer. In lay terms, it’s a synthetic rubber composed mostly of carbon and fluorine. In Europe fluoroelastomers are designated as FPM while here in the US we use the ASTM abbreviation of FKM. Whichever term you use, they’re essentially the same thing.

Properties of Viton and Other Fluoroelastomers

Viton and other fluoroelastomers are more expensive than almost any other gasket material, but three characteristics make them the preferred solution for the toughest sealing challenges:

1. Excellent resistance to oil-induced swelling
2. Highly resistant to most chemicals
3. High-temperature strength (Viton goes to 400⁰F (204⁰C) and higher)

In addition, Viton has good UV and ozone resistance. Other points to note are that, while sufficient for most applications, tensile strength and resilience or elasticity are not high. Also, Viton is incompatible with acetone and many organic acids.

Applications for Viton Washers

High cost means Viton is reserved for difficult applications. Sealing pipes and fittings in fuel and hydraulic oil systems is a good example. Viton washers are a cost-effective way of minimizing the risk of potentially hazardous leaks and costly downtime in these situations. Likewise, it’s often the smart choice in systems handling corrosive chemicals where leaks must be prevented at all costs.

Viton Washers and Gaskets From Hennig

Viton comes in sheet form and a number of grades. We can water jet, flash or die cut the size and shape you need. Our specialists can help you decide what’s right for your application. Call (312) 243-8270 or 1-800-747-7661 or contact us.

Viton is a DuPont trade name for one of the more exotic gasket materials. It’s actually a form of synthetic rubber known as a fluoroelastomer and referred to in ASTM D1418 terminology as “FKM”. Whether FKM or Viton, gaskets made from this material have an impressive range of properties. It’s downside is that the material itself is expensive. That’s why custom Viton gaskets are held in reserve for the most challenging sealing applications.

Chemistry Lesson

Most synthetic rubbers, like SBR, are composed of long chains of carbon and hydrogen atoms. These have a limited temperature range and tend to swell when exposed to oils. They also break down slowly when exposed to UV, as is found in sunlight.

Adding fluorine dramatically changes these properties. Bonding tightly to the carbon atoms, the fluorine prevents other compounds from breaking down the chains, but still provides excellent flexibility.

Key Properties

Gasket materials need good compression set resistance, (the ability to spring back or recover when a load is taken off,) a wide temperature range, and good chemical resistance. FKM performs exceptionally well in regard to all of these.

The ASTM D2000 standard for classifying elastomers grades FKM as HK. The “H” indicates it’s performance deteriorates only slightly after prolonged exposure to temperatures of 250°C (480°F), (and it still functions at 300°C (570°F).) At the other end of the temperature scale, FKM can still provide effective sealing at -40°C (-40°F).

The “K” in the ASTM grade describes resistance to swelling. “K” is the lowest possible rating, meaning FKM swells less than almost any other elastomeric material. (For comparison, SBR is typically graded as “AA”.)

As regards other aspects of chemical resistance, FKM withstands ozone, hydrocarbon lubricating oils and typical automotive fuels. Where it performs less well is against strong acids, alkalies and ketones.

Good Applications for FKM

FKM is used extensively in the aerospace industry, to an extent in automotive applications, and more prosaically, around freezer doors. It’s UV resistance also makes it good choice in situations of prolonged exposure to sunlight.

One consideration when comparing FKM gaskets with less costly alternatives is the cost of gasket replacement. As FKM holds up so much better to harsh conditions it often lasts several times longer than other gasket materials. Thus FKM can pay for itself by reducing maintenance costs.

Choices

The names Viton and FKM both describe a family of fluoroelastomers, rather than just one material. There are variations in properties between the different grades. Before ordering Viton gasket material consult a product specialist to determine which grade might be most appropriate for your application.