What Is a Viton Material?
Viton is a proprietary elastomer designed on a fluorocarbon base by DuPont, now Chemours, in the 1950s. It is a specialized synthetic rubber that is meant for high-temperature applications. Viton is a trademarked name, and the scientific name for this unique rubber is Fluoroelastomer, shortened to FKM.
As the rubber is designed for high-temperature applications, Viton seals and o-rings are an excellent fit for car engines and other heavy machinery.
What Is a Buna Elastomer?
Buna is a butadiene-based synthetic rubber invented by a pair of German chemists in 1934. It is a low-cost rubber solution with exceptionally high tensile strength and decent chemical resistance. Buna rubber is commonly used in producing seals, O-rings, and silicone gloves.
Buna rubber comes in two variations based on its ingredients. Buna with an acrylonitrile group is called Buna-N or NBR (Acrylonitrile Butadiene), while one with a styrene group is called Buna-S or SBR (Styrene Butadiene).
What Is the Difference between Viton and Buna O-rings?
Viton and Buna are two very different rubber compounds invented for different applications. For easier understanding, we can simplify the differences between the two rubbers. Buna is stronger and stretchier, while Viton is heat resistant. Following is a breakdown of other differences between the two materials. Let’s take a look together!
Mechanical & Physical Properties
A rubber’s mechanical and physical properties determine its strength, stretchiness, tear resistance, and resilience, the ability to bounce back to its original shape. Here is a list of common mechanical properties that affect the overall performance of both Buna and Viton o-rings.
| Mechanical & Physical Properties | Viton (FKM) | Buna (NBR) |
| Hardness | 50-95 Shore A | 20-95 Shore A |
| Tensile Strength | 500-2000 Psi | 200-3500 Psi |
| Elongation | 400-500% | 350-650% |
| Abrasion Resistance | Good | Great |
| Compression Set | Great | Great |
| Impact Resistance | Good | Fair |
| Resilience | Poor | Good |
| Tear Resistance | Good | Great |
| Vibration Dampening | Fair | Fair |
As we can see, Buna and Viton are similar in terms of physical properties. Both materials have excellent resistance of compression set and a good shore hardness range. However, Buna can withstand more tensile stress and has better abrasion and tear resistance.
Buna rubber offers reliable strength and cost-efficiency, making it suitable for a wide range of applications. It is commonly used in cookware, smartphones, and construction parts. Buna o-rings deliver dependable performance at a lower price. For most standard applications, Buna is more practical than higher-cost alternatives such as Viton.
Thermal Properties
Rubber compounds often melt under high temperatures and become brittle in colder environments. These temperature restrictions limit the sealing applications of rubber o-rings significantly.
Regarding rubber temperature resistance, we separately measure the operating temperature for high and low temperatures. The following is a Viton temperature chart comparing it directly to the Buna-N temperature range.
| Temperature Properties | Viton (FKM) | Buna (NBR) |
| Cold Resistance | -30º to 0º F | -70º to 0º F |
| Heat Resistance | 450º to 500º F | 210º to 250º F |
The difference in temperature resistance is to be expected as Viton seals are specially designed for engine blocks. Viton has better heat resistance, while Buna has better cold resistance.
It should be noted that for colder locations like Iceland or Alaska, the low-temperature resistance of Buna will be more helpful. The Viton seal temperature range is much more comprehensive, making it a better option for high-performance industrial applications.
Environmental Resistance
Environmental resistance refers to material protection from natural elements like ozone, water, or UV exposure. Good environmental resistance is necessary for the longevity of an O-ring.
| Environmental Resistance | Viton (FKM) | Buna (NBR) |
| Colorability | Great | Excellent |
| Flame | Great | Poor |
| Gas Permeability | Great | Good |
| Ozone | Excellent | Fair |
| Sunlight | Great | Good |
| Water | Excellent | Great |
Here we see that the environmental resistance of Viton is miles ahead of Buna. Buna seals and o-rings can only withstand short-term exposure to water and sunlight. In contrast, Viton products can be deployed in outdoor applications without fear of environmental damage.
Chemical Resistance
All synthetic and natural rubber compounds are very susceptible to chemical damage. Rubbers in high-performance applications often run into harsh chemical liquids and gases.
These chemicals can quickly dissolve and corrode rubber seals and O-rings. So, for deployment in large industrial spaces and hazardous environments, you need a type of rubber material with excellent resistance to all chemicals.
| Chemical Resistance | Viton (FKM) | Buna (NBR) |
| Acids | Great | Fair |
| Alkalies | Fair | Good |
| Amines | Poor | Poor |
| Vegetable Oils | Excellent | Great |
| Fuels | Excellent | Good |
| Ketones | Poor | Poor |
| Petroleum | Excellent | Good |
| Refrigerant | Great | Great |
| Silicone Oil | Excellent | Good |
| Solvents | Excellent | Great |
Buna rubber has better chemical resistance than most commonly used elastomers. But compared to Viton with excellent resistance to petroleum-based lubricants, mineral acids, silicone greases, and other solvents, Buna rubber fails.
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How Can You Tell If an O-ring Is Made from Viton or Buna?
All synthetic rubbers look very similar, and with the addition of colors, you cannot tell them apart quickly. However, you can use a few methods to tell if an o-ring is made from Viton or Buna rubber.
1. Un-colored Rubber Appearance
Pure, uncolored Viton o-rings have a greenish-brown hue. In comparison, uncolored Buna-N o-rings have a slight yellow hue.
Uncolored here means that no artificial coloring agents were used to change the color of the rubber. However, most commercially available O-rings will be colored black for better aesthetics.
2. Elongation Capabilities
Buna-N can be stretched much further than Viton before breaking. A standard Buna-N o-ring will be almost twice as stretchy as a Viton one under standard operating conditions.
3. Reaction to High Heat
Another way to tell apart two o-rings is to place a small piece of them in a 300º-350ºF oven. If the rubber pieces melt within a minute, it is made of Buna. Otherwise, it’s Viton.
One important thing to consider here is that other synthetic rubbers like silicone and fluoro silicone, can also withstand high temperatures.
4. Submersion in a Harsh Chemical
If all else fails, you can submerge the O-ring in harsh chemicals to check its resistance. If the o-ring is dissolved in a halogenated solvent, it is made of Buna. If it dissolves in refrigerant ammonia, then it is made of Viton.
Viton vs. Buna: Which Is Better for O-rings?
All o-rings have a best-suited application and a worst-suited application. So the difference between rubber o-rings should be seen as a relative assessment.
When Should You Use Viton O-rings?
Viton o-rings are better for the automotive and fuel refining industries. The higher oil resistance helps them in fuel industries, where they will be constantly exposed to petroleum-based oils, gasoline, and hydraulic fluids.
While the resistance to higher temperatures helps it in extreme environments like engine blocks, Viton is also quite expensive and should be reserved for high-performance applications.
EPDM is a weaker version of Viton. It cannot compete with Viton’s chemical compatibility and thermal performance. But in rare conditions, EPDM can outperform Viton rubber, specifically when exposed to alcohols, ketones, and concentrated acids.
When Should You Use Buna O-rings?
Buna seals and o-rings are very resilient and can withstand moderate temperature applications. So they can be used in most applications under reasonable operating conditions. But the best application for Buna O-rings might be heavy-duty industrial applications, which can take full advantage of its superior strength.
The lower cost of Buna makes it a better option for low-cost applications like domestic appliances.
Buna-N vs. Silicone
| Property | Buna-N (Nitrile) | Silicone |
|---|---|---|
| Oil Resistance | Good | Poor |
| Fuel Resistance | Good | Poor |
| Temperature Range | -40 to 120°C (-40 to 248°F) | -55 to 230°C (-67 to 446°F) |
| Weathering | Poor | Excellent |
| Ozone Resistance | Poor | Excellent |
| UV Resistance | Poor | Excellent |
| Abrasion Resistance | Good | Poor |
| Tensile Strength | Good | Fair |
| Acid Resistance | Fair to Poor | Fair to Good |
| Alkali Resistance | Good | Good |
| Electrical Insulating Properties | Poor | Excellent |
Silicone is a more robust rubber material with better stretchiness and environmental resistance. But it lacks Buna-N’s chemical compatibility. Buna-N can be used to replace silicone o-rings for higher performance.
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Conclusion
In summary, Viton O-rings and Buna O-rings are both commonly used as seals in various applications. Viton excels in extreme heat and harsh chemicals, ideal for automotive or industrial seals. Buna has superior tensile strength and cold resistance at a lower cost, suitable for general-purpose use.
Both materials have their own pros and cons, and the best option must be chosen based on the specific needs of the task at hand.
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FAQs
Q1: What is the main difference between Viton and Buna O-rings?
Viton (FKM) and Buna (NBR) are suitable for different applications. Viton is a specialized, high-performance synthetic rubber known for its superior heat and chemical resistance. Buna is lower-cost, and it has excellent tensile strength, stretchiness, and abrasion resistance.
Q2: Which material is better for extreme temperatures?
Viton has superior heat resistance, with an operating range of 450º to 500º F, making it ideal for engine blocks. In contrast, Buna offers better cold resistance, with an operating range down to -70º F, making it more suitable for colder climates.
Q3: Which O-ring is better for exposure to chemicals and fuels?
Viton is generally much better. While Buna has decent chemical resistance, Viton has excellent resistance to petroleum-based lubricants, fuels, mineral acids, and solvents, making it a better choice for the automotive and fuel industries.
