Gearbox seal: FKM or NBR - Apex Dynamics

May. 13, 2024

Gearbox seal: FKM or NBR - Apex Dynamics

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Gearbox seal: FKM or NBR ?

How self-evident is the correct sealing of a gearbox? A standard rubber seal is used in many gearboxes. But these seals often do not fulfill the requirements of a gearboxes due to the high speeds, dynamics and duty cycle of the application. And what if an application is placed in a special environment? Or when it is a special application?

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In this article we discuss the characteristics and properties of High-end sealing materials and the questions that you might ask yourself before you make a choice.

Gearbox sealing material

To keep the lubricant inside and contamination outside of our gearboxes, Apex Dynamics is using seals for its gearboxes. The seals on the input and output side of the gearbox of Apex Dynamics are vulcanized around a steel support, so that the seal is form-retained and can always be found with a metal detector. Depending on the application, two high-quality materials are used as standard: FKM and NBR.

Viton® / FKM seal

Viton® is the trade name of this type of elastomer from inventor Dupont. But in practice we also call it Fluorocarbon or FKM. In this article we will use the name FKM.

NBR seal

NBR is also called Nitrile or Nitrile rubber and stands for Nitrile Butadiene Rubber. If it is hydrogenated, it becomes HNBR (Hydrogenated Nitrile Butadiene Rubber).

FKM and NBR are two commonly used elastomers for high-end sealing applications, and not without reason. Both materials are suitable for a wide range of applications. They offer excellent compression resistance and both are resistant to most oils and lubricants, especially petroleum-based lubricants. In addition, applications with moderate temperatures between -15° C and 110° C are suitable for both types, making both materials a very good choice for heavy industrial use.

Which seal is optimal for your application?

Due to the wide range of available materials it is sometimes difficult to determine which seal is most suitable for your project. In many cases, a fairly simple assessment of the elasticity or tear resistance that your application requires is sufficient, but sometimes it is crucial to pay more attention to the choice of materials.

Important circumstances to consider are:

Temperature of your application/environment
Chemical resistance

Temperature of your application/environment

Standard FKM connections can continuously seal at temperatures up to approximately 205° C. Standard NBR, on the other hand, is only effective for continuous sealing at temperatures up to 110° C. But at temperatures below -20° C, standard FKM seals are again less effective because they become relatively hard and inflexible. Special FKM joints can offer low temperature capacities of -40° C, but standard NBR works successfully at -35° C and even up to -55° C with a special composition.

Chemical resistance

FKM has a wide range of chemical resistance, making it ideal for most applications with oils, fuels and mineral acids. FKM also offers excellent resistance to oxidation, ozone, exposure to UV radiation, weather and fungi. Although NBR also supports some of the same chemical resistances, it is much less universally resistant than its FKM counterpart, and is affected by weather and ozone exposure. But NBR has superior wear and tear resistance and is therefore better suited for heavier, industrial applications.

Choice of sealing material

In short, consider the following conditions to get a good idea of which sealing material fits the best your application:

Fabrics in process and environment
Required tear and abrasion resistance
Temperature
Chemical resistance
Lifespan

Do you have a specific question about a seal? Then contact Eastern Seals. Do you have a specific question about a gearbox? Then contact Apex Dynamics.

Fluoroelastomer (FKM / Viton™) vs Nitrile (NBR / Buna-N)

Updated: November 2023

FKM (Viton™) and Nitrile (NBR) are two of the most used elastomers for sealing applications. These materials are suited for all-purpose general use applications. They both offer key properties that allow for great flexibility for different tasks throughout the industry. They both offer excellent compression set resistance, great oil and petroleum resistance, and both can work in temperatures between 0-230ºF, which makes both excellent choices for general industrial use.

Because of the wide range of other materials available, selecting the best O-ring for your application can be a daunting task. It is important to understand the key differences hidden behind the similarities of these materials to avoid premature breaking.

Fluoroelastomer / Fluorocarbon (FMK / Viton™)

Fluoroelastomer rubber (Viton) performs well in many different environments such as a variety of oil and petroleum products, high vacuum situations, ozone, weather, high temperatures, and strong acids. This material is commonly used to seal leaks, valves, or pumps within the aircraft or automotive industries but can extend well beyond that.

FKM has an outstanding resistance to heat, reaching sustained temperatures of 400ºF or even higher for shorter periods of time. Since most compounds can fail in extreme high temperature environments, FKM is an excellent choice.

Temperature Range: -15ºF up to 400ºF

Fluoroelastomer is known to have excellent chemical resistance, making it the standard for o-ring materials. Typically, when rubber is introduced to harsh chemicals it can deform and swell up causing damage to the seal and potentially the machine or equipment. FKM offers superior chemical and swell resistance within high octane and oxygenated fuel blends.

Fluoroelastomer (FKM / Viton™) Pros

High heat resistance
Resistance to many chemicals and bases
Superior swell resistance

Fluoroelastomer (FKM / Viton™) Cons

Lsydrol® Fluids
Ketones
Amines
Methyl
Organic Acids

Nitrile (NBR / Buna-N)

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Nitrile (Buna / NBR) is a synthetic rubber, composed of acrylonitrile (ANC) and butadiene. Depending on the ratio of ANC and butadiene, the working properties may vary. A lower ANC would be able to withstand a colder temperature before transitioning into a brittle state. This rubber elastomer is used in a variety of industries such as automotive, oil and gas, military, and more.

Buna-N O-rings, gaskets, and other sealing devices offer a large number of beneficial properties such as oil and gas products, superior compression set (ability to be squeezed and maintain its shape and sealing ability), and abrasion resistance (ability to withstand wear and tear of friction caused by moving parts).

Temperature Range: -40ºF up to 250ºF

Nitrile (NBR / Buna-N) Pros:

Low compression set
High tensile strength
High abrasion resistance
Can be compounded into FDA standards

Nitrile (NBR / Buna-N) Cons:

Poor performance in UV light and exposure to ozone
Poor steam performance

Comparing Nitrile and Viton™

Nitrile and FKM have many similarities which allow them to be suited for an extensive list of general use applications and serve as excellent seals in many industries. Both have great resistance to certain chemicals, oils, and petroleum.

FKM / Viton® offers excellent resistance to ozone, oxidation, and UV light while Nitrile performs poorly in those environments. Although Nitrile / Buna-N supports many of the same chemical resistances as FKM, it has a much lower list of compatible chemicals.

Nitrile offers better resistance to tearing and abrasion which allows it to be more suited for heavy industrial application with moving mechanical parts. Its lower compression set allows Nitrile to be compressed tighter without losing sealability or breaking.

Nitrile (NBR / Buna-N)Fluoroelastomer (FKM / Viton®)Temperature Range-40ºF up to 250ºF-15ºF up to 400ºFProsGreat for sealing petroleum oils, water, and hydraulic fluids. Great tear and abrasion resistance.Diverse sealing applications. Great for sealing petroleum, silicone-based fluid and gases, acids, halogenated hydrocarbons, and more.ConsCan be used in hydraulic systems, oil and gas industries, water systems, automotive, military, and general use applications.Can be used in chemical processing, automotive, aerospace, oil, and gas industries.

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Gearbox seal: FKM or NBR - Apex Dynamics