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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.

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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

Buna-N O-Rings (NBR Nitrile) Selection Guide

Buna-N o-rings also referred to as NBR o-rings and Nitrile o-rings are the most widely used o-ring material in the word because of low cost, good mechanical performance with resistance to water, most basic oils, lubricants and some fuels, many pneumatic, hydraulic systems, and the default choice for basic applications. Buna-N o-rings are not recommended for exposure to sunlight, UV light, ozone and general outdoor weathering or hash chemicals, acids, keytones and many others.

Custom size Buna-N o-rings can typically be supplied without additional tooling fees within a few weeks. As the world's largest o-ring inventory network, Marco Rubber's direct purchasing power can deliver substantial savings on Buna-N o-rings. Order Buna-N o-rings online today!

Explore Buna-N Compounds

Compound # Datasheet Color Hardness (Shore A) Low Temp °F (°C) High Temp °F (°C) Features BBlack70-31(-35)250(121)Lowest cost highest inventory general purpose commodity NBR compound. Compare to Parker N-70 and N-70 and Parco -70 and -70. Available in nearly any color and hardness.BBlack90-31(-35)250(121)General purpose, higher pressure applications. Compare to Parker N-90 and N-90 and Parco -90 and -90.BBlack70-31(-35)250(121)FDA compliant per 21 CFR 177.. Compare to Parker N-75 and N-70.BBlack90-31(-35)250(121)FDA compliant, higher hardness.BBlack50-31(-35)250(121)General purpose, lower hardness for lower closure force applications. FDA compliant and alternative colors available. Compare to Parker N-50.BBlack80-31(-35)225(107)General purpose, higher hardness. Compare to Parker N-80.BBlack70-31(-35)230(110)Internally lubricated with PTFE to reduce friction. Silicone oil and Moly (MOS2) internal lubricants available. Alternative hardness and colors also available.BBlack70-35(-37)250(121)UL 157 listed for several approved uses.BBlack70-31(-35)250(121)NSF 61 certified for drinking water applications.BBlack95-31(-35)250(121)Very high hardness for extreme pressure applications.BBlack70-65(-54)275(135)Improved lower and higher temperature resistance and improved oil resistance at higher temperature. Compare to Parker N-75 and M and Parco -70.BBlack70-31(-35)250(121)Metal detectable for contamination detection sensors. FDA compliant per 21 CFR 177.. Formulated for food contact and life science applications. Additional colors available.BBlack70-31(-35)250(121)NSF 51 certified for food contact.MBlack70-65(-54)275(135)Mil Spec (Military specification) AMS-P-, MS-### per MIL-P-C-(1).MBlack75-65(-54)275(135)Mil Spec (Military specification) AMS-P-, M/1-### per MIL-P-B#3. Improved low temperature resistance and hydraulic fluid resistance.MBlack65-65(-54)250(121)Mil Spec (Military specification) MS-###, MS-##, AMS-P-B.MBlack90-65(-54)275(135)Mil Spec (Military specification) MS, AMS-P-C.MBlack65-70(-57)200(93)Mil Spec (Military specification) AMS, AS.

The information on this page is to the best of our knowledge accurate and reliable. However, Marco Rubber makes no warranty, expressed or implied, that parts manufactured from this material will perform satisfactorily in the customer's application. It's the customer's responsibility to evaluate parts prior to use.

The temperature ranges presented on this page are approximations for dry air service only and should not be used to determine design specifications or end-use temperature limits. Actual temperature range of a compound in an end-use application is highly dependent on part type, hardware configuration, applied forces, chemical media, pressure and thermal cycling effects, and other factors. The most practical way of determining an end-use temperature range is testing in the actual application conditions. Consult a Marco Engineer for more details.

Common Names

Buna-N, Nitrile, NBR, Acrylonitrile Butadiene Rubber

Trade Names

Nipol®

Typical Applications and Products

The range of performance characteristics of Buna-N allows it to be utilized in a diverse set of applications. NBR is often used for gaskets and o-rings in pneumatic, hydraulic, and fuel systems. V-packings and backup rings made from high-hardness Nitrile compounds are common in high pressure environments in the Oil and Gas industry. The abrasion and wear resistance of NBR make it useful for dynamic oil seals for rotary and reciprocating shafts. NBR is relatively easy to process which keeps costs down for custom extrusions and complex molds. Hardness ranges from 40 Shore A to 90 Shore A. Hydrogenated versions of NBR (HNBR) have enhanced mechanical properties as well as greater thermal and chemical stability. Specific physical properties and chemical resistances vary by compound formulation.

NBR can be compounded for enhanced oil and fuel resistance, increased temperature flexibility, high hardness and extrusion resistance, low compression set, and a variety of other attributes. The physical properties of the compound largely depend on the Acrylonitrile content of the formulation. For example, high Acrylonitrile content causes increased oil and fuel resistance while adversely affecting low temperature flexibility and compression set resistance. It is important to consider the offsetting attributes when selecting an NBR formulation. Please contact a Marco Rubber engineer for assistance finding the best compound for your application.

Chemical Compatibility and Specialty Resistances

• Petroleum oils / Fuels / Greases
• Mineral Oils, Vegetable Oils
• Silicone Greases / Oils
• Aliphatic Hydrocarbons
• Hydraulic Fluids (HFA, HFB, HFC types)
• Ethylene Glycol Fluids
• Limited resistance to Dilute Acids, Alkalis, and Solvents

Limitations

• Not resistant to Ketones (MEK)
• Not resistant to Halogenated Hydrocarbons
• Not resistant to Chlorinated Hydrocarbons
• Not resistant to Auto / Aircraft Brake Fluids
• Not resistant to Strong Acids
• Not resistant to Weathering, Sunlight and Ozone
• Not resistant to Highly Aromatic fuels and hydrocarbons
• Not resistant to Polar solvents

Mechanical Properties

• Good Wear Resistance
• Good Compression Set Resistance
• Good Short-Term Resilience
• Good Permeation Resistance

Product Options

• Internal Lubrication with PTFE and others
• High strength
• Flame resistant
• ABS compatible
• Anti-Static
• WRAS, KTW and NSF Compliant
• FDA compliant
• Metal and X-ray detectable
• Gamma Radiation Resistance
• Tight and/or specific tolerances
• Specific AQL Inspection requirement
• Surface free of silicone oil
• PTFE coated in choice color
• Special tumbling for complete flash removal
• Talcum powder on surface to reduce sticking
• Specific packaging requirements
• Special bag and Label requirements
• Variety of colors available

Please contact a Marco Sales Consultant or Engineer to discuss additional options.

The company is the world’s best NBR Rubber OIL SEAL supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.