BUSHINGS & O-RINGS
FFKM, or perfluoroelastomer, contains higher amounts of fluorine than standard FKM, and features higher temperature ratings, up to approximately 325°C (617°F). FFKM also has improved chemical resistance, with nearly universal chemical compatibility. This combination of high-performance capabilities makes FFKM seals the premium choice for the most challenging applications.
The first commercially available FFKM seal was produced in the late 1960s. However, widespread manufacturing of FFKM materials did not occur until the late 1980s due to patent restrictions.
FFKM is used in o-rings and seals in environments with high temperatures and/or harsh chemicals in the aerospace, semiconductor, energy, pharmaceutical, and industrial industries.
Greene Tweed’s Chemraz® is the ultimate elastomeric FFKM material. Chemraz® is a polymer of three or more monomers in which all hydrogen positions have been replaced with fluorine. It has the broadest chemical resistance of any elastomeric material.
Xyfluor® is a proprietary, highly fluorinated elastomer with a chemical compatibility which surpasses that of an FKM and can handle amines, ketones, and hydrofluoric acid for static applications in temperatures ranging from -60°C to 232°C (-76°F to 450°F). It is available in both compression and injection molded grades.
Xyfluor® is ideal for use in demanding high-volume applications such as mechanical seals and gaskets in a range of metering pumps, valves and other high-performance equipment.
Fluoraz® FEPM elastomers deliver excellent chemical resistance against acids and bases such as methanol, amines, ammonia, urea, hydrochloric acid, and steam at temperatures up to 232°C (450°F). Fluoraz® is generally not recommended for aromatic hydrocarbons.
Products engineered from Fluoraz® are used in a variety of industries, including automotive and oil & gas. In certain applications, Fluoraz® FEPM may offer performance advantages over an FKM solution. A Greene Tweed engineer can help determine which material will be best suited for your application – Contact us today for more information.
FKM is the ASTM designation for a class of fluorinated, carbon-based synthetic rubber, commonly known as fluoroelastomers. FKM has impressive heat resistance, allowing FKM seals to withstand temperatures greater than 200°C. FKM also exhibits extraordinary levels of resistance to high pressures, chemicals, and other fluids (including several fuels).
FKM was originally developed in the late 1950s in response to demand for high performance seals in the aerospace industry. Development of FKMs continued through the 1980s, with advancements including greater thermal stability and improved heat, solvent, and compression resistance.
Today, FKM materials are commonly used to manufacture o-rings, seals, and gaskets for a variety of high-performance applications in the automotive, aerospace, energy, semiconductor, and industrial industries.
Greene Tweed’s Fusion™ elastomers have been engineered to withstand conditions such as RGD and low and high temperatures, and to ensure minimal particulation in clean environments.
HNBR & NBR
NBR, or nitrile rubber (also commonly referred to as buna-N rubber or perbunan), is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. Higher ACN content yields better resistance to hydrocarbon oils, while lower ACN content provides better flexibility in low-temperature applications. NBR seals with a medium ACN content (approximately 30-45%) are the most commonly used because of their balanced attributes and applicability to most environments.
HNBR, or hydrogenated nitrile butadiene rubber, has a higher temperature rating than standard NBR, and exhibits high tensile strength and great resistance to oil and chemicals.
Ethylene propylene (EPM or EP) rubber is a form of non-polar synthetic rubber that can only be cured with peroxide or radiation. EPDM consists of an additional monomer, diene, and can be cured using peroxide- or sulfur-based chemistries. EPM and EPDM seals only differ slightly in performance. Both provide outstanding resistance to hot water/steam and polar solvents, along with excellent ozone resistance.
O-rings are circular sealing elements with a circular cross-section. The simplicity of the shape of an O-ring combined with the elasticity of the materials of which O-rings are made give the O-ring universal properties and make it the most widely used sealing element. O-rings can be produced from many diff erent elastomer materials and a wide range of O-rings of standard materials is available from stock. The bandwidth of available O-rings is so wide and so closely graded that almost any application is covered. O-rings are standardized in DIN ISO 3601 (former DIN 3771).
O-ring seals are used in all areas of industrial technology. The applications are divided into static applications (no relative movement between the sealed parts of a machine) and dynamic applications (the sealed parts of a machine move in relation to each other). The vast majority of O-ring are used for static or slowly moving machine parts.
NBR (NITRILE / BUNA-N)
Among standard seals such as O-rings and radial shaft seals, NBR is the most widely used material. The reasons for this are good mechanical properties, high abrasion resistance, low gas permeability and the high resistance to mineral oil based oils and greases. NBR is a copolymer of butadiene and acrylonitrile. Depending on the application, the content of acrylonitrile can vary between 18% and 50%. Low ACN content improves cold fl exibility at the expense of the resistance to oil and fuel. High ACN content improves the resistance to oil and fuel while reducing the cold fl exibility and increasing compression set. To obtain balanced properties, our standard NBR materials have an average ACN content around 30%
NBR has good resistance to: mineral oil-based oils and greases aliphatic hydrocarbons vegetable and animal oils and fats hydraulic oils H, H-L, H-LP hydraulic fl uids HFA, HFB, HFC silicone oils and silicone greases water (max. 80°C).
NBR is not resistant to: fuels with high aromatic content aromatic hydrocarbons chlorinated hydrocarbons non-polar solvents hydraulic fl uid HFD glycol-based brake fluids ozone, weathering, ageing
Application temperature range: Standard types -30°C to +100°C (short term +120°C) Special grades possible down to -50°C
FKM (a.k.a VITON®)
FKM materials have conquered many applications in which high thermal and / or chemical resistance is required. FKM also has excellent resistance to ozone, weathering and ageing. Very low gas permeability, FKM is recommended for vacuum applications.
FKM has good resistance to: mineral oil-based oils and greases aliphatic hydrocarbons aromatic hydrocarbons chlorinated hydrocarbons hydraulic fl uids HFD vegetable and animal oils and fats silicone oils and silicone greases fuels non-polar solvents ozone, weathering, ageing
FKM is not resistant to: glycol-based brake fluids polar solvents (e.g., acetone) super heated steam (special grades) hot water (special grades) amines, alkalis (special grades) low-molecular organic acids (e.g., acetic acid)
Application temperature range: -15 to +200°C (short term +220°C) down to -61°C and up to 260° C is realistic with special grades
ETHYLENE PROPYLENE DIENE (EPDM)
EPDM can be used in a wide temperature range, has good resistance to ozone, weathering and ageing and is resistant to hot water and steam. Peroxide cured EPDM materials have better resistance to temperature and chemicals and obtain better compression set values than sulfur cured EPDM.
EPDM has good resistance to: hot water and hot steam many polar solvents (e.g., alcohols, ketones, esters) many organic and inorganic acids and bases washing brines silicone oils and silicone greases glycol-based brake fluids (special grades required) ozone, weathering, ageing
EPDM is not resistant to: all kinds of mineral oil products (oils, greases, fuels)
Application temperature range: -45°C to +130°C (sulfur cured) -55°C to +150°C (peroxide cured)
TETRAFLUOROETHYLENE-PROPYLENE / FEPM (a.k.a AFLAS®)
FEPM materials are special elastomers from the group of fl uoroelastomers. They have good chemical resistance and cover a wide range of temperature applications. Their main applications include oil fi eld and chemical industry applications
FEPM has good resistance to: crude oil sour gas hot water, steam polar solvents, alcohols, amines many concentrated acids and bases engine and gear oil containing additives
Application temperature range: 10°C (-20°C) to +200°C (short term +230°C)
Silicone materials have excellent aging resistance, oxygen, ozone, ultraviolet radiation and weathering and a very wide application temperature range with excellent cold fl exibility. Silicone is physiologically harmless and therefore very good in food and medical product applications. Silicone has good electrical insulation properties and is highly permeable to gas. Due to the weak mechanical properties, silicone O-rings are preferably used in static.
SILICON has good resistance to: animal and vegetable oils and fats water (max.100°C) aliphatic engine and gear oils ozone, weathering, ageing
SILICON is not resistant to: silicone oils and greases aromatic mineral oils fuels steam over 120°C acids and alkalis
Application temperature range: -60°C to +200°C +230°C can be obtained by special grades
HOFFMAN-KANE ENCAPSULATED O-RINGS
Encapsulated O-rings are specially developed seals which solve a common problem in many industries. Sometimes you need the chemical and temperature resistance of PTFE, but a PTFE O-ring wouldn’t have the flexibility you need for compressive fluid sealing. Or perhaps you want a flexible elastomer but can’t rely on the material to resist the chemicals you are dealing with.
An encapsulated O-ring brings the best of both worlds together. The outer jacket is made from Teflon, giving the seal high thermal stability and resistance to corrosion, while the rubber inner ore provides compressional and elasticity.
TYPES OF ENCAPSULATED O-RINGS
Encapsulated O-rings can have two different types of core, which enables them to be suitable for different applications. The two types are:
Solid core: These are standard encapsulated O-rings which have either a silicone energiser ore or a core made from FKM, also known as Viton. FKM cores have excellent elasticity and a good compression set. Silicone has very much the same benefits, but because it is softer it has a higher standard of heat resistance. For very cold temperatures, a silicone core would be recommended as they remain flexible to a lower temperature too.
Hollow core: For applications where extreme elasticity is required, no core at all outperforms both FKM and silicone cores. This may come with a compromise in terms of compression set and recovery, but for fragile applications a hollow core encapsulated O-ring will perform well.
As well as having various options for the elastomeric core, the outer jacket of the encapsulated O-ring can be made in a choice of materials too. Most commonly, we make them with either PFA or FEP outer jackets.
PFA: To give it its full title, perfluoroalkoxycopolymer is excellent at resisting a range of corrosive chemicals. These include alcohol, naphtha, acid, petroleum and aromatic solvents. Compression set is low, and their operating temperatures range from -60°C to +260° Compared to FEP, they have higher mechanical strength and improved resistance to cracking and stress.
FEP: Fluorinated ethylene propylene jackets for encapsulated O-rings have very similar qualities to those of PFA. They resist chemicals, have low coefficient of friction and a low compression set. However, they are slightly weaker mechanically and have a narrower operating temperature range, of -60°C up to +205° Their service life is slightly shorter, but they are FDA approved and are generally lower cost too.
ADVANTAGES OF ENCAPSULATED O-RINGS
As you can see from the description of the materials, encapsulated O-rings have excellent resistance to almost all types of media. They work in a wide temperature range and an be made from FDA approved materials to suit food and drugs processing applications.
Their non-contaminating material makes them ideal for use where hygiene is required. The chemical resistance of the materials also means they are a good solution for chemical and petrochemical industries.
The combination of the elastomer-like flexibility with the PTFE-like chemical resistance brings unique advantages to encapsulated O-rings over other types of seals.
LIMITATIONS OF ENCAPSULATED O-RINGS
In general, encapsulated O-rings have many properties which make them a top choice for strenuous processes. However, there are some situations where they are not the best choice.
The thin outer jacket means they are susceptible to scratching, so should not be used in applications containing abrasive slurries or powders.
We find that encapsulated O-rings are generally best suited to static applications, or at best in slow moving rotary applications. Highly dynamic systems may not be best suited to the use of encapsulated O-rings.
Overall, the success of an encapsulated O-ring will depend on the right product being selected for the job. Hoffman-Kane can help you choose the best product for your needs, whether that’s an encapsulated O-ring or something else. We can manufacture custom sizes and profiles to suit your application too; just talk to our team for further information.
BUSHINGS / THERMOPLASTICS
Greene Tweed’s AETs are a specialized family of high-performance thermoplastics with exceptional properties, including short- and long-term thermal stability, enhanced mechanical performance, excellent chemical resistance, superior wear properties, and good fire performance thermal properties.
Compared to low-performance commodity plastics, AETs provide numerous advantages over metallic materials, including lower density for weight reduction, good vibration damping characteristics, electrical or thermal insulation, chemical and corrosion resistance, increased design freedom, and fatigue resistance.
Greene Tweed’s high-performance AETs include:
Arlon® materials are proprietary PAEK (polyaryletherketone) thermoplastic compounds, which include the PEEK (polyetheretherketone) and PEK (polyetherketone) subsets of compounds that provide high strength and wear resistance and are well suited for use in harsh or extreme environments and highly dynamic applications.
What is PEEK?
PEEK material (polyetheretherketone) is a high-performance, semi-crystalline engineering thermoplastic with outstanding harsh chemical resistance, excellent mechanical strength across a broad temperature range, and good dimensional stability.
PEEK is also tough, strong, and rigid, with superior creep resistance, and is excellent for applications where thermal, chemical, and combustion properties are critical to performance. PEEK polymer retains stiffness and strength for use in harsh HPHT environments.
PEEK is often used as the body for electrical connectors, in a broad range of industries, including aerospace and oil & gas, to minimize thermal expansion, provide chemical resistance, greater pin density, and can be used as sealing.
Greene Tweed also uses PEEK materials for a variety of sealing system components, as well as sensor housings and numerous high-performance applications in aircraft engines and other demanding environments.
PEEK VS PEK
ARLON 3000 XT®
Arlon® 3000 XT is an engineering thermoplastic developed to withstand these extreme conditions. With improved creep and extrusion resistance at temperatures above 350°F (177°C), it enhances performance over existing PAEK polymers. In DMA (Dynamic Mechanical Analysis), Arlon 3000 XT had a Tg 35°F (20°C) higher than PEEK, and provided superior mechanical property retention from 350°F (177°C) – 600° F (316°C). In extrusion testing at 35 ksi and 550°F (288°C), it outperformed both virgin and filled grades of PEEK and PEKEKK. In addition, Arlon 3000 XT exhibits chemical resistance comparable to PEEK. Arlon 3000 XT delivers enhanced mechanical performance in HPHT conditions. Through increased reliability and extended service life, it expands design headroom overall. The result is safer, more efficient operations in extreme drilling environments
Greene Tweed has formulated and developed custom grades of our Avalon® family to meet the requirements of oilfield environments. Our product capability ranges from wear-resistant grades to low-friction and cryogenic capable materials specifically developed to provide sealing and anti-extrusion functionality.
Thermoplastic composites are produced using thermoplastic polymers as matrix materials, which soften upon heating to elevated temperatures for processing, and harden upon cooling. High-performance thermoplastic polymers used for thermoplastic composites provide a number of benefits compared to traditional thermoset resins, such as epoxies, including higher service temperature capability, lower moisture uptake, improved toughness, and increased chemical resistance.
Thermoplastic composites can also be reheated and reformed, providing benefits for manufacturing processes such as thermoforming and various thermal fusion/welding/joining processes. Unlike thermoset materials, thermoplastic composites do not require a chemical reaction or “cure,” and can be processed with much shorter molding cycle times. In addition, thermoplastic materials do not require refrigeration and have unlimited shelf life to further simplify and streamline the overall manufacturing process.
Thermoplastic composites typically use glass, carbon, or aramid fibers as reinforcement for the thermoplastic polymer matrix:
Glass fibers – used in a wide range of structural and mechanical parts; improve most mechanical properties, including strength and stiffness; non-conductive; provides dimensional stability
Carbon fibers – best strength and stiffness performance; lower density than glass; low coefficient of expansion; improved creep and wear resistance
Aramid fibers – low coefficient of friction and thermal expansion; very good toughness; excellent wear and abrasion resistance
These reinforcements can also provide various benefits based on their physical configuration. For example, carbon fibers can be produced in continuous and discontinuous strands, and even flakes, each of which creates different properties in the finished product and allows use of different manufacturing processes. This design versatility allows thermoplastic composite materials to be developed for a wide range of use conditions.
Thermoplastic composites have become a viable alternative to metal assemblies, die castings, and traditional thermoset composite materials in the aerospace/defense and automotive industries, and in consumer goods and electronics. For example, rising fuel costs have compelled the aerospace industry to increase the use of thermoplastic composites in the manufacture of lightweight metal replacement components that were not previously cost effective with traditional thermoset materials.
Features and benefits of high-performance thermoplastic composites:
Weight savings, fatigue performance, and corrosion resistance vs. metals
Cost-effective manufacturing with reduced waste
X-ray transparency (radiolucent)
Improved damping vs. thermosets or metals
Low moisture uptake, providing very good hot-wet properties
Excellent chemical resistance
Excellent fire performance
High service temperature capability
The AR® (Abrasion Resistant) line offers superior abrasion resistance and is less harsh to mating hardware compared to competing materials. The AR® line extends the service life of pumps and reduces downtime for pumps handling media-containing abrasives such as sand, coal ash, and other solids, which can wreak havoc in pumps.
Greene Tweed’s AR® family of materials can operate in subzero temperatures up to 121°C (250°F). The AR® 1 material is filled PTFE, while AR® HT is a blend of PTFE and PEEK.
AR® 1 provides general abrasion resistance and is particularly suitable for vertical pumps, while AR® HT is suitable for high-temperature, abrasive-resistant applications, such as vertical water feed pumps in nuclear facilities.
Greene, Tweed’s AR®1 is made of filled PTFE and is engineered to be abrasion-resistant. It can operate from subzero conditions up to 120°F (49°C), and is suitable for general abrasive resistance applications, particularly vertical pumps.
AR®1 is available as unfinished tubes, finished parts, or completed
assemblies, in tubes from 1.25-inch OD to 18.5-inch OD in 0.25-inch
increments. Lengths up to 9 inches are available for tubes up to
11.25 inch OD, and 6 inches for tubes with larger ODs
Greene, Tweed’s AR®HT, a proprietary blend of PTFE and PEEK,
offers abrasion resistance in higher operating temperatures, with a
temperature range from subzero to over 250°F (121°C). AR®HT is suitable for high-temperature, abrasive-resistant applications, such
as vertical water feed pumps in nuclear facilities.
AR®HT is available as unfinished tubes, finished parts, or completed
assemblies, and available as billets or tubes from 1-inch OD up to
90-inch OD in lengths from 3 inches to 8 inches, depending on the
The WR® (Wear Resistant) line offers excellent wear and friction properties, along with superior non-galling and non-seizing performance. The WR® material portfolio enables extended MTBR and improved reliability.
Offering extended dry-run performance and exceptional chemical resistance, our WR® materials reduce running clearances by more than 50% in many cases. These reduced clearances minimize recirculation, which maximizes rotor stability (reducing vibration) and overall efficiency.
WR® materials operate in cryogenic temperatures up to 274°C (525°F). WR® materials are typically PEEK with carbon fibers, although our newest offering in the WR® line, WR® 650, is made of PFA with carbon fibers and provides the best overall performance in the portfolio.
Greene, Tweed’s WR®300 is composed of PEEK reinforced with short, random carbon fibers with a temperature range from subzero to 275°F(135°C). WR®300 is suitable for general wear resistance applications and is often used in pump bushings and cases or impeller wear rings.
WR®300 provides excellent chemical resistance, has non-galling/
non-seizing properties, and offers maximum service life in clean, lubricated, and moist environments. It enables pump users to increase efficiency with tighter wear ring clearances while decreasing potential damage.
WR®300 is available from our inventory in many common sizes, and is available as billets or tubes from 1-inch OD up to 90-inch OD in lengths from 3 inches to 8 inches, depending on the OD configuration.
Greene, Tweed’s WR®525 is made of PEEK reinforced with continuous
hoop-wound carbon fibers and is ideal for use as impeller wear rings,
bushings, and case wear rings in high-pressure and high-temperature
(HPHT) conditions. WR®525‘s temperature range of subzero to 525°F
(274°C) is suitable for stationary and rotating applications and allows
users to increase efficiency with tighter wear ring clearances and
decrease potential damage.
WR®525 has non-galling/non-seizing properties and excellent
chemical resistance. It is available in unfinished tubes, finished parts, and completed assemblies. Tubes are available in any length with 1-inch wall thickness and a minimum inside diameter (ID) of 0.75 inches. Greene, Tweed can provide large tubes using this process, up to
32 inches OD.
Greene, Tweed’s WR®575 thrust pads are PEEK reinforced with carbon, and are used in high-speed machinery such as pumps, compressors, and turbines to handle axial bearing loads and counterbalance the force applied on the shaft. WR®575 thrust pads have a temperature range from subzero to over 480°F (249°C), and do not require an oil lubrication system because they use the application’s existing media for lubrication. In addition, they will not crack or wear into fine powder under high shock or impact like carbon or ceramic pads. They resist aggressive chemicals and corrosion, won’t gall or seize like metal alloys, and can be used in refining, chemical, power, and water applications.
WR®575 is available in 22- by 28- by 1.25-inch plates as well as
custom-shaped finished parts and thrust ring designs.
One of the biggest threats to pumps is running dry with no lubrication,
which may occur daily in a refinery, even if just momentarily.
Non-lubricated metal wear parts may degrade over time, leading to
a potentially catastrophic equipment failure.
WR®650 is Greene, Tweed’s most innovative performance wear material.
This next-generation PFA reinforced with carbon composite offers
superior dry run capability along with excellent thermal and chemical
resistance and non-galling/non-seizing characteristics.
WR®650 can perform in temperature conditions from subzero to
500°F (260°C), provides universal chemical resistance, and can handle
pro-longed dry runs to increase mean time between repairs. Its enhanced vibration damping capability extends the reliability and lifetime of pumps.
Greene, Tweed’s WR®650 composite wear parts are reinforced with
3D carbon fiber and can handle 2.5 times higher dry wear performance
than other PFA composites, providing the extra time needed to safely
shut down pumps without damage.
Available in unfinished tubes, finished machined parts, and complete
assemblies, tubes of WR®650 in lengths of 6 inches with 0.75-inch wall
thickness are available with outside diameters (ODs) of 2.5 inches to
12 inches, in increments of 0.5 inches, for immediate shipment.